Tunable capacitor and method of fabricating the same

专利摘要:
It is an object of the present invention to provide a variable capacitor having a small capacity, a large ratio of capacity change and a large Q value, and excellent impact resistance capable of fine adjustment of capacity, and a method of manufacturing the same. A substrate 31, a fixed electrode 38 and a movable electrode 39 of a capacitor supported on the substrate, a plurality of piezoelectric actuators 36 1 -36 4 supported on the substrate and driving the movable electrode; And a dielectric layer 37 disposed between the fixed electrode and the movable electrode. Since the capacitor and the piezoelectric actuator are formed to be supported on the same substrate, they are compact. In addition, since a dielectric layer is interposed between the fixed electrode and the movable electrode of the capacitor, both the capacitance, the rate of change of capacitance, and the Q value are large, and the capacitance can be finely adjusted and the impact resistance is excellent.
公开号:KR20030077405A
申请号:KR10-2003-0018150
申请日:2003-03-24
公开日:2003-10-01
发明作者:시마노우찌다께아끼；이마이마사히꼬；나까따니다다시；미야시따쯔또무；사또요시오
申请人:후지쓰 메디아 데바이스 가부시키가이샤；후지쯔 가부시끼가이샤；
IPC主号:

专利说明:

Variable Capacitor and Manufacturing Method Thereof {TUNABLE CAPACITOR AND METHOD OF FABRICATING THE SAME}
[52] The present invention relates to a variable capacitor, and more particularly, to a variable capacitor using MEMS (Microelectro Mechanical System) technology and a method of manufacturing the same.
[53] Variable capacitors are important components in electrical circuits including variable frequency oscillators (VFOs), tuning amplifiers, phase shifters, impedance matching circuits, and the like, and mounting in portable devices is increasing recently.
[54] In addition, in comparison with varactor diodes, which are a type of variable capacitors currently used, variable capacitors produced by MEMS technology can reduce the loss and increase the Q value, and therefore are in a hurry to develop. EMBODIMENT OF THE INVENTION Hereinafter, the prior art is demonstrated using drawing.
[55] First, FIG. 1 shows a structural cross-sectional view of a variable capacitor reported in Jan Y. Park, et al., "MICROMACHINED RF MEMS TUNABLE CAPACITORS USING PIEZOELECTRIC ACTUATORS", IEEE International Microwave Symposium, 2001.
[56] The variable capacitor includes a movable electrode substrate 11 including the unimorphic piezoelectric actuator 12 and the movable electrode 13, and a fixed electrode substrate 15 on which the fixed electrode 16 is disposed. 13) and the fixed electrode 16 are joined to each other by the solder bumps 14 so as to face each other. By driving the piezoelectric actuator 12, the distance between the movable electrode 13 and the fixed electrode 16 is changed to control the capacitance.
[57] Next, FIG. 2 shows a cross-sectional view of the variable capacitor as reported in Charles L. Goldsmith, et al., "RF MEMs Variable Capacitors for Tunable Filters", Wiley RF and Microwave Computer Aided Design, pp 362-374, 1999.
[58] The fixed electrode 20 via the insulating layer on the substrate 17, the dielectric layer 19 on the fixed electrode 20, and the spacer 18 on the substrate 17 via the fixed electrode. A membrane-type movable electrode 21 is disposed opposite to the 20 and the dielectric layer 19. The membrane-type movable electrode 21 is in contact with the dielectric layer 19 by the electrostatic force generated by applying a DC voltage between the movable electrode 21 and the fixed electrode 20. The electrostatic force F which functions to reduce the space | interval of such parallel plates is
[59]
[60] It is expressed as Where S is the electrode area, d is the electrode spacing, ε _o is the dielectric constant in vacuum, ε _r is the relative dielectric constant between the electrodes, and V is the applied voltage. When a dielectric layer exists between parallel plates, the following relation holds between the relative dielectric constant and the interval d.
[61]
[62] ε _dielectric , ε _air is the dielectric layer, d _dielectric , d _air is the dielectric layer, the air layer spacing.
[63] However, the prior art shown in FIG. 1 has the following problems. Since the space | interval of the movable electrode 13 and the fixed electrode 16 is controlled by the solder bump 14, a space | interval cannot be made small and the capacity | capacitance of the initial state of the piezoelectric actuator 12 becomes small. In addition, in order to increase the electrostatic capacity, when the deformation amount of the piezoelectric actuator 12 is increased, and the gap between the movable electrode 13 and the fixed electrode 16 is reduced, the spring property of the piezoelectric actuator 12 becomes small, thereby carrying When mounted on a device or the like, there is a problem that the movable electrode 13 and the fixed electrode 16 are damaged due to contact from the outside by the impact from the outside. For this reason, even if the displacement of the piezoelectric actuator 12 is used, the movable electrode 13 and the fixed electrode 16 cannot be approached, and a capacitance cannot be adjusted suitably.
[64] In addition, the prior art shown in Figs. 2A and 2B has the following problems. As described above, when a dielectric layer is present between parallel plates, the capacitance can be increased by the presence of the dielectric layer, but when the distance d changes, the relative dielectric constant ε _r also changes. Is difficult to control, and as a result, the state of the movable electrode 21 and the dielectric layer 19 can take only two states, a separated state or a contact state. That is, only the variable capacitor whose capacity is only two states can be formed. In addition, although a plurality of variable capacitors having a small capacity are connected in parallel to secure a desired capacity, in this case, the wiring resistance of the wiring for connecting the variable capacitors is increased, whereby the Q value (numerical value indicating a loss in the circuit; Q The larger the value, the smaller the loss).
[65] Accordingly, an object of the present invention is to provide a variable capacitor having a small size, a large capacity, a rate of change of capacity and a high Q value, and excellent impact resistance capable of fine adjustment of capacity, and a method of manufacturing the same. It is done.
[1] 1 is a cross-sectional view of a variable capacitor according to the prior art
[2] 2 is a cross-sectional view of another capacitor according to the related art.
[3] 3 is an exploded perspective view of a variable capacitor according to a first embodiment of the present invention;
[4] 4 is a perspective view of a common electrode used in the first embodiment of the present invention;
[5] FIG. 5 is a cross sectional view of the manufacturing method of the variable capacitor shown in FIG. 3 (part 1). FIG.
[6] FIG. 6 is a cross sectional view of the manufacturing method of the variable capacitor shown in FIG. 3 (part 2). FIG.
[7] 7 is a view for explaining unimorph (unimorph)
[8] FIG. 8 is a diagram for explaining bimorph. FIG.
[9] 9 is a view for explaining the effect of a variable capacitor according to a first embodiment of the present invention;
[10] 10 is a cross-sectional view illustrating another manufacturing method of the variable capacitor illustrated in FIG. 3.
[11] 11 is an exploded perspective view of a variable capacitor according to a second embodiment of the present invention.
[12] 12 is a cross-sectional view taken along the line XII-XII in FIG. 11.
[13] 13 is an exploded perspective view of a variable capacitor according to a modification of the second embodiment of the present invention;
[14] 14 is a plan view of the variable capacitor shown in FIG. 13.
[15] 15 is an exploded perspective view of a variable capacitor according to a third embodiment of the present invention.
[16] FIG. 16 is a cross sectional view of the manufacturing method of the variable capacitor shown in FIGS. 13 and 14 (No. 1).
[17] FIG. 17 is a cross sectional view of a method for manufacturing the variable capacitor shown in FIGS. 13 and 14 (No. 2).
[18] FIG. 18 is a cross sectional view of another manufacturing method of the variable capacitor illustrated in FIGS. 13 and 14.
[19] 19 is an exploded perspective view of a variable capacitor according to a fourth embodiment of the present invention.
[20] 20 is a cross-sectional view taken along the line XX-XX of FIG. 19.
[21] 21 is an exploded perspective view of a variable capacitor according to a fifth embodiment of the present invention.
[22] FIG. 22 is a plan view of the variable capacitor shown in FIG. 21.
[23] 23 is an exploded perspective view of a variable capacitor according to a sixth embodiment of the present invention.
[24] 24 is a plan view of the variable capacitor shown in FIG. 23.
[25] FIG. 25 is an enlarged perspective view of a part of the variable capacitor shown in FIG. 23. FIG.
[26] 26 is a cross-sectional view illustrating a method of manufacturing the variable capacitor shown in FIG. 23.
[27] 27 is an exploded perspective view of a variable capacitor according to a seventh embodiment of the present invention.
[28] 28 is a plan view of the variable capacitor shown in FIG. 27.
[29] FIG. 29 is an enlarged perspective view of a part of the variable capacitor shown in FIG. 27. FIG.
[30] 30 is an exploded perspective view of a variable capacitor according to an eighth embodiment of the present invention.
[31] FIG. 31 is an enlarged perspective view of a part of the variable capacitor shown in FIG. 30. FIG.
[32] 32 is a cross-sectional view illustrating a method of manufacturing the variable capacitor shown in FIG. 30.
[33] 33 is an exploded perspective view of a variable capacitor according to a ninth embodiment of the present invention.
[34] 34 is an enlarged perspective view of a part of the variable capacitor shown in FIG. 33.
[35] 35 is a cross-sectional view illustrating a method of manufacturing a variable capacitor according to an embodiment in which a fixed electrode is formed from a plurality of layers.
[36] <Explanation of symbols for the main parts of the drawings>
[37] 31, 131: substrate
[38] 32, 132: insulation layer
[39] 33 _l -33 ₄ , 133 _l -133 ₄ , 53 ₁ -53 ₄ : Lower drive electrode
[40] 33a-33d, 47, 49, 50, 72, 73, 74, 75: pad
[41] 34 ₁ -34 ₄ , 134 ₁ -134 ₄ , 54 ₁ -54 ₄ : Piezoelectric element
[42] 35 _l -35 ₄ , 135 ₁ -135 ₄ , 55 _l -55 ₄ : Upper drive electrode
[43] 36 ₁ -36 ₄ , 136 ₁ -136 ₄ , 56 ₁ -56 ₄ : Piezo actuator
[44] 37, 137, 237, 237A, 57: dielectric layer
[45] 38, 138, 238, 52: fixed electrode
[46] 39, 139, 59: movable electrode
[47] 40, 140: opening
[48] 41, 48, 58, 70: common electrode
[49] 42: gap
[50] 44, 144, 60: sacrificial layer
[51] 45, 45c, 46, 61: etching hole
[66] The present invention provides a substrate, a fixed electrode and a movable electrode of a capacitor supported on the substrate, a piezoelectric actuator supported on the substrate and driving the movable electrode, and a dielectric layer disposed between the fixed electrode and the movable electrode. It is a variable capacitor characterized by including. Since the capacitor and the piezoelectric actuator are formed to be supported by the same substrate, they are compact. In addition, since a dielectric layer is interposed between the fixed electrode and the movable electrode of the capacitor, both the capacitance, the ratio of the capacitance change, and the Q value are large, and the capacitance can be finely adjusted, and the impact resistance is excellent.
[67] In the variable capacitor according to the present invention, the dielectric layer is supported by either the fixed electrode or the movable electrode. The configuration in which the dielectric layer is supported by the fixed electrode is illustrated as the first, third and fifth embodiments described later, and the configuration in which the dielectric layer is supported by the movable electrodes is illustrated as the second and fourth embodiments described below.
[68] In the variable capacitor according to the present invention, each of the plurality of piezoelectric actuators is located in a space on the substrate, including a pair of electrodes and a piezoelectric element disposed therebetween. One configuration example of the piezoelectric actuator is specified, and is shown in FIG. 6 (j) described later, for example.
[69] In the variable capacitor according to the present invention, one of the pair of electrodes of the plurality of piezoelectric actuators and the movable electrode are integrally formed. For example, below the lower driving electrodes (33 ₁ -33 ₄₎ and the movable electrode 39 is composed of one body (see Fig. 4).
[70] In the variable capacitor according to the present invention, the dielectric layer is attached to the fixed electrode and faces the movable electrode via the air layer. The first, third and fifth embodiments described later have this configuration.
[71] In the variable capacitor according to the present invention, the dielectric layer is attached to the movable electrode and faces the fixed electrode via an air layer. The second and fourth embodiments described later have this configuration.
[72] In the variable capacitor according to the present invention, the fixed electrode has a portion that bridges on the movable electrode, and the dielectric layer attached to the portion faces the movable electrode via an air layer. For example, the fixed electrode 38 of 1st Example mentioned later (refer FIG. 3) is equipped with the part which bridges on the movable electrode 39, and the dielectric layer 37 is attached to it.
[73] In the variable capacitor according to the present invention, the fixed electrode has a portion that bridges on the movable electrode, and the dielectric layer is disposed on the movable electrode and faces the fixed electrode via an air layer. For example, the second embodiment described later has this configuration.
[74] In the variable capacitor according to the present invention, the fixed electrode is formed on an insulating layer formed on the substrate, the dielectric layer is disposed on the fixed electrode, and the movable electrode faces the dielectric layer via an air layer. For example, the third embodiment described later has this configuration (see Fig. 15). The fixed electrode 52 is formed on the insulating layer 32, and the dielectric layer 57 is disposed on the fixed electrode 52.
[75] In the variable capacitor according to the present invention, the fixed electrode is formed on an insulating layer formed on the substrate, and the dielectric layer is attached to the movable electrode and faces the fixed electrode via an air layer. For example, the fourth embodiment described later has this configuration (see Fig. 19). The fixed electrode 52 is formed on the insulating layer 32, and the dielectric layer 57 is attached to the movable electrode 59.
[76] In the variable capacitor according to the present invention, the fixed electrode is supported by the substrate via an insulating layer disposed on the substrate. The third to fifth embodiments described later have this configuration.
[77] In the variable capacitor according to the present invention, the piezoelectric actuator is of a unimorph type.
[78] In the variable capacitor according to the present invention, the piezoelectric actuator is a bimorph type.
[79] In the variable capacitor according to the present invention, the fixed electrode and the movable electrode each have a pad for external connection, the pad being positioned on an insulating layer disposed on the substrate. For example, the embodiment shown in FIGS. 13, 14, 21, and 22 described later has a pad for external connection that is relatively larger than other embodiments.
[80] In the variable capacitor according to the present invention, the piezoelectric actuator has a plurality of deformation parts including a pair of electrodes and a piezoelectric element disposed therebetween, the pair of electrodes each having an external connection pad, and the pad is the substrate. It is located on an insulating layer disposed on. For example, reference numerals 33a-33d in FIG. 4 correspond to this pad. Electrodes (35 ₁ -35 ₄₎ of Figure 4 also has a pad of the wide portion. In addition, the external connection pad includes not only the connection wiring to the outside but also the connection electrode (wire) formed on the insulating layer, for example.
[81] In the variable capacitor according to the present invention, one of the pair of electrodes of the plurality of piezoelectric actuators is an electrode commonly connected through the movable electrode. This configuration corresponds to, for example, the electrode 41 of FIG. 4.
[82] In the variable capacitor according to the present invention, one of the pair of electrodes of each of the plurality of piezoelectric actuators is an independent electrode. This configuration example corresponds to the electrode of Figure 3 (31 ₁ -35 _4).
[83] In the variable capacitor according to the present invention, one of the pair of electrodes of the plurality of piezoelectric actuators is configured by a plurality of common electrodes. For example, the fifth embodiment described later uses two common electrodes (an electrode having a pad 74 and an electrode having a pad 75).
[84] In the variable capacitor according to the present invention, the fixed electrode has a bridge portion which bridges on the movable electrode, the bridge portion being substantially the same shape as the movable electrode and facing the movable electrode via the dielectric layer. By this structure, the length of the bridge portion can be shortened, and influences such as residual stress generated at the time of forming the fixed electrode and surface tension of water generated at the time of cleaning can be eliminated. This high variable capacitor can be realized. In addition, the fixed electrode can be disposed so as not to span the piezoelectric actuator, and no parasitic capacitance is generated. The sixth to ninth embodiments described later have such a configuration.
[85] In the variable capacitor according to the present invention, the fixed electrode has a bridge portion which bridges on the movable electrode, the bridge portion is substantially the same shape as the movable electrode, and faces the movable electrode via the dielectric layer. The fixed electrode has three or more supports, and the supports are disposed on an insulating layer formed on the substrate. Since the bridge portion is supported by three or more supports, the effect obtained by such a configuration becomes even more remarkable. The seventh and ninth embodiments described later have this configuration.
[86] In the variable capacitor according to the present invention, the fixed electrode has a bridge portion for bridging the movable electrode, the bridge portion is substantially the same shape as the movable electrode, and faces the movable electrode via the dielectric layer. The dielectric layer attached to the fixed electrode is also formed to bridge the movable electrode. Since the dielectric layer is also formed on the substrate so as to bridge the movable electrode, the effect obtained with this configuration becomes even more remarkable. The eighth and ninth embodiments described later have this configuration.
[87] In the variable capacitor according to the present invention, the fixed electrode has a plurality of layers, the plurality of layers including a layer in which tensile stress is generated and a layer in which compressive stress is generated. As a result, residual stress generated in the fixed electrode can be alleviated.
[88] In the variable capacitor according to the present invention, the dielectric layer is formed of any one selected from the group consisting of beryllium oxide, aluminum oxide, aluminum nitride, barium titanate, magnesium titanate, titanium oxide, glass, and silicon nitride.
[89] In the variable capacitor according to the present invention, the movable electrode is in contact with the fixed electrode, the dielectric layer and the movable electrode in a state where an air layer is interposed between the dielectric layer and the fixed electrode or between the dielectric layer and the movable electrode. It has a range of operation up to.
[90] In the variable capacitor according to the present invention, the dielectric layer is attached to the fixed electrode, and the dielectric layer and the fixed electrode have a plurality of holes therethrough. For example, the hole 46 of FIG. 10 (j) described later corresponds to this.
[91] In the variable capacitor according to the present invention, the dielectric layer is attached to the fixed electrode, and the movable electrode has a plurality of holes therethrough. For example, the hole 61 of FIG. 18 (i) mentioned later corresponds to this.
[92] In the variable capacitor according to the present invention, the variable capacitor includes four piezoelectric actuators.
[93] In the variable capacitor according to the present invention, the substrate has an opening, and the fixed electrode, the movable electrode, the dielectric layer, and the piezoelectric actuator are disposed on the opening. This opening is the opening 40 mentioned later, for example.
[94] In the variable capacitor according to the present invention, the substrate has an opening, and an insulating layer is disposed to cover the opening. For example, the third to fifth embodiments have this configuration.
[95] Moreover, the subject of this invention is the process of forming the fixed electrode and the movable electrode of the capacitor supported by the board | substrate, the process of forming the piezoelectric actuator supported by the said board | substrate and driving the said movable electrode, The said fixed electrode and the said Forming a dielectric layer disposed between the movable electrodes, forming a sacrificial layer for forming a gap between the fixed electrode and the movable electrode and a dielectric layer, and removing the sacrificial layer. It can achieve by the manufacturing method of the variable capacitor characterized by the above-mentioned. By using the sacrificial layer, a gap can be formed between one of the fixed electrode and the movable electrode and the dielectric layer.
[96] In the method of manufacturing a variable capacitor according to the present invention, a step of forming an etching hole in a layer formed on the sacrificial layer before the step of removing the sacrificial layer.
[97] In the method of manufacturing a variable capacitor according to the present invention, the step of forming the sacrificial layer forms the sacrificial layer on the movable electrode.
[98] In the method of manufacturing a variable capacitor according to the present invention, the step of forming the sacrificial layer forms the sacrificial layer on the dielectric layer.
[99] In the method of manufacturing a variable capacitor according to the present invention, a step of forming an etching hole in the dielectric layer and the fixed electrode formed on the sacrificial layer before the step of removing the sacrificial layer.
[100] The method of manufacturing a variable capacitor according to the present invention includes a step of forming an etching hole in the movable electrode formed on the sacrificial layer before the step of removing the sacrificial layer.
[101] Further, in the manufacturing method of the variable capacitor according to the present invention, the manufacturing method further includes the step of etching the substrate to form an opening at least at a position facing the movable electrode and the piezoelectric actuator.
[102] In the method of manufacturing a variable capacitor according to the present invention, the substrate is formed of silicon, and the step of etching the substrate uses sulfur hexafluoride (SF6) as an etching gas, and a resist is used as a mask for forming the opening. It is based on the used differential ion etching (DRIE).
[103] In the method of manufacturing a variable capacitor according to the present invention, the substrate is a silicon substrate having a (100) plane or a (110) plane, and anisotropically etches the substrate to at least open an opening at a position facing the movable electrode and the piezoelectric actuator. Forming process.
[104] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[105] (First embodiment)
[106] 3 is an exploded perspective view of a variable capacitor according to a first embodiment of the present invention. The insulating layer 32 is arrange | positioned on the board | substrate 31. FIG. The substrate 31 is made of silicon, a compound semiconductor, or the like and has an opening 40 in the center thereof. The opening 40 is also connected to the insulating layer 32. The capacitor includes a fixed electrode 38, a movable electrode 39, and a dielectric layer 37 supported on the fixed electrode 38. The movable electrode 39 is driven by four piezoelectric actuators. In addition, FIG. 3, denoted by the reference numbers for convenience only, one piezoelectric actuator (36 _1). The piezoelectric actuator (36 ₁₎ comprises a lower drive electrode (33 _1), the piezoelectric element (34 ₁₎ and the upper drive electrode (36 _1). The same is true for other piezo actuators. In this specification, there is a case called by incorporating a piezoelectric actuator (36 ₁ -36 _4), said piezoelectric actuator, in this case, may be called as a deformation of each of the piezoelectric actuator (36 ₁ -36 _4).
[107] As shown in FIG. 4, the lower drive electrodes 33 ₁ , 33 ₂ , 33 _3, and 33 ₄ and the movable electrode 39 of the four piezoelectric actuators are formed of one common electrode 41. In other words, the lower driving electrodes 33 ₁ , 33 ₂ , 33 ₃ and 33 ₄ and the movable electrode 39 are integrally formed. Pads 33a, 33b, 33c, and 33d are formed at the distal ends of the lower drive electrodes 33 ₁ , 33 ₂ , 33 _3, and 33 ₄ commonly connected via the movable electrode 39. These pads 33a-33d are located on the insulating layer 32 on the substrate 31. In addition, the external connection pad includes not only the connection wiring to the outside but also the lead electrode (line) formed on the insulating layer, for example. The lower drive electrodes 33 ₁ , 33 ₂ , 33 ₃ and 33 ₄ and the movable electrode 39 are located on the opening 40 formed in the substrate 31. In addition, as will be apparent from the description of the manufacturing method described later, an insulating layer is formed behind the common electrode 41.
[108] Rectangular piezoelectric elements 34 ₁ , 34 ₂ , 34 _3, and 34 ₄ are disposed on the lower drive electrodes 33 ₁ , 33 ₂ , 33 _3, and 33 ₄ , respectively. The piezoelectric elements 34 ₁ , 34 ₂ , 34 _3, and 34 ₄ are, for example, piezoelectric materials of PZT (lead zirconate titanate) type and have a property of stretching in a direction perpendicular to the driving electric field. On the rectangular piezoelectric elements 34 ₁ , 34 ₂ , 34 ₃ and 34 ₄ , individually independent substantially rectangular upper drive electrodes 35 ₁ , 35 ₂ , 35 ₃ and 35 ₄ are arranged. As will be described later, when a voltage is applied between the upper driving electrodes 35 ₁ , 35 ₂ , 35 ₃ , and 35 ₄ and the lower driving electrodes 33 ₁ , 33 ₂ , 33 ₃ and 33 ₄ , the piezoelectric element 34 ₁ is applied. , 34 ₂ , 34 ₃ and 34 ₄ are displaced so that the movable electrode 39 is displaced in the vertical direction of the substrate 31.
[109] The fixed electrode 38 is bent at two positions 38a and 38b, and is arranged to span the movable electrode 39. Both sides of the fixed electrode 38 are positioned on the insulating layer 32. The dielectric layer 37 is disposed on the inner side of the central portion of the fixed electrode 38. The dielectric layer 37 is smaller in size than the space formed by the upper driving electrodes 35 ₁ , 35 ₂ , 35 _3, and 35 ₄ . The fixed electrode 38 may use a straight plate shape. In this case, the spacers are disposed on the insulating layer 32 so as to sandwich the two electrodes and the movable electrodes 39 in the longitudinal direction of the substrate 31, and the fixed electrodes are disposed on the spacers.
[110] FIG. 6J is a cross-sectional view taken along the line VI-VI in FIG. 3. 5 and 6 are views for explaining the manufacturing method of the variable capacitor shown in FIG. The manufacturing method will be described later. (J) of FIG. 6, the piezoelectric actuator (36 ₃₎ constituted by the piezoelectric actuator (36 ₁₎ and a lower drive electrode (33 _3), a piezoelectric element (34 _3), the upper drive electrode (35 ₃₎ shown It is. The piezoelectric actuators 36 ₁ and 36 ₃ and the movable electrode 39 stand up by themselves in the space on the opening 40 formed in the substrate 31. The same applies to the other piezoelectric actuators 36 ₂ and 36 ₄ . The dielectric layer 37 is supported on the fixed substrate 38 is located in a space surrounded by four piezoelectric actuators (36 ₁ -36 _4), and faces the movable electrode 39 via a gap 42. The By driving the piezoelectric actuator (36 ₁ -36 _4), the movable electrode 39 can be displaced to a position in contact with the dielectric layer 37 from the state shown in (j) of FIG. As a result, the distance between the fixed electrode 38 and the movable electrode 39 is changed to change the capacitance. Since the dielectric layer 37 is interposed between the fixed electrode 38 and the movable electrode 39, the dielectric constant also changes, and the change in capacitance between the fixed electrode 38 and the movable electrode 39 is very large.
[111] 7 is a view for explaining the operation of the piezoelectric actuator (36 _1). The piezoelectric actuator (36 ₁₎ is a uni-morph made of a lower driving electrodes (33 ₁₎ and the piezoelectric element (34 ₁₎ and the upper drive electrode (35 _1). The piezoelectric element 34 ₁ is polarized in the direction of the arrow shown. When applying a direct current voltage V between the lower drive electrode (33 ₁₎ and the upper drive electrode (35 _1), a fixed electrode 38 of the piezoelectric element (34 ₁₎ cantilevered (cantilever) side is contracted in the piezoelectric constant d31 direction , The other side is inflated. Thus, the piezoelectric actuator (36 ₁₎ is deformed as illustrated. When to apply the direct current voltage V pad (33a) in FIG. 4 cheukin (side that is connected to the movable electrode 39) opposite to the piezoelectric actuator (36 ₁₎ is lifted the lower driving electrodes (33 ₁₎ and The movable electrode 39 formed integrally displaces in the direction of the dielectric layer 37. Other piezoelectric actuator (36 ₂ -36 ₄₎ is similarly lift the movable electrode 39. As a result, the movable electrode 39 is close to the dielectric layer 37. In this way, the capacitance can be controlled by adjusting the gap. Further, the movable electrode 39 and the dielectric layer until the 37 is in contact, even when deformation of a piezoelectric actuator (36 ₁ -36 _4), these driving the upper electrode (35 ₁ -35 ₄₎ and the fixed electrode 38 Do not touch
[112] In order for the configuration shown in FIG. 7 to operate as described above, it is necessary to satisfy any of the following conditions. The lower driving electrode 33 ₁ and the upper driving electrode 35 ₁ are formed of different materials (the lower driving electrode 33 ₁ is formed of a material having a relatively high Young's modulus). For example, the lower driving electrode 33 ₁ is formed of a metal containing platinum, and the upper driving electrode 35 ₁ is formed of ruthenium oxide (RuO ₂ ). In the case of the lower driving electrodes (33 ₁₎ and the upper drive electrode (35 ₁₎ of the same material, and formed to have a different thickness (and the lower driving electrodes (33 ₁₎ to form a thick side). For example, the lower driving electrodes (33 _1), p. 2 to 5 times thicker. Further, as another means, and said means, the drive electrode and forms a different layer to the lower driving electrodes (33 ₁₎ or the upper driving electrodes (35 ₁₎ (formed on the lower driving electrodes (33 ₁₎ thereof). Moreover, you may use together the said means. As described later, in the first embodiment, the lower drive electrode 33 ₁ is formed on the insulating layer 32, and the lower drive electrode 33 ₁ is either platinum / tantalum (Pt / Ta) or The upper drive electrode 35 ₁ is formed of a laminate of platinum / titanium (Pt / Ti) and ruthenium oxide.
[113] The piezoelectric actuator (36 ₁ -36 ₄₎ is connected in parallel uni shown in not limited to the morphs, in Figure 8 (a) by mole peuna type, series-connected bi-morph shown in FIG. 8 (b) It may be. In FIGS. 8A and 8B, piezoelectric elements 34 _1a and 34 _1b polarized in the direction of the arrow _{shown above} and below the intermediate electrode 43 are disposed. A piezoelectric element (34 _1a) there is a lower driving electrodes (33 ₁₎ arranged, the piezoelectric element (34 _1b) is arranged in the upper drive electrode (35 _1). As shown, the bimorph is deformed when the DC voltage V is applied.
[114] 9 is a view for explaining the effect of the present invention. As shown in Fig. 9A, the thickness of the _dielectric layer 37 is d _dielectric , and the thickness of the air layer formed between the dielectric layer 37 and the movable electrode 39 is d _air . In this case, the distance d between the fixed electrode 38 and the movable electrode 39 is d = d _dielectric + d _air . FIG. 9B is a diagram showing a change in capacitance C [F] when the movable electrode 39 is driven to change the thickness d _air of the air layer. The movable electrode 39 and the fixed electrode 38 were square, and the area was 230 micrometers * 230 micrometers. Moreover, distance d was d = 0.75 micrometers, the thickness d _air of the _air layer was d _air = 0.3 micrometer, and d _air /d=0.4. As the dielectric layer 37, alumina Al ₂ O ₃ (ε = 10), which is a material having a low dielectric loss, was used. As the movable electrode 39 shown in FIG. 9A, one formed of the common electrode 41 having the size shown in FIG. 4B was used. The piezoelectric actuator (36 ₁ -36 ₄₎ has the following configuration. The upper drive electrodes 35 _{1-3 4 4} were formed of platinum, and the thickness was 0.5 μm. Forming a piezoelectric element (34 ₁ -34 ₄₎ to the PZT, and had a thickness of 1.0μm. Forming a lower driving electrodes (33 ₁ -33 ₄₎ of platinum and had a thickness of 0.5μm. An insulating layer 32 to the Si ₃ N _4, and had a thickness of 2.0μm.
[115] As a comparative example, the change in capacitance C when the dielectric layer 37 was removed was also measured. As shown in FIG. 9B, the variable capacitor having the dielectric layer 37 disposed therein is about 1.36 pF in the initial state (the movable electrode 39 is not displaced), and the movable electrode 39 is formed of the dielectric layer 37. ) Has a capacity of about 10.4 pF, the ratio is about 7.6 times, and the increment ΔC is about 660%. In contrast, it can be seen that there is almost no change in capacity of the comparative example. As described above, the variable capacitor according to the first embodiment of the present invention has a very large capacity, and the variable range of the capacity is very large. In addition, since the control of the movable electrode 39 to the expansion and contraction of the piezoelectric actuator (36 ₁ -36 _4), it is possible to change the thickness of the layer of air d _air continuously, it is possible to fine adjustment of the capacity.
[116] In addition, since the fixed electrode 38, the movable electrode 39, the dielectric layer 37, and the piezoelectric actuators 36 _{1 to} 36 ₄ are formed on the same substrate 31, they are compact and low in cost. Moreover, since the dielectric layer 37 is supported by the fixed electrode 38, the mass of the movable part becomes only the mass of the movable electrode 39, so that the effect excellent in impact resistance is also exhibited. In addition, there is no risk of the movable electrode 39 contacting the fixed electrode 38 due to the presence of the dielectric layer 37, and the breakage of the variable capacitor due to the short does not occur.
[117] Next, a method of manufacturing the variable capacitor will be described with reference to FIGS. 5 and 6. In the following description, the piezoelectric actuators 36 ₃ will be described with attention, but other piezoelectric actuators are also formed at the same time. 5 and 6 are sectional views taken along the line VI-VI in FIG. 2.
[118] First, as shown in Fig. 5A, an insulating layer 32 made of silicon nitride of low stress is formed by a low pressure chemical vapor deposition (LPCVD) method on a substrate 31 made of silicon. To form.
[119] Next, as shown in FIG. 5B, the movable electrode 39 and the lower drive electrode 33 _{3 of} pt / Ti (platinum / titanium) are formed on the insulating layer 32 by photolithography. Are simultaneously formed into a predetermined shape. The thickness of Pt / Ti is 4500 kV / 500 kV, for example. Patterning is performed by RIE using Cl ₂ O ₂ (chlorine / oxygen) -based gas. Of course, other lower drive electrodes 33 ₁ , 33 ₂ , 33 ₄ are also formed at the same time.
[120] And, as shown in FIG. 5 (c), a sputtering method, a sol-gel, MOCVD (Metalorganic CVD) by a method or a laser ablation method, on the lower driving electrodes (33 _3), lithium niobate, barium titanate, to form a piezoelectric element (34 ₃₎ having a predetermined shape to the open titanate, zirconate titanate sanyeon, bismuth titanate of the material. Patterning is performed by RIE using Cl ₂ O ₂ (chlorine / oxygen) -based gas.
[121] That performs the post, one, after the formation of the upper driving electrodes (35 ₃₎ of ruthenium or platinum oxide in a predetermined shape, the heat treatment at a temperature of 750 ℃ from 650 ℃ as shown in Figure 5 (d), 5 of by etching the insulating layer 32 as shown in (e) in a predetermined pattern, the insulating layer lower driving electrodes (33 ₃₎ formed on a 32, a piezoelectric element (34 ₃₎ and the upper driving electrodes (35 ₃ The unimorph piezoelectric actuator (36 ₃ ) consisting of a) is formed. The piezoelectric actuator (36 _3), may be defined as consisting of the insulating layer 32, the lower driving electrodes (33 _3), a piezoelectric element (34 ₃₎ and the upper driving electrodes (35 _3). Further, the heat treatment after forming, and a piezoelectric element (34 _3), may be performed before the formation of the upper driving electrodes (35 _3).
[122] 6, the sacrificial layer 44, the dielectric layer 37, and the fixed electrode 38 made of a resist material are sequentially formed as shown in Figs. 6F, 6G, and h. As shown in (i), the sacrificial layer 44 is removed to secure a gap 42 between the dielectric layer 37 and the movable electrode 39. As the material of the dielectric layer 37, beryllium oxide, aluminum oxide, aluminum nitride, barium titanate, magnesium titanate, titanium oxide, glass, silicon nitride and the like are preferable. Examples of the resist material include polyimide resist (removal of resist stripping solution), metal oxides such as magnesium oxide (MgO) (removal of acetic acid solution), metal oxides such as PSG (Phosphosilicate Glass) (removal of hydrofluoric acid solution), and the like. There is this. In addition, the thickness of the sacrificial layer 44 is 0.3 micrometer, for example.
[123] Finally, as shown in FIG. 6 (j), the piezoelectric actuator (36 ₃₎ and the movable electrode (39) RIE with the substrate 31 of the surrounding insulating layer 32 lower from the substrate 31 side (Reactive Ion etching) of the support structure in by forming the opening 40 is etched by the apparatus, the movable electrode 39 and the lower insulating layer (32) is a piezoelectric actuator (36 ₃₎ the substrate 31 via the Obtain a variable capacitor. When the substrate 31 is silicon, the etching can be performed by deep RIE. The etching gas in this case uses SF6 (sulfur hexafluoride), and the mask for forming the opening 40 is a resist. In this case, a piezoelectric actuator or the like is formed on the (100) surface or the (110) surface of the silicon substrate 31, and the etching is performed by anisotropic etching. The etchant is KOH (potassium hydroxide), for example, and the mask material is formed of SiO ₂ , Si ₃ N ₄ , Cr, Au, or the like.
[124] In the above manufacturing method, since the sacrificial layer 44 and the fixed electrode 38 are formed after the heat treatment for the piezoelectric actuator performed in FIG. 5D, the sacrificial layer 44 and the fixed electrode 38 are formed. The material can be selected without depending on the heat treatment conditions. Also, after the above description it has been described using an example form the movable electrode 39 and the upper driving electrodes (35 ₁ -35 ₄₎ of the piezoelectric actuator at the same time, forming only the upper drive electrodes (35 ₁ -35 _4), After heat-processing, you may form the movable electrode 39 which uses Cu, Al, etc. as a material. Since the movable electrode 39 is formed after the heat treatment for the piezoelectric actuator, the wiring resistance can be made lower.
[125] 10 is a modified example of the manufacturing method. The manufacturing method according to the modification is characterized in that the sacrificial layer 44 is more effectively removed. FIG.10 (f)-(j) has shown the process substituted by FIG.6 (f)-(j). Step (f) of FIG. 10 is performed after the steps shown in (a) to (e) of FIG. 5. As shown in FIG. 10F, a sacrificial layer 44 made of a resist material is formed on the movable electrode 39.
[126] Next, as shown in FIG. 10G, after forming the dielectric layer 37, a plurality of etching holes 45 are formed in the dielectric layer 37. Formation of the etching holes 45, for example, forms a mask in the dielectric layer 37 to etch the dielectric layer 37. For example, the etching holes 45 are arranged in a matrix shape. Each etching hole 45 may be the same size or may be partially different sizes. In the example shown to FIG. 10G, the etching hole 45c of a center part has a diameter larger than the etching hole 45 of a peripheral part. This is because the sacrificial layer 44 in the center portion is mainly removed through the etching hole 45, so that the opening of the etching hole 45c is made relatively large so that the removal of this portion can be efficiently performed.
[127] Next, as shown in FIG. 10 (h), after the fixed electrode 38 is formed, the fixed electrode 38 is etched using a mask having the same pattern as the mask used in FIG. 10 (g). An etching hole 46 continuous to the hole 45 is formed. Then, as shown in FIG. 10 (i), the sacrificial layer 44 is removed. At this time, since the sacrificial layer 44 is removed through not only the side but also the etching hole, as indicated by the arrow, the sacrificial layer 44 can be removed more efficiently and effectively than in the case of FIG. 6 (i). have.
[128] Finally, a piezoelectric actuator (36 ₃₎ and the movable electrode 39 to the peripheral lower portion of the insulating layer 32, the substrate 31, the substrate 31 by the RIE apparatus as shown in (j) of FIG. 10 by etching from the side, via the movable electrode 39 and the lower portion of the insulating layer 32, the piezoelectric actuator (36 ₁ -36 ₄₎ (if more specific, the lower movable electrode (33 ₁ -33 ₄₎₎ A variable capacitor having a structure supported by the substrate 31 and having holes arranged in a matrix form penetrating through the fixed electrode 38 and the dielectric layer 37 is obtained. The movable electrode 39 can also be said to be supported on the substrate 31 via the piezoelectric actuator (36 ₁ -36 _4).
[129] (2nd Example)
[130] 11 is an exploded perspective view of a variable capacitor according to a second embodiment of the present invention. 12 is a sectional view taken along the line XII-XII in FIG. 11.
[131] The present embodiment is characterized in that the dielectric layer 37 is formed on the movable electrode 39. Except for this point, it is similar to the first embodiment of the present invention. Since the dielectric layer 37 is disposed on the movable electrode 39, the impact resistance is slightly inferior to that of the first embodiment, but the other effects are the same. What is necessary is just to reverse the process of FIG.6 (f) and (g) mentioned above with the manufacturing method of 2nd Example. That is, instead of forming the sacrificial layer 44 in FIG. 6F, the dielectric layer 37 is formed, and instead of forming the dielectric layer 37 in FIG. 6G, the sacrificial layer 44 is formed. do. The other manufacturing process is the same as the manufacturing process of a 1st Example. In addition, it is also possible to use the etching hole demonstrated with reference to FIG. Instead of forming the sacrificial layer 44 in FIG. 10F, the dielectric layer 37 is formed. Instead of forming the dielectric layer 37 in FIG. 10G, the sacrificial layer 44 is formed. In FIG. 10H, the fixed electrode 38 is formed and the etching hole 46 is formed. The other manufacturing process is the same as the manufacturing process of a 1st Example.
[132] 13 is a perspective view of a modification of the second embodiment, and FIG. 14 is a plan view. In the drawings, the same reference numerals are given to the same components as those described above.
[133] In the second embodiment described above, compared to the use of upper drive electrodes (35 ₁ -35 ₄₎ of the individual, this embodiment uses the common electrode 48. The common electrode 48 has an arm (arm) portion formed on the piezoelectric element (34 ₁ -34 _4), connecting portions, each arm portion. In addition, the common electrode 48 is connected to the pad 49 for external connection formed integrally. The pad 49 is formed on the insulating layer 32 on the substrate 31. The pad 50 is disposed at a position opposite to the pad 49 with the fixed electrode 38 therebetween. The pad 50 is also formed on the insulating layer 32. Pad 50 is connected to the movable electrode 39 and the piezoelectric actuator (36 ₁ -36 _4), the lower driving electrodes (33 ₁ -33 _4). Further, pads 47 for connecting the fixed electrode 38 to the outside are formed on both sides in the longitudinal direction of the fixed electrode 38. The modification of the said structure exhibits the effect | action and effect similar to 2nd Example.
[134] In addition, the common electrode 48 may be applied to the first embodiment. It is also possible to use the pads 47, 49 and 50 in the first embodiment. Thus, by using the pad with a large area, external connection can be formed more easily.
[135] (Third Embodiment)
[136] 15 is an exploded perspective view of a variable capacitor according to a third embodiment of the present invention. This embodiment is characterized in that the fixed electrode is arranged on the substrate side. In addition, in the following description, reference is made to FIG. 17 (i) with FIG. FIG. 17 (i) is sectional drawing along the XVII-XVII line of FIG. FIG. 17 is a cross sectional view showing the manufacturing method of the variable capacitor according to the present embodiment together with FIG.
[137] The insulating layer 32 is arrange | positioned on the board | substrate 31. FIG. The board | substrate 31 has the opening 40, and the insulating layer 32 is formed so that it may cross. In other words, the insulating layer 32 is arranged in a diaphragm shape. This point is different from the insulating layer 32 of the first embodiment. The capacitor includes a fixed electrode 52, a movable electrode 59, and a dielectric layer 57 supported by the fixed electrode 52. The movable electrode 59 is driven by four piezoelectric actuators. In FIG. 17 (i), two piezoelectric actuators 56 ₁ and 56 _{3 are} shown among four piezoelectric actuators. Moreover, let the remaining piezoelectric actuators be 56 ₂ and 56 ₄ . The piezoelectric actuator (56 ₁₎ is, Uni mole peuhyeong including a lower driving electrodes (53 _1), the piezoelectric element (54 ₁₎ and the upper drive electrode (56 _1). Similarly, as shown in Fig. 17 (i), it comprises a piezoelectric actuator (56 _3), the lower driving electrodes (53 _3), a piezoelectric element (54 ₃₎ and the upper driving electrodes (56 _3). Lower driving electrodes (53 ₃₎ is located in the upper portion of the opening 40 formed on the substrate 31 via the insulating layer 32,. The same applies to other piezoelectric actuators 56 ₁ , 56 ₂ and 56 ₄ .
[138] The fixed electrode 52 is disposed on the insulating layer 32. The fixed electrode 52 is flat and different from the fixed electrode 38 described above. The dielectric layer 57 is disposed on the fixed electrode 52. The movable electrode 59 is disposed so as to face the dielectric layer 57 via the air layer. The movable electrode 59 is part of the common electrode 58. The common electrode 58 includes upper drive electrodes 55 ₁ , 55 ₂ , 55 ₃ and 55 ₄ , which are connected to the movable electrode 59. Separate lower drive electrodes 53 ₁ , 53 ₂ , 53 _3, and 53 ₄ are disposed at positions opposing the upper drive electrodes 55 ₁ , 55 ₂ , 55 _3, and 55 ₄ . The piezoelectric elements 54 ₁ , 54 ₂ , 54 _3, and 54 between the lower drive electrodes 53 ₁ , 53 ₂ , 53 _3, and 53 ₄ and the upper drive electrodes 55 ₁ , 55 ₂ , 55 _3, and 55 ₄ , respectively. ₄ ) is arranged. In the lower driving electrodes 53 ₁ , 53 ₂ , 53 _3, and 53 ₄ , a wide pad portion is formed on the insulating layer 32.
[139] The third embodiment of the present invention operates in the same manner as the first embodiment of the present invention described above. Lower driving electrodes (53 ₁ -53 ₄₎ and the piezoelectric element (54 ₁ -54 ₄₎ according to that placing a voltage between the upper driving electrodes (55 ₁ -55 _4), the voltage applied size is contracted in the direction d31 . At the same time, the movable electrode 59 moves toward the fixed electrode 52, and the distance between the movable electrode 59 and the fixed electrode 52 changes. At this time, since the dielectric layer 57 is interposed therebetween, the dielectric constant also changes, and the capacitance between the movable electrode 59 and the fixed electrode 52 changes significantly.
[140] The variable capacitor according to the third embodiment of the present invention has a considerably large capacity, and the variable range of the capacity is also very large. In addition, since the control of the movable electrode 59 to the expansion and contraction of the piezoelectric actuator (56 ₁ -56 _4), it is possible to vary the thickness of the aforementioned layer of air d _air continuously, it is possible to fine adjustment of the capacity. In particular, the change in capacitance increases as the movable electrode 59 approaches the dielectric layer 57, and the Q value in the vicinity thereof is particularly large.
[141] In addition, because it is formed on the fixed electrode 52, movable electrode 59, a dielectric layer 57 and the piezoelectric actuator (56 ₁ -56 ₄₎ is the same substrate 31, a small-sized and low cost. Moreover, since the dielectric layer 57 is supported by the fixed electrode 52, the mass of the movable part becomes only the mass of the movable electrode 59, and also exhibits an excellent effect on impact resistance. In addition, there is no risk that the movable electrode 59 contacts the fixed electrode 52 due to the presence of the dielectric layer 57, and therefore the breakage of the variable capacitor due to the short does not occur.
[142] Next, referring to Figs. 16 and 17, a manufacturing method of the variable capacitor according to the third embodiment will be described. Further, in the following description noted by the piezoelectric actuator (56 _3), but it is also formed at the same time the other piezoelectric actuators. 16 and 17 are sectional views taken along the line XVII-XVII in FIG. 15.
[143] First, as shown in Fig. 16A, an insulating layer 32 of silicon nitride or silicon oxide is formed on a substrate 31 made of silicon. Next, as shown in FIGS. 16B and 16C, the fixed electrode 52 and the dielectric layer 57 having a predetermined shape are formed on the insulating layer 32 by photolithography.
[144] As shown in Fig. 16D, after the sacrificial layer 60 made of a resist material is formed on the entire surface, it is shown in Figs. 16E, 17F, and 17G. forming a piezoelectric actuator (56 ₃₎ of the uni-peuhyeong mol, composed of a lower driving electrodes (53 _1), the piezoelectric element (54 _1), the upper drive electrode (55 ₁₎ as described. Of course, other piezoelectric actuators 56 ₁ , 56 ₂ and 56 ₄ are also formed at the same time. The movable electrode 59 is also formed at this time.
[145] And, as shown in (h) of Figure 17, by removing the sacrificial layer 60, by securing a space between the dielectric 57 and the movable electrode 59, the piezoelectric element (54 ₁ -54 ₄₎ Heat treatment is performed.
[146] Finally, as shown in Fig.'S 17 (i), the piezoelectric actuator (56 ₁ -56 ₄₎ and the movable electrode 59 of the peripheral lower portion of the insulating layer 32, the substrate 31, the substrate 31 side By etching with the RIE apparatus from the above, the desired variable capacitor is obtained by making the fixed electrode 52 and the lower insulating layer 32 into a diaphragm shape.
[147] Similarly to the first embodiment Although not shown, the movable electrode 59 and the dielectric layer (57) until it contacts the piezoelectric actuator (56 ₁ -56 _4), even when a variation, the top of these driving electrodes (55 ₁ -55 ₄ ) and the fixed electrode 52 are configured not to contact.
[148] 18 is a modification of the manufacturing method. The manufacturing method according to the modification is characterized in that the sacrificial layer 60 is more effectively removed. 18 (f) to (i) show a step of replacing with (f) to (i) in FIG. 17. Step (f) of FIG. 18 is performed after the steps shown in (a) to (e) of FIG. 17. As shown in FIG. 18 (f), to form a lower driving electrodes (53 ₃₎ and the piezoelectric element (54 ₃₎ on the sacrificial layer 60. Next, Figure 18, as shown in (g), the upper drive electrode (55 ₃₎ and the movable electrode 59 to form the movable electrode 59, for example an etched hole (61 arranged in a matrix in ).
[149] Then, the free space between, as shown in Fig. 18 (h), by removing the sacrificial layer 60, dielectric layer 57 and the movable electrode 59 and the piezoelectric element (54 ₁ -54 ₄₎ Heat treatment is performed. Since the sacrificial layer 60 is removed not only on the side but also through the etching hole 61, the sacrificial layer 60 can be removed efficiently and effectively. Finally, as shown in Fig.'S 18 (i), the piezoelectric actuator (56 ₁ -56 ₄₎ and the movable electrode 59 of the peripheral lower portion of the insulating layer 32, the substrate 31, the substrate 31 side By etching with the RIE device in this manner, the fixed electrode 52 and the insulating layer 32 below it are formed into a diaphragm to obtain a desired variable capacitor.
[150] (Example 4)
[151] 19 is an exploded perspective view of a variable capacitor according to a fourth embodiment of the present invention. 20 is a sectional view taken along the line XX-XX in FIG. 19.
[152] The present embodiment is characterized in that the dielectric layer 57 is formed on the inner side surface of the movable electrode 59. Except for this point, it is similar to the third embodiment of the present invention. Since the dielectric layer 57 is disposed on the movable electrode 59, the impact resistance is slightly inferior to that of the third embodiment, but other effects are the same. In the manufacturing method of the fourth embodiment, the steps of FIGS. 16 and 17 may be changed to form the sacrificial layer 60 first and then the dielectric layer.
[153] (Example 5)
[154] FIG. 21 is an exploded perspective view of a variable capacitor according to a fifth embodiment of the present invention, and FIG. 22 is a plan view of the variable capacitor shown in FIG. In Figs. 21 and 22, the same reference numerals are given to the same components as those described above.
[155] In this embodiment, the fixed electrode 52 is located on the substrate side. A common electrode 70, and has a movable electrode 59, the upper driving electrodes (55 ₁ -55 ₄₎ and a pad for external connection (72, 73). The pads 72 and 73 are arranged in point symmetry (or diagonally of the movable electrode 59) with respect to the movable electrode 59. The lower drive electrodes of the four piezoelectric actuators are formed of a common electrode having a pad 74 and a common electrode having a pad 75. The common electrode with the pad 74 has two lower drive electrodes. One of them extends straight in the longitudinal direction of the substrate 31 and is folded in the middle, and the other is bent in an L shape to extend straight in the direction of the short side of the substrate 31. Similarly, the common electrode with pad 75 has two lower drive electrodes. One of them extends straight in the longitudinal direction of the substrate 31 and is folded in the middle, and the other is bent in an L shape to extend straight in the direction of the short side of the substrate 31. The pads 74 and 75 are arranged on the other diagonal line of the movable electrode 59. The dielectric layer 57 is disposed on the fixed electrode 52.
[156] The variable capacitors shown in Figs. 21 and 22 have an additional effect of making the connection to the outside easier because the pad has a wider width than the variable capacitor shown in Fig. 15. In addition, since it is obvious to those skilled in the art in the manufacturing method of FIG. 21 and FIG. 22, what is necessary is just to modify FIG. 16, FIG.
[157] (Example 6)
[158] FIG. 23 is an exploded perspective view of a variable capacitor according to a sixth embodiment of the present invention, FIG. 24 is a plan view of this variable capacitor, and FIG. 25 is an enlarged perspective view of a part of the variable capacitor shown in FIG.
[159] The variable capacitor of this embodiment has a substrate 131, four piezoelectric actuators 136 _{1 to} 136 ₄ , a movable electrode 139, a dielectric layer 137, and a fixed electrode 138. The fixed electrode has a portion (hereinafter referred to as a bridge portion) 138a that bridges the movable electrode 139, which is substantially the same shape as the movable electrode 139, and has a dielectric layer 137 interposed therebetween. It is arranged so as to face the movable electrode 139. In other words, the bridge portion 138a of the fixed electrode 138 faces only the movable electrode 139. The supporting portion 138b of the fixed electrode 138 is disposed in an inclined direction with respect to the direction in which the piezoelectric actuators 136 _{1 to} 136 ₄ extend, and is disposed along one corresponding side of the movable electrode 139. The bridge portion 138a is disposed obliquely with respect to the pad portion 138c (which is also a support portion of the bridge portion 138a). The movable portion 138a does not have any of the piezoelectric actuators 136 _{1 to} 136 ₄ .
[160] By using the fixed electrode 138 of the above structure, the following problem can be eliminated. If the bridge portion is long and is formed so as to bridge portions other than the movable electrode, it is easily affected by residual stress generated at the time of forming the fixed electrode and surface tension (water or solution) during drying after washing. For this reason, the bridge portion is deformed on the movable electrode side and vice versa, so that the distance between the movable electrode and the fixed electrode cannot be kept constant, the variation in the value of the capacitance to be formed may increase, and the yield may decrease. In particular, when the tensile stress remains as a residual stress in the fixed electrode or when the fixed electrode deforms toward the movable electrode due to the surface tension of water, the gap between the upper drive electrode forming the piezoelectric actuator and the fixed electrode is narrowed and is in contact with the piezoelectric element. The actuator, movable electrode or fixed electrode may be damaged. Furthermore, if the fixed electrode is over the piezoelectric actuator, parasitic capacitance is generated between the fixed electrode and the electrode of the piezoelectric actuator.
[161] On the other hand, since the fixed electrode 138 has a short length of the bridge portion 138a which covers the movable electrode, the bridge portion 138a has a high strength. As a result, by eliminating influences such as residual stress generated at the time of forming the fixed electrode and surface tension of water generated at the time of cleaning, a variable capacitor having a small variation in capacitance and a high yield can be realized. In addition, since the fixed electrode 138 does not extend the piezoelectric actuators 136 _{1 to} 136 ₄ , no parasitic capacitance is generated.
[162] Moreover, the other parts of 6th Example are comprised as follows. The dielectric layer 137 is attached to the bridge portion 138a. An opening 140 formed in the substrate 131 is disposed on the back surface of the movable electrode 139 (FIG. 25). A piezoelectric actuator (136 _1), the lower drive electrode is formed in a _{(133: 1),} the piezoelectric element (134 _1), and the upper driving electrodes (135 _1). Similarly, the other piezoelectric actuators 136 ₂ , 136 ₃ , 136 ₄ also have lower drive electrodes 133 ₂ , 133 ₃ , 133 ₄ , piezoelectric elements 1342 ₂ , 134 ₃ , 134 ₄ , and upper drive electrodes, respectively. (135 ₃ , 135 ₃ , 135 ₄ ). The movable electrode 139 and the lower driving electrodes 133 _{1 to} 133 ₄ are integrally formed common electrodes. The common electrode has pads 139a and 139b for external connection formed on the insulating layer 132 on the substrate 131. The upper drive electrodes 135 _{1 to} 135 ₄ are also formed integrally and have an external connection pad 148a.
[163] FIG. 26: is sectional drawing explaining the manufacturing method of the variable capacitor shown to FIGS. 23-25, and shows the cross section at the time of dividing a variable capacitor in parallel to the short side direction of a variable capacitor. (E)-(j) of FIG. 26 continue to FIG. 5 (a)-(d) mentioned above. In addition, in FIG. 26 (e)-(j), illustration of the piezoelectric actuator is abbreviate | omitted in order to simplify drawing. In addition, the matter demonstrated by the manufacturing method mentioned above, such as process conditions and a material, is abbreviate | omitted in the following description.
[164] In FIG. 26E, the movable electrode 139 is formed on the insulating layer 132. The insulating layer 132 has a groove 143 formed by patterning. The movable electrode 139 is formed on the insulating layer 132 surrounded by the groove 143.
[165] Next, as shown in FIG. 26F, the sacrificial layer 144 is formed on the movable electrode 139. At this time, the sacrificial layer 144 is also formed in the groove 143.
[166] Next, as shown in FIG. 26G, the dielectric layer 137 is formed on the sacrificial layer 144.
[167] Next, as shown in FIG. 26H, the fixed electrode 138 is formed on the dielectric layer 137 and the insulating layer 132.
[168] Next, as shown in FIG. 26I, the substrate 131 is etched to form an opening 140 under the movable electrode 139.
[169] Finally, as shown in FIG. 26J, the sacrificial layer 144 is removed.
[170] In the steps of FIGS. 26G and 26H, it is preferable to form etching holes similar to the etching holes described in FIGS. 10G and 10H. By forming the etching holes, the sacrificial layer 144 can be removed more effectively and efficiently in the step (j) of FIG. 26.
[171] (Example 7)
[172] FIG. 27 is an exploded perspective view of a variable capacitor according to a seventh embodiment of the present invention, FIG. 28 is a plan view of this variable capacitor, and FIG. 29 is an enlarged perspective view of a part of the variable capacitor shown in FIG. In the drawings, the same reference numerals are assigned to the same components as those shown in FIGS. 23 to 25.
[173] The variable capacitor of this embodiment includes a substrate 131, four piezoelectric actuators 136 _{1 to} 136 ₄ , a movable electrode 139, a dielectric layer 137, and a fixed electrode 238. The configuration of the fixed electrode 238 is different from that of the sixth embodiment described above. The fixed electrode 238 has support portions 238d and 238e in addition to the bridge portion 238a, the support portion 238b, and the pad portion 238c (which is also a support portion of the bridge portion 238a). The bridge portion 238a is supported on the insulating layer 132 on the substrate 131 at four places of the support portions 238b, 238c, 238d, and 238e. These support parts 238b to 238e are disposed along four sides of the movable electrode 139. Thus, the fixed electrode 238 is the structure which arrange | positioned the support part 238d and 238e to the fixed electrode 138 shown to FIGS. 23-25. Since the bridge portion 238a is supported at four places, higher strength can be obtained. In addition, the support of the bridge part 238a is not limited to four places, but may be three or five places or more.
[174] (Example 8)
[175] 30 is an exploded perspective view of a variable capacitor according to an eighth embodiment of the present invention, and FIG. 31 is an enlarged perspective view of a part of the variable capacitor. In the drawings, the same reference numerals are assigned to the same components as those shown in FIGS. 23 to 25.
[176] The variable capacitor of this embodiment has a substrate 131, four piezoelectric actuators 136 _{1 to} 136 ₄ , a movable electrode 139, a dielectric layer 237, and a fixed electrode 138. The structure of the dielectric layer 237 is different from the dielectric layer 137 of the sixth embodiment described above. The dielectric layer 237 bridges the movable electrode 139 similarly to the bridge portion 138a of the fixed electrode 138. The dielectric layer 237 has support portions 237a and 237b on two opposing sides. The support portions 237a and 237b are disposed on the substrate 131 and are supported on the substrate 131. As a result, the strength of the bridge portion 138a can be further increased.
[177] 32 is a cross-sectional view illustrating the method of manufacturing the variable capacitor illustrated in FIGS. 30 to 31, and illustrates a cross section when the variable capacitor is divided in parallel in the short side direction of the variable capacitor. (E)-(j) of FIG. 32 is continued from FIG. 5 (a)-(d) mentioned above. In addition, in FIG. 32 (e)-(j), illustration of the piezoelectric actuator is abbreviate | omitted in order to simplify drawing. In addition, in description of process conditions, a material, etc., the matter demonstrated by the manufacturing method mentioned above is abbreviate | omitted in the following description.
[178] In FIG. 32E, the movable electrode 139 is formed on the insulating layer 132. The insulating layer 132 has a groove 143 formed by patterning. The movable electrode 139 is formed on the insulating layer 132 surrounded by the groove 143.
[179] Next, as shown in FIG. 32F, a sacrificial layer 144 is formed on the movable electrode 139. At this time, the sacrificial layer 144 is formed in the groove 143. The groove 143 is large enough to have an opening even when the sacrificial layer 144 is formed.
[180] Next, as shown in FIG. 32G, the dielectric layer 237 is formed on the sacrificial layer 144. The side portion of the dielectric layer 237 enters the opening 143 and is in contact with the insulating layer 132.
[181] Next, as shown in FIG. 32H, the fixed electrode 138 is formed on the dielectric layer 237 and the insulating layer 132.
[182] Next, as shown in FIG. 32I, the substrate 131 is etched to form the opening 140 under the movable electrode 139.
[183] Finally, as shown in FIG. 32 (j), the sacrificial layer 144 is removed.
[184] In the steps of FIGS. 32G and 32H, it is preferable to form etching holes similar to the etching holes described in FIGS. 10G and 10H. By forming the etching holes, the sacrificial layer 144 can be removed more effectively and efficiently in the process of FIG. 32 (j).
[185] (Example 9)
[186] 33 is an exploded perspective view of a variable capacitor according to a ninth embodiment of the present invention, and FIG. 34 is an enlarged perspective view of a part of the variable capacitor. In the drawings, the same reference numerals are assigned to the same components as those shown in FIGS. 27 to 29.
[187] The variable capacitor of this embodiment includes a substrate 131, four piezoelectric actuators 136 _{1 to} 136 ₄ , a movable electrode 139, a dielectric layer 237A, and a fixed electrode 238. The structure of the dielectric layer 237 is different from the dielectric layer 137 of the seventh embodiment and the dielectric layer 237 of the eighth embodiment. The dielectric layer 237A has a structure in which the supporting portions 237c and 237d are disposed on two sides of the dielectric layer 237. As a result, the dielectric layer 237A has a bridge structure supported on the substrate 131 at four places. Since the fixed electrode 238 and the dielectric layer 238 are supported on the substrate 131 in four places, the strength of the bridge portion can be further increased. In addition, the dielectric layer 237A may be deformed to support three or five or more locations.
[188] (Other Embodiments)
[189] The fixed electrode of each said Example is a single layer structure. The fixed electrode is not limited to the single layer configuration, but may be composed of a plurality of layers. In the thin film, the residual stress is greatly changed by the film forming method and the film forming conditions. By laminating the layer generating the tensile stress and the layer generating the compressive stress, the residual stress of the fixed electrode can be alleviated, and variations in the distance between the fixed electrode and the movable electrode can be suppressed.
[190] FIG. 35 shows a method of manufacturing a variable capacitor in which the fixed electrode 138 of the sixth embodiment described above is composed of two layers of two layers 138 ₁ and 138 ₂ . In the process of FIG. 35H, two layers 138 ₁ and 138 ₂ are formed in this order. The two layers 138 ₁ and 138 ₂ may both be conductor layers or conductor layers and insulating layers. Generally, Cu, Al, Ti, Cr, Mo, Ni, Au, Pt, and the like tend to generate tensile stress, and SiO ₂ , Al ₂ O ₃ , Ru, Ta, and the like tend to generate compressive stress. By combining these films of tensile stress and films of compressive stress, the film thickness is appropriately changed to set so that the residual stress is alleviated throughout the fixed electrode.
[191] As an example of FIG. 35H, Cu (1 μm) and SiO ₂ (0.3 μm) are laminated by using a magnetron sputtering device at an electrode of 1 kW and a gas pressure of 0.64 Pa to form a fixed electrode 138.
[192] Moreover, you may form a fixed electrode in three or more layers. The material of a layer is suitably selected so that a residual layer may relieve residual stress as a whole, such as one layer and the remainder an insulating layer.
[193] In addition, even if the fixed electrode has a one-layer structure, residual stress can be alleviated in the entire bridge portion including the dielectric layer attached thereto. For example, when the fixed electrode 138 of FIG. 26 is formed of Cu (tensile stress) and the dielectric layer 137 is formed of Al ₂ O ₃ (compressive stress), residual stress of the entire bridge portion can be alleviated. .
[194] In addition, you may form the fixed electrode used by each Example except the structure of FIG. 35 in multiple layers from a viewpoint of residual stress relaxation as mentioned above.
[195] Since the fixed electrode has a laminated structure, the film thickness of the fixed electrode can be made thick, so that the strength of the bridge portion can be increased, and at the same time, it is possible to widen the material selection range. Further, the wiring resistance can be reduced, and the Q value can be improved.
[196] In the above, the Example of this invention and its modification were demonstrated. The present invention is not limited to the above embodiments and modifications, and includes other various embodiments and modifications. For example, in the above embodiments and modifications, the piezoelectric actuator is driven so that the gap between the movable electrode and the dielectric layer is narrowed. Contrary to this configuration, the piezoelectric actuator may be driven so as to widen the gap between the movable electrode and the dielectric layer (in the direction of decreasing the capacitance). In this case, the direction in which the unimorph piezoelectric actuator shown in FIG. 7 deforms may be reversed to the deformation direction in FIG. That is, the polarization direction may be reversed and the applied voltage V may be reverse polarity.
[197] The variable capacitors of the first to ninth embodiments may be accommodated in a package such as ceramics. The external connection terminals arranged in the package and the pads arranged on the substrate 31 are connected by connection means such as wires or bumps.
[198] As described above, according to the present invention, it is possible to provide a variable capacitor and a method of manufacturing the same, which are compact, have a large capacity, a rate of change of capacity and a high Q value, and are excellent in impact resistance capable of fine adjustment of capacity.

权利要求:
Claims (38)
[1" claim-type="Currently amended] A substrate, a fixed electrode and a movable electrode of a capacitor supported on the substrate, a plurality of piezoelectric actuators supported on the substrate and driving the movable electrode, and a dielectric layer disposed between the fixed electrode and the movable electrode. Variable capacitor.
[2" claim-type="Currently amended] The method of claim 1,
The dielectric layer is supported by either one of the fixed electrode and the movable electrode.
[3" claim-type="Currently amended] The method according to claim 1 or 2,
Each of the plurality of piezoelectric actuators includes a pair of electrodes and a piezoelectric element disposed therebetween, and is located in a space on the substrate.
[4" claim-type="Currently amended] The method of claim 3,
One of a pair of electrodes of the said piezoelectric actuator and the said movable electrode are comprised integrally, The variable capacitor characterized by the above-mentioned.
[5" claim-type="Currently amended] The method of claim 1,
And the dielectric layer is attached to the fixed electrode, and faces the movable electrode through an air layer.
[6" claim-type="Currently amended] The method of claim 1,
And the dielectric layer is attached to the movable electrode and faces the fixed electrode through an air layer.
[7" claim-type="Currently amended] The method of claim 1,
And said fixed electrode has a portion that bridges on said movable electrode, and said dielectric layer attached to said portion faces said movable electrode through an air layer.
[8" claim-type="Currently amended] The method of claim 1,
And said fixed electrode has a portion that bridges over said movable electrode, and said dielectric layer is disposed on said movable electrode and faces said fixed electrode via an air layer.
[9" claim-type="Currently amended] The method of claim 1,
The fixed electrode is formed on an insulating layer formed on the substrate, the dielectric layer is disposed on the fixed electrode, and the movable electrode faces the dielectric layer via an air layer.
[10" claim-type="Currently amended] The method of claim 1,
The fixed electrode is formed on an insulating layer formed on the substrate, the dielectric layer is attached to the movable electrode, the variable capacitor, characterized in that facing the fixed electrode via an air layer.
[11" claim-type="Currently amended] The method of claim 1,
The fixed electrode is supported on the substrate via an insulating layer disposed on the substrate.
[12" claim-type="Currently amended] The method according to any one of claims 1 to 11,
The piezoelectric actuator is a unimorph (unimorph) type variable capacitor, characterized in that.
[13" claim-type="Currently amended] The method according to any one of claims 1 to 11,
The piezoelectric actuator is a variable capacitor, characterized in that the bimorph (bimorph) type.
[14" claim-type="Currently amended] The method of claim 1,
The fixed electrode and the movable electrode each have a pad for external connection, wherein the pad is located on an insulating layer disposed on the substrate.
[15" claim-type="Currently amended] The method of claim 1,
The piezoelectric actuator has a plurality of deformation parts including a pair of electrodes and piezoelectric elements disposed therebetween, the pair of electrodes each having pads for external connection, and the pads on an insulating layer disposed on the substrate. A variable capacitor, characterized in that located.
[16" claim-type="Currently amended] The method of claim 1,
One of the pair of electrodes of the plurality of piezoelectric actuators, one electrode is an electrode connected in common via the movable electrode, characterized in that the variable capacitor.
[17" claim-type="Currently amended] The method of claim 1,
A variable capacitor, wherein one of the pair of electrodes of each of the plurality of piezoelectric actuators is an independent electrode.
[18" claim-type="Currently amended] The method of claim 1,
One of the pair of electrodes of the plurality of piezoelectric actuators, one electrode is composed of a plurality of common electrodes.
[19" claim-type="Currently amended] The method of claim 1,
The fixed electrode has a bridge portion that bridges on the movable electrode, wherein the bridge portion is substantially the same shape as the movable electrode and faces the movable electrode via the dielectric layer.
[20" claim-type="Currently amended] The method of claim 1,
The fixed electrode has a bridge portion that bridges on the movable electrode, the bridge portion being substantially the same shape as the movable electrode and facing the movable electrode via the dielectric layer, the fixed electrode further having three or more support portions, The support portion is a variable capacitor, characterized in that disposed on the insulating layer formed on the substrate.
[21" claim-type="Currently amended] The method of claim 1,
The fixed electrode has a bridge portion that bridges on the movable electrode, the bridge portion being substantially the same shape as the movable electrode and facing the movable electrode via the dielectric layer, and the dielectric layer attached to the fixed electrode is also the movable electrode. A variable capacitor, characterized in that formed to bridge the.
[22" claim-type="Currently amended] The method according to any one of claims 1 to 21,
The fixed electrode has a plurality of layers, wherein the plurality of layers includes a layer in which tensile stress is generated and a layer in which compressive stress is generated.
[23" claim-type="Currently amended] The method according to any one of claims 1 to 22,
And the dielectric layer is formed of any one selected from the group consisting of beryllium oxide, aluminum oxide, aluminum nitride, barium titanate, magnesium titanate, titanium oxide, glass and silicon nitride.
[24" claim-type="Currently amended] The method according to any one of claims 1 to 22,
The movable electrode has a movable range from a state in which an air layer is interposed between the dielectric layer and the fixed electrode or between the dielectric layer and the movable electrode to a state where the fixed electrode, the dielectric layer and the movable electrode are in contact with each other. Variable capacitor.
[25" claim-type="Currently amended] The method according to any one of claims 1 to 24,
And the dielectric layer is attached to the fixed electrode, and the dielectric layer and the fixed electrode have a plurality of holes therethrough.
[26" claim-type="Currently amended] The method according to any one of claims 1 to 24,
And said dielectric layer is attached to said fixed electrode, said movable electrode having a plurality of holes therethrough.
[27" claim-type="Currently amended] The method according to any one of claims 1 to 26,
The piezoelectric actuator is characterized in that the four capacitors.
[28" claim-type="Currently amended] The method according to any one of claims 1 to 27,
The substrate has an opening, and the fixed electrode, the movable electrode, the dielectric layer, and the piezoelectric actuator are disposed on the opening.
[29" claim-type="Currently amended] The method of claim 1,
The substrate has an opening, and an insulating layer is disposed so as to span the opening.
[30" claim-type="Currently amended] Forming a fixed electrode and a movable electrode of a capacitor supported on the substrate; forming a piezoelectric actuator supported on the substrate and driving the movable electrode; and forming a dielectric layer disposed between the fixed electrode and the movable electrode. And a step of forming a sacrificial layer for forming a gap between one of the fixed electrode and the movable electrode and a dielectric layer, and a step of removing the sacrificial layer.
[31" claim-type="Currently amended] The method of claim 30,
And forming an etching hole in the layer formed on the sacrificial layer before removing the sacrificial layer.
[32" claim-type="Currently amended] The method of claim 30,
In the forming of the sacrificial layer, the sacrificial layer is formed on the movable electrode.
[33" claim-type="Currently amended] The method of claim 30,
In the forming of the sacrificial layer, the sacrificial layer is formed on the dielectric layer.
[34" claim-type="Currently amended] The method of claim 30,
And forming an etching hole in the dielectric layer and the fixed electrode formed on the sacrificial layer before removing the sacrificial layer.
[35" claim-type="Currently amended] The method of claim 30,
And forming an etching hole in the movable electrode formed on the sacrificial layer, before the removing the sacrificial layer.
[36" claim-type="Currently amended] The method according to any one of claims 30 to 35,
And etching the substrate to form an opening at a position facing at least the movable electrode and the piezoelectric actuator.
[37" claim-type="Currently amended] The method of claim 36,
The substrate is formed of silicon, and the step of etching the substrate is performed by using differential ionic etching (DRIE) using sulfur hexafluoride as an etching gas and using a resist as a mask for forming the opening. A manufacturing method of a variable capacitor.
[38" claim-type="Currently amended] The method according to any one of claims 30 to 35,
The substrate is a silicon substrate having a (100) plane or a (110) plane, and further comprising the step of anisotropically etching the substrate to form an opening at a position opposite at least the movable electrode and the piezoelectric actuator. Method of manufacturing a capacitor.

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同族专利:

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公开号 | 公开日

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KR100643108B1|2006-11-10|

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JP3712123B2|2005-11-02|

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US6992878B2|2006-01-31|

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US20030179535A1|2003-09-25|

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JP2004006588A|2004-01-08|

---

CN1447453A|2003-10-08|

---

DE10310342A1|2003-11-13|

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CN100477313C|2009-04-08|

引用文献:

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公开号 | 申请日 | 公开日 | 申请人 | 专利标题

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法律状态:
2002-03-25|Priority to JPJP-P-2002-00084600

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2002-03-25|Priority to JP2002084600

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2002-09-04|Priority to JPJP-P-2002-00258559

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2002-09-04|Priority to JP2002258559A

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2003-03-24|Application filed by 후지쓰 메디아 데바이스 가부시키가이샤, 후지쯔 가부시끼가이샤

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2003-10-01|Publication of KR20030077405A

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2006-11-10|Application granted

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2006-11-10|Publication of KR100643108B1

优先权:

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申请号 | 申请日 | 专利标题

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JPJP-P-2002-00084600|2002-03-25|

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JP2002084600|2002-03-25|

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JPJP-P-2002-00258559|2002-09-04|

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JP2002258559A|JP3712123B2|2002-03-25|2002-09-04|Variable capacitor and manufacturing method thereof|