• 专利附录
  • 专利说明
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  • 优先权
    • 专利摘要:
    Method for producing a spiral spring with a core made of a substrate (204) and a piezoelectric coating (207), the said coating being applied to this substrate (204) by means of a pulsed coating process.
    公开号:CH711275B1
    申请号:CH00791/16
    申请日:2016-06-22
    公开日:2020-12-30
    发明作者:Schafroth Konrad
    申请人:Xc Tracer Gmbh；
    IPC主号:
    专利说明:

    Technical area
    The invention relates to a mechanical watch whose control element with a balance and a spiral spring is replaced by a control element with better accuracy. According to the invention, a balance is used with a spiral spring made of piezoelectric material and small electronics that regulate the rate of the balance.
    State of the art
    It is a unrest with a coil spring made of piezoelectric material and a small electronics regulating the movement of the unrest is used. Such a clockwork with a piezoelectric spiral spring is already known from JP2002228774A.
    From the international application WO2011131784 and from CH20100001298, the content of which is hereby incorporated by reference, a method is described in which a piezoelectric coil spring is produced by providing a coil spring made of silicon with a piezoelectric coating and the corresponding electrodes. According to this application, the piezoelectric coating is produced by means of metal-organic chemical vapor deposition (MOCVD). After the spiral spring has been provided with the piezoelectric coating, the electrodes are structured by means of sputtering and subsequent etching. The disadvantage of this method is that the desired quality of the piezoelectric coating, in this case aluminum nitride AIN, can only be achieved at high temperatures in the range of 1100-1300 degrees Celsius. When the spiral spring cools down to room temperature, the different expansion coefficients of silicon and AlN cause great stresses.
    These stresses can be partially reduced by growing intermediate layers of aluminum nitride alternately with layers of AlGaN or GaN. Due to the smaller lattice constant of the aluminum nitride, the AlGaN or GaN growing on it is slightly compressed, which counteracts the tensile stress that already arises during growth and, above all, during cooling. Thus, in theory, one can obtain an almost stress-free material. In practice, however, it has been found that this is not that easy. In addition, GaN has a smaller piezo coefficient than AIN. Furthermore, it is hardly possible to dope the AlN with scandium, for example, which would significantly increase the piezo coefficient.
    An orientation of the piezoelectric coating with the piezoelectric axis perpendicular to the surface is essential for a function of the spiral spring according to the invention. In principle, this is only possible with processes that do not imprint any preferred direction associated with the material source, such as B. the MOCVD, but not with conventional DC or RF sputter deposition. With these methods, for example, the c-axis of AIN is always aligned perpendicular to the sputtering source, which can be used to achieve an inclined c-axis orientation of the sputtered layer by tilting the sample.
    Presentation of the invention
    The aim of the present invention is to propose a method for a piezoelectric coating of a spiral spring, which can be produced at low temperatures, and a correspondingly coated spiral spring.
    Another task is to make the coil spring more resistant to breakage.
    According to the invention, these problems are solved in that the AIN is not applied by means of MOCVD, but by means of a pulsed coating process based on a target and a pulsed excitation source.
    Among other things, this has the advantage that the coating can be carried out at room temperature, or at least at a temperature below 80.degree. This avoids stresses at the interface between substrate and coating, which would otherwise arise due to different thermal expansion coefficients if the spring catches cold again after a high-temperature coating.
    This also has the advantage that the coating becomes much more homogeneous. The crystal structure of the piezoelectric layer is less interrupted, so that a higher piezoelectric voltage is generated.
    In one embodiment, the coating is carried out by means of high-energy pulse magnetron sputtering (HiPIMS) (high power pulse magnetron sputtering, HiPIMS, or high power pulsed magnetron sputtering, HPPMS).
    In one embodiment, the coating takes place by means of a pulsed laser deposition.
    In one embodiment, the coating takes place by means of a pulsed laser epitaxy.
    [0014] Further advantageous embodiments are specified in the dependent claims.
    Brief description of the figures
    The invention is explained in more detail with reference to the accompanying figure, wherein Fig.1a shows a cross section through a single turn of the spiral spring. Fig.1b shows a detail from the cross section through a single turn of the spiral spring.
    Ways of Carrying Out the Invention
    Figures 1a and 1b show a cross section 200 through a single turn of the spiral spring. The core of the coil spring consists of a substrate 204 made of silicon. An amorphous intermediate layer 205 is present thereon, for example sputtered on or implemented by oxidation. In one example, the layer consists of silicon oxide with a thickness of, for example, 1000 nm, applied, for example, by oxidizing the silicon wafer after the etching / structuring of the spiral spring 20. The thickness is thus significantly greater than the thickness of the native SiO2 layer.
    This amorphous layer has on the one hand the advantage that the surface of the spiral spring is smoothed, and on the other hand a temperature compensation is achieved so that the oscillation frequency of the balance / spiral spring combination remains essentially stable or changes only slightly even with temperature changes.
    On this layer of amorphous silicon dioxide, a conductive layer is applied as an inner electrode 206 by means of sputtering, for example a layer of titanium, with a thickness of 10-50 nm. However, another conductive material can also be used, for example aluminum, or a conductive layer made of titanium nidride or another suitable material, for example molybdenum and generally a conductive oxide such as indium tin oxide, Al-doped ZnO or a conductive one Nitride such as B. highly Ge doped GaN as described in DE 10 2015 108 875. If the silicon oxide layer 205 is dispensed with, even the core of the spiral spring made of silicon can be used as the inner electrode, in which case only electrically conductive silicon has to be used.
    A piezoelectrically active layer 207 is applied to the inner electrode 206 made of titanium, for example a layer which contains at least 30% aluminum nitride. The layer thickness is preferably between 500 and 3000 nm, for example 1000 nm. The use of aluminum-scandium nitride is even better, as this has a piezo coefficient that is 2-5 times higher than that of AIN. The electrode, for example 50-200 nm made of chromium / nickel / gold, is then applied to the layer of piezoelectrically active material. The electrodes are arranged on both vertical side flanks of the spiral spring; there are no electrodes on the top and bottom of the spiral spring 20. This can already be done during the coating or by subsequent processing in which the coating is removed from the top and, if necessary, also the bottom.
    According to the invention, the coating is carried out using a pulsed coating process that works with a plasma from the target to the wafer.
    In one embodiment, the piezoelectric coating 207 made of AIN is applied by means of high-energy pulse magnetron sputtering (high power impulse magnetron sputtering, HiPIMS, or high power pulsed magnetron sputtering, HPPMS).
    Alternatively, the coating takes place by means of PLD (pulsed laser deposition), or by means of PLE (pulsed laser epitaxy).
    HiPIMS is a special magnetron sputtering process for the deposition of thin films. HiPIMS uses very high target power densities of a few kW · cm-2 in short pulses of a few tens of microseconds with a low duty cycle (on-off ratio) of less than 10%. A characteristic feature of the HiPIMS is the high degree of ionization of the sputtered donor material and the high rate of molecular gas dissociation. Since the pulses with HiPIMS only act on the target material for a very short time and this is followed by a relatively long "off time", the average cathode power is low (1-10 kW). In this way, the target material can cool down during the off times and the process is more stable.
    Using HiPIMS, it is therefore possible to apply AIN practically at room temperature. This is why, in contrast to MOCVD, HiPIMS does not have the problem of thermal distortion or hardly any. This is why spiral springs that have been coated with HiPIMS are much more stable than spiral springs that have been coated with MOCVD. Another advantage over conventional sputtering methods in the case of pulsed plasma processes is the significantly reduced inclination of the alignment of the applied layer in relation to the source. With the pulsed method z. B. realize simple AIN layers that grow with their piezoelectric c-axis perpendicular to the surface.
    Another advantage of HiPIMS is that the AlN 207 can be easily doped with, for example, scandium, by co-sputtering with a second target made of scandium; the first target is made of aluminum. In contrast to MOCVD, there is no need to use expensive and exotic precursors.
    Another advantage of HiPIMS is that only nitrogen and aluminum or scandium have to be used for the production of AlN layers, in contrast to the production of thin AlN layers using MOCVD and trimethylaluminum C3H9AI, where ammonia and hydrogen are still required.
    But there is also the possibility of influencing the growth of the layer with gases. For example, the polarity of the layer can be adjusted by adding oxygen. It is therefore very important that the composition of the gases in the reactor is set and controlled very precisely with the HiPIMS process.
    Another advantage of HiPIMS is the possibility of being able to “stack” several different layers on top of one another. For example, the spiral spring can be oxidized first, so that a layer of amorphous silicon dioxide is present on the entire surface of the spiral spring. This has the advantage that a spiral spring coated with silicon dioxide hardly changes the frequency when the temperature changes, since the variations in the Young's modulus of silicon and silicon dioxide more or less compensate one another.
    With HiPIMS, AlN 207 can be coated directly onto the silicon dioxide 205. This is not possible with MOCVD, because at the high temperatures the aluminum reacts with the silicon dioxide and attacks the silicon dioxide layer or even dissolves it completely, which results in a poor quality of the AIN that has grown on it.
    When coating with HiPIMS, a spiral spring made of silicon, the surface of which has been oxidized, can also be coated with high quality AlN without the silicon dioxide 205 being attacked during the coating process. Ideally, a thin layer 206 of, for example, 10-50 nm titanium is first applied to silicon dioxide 205, but a thin layer of 10-50 nm pure aluminum can also be applied first by sputtering or another suitable conductive material. This layer 206 made of electrically conductive material serves as an internal electrode. A 1-3 µm thick layer 207 of AlN is then sputtered onto this thin conductive layer 206. The piezoelectric properties of the aluminum nitride AIN can be further improved if scandium is added during the sputtering, for example by co-sputtering scandium. In this way, a 1-3 µm thick layer 207 of aluminum-scandium nitride AxSc1-xN can be realized.
    Another possibility is to grow a gradient, i.e. first only to sputter AIN, and then in the further course of the coating process to make a co-sputtering with scandium or gallium and continuously increase the scandium or gallium content. As a result, the material grows under compression, since Al (x) Ga (1-x) N or Al (x) Sc (1-x) N has a larger lattice constant than AIN. This can be helpful if the temperature in the coating chamber has to be increased in order to increase the quality of the coating. Then tensile stresses could occur again after the coating has cooled to room temperature, since the expansion coefficients of Si and AlN are not the same. Such tension is prevented by adapted gradients.
    The AlN or AxSc1-xN 207 sputtered by means of HiPIMS has a crystalline structure, the growth is preferably oriented c-axes, i.e. the orientation of the grown crystals is perpendicular to the surface on which the AlN grows. Since the surface of the spiral spring is curved, the AlN or AxSc1-xN cannot be grown as a monocrystal, but rather columnar polycrystalline AlN is created. In the case of polycrystalline materials, however, mechanical loads can cause cracks at the boundaries of the crystallites. According to the invention, this risk is reduced by applying a 10-100 nm thick layer of amorphous silicon nitride or a similar suitable material to the 1-3 µm thick layer of AlN or AxSc1-xN by a sputtering process or preferably by means of atomic layer deposition ALD. On the one hand, this has the advantage that the AlN or AxSc1-xN is well protected against environmental influences, and that the spiral spring is much more resistant to breakage, since the amorphous silicon nitride can reduce or even eliminate voltage peaks in the AIN. Another advantage is that during the subsequent coating of the spiral spring with electrodes by means of sputtering, no metal atoms can penetrate into the AlN along the grain boundaries of the AlN and impair the electrical properties of the spiral spring.
    Another advantage of coating the spiral springs using HiPIMS is the possibility of applying all the required layers in the same operation. For example, an amorphous layer of, for example, silicon nitride can first be applied to the silicon, and then the inner electrode is applied. However, it is also possible to dispense with the inner electrode if the amorphous intermediate layer is only very thin, and to use the highly doped and thus conductive silicon of the spiral spring as the inner electrode.
    A seed layer made of, for example, AlN is then applied to the amorphous intermediate layer, and then the piezoelectrically active layer made of AlN and AxSc1-xN is applied. After applying the AlN / AxSc1-xN layer, which has a total layer thickness of 2 µm, for example, the electrodes are then sputtered on in the same process, for example with an adhesive layer made of titanium and a conductive layer made of gold. In this way, all functional layers that are necessary can be applied in the same process. It is then only necessary after the coating process to remove the conductive layer on the top and bottom of the wafer by means of a suitable method, preferably by etching. This divides this layer into two parts that are used as electrodes.
    In order to achieve a layer thickness that is as uniform as possible, the wafer is ideally rotated about at least one axis during the coating process. It is better to rotate the wafer around 2 axes. This can be done, for example, by placing the wafer vertically in the reactor. First of all, the wafer is now rotated around the horizontal axis, just like a wheel rotates around its own axis. In addition to this, the wafer is also rotated around a vertical axis. This ensures that gravity has only a minimal influence on the geometry of the spiral springs that are movable in the wafer, since the deformations due to gravity cancel each other out on average during one rotation around the horizontal axis.
    Typically, sputtering is a directed process. This can lead to the layer growing in the direction from which the sputtering takes place. AIN normally always grows up perpendicular to the surface. In normal sputtering, however, the directional sputtering process can lead to the crystals not growing perpendicular (i.e. C-axis orientation) to the surface of the wafer, but rather at an angle to the surface.
    Rotating the wafer about at least one axis also has the advantage that on average sputtering is no longer a directed process. The coating takes place from all possible directions. If, for example, the targets are arranged vertically and the sputtering takes place horizontally, it makes sense to rotate the wafer about at least the vertical axis. This then leads to the wafer being bombarded with atoms from all possible directions, and not just from one direction. If the wafer is then rotated about a horizontal axis at the same time as the rotation about the vertical axis, it can be ensured that on average the layer grows uniformly and the orientation of the crystals is not disturbed.
    In order to counteract a possible deformation of the coil springs during the coating by the effects of gravity, the wafer is brought into a different position one or more times during the manufacturing process. Thus, the effects of gravity during the coating process should be reduced or eliminated entirely.
    权利要求:
    Claims (16)
    [1]
    1. Process for coating a spiral spring, with the following steps:a substrate (204) is provided;a piezoelectric coating (207) is applied to this substrate;characterized in that- said piezoelectric coating (207) has a crystalline structure in which the orientation of the grown crystals is essentially perpendicular to the surface and thatthe named coating is applied by means of a pulsed coating process based on a target and a pulsed excitation source.
    [2]
    2. The method according to claim 1, characterized in that said coating is applied by means of high-energy pulse magnetron sputtering (HiPIMS).
    [3]
    3. The method according to claim 1, characterized in that said coating is applied by means of a pulsed laser deposition.
    [4]
    4. The method according to claim 1, characterized in that said coating is applied by means of a pulsed laser epitaxy.
    [5]
    5. The method according to any one of claims 1 to 4, in which said piezoelectric coating (207) consists of one or more different layers.
    [6]
    6. The method according to claim 5, in which at least one layer which contains at least 30% aluminum nitride or at least 30% aluminum-scandium nitride comprises.
    [7]
    7. The method according to claim 6, in which the piezoelectric properties of an aluminum nitride layer (207) are improved by adding scandium during the sputtering.
    [8]
    8. The method according to any one of claims 1 to 7, in which the thickness of said piezoelectric coating (207) is between 1 and 3 microns.
    [9]
    9. The method according to any one of claims 1 to 8, in which said substrate (204) comprises silicon.
    [10]
    10. The method according to any one of claims 1 to 9, in which an amorphous intermediate layer, for example a silicon dioxide layer (205), is present on said substrate (204).
    [11]
    11. The method according to claim 10, in which a conductive layer, for example a layer of for example 10-50 nm titanium or aluminum (206), is applied to the amorphous intermediate layer (205).
    [12]
    12. The method according to any one of claims 1 to 11, in which a 10-100 nm thick layer of amorphous material is applied to the named piezoelectric layer (207) by means of atomic layer deposition (ALD).
    [13]
    13. The method according to any one of claims 1 to 12, in which two electrodes (208) are attached to the piezoelectric layer (207) by sputtering a conductive layer and then separating this layer into two electrodes.
    [14]
    14. The method according to any one of claims 1 to 13, in which said substrate is rotated about two axes during coating.
    [15]
    15. Coil spring which was produced by the method of any one of claims 1 to 14.
    [16]
    16. Control element with a balance, a spiral spring made of piezoelectric material, which was produced with the method of one of claims 1 to 14, and electronics regulating the course of the balance.
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    同族专利:
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    引用文献:
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    法律状态:
    2020-10-15| PFA| Name/firm changed|Owner name: XC TRACER GMBH, CH Free format text: FORMER OWNER: KONRAD SCHAFROTH, CH |
    优先权:
    申请号 | 申请日 | 专利标题
    CH8912015|2015-06-22|
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