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    • 专利摘要:
    Bolometric resistive sensor (22) comprising a thin film (23) based on a high-temperature superconducting sensor that heats up when it absorbs electromagnetic radiation, varying its electrical resistance: and means (11) to measure said variation in electrical resistance and infer a quantity of radiation absorbed. Said thin film (23) includes one or more regions with a non-optimal doping level, so that it does not maximize a critical superconducting temperature of the bolometric sensor (22). (Machine-translation by Google Translate, not legally binding)
    公开号:ES2773726A1
    申请号:ES201930020
    申请日:2019-01-14
    公开日:2020-07-14
    发明作者:Ramallo Manuel Vazquez；Verde José Lorenzo Castano；Viz Alberto Sebastian；Orille Carlos Montero
    申请人:Universidade de Santiago de Compostela；
    IPC主号:
    专利说明:

    [0002] Resistive bolometric sensor
    [0004] Technique field
    [0006] The present invention relates generally to the field of bolometers. In particular, the invention relates to a resistive bolometric sensor based on high temperature superconductors.
    [0008] Background of the invention
    [0010] Bolometers are electromagnetic radiation detectors that use a sensor that heats up when it absorbs the radiation. The increase in temperature results in a change in the electrical resistance of the sensor and this is used to infer the radiation it has received. The scheme of operation of a bolometer is summarized in Figs. 1 and 2.
    [0012] The main advantages of bolometers compared to other radiation sensors (such as those based on the photoelectric effect, photodiodes, phototransistors, or CCD and CMOS sensors) are: greater spectral range, greater speed and more sensitivity to very radiation. weak.
    [0014] The main types of bolometer sensors that currently exist are:
    [0016] a) semiconductor sensors - they are the most used, especially VxOy (usually V2O5). They require a thermal bath, but not cryogenic. However, they are often operated at cryogenic temperatures if the radiation to be measured is so weak as to require avoiding self-noise (friendly military fire detection, etc.) or in certain special environments (satellites, for example).
    [0018] b) LTS-TES sensors, or low temperature superconducting sensors - they use superconductors such as Al or Ti, which due to their small critical temperature value Tc require cryogenics based on liquid He (LHe, boiling temperature 4.2K at ambient pressure) . They are used mainly in some applications for astrophysics and where a very high sensitivity is required, due to the extreme weakness of the radiation to be measured. In fact, they are often operated at temperatures even much lower than 4.2K (approximately 10 mK) in order to eliminate the thermal self-noise that would influence such applications.
    [0019] c) HTS-TES sensors, or high temperature superconducting sensors - they use superconductors with a critical temperature equal to or greater than 77K, which requires cryogenics but the one based on Liquid Nitrogen (LN2) is sufficient, much simpler (and cheaper) than the one based on LHe. The HTS-TES sensors proposed so far use the optimal doping level (that is, the chemical composition that maximizes its critical temperature; for example, in the most widely used compound, YBa2Cu3O (7-5), nominal doping 5 = 0.07 is used which corresponds to Tc ~ 90K). Then the spatial inhomogeneities of critical temperature associated with small variations in the local value of doping are negligible (since the slope of the Tc (5) dependency is zero when operating at a maximum of said curve).
    [0021] Although the existing HTS-TES sensors (or proposed so far) have some advantages over the other options (LTS-TES and semiconductors), their disadvantages with respect to them mean that their use is currently very scarce. The main advantages and disadvantages are summarized in Table 1 below:
    [0023]
    [0025] Table 1. Operating parameters of the main existing bolometric sensors. The quantities correspond to the same microbolometer with common typical parameters, varying only the material used as sensor (in particular, dimensions 6pmx6pmx100nm, and we assume that the cooling is carried out by direct contact with the film and the substrate).
    [0027] With respect to the LTS-TES sensors, the HTS-TES have a more economical cooling (LN2 vs LHe) and a much higher saturation power (the maximum measurable incident radiation), but this is accompanied by a sensitivity (according to their TCR factor , defined as the slope of the curve R (T) in the linear region of temperatures where the bolometer operates) about two orders of magnitude lower. Furthermore, cryogenics requires AT stability of less than 1K, which can be difficult to obtain with LN2 (much more expensive and complex LHe cryogenics is also much more stable).
    [0029] With respect to semiconductor sensors, the most used, although the existing HTS-TES sensors have a TCR sensitivity about 50 times higher, they have the disadvantages of requiring more expensive and complicated cooling (LN2 stabilized with AT of less than 1K, compared to to non-cryogenic refrigeration) and to saturate much earlier (its saturation power being an order of magnitude less than for semiconductor sensors).
    [0031] Presentation of the invention
    [0033] In order to eliminate some of the disadvantages of HTS-TES sensors compared to semiconductor sensors, in particular, increase the saturation power to make it comparable to semiconductor sensors, and also relax the stability requirements of the cryogenic bath, thus making it less complex, the present invention provides a resistive bolometric sensor that, like the bolometers of the state of the art, comprises a thin film based on a high temperature superconducting sensor that heats up when it absorbs electromagnetic radiation, varying an electrical resistance of the bolometric sensor; and means for measuring said variation in electrical resistance and inferring the amount of radiation absorbed.
    [0035] Unlike the known proposals, in the proposed bolometric sensor said thin film includes one or more regions with a non-optimal level of doping, so that it does not maximize its critical superconducting temperature Tc.
    [0037] In particular, according to the present invention, the thin film has a thickness comprised between 50 and 400 nanometers, preferably 100 nanometers, and an area of the order of microns.
    [0039] In an exemplary embodiment, the thin film is a high-temperature superconducting perovskite such as: YBa2Cu3O693 doped with O; YBa2Cu3O693 doped with Zn; La1.84Sr0.16CuO4 doped with Sr; La184Sr016CuO4 doped with O; Bi2Sr2CaCu2O8 + x doped with Pb; Bi2Sr2CaCu2O8 + x doped with O; or HgBa2CaCu2O621 doped with O.
    [0041] In an exemplary embodiment, said thin film comprises a single nominal doping region along its entire surface. This unique region has a nominal value homogeneous but not optimal, thus presenting random variations of the critical superconducting temperature on the nanometric scale.
    [0043] Alternatively, in another embodiment, said thin film comprises different regions of nominal doping along its entire surface, including non-optimal regions or non-optimal and optimal regions. The different doping regions can be arranged forming different nominal doping distributions, highlighting the following possibilities: with constant variation, quasi-exponential variation, discretized quasi-exponential variation.
    [0045] The proposed bolometric sensor optimizes the saturation limit by widening the linear region of the transition, maintaining a TCR sensitivity of the same order of magnitude (or even increasing it). The operating temperature is kept at the values corresponding to LN2 cooling, but the tolerance range for thermal stabilization is increased, so that the necessary cryogenics will have a lower cost than the HTS-TES bolometers existing until now.
    [0047] Brief description of the drawings
    [0049] The above and other characteristics and advantages will be more fully understood from the following detailed description of some exemplary embodiments, merely illustrative and not limiting, with reference to the accompanying drawings, in which:
    [0051] Fig. 1 illustrates an explanatory diagram of the operation of a resistive bolometer as known in the state of the art. The upper figure shows the basic operating set up, composed of the incident radiation 10, the focusing lens (s) 5 and an array of microbolometers 21 with the thermal bath 13. The lower figure is a zoom 22 to a microbolometer, to illustrate the parts that make it up, that is, a thermal link 12, electrical cables to perform the measurement 11 and a thin film 23.
    [0053] Fig. 2 represents the operational principles of resistive bolometers. The upper figure (A) represents the excitation phase, when the incident radiation heats up the bolometer, and its resistivity varies. In turn, the different areas of the bolometer resistance curve are shown in the upper right. The lower figure (B) shows the relaxation phase, when there is no longer incident radiation and the bolometer returns to its initial thermal state.
    [0055] Fig. 3 illustrates the results of the finite element simulation for microbolometers with a single nominal doping zone, the four nominal dopes described in Table 2 (circles, squares, rhombuses and triangles) and the estimates obtained by means of the effective mean theory for the same nominal doping (black lines). In addition, the width of the linear region is shown, which is the operating region of each bolometer. For comparison with the results obtainable using the existing state of the art, the results with an optimal nominal doping zone are also shown (case p = 0.155)
    [0056] Fig. 4 is a representative diagram of the proposed bolometric sensor now assuming several nominal doping zones p, such that p (x) presents a linear variation along the longitudinal coordinate x. On the left the nominal doping is plotted against the longitudinal coordinate. The figure is a 2D representation of the nominal doping distribution with a gray scale represented by the upper right bar. In turn, the intrinsic random Gaussian distribution of local doping p (x, y) is represented in the lower right.
    [0058] Fig. 5 is a representation of resistance versus temperature for the bolometric sensor proposed in Fig. 4. The line represents the estimate obtained by means of the effective mean theory, and the circles represent the calculations performed by finite elements . In turn, the AT width of the linear zone of the bolometer is displayed.
    [0060] Fig. 6 is a representative diagram of the proposed bolometric sensor now assuming several nominal doping zones p such that p (x) follow an exponential function for the dx / dp function (corresponds to equation (3)). On the left the nominal doping is plotted against the longitudinal coordinate. The figure is a 2D representation of the nominal doping distribution with a gray scale represented by the upper right bar. In turn, the intrinsic random Gaussian distribution of local doping p (x, y) is represented in the lower right.
    [0062] Fig. 7 is a representation of resistance versus temperature for the bolometric sensor proposed in Fig. 6. The line represents the estimate obtained by effective means, and the circles represent the calculations performed by finite elements. In turn, the width of the linear area of the bolometer is displayed.
    [0064] Fig. 8 is a representative diagram of the proposed bolometric sensor assuming several areas of p, following an exponential distribution of the dx / dp function but now discretized with nominal doping p = 0.136, 0.141, 0.145 and 0.160. On the left the nominal doping is plotted against the longitudinal coordinate. The figure is a 2D representation of the nominal doping distribution with a gray scale represented by the upper right bar. In turn, the intrinsic random Gaussian distribution of local doping p (x, y) is represented in the lower right.
    [0066] Fig. 9 is a plot of resistance versus temperature for the bolometric sensor proposed in Fig.8. The line represents the estimate obtained by effective means, and the circles represent the calculations performed by finite elements. In turn, the width of the linear area of the bolometer is displayed.
    [0068] Detailed description of the invention and some embodiments
    [0070] The present invention provides a resistive bolometric sensor 22, that is, a thermal detector for electromagnetic radiation, including a thin film 23 based on high temperature superconductors. The thin film 23, depending on the exemplary embodiment, may include one or more regions with a non-optimal level of doping.
    [0072] In an embodiment, the bolometric sensor 22 can be based on high-temperature superconductors with non-optimal doping and a homogeneous nominal value over the entire surface of the thin film 23, which entails a random Gaussian spatial distribution for doping and critical temperature. Local Tc.
    [0074] In another embodiment, the bolometric sensor 22 may be based on high temperature superconductors with a regular distribution in space (patterned) of the nominal doping and consequently a spatial distribution of the critical temperature that is the sum of two contributions: a regular one. (following the nominal doping pattern) plus another random Gaussian (corresponding to the differences between local and nominal doping for non-optimal nominal doping).
    [0076] In yet another embodiment, the bolometric sensor 22 can be based on high-temperature superconductors with a regular distribution in space (patterned) of the local critical temperature through procedures such as variation of the thickness of the thin film or others that do not involve a additional random distribution of critical temperature.
    [0078] Preferably, the proposed bolometric sensor 22 comprises a thin film 23 of thickness 100nm and area 6pmx6pm, where the HTS material is YBa2Cu3O7.5 (abbreviated YBCO). However it should be noted that other materials could also be used, for example: Sr-doped La184Sr016CuO4; La184Sr016CuO4 doped with OR; Bi2Sr2CaCu2O8 + x doped with Pb; Bi2Sr2CaCu2O8 + x doped with O; or HgBa2CaCu2O6.21 doped with O.
    [0080] Likewise, the surface of the bolometric sensor 22 can be considered divided into small domains of approximately 30nmx30nm, each with a single local doping and critical temperature, p (x, y) and Tc (x, y). Each monodomain is assigned a local doping value p (x, y) resulting from the sum of the nominal doping p (x) and the nano-metric random variations corresponding to said nominal value. It should be noted that in all the illustrated embodiments, nominal doping is considered varying only in one direction, plus a Gaussian random distribution. This results in the value p (x, y), and with it Tc (x, y), of each monodomain.
    [0082] Thus, the overall electrical behavior of the bolometric sensor 22 results from the behavior as a resistor mesh of the set of monodomains. This is equivalent to a 200x200 element network, which is representable by 40001 variable electrical mesh equations (details of these equations, which are non-linear in the superconducting case, can be found in JC Verde et al, IEEE Trans. Appl. Supercond .
    [0083] 26 (2016) 8800204; these equations are solved, for each temperature, in the parallel superconductor LBTS-epsilon lbts.esc.es/epsilon).
    [0085] Additionally, it is possible to estimate the global behavior of the bolometric sensor 22 through the approximation known as "effective mean", summarized in J. Maza et al. Phys. Rev. B 43, (1991) 10560. The results will only be an approximation basic, but computationally fast and constitute a test to confirm the qualitative results.
    [0087] Different embodiments will be detailed below according to the doping included in the thin film 23.
    [0089] HTS-TES with uniform y (x):
    [0091] With reference now to Fig. 3 and Table 2, they show the results obtained for a single value of the nominal doping p in the entire bolometric sensor 22 proposed (The p-value = 0.155 corresponds to the optimal doping, that is say traditionally used for HTS-TES sensors, and is shown for reference only to compare with the prior art). It is observed in Fig. 3 that as the nominal doping decreases the transition becomes wider.
    [0092]
    [0094] Table 2. Operational parameters achievable with the present invention with uniform nominal doping (p-value = 0.155 corresponds to the prior state of the art). The quantities correspond to the same bolometric sensor with common typical parameters as in table 1, only varying the material used as sensor.
    [0096] HTS-TES with constant gradient of p (x)
    [0098] In Fig. 4 you can see the scheme associated with the bolometric sensor 22 with unp (x) that has a linear variation with the longitudinal coordinate of the thin film 23, that is:
    [0100] p (x) = Pf-Pi x p. ( 1 )
    [0102] Being p . and pP the initial and final doping values, and L the length of the thin film 23. Then, in this case all the nominal doping values between the initial and final values, pi and pf, are found with the same relative weight, W ( p), in the composition of the sample, in this case W (p) being the value:
    [0104] w (p) = i
    [0105] Pf-Pi
    [0106] The results obtained are shown in Fig. 5 and Table 3. As can be seen, in this first example with variable p (x) the TCR and AT results do not improve those obtained for HTS-TES bolometers with a non-optimal uniform nominal doping. In particular, both the TCR sensitivity and the width of the linear zone, AT, are higher for cases in which the HTS-TES is formed by a thin film 23 with a nominal non-optimal doping. On the other hand, the implementation would be useful in the case that non-linear operating zones were admitted, since the width in temperature of the transition would take a greatly expanded value, ATnoliñ 15K.
    [0108]
    [0110] Table 3. Operational parameters achievable with the present invention with a linear variation of the nominal doping (x) along its longitudinal coordinate. The quantities correspond to the same bolometric sensor with common typical parameters as in table 1.
    [0112] HTS-TES with a continuous exponential distribution of p (x)
    [0114] In this case, an exponential distribution of the function w (p) is used, the fraction of the sensor that has a nominal doping p, as follows:
    [0116] --- 1 dx _ rPl ~ P
    [0117] w (P) = rd = Cexp (~)
    [0119] Where C is a constant that is given by:
    [0124] This distribution corresponds to the following distribution p (x):
    [0129] In Fig. 6 the scheme associated with this distribution of nominal doping is observed taking as numerical values pi = 0.135, pf = 0.161 and p0 = 0.007. On the other hand in Fig. 7 and Table 4 shows the results obtained, which, as can be seen, are clearly better than with the simpler distributions previously tested, both in terms of TCR sensitivity and in the broadening of the linear zone and in the maximum measurable power.
    [0131]
    [0133] Table 4. Operational parameters achievable with the present invention with an exponential distribution of the function w "(p). The quantities correspond to the same bolometric sensor with common typical parameters as in table 1.
    [0135] HTS-TES with a discretized exponential distribution dep (x)
    [0137] Although the continuous exponential distribution tested previously provides excellent results, it could be objected that its practical realization may be difficult, as it implies a very advanced (although not impossible) degree of precision in the structuring techniques of HTS materials. Motivated by this argument, in the proposed bolometric sensor 22 doping distributions p (x) consisting of discrete steps of various sizes, rather than continuous variations, have also been tested.
    [0139] An example of such a stepwise distribution is shown in Fig. 8. In this particular case, four nominal doping are applied, p (x) = 0.136, 0141, 0.145 and 0.160, each with a weight of 2.6%, 10.2%, 30.8% and 56.4% of the sample, consistent with an exponential dependence with p proportional to an exponential
    [0141] vv = Cexp ( P-)
    [0142] p o
    [0144] With p0 = 0.007 and C = 1.523x108.
    [0146] In Fig. 9 and Table 5 the results obtained for said distribution are also shown. As can be seen, not only is the quality of the sensor obtained for the continuous case equal, but the characteristics of the proposed bolometric sensor 22 are improved.
    [0148] Table 5. Operational parameters achievable with the present invention with an exponential distribution of the discretized w "(p) function with nominal doping p (x) = 0.136, 0141, 0.145 and 0.160. The quantities correspond to the same bolometric sensor with common typical parameters as in table 1.
    [0149] The scope of the present invention is defined in the appended claims.
    权利要求:
    Claims (8)
    [1]
    1. Resistive bolometric sensor, comprises:
    a thin film (23) based on a high temperature superconducting sensor that heats up when it absorbs electromagnetic radiation, varying an electrical resistance of the bolometric sensor (22); and
    means (11) for measuring said variation in electrical resistance and inferring an amount of absorbed radiation,
    characterized in that said thin film (23) includes one or more regions with a non-optimal doping level, such that it does not maximize a critical superconducting temperature of the bolometric sensor (22).
    [2]
    Bolometric sensor according to claim 1, wherein said thin film (23) comprises a single nominal doping region along its entire surface, wherein said single region has a homogeneous and non-optimal nominal value.
    [3]
    3. Bolometric sensor according to claim 1, wherein said thin film (23) comprises different regions of nominal doping along its entire surface, including non-optimal regions or non-optimal and optimal regions.
    [4]
    Bolometric sensor according to claim 3, wherein each of the different doping regions has a different nominal doping value.
    [5]
    Bolometric sensor according to claim 3, wherein each of the different doping regions has a homogeneous doping nominal value.
    [6]
    6. Bolometric sensor according to claim 3, wherein the different doping regions are arranged to form a nominal doping distribution with any of the following characteristics: constant variation, quasi-exponential variation, discretized quasi-exponential variation.
    [7]
    Bolometric sensor according to the preceding claims, wherein said thin film (23) has a thickness comprised between 50 and 400 nanometers, preferably 100 nanometers, and an area of the order of microns.
    [8]
    Bolometric sensor according to the preceding claims, wherein said thin film (23) is made of a high temperature superconducting perovskite such as:
    - YBa2Cu3O693 doped with O;
    - YBa2Cu3O693 doped with Zn;
    - La1.84Sro.i 6 CuO 4 doped with Sr; - La184Sr016CuO4 doped with O; - Bi2Sr2CaCu 2 O8 + x doped with Pb; - Bi2Sr2CaCu2O8 + x doped with O; o - HgBa2CaCu2O621 doped with O.
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    引用文献:
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