Abstract:
A system and method for using one or more localized weak-link structures, and damping on the electrical bias circuit, to improve the performance of superconducting transition-edge sensors (TES). The weak links generally consist of an area or areas having a reduction in cross-sectional geometry in an otherwise uniform bilayer TES applied to a substrate. The weak links control the dissipation of power in the sensor, making it quieter and making its electrical response smoother and less hysteretic. The TES response is also made smoother by implementing a damping circuit on the electrical output of the TES.

Description:
FIELD OF THE INVENTION 
     This invention relates to superconducting transition-edge sensors, and more particularly to those having weak links. 
     BACKGROUND OF THE INVENTION 
     The accurate detection of particles, including photons, molecules, electrons, ions and phonons, is essential to many industrial and research measurements. X-ray microcalorimeters convert the x-ray energy into heat in the form of hot-electrons or phonons. An x-ray microcalorimeter consists of an absorber to stop and thermalize incident x-rays and a thermometer to measure the resulting temperature rise. The first x-ray microcalorimeters used insulating or superconducting absorbers (for low heat capacity) and a semiconductor thermistor thermometer. While these achieve adequate energy resolution (7.1 eV FWHM at 6 keV), the response time is intrinsically slow. A known X-ray microcalorimeter uses a normal-metal absorber and a NIS tunnel junction to measure the temperature rise. The response is fast, but the best achieved energy resolution is 18 eV FWHM at 6 keV. 
     Superconducting transition-edge sensors have been proposed for use as a thermometer within an x-ray microcalorimeter. The temperature of a superconducting film is held within the superconducting transition, and heat deposited in the film is measured via the strong temperature dependence of the film&#39;s electrical resistance in this region. For x-ray detection the optimum transition temperature is between about 50 and 150 mK. The choice of the T c  within this range depends on the desired detector parameters. Superconducting tungsten films having T c =70 mK have been used for x-ray detection. For an elemental superconductor such as tungsten, the transition temperature tends to be a fixed property of the metal and is difficult to tune to suit specific applications. For alloys of superconductors with normal metals, the T c  can be adjusted, but the transition edge is not sharp, and the alloys are not stable. The transition temperature can also be adjusted via the proximity effect in superconductor/normal-metal bilayers. When a clean interface is made between a superconducting film and a normal-metal film, and the films are thinner than the relevant coherence lengths, the bilayer acts as a single superconducting film with a transition temperature suppressed from that of the bare superconductor. By varying the relative film thickness, the T c  of the bilayer can be adjusted. Iridium/gold bilayers have been described for particle detection. The T c  of elemental iridium is 112 mK, which is within the target range for x-ray detection. However, the Ir/Au system is very difficult to reproducibly fabricate. It requires the substrate to be heated, it requires a very clean, high vacuum deposition system, and the transition temperature of such bilayers is limited to less than 112 mK. Other bilayer systems have been developed using an aluminum/normal-metal bilayer that have a larger tunable transition range, that are more easily deposited, that are deposited without heating the substrate, that are deposited in a deposition system with only moderate vacuum (˜1e−7 torr, ˜1e−7 millimeter mercury, to ˜0.019336 pound force per square inch, ˜−931 Pa), that are more reliably reproducible, and that are sharper superconducting transitions. Aluminum/normal-metal bilayers have been used as TES&#39;s since they have reproducible transition temperatures. The T c  can be reduced by more than an order of magnitude, the T c  is tunable in a predictable fashion as a function of the thicknesses of the individual layers, and the transition edge is extremely sharp. 
     During operation the TES is maintained within the transition region by electrothermal feedback (ETF). The transition from the superconducting to the normal state is measured to determine the energy deposited in the system by particles. The bilayer resistance can be monitored by voltage biasing the bilayer and measuring the current through the bilayer, for example with a superconducting quantum interference device (SQUID). The increase in bilayer resistance with temperature leads to a reduction in measured current. With an ETF-TES the energy deposited in the bilayer is approximately the integral of the reduction in feedback Joule heating, or the bias voltage multiplied by the integral of the change in measured current. Alternatively the bilayer resistance can be monitored by current biasing and measuring the voltage across the bilayer with a FET. There is a continuum of biasing conditions between voltage biasing and current biasing which can be used in the measurement. The superconducting transition can also be measured, for instance, via the change in the self or mutual magnetic inductance of a coil or coils placed around the bilayer, or by a kinetic inductance measurement. 
     Representative of the art is: 
     U.S. Pat. No. 5,641,961 (1997) to Irwin et al. discloses a superconducting transition edge detector using electrothermal feedback. The sensor comprises a primary heat sink such as a substrate, a variable resistor made of a superconducting material deposited on the substrate, and a current sensing means such as a SQUID array for measuring the current through the variable resistor. The resistor is voltage biased, and the bias voltage is chosen such that the resistor is maintained within its superconducting transition region by electrothermal feedback. 
     U.S. Pat. No. 5,610,510 (1997) to Boone et al. discloses a that granular film [multiple Josephson junction] detectors display nonbolometric behavior which is presumably caused by weak links. Boone further discloses that a nonbolometric mechanism may be a better means of making a detector, particularly for microwave frequencies. 
     U.S. Pat. No. 5,571,778 (1996) to Fujimoto et al. discloses a superconductor junction material which comprises a substrate of a single crystal, and at least one flux flow element, and optionally at least one Josephson junction element, provided on the surface, each of the flux flow and Josephson junction elements being formed of a superconducting oxide layer having a weak link. 
     U.S. Pat. No. 5,552,375 (1996) to Nishino et al. discloses a method of forming superconducting devices including a type having a structure of a superconductor—a normal conductor (or a semiconductor)—a superconductor, and a type having a superconducting weak-link portion between superconductors. 
     U.S. Pat. No. 5,532,485 (1996) to Bluzer et al. discloses a multispectral superconductive quantum detector. Each quantum detector is connected to a read-out loop [SQUID] which includes superconductive material that defines a path. The SQUID read out of the superconductive quantum detector is using a direct coupled approach. A SQUID bias current I SQ  is needed to cause the SQUID to maintain proper operation of the SQUID in the voltage state. 
     U.S. Pat. No. 5,356,870 (1994) to Fujiwara et al. discloses an ion beam irradiated to an oxide superconducting thin film formed on a substrate to disturb the crystal structure of the superconducting thin film and thus forming a damaged layer. 
     U.S. Pat. No. 5,331,162 (1994) to Silver et al. discloses a sensitive, low-noise, superconductive infrared photo detector. Each detector element includes a thin granular film of superconducting material which forms a randomly-connected array of weakly coupled superconductors. The weakly coupled superconductors promote the formation of oppositely polarized fluxons which are driven toward opposite sides of the film when subjected to the bias current. The detector array is connected to a current source, and a SQUID read-out circuit. 
     U.S. Pat. No. 5,219,826 (1993) to Kapitulnik discloses a superconducting Josephson junction created in high T c  superconducting film with a bridge connecting two superconducting banks by subjecting the bridge to a tunneling electron current from a sharp electrode close to the bridge. 
     U.S. Pat. No. 5,179,072 (1993) to Bluzer discloses a multispectral superconductive quantum radiant energy detector and related method utilizing a closed loop of superconductive material having spaced legs, one of which is disposed to ambient. 
     U.S. Pat. No. 5,126,315 (1992) to Nishino et al. discloses a superconducting device including a type having a structure of a superconductor—a normal conductor (or a semiconductor)—a superconductor, and a type having a superconducting weak-link portion between superconductors. 
     U.S. Pat. No. 5,021,658 (1991) to Bluzer discloses a superconducting infrared detector. The detector is also connected to a SQUID amplifier. The SQUID amplifier is connected to a bias current source so that its output voltage is a function of the flux coupled to the SQUID. The electrical connections disclosed in this patent are analogous to the described invention. 
     U.S. Pat. No. 5,019,721 (1991) to Martens et al. discloses active superconducting devices formed of thin films of superconductor which include a main conduction channel which has an active weak link region. 
     U.S. Pat. No. 4,983,971 (1991) to Przybysz et al. discloses a superconducting analog-to digital converter for producing a digital output signal which is a function of an analog input signal. 
     U.S. Pat. No. 4,970,395 (1990) to Kruse, Jr. discloses a phonon detector based upon phonon-assisted tunneling in superconductor-insulator-superconductor or super-Schottky structures in which the superconductor is a high-transition temperature superconductor. 
     U.S. Pat. No. 4,831,421 (1989) to Gallagher et al. discloses a switch that introduces quasiparticles at an asymmetric location into a reduced cross-sectional area microbridge link that is part of an output path. 
     U.S. Pat. No. 4,578,691 (1986) to Murakami et al. discloses a photodetecting device having Josephson junctions, comprising an insulating substrate, a polycrystalline superconductor film formed on the insulating substrate such that Josephson junctions are formed at grain boundaries. 
     U.S. Pat. No. 4,521,682 (1985) to Murakami et al. discloses a photodetecting device having Josephson junctions, comprising an insulating substrate, a polycrystalline superconductor film formed on the insulating substrate such that Josephson junction are formed at grain boundaries. 
     U.S. Pat. No. 4,096,508 (1978) to Fulton discloses a supercurrent memory device comprising a plurality of extended Josephson junctions coupled to one another by having their weak-link layers in contact. 
     K. D. Irwin, G. C. Hilton, D. A., Wollman, J. M. Martinis, “X-ray detection using a superconducting transition edge sensor microcalorimeter with electrothermal feedback”, Appl.Phy.Lett.69, 1945 (1996). 
     K. D. Irwin, G. C Hilton, J. M. Martinis, B. Cabrera, “A hot electron calorimeter for x-ray detection using a superconducting transition edge sensor with electrothermal feedback”, Nucl.Inst.and Meth.A 370, 177-179 (1996). 
     D. A. Wollman, K. D. Irwin, G. C. Hilton, L. L. Dulcie, J. M. Martinis, “High-resolution, energy dispersive microcalorimeter spectrometer for x-ray microanalysis”, J.Microscopy, vol 188 (part 3), 196-223 (1997). 
     W. J. Skocpol, M. R. Beasley, M. Tinkham, “Phase Slip Centers and Nonequilibrium Processes in Superconducting Tin Microbridges,” Journ. of Low Temp. Physics 16, 145-167 (1974). 
     D. E. Chimenti, H. L. Watson, R. P. Huebener, “Current-Induced Breakdown of Superconductivity in Constricted Type I Superconducting Films, “Journ. of Low Temp. Physics. 23, 303-318 (1976). 
     The foregoing TES&#39;s are deficient from the disclosed invention in a number of ways. The deficiencies are satisfied by the present invention. What is provided is a TES having a weak link to reduce noise due to phase slip line motion and irreproducibility. What is provided is a TES having a step edge weak link. What is provided is a TES having a thinned weak link. What is provided is a TES having a perforated weak link. What is provided is a TES having a reduced T c  weak link. What is provided is a TES having impurity weak links. What is provided is a TES having multiple weak links. 
     SUMMARY OF THE INVENTION 
     The primary aspect of the present invention is to provide a weak link in a TES. 
     Another aspect of the present invention is to provide a TES having a weak link to reduce noise due to phase slip line motion and irreproducibility. 
     Another aspect of the present invention is to provide a TES having a weak link with less electrical noise. 
     Another aspect of the present invention is to provide a TES having a weak link to give a non-hysteretic electrical response. 
     Another aspect of the present invention is to provide a TES having a weak link to give a smoother electrical response. 
     Another aspect of the present invention is to provide a step edge weak link in a TES. 
     Another aspect of the present invention is to provide a thinned TES weak link in a TES. 
     Another aspect of the present invention is to provide a perforated weak link in a TES. 
     Another aspect of the present invention is to provide a reduced T c  weak link in a TES. 
     Another aspect of the present invention is to provide an impurity seam weak link in a TES. 
     Another aspect of the present invention is to provide a plurality of weak links in a TES. 
     Other objects of this invention will appear from the following description and appended claims, reference being made to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views. 
     The physics of superconducting films with weak links has been previously studied, however, the use of weak links in transition-edge sensors (TES) has not been pursued since the weak links lead to a reduction in critical current, I c . The critical current is an important parameter for a superconducting transition-edge sensor. The higher the critical current, the faster the TES can be made to operate. Although weak links reduce the critical current, the other beneficial effects of weak links (smoother, quieter, non-hysteretic response) significantly compensate for the small degradation in performance from the reduction in critical current. 
     The instant invention is an improvement of the prior art TES comprising a TES with localized weak-link structures and damping of the electrical bias circuit. These are used to control the response function of the TES by removing glitches and steps in the output. The weak links also make the electrical characteristics of the TES output quiet and non-hysteretic. 
     This invention utilizes a superconductor/normal-metal bilayer transition-edge sensor having a weak link. The TES is maintained in the transition region where its properties are extremely sensitive to temperature. In the detector, the energy of an absorbed particle is converted to heat by the absorber, and the transition from the bilayer&#39;s superconducting to normal state is used to sense the temperature rise. The transition temperature, T c , of the bilayer can be reproducibly controlled as a function of the relative thicknesses and the total thickness of the superconducting and normal-metal layers. The range of available T c &#39;s extends from below 50 mK to above 1.0 K, allowing the detector to be tailored to the application. For x-ray detection the preferred T c  is about 50-150 mK. The width of the transition edge can be less than 0.1 mK, which allows very high detector sensitivity. 
     The TES is fabricated having a bilayer with a superconducting transition-edge near 100 mK. The weak links are incorporated into the TES during the fabrication of the TES. One embodiment comprises a TES having a step edge weak link. The step edge weak link is created by first etching a step into the substrate. Then the TES is applied over the substrate, which creates a step edge in the TES bilayer. The reduction in the cross-sectional area of the TES at the step edge gives the desired reduction in the critical current. The reduction in the critical current is achieved by all of the described embodiments. In another embodiment, a thinned TES weak link is created by localized reduction in the thickness of the superconducting layer of the TES. This may be accomplished by using a notch in the superconducting layer. In yet another embodiment, a weak link may be created by completely or partially perforating the TES. In yet another embodiment, a weak link may be created by reduction of T c  in the superconducting film. This is accomplished by deposition of a normal metal line above or below the TES, with the reduction in T c  occurring by the proximity effect. In yet another embodiment, a weak link may be created by incorporating impurities in the superconducting layer resulting in a reduction in the critical current. In yet another embodiment, multiple weak links may be created by including in a single TES a plurality of any of the foregoing weak link structures. 
     A voltage is applied across the sensor, and the resulting current is measured using a current amplifier such as a SQUID. The current that flows through the film is a function of the applied voltage and the temperature. The current response of the sensor to the voltage and temperature without the weak links could be varied and would otherwise have steps and glitches, extra noise, and hysteretic. 
     Prior to the present invention it was necessary to apply a magnetic field to the TES to eliminate noise due to phase slip lines. The present invention utilizing weak links eliminates the need to apply the magnetic field. 
     Further improvement in the smoothness of the response of transition-edge sensors can be achieved by the use of a damping circuit on the electrical output. Whenever the Josephson effect occurs in the transition-edge sensor, high-frequency resonances in the bias circuit can interact with the Josephson oscillations to produce steps in the electrical response of the TES. The present invention incorporates damping schemes for the electrical bias circuit which prevents high-frequency oscillations from entering the TES, thereby removing these voltage steps, and leading to a smoother detector electrical response. 
     The fabrication of localized weak links, and the implementation of a damping scheme on the bias circuit of a transition-edge sensor, are important improvements in x-ray detectors, as they improve the detector performance. They eliminate step like structures in the I-V characteristics caused by ac Josephson effect, thereby resulting in smoother I-V characteristics which makes operation significantly simpler. 
     The detector can be used with many types of particles, including photons, molecules, electrons, ions and phonons. In the preferred embodiment the particles are x-ray photons. Depending on the type of particle, the absorber can be a normal metal, a superconductor, semiconductor, an insulator, the bilayer substrate, or the bilayer itself. In the preferred embodiment it is a normal metal. The bilayer normal metal can be any metal which is a normal conductor at the operating temperature. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side plan view of the prior art. 
     FIG. 2 is a top plan view of the prior art. 
     FIG. 3 is a side plan view of the bilayer TES prior art. 
     FIG. 4 is a top plan view of the bilayer TES prior art. 
     FIG. 5 is a side plan view of a TES with a bilayer step edge weak link. 
     FIG. 6 is a top plan view of a TES with a bilayer step edge weak link. 
     FIG. 7 is a side view of the single layer step edge embodiment. 
     FIG. 8 is a top plan view of the single layer step edge embodiment. 
     FIG. 9 is a side plan view of a TES with a single layer multi-step edge weak link. 
     FIG. 10 is a top plan view of a TES with a single layer multi-step edge weak link. 
     FIG. 11 is a side plan view of the bilayer multi-step edge weak link. 
     FIG. 12 is a top plan view of the bilayer multi-step edge weak link. 
     FIG. 13 is a side plan view of a TES with a notch weak link. 
     FIG. 14 is a top plan view of a TES with a notch weak link. 
     FIG. 15 is a side plan view of the multiple notch embodiment. 
     FIG. 16 is a top plan view of the multiple notch embodiment. 
     FIG. 17 is a side plan view of a notched bilayer embodiment. 
     FIG. 18 is a top plan view of an notched bilayer embodiment. 
     FIG. 19 is a side plan view of a multiple notched bilayer embodiment. 
     FIG. 20 is a top plan view of a multiple notched bilayer embodiment. 
     FIG. 21 is a side plan view of a TES with a single layer perforated weak link. 
     FIG. 22 is a top plan view of a TES with a single layer perforated weak link. 
     FIG. 23 is a side plan view of a bilayer TES with a bilayer perforated weak link. 
     FIG. 24 is a top plan view of a bilayer TES with a bilayer perforated weak link. 
     FIG. 25 is a side plan view of a multiple perforation embodiment. 
     FIG. 26 is a top plan view of a multiple perforation embodiment. 
     FIG. 27 is a side plan view of the bilayer multiple perforation embodiment. 
     FIG. 28 is a top plan view of the bilayer multiple perforation embodiment. 
     FIG. 29 is a side plan view of a TES with a single layer and a reduced T c  weak link having a normal metal line. 
     FIG. 30 is a top plan view of a TES with a single layer and a reduced T c  weak link having a normal metal line. 
     FIG. 31 is a side plan view of a bilayer TES with a normal metal line. 
     FIG. 32 is a top plan view of a bilayer TES with a normal metal line. 
     FIG. 33 is a side plan view of a single layer TES with multiple normal metal weak links. 
     FIG. 34 which is a top plan view of a single layer TES with multiple normal metal line weak links. 
     FIG. 35 is a side plan view of a bilayer TES with multiple normal metal line weak links. 
     FIG. 36 is a top plan view of a bilayer TES with multiple normal metal line weak links. 
     FIG. 37 is a side plan view of a TES having an impurity seam in the superconducting layer. 
     FIG. 38 is a top plan view of a TES having an impurity seam in the superconducting layer. 
     FIG. 39 is a side plan view of a TES having multiple impurity seams in the superconducting layer. 
     FIG. 40 is a top plan view of a TES having multiple impurity seams in the superconducting layer. 
     FIG. 41 is a side plan view of a TES having an impurity seam in a bilayer. 
     FIG. 42 is a top plan view of a TES having an impurity seam in a bilayer. 
     FIG. 43 is a side plan view of a TES having multiple bilayer impurity seams. 
     FIG. 44 is a top plan view of a TES having multiple bilayer impurity seams. 
     FIG. 45 is a side plan view of a TES having slots. 
     FIG. 46 is a top plan view of a TES having slots. 
     FIG. 47 is a side plan view of a bilayer TES having slots. 
     FIG. 48 is a top plan view of a bilayer TES having slots. 
     FIG. 49 is a side plan view of a TES having multiple slots. 
     FIG. 50 is a top plan view of a TES having multiple slots. 
     FIG. 51 is a side plan view of a bilayer TES having multiple slots. 
     FIG. 52 is a top plan view of a bilayer TES having multiple slots. 
     FIG. 53 is a comparison plot of the dynamic resistance versus bias current for a continuous TES and the present invention. 
     FIG. 54 is a schematic view of an undamped bias circuit. 
     FIG. 55 is a schematic of a damped bias circuit. 
    
    
     Before explaining the disclosed embodiment of the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the particular arrangements shown, since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a side plan view of the Prior Art. Membrane film A is deposited on substrate B. The membrane film A provides thermal isolation. Transition edge sensor (TES) C is deposited on membrane film A. TES C may consist of a single superconducting material or of a bilayer comprising a normal-metal layer and a superconducting layer. Superconducting contacts D are applied to the TES C. The structure of TES C with a single superconductor is illustrated in FIG.  1 . In the bilayer version shown in FIG. 3, the TES comprises a normal-conductor layer N and an aluminum layer L. The substrate is preferably a material which is not a source of impurities. In one version, the substrate B is crystalline silicon coated with a SiN x  layer. In another version the substrate B is an SiN x  membrane having low thermal conductivity. The substrate can also serve as a substrate for an absorber and for measurement circuit connections. In the bilayer version, the normal-metal layer is made of any metal or metal alloy which is a normal conductor at the operating temperature of the sensor. Preferred normal metals include gold, silver, copper, palladium, platinum, and alloys of these metals; gold/copper alloys and palladium/gold alloys. The normal metal can be a material such as tungsten which is a superconductor having a T c  below the operating temperature of the sensor, but is a normal conductor at the operating temperature. 
     FIG. 2 is a top plan view of the Prior Art as previously described in FIG. 1 depicting the single layer TES. 
     FIG. 4 is a top plan view of the Prior Art as shown in FIG. 3 depicting the bilayer TES. 
     A number of different localized weak links are disclosed herein to improve the electrical performance of a transition-edge sensor (TES). The preferred embodiment uses a weak link consisting of a step edge in the substrate on which the TES is deposited. 
     Referring to FIG. 5, the preferred embodiment, the step edge  11  is introduced into the membrane film  10  by photolithographic etching. Membrane film  10  is deposited on substrate  20 . This is well known in the art. The TES bilayer  30  is then deposited over the substrate step edge  11  creating step edge  31  in the bilayer of height “H”. The bilayer consists of normal layer  33  and superconducting layer  34  whose thicknesses are chosen to achieve the desired superconducting transition temperature. Depending upon the particular materials chosen for each layer, the arrangement of the layers on the substrate can be reversed. For example, superconducting aluminum can be placed on top of or below the normal metal layer, such as silver. The step in the bilayer results in a reduction in thickness H, resulting in turn in a reduced cross-sectional area  32  as compared to the thickness and cross-sectional area of the bilayer  30 . The reduced cross-sectional area  32  results in a reduction in the critical current, I c , of the TES in the region of the step edge  11 , thereby forming a weak link. The step edge  11  should be of such a size so as to reduce the critical current of the TES, I c , by 10% to 90% of the “bulk” TES value, which is predicted, for example, by the Ginzberg-Landau theory. The step edge height necessary to achieve the desired critical current reduction varies with the steepness of the step edge. For vertical step edges, 90 degrees from the horizontal, a step edge height of 10% to 90% of the TES thickness is necessary. As the step edge angle is reduced the step edge height needs to be increased to cause the necessary cross-section reduction. The TES is connected to the rest of the circuit with superconducting contacts  40  and  41 . These are typically depicted in all relevant figures. 
     FIG. 6 is a top plan view of a bilayer TES with a step edge weak link  32 , as described in FIG.  5 . 
     FIG. 7 is a side view of the single layer step edge embodiment. The features are as described in FIG. 5 with the exception that the bilayer  30  in FIG. 5 is replaced by a single layer comprising a superconducting layer  88 . 
     FIG. 8 is a top plan view of the single step edge embodiment depicted in FIG.  7 . 
     FIG. 9 is a side plan view of a TES with a single layer multi-step edge weak link. Multiple steps as described in FIG. 9 are fabricated into superconducting layer  603 . Steps  602  in the membrane  609  result in areas of reduced cross-sectional area  605  in superconducting layer  603 . The steps may be fabricated by photolithographic etching. The number of step edge weak links chosen may be sufficient to fill a portion of the TES or the entire length of the TES. 
     For example: 
     In the case of a bilayer detector without an absorber, a square detector that is on the order of 400 μm on a side is specified. In order to minimize thermal diffusion times in the TES, a TES thickness of 300 nm is chosen. The selected operating temperature is 100 mK. In order to obtain this operating temperature, the TES is fabricated from roughly 100 nm of Al and 200 nm of Ag. The heat capacity of the detector is the roughly 0.3 pJ/K. With proper bias, this allows a 6 keV saturation energy. If the detector is biased at 0.99 T c , then λ Q , the charge imbalance relaxation length, for this bilayer is on the order of 30 μm. The quantity, λ Q , is known in the art. The multiple step edge weak links are then spaced at twice λ Q  or 60 μm. The weak links are spaced between 0.3 and 10 times λ Q , which is a material dependent parameter. This gives a result of six step edge weak links within the given size TES. 
     FIG. 10 is a top plan view of a TES with a single layer multi-step edge weak link. Steps  602  completely span the width W of superconducting layer  603 . Although FIG. 10 depicts eight steps, this is not offered as a limitation as any number of steps may be used according to the needs of an operator. 
     FIG. 11 is a side plan view of the bilayer multi-step edge weak link. The features are as described in FIG. 9 with the exception that the single superconducting layer  603  in FIG. 9 is replaced by a bilayer comprising a normal metal layer  610  and a superconducting layer  611 . 
     FIG. 12 is a top plan view of the bilayer multiple step edge weak link depicted in FIG.  11 . 
     FIG. 13 is a side plan view of a TES with a notch weak link. In an alternate embodiment a weak link is created by a localized thinning or narrowing of the TES  70  thereby creating a notch. The thinning involves localized reduction of the superconducting layer  73  of the bilayer TES  70 . The thinning of the superconducting layer  73  of TES  70  may be accomplished in many ways, for example, through the use of a notch  71  fabricated by photolithographic means. This results in reduced cross-sectional area of the thinned region  72  of the TES  70  as compared to the thickness of the unthinned superconducting layer. Due to the area of reduced cross-section, the local critical current of the thinned region  72  is decreased, thereby forming the weak link. The thinning the bilayer TES can tolerate is in the range of 1% to 100% while still functioning as required. Membrane  50  is deposited upon substrate  60 . 
     FIG. 14 depicts a top plan view of the TES  70  with the notch  71  and with a thinned region weak link  72  depicted in FIG.  13 . 
     FIG. 15 is a side plan view of the multiple notch embodiment. Superconducting layer  702  is mounted to substrate  708 . Notches  701  are etched into superconducting layer  702  resulting in reduced area  704  beneath each notch. The reduced areas  704  need not be of identical cross-sectional area. Further, the number of notches can be of any number depending upon the needs of a user. 
     FIG. 16 is a top plan view of the multiple notch embodiment. Superconducting layer  702  is mounted to substrate  708 . Notches  701  are etched into superconducting layer  702  resulting in reduced area  704  beneath each notch. Notches  701  span the entire width W of the superconducting layer  702 . 
     FIG. 17 is a side plan view of a notched bilayer embodiment. Normal metal layer  801  and superconducting layer  802  are mounted to substrate  804 . Notch  803  is etched into layer  802  using photolithographic methods known in the art. Notch  803  may or may not completely bifurcate penetrated layer  802 , thereby leaving a section of reduced area  805  and thus reduced transition temperature in the TES. 
     FIG. 18 is a top plan view of a notched bilayer embodiment. Normal metal layer  801  and superconducting layer  802  are mounted to substrate  804 . Notch  803  is etched into layer  802  spanning the entire width W of layer  802 . 
     FIG. 19 is a side plan view of a multiple notched bilayer embodiment. Normal metal layer  902  and superconducting layer  903  are mounted to substrate  905 . Notches  901  are etched into layer  903 . Notches  901  may or may not completely bifurcate penetrated layer  903 , thereby leaving a sections of reduced area  904  in layer  903 . Further, the number of notches can be of any number depending upon the needs of a user. 
     FIG. 20 is a top plan view of a multiple notched bilayer embodiment. Superconducting layer  903  and normal-metal layer  902  are mounted to substrate  905 . Notches  901  are etched into layer  903 . Notches  901  completely span the width W of layer  903 . 
     FIG. 21 is a side plan view of a TES with a single layer perforated weak link. In this alternate embodiment a weak link is created by the fabrication of a series of holes in the superconducting layer  110 . Perforations  111  may consist of complete penetration of the layer  110  or partial penetration. Complete perforation causes a reduction in the cross-sectional area corresponding to the width of the perforations. Complete or partial perforation results in weak link(s) being created in the TES. Membrane  90  is mounted upon substrate  100 . 
     FIG. 22 is a top plan view of a TES with single layer weak link perforations  111 . Even though FIG. 22 depicts a row of perforations  111 , any pattern of arrangement of the perforations is acceptable and will result in the desired characteristics for the invention. 
     FIG. 23 is a side plan view of a bilayer TES with a perforated weak link. The features are as described in FIG. 21 with the exception that the single superconducting layer  110  in FIG. 21 is replaced by a bilayer comprising a normal metal layer  130  and a superconducting layer  131 . 
     FIG. 24 is a top plan view of a bilayer TES with a perforated weak link depicted in FIG.  23 . 
     FIG. 25 is a side plan view of a multiple perforation embodiment. Perforations  1010  completely penetrate superconducting layer  1000 . The perforations result in areas of reduced cross section  1030  between each perforation. Perforations  1010  may be fabricated in any pattern, symmetrically or asymmetrically, using photolithographic methods known in the art. The depiction shown in FIG. 26 is representative of a possible perforation arrangement. 
     FIG. 26 is a top plan view of a multiple perforation embodiment. Perforations  1010  completely penetrate superconducting layer  1000 . Perforations  1010  may occur in any pattern, symmetrically or asymmetrically. The depiction shown in FIG. 26 is representative of a possible perforation arrangement. The arrangement of the perforations  1010  result in sections of reduced area  1030 . The form of the sections of reduced area are a function of the arrangement of the perforations. 
     FIG. 27 is a side plan view of the bilayer multiple perforation embodiment. The features are as described in FIG. 25 with the exception that the single superconducting layer  1000  in FIG. 25 is replaced by a bilayer comprising a normal metal layer  1040  and a superconducting layer  1050 . 
     FIG. 28 is a top plan view of the bilayer multiple perforation embodiment depicted in FIG.  27 . 
     FIG. 29 is a side plan view of a TES with a single layer and normal metal line reduced T c  weak link. In this alternate embodiment, weak links are created by a localized reduction in the critical temperature of the superconducting film  150 . This is accomplished with the deposition of a normal metal line  151  on the upper surface  152  or lower surface  153  of the layer  150 . The normal metal line may also be deposited upon the substrate  140 , resulting in a location between the layer  150  and substrate  140 . The reduction in T c  due to the normal metal line  151  is caused by the proximity effect, which is known in the art. FIG. 29 depicts the normal metal line  151  deposited on the lower surface of the layer  150 . 
     FIG. 30 is a top plan view of a TES having a single layer with a normal metal line reduced T c  weak link normal metal line  151  spanning the width W of layer  150 . 
     FIG. 31 is a side plan view of a bilayer TES with a normal metal line. The features are as described in FIG. 29 with the exception that the single superconducting layer  150  in FIG. 29 is replaced by a bilayer comprising a normal metal layer  170  and a superconducting layer  171 . 
     FIG. 32 is a top plan view of a bilayer TES with a normal metal line depicted in FIG.  31 . 
     FIG. 33 is a side plan view of a TES with multiple normal metal line weak links. In this alternate embodiment, multiple normal metal line weak links  191  are incorporated into the superconducting layer  190 . As shown in FIG. 5, the TES is connected to the rest of the circuit with superconducting links  200  and  201 . 
     Reference is made to FIG. 34 which is a top plan view of a TES with multiple normal metal line weak links  191  as described in FIG.  33 . 
     FIG. 35 is a side plan view of a bilayer TES with multiple normal metal line weak links. The features are as described in FIG. 33 with the exception that the single superconducting layer  190  in FIG. 33 is replaced by a bilayer comprising a normal metal layer  192  and a superconducting layer  193 . 
     FIG. 36 is a top plan view of a bilayer TES with multiple normal metal line weak links depicted in FIG.  35 . 
     FIG. 37 is a side plan view of a TES having an impurity seam. Poisoning of the superconducting layer  1100  is achieved with impurities  1110 . Superconducting layer  1100  is mounted to substrate  1120 . A seam of impurities  1110  is fabricated into layer  1100 . The impurities span the entire cross-sectional area of the layer  1100 . The impurities may consist of any material, including magnetic materials. The impurities result in reduced conductivity in layer  1100 . 
     FIG. 38 is a top plan view of a TES having an impurity seam in the superconducting layer. Superconducting layer  1100  is mounted to substrate  1120 . A seam of impurities  1110  are fabricated into layer  1100 . The impurities  1110  may consist of any material. The impurities result in areas of reduced conductivity in layer  1100 . The area containing the impurities may span the entire width of the layer  1100 , or may be adjusted to accommodate the particular needs of an operator. 
     FIG. 39 is a side plan view of a TES having multiple inclusions of impurities in the superconducting layer. Multiple seams of impurities  1210  are fabricated into superconducting layer  1200 . The impurities  1210  may consist of any material. The impurities result in reduced areas of conductivity in layer  1200 . 
     FIG. 40 is a top plan view of a TES having multiple impurity seams in the superconducting layer. Multiple seams of impurities  1210  are arranged across the entire width W of superconducting layer  1200 . Any number of seams in any arrangement may be used to achieve the desired effect. 
     FIG. 41 is a side plan view of a TES having an impurity seam in a bilayer. A seam of impurities  1310  is fabricated into normal metal layer  1300  and superconducting layer  1320 . The impurities  1310  may consist of any material. The impurities result in reduced conductivity in layer  1300  and/or  1320 . 
     FIG. 42 is a top plan view of a TES having an impurity seam in a bilayer. Seams of impurities  1310  completely span the width W of normal metal layer  1300  and superconducting layer  1320 . 
     FIG. 43 is a side plan view of a TES having multiple bilayer impurity seams. Multiple seams of impurities  1410  are fabricated into normal metal layer  1400  and superconducting layer  1420 . The seams of impurities  1410  may consist of any material. The impurities result in reduced conductivity in layer  1400  and  1420 . 
     FIG. 44 is a top plan view of a TES having multiple bilayer impurity seams. Multiple seams of impurities are fabricated into layer  1400  and  1420 . Each seam of impurities completely spans the width W of layer  1400  and  1420 . 
     FIG. 45 is a side plan view of a TES having a single layer having slots. Superconducting layer  1500  is fabricated with cooperating slots  1510 . Slots  1510  are fabricated relative to each other so as to result in an area of reduced cross-sectional area  1520  in layer  1500 . The fabrication of slots  1510  may be accomplished using photolithographic methods known in the art. 
     FIG. 46 is a top plan view of a TES having a single layer having slots. Slots  1510  result in an area of reduced cross section  1520  in layer  1500 . 
     FIG. 47 is a side plan view of a bilayer TES having slots. The features are as described in FIG. 45 with the exception that the single superconducting layer  1500  in FIG. 45 is replaced by a bilayer comprising a normal metal layer  1530  and a superconducting layer  1540 . 
     FIG. 48 is a top plan view of a bilayer TES having slots. depicted in FIG.  47 . 
     FIG. 49 is a side plan view of a TES having multiple slots. Superconducting layer  1600  contains slots  1610 , each fabricated as described for FIGS. 45 and 46. 
     FIG. 50 is a top plan view of a TES having multiple slots. Superconducting layer  1600  contains cooperating slots  1610 . These are fabricated into layer  1600  by using photolithographic methods known in the art. The slots  1610  result in sections of reduced cross-sectional area  1620 . 
     FIG. 51 is a side plan view of a bilayer TES having multiple slots. The features are as described in FIG. 49 with the exception that the single superconducting layer  1600  in FIG. 49 is replaced by a bilayer comprising a normal metal layer  1630  and a superconducting layer  1640 . 
     FIG. 52 is a top plan view of a bilayer TES having multiple slots as depicted in FIG.  51 . 
     FIG. 53 is a comparison plot of the dynamic resistance versus bias current for a continuous TES and the present invention. The continuous TES has no weak link structure as disclosed for the present invention. The weak link TES response shown is for a step edge weak link. The dynamic resistance of the continuous TES is a rapidly varying function of the bias point for the continuous TES. This behavior, shown as peaks on the graph, is due to phase slip line formation. In the case of the step edge weak link TES, the dynamic resistance varies more smoothly. 
     FIG. 54 is a schematic view of an undamped bias circuit. In the present invention, a voltage source  400  is connected across the TES to create the necessary voltage potential across the TES. The voltage source is typically set at 0.05 to 5.0 μV. The electrical readout is provided by a SQUID current amplifier  500 . The relative inductance of the input coil or SQUID is on the order of ≈0.6 μH. The SQUID  500  is connected to the TES  300  through long (˜0.5 m) superconducting wires  200 . The wires can be a twisted pair or a coaxial line, and can be modeled as a transmission line of impedance Z tr , which is approximately 50Ω. The twisted conductor pair  200  forms a transmission line with mismatched impedance&#39;s. The characteristic impedance of the transmission line is on the order of 50Ω. The resistance of the TES  300 , much less than Z tr  and is on the order of 0.1Ω. The resonant frequencies of the system are determined by the length of the conductor pair  200 . As described previously, high-frequency resonances in the electrical bias circuit of the TES can excite Josephson processes in the TES, leading to voltage steps in the electrical response of the TES. The magnitude between voltage steps are V=hf/2e, where f is the resonant frequency of the bias circuit, and e is the charge of the electron, and h is Planck&#39;s constant. 
     FIG. 55 is a schematic of a damped bias circuit. The high-frequency resonance described in FIG. 54 is damped by placing a small resistor R across the conductor pair  200  connected to the SQUID  500 . The resistor R has a resistance value on the order of 1Ω. The resistor R damps the bias circuit resonance, giving a smooth I-V relationship without the voltage steps described in FIG.  53 . 
     Although the present invention has been described with reference to preferred embodiments, numerous modifications and variations can be made and still the result will come within the scope of the invention. No limitation with respect to the specific embodiments disclosed herein is intended or should be inferred.