Superconducting detector technology and development

    Abstract: This article introduces the technical performance, characteristics and applications of high Tc superconducting infrared detectors, discusses various detection mechanisms and modes, and briefly introduces the research status and development trends of various new high-performance infrared products and technologies.

    Keywords: superconducting infrared detector; detection mechanism; high temperature superconducting device

At present, the research on high Tc superconducting infrared detectors has become one of the important contents in superconducting electronics. This is because the development level of high Tc superconducting detectors has entered the practical stage and has become a new step in the development of photoelectric detection technology. Direction. Compared with traditional semiconductor detectors, high-Tc superconducting detectors will become excellent receivers in long-wave detection greater than 20 μm , which fills the gap in the far-infrared to millimeter-wave bands in the electromagnetic spectrum. In addition, it also has the advantages of high integration, low power, high yield, and low price. It is expected that this technology will be widely used in the fields of astronomical exploration, spectral research, far-infrared laser reception and military optics.

1 Mechanism of superconducting expedition testing

The use of superconductors to detect infrared radiation began as early as the 1950s, but has been stagnant due to the limitations of working conditions at low temperatures below 20K. The advent of high Tc superconducting materials has given this technology a new lease of life. Its detection mechanisms include the following:

1.1 Mechanism of relationship between resistance and temperature

This principle uses the characteristic that when a superconductor changes from a normal state to a superconducting state, the resistance changes sharply with temperature changes to detect infrared radiation. The existing high Tc bolometer is developed based on this principle.

1.2 Mechanism of relationship between inductance and temperature

This mechanism is realized based on the fact that the dynamic inductance of the superconducting film changes sharply with temperature changes under the Tc detection rate. This kind of detector works under Tc, can eliminate the bolometer thermal noise, and can very accurately measure the frequency change caused by the dynamic inductance Lk. It has the characteristics of simple production and high sensitivity.

1.3 Mechanism of relationship between magnetic susceptibility and temperature

When infrared radiation shines on a superconducting sensitive element and causes the temperature to rise, its magnetic susceptibility will change rapidly, a phenomenon like a "magnetic field shutter." This phenomenon can be used to detect incident radiation through changes in the magnetic mechanism or changes in AC magnetic susceptibility. The NEP~10-11W·HZ-1/2 detector has been trial-produced based on this mechanism. This detector is advantageously designed to operate at low temperatures and read signals at room temperature.

1. 4 Light-assisted tunneling effect

In 1962, Josepson theoretically predicted that if there is a very thin layer of insulating medium (about a few nanometers) between two superconductors, then a weak current ( μA to mA) can pass through without hindrance. This prediction was soon confirmed by experiments at Bell Labs. This phenomenon is called the Josephson effect.

1.5 Non-equilibrium photoelectric effect

Testardi believes that destroying superconducting Cooper electron pairs with photons can produce quasiparticles. The existence of quasiparticles will compress the superconducting energy gap and destroy superconductivity. This phenomenon can therefore be used to detect infrared radiation.

Now, researchers have observed this phenomenon in materials such as Sn, Pb and its oxides, BaPb-BiO, and YBCO. Its response time is better than 10-4 seconds.

1.6 Optomagnetic quantum effects

This effect was developed from the physical concept of superconducting phase slip. In 1990, AM Kakin and others formed a new mechanism for optical and magnetic quantum detection of infrared radiation. When the width of the strip conductor is smaller than the superconducting coherence length, under the action of the critical current Ic, its superconductivity will be destroyed through local phase slip and a central vortex will be formed. That is, the superconducting energy gap Δ is locally compressed to zero, and the superconductor slips repeatedly accordingly. For two-dimensional superconductors, this slip process connects into circles to form a vortex-antivortex pair, and the two vortices repel each other and separate due to the transverse Lorentz force generated. At the same time, a voltage pulse with a net magnetic flux of φ0 is generated . Nowadays, the microscopic mechanism of this light-assisted vortex quantum detection radiation has been experimentally confirmed using NbN and BaPbBiO films, and the results of Rv of 6000V/W and 104V/W were obtained respectively, with a τ value better than nanoseconds.

1. 7 Nernst effect

When incident light shines on a high TC film, a humidity gradient perpendicular to the surface will be generated in the film. Under an external magnetic field, the presence of infrared radiation can be measured along the film surface. It uses the mechanism of de-pinning of magnetic flux lines and temperature gradient to drive magnetic flux lines to achieve detection. Its response speed is fast, usually 10-6 seconds.

1.8 Mechanism of relationship between current and humidity

In 1993, MIFiik et al. envisioned a new type of radiation loss detector called the intrinsic superconducting radiation detector (ISRD). It is made by using the relationship between the critical current Ic and T of the superconducting film. MIT obtains W·Hz1/2, D=2.7×109cm·H-1·W-1. The detector has the ability to reach phonon noise wired potential.

1.9

This is a deep cryogenic detector proposed by Beukeley University. It can be as large as 1.15×1015cm·W-1 and has high performance.

2 Performance characteristics of superconducting infrared detectors

Various styles of high Tc superconducting infrared detectors have been designed and manufactured based on the above nine detection mechanisms, among which the most mature ones are bolometer-type devices manufactured based on the R~T relationship. Followed by Josephson junction devices. Table 1 lists the main performances of several high-level detectors at this stage.

As can be seen from Table 1, the performance of the unit superconducting detector has reached practical levels. Most of them are made of YiBa2Cu3O7 material, mainly because the film production process of this material is mature and the Tc can reach 90K. Therefore, the thermal design of the detector is relatively easy to implement.

Table 1 Important properties of high Tc superconductors

Due to the needs of practical applications, research on multi-element arrays (FPA) is currently extremely active. There are now reports of 1×8 yuan, 1×12 yuan, 1×64 yuan line arrays, 3×4 yuan, and 8×8 yuan area arrays. , it is particularly noteworthy that there are more than a dozen research institutions conducting high-Tc infrared FPA, such as Honrywell, TRW, Westinghouse, Superconducting Corporation, NASA/Goddard Space Center, Naval Research Laboratory (NRL) and the University of California, etc. Figure 1 is a schematic structural diagram of the 4*4 element area array trial produced by the Shanghai Institute of Technical Physics. For this resistance type bolometer, each sensitive element has two signal readout lines. The manufacturing and process realization of the area array device is a difficult point. As can be seen from Figure 1, each sensitive element in the area array has two signal readout lines, and the manufacturing and process implementation of the area array device is a difficult point. As can be seen from Figure 1, the D value of the 4*4 element area array produced by using the ingenious design of common electrode programming for each sensitive element in the area array and using integrated micro-machining technology to photolithography the YBCO film is in the range of (1.2-7.2 )×104cm·Hz1/2·W-1, the operating temperature is 88K. Compared with the delay line clock pulse reading signal method, it has the advantage of two-dimensional simultaneous signal reading. This unique design method can also be used to trial-produce 4N series focal plane devices (such as 4×8 yuan, 4×128 yuan, etc.), and can introduce the manufacturing technology of traditional infrared detector area arrays such as photoconductive HgCdTe and thermistors. Under development.

Figure 2 is a diagram of the sensitive element of a high Tc superconducting detector using a synchrotron radiation source to lithograph 0.8 μm lines. Utilizing this sensitive element can not only increase the energy received by incident radiation, but also lay a technical foundation for manufacturing high-density multi-element arrays.

Photonic Josephson type high Tc detectors currently mainly include four types: SIS junction, SNS junction, grain boundary junction and Josephson micro-bridge. However, these four structures have complex processes and unstable junctions. Experimentally, they are made of TdBaCaCuO. The D value of the Josephson junction can reach 1010 cm·Hz1/2·W-1, and the response time τ is 10-9 seconds. This type of fast, high-performance detector is particularly suitable for

In the far infrared and millimeter wave regions.

Currently, semiconductor infrared focal plane arrays face two problems: one is the manufacturing process; the other is power consumption. From the perspective of manufacturing process, semiconductor IRFPA includes detector assembly, preamplifier and two-dimensional signal readout circuit. It is quite difficult to use such a hybrid structure to manufacture a large-area array with uniform electrical properties on a single substrate, and it is difficult to require the structure to be smaller than 100 μm2. Therefore, devices with an FPA of 100×100 or more elements must be inlaid. Assemblies. Usually, the size of superchip circuits is only microns, while semiconductor circuits are tens of microns. Therefore, in a certain area, superconducting circuits can complete more complex information processing. Regarding power consumption, the U.S. Strategic Defense Agency (SDIO) has an indicator that the power consumption of each pixel of the designed system is required to be within 10 μW. According to this requirement, for a semiconductor FPA system with a huge number of pixels, the total power consumption is also quite large. For example, a 1000×1000 pixel area array will have a power consumption of 10W, which will bring great consequences to the aviation or aerospace system. Lots of technical difficulties.

The superconducting FPA technology being developed can effectively overcome the above difficulties of semiconductor FPA. And it shows good prospects for the development of high-density and low-power FPA. To sum up, the advantages are as follows:

●Low power consumption

Superconducting circuits can be considered powerless, but in fact power consumption does exist. Typically it is two orders of magnitude lower than the power consumption of a semiconductor circuit for the same function. The research content of superconducting FPA includes, in addition to sensitive elements, preamplifier (optional SQUD), A/D conversion and information processing circuits. Generally speaking, the power consumption of superconducting circuits is 1 to 2 orders of magnitude lower than that of semiconductor circuits.

●Superconducting lines are extremely small in size

Judging from research reports on submicron and nanostructures, micron-level devices plus micron-level circuits will have higher density than semiconductor FPA, and thus can complete more complex information processing work.

●Easy to develop large-area uniform arrays

Since the superconducting uniform film already has a size of φ76mm, it is completely possible to manufacture large-area uniform sensitive elements using existing photolithography technology. And there are very few or no bad components.

●High yield and low price

This is determined by the reliability of superconducting filmmaking and photolithography processes. Bolomerer devices made from thin films of high-Te superconductors deposited on Si microstructures have a high yield and cost 5 to 6 orders of magnitude lower than HgCdTe.

The main problem of superconducting FPA technology is that both superconducting devices and circuits have low impedance, so the matching problem of information readout must be solved. DL, Smetana and others proposed a plan to use a high Tc superconducting impedance converter to decouple a low-impedance detector and connect it with a C-MOS processing multiplex transmission line. This is actually a Z-plane FPA readout structure. . In addition, progress has been made in using superconducting A/D converters in more than FPA. Westinghouse's superconducting IR-FPA research group has used superconducting A/D conversion in infrared imaging systems.

3 Research fields and development trends

As an important application of superconducting electronics, research on high-Tc superconducting infrared detectors is quite active, mainly in developing new materials, improving the performance of existing detectors, and promoting applications. It is now summarized into the following 7 contents:

(1) New high Tc material devices

Most of the high Tc superconducting devices made so far are YBCO materials, but this is not the best choice. Its electron density at the Fermi level is far inferior to materials such as BakBiO and BaPbBiO. Japanese NTT Company uses these two materials. Faster devices than 10 -6 seconds. The University of California used ErBCO to make high-performance devices that respond from X-ray to microwave, with an NEP value of 10 -12W.Hz -1/2.

Recently, through the synthesis of Hg-1223 and the study of the Hg annealing process, the result of Tc=139K was obtained. Moreover, the test analysis and confirmation process are still in progress. The pursuit of room temperature superconductors is an extremely attractive goal. .

(2) Superconductor/semiconductor hybrid device

The work combined with existing semiconductor technology is mainly reflected in the combined structure of YBCO and Si integration. Vir-ginia University made YZS islands on Si substrates and transitioned into YBCC-Si microbridges. The National Institute of Standards and Technology (NIST) used Au or Ag to interconnect YBCO and Si to realize a super-semi-hybrid device trial-produced by a conventional Si-oxide-semiconductor process, thus providing a technical basis for connection with the CMOS readout circuit.

(3) Fast devices

The response speed τ of the high Tc detector is on the millisecond level. Therefore, developing block-speed devices has become a pursuit goal. The microbridge manufactured by Boeing can achieve a τ value of 10μs with Joule-Thomson cooling. Moscow Normal University in Russia has produced a 0.15μm submicron bridge with a τ value of 1 to 2ps (10 -12s), a response wavelength of 0.8 millimeter waves, and NEP = 3×10 -11W.Hz -1/2.

(4) Long wave devices

The so-called long wave refers to the spectrum region from 20μm to mm. Due to the application needs of spectral research, astronomical observation and far-red laser reception, high Tc superconducting devices are undoubtedly the best choice. The wavelength of the device produced by the University of Copenhagen in Denmark is 90-600μm, and the NEP is 4×10 11W.Hz -12.

(5) New detection mechanism devices

The quantum superconducting detector proposed by N. Blujer et al. in 1994 is based on the detection of incident radiation through quantum resonance in the superconducting state. The inductively coupled infrared staring device based on the co-optical magnetic quantum effect proposed by ADHibbs et al. has a pixel up to 10×10μm2.

(6) Introduce new technical means to improve device performance

Many mature scientific methods can be used, such as the use of synchrotron radiation light sources and electron beam direct lithography to obtain submicron and nanoscale sensitive elements, coupling of antennas and sensitive elements, and Si diaphragm processes.

4 Application prospects

At present, although there are still some technical difficulties in thermal-sensitive devices, there are no major insurmountable obstacles. It is expected that more mature units and line arrays will enter the practical application stage before 2010 and can be partially commercialized. Photonic devices will also have technological breakthroughs and trials. It can be foreseen that photonic devices and infrared detectors will be two major categories of detectors developed in parallel.

In the future, with the development of high Tc superconducting devices, they will be widely used in the following fields:

(1) Spectrometer: High-Tc superconducting devices are superior to thermopile and pyroelectric devices when used in the mid- and far-infrared regions of Fourier spectrometers, especially fast-scanning Fourier spectrometers.

(2) Rapid low temperature thermometer and radiometer.

(3) Thermal imaging camera: High Tc superconducting devices are undoubtedly the best devices for imaging in the wavelength range from greater than 20 μm to sub-millimeter.

(4) Ground object spectrometer: that is, long-wave ground object radiation spectrum detection.

(5) Far-infrared laser reception.

(6) Measurement of Tokmak plasma electron temperature.

(7) Radio astronomy submillimeter wave receivers and astronomical detection spectrometers, especially in the detection of outer space by astronomical satellites.

(8) Various military equipment: such as active submillimeter waveform scanners, infrared front-view devices, etc.