JPH0346520A - Signal detector - Google Patents

Abstract

PURPOSE:To detect signals of a wide range of wavelength bands by providing a signal input part where a current is generated by the input of a light signal and a signal detecting part consisting of a superconductor of a Josephson junction which detects the magnetic field generated by this current. CONSTITUTION:The oxide superconductor 1 is made into a band shape and a microbridge part is formed to about 8X12mum. Four pieces of electrodes consisting of Cr and Au are produced on the superconductor 1 to form the electrodes 2 for current implantation and the electrodes 3 for voltage measurement. A thin film of MgO is formed in the central part of the band to be an insulating layer. A CdS film is formed thereon as the signal input part (photoconductor) 6. This detector is put into liquid nitrogen and a prescribed voltage is impressed to a power source 5 for impressing bias current and a power source 7 for driving the photoconductor. A voltmeter 8 for signal detection is 0V and the superconduction is not broken when the photoconductor 6 is not irradiated with light at this time. The voltmeter 8 registers several mV when the photoconductor 6 is irradiated with an He-Ne laser. The generation of this voltage indicates that a photocurrent is generated in the photoconductor 6 and the critical current value is suppressed by the consequently generated magnetic field, by which the superconducting state is broken.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a signal detection method that utilizes the magnetic properties of a superconductor to convert an input signal into a magnetic signal and detect an optical signal.

[Prior Art] As a conventional signal detector using a superconductor, especially a detector for detecting optical signals, one using a Josephson junction is known [Japanese Journal o
f Applied Physics vol, 23
L333 (1984)]. This optical signal detector
As shown in the figure, oxide superconductors BaPbo, , Bi,
, 5o3 (BPBO) thin film is used to form a microbridge type Josephson junction, this junction is irradiated with light, and changes in the critical current value of the Josephson junction are utilized. In such a detector, BPn is used as the material of the light receiving part.
O is used, which has a low critical temperature of about 13. That is, liquid helium or the like must be used to operate the detector. In addition, the characteristics of such a detector are:
Determined by the properties of the Josephson junction.

[Problems to be Solved by the Invention] In the above conventional example, when a large number of detectors are used simultaneously, such as in an image sensor, it is difficult to correct variations in characteristics between detectors due to variations in processing, etc. There is a problem.

Additionally, the wavelength range of light to be detected is limited due to the spectral characteristics of the superconductor, so there is also the problem that it is not suitable for signal detection over a wide range of wavelength bands.

Furthermore, since the area of light irradiation to the joint is very limited, there is also the problem that alignment accuracy is required.

That is, an object of the present invention is to solve the above-mentioned problems by utilizing the magnetic properties of superconducting materials.

[Means for Solving the Problems] The present invention is characterized by a signal input section that generates a current upon input of an optical signal, and a superconductor using the Josephson effect that detects the magnetic field generated by the current. A signal detector comprising at least a signal detection section comprising:

The present invention also provides a signal detector using a microbridge type Josephson junction in the signal detection section.

Furthermore, the present invention is characterized by a signal detector using a photoconductive material in the signal input section.

Here, the superconductor used as the signal detecting section used to remotely construct such a signal detector is preferably a single crystal or polycrystalline material having superconducting properties. Note that in order to operate the detector at a higher temperature, a material with a high critical temperature is preferable. In this respect, Y-Ba-Cu-0 system,
B1-5r-Ca-Cu-0 system, T? 5r-Ca-Cu
A material having a critical temperature higher than 77, which is the boiling point of liquid nitrogen, such as a -0 series ceramics material, is suitable.

On the other hand, the operating temperature of the detector may be lower than the critical temperature of the superconductor used, but a temperature close to the critical temperature is more preferable in order to increase the detection sensitivity of the input signal.

In addition, the materials used for the signal input section include infrared, visible,
Photoconductive materials that are compatible with optical signals such as ultraviolet light are preferred.

In particular, materials that generate a large photocurrent include InSb,
Si, GaAs, a-5i, CdS, GdS
e etc. are preferred.

Further, it goes without saying that the photocurrent generating section may be a signal receiving section, or may be a conducting wire connected to the signal receiving section, for example, a wiring made of a metal material.

For example, when a signal input section made of a photoconductive material is irradiated with light, electrons in the valence band are excited and transition to the conduction band. A photocurrent is generated when electrons excited in this conduction band move due to an applied electric field.

On the other hand, it is well known as a fundamental law of physics that when an electric current flows through a substance, a magnetic field is generated by this electric current.

In addition, there are two types of superconductors: type 1 and type 2 superconductors.
When a magnetic field unique to the material, that is, a magnetic field larger than the critical magnetic field, is applied, the superconducting state is destroyed in type 1 superconductors, and in type 2 superconductors, the superconductor state is broken due to a magnetic field stronger than the magnetic field unique to the material (ICI). By entering a part of the magnetic flux into the material and applying a stronger material-specific magnetic field ()lc2),
It is known that the superconducting state breaks down and transitions to the normal conducting state. The present invention utilizes such a physical phenomenon.

That is, as shown in FIG. 2, a critical current I and a slightly smaller bias current 1o are caused to flow across the superconductor.

Here, the photoconductive material provided above the superconductor is irradiated with light and causes a photocurrent to flow. This photocurrent generates a magnetic field corresponding to the amount of photocurrent, and this magnetic field suppresses the superconducting current and generates a voltage between the junctions.

By connecting this Josephson junction and a load resistor in parallel, the operating point shifts from A to B, making it possible to read changes in voltage. The current applied here is
It is not limited to the one based on the photoconductive effect, but any type that can generate current, such as the photovoltaic effect, may be used.

[Example] Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 1 does not show a conceptual diagram of an embodiment based on the present invention. In the figure, 1 is a superconductor, 2 is an electrode for current injection, 3 is an electrode for voltage measurement, 4 is a load resistor, 5 is a power source for bias current application, 6 is a photoconductor, 7 is a power source for driving the photoconductor, 8 is a voltmeter for signal detection.

First, the oxide superconductor YBa2Ca307 (0≦
δ≦−δ 0.5) is formed on an MgO substrate (not shown) by magnetron sputtering or the like, and the obtained thin film is processed by microfabrication technology such as photolithography.

In this example, the oxide superconductor has a thickness of 5000 Å and a width of 2
The microbridge portion had a width of 8 μm and a length of 12 μm. Next, four Cr, 8U electrodes with a thickness of 1000mm and a width of 500mm were placed on this superconductor.
μm, and were used as a current injection electrode 2 and a voltage measurement electrode 3. Furthermore, a MgO thin film was formed at the center of the band to serve as an insulating layer, and finally a CdS film was formed on the MgO film to form a signal input section 6.

The critical temperature of the superconductor in this configuration was 85. This detector was placed in liquid nitrogen (77 K), and 10 mV was applied to the bias current applying power source 5 and IOV was applied to the photoconductor driving power source 7. Here, when no light was shined on the leading electric body 6, the signal detection voltmeter 8 was OV, and the superconductivity was not broken.

Next, a 5 mW II e-N e laser was applied to the photoconductor 6.
When the voltage was irradiated, the signal detection voltmeter 8 showed 3 mV. This means that a photocurrent was generated in the photoconductor 6 by the light irradiation, and the critical current value was suppressed by the resulting magnetic field, destroying the superconducting state.

10 fruits 1 A second embodiment of the invention is shown in FIG.

The configuration of such a detector is such that the signal input section 6 is separated from the detection section in the configuration of Example 1, and a new electrode 9 is provided in its place. Therefore, the photoconductor 6, which is the signal input section, does not need to be cooled with liquid nitrogen, and the photoconductor 6 that is the signal input section does not need to be cooled with liquid nitrogen.
When similar measurements were performed, it was confirmed that the presence or absence of light irradiation corresponded to the presence or absence of the voltage of the detection voltmeter, and that optical detection was possible.

Example 3 In Example 1, current injection electrode 2. The voltage measurement electrode 3 was made of metal, but in this example, a superconductor (for example, YBa2Cu30.-6) was used. It was confirmed that light detection was possible with this configuration as well.

Marukyori 1 Figure 4 shows the basic structure of the spectrometer according to the present invention.
The figure shows a conceptual diagram of the photodetection array.

In the spectrometer shown in FIG. 4, incident light 1o is incident on a diffraction grating (or other dispersive element) 13 via a slit 11 and a filter 12. The diffraction grating 13 is fixed, and the reflected light is made incident on the photodetection array 14. The photodetecting element array 14 is composed of photodetecting elements using a Josephson junction, which are bonded onto the cooling block 15 and provided on the substrate 16.

In the photodetection array shown in FIG. 5, 17 is an oxide superconductor thin film, 18 is a photoconductor thin film, 19 is a current terminal, 20.
21 and 22 are voltage terminals.

First, a superconducting thin film (here, B1-5
r-Ca-Cu-0 was used. ) was formed into a film, and a pattern of a superconductor thin film 17 was created using microfabrication technology. If necessary, the micro bridge part is made of an insulating film (here, 5i
02 etc.). Next, a photoconductor thin film 18 (here, a-5t) was produced. Furthermore, electrodes (here, Cr-8U) are deposited, and wiring and current terminals 19
, voltage terminals 20, 21, and 22 were fabricated. Then, a lead wire from the outside was connected to it.

In the apparatus shown in FIG. 4, the area around the cooling block was placed in a dewar which was evacuated to keep it warm, and the photodetector element was operated at a temperature around 77°C.

[Effects of the Invention] As described above, according to the present invention, the magnetic field generated by the current generated in the signal input section can be detected using a superconductor. Furthermore, since the input section and the detection section can be separated, it is not necessary to directly irradiate the input signal to the Josephson junction. Therefore, alignment of the signal and the detector becomes easier than before. Furthermore, by selecting the material of the input section, it becomes possible to freely select the detection signal (for example, the wavelength band to be detected).

Furthermore, detection sensitivity can be increased by operating the microbridge type Josephson junction in the detection section at a temperature closer to the critical temperature.

[Brief explanation of drawings]

FIG. 1 shows a conceptual diagram of Embodiment 1 of the present invention. FIG. 2 shows a graph showing changes in the IV characteristics of the detector according to the present invention due to light irradiation, and an equivalent circuit. FIG. 3 shows a conceptual diagram of Example 2 of the present invention. FIG. 4 shows a basic structural diagram of the spectrometer of Example 4. FIG. 5 shows a conceptual diagram of the pattern of the photodetection array of Example 4. FIG. 6 shows a conceptual diagram of a detector used in the conventional detection method. 1.17...Superconductor, 2...Electrode for current injection 3...Electrode for voltage measurement 4...Load resistance 5...
Power supply for applying bias current 6.18...Photoconductor (signal input section) 7...Power supply for driving photoconductor 8...Voltmeter for signal detection 10...Incoming light 11...
- Slit 13...Diffraction grating 15...Cooling block 19...Current terminal 12...Filter 14...Photodetection array 16...Substrate 20, 21.22...Voltage terminal

Claims (3)

[Claims] (1) A signal input section that generates a current when an optical signal is input;
A signal detector comprising at least a signal detecting section made of a superconductor using the Josephson effect and detecting a magnetic field generated by the current. (2) The signal detector according to claim 1, wherein a microbridge type Josephson junction is used in the signal detection section. (3) The signal detector according to claim 1 or 2, wherein a photoconductive material is used for the signal input section.