JP2715321B2 - Photo detector - Google Patents

Description

The present invention relates to a photodetector that converts light into a magnetic signal and detects a magnetic field using the magnetic properties of a superconductor, and in particular, confine the generated magnetic field. The present invention relates to a photodetector having a superconductor.

2. Description of the Related Art As a conventional signal detector using a superconductor, in particular, a photodetector using a Josephson junction is known, which detects an optical signal. [Japanese Journal of Applied
Physics vol.23 L333 (1984)]. This optical signal detector is composed of an oxide superconductor BaPb _0.7 Bi _0.3 O _{3 as} shown in FIG.
(BPBO) A microbridge-type Josephson junction is formed from a thin film, and this junction is irradiated with light to utilize the change in the critical current value of the Josephson junction. In such a detector, BPBO is used as the material of the light receiving section, and its critical temperature is as low as about 13K. That is, to operate the detector, liquid helium or the like must be used. The characteristics of such a detector are determined by the characteristics of the Josephson junction.

[Problems to be Solved by the Invention] In the above conventional example, when a large number of detectors are used at the same time, for example, as in an image sensor, it is difficult to correct variations in characteristics between the detectors due to processing variations and the like. There's a problem.

Further, since the wavelength range of light to be detected is also limited by the spectral characteristics of the superconductor, there is a problem that it is not suitable for signal detection in a wide wavelength band.

Further, there is a problem that the accuracy of alignment is required because the area of the light irradiation to the joint is very limited.

Also, the Josephson junction is very sensitive to changes in the magnetic field, for example, when using multiple detectors at the same time like an image sensor, it is affected by the magnetic field generated by the current flowing through other parts. Also, there is a problem that the light detection characteristics change and integration is difficult.

Further, there is also a problem that the local area generated by the current generated by the light input leaks to the outside, so that it is not effectively used and the detection efficiency is low.

That is, an object of the present invention is to provide a photodetector which solves the above-mentioned problems by utilizing the magnetic properties of a superconducting material.

[Means for Solving the Problems] A feature of the present invention is that an optical input unit that generates a current by inputting an optical signal, and a magnetic field detection unit that includes a superconductor that detects a magnetic field generated by the current. And a magnetic field confining superconductor for confining the generated magnetic field by the Meissner effect.

Further, the invention is characterized by a photodetector using a photoconductive material as the light input section.

Here, as the superconductor used to achieve the present invention, any material having a superconducting property made of a single crystal or a polycrystal may be used. In order to operate the detector at a higher temperature, a material having a higher critical temperature is preferable. In this regard, Y-Ba-Cu-O, Bi-Sr-Ca-Cu-O
A substance having a critical temperature higher than the boiling point of liquid nitrogen, 77 K, such as a Tl-Sr-Ca-Cu-O-based ceramic material is suitable.

The superconducting material used for the magnetic field detecting unit and the superconducting material used for confining the magnetic field may be the same or different. However, the superconducting material used for confining the magnetic field must be a material having a critical magnetic field larger than the generated magnetic field.

Further, the type and method of the magnetic field detecting unit are not limited as long as its characteristics change due to a magnetic field such as a Josephson junction such as a mycrocross bridge type or SIS type, a SQUID, or a mere superconductor. Further, the above-mentioned magnetic field may be caused by a current flowing through the light input portion itself or by a current flowing through a conductor connected to the light input portion, for example, a wiring using a metal material or a superconducting material. It doesn't matter.

The materials used for the light input section are infrared, visible,
Any material can be used as long as it can respond to an optical signal such as ultraviolet light, but a photoconductive material is particularly preferable.

Materials that generate a particularly large photocurrent include InSb, Si,
GaAs, a-Si, CdS, CdSe and the like are preferable.

In order to obtain such a current, the current is not limited to the above-described photoconductive effect, but may be anything that can generate a current, such as a photovoltaic effect and a Denver effect. Here, as a material for generating a high electromotive force, there is a PH junction of Si, a-Si or the like, a Schottky junction, or the like.

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

[Operation] For example, when light is applied to a light input portion made of a photoconductive material, electrons in the valence band are excited and transit to the conduction band.
The electrons excited in this conduction band are moved by an applied electric field (not shown) to generate a photocurrent.

On the other hand, when a current flows through a substance, the generation of a magnetic field by the current is well known as a basic law of physics.

That is, the photocurrent generates a magnetic field corresponding to the photoelectric flow, and the magnetic field changes the electrical characteristics of the superconductor. Possible changes in the electrical properties of superconductors include a decrease in the value of the current flowing through the superconductor, or a change in the superconducting state resulting in electrical resistance. Anything is fine.

By detecting such a change, an optical signal can be detected.

At this time, the superconducting layer provided so as to cover the upper part separately from the superconductor for the detection unit is in a state where the Meissner effect is occurring, so that the generated magnetic field leaks to the outside, or It is suppressed that each detector influences each other.

This leads to an improvement in the detection efficiency of the detector, and it is possible to use a plurality of detectors at the same time.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples.

Embodiment 1 FIG. 1 shows a conceptual diagram of an embodiment according to the present invention and a top view of a device manufacturing process using this method.

First, as shown in FIG. 1A, Y ₁ Ba ₂ C was formed on a MgO single crystal substrate 1 by using a cluster ion beam evaporation method.
A 8000 u thin film of u ₃ O _7- x (0 ≦ X ≦ 0.5) was deposited and processed by photolithography into a thin strip having a width of 10 μm and a length of 2 mm to form superconducting electrodes 2 and 3 as magnetic field detecting portions. The electrode spacing at this time is 5 μm. Next, a Pt thin film is deposited by ion beam sputtering, and the superconducting electrodes 2,
Current on 4, current electrodes 5, 5 and 8, 9 respectively, voltage electrodes 6, 7 and 1
0,11 was formed. Next, as shown in FIG. 1 (b), a MgO thin film is deposited as an insulating layer 12 by using a magnetron sputtering method to a thickness of 1 μm, and then a CdS thin film is deposited, and the upper portions of the superconducting electrodes 2, 3 are deposited by photolithography. Light input portions 13 and 14 having a size of 10 μm in width and 1.0 mm in length were formed so as to overlap with. Further, a Pt electrode 1 is provided on the light input sections 13 and 14.
5,16 were formed. Next, as shown in FIG. 1 (c), an MgO thin film is formed as the insulating layer 17 to a thickness of 1 μm in the same manner as the insulating layer 12, and further Y ₁ Ba ₂ C is formed thereon similarly to the superconducting electrodes 2 and 3.
A u ₃ O _7- x (0 ≦ X ≦ 0.5) thin film was formed, and a superconducting layer 18 for confining a magnetic field was formed. Finally, using photolithography, the width 1 is set so that the light input portions 13 and 14 are partially exposed.
Windows 19 and 20 having a size of 0 μm and a length of 800 μm were prepared.

In the detector having such a configuration, the superconducting electrodes 2 and 3 and the superconducting layer for confining magnetic field 18 became superconducting at a temperature of 82 K or less. This detector was immersed in liquid nitrogen and cooled to 77 K. While applying a constant voltage of 1.0 V between the electrodes 15 and 16, Ar ⁺ laser light (wavelength 514.5 mm, output 5 m) was applied to the windows 19 and 20.
Irradiation of W) reduced the critical current superconductor Ic of the superconducting electrodes 2 and 3 from 0.5 mA to 0.4 mA.

Comparative Example Next, as a comparative example, to produce a device that is not provided only 20 of the two windows at the same specifications as in Example 1 was subjected to a similar experiment, the Ar ⁺ laser beam applied to the window 19 The Ic of the superconducting electrode 2 decreased, but the Ic of the superconducting electrode 3 did not change at all.

Further, as another comparative example, the insulating layer 17 and the superconducting layer 18 for confining the magnetic field were not formed in the same specification as in Example 1,
When a device in which no magnetic field was confined was manufactured and a similar experiment was performed, the detection effect was 5 to 50% lower than that of Example 1.

That is, according to the present invention, it is possible to detect light without affecting each other even between very close detectors, which means that integration is possible. Further, the present invention makes it possible to improve the light detection efficiency.

Embodiment 2 FIG. 2 shows a second embodiment of the present invention. In the present embodiment, the light input unit and the magnetic field detection unit were separated, the current generated in the light input unit was led to the vicinity of the magnetic field detection unit using wiring, and the magnetic field generated there was detected.

First, as shown in FIG. 2 (a), Bi ₂
After depositing Sr ₂ Ca ₂ Cu ₃ Ox oxide superconducting thin film by 5000 mm by magnetron patter, superconducting electrode 2 which is 10 μm wide and 50 μm long magnetic field detecting part by photolithography
And 3 were formed. Further, DC electrodes 4, 5, 8, 9 and voltage electrodes 6, 7, 10, 11 were formed by resistance heating of Pt. Next, α-Si was deposited at a position 10 mm away from these, and the light input section 1 was deposited.
3,14 were formed.

Next, as shown in FIG. 2 (b), after depositing an MgO insulating layer 12 on the magnetic field detecting portion, electrodes 15, 16; wires 21, 22; and comb electrodes 23, 24 were formed. Further, as shown in FIG. 2 (c), after the MgO insulating layer 17 was formed on the wirings 21 and 22, the superconducting layer 18 for confining the magnetic field was formed.

Also in the element having such a configuration, light detection could be performed at 77K as in Example 1.

In this embodiment, only the magnetic field detecting unit side needs to be cooled except for the light input side, and there is a merit of miniaturization in terms of a cooling device and the like. Furthermore, the light input unit and the magnetic field detection unit can be set to the respective optimum operating temperatures, and the characteristics can be improved.

[Effects of the Invention] As described above, according to the present invention, the current generated in the signal receiving unit can be detected by the superconductor. That is, according to the present invention, (1). Compared with the conventional method (for example, when irradiating light to a junction of a Josephson junction), it is easier to align a light signal with a detector, that is, input a signal to a light input unit of any size required. Becomes possible.

(2). By appropriately selecting the material of the light input unit, it is possible to detect a signal with a wider wavelength than in the past.

(3). Compared with the conventional case (for example, in the case of a Josephson junction, the detection characteristics are determined by the junction characteristics, and when a multi-configuration is used, the characteristics of the element vary widely). As a result, processing accuracy, reproducibility, reliability, and the like are improved, and variations in characteristics are reduced.

(4) By confining the magnetic field generated by the electric current generated by the light input using the Meissner effect of the superconductor, the detection sensitivity can be increased and the mutual influence between the detectors is eliminated, and the integration is performed. And the detection efficiency can be improved.

There are such effects.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a photodetector according to an embodiment of the present invention in which a light input unit and a magnetic field detection unit are integrally formed. FIG. 2 is a configuration diagram of a photodetector according to an embodiment of the present invention, in which a light input unit and a magnetic field detection unit are separated. FIG. 3 shows a configuration diagram of a photodetector used for a conventional detection method. 1 ... Substrate 2,3 ... Superconducting electrode (magnetic field detecting part) 4,5,8,9 ... Current electrode 6,7,10,11 ... Voltage electrode 12,17 ... Insulating layer 13,14 ... … Light input section 15,16… electrode 18… superconducting layer for confining magnetic field 19,20… window 21,22… wiring 23,24… comb-shaped electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toru Tadashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Norio Kaneko 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (56) References JP-A-64-86575 (JP, A)

Claims (2)

(57) [Claims] An optical input unit for generating a current by inputting an optical signal, a magnetic field detecting unit comprising a superconductor for detecting a magnetic field generated by the current, and a magnetic field confinement unit for confining the generated magnetic field by a minor effect A photodetector comprising at least a conductor. 2. The photodetector according to claim 1, wherein a photoconductive material is used for said light input section.