JPS63103924A - Infrared light detecting element - Google Patents

Abstract

PURPOSE:To obtain a high-sensitivity detecting element which is improved in output electric power by using loss energy on the photodetection surface effectively by constituting a detection part in multilayered structure. CONSTITUTION:This element consists of a lower photodetection part 1-a and an upper photodetection part 1-b consisting of BPB (BaPb1-xBixO3) crystal thin films with intercrystalline Josephson junctions, a substrate 2 of sapphire, etc., a current terminal 3, and a voltage terminal 4 for measurement. Then, a DC current is applied 3 to place the Josephson junctions of the detection parts 1-a and 1-b in voltage state and hold a bias current constant, and light is made incident on the substrate 2 vertically to take a measurement 4 of variation in the super-conduction parameter of the BPB owing to light irradiation, thereby performing photodetection. Consequently, patterns with two-layer meander line structure are formed without overlapping with each other at the photodetection parts to provide the BPB photodetection parts over the light irradiated surface, so that the length of the detection parts can be increased twice even when they are equal in photodetection area. Therefore, an output voltage which is doubled is obtained and the S/N is improved about 1.5 times.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a highly sensitive infrared light detection element.

[Conventional technology]

As an infrared light detection element, an element using an excitation phenomenon between a narrow energy gap of a superconductor has been developed (see Japanese Patent Application No. 173,668/1982).

In this device, changes in superconducting parameters caused by light irradiation are converted into voltage using a tunnel junction. Therefore, in order to increase the output voltage and increase the sensitivity,
It is effective to connect a large number of tunnel junctions in series and use the additive effect.As an example, the meander line structure shown in Fig. 4 has been devised (Japanese Patent Application No. 58-2
(See No. 37607). In Figure 4, BaPb+-xBixos (hereinafter F3PB
2 is a substrate such as sapphire, 3 is a current terminal, and 4 is a voltage terminal for measurement. Due to the meander line structure, the distance between the detection parts becomes long, but as can be seen from FIG. 4, light is also irradiated to areas where there is no BPB detection part, reducing efficiency. The region without the BPB detection part needs to have a gap that can withstand the applied voltage and has a sufficient width, and the area ratio of the light irradiation region becomes large when the pattern is fine. Fourth
It depends on the pattern dimension W (VS) in the figure and is expressed by the following equation.

yAAI(v)=10Vxw (sue) This formula is
Bias voltage of grain boundary Josephson junction 2 m V / l
The number of junctions included in the length of the junction and W (crystal grain size (0.2 μ
(proportional to the reciprocal of m). For example, when W is 5 hours, VAA' reaches 100V, and a gap width of 5 μm or more is required from the dielectric breakdown voltage of liquid helium.

[Problem that the invention seeks to solve]

As described above, the existence of a region that does not contribute to light detection within the light receiving surface, and the proportion of the region occupying the light receiving surface, has become a problem as the narrow pattern width for achieving higher sensitivity becomes larger.

An object of the present invention is to provide a high-sensitivity infrared light detection element that effectively uses the energy lost at the light-receiving surface and improves the output voltage.

[Means and effects for solving the problems] In order to achieve the above object, the present invention includes a lower photodetecting section having a meander-line structure and an intermediate layer provided thereon in the wavelength range used. 3r@ of the upper photodetecting section which has an insulating layer with low optical reflectance and a meander line structure that does not prevent light from entering the lower photodetecting section and is provided in an area where there is no lower photodetecting section.
The main feature is that the detection part has a multilayer structure. Since the conventional structure is planar, it requires a rough area for photodetection in order to maintain the voltage applied to the detection part within the light receiving surface, but the present invention has a structure in which the voltage application direction is perpendicular to the substrate. By making the direction and three-dimensional,
A photodetector can be provided over the entire light-receiving surface.

As a result, the light detection sensitivity is improved, so that weak light in the infrared region can be detected.

〔Example〕

(Example 1) FIG. 1 is a diagram explaining the first example of the present invention,
1-a is a lower photodetector made of a BPB polycrystalline thin film with a grain boundary junction, 1 and -b are upper photodetectors made of a BPB crystal thin film, and 2 is a substrate made of sapphire or the like. , 3 is a current terminal, and 4 is a voltage terminal for measurement.

To operate this device, a DC current is introduced through the current terminal 3 to bring the Josephson junctions at the grain boundaries of the BPB polycrystalline thin films of the detection sections 1-a and 1-b into a voltage state, and then the bias voltage is applied. Keep the current constant. In this state, light is perpendicularly incident on the substrate 2, and the change in the superconducting parameter of the BPB due to the light irradiation is measured by the voltage terminal 4, thereby making it possible to perform optical detection. As can be seen from Figure 1, the pattern with a two-layer meander line structure is formed so that it does not overlap each other in the light receiving area, so the BPB photodetecting area can be provided over the entire surface of the light irradiation area. . Therefore, compared to the case of -1f5, even if the light receiving area is the same, the length of the detection part is 2 as shown in the equivalent circuit in Figure 2.
The output voltage can be doubled, and the IC and S/N ratio can be improved by 1.5 times. 7 in Figure 2
indicates a di-U cehun junction. Note that since a voltage corresponding to the bias voltage is applied between the upper detection pattern and the lower detection pattern, an insulating layer is required to separate the two. However, the dielectric breakdown voltage of the solid used for this voltage separation is higher than that of gas and liquid, and it is possible to make the material thinner. Furthermore, the insulator has a low optical reflectance, and it is also possible to increase the incidence efficiency. A, /, 0. used in this example. has a withstand voltage of 10' V/U, so in the structure of this embodiment, a thickness of several μm is sufficient. Moreover, in this structure, the gap width can be further narrowed by coating the patterns with AA, O, even for a voltage of 7 A/A applied between the patterns in the same plane. It is possible to increase the pattern length and increase the sensitivity.

(Example 2) FIG. 3 is a sectional view of a device illustrating the structural cross section and manufacturing process of a second example of the present invention. 1-a.

1-b and 1-c are first, second, and third layer photodetecting portions each having a meander line structure made of a BPB polycrystalline thin film having grain-boundary Josephson junctions. 2 is a sapphire substrate, 3 is a current terminal made of K Au vapor deposited on a BPB film, 4 is a measurement voltage terminal made of an Au vapor deposited film on the BPB film, and 5 is an intermediate insulating layer that electrically separates the photodetecting parts of each layer. It is. The operating method of this device is the same as in the first embodiment, in which a DC bias current is introduced through the current terminal 3, and an optical signal is detected by the voltage change caused by light irradiation through the measurement voltage terminal 4. As can be seen from the final structure diagram in FIG. 3 (vl), the light that is perpendicularly incident on the substrate 2 is not absorbed by the BPB detection section over the entire surface of the light receiving section, so that the incident light can be used effectively. Can be done.

Compared to Example 1, Example 2 requires more manufacturing processes as described below, but is effective when the detection part BPB electrode pattern width is narrower than the withstand voltage region. By increasing the number of layers, sensitivity can be improved.

The manufacturing process will be explained based on FIG. Sapphire substrate 2
Ba Pb1-xB
ixOs (0.05≦x≦0.35) A polycrystalline thin film is formed. Here, X is a region that becomes a superconductor.

Next, form a resist pattern 6 using the lithogelaph shown below.
i), etching the 17th A B P B thin I% (1-a) into a meander line structure by a chemical method (ii)
.

Next, on the structure shown in (iii), an A/03 insulating layer 5 is formed by vacuum evaporation using a lift-off method.

A7. o, was selected because it does not react with BPB even at high temperatures and has the same coefficient of thermal expansion as the substrate, resulting in small thermal strain and stability against temperature cycles between cryogenic temperatures and room temperature. Besides this, Tie! It is also stable and can be selected depending on the wavelength range used. Thereafter, after forming BPB[ by high frequency sputtering method, the second layer photodetector 1-a has a meander line structure shifted by the pattern width from the meander line structure of the first layer photodetector 1-a. -b by etching method! l
Make one (1v). Then again A, g, O8 insulating layer 5
is formed on the second layer photodetection section 1-b (vl. As shown in (vD), B for the third layer photodetection section 1-c is formed on the second layer photodetection section 1-b.
An infrared light detection element can be manufactured by manufacturing a PB pattern using the same method as in (i) and (ii) above.

〔Effect of the invention〕

As explained above, there is an advantage in detecting weak light in the infrared region because the light detection sensitivity can be improved. Therefore, it is effective as a photodetector for far-infrared spectrometers or for astronomical observation where only a weak light source output is obtained.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a perspective view of the first embodiment showing the features of the photodetecting element of the present invention, FIG. 2 is an equivalent circuit diagram of the first embodiment of the present invention, and FIG. 3 is the present invention. FIG. 4 is a cross-sectional view of the device structure in each manufacturing process of the second embodiment of the invention, and a plan view of a photodetecting device having a conventional meander line structure. 1-B P B thin film, 1-a, 1-b, 1-c ・-・
Photodetection section, 2... Sapphire substrate, 3... Current terminal, 4... Voltage terminal for measurement, 5... Intermediate insulating layer, 6...
...Resist pattern. Applicant's agent Patent attorney Takehiko Suzue Figure 3 Figure 4

Claims (2)

[Claims] (1) A lower photo-detecting section with a meander line structure, an insulating layer with low optical reflectance in the wavelength range used as an intermediate layer provided on the lower photo-detecting section, and a lower photo-detecting section that does not prevent light from entering the lower photo-detecting section. An infrared light detection element comprising a three-layer structure including an upper photodetection section having a meander line structure provided in an area without a photodetection section. (2) The photodetector is an oxide superconductor BaPb_1_-_x
The infrared light detection element according to claim 1, characterized in that it is made of a Bi_xO_3 (0.05≦x≦0.35) thin film, and the intermediate layer is made of Al_2O_3 or TiO_2.