JP2935738B2 - Infrared detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared detecting element, and more particularly, to an infrared detecting element for detecting an amount of infrared light using a semiconductor fiber whose electric resistance changes by infrared light.

[Prior Art] Conventionally, as an infrared detecting element, an infrared detecting element using a pyroelectric element utilizing a pyroelectric effect, a thermopile integrating thermocouples, or the like is known.

However, these infrared detecting elements have drawbacks in response time in applications where a high response speed is required, and there is a limit in the use of the infrared light source to be detected for position detection. Further, the above-mentioned conventional infrared detecting element is disadvantageous in terms of price.

The present inventors have previously proposed an infrared detecting element using a semiconductor fiber whose electric resistance changes with temperature (Japanese Unexamined Patent Publication No.
No. 71121 [Japanese Patent Application No. 63-222506], an infrared detecting element using a specific silicon carbide fiber as the semiconductor fiber (Japanese Patent Application No. 1-131435), and an infrared detecting element using a specific carbon fiber. (Japanese Patent Application No. 1-2232888, Japanese Patent Application No.
277050).

The infrared detecting element of the present inventors has a sufficiently small time constant (τ), is advantageous in terms of cost, and can eliminate the disadvantages of the conventional infrared detecting element.

[Problems to be Solved by the Invention] However, even in the above-described infrared detecting element of the present inventors, higher output, that is, improvement in sensitivity has been desired in order to further shorten the response time.

The present invention has been made in view of such a problem of the related art, and in an infrared detecting element that detects an amount of infrared light using a semiconductor fiber whose electric resistance changes due to infrared light, the output is increased without adversely affecting a time constant. The purpose is to enable.

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, the distance between the semiconductor fibers, the diameter of the semiconductor fibers, and the incident angle of the infrared light with respect to the lower end wavelength of the infrared light to be detected. The inventors have found that the above problem can be solved by arranging the semiconductor fibers in a specific relationship, and arrived at the present invention.

That is, the infrared detecting element of the present invention is an infrared detecting element that detects the amount of infrared light by electric resistance change due to infrared light, and detects a plurality of semiconductor fibers whose electric resistance changes due to infrared light, with respect to the lower end wavelength of the detected infrared light. The following formula (I) 0 <P · cos θ−D _f ≦ λ (I) [wherein P is the distance from the center of the semiconductor fiber to the center of the adjacent semiconductor fiber, and θ is the infrared ray with respect to the normal to the element surface. The incident angle (0 ≦ θ <90 °), D _f is the diameter of the semiconductor fiber, and λ is the bottom wavelength of the infrared light to be detected.] It is characterized by being arranged.

Further, another infrared detecting element of the present invention is an infrared detecting element that detects the amount of infrared light by a change in electric resistance due to infrared light, and detects a plurality of semiconductor fibers whose electric resistance changes due to infrared light at the lower end wavelength of the detected infrared light. On the other hand, the following formula (II) 0 <Lmax · cos θ−D _f ≦ λ (II) [where Lmax is the longest distance from the center of the semiconductor fiber to the center of the adjacent semiconductor fiber, and θ is the normal to the element surface. Incident angle of infrared rays (0 ≦ θ <90 °), D _f is the diameter of the semiconductor fiber,
λ indicates the lower wavelength of the infrared light to be detected.] The electrodes are regularly aligned or arranged in an irregular lattice pattern so as to satisfy the following relationship.

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

FIG. 1 (a) is a front view showing an example of an infrared detecting element in which semiconductor fibers are regularly aligned at substantially equal intervals, and FIG. 1 (b) is a front view of FIG. 1 (a). It is a partial expanded sectional view of an infrared detecting element. 1 (a) and 1 (b), reference numeral 1 denotes a semiconductor fiber, reference numeral 2 denotes an electrode, reference numeral 3 denotes a lead wire connecting an element to an electric circuit, and reference character P denotes a semiconductor fiber 1 adjacent to the center of the semiconductor fiber 1. The distance to the center, θ is the incident angle of the infrared ray I with respect to the normal 1 to the element surface, and D _f is the semiconductor fiber 1
Are shown respectively. The above θ is 0 ° or more and
Less than 90 ゜.

In the present invention, the P, theta, and D _f, the following expression for the lower end wavelength lambda of detect infrared I (I) 0 <to satisfy the relationship of _{P · cosθ-D f ≦ λ} (I) Must be. (P ・ cos
The absorption efficiency of infrared rays I having a lower wavelength λ smaller than the value of θ−D _f ) is reduced, and a high output cannot be obtained. Also, (P · cosθ
When the value of −D _f ) is negative, the absorption efficiency also decreases.

For example, in the case of detecting the infrared light I having the speckled distribution shown in FIG. 2, the value of (P · cos θ−D _f ) is determined by using the peak wavelength
If λa is set to be sufficiently smaller, a region where the absorption efficiency is high becomes a shaded portion in the figure, and a high output can be obtained. On the other hand, P · cosθ−D
_{When f} = λb, the high absorption region is only the vertical line in the figure,
High output cannot be obtained. Therefore, it is practically preferable to set (P · cos θ−D _f ) to be sufficiently smaller than the peak wavelength λmax.

When the semiconductor fibers 1 are aligned between the electrodes 2, it is preferable to minimize the reflection of infrared rays I.
That is, the reflectance (γ _p ) is expressed by the following equation (III): γ _p = tan (ψ−φ) / tan (ψ + φ) (III) [where γ _p is the reflectance, and ψ is the surface orthogonal to the semiconductor fiber 1. The incident angle of the infrared ray I with respect to X, φ indicates the angle of the absorbed infrared ray i with respect to the surface X (see FIG. 3). Therefore, when ψ + φ = π / 2, γ _p →
Since it becomes 0, it is preferable to use ψ by adjusting ψ so that γ _p approaches 0 as much as possible.

FIG. 4 (a) is a front view showing an example of an infrared detecting element in which semiconductor fibers are regularly arranged in a grid at substantially equal intervals, and FIG. 4 (b) is a front view of FIG. 4 (a). It is a partial expanded sectional view of an infrared detecting element. Each symbol in FIGS. 4 (a) and 4 (b) indicates the same one as in FIGS. 1 (a) and 1 (b).

Also in this case, in the present invention, the above-mentioned P, θ, and D _f are related to the lower end wavelength λ of the infrared ray I to be detected by the following formula (I): 0 <P · cos θ−D _f ≦ λ (I) Must be satisfied.

FIG. 5 (a) is a front view showing an example of an infrared detecting element in which semiconductor fibers are irregularly aligned and arranged, and FIG. 5 (b) is an infrared detecting element of FIG. 5 (a). It is the elements on larger scale sectional view. 5 (a) and 5 (b), Lmax indicates the longest distance from the center of the semiconductor fiber to the center of the adjacent semiconductor fiber, and other symbols are those in FIGS. 1 (a) and 1 (b). The same thing as (b) is shown.

When the semiconductor fibers are arranged irregularly, the above P
May be replaced with Lmax, i.e. in the present invention is the Lmax, theta, and D _f, the following expression for the lower end wavelength lambda of detect infrared I (II) 0 <Lmax · cosθ-D f ≦ λ (II ) Must be satisfied. (Lmax ・ co
The absorption efficiency of infrared light I having a lower wavelength λ smaller than the value of sθ−D _f ) is reduced, and a high output cannot be obtained. Also, (Lmax ・ co
When the value of sθ−D _f ) is negative, the absorption efficiency also decreases.

FIG. 6 (a) is a front view showing an example of an infrared detecting element in which semiconductor fibers are arranged in an irregular lattice, and FIG. 6 (b) is a part of the infrared detecting element of FIG. 6 (a). It is an expanded sectional view. 6 (a) and 6 (b) indicate the same symbols as in FIGS. 5 (a) and 5 (b).

Also in this case, in the present invention, the above Lmax, θ, D _f
It is necessary to satisfy the following expression (II) 0 <Lmax · cos θ−D _f ≦ λ (II) with respect to the lower end wavelength λ of the infrared ray I to be detected.

In the above-described infrared detecting element of the present invention, the distance between the electrodes is preferably 0.5 mm or more. 0.5 between electrodes
When the distance is not less than mm, the output tends to be further improved while the time constant (τ) is kept small.

The semiconductor fibers used in the present invention preferably have a diameter of 200 μm or less. When a semiconductor fiber having a diameter of 200 μm or less is used, the output tends to be able to be further improved while keeping the time constant (τ) small.

The semiconductor fiber used in the present invention may be any one as long as its electric resistance changes due to infrared rays, but at least one selected from the group consisting of silicon carbide fiber, carbon fiber and their precursor fibers is preferable.

As the silicon carbide fiber, the room temperature resistivity is 10 to 6000.
Ω · cm and the thermistor constant B are preferably 100 to 8000 k. Such a silicon carbide fiber is produced, for example, by the following method. That is, after an organic polymer compound such as polycarbosilane is melt-spun, under an oxidizing atmosphere, 10
It is obtained by infusibility to 0 to 300 ° C. or insolubilization by irradiating an electron beam in an inert atmosphere or the like, and then heat-treating to 1200 to 1500 ° C. in an inert atmosphere.

Further, as the carbon fiber, the room temperature resistivity is 10 to 4000
Ω · cm and a thermistor constant B of 500 to 7000 k are preferable. Such carbon fibers are produced, for example, by the following method. That is, it is obtained by heat-treating spun fibers such as PAN, pitch and rayon to 150 to 250 ° C. in an oxidizing atmosphere and then to 500 to 800 ° C. in an inert atmosphere.

EXAMPLES Hereinafter, the present invention will be described in more detail based on examples and comparative examples.

Example 1 Polycarbosilane spun fiber was subjected to infusibilization treatment in air at 200 ° C. for 60 minutes, and then heated to 1200 ° C. in an inert gas and heat-treated to obtain the following silicon carbide fiber.

(Silicon carbide fiber) ・ Diameter (D _f ): 15 μm ・ Composition: Si: 57.5 wt%, C: 31.0 wt%, O: 11.0 wt%,
The remainder: 0.5 wt%,-Room temperature specific resistance: 1000 Ω-cm,-Thermistor constant: 1000 k.

This monofilament of silicon carbide fiber is cut into 5 mm, and 100 filaments are arranged at substantially equal intervals (P = 40 μm), arranged and connected between electrodes (interelectrode distance: 2.5 mm), and FIG. The infrared detecting element of the present invention as exemplified in (1) was obtained.

A DC voltage of 8 V is applied to this detector, and a black body furnace (temperature
Infrared (peak wavelength λmax: 6.4μ) emitted from 450 ゜ k)
m) was intermittently irradiated using a camera shutter (opening / closing speed: 500 μsec) at a state of θ = 60 °, and an output voltage due to a change in resistance of the filament was obtained. As a result, the output voltage was 72 mV.

In this case, P · cos θ−D _f = 5.

Comparative Example 1 An infrared detecting element was obtained in the same manner as in Example 1 except that P was set to 60 μm, and the output voltage was obtained in the same manner as in Example 1. As a result, the output voltage was 13 mV.

In this case, P · cos θ−D _f = 15.

Example 2 A polyacrylonitrile (PAN) fiber filament was infusibilized at 250 ° C. for 1 hour in air, and then heated to 700 ° C. in N ₂ gas.
C. and heat-treated to obtain the following carbon fiber filament.

(Carbon fiber filament) ・ Diameter (D _f ): 6.5 μm ・ Specific resistance at room temperature: 780Ω ・ cm ・ Thermistor constant: 2300k

Cut this carbon fiber filament to 5mm
The infrared detecting elements of the present invention as illustrated in FIG. 4 (a) are arranged and connected in a grid pattern at substantially equal intervals (P = 16 μm) between the electrodes (distance between the electrodes: 3 mm). Obtained.

A DC voltage of 8 V is applied to this detector, and a black body furnace (temperature
Infrared (peak wavelength λmax: 9.7μ) emitted from 300 ゜ k)
m) was intermittently irradiated at θ = 0 ° using a camera shutter (opening / closing speed: 500 μsec), and the output voltage due to the resistance change of the filament was determined. As a result, the output voltage is 68mV
Met.

In this case, P · cos θ−D _f = 9.5.

Comparative Example 2 An infrared detecting element was obtained in the same manner as in Example 2 except that P was set to 20 μm, and the output voltage was obtained in the same manner as in Example 2. As a result, the output voltage was 16 mV.

In this case, P · cos θ−D _f = 13.5.

Example 3 The same silicon carbide fiber filament as in Example 1 was
The infrared detecting element of the present invention as illustrated in FIG. 6 (a) is arranged and connected between the electrodes (distance between the electrodes: 1 mm) in an irregular lattice (Lmax = 23 μm) by 50 lines each. Obtained.

The output voltage of this detection element was determined in the same manner as in Example 2. As a result, the output voltage was 63 mV.

In this case, Lmax · cos θ−D _f = 8.

Comparative Example 3 An infrared detecting element was obtained in the same manner as in Example 3 except that Lmax was set to 32 μm, and the output voltage was obtained in the same manner as in Example 3. As a result, the output voltage was 25 mV.

In this case, Lmax · cos θ−D _f = 17.

Examples 4 to 9 and Comparative Examples 4 to 5 Polycarbosilane was melt-spun at different draw ratios to obtain filaments having different diameters, which were infusibilized in air at 200 ° C. for 1 hour, and then N ₂ gas was added. Medium, 1-3 at 1200-1500 ° C
Silicon carbide fibers having the properties shown in Table 1 after heat treatment (composition: Si: 55 to 58 wt%, C: 29 to 31 wt%, O: 10 to 13 wt%)
%, H ... 0.5 to 1.0 wt%).

Using this silicon carbide fiber, infrared detecting elements shown in Table 1 were obtained. Then, a DC voltage of 8 V was applied to this element, and infrared rays (peak wavelength λmax: 8.3 μm) emitted from a black body furnace (temperature 350 ° k) were taken by a camera shutter (opening / closing speed: 500
(μsec) and intermittent irradiation at θ = 45 ° to determine the output voltage due to the change in resistance of the filament. Table 1 shows the results.

Examples 10-14 and Comparative Examples 6-7 Melt spinning using coal pitch (softening point: 270 ° C., number average molecular weight: 2000) at different draw ratios to obtain filaments having different diameters, After infusibilizing at 250 ° C. for 1 hour, heat treatment was performed in N ₂ gas at 500 to 800 ° C. for 0.5 to 16 hours to obtain carbon fibers having the characteristics shown in Table 1.

Using the carbon fibers, infrared detecting elements shown in Table 1 were obtained, and output voltages were obtained in the same manner as in Examples 4 to 9 and Comparative Examples 4 and 5. Table 1 shows the results.

Results of Examples 1 to 3 and Comparative Examples 1 to 3, and
As apparent from Table, then set the peak wavelength .lambda.max as lower wavelength of the infrared detecting lambda, the following expression for λmax (I) 0 <P · cosθ-D f ≦ λmax (I) or formula (II) 0 <Lmax · cos θ−D _f ≦ λmax (II) Although all of the infrared detecting elements satisfying the condition of (II), high output voltage was obtained, the infrared detecting elements of Comparative Examples 1 to 7 which did not satisfy the above condition were obtained. Each of the devices had a low output voltage.

[Effects of the Invention] As described above, the infrared detecting element of the present invention can obtain a sufficiently high output while keeping the time constant small, and as a result, the response time can be further shortened. It becomes possible.

Therefore, the infrared detecting element of the present invention is very effective for a security system or the like utilizing infrared detection.

Further, since the infrared detecting element of the present invention can detect infrared light of a specific wavelength with an excellent output voltage, it can be applied to applications such as detection of minute infrared light and measurement of the amount of infrared light. Further, the infrared detecting element of the present invention can be applied to applications such as radiation, a diffraction grating, a polarizing plate, and an infrared multiplier by combining the elements, and is extremely useful industrially.

[Brief description of the drawings]

FIG. 1 (a) is a front view showing an example of an infrared detecting element in which semiconductor fibers are regularly aligned and arranged at substantially equal intervals, and FIG. 1 (b) is a front view of FIG. 1 (a). FIG. 2 is a partial enlarged cross-sectional view of the infrared detecting element, FIG. 2 is a reference diagram for explaining the absorption efficiency of a certain infrared ray, FIG. 3 is a reference diagram for explaining the reflectance of the infrared ray, FIG. FIG. 4A is a front view showing an example of an infrared detecting element in which semiconductor fibers are regularly arranged in a grid at substantially equal intervals, and FIG. 4B is a front view of the infrared detecting element shown in FIG. FIG. 5 (a) is a front view showing an example of an infrared detecting element in which semiconductor fibers are arranged in an irregularly aligned manner, and FIG. 5 (b) is a partial enlarged sectional view of the element. FIG. 5 (a) is a partially enlarged cross-sectional view of the infrared detecting element, and FIG. 6 (a) is a diagram in which semiconductor fibers are arranged in an irregular lattice shape. That is a front view showing an example of the infrared detection element, FIG. 6 (b) is a partially enlarged cross-sectional view of the infrared detector of Figure 6 (a). 1: semiconductor fiber, 2: electrode, 3: lead wire connecting the element to the electric circuit, P: distance from the center of the semiconductor fiber to the center of the adjacent semiconductor fiber, θ: infrared ray I with respect to the normal l of the element surface angle of incidence, D _f: the semiconductor fiber 1 diameter, Lmax: longest distance from the center of the semiconductor fibers to the center of the semiconductor fibers next.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Norio Muto 1-5-18 Miyashita Honcho, Sagamihara City, Kanagawa Prefecture (72) Inventor Takeshi Notake 375-8 Washigosu, Sugito-cho, Kitakatsushika-gun, Saitama Prefecture (72) Inventor Hiroshi Ichikawa Kanagawa (72) Inventor Yoshikazu Imai 1-39-34 Sanno, Ota-ku, Tokyo (72) Inventor Hirofumi Harada 1-16-26 Tsujido Taiheidai, Fujisawa-shi, Kanagawa Prefecture (72) Invention Person Akira Urano 3-8-12 Namamugi, Tsurumi-ku, Yokohama-shi, Kanagawa (56) References JP-A-2-71121 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 31 / 08

Claims (4)

(57) [Claims] An infrared detecting element for detecting an amount of infrared light by a change in electric resistance due to infrared light, wherein a plurality of semiconductor fibers whose electric resistance changes by infrared light are detected by the following formula (I) 0 <P · cos θ−D _f ≦ λ (I) [where P is the distance from the center of the semiconductor fiber to the center of the adjacent semiconductor fiber, and θ is the incident angle of infrared rays with respect to the normal to the element surface (0 ≦ θ <90 °), D _f is the diameter of the semiconductor fiber, and λ is the lower end wavelength of the infrared light to be detected.] An infrared detecting element characterized by the above-mentioned. 2. An infrared detecting element for detecting an amount of infrared rays by a change in electric resistance caused by infrared rays, wherein a plurality of semiconductor fibers whose electric resistance changes by infrared rays are detected by the following formula (II) with respect to the lower end wavelength of the detected infrared rays. 0 <Lmax · cos θ−D _f ≦ λ (II) [where Lmax is the longest distance from the center of the semiconductor fiber to the center of the adjacent semiconductor fiber, and θ is the angle of incidence of infrared rays with respect to the normal to the element surface (0 ≦ θ <90 °), D _f is the diameter of the semiconductor fiber,
[lambda] indicates the lower end wavelength of infrared light to be detected, respectively]. An infrared detecting element characterized in that the electrodes are regularly aligned or arranged in an irregular lattice so as to satisfy the following relationship. 3. The infrared detecting element according to claim 1, wherein the diameter of the semiconductor fiber is 200 μm or less, and the distance between the electrodes is 0.5 mm or more. 4. The infrared detecting element according to claim 1, wherein said semiconductor fibers are at least one selected from the group consisting of silicon carbide fibers, carbon fibers, and precursor fibers thereof.