JPH0674818A - Infrared detecting device - Google Patents

Abstract

PURPOSE:To prevent the lowering of sensitivity due to aging and enable exhibition of high sensitivity for a long period. CONSTITUTION:A system 21 loading an infrared detecting element 10 is sealed with a cap 25 by welding. By performing the welding seal work in a chamber charged with Xe gas (ca. 1/5 of air heat conductance) at 1 atmospheric pressure for example, the sealed space (c) in the package 20 is filled with Xe gas and the infrared detection part (a) is in the state sealed in Xe gas atmosphere. By this, the heat flow from the surface of the detection part (a) to the surrounding atmosphere is prevented. Therefore, the heat generated by the infrared irradiation to the detection part (a) flows out to neither of a base plate nor the surrounding atmosphere, temperature rising of the detection part (a) is done efficiently, and the detection sensitivity of infrared is improved. Also, the detection part (a) is maintained in good heat insulated state for a long period and high sensitivity is attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared detecting device, and more particularly to an infrared detecting device provided with a thermal infrared element for detecting infrared rays by detecting temperature change due to absorption of infrared rays.

[0002]

2. Description of the Related Art There are two types of infrared detecting elements, so-called quantum type and thermal type. Although the quantum type infrared detecting element has a very high sensitivity, it needs to be cooled to a low temperature before use, and it is difficult to handle and the manufacturing cost is high. Although the thermal type infrared detection element is not as sensitive as the quantum type in terms of sensitivity, it does not require cooling, has a simple structure and is inexpensive to manufacture, and is therefore widely used in various practical applications.

There are three main types of thermal infrared detecting elements, one using a pyroelectric element, one using a thermocouple, and one using a resistor. All of them are infrared rays detected by irradiation of infrared rays. Infrared rays are detected by converting the thermal behavior of the part, that is, the temperature change into an electrical change. In any type, in order to improve the sensitivity, it is necessary to devise a method for increasing the temperature change of the infrared detecting section when infrared rays are incident. For example, when the infrared detecting element as described above is used for the purpose of detecting infrared radiation from a human body to detect the presence or approach of a human, an infrared detecting element having a very high sensitivity is required.

As a method of increasing the sensitivity of the infrared detecting element, for example, it has been considered to add a material having a high infrared absorption rate to the infrared detecting portion. However, within the range of commonly available materials, there is a limit to significantly improving the infrared absorption rate. As another method, it has been considered to improve the thermal insulation of the infrared detecting section. If the heat generated in the infrared detecting section when the infrared ray hits is prevented from escaping to the outside as much as possible, the temperature change of the infrared detecting section becomes large and the detection signal becomes strong.

As a method of improving the thermal insulation of the infrared detecting section, the infrared detecting section is provided on the substrate through a thin thermal insulating film, and the substrate on the back side of the infrared detecting section is largely dug to obtain the so-called heat. A method has been proposed in which a separation space is provided and the infrared detection section is supported by the substrate only by the thin thermal insulation film, that is, the thin film bridge. Since heat is transferred from the infrared detecting section to the substrate only by the thin thermal insulating film, it is difficult for heat to escape from the infrared detecting section to the substrate. A technique using such a thin film bridge is disclosed in Japanese Patent Application No. 2-284779, which the applicants of the present invention have previously filed.

Further, there has been proposed a method of adopting the above-mentioned thin film bridge structure and sealing the infrared detecting portion and the thin film bridge portion in a vacuum. According to this method, it is possible to favorably prevent the heat from escaping from the infrared detection section to the surrounding air that is in contact with the infrared detection section.

[0007]

However, in the infrared detection device having the above-mentioned vacuum sealing structure, even if the sensitivity immediately after manufacturing is good, the sensitivity sharply decreases with time, There is a problem that the effect of improving the sensitivity by the vacuum sealing structure does not last long and the life is short. this is,
If the infrared detector package is evacuated,
Adsorption or desorption of stored gas, gas permeation, leakage from poorly airtight parts, etc. causes gas to be mixed in the package, and heat easily escapes through this gas. It is thought that this is due to a matter.

Further, if a welding sealing method used for sealing a general metal is adopted for vacuum sealing of a package, there is a problem that the sensitivity is not improved so much even immediately after manufacturing. It is considered that this is because, at the time of welding, the welding point becomes hot and gas is generated, and this gas is mixed in the package, so that the effect of vacuum sealing is not exerted. In order to prevent the above problems, if you perform sufficient cleaning, baking, degassing before packing the package, optimize the materials used, complete sealing work, optimize the sealing method, etc. In addition, it is possible to prevent, to some extent, gas contamination during manufacture and sensitivity deterioration with time. However, in this case, in the manufacturing process, long-time processing, high-temperature processing, special equipment are required, and the manufacturing cost becomes high. It is impossible to take all these measures as a practical product. Therefore, in practice, it was extremely difficult to prevent the sensitivity of the infrared detection element from decreasing with time.

Therefore, an object of the present invention is to prevent a decrease in sensitivity with time in the infrared detecting device as described above, to exhibit high sensitivity for a long period of time, and to have a relatively simple structure and low manufacturing cost. Another object is to provide an infrared detection device.

[0010]

In order to solve the above problems, an infrared detecting device according to the present invention is an infrared detecting device having an infrared detecting element having a thermal infrared detecting portion provided on a thin film bridge. The infrared detecting section is enclosed in a low thermal conductive gas atmosphere. As the basic structure of the infrared detection element, the structure of a conventional thermal infrared detection element that has been used conventionally can be employed as it is. Specifically, it consists of the pyroelectric element, thermocouple, resistor, etc.,
A so-called thermal type infrared detector, which absorbs infrared rays and generates heat, and the accompanying temperature change is converted into an electrical change to detect infrared rays, through a thin film bridge made of a heat insulating film. Are provided on a support structure such as a substrate. The electrical changes caused by infrared detection are:
There are various modes such as a pyroelectric effect, a change in resistance value, and a change in electromotive force, depending on the detection principle or structure of the infrared detection unit, and the present invention can be applied to any of these modes. The material and the specific structure of the thin film bridge may be the same as those of the thin film bridge structure in various ordinary sensors and electronic element parts.

The infrared detecting device is equipped with the above infrared detecting element, a lead terminal for connecting an external circuit to the infrared detecting element, a filter for transmitting only infrared rays of a specific wavelength to be measured, Other necessary components are incorporated into the package to facilitate handling and use. The components and structure of the infrared detection device may be the same as those of a normal infrared detection device.

As the low thermal conductivity gas, various ordinary gases can be used as long as they have a lower thermal conductivity than ordinary air and do not corrode the infrared detecting portion or impair their functions. . An inert gas is preferred as the low thermal conductivity gas. Further, the larger the molecules of the low thermal conductivity gas, the less likely the leakage from the enclosed portion occurs. A preferable specific example of the low thermal conductivity gas is xenon gas.

As means for enclosing the infrared detecting section in the atmosphere of low thermal conductivity gas, the infrared detecting section is enclosed in a package made of metal, glass, ceramic, synthetic resin or the like, and is enclosed in this package. The space may be filled with the low thermal conductivity gas as described above. In the low thermal conductivity gas atmosphere, only the infrared detection part may be enclosed, or a part or the whole of the supporting structure such as the thin film bridge or the substrate supporting the infrared detection part may be enclosed in the low thermal conductivity gas atmosphere. It may be enclosed in. As the package for enclosing the infrared detecting section, the package forming the entire structure of the infrared detecting device can be used.

The low thermal conductive gas atmosphere may be atmospheric pressure, that is, normal pressure, a reduced pressure state lower than atmospheric pressure, or a pressurized state higher than atmospheric pressure. Practically, a pressure around atmospheric pressure is preferable because it is easy to manufacture and handle.

[0015]

In the infrared detecting device of the present invention, the outflow of heat from the infrared detecting portion of the infrared detecting element to the substrate due to heat conduction is favorably blocked by the thin film bridge having a high thermal insulation property. In addition, since the low thermal conductivity gas exists around the infrared detecting section, heat is prevented from flowing out from the surface of the infrared detecting section to the surrounding atmosphere. Specifically, when the low thermal conductivity gas is xenon gas, the thermal conductivity is about 1/5 compared to normal air, and the heat outflow from the infrared detection unit to the surrounding atmosphere is significantly reduced. Will be done.

Therefore, the heat generated by the infrared detecting section when the infrared detecting section is irradiated with the infrared ray does not flow out to either the substrate or the surrounding atmosphere, and the temperature of the infrared detecting section is efficiently raised. As a result, the infrared detection sensitivity is significantly improved. Further, since the infrared detecting section is covered with the low thermal conductive gas, adsorption after sealing, desorption of stored gas, permeation of gas from the outside, etc. do not occur unlike the above-mentioned vacuum sealing structure. As a result, the infrared detecting section can be maintained in a good thermal insulation state for a long period of time to exhibit high sensitivity, and the life of the infrared detecting element can be greatly extended.

In particular, when the low heat conductive gas is sealed at a pressure of about atmospheric pressure, the pressure difference from the external environment is small, so that gas intrusion from the outside or desorption of the stored gas occurs. It is difficult, and even if some gas is generated, it is not a big problem because the influence is eliminated by the low thermal conductivity gas which occupies most of it. As a result, the excellent performance of the infrared detection element can be stably exhibited satisfactorily over a long period of time. Further, the step of enclosing the infrared detection section can be performed much easier and more efficiently than the step of vacuum sealing.

Further, if the low thermal conductivity gas is a gas having a large molecule such as xenon gas, even if there is a poor airtight portion or a poor sealing portion, the gas will not escape from the portion and the low thermal conductivity will be low. The effect of the volatile gas can be satisfactorily exerted over a long period of time. If the low thermal conductivity gas is an inert gas, it is possible to prevent corrosion and contamination of the materials that make up the infrared detection unit, and the function and performance of each component of the infrared detection unit can be improved over a long period of time. Can be demonstrated.

If the entire infrared detecting element is filled with a gas having a low thermal conductivity, not only the infrared detecting portion but also the support structure can be prevented from flowing out heat, and the supporting structure can be prevented from being corroded or contaminated. It can be prevented, and the high sensitivity and other performances of the infrared detection element can be favorably maintained.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall structure of the infrared detection device, and FIG. 2 shows the detailed structure of the infrared detection element. As shown in FIG. 2, the infrared detection element 10 comprises a substrate 11 having a silicon single crystal (100) plane as a surface and a thickness of 300 μm, and a thermal insulation film made of a composite film of silicon nitride and silicon oxide having a thickness of 1.0 μm. The film 12 is formed. A part of the substrate 11 is the substrate 11
It is removed from the back side of the substrate until it reaches the heat insulating film 12, and becomes a heat separation space 13. At the position of the heat separation space 13, the heat insulating film 12 is hollow and is supported only by the outer periphery of the heat insulating film 12 on the substrate 11 to form a so-called thin film bridge b.

On the thin film bridge b, a thin film resistor 15 made of amorphous silicon and having a thickness of 1.0 μm, and a thin film resistor 14 made of chromium and having a thickness of 0.2 μm.
A pair of electrodes 15 and 15 are arranged in a pattern on the upper and lower sides of the electrode. With the electrodes 15 and 15, the resistance value of the thin film resistor 14 can be detected and taken out to an external circuit. The electrodes 15 and 15 are extended to the outer peripheral side on the thin film bridge b, and on the heat insulating film 12 of the substrate 11, the electrodes 1 and 15 are formed.
Electrode terminals 16 and 16 are provided at 5 and 15, respectively.

An infrared absorption layer 17 made of silicon oxide is formed so as to cover the infrared detection section a having a sandwich structure of the thin-film resistor 14 and the upper and lower electrodes 15 and 15. The infrared absorption layer 17 serves to detect infrared rays. Increase absorption,
The temperature of the infrared detecting section a is properly raised. Next, an example of a method of manufacturing the infrared detection element having the above structure will be described.

First, the thermal insulating film 12 made of silicon nitride and silicon oxide is formed on one surface of the silicon substrate 11 by the plasma CVD method. At this time, monosilane and ammonia, or monosilane and carbon monoxide were used as introduced gases, the substrate temperature was 400 ° C., and the frequency was 13.56.
The processing condition of MHz is adopted. A thin film of silicon nitride is formed on the opposite surface of the substrate 11 by the same means as above.

On the heat insulating film 12 of the substrate 11, chromium having a thickness of 0.2 μm is deposited at a substrate temperature of 150 ° C. by a vacuum vapor deposition method. A resist layer is formed and patterned on the chrome layer to be this electrode by using a normal photolithography technique. Using the resist pattern as a mask, the chromium layer is etched with an etching solution containing cerium ammonium nitrate to form the electrode 15 on the lower side of the predetermined pattern. After the etching is completed, the unnecessary resist pattern is removed.

Next, an amorphous silicon layer to be a thin film resistor is deposited by the plasma CVD method. A resist pattern is formed on the amorphous silicon layer by the same means as described above, and the amorphous silicon layer is etched with an etching solution containing nitric acid, acetic acid and hydrofluoric acid using the resist pattern as a mask to form a predetermined pattern. The thin film resistor 14 is formed.

The upper electrode 15 made of chromium is formed on the thin film resistor 14 through the same steps as those for the lower electrode 15. A thin film of silicon oxide to be an infrared absorption layer is deposited on the thin film resistor 14 and the electrodes 15 and 15 by the plasma CVD method similar to the step of forming the heat insulating film 12. Further, after forming a resist pattern, the silicon oxide layer is etched with an etching solution containing hydrofluoric acid and ammonium fluoride to form an infrared absorption layer 17 having a predetermined pattern.

Further thereon, an aluminum layer having a thickness of 1.5 μm is deposited at a substrate temperature of 150 ° C. by using a vacuum vapor deposition method. After forming a resist pattern serving as a mask, the aluminum layer is etched with an etching solution containing phosphoric acid, acetic acid, and nitric acid to form electrode terminals 16 and 16 having a predetermined pattern. Next, a resist pattern for forming a heat separation space is formed on the surface of the substrate 11 on the back side of the surface on which the above infrared detecting section is formed.
Using this resist pattern as a mask, the silicon nitride layer previously formed on the surface of the substrate 11 is patterned by the plasma etching method. The plasma etching conditions at this time are as follows: power 200 W, gas pressure 400 mTorr
Then, carbon tetrafluoride is used as the introduced gas.

After removing the resist, the silicon constituting the substrate 11 is etched by a so-called anisotropic etching method using the patterned silicon nitride layer as a mask to form the thermal separation space 13. The anisotropic etching treatment conditions include potassium hydroxide as an etchant, an etchant concentration of 40 wt% and a liquid temperature of 80 ° C. The infrared detection element 10 manufactured as described above is used while being housed in the package 20, as shown in FIG.

The infrared detecting element 10 is bonded and bonded to the metal stem 21 with the adhesive 22. The lead terminal 2 which is installed so as to penetrate the upper and lower surfaces of the stem 21.
3, 23 and the electrode terminal 16 of the infrared detection element 10,
16 are bonded and connected by wires 24 made of gold, and the resistance value of the thin film resistor 14 is set to the lead terminal 23,
It can be taken out from 23.

A metallic cap 25 is placed over the stem 21, and the outer peripheral portion is welded and sealed to the stem 21.
An infrared incident window 27 provided with a filter 26 that selectively transmits infrared rays having a specific wavelength is provided at a position of the cap 25 facing the infrared detecting portion a of the infrared detecting element 10.
Are formed. The filter 26 is made by depositing a selective transmission film on the surface of a silicon substrate and has a characteristic of cutting a wavelength of 5 μm or less, and a low melting point glass is used for the infrared incident window 27 of the cap 25. And glue it.

In the above process, when the stem 21 having the infrared detecting element 10 mounted thereon is welded and sealed by the cap 25, this welding and sealing work is performed in a chamber filled with 1 atmosphere of xenon gas. As a result, the enclosed space c of the package 20 is filled with xenon gas,
The infrared detecting section a of the infrared detecting element 10 is sealed in the xenon gas atmosphere. However, as a means for enclosing the xenon gas, a usual gas enclosing means in various devices can be freely applied such as filling the enclosed space c with the xenon gas after the package 20 is manufactured.

An infrared detecting device having the above structure was manufactured and its sensitivity was measured. For the purpose of comparison, the same structure having the enclosed space c of the package 20 filled with air was also manufactured, and the same measurement was performed. As a result, as shown in the left end of FIG. 3, the sensitivity of the example of the present invention sealed in xenon gas is improved by about four times as compared with Comparative example 1 sealed in air. I understood.

Next, FIG. 3 shows the result of measuring the change with time of the sensitivity of the infrared detecting device of the embodiment. In addition, FIG. 4 shows a result of performing the same measurement as a comparative example 2 in which an infrared detection device in which the enclosed space c of the package 20 is in a vacuum state of 1 × 10 ⁻³ Torr is manufactured. From the measurement results, it can be seen that in Comparative Example 2, the sensitivity immediately after manufacture is very high, but the sensitivity drops sharply with time. With this, stable performance cannot be exhibited and the life is shortened. On the other hand, in the examples of the present invention, it was proved that even if the usage time exceeded 1000 hours, the sensitivity was hardly reduced, and good sensitivity could be stably exhibited for a long period of time.

[0034]

As described above, in the infrared detector according to the present invention, the thermal infrared detector is sealed in a low thermal conductive gas atmosphere so that heat from the infrared detector to the surrounding atmosphere can be reduced. Can be satisfactorily blocked, and the detection sensitivity of the infrared detection section can be improved.

Moreover, compared with the structure in which the infrared detecting section is vacuum-sealed, adsorption and desorption of stored gas after sealing and gas mixture due to gas permeation from the outside do not occur, and thus the infrared detecting section is prevented. The high sensitivity can be stably exhibited over a long period of time, and the service life of the infrared detection device can be significantly improved. Further, since the vacuum sealing is not performed, the sealing structure and the sealing work are simplified and the productivity is improved.

[Brief description of drawings]

FIG. 1 is a sectional view of the entire structure of an infrared detection device showing an embodiment of the present invention.

FIG. 2 is an enlarged sectional structure diagram of an infrared detection element.

FIG. 3 is a diagram showing the results of measuring the performance over time of Examples.

FIG. 4 is a diagram showing the results of measuring the performance over time of a comparative example.

[Explanation of symbols]

 10 Infrared Detection Element 11 Substrate 12 Thermal Insulation Film 13 Thermal Separation Space 14 Thin Film Resistor 15 Electrode 20 Package 21 Stem 25 Cap a Infrared Detector b Thin Film Bridge c Enclosed Space

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[Procedure amendment]

[Submission date] December 21, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

First, the thermal insulating film 12 made of silicon nitride and silicon oxide is formed on one surface of the silicon substrate 11 by the plasma CVD method. At this time, as an introduction gas, monosilane and ammonia, and, monosilane and dinitrogen nitrogen, a substrate temperature of 400 ° C., a frequency 13.5
A processing condition of 6 MHz was adopted. A thin film of silicon nitride is formed on the opposite surface of the substrate 11 by the same means as above.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jun Sakai, 1048, Kadoma, Kadoma, Osaka Prefecture, Matsushita Electric Works Co., Ltd. (72) Inventor, Takuro Nakamura, 1048, Kadoma, Kadoma, Osaka Prefecture, Matsuda Electric Works Co., Ltd. 72) Inventor Takuro Ishida 1048, Kadoma, Kadoma-shi, Osaka Prefecture Matsushita Electric Works Co., Ltd. (72) Shigenari Takami, 1048, Kadoma, Kadoma-shi, Osaka Matsushita Electric Works Co., Ltd. (72) Inventor, Sadayuki Kaku Osaka Fudomon, Kadoma, 1048, Kadoma, Matsushita Electric Works Co., Ltd. (72) Hidekazu Himezawa, Kadoma, Osaka, Kadoma, 1048 Kadoma, Matsushita Electric Works, Ltd. (72) Inventor, Fumihiro Kamiya, 1048, Kadoma, Kadoma, Osaka Banchi Matsushita Electric Works Co., Ltd.

Claims (1)

[Claims] 1. An infrared detecting device comprising an infrared detecting element comprising a thermal infrared detecting section provided on a thin film bridge, wherein the infrared detecting section is enclosed in a low thermal conductive gas atmosphere. Infrared detector.