JPH09257584A - Thermal infrared detector - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a thermal infrared detection device that achieves both sensitivity and response speed and is less susceptible to noise. A substrate, a thermopile on the substrate, a heat separation region for thermally separating the vicinity of the thermopile's hot junction from the substrate, an incident infrared absorption region provided near the thermopile's hot junction, and a cooling of the thermopile. It has a cold junction temperature control means provided in the vicinity of the contact, and a control means for controlling the amount of heat generated by the cold junction temperature control means based on the thermoelectromotive force generated in the thermopile.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type infrared detector using a thermopile.

[0002]

2. Description of the Related Art A conventional thermal infrared detector using a thermopile is disclosed in Japanese Patent Application Laid-Open No. 57-113332.

A structural sectional view of a conventional thermal infrared detecting device is shown in FIG. 4, and a plan view thereof is shown in FIG.

In FIG. 4, a package 1 such as TO-8
An infrared transmission window 102 is provided at 01. Substrate 1
03 is formed of Si or Ge. A hole 104 is provided in the central portion of the substrate 103, and a film 108 is provided on the back side of the substrate 103.
The thermopile 107 of 06 is formed. Further, a blackening film 109 is formed on the front side of the substrate 103 by sputtering or the like. 110 is a lead and 111 is a hermetic seal.

In FIG. 5, a hot junction is formed in the center and a cold junction is formed on the outside. Further, a temperature sensitive element 112 including a diode is formed on a part of the cold junction. The ambient temperature is measured by the overflow element 112, and the ambient temperature is corrected using the result.

[0006]

SUMMARY OF THE INVENTION In a conventional thermal infrared detector using a thermopile, it is necessary to perform high-magnification amplification because the output signal is very weak when measuring a heat source at a long distance. However, since the internal resistance of the thermopile was large, it was difficult to perform measurement with low noise.

Further, since the thermopile utilizes the heat flow flowing from the hot junction, the response time is determined by the thermal time constant. Therefore, it has been difficult to produce a device having both sensitivity and response speed.

In the conventional example, the method of measuring the temperature of the cold junction and correcting the result is adopted, but the method of positively controlling the temperature of the cold junction has not been adopted.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide a thermal infrared detecting device that is compatible with both sensitivity and response speed and is less susceptible to noise.

[0010]

In order to solve the above problems, the present invention is directed to a substrate, a thermopile on the substrate, a thermal isolation region for thermally isolating the vicinity of the thermopile's hot junction from the substrate, and a thermopile. Controls the amount of heat generated by the cold junction temperature control means based on the incident infrared absorption area provided near the hot junction, the cold junction temperature control means provided near the cold junction of the thermopile, and the thermoelectromotive force generated at the thermopile. And a control means for controlling.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 3 is a block diagram of an embodiment of a thermal infrared detecting device according to the present invention. In FIG. 3, p-type semiconductor 3
The n-type semiconductor 4 and the n-type semiconductor 4 are connected by an Al thin film and are connected to the thermopile 21.
Is formed. An infrared absorption region 7 is formed near the hot junction 5 of this thermopile. The heat of the infrared absorption region 7 heated by the incident infrared ray 41 mainly flows to the hot junction 5 by heat conduction (heat flow 42) and raises the temperature of the hot junction 5. Although the cold junction 6 is kept at the same temperature as the ambient temperature in the initial state, the temperature does not rise directly due to the incident infrared ray 41, but rises solely due to heat conduction from the hot junction 5. Therefore, since a temperature difference occurs between the hot junction 5 and the cold junction 6, a thermoelectromotive force is generated by the Seebeck effect.
At this time, the temperature of the hot junction 5 rises due to the thermal time constant calculated from the thermal resistance and the thermal capacity, heat is transferred to the cold junction 6, and there is a time delay until the thermoelectromotive force becomes stable.

However, in the present embodiment, the cold junction temperature control means 22 whose operation is controlled by the thermoelectromotive force is used.
The feedback control is performed so that the temperature of the cold junction 6 becomes equal to that of the hot junction 5. Specifically, the thermoelectromotive force amplified by the amplifier 31 controls the current of the Joule heat source 34, that is, the heat generation amount through the control Tr 32. When infrared rays are incident and the temperature of the hot junction 5 starts to rise and the thermoelectromotive force starts to increase, a large amount of current value is supplied to the Joule heat source 34 to raise the temperature of the cold junction 5 by heat conduction (heat flow 43). At this time, unlike the normal thermopile, the heat flow flowing through the thermopile flows out of either the hot junction 5 or the cold junction 6, so that the length of heat transmission is reduced to about half, so the response is greatly improved.

Since the electric time constant of the control circuit 23 is smaller than the thermal time constant by one digit or more, the control circuit does not limit the rate. When a certain time passes and the temperatures of the cold junction 6 and the hot junction 5 become the same, an electrical and thermal equilibrium state is reached.
The current amount I supplied to the Joule heat source 34 at this time is changed into a voltage value and output from the output terminal 33. Current I
Depends on the intensity of the incident infrared ray, and the intensity of the incident infrared ray can be measured by the current amount I. In this case, the output value with respect to the amount of incident infrared rays can be changed by changing the thermal coupling between the control circuit 23 and the cold junction 6, that is, changing the thermal resistance and the thermal capacity. That is, since the output value can be increased with respect to the minute incident infrared rays, the S / N ratio can be easily ensured by the subsequent signal processing, for example, voltage amplification or A / D conversion. In addition, since the thermal time constant is larger than the electrical time constant, there is also an effect of band limiting the signal, which facilitates signal detection.

(First Embodiment) FIG. 1 is a plan view (A) for explaining the first embodiment of the sensing element shown in FIG.
And (a) is a sectional view taken along the line segment AA 'in the plan view (a).

First, the structure will be described. In FIG. 1, S
The membrane 2 supporting the thermopile 21 is formed on the main plane of the substrate 1 by i or the like by the CVD method or the like. On top of this is a thermopile 21 composed of polysilicon and an Al thin film. p-type polysilicon 3 is p
N-type polysilicon 4 is n-type doped. The connection region between the polysilicon and the Al thin film on the right side of the figure is the hot junction 5, and the left side of the figure is the cold junction 6. A Joule heat source 34 is arranged near the cold junction 6. A polysilicon resistor or the like is used for the Joule heat source 34. An infrared absorption region 7 is formed in the vicinity of the protective film 9 made of PSG and the hot junction 5 on this. Further, the membrane 2 is partially formed with an etching hole 10. The thermal separation region 11 is formed through the etching hole 10 by dry etching and anisotropic wet etching. However, the substrate 1 below the cold junction 5 is not completely removed but serves as the heat sink 8. This etching method is disclosed in JP-A-2-30304.
This is described in detail in Japanese Patent Publication No. 8.

Next, the operation will be described. Incident infrared rays are absorbed by the infrared absorption area 7 and are absorbed by the infrared absorption area 7.
Raise the temperature of. This heat reaches the hot junction 5 of the thermopile 21 by heat conduction and raises the temperature of the hot junction 5. Since the vicinity of the hot junction 5 is thermally separated from the substrate 1 by the heat separation region 11, the temperature rises due to the minute incident infrared rays. When a temperature difference occurs between the hot junction 5 and the cold junction 6, a thermoelectromotive force is generated by the Seebeck effect and a potential difference starts to occur between the two cold junctions. This potential difference is input to the control circuit 23 and sent to the cold junction temperature control means 22 by signal processing such as amplification, and the cold junction 6 is heated by the heat generated by the Joule heat source 34. This operation is continued until the thermoelectromotive force disappears, that is, the temperature difference between the hot junction 5 and the cold junction 6 disappears, and the equilibrium state is reached. Further, since the thermopile is heated from both sides, the thermopile is heated at a higher speed than a normal thermopile. At this time, the thermal time constant near the cold junction 6 determines the operation speed, but this can be improved by reducing the thermal resistance between the cold junction temperature control means 22 and the cold junction 6. When the heat source disappears, the temperature of the hot junction 5 starts to drop because the heat supply to the hot junction 5 is stopped, and the temperature of the cold junction 6 becomes higher, so that the thermoelectromotive force is reversed. The signal value from the control circuit 23 decreases and the amount of heat generated by the cold junction temperature control means 22 decreases. The time constant at this time is never faster than the thermal time constant of the cold junction 6,
Since it is limited by the thermal time constant of the hot junction 5, it becomes slower than the rising response speed, and there is not much difference from the normal thermopile.

(Second Embodiment) FIG. 2 is a diagram for explaining a sensing element according to a second embodiment of the present invention. 2A is a plan view and FIG. 2A is a sectional view.

Only the parts different from the first embodiment will be described. In the first embodiment, the rising response speed was improved, but the rising response speed did not change. This is because the cold junction temperature control means 22 has only the heating means, so that in the second embodiment, the heating / cooling means is realized by the Peltier element.

First, regarding the structure, a Peltier element is used instead of the polysilicon heater in the first embodiment. The structure of the Peltier device is the same as that of the thermopile, but different conductors or semiconductors are connected to each other and a current is passed through the conductors or semiconductors to raise or lower the temperature of the contacts. It can be made of polysilicon, but ZnSe35-Pb
If S36 or the like is used, an efficient product can be obtained.

According to the second embodiment, a current is caused to flow in the direction of increasing the temperature of the cold junction 6 at the rising time, and a current is caused to flow in the direction of decreasing the temperature of the cold junction 6 at the falling time to quickly equilibrate. Since the state can be set, the response speed is further improved.

In the conventional element, the temperature of the cold junction is set to a fixed value, and the temperature difference generated between the cold junction and the hot junction is converted into a thermoelectromotive force by the Seebeck effect, and the voltage value is directly used as the output value. According to the present invention, temperature control means, for example, a Joule heat source or a Peltier element is provided near the cold junction to positively control the temperature of the cold junction and bring the value of the thermoelectromotive force to a predetermined value. That is, the temperature difference between the hot junction and the cold junction is controlled so as to approach a predetermined value without limit. At this time, the value of a physical quantity such as energy or voltage used to control the temperature of the cold junction is used as the output value.

[0023]

The effects obtained by the typical ones of the present invention will be briefly described as follows.

(1) In the conventional example, since heat was unidirectionally flowing from the hot junction to the cold junction, it took time for the heat of the hot junction to reach the cold junction, so that high-speed operation could not be expected. According to the present invention, heat also flows from either direction of the hot junction and the cold junction, so that the flow distance of the heat flow is shortened to about half, the response speed is improved, and compatibility with the sensitivity is possible. .

(2) In the conventional example, since the thermoelectromotive force itself is output, the output value becomes very small when detecting an object at a long distance, and it is difficult to amplify it without degrading it to a size that can be processed. However, since the signal value can be increased in advance by setting the thermal coupling (conduction or radiation) to the cold junction and the temperature control means to an appropriate value, it is less susceptible to noise.

(3) When the thermal coupling is performed mainly by conduction Since the thermal time constant is generally larger than the electrical time constant, it becomes possible to give the effect of a filter, and the external high frequency noise as in the conventional type suffers. Never be

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a detection element according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a detection element according to a second embodiment of the present invention.

FIG. 3 is a conceptual diagram illustrating the operation of the thermal infrared detection device of the present invention.

FIG. 4 is a structural cross-sectional view of a conventional thermal infrared detection device.

FIG. 5 is a plan view of a conventional thermal infrared detection device.

[Explanation of symbols]

 1 Substrate 2 Membrane 3 p-type Polysilicon 4 n-type Polysilicon 5 Hot Junction 6 Cold Junction 7 Infrared Absorption Area 8 Heat Sink 9 Protective Film 10 Etching Hole 11 Heat Separation Area 21 Thermopile 22 Cold Junction Temperature Control Means 23 Control Circuit 31 Amplifier 32 Control Tr 33 Output Terminal 34 Joule Heat Source 35 ZnSe 36 Pbs 41 Incident Infrared 42 Heat Flow 1 43 Heat Flow 2

Claims (5)

[Claims] 1. A substrate, a thermopile on the substrate, a heat separation region that thermally separates the vicinity of a hot junction of the thermopile from the substrate, and an incident infrared absorption region provided near the hot contact of the thermopile. Thermal infrared detection having cold junction temperature control means provided near the cold junction of the thermopile and control means for controlling the amount of heat generated by the cold junction temperature control means based on the thermoelectromotive force generated in the thermopile apparatus. 2. The hot junction has a smaller thermal weather between the incident infrared absorption region and the cold junction temperature control means, and the cold junction has a thermal resistance between the entrance examination and the infrared absorption region than the cold junction temperature control means. The thermal infrared detection device according to claim 1, wherein the thermal infrared detection device is also large. 3. The thermal infrared detection device according to claim 1, wherein the cold junction temperature control means generates Joule heat. 4. The thermal infrared detecting device according to claim 1, wherein the cold junction temperature control means uses a Peltier effect. 5. The thermal infrared detection device according to claim 1, wherein the vicinity of the cold junction is also thermally separated from the substrate.