CN114975755A - Infrared detector for non-dispersive infrared gas sensor - Google Patents

Abstract

The present invention provides an infrared detector for use in a non-split infrared gas sensor. The infrared detector includes a base and a thermopile arranged on the base. The thermopile is formed by connecting multiple pairs of thermocouples in series. The thermocouple has a cold end and a hot end. The cold end is attached to the base. A suspension structure is formed, and a thermally conductive through hole is opened on the upper insulating layer of the hot end to connect the top infrared absorption area. The upper through hole structure of the hot end can directly connect the hot end and the absorption area, and transfer most of the heat in the absorption area to the hot end of the thermopile. The hot end forms a suspended structure, which can reduce the heat conduction loss from the hot end to the substrate, and the cold end is directly connected to the substrate to achieve heat conduction, so that the cold and hot ends have a large temperature difference. The size, connection structure and arrangement of the thermopile increase the output voltage of the detector. Finally, the requirement of infrared detection in the non-spectroscopic infrared gas sensor is satisfied, and the structure of the through hole, the back etching and the thermopile structure is simple, and the process can be realized.

Description

An infrared detector for non-split infrared gas sensor

technical field

The invention belongs to the field of the structure of a thermopile infrared detector, in particular to an infrared detector used for a non-spectrometric infrared gas sensor.

Background technique

The principle of non-dispersive infrared (NDIR) technology for gas concentration measurement is as follows: according to the Lambert-Beer law, when a beam of monochromatic light passes through a certain absorbing medium, a part of the light energy will be absorbed by the medium, and the transmitted light intensity will be changed accordingly. The proportion that is absorbed is related to the concentration value of the measured gas, the length of interaction between the infrared light and the measured gas from the infrared light source to the detector, and the absorption coefficient.

The relationship between the intensity of incident and outgoing light:

I=I ₀ e ^-KCL

I ₀ ——incident light intensity, the light intensity before infrared rays pass through the gas to be measured;

I——Intensity of outgoing light, the light intensity of infrared rays after passing through the gas to be measured;

C——concentration, the concentration value of the measured gas;

L——Optical path length, from the infrared light source to the detector, the length of the interaction between the infrared light and the measured gas;

K - absorption coefficient, the coefficient depends on the absorption spectrum of the measured object.

Therefore, an infrared detector needs to be installed inside the gas sensor to measure the light intensity by measuring the intensity of infrared radiation.

Based on different detection mechanisms, infrared detectors are generally divided into two categories: photon detectors and thermal detectors. The photon detector is based on the photoelectric effect, and its temperature is basically kept stable during the detection process; the thermal detector relies on the absorption of infrared radiation to make the temperature rise and then convert it into electrical energy. Since the thermal effect of infrared rays is very significant, and the sensitivity of thermal detectors is better than that of photon detectors, thermal detectors are generally selected when infrared detectors are used. The commonly used heat detectors include thermal resistance detectors, pyroelectric detectors, and thermopile detectors. Among them, thermal resistance detectors rely on the temperature change of resistance to measure related parameters. Generally, materials such as platinum and copper with large temperature coefficient of resistance, large resistivity, small heat capacity, good linearity and stable performance are used as thermal resistances. The thermal resistance made of these materials has a wide temperature measurement range, and the structure is relatively simple, but the performance is poor. The operating mechanism of the pyroelectric detector is that some crystals inside the detector generate equal and different charges when exposed to high temperature. This electric polarization phenomenon formed by the change of temperature is the pyroelectric effect. This kind of detector has It has the characteristics of high efficiency, small size, high stability and long life, but the pyroelectric effect requires the temperature in the detector to change all the time, which is not suitable for the static temperature environment in the gas sensor. The operating principle of the thermopile infrared detector is based on the Seebeck effect, the temperature difference between the two ends of the semiconductor material will be converted into thermoelectric potential, and the output thermoelectric potential is related to the Seebeck coefficient α of the semiconductor material. Thermocouples made of semiconductor materials can be connected in series to form a thermopile to achieve voltage superposition.

Therefore, after the absorption layer of the thermopile infrared detector absorbs infrared radiation, the temperature of the hot end rises, and a temperature difference is generated between the hot end and the cold end, and this temperature difference can be directly converted into a voltage output. Finally, the infrared radiation intensity is obtained by measuring the voltage and its change.

Output voltage relationship:

V _out = ΔT(α _A −α _B ).

Thermopile infrared detectors are widely used in the field of infrared detection due to their high measurement accuracy, wide range, sensitive response and extremely high temperature resistance.

Due to the good thermal conductivity of silicon, the infrared radiation energy absorbed by the existing thermopile infrared detectors will be dissipated in a large amount through the silicon substrate, resulting in thermal short circuit of the thermopile. The temperature difference between the hot and cold temperature of the infrared detector is not obvious, which leads to the low output voltage of the detector, which reduces the performance of the entire gas sensor or even cannot be used.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an infrared detector for a non-split infrared gas sensor, so as to solve the problem that the temperature difference between the hot and cold ends of the thermopile infrared detector used for the non-split infrared gas sensor is not obvious, and the output voltage of the infrared detector is too low, which affects the Technical aspects of the entire non-split infrared gas sensor performance.

For solving the above-mentioned technical problems, the concrete technical scheme of the present invention is as follows:

An infrared detector used in a non-split infrared gas sensor, comprising a substrate, a thermopile arranged on the substrate, a support layer assembly and an absorption layer;

The thermopile includes the cold end of the thermopile and the hot end of the thermopile, the cold end of the thermopile is attached to the substrate, the hot end of the thermopile is provided with a thermally conductive through hole, and the thermally conductive through hole connects the hot end and the absorption layer. The back side of the end bottom is etched to form a back cavity, forming a suspended structure;

The thermopile includes multiple pairs of thermocouples;

The multiple pairs of thermocouples are arranged in a double-layer stack, and the thermocouples include a first thermocouple bar arranged on the base in turn and a second thermocouple bar arranged on the first thermocouple bar;

The thermal conduction through hole is arranged in the silicon oxide layer on the upper part of the second thermocouple strip;

a support layer assembly is arranged between the substrate and the thermopile;

The absorption layer is arranged on the upper part of the thermopile.

Further, the first thermocouple bar includes a hot end of the first thermocouple bar and a cold end of the first thermocouple bar, and the second thermocouple bar includes a hot end of the second thermocouple bar and a cold end of the second thermocouple bar ; The hot end of the first thermocouple bar is connected with the hot end of the second thermocouple bar, and the cold end of the first thermocouple bar is connected with the cold end of the adjacent second thermocouple bar, thereby connecting the first thermocouple and the second thermocouple bar. The thermocouples are connected in series, and the adjacent thermocouple bars are also connected in series.

Further, a first silicon oxide layer is filled between the first thermocouple bar and the second thermocouple bar and between adjacent thermocouples.

Further, the support layer assembly includes a first silicon oxide layer, a silicon nitride layer and a second silicon dioxide layer which are arranged in sequence.

Further, the thermal conductive via and the material of the absorption layer are made of silicon nitride.

Further, the substrate is divided into four regions by diagonal division, and a plurality of thermocouples connected in parallel with each other in series are arranged at 45° in each region, and the central region of the diagonal division is an absorption region.

Further, the cold end of the thermopile and the hot end of the thermopile are respectively located at opposite ends of the thermopile, the first thermocouple bar is made of N-type doped silicon material, and the second thermocouple bar is made of P-type doped silicon material. material.

An infrared detector for a non-spectrometric infrared gas sensor of the present invention has the following advantages:

1. The present invention realizes the connection with the absorption area in the center of the infrared detector by opening a heat conduction through hole at the hot end of the second thermocouple, so that most of the heat in the absorption area can be transferred to the hot end of the thermopile and the cold end of the thermopile. Directly connect the substrate 1, keep the cold end consistent with the ambient temperature, and etch the back of the bottom substrate of the hot end of the thermopile to form a suspension structure, reduce the heat conduction from the hot end of the thermopile to the substrate, and make the cold end of the thermopile and the heat of the thermopile. There is a large temperature difference between the ends, so as to increase the output signal, and the thermal conduction through hole and the backside etching structure are simple, the process can be realized, and good results can be achieved;

2. The thermocouple strips in the thermopile of the present invention are arranged in a double-layer stack, which can save the space of the device, so that more groups of thermocouples can be arranged on the entire substrate as much as possible, and the size of the infrared detector is controlled at the same time, so as to be suitable for non-split infrared Inside the gas sensor. By designing the length, width, height, connection structure, arrangement, etc. of the thermocouple 6, the structure of the thermopile is optimized, so that the cold end 21 of the thermopile and the hot end 22 of the thermopile have a large temperature difference, thereby realizing the increase of the output signal. .

Description of drawings

1 is a schematic structural diagram of a thermopile infrared detector provided by an embodiment of the present invention;

Fig. 2 is the structural schematic diagram of the single thermocouple longitudinal section (section one) of the thermopile infrared detector provided by the embodiment of the present invention;

3 is a schematic structural diagram of a cross-section (section 2) of a connection between adjacent thermocouples of a thermopile infrared detector according to an embodiment of the present invention.

Description of symbols in the figure: 1. Substrate; 2. Thermopile; 21. Cold end of thermopile; 22. Hot end of thermopile; 3. Supporting membrane module; 31. First silicon oxide layer; 32. Silicon nitride layer 33, the second silicon dioxide layer; 4, the absorption layer; 5, the back cavity; 6, the thermocouple; 61, the first thermocouple bar; 62, the second thermocouple bar; 9. Electrodes.

Detailed ways

In order to better understand the purpose, structure and function of the present invention, an infrared detector for a non-spectrographic infrared gas sensor of the present invention will be described in further detail below with reference to the accompanying drawings.

As shown in FIG. 1 to FIG. 3 , the infrared detector provided by the present invention will now be described. The infrared detector includes a substrate 1, a thermopile 2 arranged on the substrate 1, a support layer assembly 3 and an absorption layer 4;

The thermopile 2 includes a cold end 21 of the thermopile and a hot end 22 of the thermopile. The cold end 21 of the thermopile is attached to the substrate 1 , and the hot end 22 of the thermopile is provided with a thermally conductive through hole 7 , and the thermally conductive through hole 7 is connected to the hot end 22 and the absorption layer 4, the bottom back of the hot end 22 of the thermopile is etched to form a back cavity 5 to form a suspension structure.

The thermopile 2 includes multiple pairs of thermocouples 6;

A plurality of pairs of thermocouples 6 are arranged in a double-layer stack, and the thermocouples 6 include a first thermocouple bar 61 arranged on the substrate 1 in sequence and a second thermocouple bar 62 arranged on the first thermocouple bar 61. ;

The thermally conductive via 7 is arranged in the silicon oxide layer on the upper part of the second thermocouple bar 62;

The support layer assembly 3 is arranged between the substrate 1 and the thermopile 2;

The absorption layer 4 is arranged on the top layer of the infrared detector.

Compared with the prior art, the infrared detector provided by the present invention is connected with the absorption area 8 in the center of the infrared detector by opening a thermal conduction through hole 7 in the hot end 22 of the second thermocouple 62, so that the absorption area 8 of the absorption area 8 can be connected. Most of the heat is transferred to the hot end 22 of the thermopile, and the cold end 21 of the thermopile is directly connected to the substrate 1 to keep the cold end consistent with the ambient temperature. The hot end 22 of the thermopile conducts heat to the substrate 1, so that the cold end 21 of the thermopile and the hot end 22 of the thermopile have a large temperature difference, thereby increasing the output signal, and the thermally conductive vias 7 and the backside are etched The structure is simple, the process can be realized, and good effects can be achieved. At the same time, the thermocouple strips in the thermopile 2 are arranged in a double-layer stack, which can save the space of the device, so that more groups of thermocouples can be arranged on the entire substrate 1 as much as possible. By designing the length, width, height, connection structure, arrangement, etc. of the thermocouple 6, the structure of the thermopile is optimized, so that the output voltage of the thermopile 2 is increased, thereby satisfying the measurement accuracy of the infrared detector in the NDIR gas sensor.

The substrate 1 is generally made of silicon. The cold end 22 of the thermopile and the hot end 21 of the thermopile are located at opposite ends of the thermopile 2 respectively. The first thermocouple bar 61 is generally made of N-type doped silicon material, and the second thermocouple bar 62 is generally P-type. Doped silicon material, the absorption layer 4 and the through hole 7 are made of silicon nitride, a material with strong light absorption and thermal conductivity.

FIG. 1 to FIG. 3 are a specific embodiment of the infrared detector provided by the present invention. The support layer assembly 3 includes a first silicon oxide layer 31 , a silicon nitride layer 32 and a second silicon dioxide layer 33 stacked in sequence. , the absorption layer 4 can be isolated from the substrate 1, the first thermocouple 62 and the second thermocouple 61 can be isolated by the first silicon oxide layer 31 of the support layer assembly 3, the adjacent thermocouples 6 can be isolated, and the support layer assembly 3. It has good stability and can prevent mutual corrosion between materials, so as to protect the infrared detector.

1 to 3, as a specific embodiment of the infrared detector provided by the present invention, at the hot end 22 of the thermopile, the first thermocouple 62 and the second thermocouple 61 of the single thermocouple 6 are connected, At the cold end 21 , the first thermocouple bar 62 is connected to the adjacent second thermocouple bar 61 , so that the first thermocouple 62 and the second thermocouple 61 are connected in series, and the adjacent thermocouple bars 6 are also connected in series. connected in series to form a thermopile.

As shown in FIG. 1 , as a specific embodiment of the infrared detector provided by the present invention, the substrate 1 is divided into four regions by diagonal division, and each region is arranged with a plurality of thermoelectric devices parallel to each other in series at 45°. For the pair 6 , all the thermocouples 6 are arranged symmetrically in the center, the cold end of the thermocouples is connected with wires, the thermocouples 6 in the four regions are also connected with wires, and the wires are connected to the electrodes 9 . The central area of the thermopile 2 is the absorption area 8, and the absorption area 8 can absorb heat and transfer the heat to the hot end 22 of the thermopile 2 through the through holes 7.

As a specific embodiment of the infrared detector provided by the present invention, parameters such as the responsivity, internal resistance, and size of the infrared detector are optimized and adjusted as much as possible according to the needs of the gas sensor for infrared detection.

It can be understood that the present invention is described by some embodiments, and those skilled in the art know that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, in the teachings of this invention, these features and embodiments may be modified to adapt a particular situation and material without departing from the spirit and scope of the invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present application fall within the protection scope of the present invention.

Claims (7)

1. An infrared detector used in a non-spectroscopic infrared gas sensor is characterized by comprising a substrate (1), a thermopile (2) arranged on the substrate (1), a supporting layer assembly (3) and an absorption layer (4);

the thermopile (2) comprises a cold end (21) of the thermopile and a hot end (22) of the thermopile, the cold end (21) of the thermopile is attached to the substrate (1), a heat conduction through hole (7) is formed in the hot end (22) of the thermopile, the heat conduction through hole (7) is connected with the hot end (22) and the absorption layer (4), and the back of the bottom of the hot end (22) of the thermopile is etched to form a back cavity (5) to form a suspension structure;

the thermopile (2) comprises a plurality of pairs of thermocouples (6);

the multiple pairs of thermocouples (6) are arranged in a double-layer stacking mode, and each thermocouple (6) comprises a first thermocouple strip (61) and a second thermocouple strip (62), wherein the first thermocouple strips (61) are sequentially arranged on the substrate (1), and the second thermocouple strips (62) are arranged on the first thermocouple strips (61);

the heat conduction through hole (7) is arranged in the silicon oxide layer on the upper part of the second thermocouple strip (62);

the support layer assembly (3) is arranged between the substrate (1) and the thermopile (2);

the absorption layer (4) is arranged on the upper part of the thermopile (2).

2. The infrared detector of claim 1, wherein said first thermocouple strip (61) comprises a hot end of the first thermocouple strip (61) and a cold end of the first thermocouple strip (61), and said second thermocouple strip (62) comprises a hot end of the second thermocouple strip (62) and a cold end of the second thermocouple strip (62); the hot end of the first thermocouple strip (61) is connected with the hot end of the second thermocouple strip (62), and the cold end of the first thermocouple strip (61) is connected with the cold end of the adjacent second thermocouple strip (62), so that the first thermocouple (62) and the second thermocouple (61) are connected in series, and the adjacent thermocouple strips (6) are also connected in series.

3. The infrared detector for use in a non-spectroscopic infrared gas sensor according to claim 2 wherein a first silicon oxide layer (31) is filled between the first thermocouple strip (61) and the second thermocouple strip (62), and between the adjacent thermocouples (6).

4. The infrared detector for use in a non-spectroscopic infrared gas sensor according to claim 1 wherein the support layer assembly (3) comprises a first silicon oxide layer (31), a silicon nitride layer (32) and a second silicon oxide layer (33) arranged in that order.

5. The infrared detector for use in a non-spectroscopic infrared gas sensor according to claim 1 wherein the material of the thermal via (7) and the absorbing layer (4) is silicon nitride.

6. The infrared detector for use in a non-spectroscopic infrared gas sensor as set forth in claim 1, wherein the substrate (1) is divided into four regions by diagonal division, and a plurality of thermocouples (6) connected in series in parallel to each other are arranged at 45 ° in each region, and the central region of the diagonal division is an absorption region (8).

7. An infrared detector as used in a non-spectroscopic infrared gas sensor in accordance with claim 1 wherein the cold end (22) of the thermopile and the hot end (21) of the thermopile are respectively located at opposite ends of the thermopile (2), the first thermocouple strip (61) being of N-doped silicon and the second thermocouple strip (62) being of P-doped silicon.

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