CN102662033A - Structure of test cavity - Google Patents

Abstract

The invention discloses a structure of a test cavity in the technical field of a gas sensor. The structure of the test cavity comprises an airflow inlet 1, an energy converter 2, an inner wall medium layer 3, a sensitive membrane 4, a test cavity 5, an airflow outlet 6 and an air pump. The test cavity is connected with the air pump through a capillary tube. With the adoption of the structure provided by the invention, the inflation volume inside the test cavity is reduced. At the same airflow, the air concentration which is close to the sensitive membrane 4 is rapidly changed, and the energy converter can achieve a stable state in a rapider manner, so that the response time of the energy converter is shortened. An area of the inner wall of the test cavity is reduced, so that the amount of absorbing the air to be detected through the inner wall is reduced. Furthermore, the absorption amount of substances to be detected through the area of the inner wall in a unit is reduced by selecting a material of the inner wall which difficultly adsorbs the air to be detected or coating the medium material on the inner wall, so that the detection precision is improved and the detection limitation value is reduced.

Description

A test chamber structure

technical field

The invention relates to the technical field of gas sensors, in particular to a test chamber structure.

Background technique

Gas sensors have good application prospects in indoor air quality detection, industrial environment detection, food industry detection, battlefield environment early warning, anti-terrorism early warning and other fields. After integration with the Internet of Things, the quality and efficiency of social production and life can be greatly improved. However, the defects of the sensor itself limit its large-scale application. The main defects are: 1. The response time of the sensor is too long; 2. The detection error of the sensor is relatively large, especially when detecting low-concentration gases, which directly affects the detection accuracy. ; 3. The detection limit of the sensor is too high to meet the demand.

At present, there are two main reasons for the long response time of the sensor: one is that the sensitive mechanism and transducer technology perceive the change of external information too slowly; The sum of the volumes of the inlet and outlet of the gas flow is too large, resulting in too slow a change in the concentration of the measured gas near the sensitive membrane. It is worth noting that issues with sensor sensitivity mechanisms and transducer technology are sometimes not easy to resolve; thus, excessive sensor response times can only be improved in other ways.

The large inflated volume inside the test chamber means that the inner wall area is large, and the amount of adsorption and condensation of the measured gas on the inner wall of the sensor is also large, so only part of the measured gas in the atmosphere can act on the sensitive membrane. In addition, the amount of gas adsorbed and condensed is affected by various factors such as ambient temperature, humidity, and the concentration of the gas to be measured, and it is difficult for the back-end algorithm to eliminate its influence. These factors can only be regarded as random errors, which not only reduce the detection accuracy of the sensor, but also increase the detection limit of the sensor. In order to avoid false alarms and false alarms, the alarm threshold of the sensor has to be increased, which is to sacrifice performance for reliability. sex. The above-mentioned problems are the biggest problems in the practical application of sensors.

Inner wall or inner wall coating material is a major method to reduce inner wall adsorption. Either choose a suitable inner wall material, or apply a coating on the inner wall. Among the materials currently used, metal (mainly gold), glass, and polytetrafluoroethylene (Teflon) have the least adsorption on the measured gas. For measured gases that are gases at normal temperature, such as CO ₂ , CO, O ₂ , SO ₂ and H ₂ S, etc., it is only required that the inner wall or coating is chemically inert and does not chemically react with the measured gas. For the measured gas that is vapor at room temperature and condenses into liquid droplets when condensed, such as volatile organic compound VOC vapor (benzene series, organic chloride, Freon series, organic ketones, amines, alcohols, ethers, esters, acids and Petroleum hydrocarbons, etc.), the requirements are higher. The "cold" surface of the metal will condense a part of the vapor that enters the test chamber. At the detection concentration of ppm or even ppb level, this condensation of metal will cause a large error in the result. Therefore, glass and polytetrafluoroethylene are more suitable. Suitable.

Contents of the invention

In view of the above-mentioned prior art, the technical problems to be solved by the present invention are: the response time of the gas sensor in the existing sensor test chamber is long, the gas detection accuracy of the sensor is low and the detection limit value is large.

In order to solve the above technical problems, the present invention adopts the following technical solutions:

A test chamber structure, including airflow inlet, transducer, inner wall medium layer, sensitive film, test chamber, airflow outlet, air pump, test chamber and air pump are connected through capillary, it is characterized in that, the three-dimensional dimension of described test chamber has at least one Dimensions are on the order of microns, and the cross-sectional size of the gas path connecting the outside world and the test chamber is on the order of microns to millimeters.

The three-dimensional size of the test chamber is 2mm×2mm×300um～4mm×4mm×300um, the size of the gas path connecting the outside world and the test chamber is: air inlet 0.3mm×0.03mm×200um～0.5mm×0.05mm×300um, Air outlet 3mm×0.2mm×200um～5mm×0.3mm×300um.

The transducer of the present invention is a part of the inner wall of the test cavity and is arranged in the test cavity.

The material of the capillary in the present invention is one of semiconductor materials such as silicon, silicon dioxide, gallium arsenide, and silicon nitride.

The inner wall medium layer of the test chamber of the present invention is a material with low surface tension and chemical inertness or a layer of low surface tension and chemically inert medium material is coated on the surface of the inner wall medium layer.

The medium layer of the inner wall of the present invention is gold, platinum, palladium, titanium, rhodium, iridium, osmium, ruthenium, polytetrafluoroethylene, parylene, polybutene, polystyrene, glass, amorphous silicon dioxide, single crystal One of silicon dioxide, silicon, silicon nitride, aluminum oxide, gallium arsenide, and metal oxides.

The dielectric material coated on the surface of the inner wall dielectric layer of the present invention is gold, platinum, palladium, titanium, rhodium, iridium, osmium, ruthenium, polytetrafluoroethylene, parylene, polybutylene, polystyrene, glass, non- One of crystalline silica, single crystal silica, silicon, alumina, silicon nitride, gallium arsenide, metal oxides, and fused silica.

The sensitive film of the present invention is one of organic polymers, small organic molecules, metals, metal oxides, non-metal oxides and biological materials.

The transducer of the present invention has heating and temperature control functions, and is one of mass type, heat induction type, optical, conduction type, capacitive type, and electrochemical type.

The transducer of the present invention uses an air pump to sample the gas in the external environment.

The sealing method of the test cavity of the present invention is bonding or a layer of dielectric material covering the entire periphery of the transducer.

Compared with prior art, the beneficial effect that the present invention has is shown in:

1. The size of the test chamber and airflow inlet has been reduced to the order of microns, which reduces the inflated volume inside the test chamber, that is, reduces the area of the inner wall, and further reduces the adsorption area of the inner wall to the gas to be measured, thus reducing the impact of the adsorbed gas on the inner wall. The interference of the detection result reduces the detection error and improves the detection accuracy.

2. The inner wall of the test chamber is made of a material with low surface tension and chemical inertness, or a layer of dielectric material with such properties is coated on the surface to reduce the amount of adsorption per unit area of the inner wall to the measured gas, thereby reducing the impact of inner wall adsorption on The interference of the detection result reduces the detection error and improves the detection accuracy.

3. Reduce the inflated volume inside the test chamber, which is the sum of the inflated volume of the test chamber and the volume of the air inlet and outlet. Supplemented with appropriate inner wall materials or inner wall coatings, it can effectively improve the performance of the sensor and promote the practicality and popularization of the sensor.

Description of drawings

Fig. 1 is a sectional view of the present invention;

Fig. 2 is the three-dimensional rendering of the present invention;

Reference numerals are: 1 is the air inlet, 2 is the transducer, 3 is the inner wall medium layer, 4 is the sensitive film, 5 is the test chamber, 6 is the air outlet, and 7 is the air pump.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

A test chamber structure, including an airflow inlet, a transducer, an inner wall medium layer, a sensitive film, a test chamber, an airflow outlet, and an air pump. The test chamber and the air pump are connected through a capillary tube to reduce the inflated volume inside the test chamber. The three-dimensional shape of the test chamber At least one dimension is on the order of microns, and the cross-sectional size of the gas path connecting the outside world and the test chamber is on the order of microns to millimeters. The transducer is a part of the inner wall of the test cavity or is arranged in the test cavity. The material of the capillary is one of semiconductor materials such as silicon, silicon dioxide, gallium arsenide, and silicon nitride. The inner wall medium layer of the test chamber is made of low surface tension and chemically inert material or a layer of low surface tension and chemically inert medium material is coated on the surface of the inner wall medium layer. The sensitive film is one of organic polymers, small organic molecules, metals, metal oxides, non-metal oxides and biological materials.

Wherein the inner wall medium layer is gold, platinum, palladium, titanium, rhodium, iridium, osmium, ruthenium, polytetrafluoroethylene, parylene, polybutylene, polystyrene, glass, amorphous silicon dioxide, single One of crystalline silicon dioxide, silicon, silicon nitride, aluminum oxide, gallium arsenide and metal oxide, or the dielectric material coated on the surface of the inner wall dielectric layer is gold, platinum, palladium, titanium, rhodium, iridium, osmium , ruthenium, PTFE, parylene, polybutylene, polystyrene, glass, amorphous silica, monocrystalline silica, silicon, alumina, silicon nitride, gallium arsenide, metal oxide One of materials and fused silica.

The transducer has heating and temperature control functions, and is one of mass type (piezoelectric acoustic wave device, cantilever beam), thermal induction type, optical, conductivity type, capacitive type, electrochemical type, and uses an air pump to Ambient gases are sampled.

The preparation method of the test chamber structure provided by the present invention is as follows:

As shown in FIG. 1 , the test chamber structure includes an airflow inlet 1 , a transducer 2 , an inner wall dielectric layer 3 , a sensitive film 4 , a test chamber 5 , an airflow outlet 6 , and an air pump 7 . Grooves with an area of 2mm×2mm and a depth of 300um were prepared on the surface of the single crystal silicon substrate by the deep reactive ion etching DRIE process, and a narrow groove was prepared at both ends of the groove, and the specifications were 0.5mm×0.05mm in area and 300um in depth. And the area is 5mm×0.3mm, the depth is 300um. The groove and the narrow groove are respectively the packaged test cavity 5 and the gas path (the inlet and outlet of the airflow). An interdigital transducer 2, a platinum heater and a platinum temperature sensor are prepared on the surface of the other silicon substrate, and the latter two are essentially platinum resistors. Except for the interdigital transducer 2 , the platinum heater and the platinum temperature sensor, a layer of parylene film is prepared on the inner wall of the test chamber to form the inner avoidance medium layer 3 . A layer of polyethylene oxide sensitive film was prepared on the surface of interdigital transducer by air spray technology. Combine the two silicon wafers together, use a baffle to block the airflow inlet and outlet, prepare a layer of parylene film on the entire outer surface of the test chamber, block all the gaps, and complete the packaging, that is, the test chamber 5, the airflow inlet 1 and the test chamber 5 are obtained. Air outlet 6. The size range of the test chamber is 2mm×2mm×300um～4mm×4mm×300um, the optimal size is 2mm×2mm×300um; the size range of the air inlet 1 is 0.3mm×0.03mm×200um～0.5mm×0.05mm×300um, The optimum size is 0.5mm×0.05mm×300um, the size range of the air outlet 6 is 3mm×0.2mm×200um～5mm×0.3mm×300um, and the optimum size is 5mm×0.3mm×300um. The sensor deposited with the interdigital transducer is put into the test chamber by buckling, and the substrate of the sensor is also a part of the test chamber structure. The quartz capillary connects the test chamber and the air pump. One end of the capillary is inserted into the air outlet of the test chamber and sealed with epoxy resin. The capillary is connected to the stainless steel pipe of the air pump through an adapter.

A groove and narrow grooves at both ends of the groove are prepared on the surface of the single crystal silicon substrate by a deep reactive ion etching DRIE process. The sealing method can cover the entire transducer periphery with a layer of dielectric material or a bonding method. When the sealing method is bonding, the direct bonding method is used. In the direct bonding method, the surface of the silicon wafer is usually pretreated with hydrophilicity before bonding, and then the silicon wafer is bonded at room temperature, and then the bonded silicon wafer is annealed at a high temperature of about 1000 ° C to achieve the final bond strength.

In the present invention, the inflated volume of the test chamber and the air inlet and outlet is reduced from the traditional 100mL to about 0.4uL, the response time is shortened from 3min to about 0.5s, the response error is reduced from 5% to 0.01%, and the detection limit value is reduced from 1000ppm down to about 5ppm.

Claims (10)

1. A test chamber structure, comprising an airflow inlet, a transducer, an inner wall dielectric layer 3, a sensitive film 4, a test chamber, an airflow outlet, an air pump, and the test chamber and the air pump are connected through a capillary, wherein the test chamber At least one of the three-dimensional dimensions is on the order of microns, and the cross-sectional size of the gas path connecting the outside world and the test chamber is on the order of microns to millimeters. 2. The test chamber structure according to claim 1, characterized in that, the three-dimensional size of the test chamber is 2mm×2mm×300um～4mm×4mm×300um, and the size of the gas path connecting the outside world and the test chamber is: air intake The port is 0.3mm×0.03mm×200um～0.5mm×0.05mm×300um, the air outlet is 3mm×0.2mm×200um～5mm×0.3mm×300um. 3 . The test cavity structure according to claim 1 , wherein the transducer, namely the interdigital transducer, is a part of the inner wall of the test cavity and is arranged in the test cavity. 4 . 4 . The test chamber structure according to claim 1 , wherein the material of the capillary is one of semiconductor materials such as silicon, silicon dioxide, gallium arsenide, and silicon nitride. 5. The test chamber structure according to claim 1, characterized in that, the inner wall medium layer of the test chamber is a material with low surface tension and chemical inertness or a layer of material with small surface tension and chemical inertness is coated on the surface of the inner wall medium layer. Inert dielectric material. 6. The test chamber structure according to claim 4, wherein the inner wall dielectric layer is gold, platinum, palladium, titanium, rhodium, iridium, osmium, ruthenium, polytetrafluoroethylene, parylene, One of polybutylene, polystyrene, glass, amorphous silica, single crystal silica, silicon, silicon nitride, alumina, gallium arsenide, and metal oxides. 7. The test chamber structure according to claim 4, wherein the dielectric material coated on the surface of the inner wall dielectric layer is gold, platinum, palladium, titanium, rhodium, iridium, osmium, ruthenium, polytetrafluoroethylene, One of parylene, polybutylene, polystyrene, glass, amorphous silica, single crystal silica, silicon, alumina, silicon nitride, gallium arsenide, metal oxides, and fused silica kind. 8. The test chamber structure according to claim 1, wherein the sensitive film is one of organic polymers, small organic molecules, metals, metal oxides, non-metal oxides and biological materials. 9. The test chamber structure according to claim 2, characterized in that, the transducer has heating and temperature control functions, and is one of mass type, thermal induction type, optical, conductivity type, capacitive type, and electrochemical type A sort of. 10. The test chamber structure according to claim 2, characterized in that the external environment gas is sampled through an air pump.

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