MEMS gas sensor and gas detection method based on heating desorption analysis

Abstract

The invention belongs to the field of gas sensors, and particularly discloses an MEMS gas sensor and a gas detection method based on heating desorption analys.The MEMS gas sensor comprises a micro cavity with holes, an adsorption and desorption element and a gas sensing element, and the adsorption and desorption element and the gas sensing element are arranged in the micro cavity with the holes; the adsorption and desorption element is used for adsorbing and desorbing target gas based on temperature change; and the gas sensing element is used for outputting a corresponding electric signal according to the target gas concentration. According to the invention, the temperature and height of the desorption peak position can be determined based on the change of the electric signal of the gas sensing element along with the temperature of the adsorption and desorption element in the adsorption and desorption process, so that the detection of high selectivity and ultra-wide concentration range of the target gas is realized, and the stability of the gas sensor is improved.

Description

Technical Field

[0001] The present invention belongs to the field of gas sensors, and more specifically, relates to a MEMS gas sensor and a gas detection method based on temperature rise desorption analysis. Background Art

[0002] With the development of the Internet of Things era, intelligent and integrated gas sensors based on MEMS technology have been expanded to many fields such as environment, home, agriculture, biology and food. MEMS gas sensor types include semiconductor type, solid electrolyte type, catalytic combustion type, thermal conductivity type, optical type, etc., especially semiconductor gas sensors, which have the characteristics of high sensitivity, simple structure, low cost, wide detection object, easy miniaturization, etc., suitable for detecting a variety of gases, and convenient for large-scale production and application. These characteristics make MEMS metal oxide semiconductor gas sensors have a wide market, but due to the defects of insufficient selectivity, zero drift and limited concentration detection range, they are limited to many low-end applications.

[0003] In terms of selectivity, most studies use a single-layer membrane structure and improve selectivity through material modification methods, but the limitations at the principle level make it impossible to achieve one-to-one high selectivity, and it is limited to special gas types or application scenarios. On this basis, sensors with multi-layer membrane structures are extended to change the catalytic ability of the membrane by filtering or regulating temperature, thereby changing the concentration of gas permeation, which can enhance selectivity to a certain extent, but still faces the problems of zero drift and limited concentration detection range.

[0004] The sensor zero point is a relative zero point. When there is no target gas, this value is also affected by factors such as the environment and aging effects, resulting in the sensor being unstable and directly affecting the accuracy of sensor detection. Dynamic online calibration and material and structure optimization methods are usually used to improve the performance. Dynamic online calibration requires real-time monitoring of sensor drift and correction, which is labor-intensive and cumbersome. Material and structure optimization methods enhance the sensitivity and stability of sensors by improving the selection of sensor materials and structural design. However, due to the microscopic uncontrollability of materials and life attenuation, this method does not produce good results.

[0005] In addition, each gas sensor has an applicable gas concentration detection range. When the gas concentration exceeds this range, it cannot be detected at extremely low concentrations, and the signal is saturated at ultra-high concentrations. This concentration detection range is affected by factors such as sensing materials, environment, and stability. Usually, material modification and sensor structure optimization are used to improve it. Although sensor material modification can reduce the detection limit as much as possible, it cannot solve the problem of material surface adsorption saturation; the sensor structure usually adopts a combination of arrays and algorithms, which also cannot solve the problem of gas adsorption saturation.

[0006] Therefore, there is an urgent need for a MEMS gas sensor and a gas detection method to solve the above problems. Summary of the invention

[0007] In view of the above defects or improvement needs of the prior art, the present invention provides a MEMS gas sensor and a gas detection method based on temperature desorption analysis, the purpose of which is to achieve high selectivity and ultra-wide concentration range detection of the target gas and improve the stability of the gas sensor.

[0008] To achieve the above object, according to one aspect of the present invention, a MEMS gas sensor is provided, comprising a micro cavity with a hole, an adsorption / desorption element and a gas sensing element, wherein:

[0009] The adsorption and desorption element and the gas sensing element are arranged in a micro cavity with holes;

[0010] The adsorption and desorption element is used to adsorb and desorb the target gas based on temperature changes;

[0011] The gas sensor element is used to output a corresponding electrical signal according to the target gas concentration.

[0012] As a further preferred embodiment, the adsorption and desorption of the target gas is achieved by the adsorption and desorption membrane in the adsorption and desorption element, and the ratio of the volume of the adsorption and desorption membrane to the volume of the micro cavity with holes is greater than 1*10 -7 .

[0013] As a further preferred embodiment, the ratio of the cross-sectional area of ​​the hole on the micro cavity with holes to the inner volume of the micro cavity with holes is less than 200 m -1 .

[0014] As further preferred, the adsorption / desorption element comprises a first micro-hot plate and an adsorption / desorption film arranged on the first micro-hot plate, wherein the first micro-hot plate comprises an insulating substrate and a heating electrode and a temperature measuring electrode arranged on the insulating substrate;

[0015] The gas sensing element comprises a second micro-hotplate and a gas-sensitive film arranged on the second micro-hotplate, wherein the second micro-hotplate comprises an insulating substrate and a heating electrode, a temperature measuring electrode and a measuring electrode arranged on the insulating substrate, wherein the measuring electrode is used to measure the resistance of the gas-sensitive film.

[0016] As a further preferred embodiment, a packaging structure is provided outside the micro cavity with holes, and a hole is opened on the packaging structure;

[0017] A support structure is provided in the packaging structure, and the support structure includes a lower gasket, an upper gasket and an upper cover arranged in sequence from bottom to top, the lower gasket is fixed to the lower part of the packaging structure, and the upper cover is provided with a through hole;

[0018] The adsorption / desorption element and the gas sensor element are both arranged between the lower gasket and the upper gasket, and the cavity formed by the adsorption / desorption element, the upper side of the gas sensor element, the upper gasket and the upper cover is a micro cavity with holes.

[0019] As further preferred, both the first micro-hotplate and the second micro-hotplate are cantilever structures.

[0020] As a further preferred embodiment, the first micro-hotplate is a suspended membrane structure, a hole is provided in the central area of ​​the insulating base of the first micro-hotplate, and the second micro-hotplate is a cantilever structure; a partition is provided in the middle of the upper gasket to separate the upper cavities of the first micro-hotplate and the second micro-hotplate, and the through hole of the upper cover is provided on one side of the cavity formed by the first micro-hotplate and the upper gasket.

[0021] As a further preference, the number of the adsorption / desorption elements and the gas sensor elements is no less than one, and they are arranged in an array.

[0022] According to another aspect of the present invention, a gas detection method based on temperature desorption analysis using the above-mentioned MEMS gas sensor is provided, comprising the following steps:

[0023] The sensor is placed in the environment to be detected, and the adsorption-desorption element adsorbs the target gas at a preset temperature for a preset time;

[0024] After the adsorption is completed, the adsorption-desorption element is heated up and then cooled down to the preset temperature. The target gas desorbed by the adsorption-desorption element generates a response on the gas sensor element, and the temperature of the adsorption-desorption element and the electrical signal of the gas sensor element during the heating and cooling process are obtained;

[0025] The adsorption and desorption element temperature corresponding to the maximum change amplitude of the gas sensor element electrical signal is taken as the desorption peak temperature, the gas sensor element electrical signal corresponding to the desorption peak temperature during the heating process is the heating signal, and the gas sensor element electrical signal corresponding to the desorption peak temperature during the cooling process is the cooling signal, and the ratio of the cooling signal to the heating signal is taken as the desorption peak height;

[0026] The gas type and concentration are determined based on the desorption peak temperature and height.

[0027] As further preferred, determining the gas type and concentration according to the detected desorption peak temperature and height includes:

[0028] The desorption peak temperature of the target gas and the calibration curve of the relationship between the desorption peak height and the target gas concentration are obtained in advance through the sensor;

[0029] If the detected desorption peak temperature is consistent with the desorption peak temperature of the target gas, it is judged that the detection environment is the target gas, otherwise it is other gases;

[0030] When the target gas is in the detection environment, the concentration of the target gas in the detection environment is determined according to the detected desorption peak height and the calibration curve.

[0031] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0032] 1. The present invention arranges an adsorption / desorption element and a gas sensor element in a porous micro-cavity, so that the desorption peak temperature and height can be determined based on the change of the electrical signal of the gas sensor element with the temperature of the adsorption / desorption element during the adsorption / desorption process, thereby achieving high selectivity and ultra-wide concentration range detection of the target gas and improving the stability of the gas sensor.

[0033] 2. Since the larger the volume of the adsorption-desorption membrane, the more gas will be adsorbed and the greater the concentration of the target gas released, the present invention further designs the ratio of the volume of the adsorption-desorption membrane to the volume of the porous micro-cavity to avoid too slight a concentration change caused by adsorption-desorption. In addition, the present invention designs the ratio of the cross-sectional area of ​​the hole on the porous micro-cavity to the volume of the porous micro-cavity to avoid the cross-sectional area of ​​the hole being too large, which causes the gas to diffuse out of the micro-cavity too quickly, further improving the detection accuracy of the gas sensor element.

[0034] 3. Perform programmed heating and cooling process on the adsorption and desorption element, extract the change value of the electrical signal of the gas sensor element in the process, and establish the zero point of the sensor through the differential signal (that is, the ratio of the electrical signal of the desorption peak temperature corresponding to the heating and cooling process). The output signal of the zero point in the absence of target gas is a specific constant, which is not affected by the environment and is a fixed value, thus solving the zero point drift problem of semiconductor sensors.

[0035] 4. In the temperature desorption test, the desorption temperature peak detected by the gas sensor element is obtained through the selective adsorption characteristics of the adsorption-desorption membrane material and the different temperature desorption characteristics of the adsorbed molecules during the on-chip programmed temperature increase process according to the desorption energy size, thereby obtaining high selectivity and solving the problem of poor selectivity of semiconductor sensors.

[0036] 5. The detection gas concentration range can be adjusted by controlling the adsorption time of the adsorption and desorption elements. For extremely low concentration gases, detection can be achieved by long-term adsorption and concentration. For extremely high concentration gases, detection can be achieved by controlling the gas adsorption amount in an extremely short adsorption time, which solves the problem of limited detection range of semiconductor sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a structural block diagram of a MEMS gas sensor according to an embodiment of the present invention;

[0038] Figure 2This is a schematic diagram of the structure of a single-element coplanar dual-cantilever micro-hotplate gas sensor according to an embodiment of the present invention;

[0039] Figure 3 This is a schematic structural diagram of a single-element coplanar suspended film plus cantilever structure micro-hotplate gas sensor according to an embodiment of the present invention;

[0040] Figure 4 This is a flow chart of a temperature-programmed desorption analysis test under clean air conditions in an embodiment of the present invention;

[0041] Figure 5 This is a flow chart of a temperature-programmed desorption analysis test in the absence of clean air according to an embodiment of the present invention;

[0042] Figure 6 This is a diagram showing the temperature signal of the adsorption and desorption element and the resistance signal of the gas sensing element in the programmed temperature desorption analysis process of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor in the presence of clean air in an embodiment of the present invention;

[0043] Figure 7 It is a diagram showing the temperature signal of the adsorption-desorption element and the resistance signal of the gas sensing element in the programmed temperature desorption analysis process in three test cycles of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor in the embodiment of the present invention under the condition of no clean air;

[0044] Figure 8 The original signal of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor in Example 1 of the present invention when testing 200ppm ethanol in the programmed temperature desorption analysis process, including the temperature signal of the adsorption and desorption element and the resistance signal diagram of the gas sensor element;

[0045] Fig. 9 This is a temperature-programmed desorption curve diagram of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor in the presence or absence of ethanol in Example 1 of the present invention, wherein the air is clean air;

[0046] Fig.10 This is a temperature-programmed desorption curve of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor for different concentrations of ethanol in Example 1 of the present invention, wherein the air is clean air;

[0047] Fig.11a The desorption peak height of the gas sensing element of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor for different concentrations of ethanol in Example 1 of the present invention;

[0048] Fig.11b The resistance value of the gas sensor element of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor in Example 1 of the present invention under different formaldehyde concentration environments, where R0 is the reference value of the gas sensor element in the absence of formaldehyde;

[0049] Fig.12The original signal of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor tested on 200 ppm ethanol and 200 ppm methanol in Example 2 of the present invention, including the temperature signal of the adsorption / desorption element and the resistance signal of the gas sensing element;

[0050] Fig.13 This is the programmed temperature desorption curve of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor under different gas environments in Example 2 of the present invention;

[0051] Fig.14 The height of the desorption peak of the gas sensing element of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor under different gas environments in Example 2 of the present invention;

[0052] Fig.15 The resistance value of the gas sensing element of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor in Example 3 of the present invention under different formaldehyde concentration environments;

[0053] Fig.16 The original signal of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor in Example 3 of the present invention when testing 100 ppb formaldehyde at an adsorption time of 10 s and 180 s, including the temperature signal of the adsorption and desorption element and the resistance signal of the gas sensor element;

[0054] Fig.17a The resistance response of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor to different concentrations of formaldehyde, and the desorption peak height of the gas sensor element at adsorption times of 10s and 180s in Example 3 of the present invention;

[0055] Fig.17b The fitting curves are the gas sensor element resistance response of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor of Example 3 of the present invention to different concentrations of formaldehyde and the gas sensor element desorption peak height at adsorption times of 10s and 180s;

[0056] Fig.18 The resistance response curve of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor to 0.5%-60% concentration ethanol solution in Example 4 of the present invention;

[0057] Fig.19 The original test curve and programmed temperature desorption curve of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor for 0.5%-60% ethanol solution in Example 4 of the present invention;

[0058] Fig. 20 The resistance response and desorption peak height comparison of the gas sensing element of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor of Example 4 of the present invention to 0.5%-60% concentration ethanol solution.

[0059] In all the drawings, the same reference numerals are used to represent the same elements or structures, where: 1-packaging structure, 2-micro cavity with holes, 1.1-shell body, 1.2-protective cover, 2.1-lower gasket, 2.2-upper gasket, 2.3-upper cover, 2.4-gas diffusion hole, 3-adsorption / desorption element, 4-gas sensor element. DETAILED DESCRIPTION

[0060] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0061] An embodiment of the present invention provides a MEMS gas sensor, such as Figure 1 As shown, it includes a micro cavity 2 with holes, an adsorption and desorption element 3 and a gas sensing element 4, wherein:

[0062] The adsorption / desorption element 3 and the gas sensing element 4 are arranged in the micro cavity 2 with holes;

[0063] The adsorption / desorption element 3 is used to adsorb and desorb the target gas based on temperature changes;

[0064] The gas sensor element 4 is used to output a corresponding electrical signal according to the target gas concentration.

[0065] Specifically, the adsorption and desorption element is a microheater that can be programmed to heat up, and as an element that can adsorb gas molecules, a gas adsorption and desorption membrane is loaded on it. The adsorption and desorption membrane can be aluminosilicate zeolite molecular sieve, aluminophosphate zeolite molecular sieve, NaX type molecular sieve, MOFs, semiconductor materials, etc., but not limited to the above materials, and is used to achieve selective adsorption and desorption of different target gases.

[0066] As a detection element that can sense gas molecules, the gas sensor element can be a micro gas detection element based on the principles of metal oxide semiconductor, thermal conductivity, catalytic combustion, optical, etc. For example, the gas sensor element is a semiconductor type, and its gas-sensitive film resistance changes with the gas concentration, and the output electrical signal is the gas-sensitive film resistance signal; the gas-sensitive film material can be SnO2, WO3, In2O3, ZnO metal oxides and their modified materials, etc., but not limited to the above materials, and is used to achieve high-sensitivity detection of the target gas. For another example, the gas sensor element is a thermal conductivity type. Based on the different thermal conductivities of different gases, the concentrations of various components in the atmosphere will affect their overall thermal conductivity, resulting in differences in the surrounding temperature field. The output electrical signal is a voltage signal generated between two temperature measuring electrodes due to changes in gas concentration. It is easy to understand that as long as the gas sensor element can output an electrical signal in response to changes in gas concentration, its specific type is not limited.

[0067] Furthermore, the adsorption and desorption of the target gas are achieved through the adsorption and desorption membrane in the adsorption and desorption element, and the ratio of the volume of the adsorption and desorption membrane to the volume of the micro cavity with holes is greater than 1*10 -7 .

[0068] Furthermore, the ratio of the cross-sectional area of ​​the hole on the micro cavity with holes to the internal volume of the micro cavity with holes is less than 200m -1 .

[0069] Furthermore, the number of adsorption / desorption elements and gas sensor elements is no less than one and they are arranged in an array.

[0070] Furthermore, a packaging structure 1 is provided on the outside of the porous micro-cavity 2, and a hole is opened on the packaging structure 1; a supporting structure is provided in the packaging structure 1, and the supporting structure includes a lower gasket 2.1, an upper gasket 2.2 and an upper cover 2.3 arranged in sequence from bottom to top, the lower gasket 2.1 is fixed at the lower part of the packaging structure 1, and the upper cover 2.3 is provided with a through hole, i.e., a gas diffusion hole 2.4; the adsorption / desorption element 3 and the gas sensor element 4 are both arranged between the lower gasket 2.1 and the upper gasket 2.2, and their edge parts are suspended under the support of the lower gasket 2.1, and the suspended area is used as a flow channel for gas diffusion; the cavity formed by the upper side of the adsorption / desorption element 3 and the gas sensor element 4 and the upper gasket 2.2 and the upper cover 2.3 is the porous micro-cavity 2.

[0071] The packaging structure 1 can be specifically a tube shell, which includes a tube shell body 1.1 at the bottom and a protective cover 1.2 at the top, and a plurality of through holes are opened on the protective cover 1.2. The gas to be measured enters the sensor cavity from the protective cover 1.2, and then enters the micro cavity with holes, interacts with the adsorption and desorption element 3 and is adsorbed by it. The adsorption and desorption element 3 completely desorbs the adsorbed gas to be measured during the programmed temperature rise process, and the gas to be measured diffuses to the gas sensor element 4, generating a characteristic signal, thereby realizing gas detection.

[0072] In some embodiments, the adsorption / desorption element 3 includes a first micro-hotplate and an adsorption / desorption film disposed on the first micro-hotplate, the first micro-hotplate includes an insulating substrate and a heating electrode and a temperature measuring electrode disposed on the insulating substrate, the heating electrode is used to heat the insulating substrate, and the temperature measuring electrode is used to measure the temperature of the adsorption / desorption film. The gas sensing element 4 includes a second micro-hotplate and a gas-sensitive film disposed on the second micro-hotplate, the second micro-hotplate includes an insulating substrate and a heating electrode, a temperature measuring electrode and a measuring electrode disposed on the insulating substrate, the heating electrode is used to heat the gas-sensitive film, the temperature measuring electrode is used to measure the temperature of the gas-sensitive film, and the measuring electrode is used to measure the resistance of the gas-sensitive film. The first micro-hotplate and the second micro-hotplate may be a coplanar integrated structure.

[0073] The micro-hotplate of the adsorption / desorption element 3 and the gas sensing element 4 is a coplanar cantilever or suspended film structure; specifically, there are the following two structures:

[0074] (1) Figure 2 As shown, the micro-hotplate of the adsorption / desorption element and the gas sensing element is a cantilever structure.

[0075] The first micro-hotplate and the second micro-hotplate are both cantilever structures, that is, the middle part is hollow; the chamber formed by the lower part of the first micro-hotplate and the tube shell is connected to the chamber formed by the lower part of the second micro-hotplate and the tube shell, and forms an integrated chamber with the micro-cavity with holes. The adsorption and desorption element and the gas sensor element form a non-contact structure. The gas to be measured enters the inner chamber from the hole on the micro-cavity with holes, and undergoes adsorption reaction with the adsorption and desorption film and the gas-sensitive film. Since the gas is in contact with the adsorption and desorption element and the gas sensor element at the same time, it is necessary to wait for the resistance of the gas sensor element to stabilize before measurement, which is more suitable for scenarios where there is no requirement for detection time or long-term monitoring is required in a low-concentration target atmosphere.

[0076] For the above structure, the gas-sensitive film is coated on the measuring electrode of the second micro-hotplate, and the adsorption-desorption film is coated on the very center of the first micro-hotplate.

[0077] (2) Figure 3 As shown, the micro-hotplate of the adsorption-desorption element is a suspended film structure, and the micro-hotplate of the gas sensing element is a cantilever structure.

[0078] The first micro-hotplate is a suspended film micro-hotplate, and a plurality of holes are arranged in the central area thereof for gas diffusion and penetration. The second micro-hotplate is a cantilever micro-hotplate, i.e., the middle part is hollowed out. The chamber formed by the lower part of the first micro-hotplate and the tube shell is connected with the chamber formed by the lower part of the second micro-hotplate and the tube shell. The middle part of the upper gasket is protruding, so that the micro-cavity with holes adds a partition between the adsorption and desorption element and the gas sensing element, so that two unconnected chambers are formed on both sides thereof. The micropores on the micro-cavity with holes (i.e., the gas diffusion holes 2.4) are only arranged on the chamber formed between it and the adsorption and desorption element. The gas to be detected enters from the micropores on the micro-cavity with holes, first undergoes an adsorption reaction with the adsorption and desorption membrane, and after the adsorption and desorption membrane is saturated with adsorption, it passes through the adsorption and desorption membrane and the holes of the suspended film micro-hotplate to reach the chamber formed with the tube shell, and diffuses to the gas sensitive membrane of the gas sensing element to undergo an adsorption reaction. Since the gas first contacts the adsorption / desorption element and then contacts the gas sensing element, there is no need to wait for the resistance of the gas-sensitive film to stabilize, and the measurement speed is faster, which is more suitable for short-time gas detection.

[0079] For the above structure, since the chamber has good airtightness, the holes of the suspended film micro-hotplate become the only channel for gas flow, the adsorption-desorption film is coated on the central punched part of the first micro-hotplate and contacts with the temperature measuring electrode; the gas sensitive film is coated on the measuring electrode of the second micro-hotplate.

[0080] Based on the above-mentioned MEMS gas sensor, an embodiment of the present invention provides a gas detection method based on temperature desorption analysis, comprising the following steps:

[0081] The sensor is placed in the environment to be detected, and the adsorption-desorption element adsorbs the target gas at a first preset temperature for a preset time.

[0082] After the adsorption is completed, the adsorption and desorption element is first heated to the second preset temperature, and then cooled back to the first preset temperature. The target gas desorbed by the adsorption and desorption element generates a response on the gas sensor element, and the temperature of the adsorption and desorption element and the electrical signal of the gas sensor element are obtained during the heating and cooling process. Among them, the first preset temperature and the second preset temperature are determined according to the type of target gas. The first preset temperature is the optimal adsorption temperature of the adsorption and desorption membrane material for the target gas, and the second preset temperature is the optimal temperature at which the adsorption and desorption membrane material can completely desorb the target gas in a short time.

[0083] The adsorption and desorption element temperature corresponding to the maximum change amplitude of the gas sensor element electrical signal is taken as the desorption peak temperature, the gas sensor element electrical signal corresponding to the desorption peak temperature during the heating process is the heating signal, and the gas sensor element electrical signal corresponding to the desorption peak temperature during the cooling process is the cooling signal, and the ratio of the cooling signal to the heating signal is taken as the desorption peak height;

[0084] Determine the gas type and concentration based on the desorption peak temperature and height, including:

[0085] The desorption peak temperature of the target gas and the calibration curve of the relationship between the desorption peak height and the target gas concentration are obtained in advance through the sensor. Since the desorption peak height is defined as the ratio of the signal, the corresponding desorption peak height when there is no target gas (concentration is 0) in the calibration curve is 1, which is the zero point of the sensor; specifically, the desorption peak height of the sensor at different target gas concentrations is detected (the test process can be found in Figure 4 The description is omitted here), thereby obtaining the calibration curve.

[0086] If the detected desorption peak temperature is consistent with the desorption peak temperature of the target gas, it is judged that the detection environment is the target gas, otherwise it is other gases; when there is a target gas in the detection environment, the concentration of the target gas in the detection environment is further determined based on the detected desorption peak height and the calibration curve.

[0087] In some embodiments, taking the electrical signal being a gas-sensitive film resistance signal as an example, the gas detection method under clean air conditions and under non-clean air conditions is described as follows.

[0088] Figure 4 The testing process for the sensor under clean air conditions includes:

[0089] S1: heating the adsorption / desorption element and the gas sensing element to a first preset temperature and a second preset temperature respectively;

[0090] S2: performing a programmed heating and cooling process on the adsorption-desorption element under preset parameters to completely desorb the gas adsorbed on its surface to remove the adsorbed impurities;

[0091] S3: placing the sensor in a target gas environment, allowing the adsorption / desorption element to adsorb the gas at a first preset temperature for a preset time, and placing the sensor in a clean air environment again after the adsorption is completed;

[0092] S4: After the resistance of the gas sensor unit is stabilized, the adsorption / desorption element is subjected to a second programmed heating and cooling process under preset parameters to obtain a desorption resistance response generated on the gas sensor element by the target gas desorbed by the adsorption / desorption element during the second programmed heating and cooling process;

[0093] S5: According to the temperature signal of the adsorption / desorption film and the gas-sensitive film resistance response generated by gas desorption, the gas desorption peak temperature and height are obtained, and the gas type and concentration are output.

[0094] Figure 6 The signals collected by the single-element coplanar dual-cantilever micro-hotplate gas sensor during the entire test process under clean air conditions include the temperature signal of the adsorption / desorption element and the resistance signal of the gas sensing element.

[0095] Figure 5 This is the test process of the sensor under the condition of no clean air. When the gas concentration is not enough to make the adsorption and desorption material quickly adsorb and saturate, the sensor can be placed in the gas environment to be tested. The adsorption amount of the adsorption and desorption element can be controlled by the temperature and time of the low-temperature adsorption of the adsorption and desorption element. The difference between the target gas concentration during programmed temperature desorption and the ambient target gas concentration is used to obtain the desorption peak height generated by the concentration difference on the gas sensor element for detection. This test process is a periodic process, and one cycle is as follows:

[0096] S1: performing gas adsorption on the adsorption-desorption element at a first relatively low preset temperature for a preset time (adjustable);

[0097] S2: After the adsorption is completed, the adsorption and desorption elements are programmed to increase and decrease the temperature under the preset parameters;

[0098] S3: obtaining a desorption resistance response generated on the gas sensor element by the target gas desorbed from the adsorption / desorption element during the programmed heating and cooling process;

[0099] S4: According to the temperature signal of the adsorption / desorption film and the gas-sensitive film resistance response generated by gas desorption, the gas desorption peak temperature and height are obtained, and the gas type and concentration are output.

[0100] The next cycle starts after the resistance of the gas sensor element stabilizes.

[0101] Figure 7 These are the signals collected by the single-element coplanar dual-cantilever micro-hotplate gas sensor during three test cycles under clean air conditions, including the temperature signal of the adsorption / desorption element and the resistance signal of the gas sensing element.

[0102] The performance of the MEMS gas sensor and the gas detection method are described below in conjunction with specific embodiments. The test procedures of embodiments 1-4 are all performed according to the test procedures under clean air.

[0103] Example 1

[0104] This embodiment is a single-element coplanar dual-cantilever micro-hotplate gas sensor. The composition of the sensor and the gas detection method are as follows:

[0105] The adsorption and desorption material of the adsorption and desorption element is ZSM-5, and the gas sensitive material of the gas sensor element is Pt@SnO2. The preset initial temperature of the adsorption and desorption element of the sensor is 60°C. The heating rate during the programmed heating process is 10°C / s, the cooling rate is 100°C / s, the high temperature is 400°C, the holding time is 2 seconds, and the low temperature is 60°C. The holding process ends after the resistance value of the gas sensor element stabilizes. The preset temperature of the gas sensor element is 400°C and remains constant.

[0106] The gas detection method of embodiment 1 is based on Figure 4 The detection process in .

[0107] Figure 8 The original signal of 200ppm ethanol is tested in the programmed temperature desorption analysis process of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor of Example 1, including the temperature signal of the adsorption and desorption element and the resistance signal of the gas sensor element; after the adsorption and desorption element completes the first programmed temperature desorption procedure, ethanol adsorption is performed, and the adsorption time is 5 seconds. In this structure, ethanol can enter through the porous microcavity and directly contact the gas-sensitive membrane. Therefore, in the process of the adsorption and desorption membrane adsorbing ethanol, the gas sensor element exhibits a resistance response of ethanol. After the resistance of the gas sensor unit is restored to stability, the adsorption and desorption element performs a second programmed temperature desorption procedure. In this process, although the sensor is in a clean air environment, the ethanol desorbed from the adsorption and desorption membrane still produces a large resistance response on the gas-sensitive membrane, and as the ethanol concentration diffuses, the resistance of the gas-sensitive membrane quickly recovers, thereby forming a peak height signal.

[0108] Fig. 9 This is the programmed temperature desorption curve of the single-element coplanar dual-cantilever micro-hotplate gas sensor in Example 1 with or without ethanol. The horizontal axis is the temperature change of the adsorption and desorption element during the second programmed temperature increase process, and the vertical axis is the resistance change of the gas sensor element during the process. It can be seen that in the absence of ethanol, the resistance of the gas sensor element does not change with the change of the temperature of the adsorption and desorption element, and is basically stable at a constant value during the heating and cooling of the adsorption and desorption element. In the ethanol environment, due to the appearance of the desorption signal, the resistance of the gas sensor element presents a peak shape during the heating and cooling of the adsorption and desorption element, and the temperature of the adsorption and desorption element corresponding to its peak value (when the resistance is minimum) is the desorption peak temperature, that is, the optimal desorption temperature of ethanol. At the same time, the resistance value R of the gas sensor element in the absence of ethanol corresponding to the desorption peak temperature of the adsorption and desorption element during the heating and cooling process is taken. 升温 and R 降温 , it can be obtained that when there is no ethanol, the value is 1, that is, the zero point of the sensor is 1, then the calculation method of the desorption peak height of the sensor is: (R 降温 / R 升温 ).

[0109] Fig.10 This is the programmed temperature desorption curve of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor for different concentrations of ethanol in Example 1. It can be seen that in the environment of different ethanol concentrations of 5-200ppm, the desorption peak height of the sensor increases monotonically with the change of ethanol concentration, and is much higher than the zero point value of the sensor, with obvious concentration recognition ability.

[0110] Fig.11aThis is the relationship between the ethanol desorption peak height and the ethanol concentration of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor in Example 1. It can be seen that when the ethanol concentration is zero, its value is 1, indicating that the zero point of the sensor is an absolute zero point. When there is no ethanol in the environment, the zero point is a fixed value, that is, the starting point of the sensor's sensitivity curve is a fixed value and is not affected by environmental factors.

[0111] Fig.11b This is the relationship between the resistance of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor and the formaldehyde concentration in Example 1. When the formaldehyde concentration is zero, it can be seen that the resistance of the gas sensor element is R0, which is the reference resistance value of the sensor. It is a relative zero point and is closely related to the material properties, environmental factors, aging effects, etc. In the absence of target gas, the change in resistance value affected by the environment is greatly affected by factors such as the environment. Therefore, the zero point obtained based on the on-chip programmed temperature analysis method makes the sensor extremely stable.

[0112] Example 2

[0113] The composition of the sensor and the gas detection process of Example 2 are the same as those of Example 1, and the desorption peak height processing method is also the same as that of Example 1, which will not be repeated here.

[0114] In Example 2, the adsorption and desorption material of the adsorption and desorption element is selected as ZSM-5, and the gas-sensitive material of the gas sensor element is selected as Pt@SnO2. The preset initial temperature of the adsorption and desorption element of the sensor is 60°C, the heating rate during the programmed heating process is 5°C / s, the cooling rate is 200°C / s, the high temperature is 400°C, the holding time is 2 seconds, and the low temperature is 60°C. The holding process ends after the resistance value of the gas sensor element stabilizes. The preset temperature of the gas sensor element is 400°C and remains constant.

[0115] Fig.12 The original signals of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor in Example 2 tested 200ppm ethanol and 200ppm methanol, including the temperature signal of the adsorption / desorption element and the resistance signal of the gas sensor element. As an example, in the adsorption stage of the adsorption / desorption element, it can be obviously seen that the resistance of the gas sensor element shows a large response, while in the second programmed temperature desorption process of the adsorption / desorption element, the resistance response generated by the desorption of methanol is significantly reduced, and is very different from that of ethanol.

[0116] Fig.13 The temperature-programmed desorption curves of the single-element coplanar dual-cantilever micro-hotplate gas sensor in Example 2 in clean air and 40 ppm ethanol, H2S, acetone, hydrogen, SO2, ammonia, CO, and methanol environments are shown. It can be seen that the zero point of the sensor is 1, which is basically the same as Example 1.

[0117] Fig.14 This is the desorption peak height of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor in Example 2 under all gas environments. It can be seen that the desorption peak height of the sensor for gases other than ethanol is much smaller than that for ethanol, indicating that the desorption peak height extracted based on the on-chip programmed temperature analysis method has extremely high selectivity.

[0118] Example 3

[0119] The composition of the sensor of Example 3 and the gas detection process of Example 1 are the same, and the desorption peak height processing method is also the same as that of Example 1, which will not be repeated here.

[0120] In Example 3, the adsorption and desorption material of the adsorption and desorption element is selected as ZSM-5, and the gas-sensitive material of the gas sensor element is selected as Pt@SnO2. The preset initial temperature of the adsorption and desorption element of the sensor is 50°C, the heating rate during the programmed heating process is 50°C / s, the cooling rate is 100°C / s, the high temperature is 400°C, the holding time is 1 second, and the low temperature is 50°C. The holding process ends after the resistance value of the gas sensor element stabilizes. The preset temperature of the gas sensor element is 400°C and remains constant.

[0121] Fig.15 The resistance values ​​of the gas sensing element of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor in Example 3 under different formaldehyde concentration environments show that the sensor has a good resistance response to formaldehyde.

[0122] Fig.16 This is the original signal of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor in Example 3 testing 100 ppb formaldehyde at adsorption times of 10 s and 180 s, including the adsorption and desorption element temperature signal and the gas sensor element resistance signal. It can be clearly seen that for the same concentration of formaldehyde, the longer the adsorption time, the more obvious the desorption resistance response.

[0123] Fig.17a and 17b The resistance response of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor in Example 3 to formaldehyde tests at different concentrations, the relationship between the desorption peak height of the gas sensor element and the concentration at adsorption times of 10s and 180s, and the fitting curve; the response value of the detection limit is set to 1.2, and it can be seen that when the adsorption time is 10 seconds, the detection limit concentration of the sensor based on the programmed temperature analysis method is about 370ppb, which is less than the 100ppb of the traditional resistance response, and when the adsorption time is 180 seconds, its detection limit concentration is 10ppb, which is much lower than the detection limit of the conventional resistance response, indicating that the detection ability of the sensor to the target gas can be greatly reduced based on the programmed temperature analysis method.

[0124] Example 4

[0125] The composition of the sensor and the gas detection process of Example 4 are the same as those of Example 1, and the desorption peak height processing method is also the same as that of Example 1, which will not be repeated here.

[0126] In Example 4, the adsorption and desorption material of the adsorption and desorption element is selected as ZSM-5, and the gas-sensitive material of the gas sensor element is selected as Pt@SnO2. The preset initial temperature of the adsorption and desorption element of the sensor is 50°C, the heating rate during the programmed heating process is 10°C / s, the cooling rate is 100°C / s, the high temperature is 400°C, the holding time is 5 seconds, and the low temperature is 50°C. The holding process ends after the resistance value of the gas sensor element stabilizes. The preset temperature of the gas sensor element is 400°C and remains constant.

[0127] Fig.18 This is the resistance response curve of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor to 0.5%-60% concentration ethanol solution according to the preferred embodiment 4 of the present invention. It can be seen that based on the traditional resistance response, the sensor has almost no resolution for ethanol solution with a concentration greater than 0.5%, and the response is in a saturated state.

[0128] Fig.19 The original test curve and programmed temperature desorption curve of the single-element coplanar dual-cantilever structure micro-hotplate gas sensor for 0.5%-60% concentration ethanol solution according to the preferred embodiment 4 of the present invention are shown in the figure. The time for the adsorption and desorption element to adsorb ethanol is 2 seconds. The desorption peak heights produced by different high-concentration ethanol solutions are significantly different, and increase with the increase of solution concentration.

[0129] Fig. 20 The resistance response and desorption peak height of the gas sensor element of the single-element coplanar dual-cantilever micro-hotplate gas sensor according to the preferred embodiment of the present invention are compared to 0.5%-60% ethanol solution. It can be seen that the sensor's resistance response to high-concentration ethanol solution is basically saturated, while the desorption peak heights of different high-concentration ethanol solutions show obvious resolution, indicating that the program temperature analysis method can greatly increase the upper limit of the sensor's detection concentration of the target gas.

[0130] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A MEMS gas sensor, characterized in that: It includes a micro cavity with holes, an adsorption and desorption element and a gas sensing element, wherein: The adsorption / desorption element and the gas sensing element are arranged in a micro cavity with holes; The adsorption and desorption element is used to adsorb and desorb the target gas based on temperature changes; The gas sensor element is used to output a corresponding electrical signal according to the target gas concentration.

2. The MEMS gas sensor according to claim 1, characterized in that: The adsorption and desorption of the target gas are achieved by the adsorption and desorption membrane in the adsorption and desorption element, and the ratio of the volume of the adsorption and desorption membrane to the volume of the micro cavity with holes is greater than 1*10 -7 .

3. The MEMS gas sensor according to claim 1, characterized in that: The ratio of the cross-sectional area of ​​the hole on the micro cavity with holes to the internal volume of the micro cavity with holes is less than 200m -1 .

4. The MEMS gas sensor according to claim 1, wherein: The adsorption / desorption element comprises a first micro-hot plate and an adsorption / desorption film arranged on the first micro-hot plate, wherein the first micro-hot plate comprises an insulating substrate and a heating electrode and a temperature measuring electrode arranged on the insulating substrate; The gas sensing element comprises a second micro-hotplate and a gas-sensitive film arranged on the second micro-hotplate, wherein the second micro-hotplate comprises an insulating substrate and a heating electrode, a temperature measuring electrode and a measuring electrode arranged on the insulating substrate, wherein the measuring electrode is used to measure the resistance of the gas-sensitive film.

5. The MEMS gas sensor according to claim 4, characterized in that: The micro cavity with holes is provided with a packaging structure outside, and the packaging structure is provided with a hole; A support structure is provided in the packaging structure, and the support structure includes a lower gasket, an upper gasket and an upper cover arranged in sequence from bottom to top, the lower gasket is fixed to the lower part of the packaging structure, and the upper cover is provided with a through hole; The adsorption / desorption element and the gas sensor element are both arranged between the lower gasket and the upper gasket, and the cavity formed by the adsorption / desorption element, the upper side of the gas sensor element, the upper gasket and the upper cover is a micro cavity with holes.

6. The MEMS gas sensor according to claim 5, characterized in that: The first micro-hotplate and the second micro-hotplate are both cantilever structures.

7. The MEMS gas sensor according to claim 5, characterized in that: The first micro-hotplate is a suspended membrane structure, a hole is opened in the central area of ​​the insulating base of the first micro-hotplate, and the second micro-hotplate is a cantilever structure; a partition is provided in the middle of the upper gasket to separate the upper cavities of the first micro-hotplate and the second micro-hotplate, and the through hole of the upper cover is opened on one side of the cavity formed by the first micro-hotplate and the upper gasket.

8. The MEMS gas sensor according to any one of claims 1 to 7, characterized in that: The number of the adsorption / desorption elements and the gas sensor elements is no less than one, and they are arranged in an array.

9. A gas detection method based on temperature desorption analysis using the MEMS gas sensor according to any one of claims 1 to 8, characterized in that: The steps include: The sensor is placed in the environment to be detected, and the adsorption-desorption element adsorbs the target gas at a preset temperature for a preset time; After the adsorption is completed, the adsorption-desorption element is heated up and then cooled down to the preset temperature. The target gas desorbed by the adsorption-desorption element generates a response on the gas sensor element, and the temperature of the adsorption-desorption element and the electrical signal of the gas sensor element during the heating and cooling process are obtained; The adsorption and desorption element temperature corresponding to the maximum change amplitude of the gas sensor element electrical signal is taken as the desorption peak temperature, the gas sensor element electrical signal corresponding to the desorption peak temperature during the heating process is the heating signal, and the gas sensor element electrical signal corresponding to the desorption peak temperature during the cooling process is the cooling signal, and the ratio of the cooling signal to the heating signal is taken as the desorption peak height; The gas type and concentration are determined based on the desorption peak temperature and height.

10. The gas detection method based on temperature rising desorption analysis according to claim 9, characterized in that: Determine the gas type and concentration based on the detected desorption peak temperature and height, including: The desorption peak temperature of the target gas and the calibration curve of the relationship between the desorption peak height and the target gas concentration are obtained in advance through the sensor; If the detected desorption peak temperature is consistent with the desorption peak temperature of the target gas, it is judged that the detection environment is the target gas, otherwise it is other gases; When the target gas is in the detection environment, the concentration of the target gas in the detection environment is determined according to the detected desorption peak height and the calibration curve.

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