MEMS chip and gas sensor

Abstract

An MEMS chip (100) and a gas sensor. The MEMS chip (100) comprises: a capacitive structure (2), a hygroscopic layer (1) and a heating structure (3), wherein the capacitive structure (2) comprises a top electrode (21) and a bottom electrode (22) that are spaced apart from each other, and an air gap (23) is formed between the top electrode (21) and the bottom electrode (22); the hygroscopic layer (1) is arranged on the side of the top electrode (21) that is away from the bottom electrode (22), and is in communication with the air gap (23), and the hygroscopic layer (1) is used for air permeability and moisture absorption; and the heating structure (3) is arranged on the side of the capacitive structure (2) that is away from the hygroscopic layer (1), and the heating structure (3) is used for heating the capacitive structure (2) and the hygroscopic layer (1). Thus, the MEMS chip has higher detection accuracy when applied to gas detection.

Description

MEMS chip and gas sensor

[0001] The present disclosure claims priority to the Chinese patent application No. 202411354907.8, filed on September 26, 2024, and entitled "MEMS chip and gas sensor", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present disclosure relates to the technical field of gas detection, and more particularly, to a MEMS chip and a gas sensor. BACKGROUND

[0003] With the development of technology, people are increasingly concerned about environmental pollution caused by potentially harmful substances, which can affect our physical health, quality of life, life safety and the operation of industrial processes, which has led to a significant increase in the research of micro, low-cost gas detection devices.

[0004] At present, there are various types of gas detection devices based on different detection mechanisms, mainly including catalytic, electrochemical, metal oxide semiconductor (MOS), selective gas adsorption capacitive, optical / infrared, surface acoustic wave, thermal conductivity, etc. detection principles containing active sensitive materials.

[0005] Among them, the detection device of the selective gas adsorption capacitive type mainly uses dielectric materials with selective gas adsorption properties, making the product have the advantages of high sensitivity, fast response, low power consumption, easy miniaturization, etc. However, it has great humidity cross-sensitivity, resulting in low precision of the detection device.

[0006] Therefore, there is an urgent need to design a gas detection device with higher precision. SUMMARY

[0007] An object of the present disclosure is to provide a new technical solution of a MEMS chip and a gas sensor to at least solve one of the problems in the background art.

[0008] According to a first aspect of the present disclosure, a MEMS chip is provided, comprising:

[0009] a capacitive structure, the capacitive structure comprising a top electrode and a bottom electrode arranged in a spaced manner, an air gap being formed between the top electrode and the bottom electrode;

[0010] a hygroscopic layer, the hygroscopic layer being arranged on a side of the top electrode away from the bottom electrode and being in communication with the air gap, the hygroscopic layer being used for air-permeable and hygroscopic;

[0011] a heating structure, the heating structure being arranged on a side of the capacitive structure away from the hygroscopic layer, the heating structure being used for heating the capacitive structure and the hygroscopic layer.

[0012] Optionally, the heating structure comprises a heating device, an upper insulating layer and a lower insulating layer.

[0013] The upper insulating layer is arranged on a side of the capacitor structure away from the moisture absorbing layer, the lower insulating layer is arranged on a side of the upper insulating layer away from the capacitor structure, and the heating device is arranged between the upper insulating layer and the lower insulating layer.

[0014] Optionally, the heating structure further comprises a heat-conducting layer, the heat-conducting layer covers the capacitor structure, and the temperature of the heating device can be conducted to the capacitor structure.

[0015] Optionally, the device further comprises a substrate and a heat insulation structure, the substrate is arranged on a side of the heating structure away from the capacitor structure, and the heat insulation structure is arranged between the heating structure and the substrate.

[0016] Optionally, the device further comprises a substrate, the substrate is arranged on a side of the heating structure away from the capacitor structure, and the substrate comprises a first substrate and a second substrate arranged outside the first substrate.

[0017] The first substrate covers the capacitor structure, the temperature of the heating device can be conducted to the capacitor structure, the second substrate is connected to the first substrate through the heating structure, and the heating device does not exceed the first substrate.

[0018] Optionally, the thickness of the first substrate is less than the thickness of the second substrate, and the second substrate is connected to the first substrate through a plurality of connecting beams.

[0019] Optionally, the heating structure further comprises a temperature sensor, the temperature sensor is arranged between the upper insulating layer and the lower insulating layer, and is used for measuring the temperature of the capacitor structure.

[0020] Optionally, the capacitor structure further comprises a support layer, the support layer is arranged between the top electrode and the moisture absorbing layer.

[0021] The top electrode and the support layer are provided with a plurality of through holes communicating with the moisture absorbing layer and the air gap, and the size ratio of the through holes to the thickness of the support layer is less than 1 / 2.

[0022] Optionally, the capacitor structure further comprises a spacer, the spacer is arranged in the air gap, and two ends of the spacer are connected to the top electrode and the bottom electrode respectively.

[0023] Optionally, the moisture absorbing layer is made of a polymer, a ceramic, a metal oxide, a nano material or a porous material.

[0024] According to a second aspect of the present disclosure, a gas sensor is provided, comprising the MEMS chip of the first aspect.

[0025] Optionally, further comprising a substrate, a package shell and an ASIC chip;

[0026] The package shell is arranged on the substrate and forms a containing cavity with the substrate, the package shell is provided with a ventilation hole communicating with the containing cavity, and the MEMS chip and the ASIC chip are both arranged on the substrate and located in the containing cavity.

[0027] According to one embodiment of the present disclosure, by arranging a moisture absorption layer on one side of the capacitor structure, and the moisture absorption layer is in communication with the air gap between the top electrode and the bottom electrode, and arranging a heating structure on the other side of the capacitor structure, so that when the MEMS chip is applied to gas detection, the moisture absorption layer and the gas in the air gap can be dehydrated by the heating structure, avoiding the influence of humidity on gas detection, and improving the detection accuracy.

[0028] Other features and advantages of the present disclosure will become apparent from the following detailed description of exemplary embodiments thereof, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0029] The accompanying drawings incorporated in and forming a part of the specification, illustrate embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0030] FIG. 1 is a structural schematic diagram of a MEMS chip provided by the present disclosure.

[0031] FIG. 2 is a structural schematic diagram of a MEMS chip provided by the present disclosure.

[0032] FIG. 3 is one of the top views of FIG. 2.

[0033] FIG. 4 is another top view of FIG. 2.

[0034] FIG. 5 is a structural schematic diagram of a MEMS chip provided by the present disclosure.

[0035] FIG. 6 is a top view of FIG. 5.

[0036] FIG. 7 is a structural schematic diagram of a MEMS chip provided by the present disclosure.

[0037] FIG. 8 is a top view of FIG. 7.

[0038] FIG. 9 is a detection principle step diagram of a MEMS chip provided by the present disclosure.

[0039] FIG. 10 is a corresponding timing waveform diagram of FIG. 9.

[0040] Fig. 11 is a structural schematic diagram of a gas sensor provided by the present disclosure.

[0041] Legend: 100, MEMS chip; 1, moisture absorption layer; 2, capacitor structure; 21, top electrode; 22, bottom electrode; 23, air gap; 24, support layer; 25, via hole; 26, spacer; 3, heating structure; 31, heating device; 32, upper insulating layer; 33, lower insulating layer; 34, heat conduction layer; 4, substrate; 41, first substrate; 42, second substrate; 43, connecting beam; 5, thermal insulation structure; 9, pad; 200, base plate; 300, package shell; 301, air hole; 400, ASIC chip. DETAILED DESCRIPTION

[0042] Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. Note that the relative arrangement, numerical expressions, and numerical values of components and steps set forth in these embodiments are not limiting to the scope of the present disclosure unless otherwise specifically stated.

[0043] The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the present disclosure or its application or uses.

[0044] Techniques, methods, and apparatus known to those of ordinary skill in the relevant art can not be discussed in detail herein, but should be considered as part of the specification, where appropriate.

[0045] In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary, and not as a limitation. Thus, other examples of the exemplary embodiments can have different values.

[0046] Note that like reference numerals and letters refer to like items in the following drawings, and thus, once an item is defined in one drawing, it need not be discussed further in subsequent drawings.

[0047] In practical applications, the gas sensor can identify or detect toxic and flammable chemicals in different environments to ensure the safety of the environment. Among them, the capacitive gas sensor usually uses dielectric materials with selective gas adsorption properties. Based on the slight difference in the dielectric constant of various gases, especially the higher the refrigeration efficiency of the refrigerant gas, the larger the dielectric constant, which will cause the capacitance of the high dielectric constant gas in the air to increase, but the content of a large amount of gas in the air is not stable, especially water vapor which has a greater impact on the dielectric constant. Therefore, the MEMS chip provided by the present disclosure mainly improves the detection accuracy of the MEMS chip from the aspect of eliminating environmental humidity.

[0048] As shown in FIGS. 1-10, according to a first aspect of the present disclosure, a MEMS (Micro-Electro-Mechanical Systems) chip 100 is provided, comprising: a capacitor structure 2, a moisture absorption layer 1, and a heating structure 3; the capacitor structure 2 comprises a top electrode 21 and a bottom electrode 22 arranged at intervals, and an air gap 23 is formed between the top electrode 21 and the bottom electrode 22; the moisture absorption layer 1 is arranged on the side of the top electrode 21 away from the bottom electrode 22 and is in communication with the air gap 23, and the moisture absorption layer 1 is used for moisture absorption and air permeation; and the heating structure 3 is arranged on the side of the capacitor structure 2 away from the moisture absorption layer 1, and the heating structure 3 is used for heating the capacitor structure 2 and the moisture absorption layer 1.

[0049] Specifically, in the present embodiment, the MEMS chip 100 adopts the form of the capacitor structure 2 plus the moisture absorption layer 1 and the heating structure 3 arranged on both sides, so that when it is applied to gas detection, the capacitor structure 2 and the moisture absorption layer 1 can be heated to a dehydration temperature (for example, 150-200°C) by the heating structure 3, and the air gap 23 in the capacitor structure 2 and the moisture absorption layer 1 are continuously heated to be dehydrated. After the moisture absorption layer 1 is completely dehydrated, the capacitor structure 2 can be cooled to a set temperature, and multiple capacitance detections are performed, and then the specific type of gas is determined according to the formula C=ε r ·ε0·A / d (wherein ε r is the relative dielectric constant, ε0 is the vacuum dielectric constant, A is the area of the plate electrode, and d is the air gap 23. Here, ε0, A, and d are all constants, and only ε r The vacuum dielectric constant ε0 of the gas is determined according to the type, content, and environment of the gas, and then the specific type of the gas is determined, as shown in FIGS. 9-10.

[0050] The moisture absorption layer 1 can adopt a moisture absorption film layer with a thickness of 1-25 um, and the material can be selected from polymers, ceramics, metal oxides, nanomaterials, or porous materials that are easy to absorb water vapor (hereinafter referred to as film). The above-mentioned materials have good air permeability, and the film layer is thin, so that the air permeation response time is about 1 ms or less. The water vapor passing through the film is limited by the condensation and diffusion speed of water molecules in the micro-nano or even molecular size capillary system in the material, and is usually much slower. For example, taking a 10 um thick PI (Polyimide) and a 0.2 um air gap (air gap distance) as an example, when the two sides are simultaneously moisture-absorbed, the time required to reach saturation at normal temperature and pressure can be as long as 10 s or more, and the amount of water absorbed in the film at saturation can reach 0.5-3 wt% (weight ratio to solid PI), which is 2-3 orders of magnitude higher than the saturated water vapor content in air.

[0051] Based on this, since the moisture absorption process of the moisture absorption layer 1 is relatively slow, it can be considered that the moisture absorption process has just started, but the air permeation process has been completed, that is, there is no water vapor in the moisture absorption layer 1, and the humidity and each gas component inside and outside the moisture absorption layer 1 have reached equilibrium. At this time, the detection of the vacuum dielectric constant of the gas eliminates the influence of water vapor in the gas, and improves the detection accuracy and stability of the MEMS chip 100. Among them, the detection of the capacitance can be performed after the capacitance structure 2 is cooled to a set temperature, and the influence of temperature is eliminated, further improving the detection accuracy. In addition, the moisture absorption layer 1 in the present disclosure is in communication with the air gap 23 of the capacitance structure 2, which is also convenient for the gas in the air gap 23 to be able to convect with the gas outside the MEMS structure to reach a balanced state.

[0052] Further, in the above structure, the top electrode 21 can adopt a low-stress doped polysilicon material with high mechanical strength, thermal conductivity and electrical conductivity, and the thickness is selected to be 0.3um-1um. The bottom electrode 22 can adopt a low-stress doped polysilicon, tungsten, tantalum nitride or the like, and the thickness is selected to be 0.1um-0.5um. The spacing between the top electrode 21 and the bottom electrode 22 (i.e. the thickness dimension of the air gap 23) is selected to be 0.05um-2um. In addition, one side of the heating structure 3 can be provided with a heat conduction structure and a substrate 4 to transfer heating and cooling to the capacitance structure 2 and the moisture absorption layer 1. The heat conduction structure can realize the uniformity of temperature transfer. In one embodiment, the heat conduction structure can be realized by thinning the substrate 4 to simplify the MEMS structure.

[0053] Optionally, as shown in FIGS. 1, 2, 5 and 7, the heating structure 3 includes a heating device 31, an upper insulating layer 32 and a lower insulating layer 33. The upper insulating layer 32 is arranged on the side of the capacitance structure 2 away from the moisture absorption layer 1, and the lower insulating layer 33 is arranged on the side of the upper insulating layer 32 away from the capacitance structure 2. The heating device 31 is arranged between the upper insulating layer 32 and the lower insulating layer 33.

[0054] Specifically, in this embodiment, the two sides of the heating structure 3 realize electrical insulation with the upper and lower devices through the upper insulating layer 32 and the lower insulating layer 33, so as to avoid short circuit between the heating device 31 and the conductive structure, thereby improving the reliability of the heating device 31 for heating the capacitance structure 2 and the moisture absorption layer 1. Among them, the heating device 31 can adopt a resistance heater or a thermal element, etc., which is arranged between the upper insulating layer 32 and the lower insulating layer 33, to ensure the reliability and uniformity of heating. In addition, the upper insulating layer 32 and the lower insulating layer 33 can be made of low-stress silicon nitride or silicon oxide, which has good insulation performance, and the thickness can be set to 0.1um-0.5um to meet the design requirements.

[0055] Optionally, referring to FIG. 1, FIG. 2, FIG. 5 and FIG. 7, the heating structure 3 further comprises a temperature sensor, which is arranged between the upper insulating layer 32 and the lower insulating layer 33, and is used to measure the temperature of the capacitor structure 2.

[0056] Specifically, the temperature sensor can also be arranged between the upper insulating layer 32 and the lower insulating layer 33 to detect the temperature of the capacitor structure 2 in real time, so as to facilitate the control of the working state of the heating structure 3 and the determination of the detection timing of the capacitor, and further improve the accuracy of the detection of the MEMS chip 100. The temperature sensor, the capacitor structure and the heating device can all be connected to external devices through the pads 9 arranged on the substrate or the upper insulating layer.

[0057] Optionally, as shown in FIG. 7, the heating structure 3 further comprises a heat-conducting layer 34, which covers the capacitor structure 2, so that the temperature of the heating device 31 can be conducted to the capacitor structure 2.

[0058] Specifically, in actual application, the heat-conducting layer 34 can be arranged on the upper side or the lower side of the heating device 31, so that the temperature heated by the heating device 31 can be uniformly transmitted to the capacitor structure 2 and even to the hygroscopic layer 1, thereby realizing the dehydration of the hygroscopic layer 1. Wherein, the covering of the capacitor structure 2 by the heat-conducting layer 34 means that the projection of the heat-conducting layer 34 on the capacitor structure 2 completely covers the capacitor structure 2, so that the heating temperature of the heating device 31 can be quickly and uniformly transmitted to all parts of the capacitor structure 2, and further transmitted to the hygroscopic layer 1 from the capacitor structure 2, so that the dehydration speed of each part of the hygroscopic layer 1 is similar, and the detection accuracy of the capacitor is improved.

[0059] In an embodiment, the heat-conducting layer 34 can be embedded in the lower insulating layer 33 at a position corresponding to the capacitor structure 2, so as to reduce the overall thickness of the heating structure 3. Wherein, the heat-conducting layer 34 can adopt a high-doped low-stress polysilicon thin film heat-conducting layer 34 with high thermal conductivity. For example, the doping concentration is 10 20 / cm 3 The tensile stress is 0-50 MPa, and the thickness is 0.5-5 um, so as to maintain the uniformity of the temperature.

[0060] Optionally, as shown in FIG. 7, the MEMS chip 100 further comprises a substrate 4 and a heat-insulating structure 5, the substrate 4 is arranged on the side of the heating structure 3 away from the capacitor structure 2, and the heat-insulating structure 5 is arranged between the heating structure 3 and the substrate 4.

[0061] Specifically, in the embodiment, the lower side of the heating structure 3 is also provided with a substrate 4 to play a certain manufacturing role for the whole MEMS chip 100, facilitating the assembly with other devices. The substrate 4 can be made of silicon or polysilicon to improve the support strength of the MEMS chip 100. Based on the fact that the substrate 4 has a certain transmission effect on the temperature of the heating structure 3, in order to avoid temperature loss, the heat insulation structure 5 is arranged between the heat conduction layer 34 and the substrate 4, so that the heating temperature of the heating structure 3 is mostly transmitted to the capacitor structure 2 and the moisture absorption layer 1, avoiding its transmission to the substrate 4, and reducing the energy consumption of the heating structure 3.

[0062] In an embodiment, the heat insulation structure 5 has a heat insulation surface layer in contact with the heat conduction structure and a plurality of columnar structures connected with the substrate 4, and the outer periphery of the heating structure 3 is sealingly connected with the outer periphery of the substrate 4 to form a vacuum sealed cavity. The heat insulation surface layer and the substrate 4 are connected and supported by the columnar structures in the vacuum sealed cavity. This form can ensure that the heating temperature of the heating device 31 is transmitted to the capacitor structure 2, so as to meet the requirements of heat resistance, power consumption and response speed.

[0063] Optionally, as shown in FIGS. 1-6, the MEMS chip 100 further includes a substrate 4 arranged on the side of the heating structure 3 away from the capacitor structure 2. The substrate 4 includes a first substrate 41 and a second substrate 42 arranged outside the first substrate 41. The first substrate 41 covers the capacitor structure 2, so that the temperature of the heating device 31 can be conducted to the capacitor structure 2. The second substrate 42 is connected with the first substrate 41 through the heating structure 3, and the heating device 31 does not exceed the first substrate 41.

[0064] Specifically, in the embodiment, referring to FIG. 3, the first substrate 41 is also used as the heat conduction layer 34 of the heating structure, and the structure of the heat conduction layer 34 is omitted, simplifying the heating structure 3, and the second substrate 42 plays a certain supporting role. The first substrate 41 covers the capacitor structure 2 to ensure that the heating temperature of the heating structure 3 can be uniformly transmitted to the capacitor structure 2. The first substrate 41 and the second substrate 42 are arranged at intervals to avoid the heating temperature of the heating structure 3 being transmitted to the second substrate 42. Meanwhile, the first substrate 41 and the second substrate 42 can be connected through the upper insulating layer 32 and the lower insulating layer 33 of the heating structure 3, and the heating device 31 can be arranged only within the range of the first substrate 41, reducing the energy consumption of the heating structure 3.

[0065] In the above embodiment, referring to FIG. 4, in order to further avoid the heating temperature of the heating device 31 from being transmitted to the second substrate 42, the part of the heating structure 3 used for connecting the first substrate 41 and the second substrate 42 can be designed in the form of multiple connecting beams 43, for example, the square-shaped capacitive structure 2 can be connected to the first substrate 41 and the second substrate 42 in the form of four connecting beams 43, which can be designed according to the specific structure, and the present disclosure does not limit this.

[0066] Optionally, referring to FIGS. 2, 4-6, the thickness of the first substrate 41 is less than the thickness of the second substrate 42, and the second substrate 42 is connected to the first substrate 41 through the multiple connecting beams 43.

[0067] Specifically, in the present embodiment, the thickness of the first substrate 41 is less than the thickness of the second substrate 42, that is, the first substrate 41 can be designed as a thinned structure, which can reduce the heat capacity and response speed of the capacitive structure 2 under the premise of ensuring the uniformity of the temperature of the capacitive structure 2. The thickness of the first substrate 41 can be selected as 1-20 μm, for example, 10 μm.

[0068] In an embodiment, as shown in FIG. 6, the first substrate 41 and the second substrate 42 are both made of silicon or polysilicon material, and the first substrate 41 and the second substrate 42 are connected in the form of multiple connecting beams 43, which can be part of the heating structure 3 or connected by multiple connecting beams 43 made of the same material as the first substrate 41 and the second substrate 42. The use of silicon or polysilicon to connect the first substrate 41 and the second substrate 42 can improve the strength of the entire device and improve the reliability of the device.

[0069] Optionally, as shown in FIGS. 1, 2, 5 and 7, the capacitive structure 2 further comprises a support layer 24 disposed between the top electrode 21 and the hygroscopic layer 1; the top electrode 21 and the support layer 24 are provided with multiple through holes 25 communicating the hygroscopic layer 1 and the air gap 23, and the size ratio of the through hole 25 to the thickness of the support layer 24 is less than 1 / 2.

[0070] Specifically, in the present embodiment, the support layer 24 in the capacitive structure 2 can be used to support and connect the hygroscopic layer 1 and the top electrode 21 of the capacitive structure 2, and the multiple through holes 25 are used to communicate the hygroscopic layer 1 and the air gap 23 of the capacitive structure 2, so that the gas in the external environment can flow from the hygroscopic layer 1 to the air gap 23, and at the same time, the gas in the air gap 23 can also flow from the hygroscopic layer 1 to the outside of the MEMS chip 100 through the through hole 25, so as to realize the detection of the gas in the external environment and ensure the safety of the environmental gas. The size ratio of the through hole 25 to the thickness of the support layer 24 is designed to be less than 1 / 2, so as to ensure that the dielectric effect of the medium / environment on the capacitive structure 2 can be ignored, and the accuracy of the detection is ensured.

[0071] In the above embodiment, the support layer 24 can be made of a low-stress high-silicon nitride silicon material with high mechanical strength and high thermal conductivity, so as to ensure the structural strength and the temperature of the capacitor structure 2 can be quickly transmitted to the moisture absorption layer 1. The thickness of the support layer 24 is selected to be 0.5um-2um, and the aperture of the through hole 25 is selected to be 0.1um-1um.

[0072] Optionally, as shown in FIGS. 1, 2, 5 and 7, the capacitor structure 2 further comprises a spacer 26, which is arranged in the air gap 23 and connected to the top electrode 21 and the bottom electrode 22 at both ends.

[0073] Specifically, in the embodiment, the top electrode 21 and the bottom electrode 22 of the capacitor structure 2 can be connected and supported by a plurality of spacers 26, so as to ensure the stability of the capacitor structure 2. The spacer 26 can be made of a low-stress silicon nitride or silicon oxide support, and the thickness thereof is matched with the air gap 23 and selected to be 0.3um-1um.

[0074] According to a second aspect of the present disclosure, as shown in FIGS. 9-11, a gas sensor is provided, comprising the MEMS chip 100 of the first aspect.

[0075] Specifically, as shown in FIG. 11, the gas sensor provided in the embodiment comprises the MEMS chip 100 of the first aspect. Based on the fact that the MEMS chip 100 has a moisture removal function and has a small mass and volume, the gas sensor can remove the influence of humidity on detection accuracy when detecting, thereby improving the detection accuracy of the gas sensor and miniaturizing the volume. The gas sensor can be used to detect the leakage of toxic gas in the environment, such as the leakage of refrigerant of an air conditioner, etc., so as to ensure the safety of the environment.

[0076] Optionally, as shown in FIG. 11, the gas sensor further comprises a substrate 200, a packaging shell 300 and an ASIC (Application-Specific Integrated Circuit) chip 400; the packaging shell 300 is arranged on the substrate 200 and forms a containing cavity with the substrate 200, the packaging shell 300 is provided with a ventilation hole 301 communicating with the containing cavity, and the MEMS chip 100 and the ASIC chip 400 are arranged on the substrate 200 and located in the containing cavity.

[0077] Specifically, the gas sensor is integrated with the MEMS chip 100 by arranging the substrate 200, the packaging shell 300 and the ASIC chip 400, so as to meet the requirements of accurate detection and miniaturization of the gas sensor, and make the gas sensor applicable to more electronic devices or environments.

[0078] The embodiment provides a detection method of a gas sensor for environmental gas, as shown in FIG. 9 and FIG. 10: before time point T0, the capacitor structure 2 is heated by the heating structure 3, and the temperature sensor is used to measure the temperature, so that the temperature reaches a high dehydration temperature, for example, 150-200 DEG C, and the high temperature is maintained to time point T1. Wherein, T1 is greater than the thermal response time constant of the capacitor structure 2, for example, the thermal response constant of the capacitor structure 2 is 0.05-0.5 s, and T1 is 0.5-5 s.

[0079] At time point T1, the capacitor structure 2 starts to cool to a set detection temperature, for example, 50 DEG C. This is time point T2. At this time, due to the relatively slow moisture absorption process of the moisture absorption layer 1, it can be considered that the moisture absorption process has just started, but the air permeation process has been completed, that is, there is no water vapor in the moisture absorption layer 1, and the humidity and each gas component inside and outside the moisture absorption layer 1 have reached equilibrium.

[0080] At time point T3, the moisture absorption process is in a state before saturation, that is, the moisture absorption / diffusion of the inner layer (close to the air gap 23 side) of the moisture absorption layer 1 (hereinafter referred to as the film) has not formed effective “contact” with the moisture absorption / diffusion of the outer layer, for example, when the diffusion coefficient of water vapor in the film is D, and √D·(T3-T2)<(0.1-0.5)·film thickness, the water absorption amount of the inner layer film from the cavity is at least film thickness / 10*saturation water absorption weight ratio of the film, which is about 0.05-0.3wt%*PI density*film thickness>700g / m 3 *film thickness.

[0081] On the other hand, if the air gap: film thickness of the moisture absorption layer 1 is 0.2:10, and the weight ratio of water vapor and air at 50% RH under normal temperature and pressure is about 1.25wt%, that is, the total amount of water vapor in the cavity is not more than 1.25wt%*1184g / m 3 *Air gap~0.30g / m 3 *film thickness, which is far less than the water vapor absorption amount of the inner layer film from the air gap 23, that is, the water vapor in the air gap 23 will be “absorbed” by the film to a relative humidity RH<0.02%. This corresponds to about 20-30ppm detection precision of refrigerant gas R290 or R32, which basically meets the requirements of the leakage detection of such emerging low GWP (Global Warming Potential) and low ODP (Ozone Depletion Potential) refrigerants.

[0082] The capacitance of the capacitance structure 2 is detected immediately after T3, and T4 completes the detection. T4 should be much smaller than T∞, i.e. the time of hygroscopic saturation. In addition, the test can be repeated multiple times between T3 and T4, and the output signal of the test circuit is used as the criterion. That is, one detection cycle includes heating and dehumidifying, cooling and drying the cavity (air gap 23), and detecting the capacitance change, and the total time is about 0.5-10 seconds. For example, if the conventional output of the detection signal is 30 seconds, the average power can be much lower than 0.2 mW, which can meet most application occasions.

[0083] The above detection process is a dynamic dehumidification technology, i.e. at the time point T0 before each detection of the gas, the capacitance structure 2 is heated to a high enough temperature and maintained at a constant temperature to achieve complete dehydration (T1), and then quickly cooled to room temperature or a set detection temperature. At this moment (time point T2), the absolute humidity in the cavity and the ambient air is about the same as usual (e.g. about 1.23wt% water vapor in air at 300K, 50% RH), and each gas component has reached uniformity through the hygroscopic layer 1. After waiting for enough time to T3, the hygroscopic has not reached saturation, i.e. the inner layer of the hygroscopic film (close to the cavity) is still in a state of absorbing limited moisture in the cavity (resulting in a rapid decrease of 2-3 orders of magnitude of the water vapor in the cavity), and the outer layer of the hygroscopic film has not diffused to the bottom layer (T∞, e.g. 10 seconds) before the detection of the gas in the dehumidification detection state (before T4), which can completely eliminate the influence of the ambient humidity and temperature, and achieve the purpose of improving the detection accuracy.

[0084] The above embodiments focus on the differences between the embodiments, and the different optimization features between the embodiments can be combined to form a better embodiment as long as they are not contradictory. Considering the brevity of the writing, it will not be repeated here.

[0085] Although some specific embodiments of the present disclosure have been described in detail through examples, those skilled in the art should understand that the above examples are only for illustration, and are not intended to limit the scope of the present disclosure. Those skilled in the art should understand that the above embodiments can be modified without departing from the scope and spirit of the present disclosure. The scope of the present disclosure is defined by the appended claims.

Claims

1. A MEMS chip, characterized by, The capacitor structure comprises top and bottom electrodes arranged at intervals, and an air gap is formed between the top and bottom electrodes. A moisture absorption layer is arranged on the side of the top electrode away from the bottom electrode and communicates with the air gap, and the moisture absorption layer is used for air-permeable moisture absorption. A heating structure is arranged on the side of the capacitor structure away from the moisture absorption layer, and the heating structure is used for heating the capacitor structure and the moisture absorption layer. The heating structure comprises a heating device, an upper insulating layer and a lower insulating layer.

2. The MEMS chip of claim 1, wherein, The upper insulating layer is arranged on the side of the capacitor structure away from the moisture absorption layer, the lower insulating layer is arranged on the side of the upper insulating layer away from the capacitor structure, and the heating device is arranged between the upper and lower insulating layers. The heating structure further comprises a heat-conducting layer covering the capacitor structure, so that the temperature of the heating device can be conducted to the capacitor structure.

3. The MEMS chip of claim 2, wherein, A substrate and a heat insulation structure are further included, the substrate is arranged on the side of the heating structure away from the capacitor structure, and the heat insulation structure is arranged between the heating structure and the substrate.

4. The MEMS chip of claim 3, wherein, A substrate is further included, the substrate is arranged on the side of the heating structure away from the capacitor structure, and the substrate comprises a first substrate and a second substrate arranged at intervals on the outside of the first substrate.

5. The MEMS chip according to any one of claims 2 to 4, characterized in that, The first substrate covers the capacitor structure, so that the temperature of the heating device can be conducted to the capacitor structure, the second substrate is connected to the first substrate through the heating structure, and the heating device does not exceed the first substrate. The thickness of the first substrate is smaller than the thickness of the second substrate, and the second substrate is connected to the first substrate through a plurality of connecting beams.

6. The MEMS chip of claim 5, wherein, The heating structure further comprises a temperature sensor arranged between the upper and lower insulating layers and used for measuring the temperature of the capacitor structure.

7. The MEMS chip according to any one of claims 2 to 6, characterized in that, The capacitor structure further comprises a support layer arranged between the top electrode and the moisture absorption layer.

8. The MEMS chip according to any one of claims 1 to 7, characterized in that, A plurality of through holes communicating the moisture absorption layer and the air gap are arranged on the top electrode and the support layer, and the size ratio of the through holes to the thickness of the support layer is less than 1 / 2. The capacitor structure further comprises a spacer arranged in the air gap and connected to the top and bottom electrodes at two ends, respectively.

9. The MEMS chip according to claim 7 or 8, characterized in that, The moisture absorption layer is made of a polymer, a ceramic, a metal oxide, a nano material or a porous material.

10. The MEMS chip according to any one of claims 1 to 9, characterized in that, The MEMS chip of any one of claims 1-10 is included.

11. A gas sensor, characterized by A substrate, a packaging shell and an ASIC chip are further included.

12. The gas sensor according to claim 11, characterized by The packaging shell is arranged on the substrate and forms a containing cavity with the substrate, the packaging shell is provided with a ventilation hole communicating with the containing cavity, and the MEMS chip and the ASIC chip are arranged on the substrate and located in the containing cavity. ​

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