MEMS chip and gas sensor

Abstract

The invention discloses an MEMS chip and a gas sensor. The MEMS chip comprises a capacitor structure, a moisture absorption layer and a heating structure, the capacitor structure comprises a top electrode and a bottom electrode which are arranged at an interval, and an air gap is formed between the top electrode and the bottom electrode; the moisture absorption layer is arranged on one side, far away from the bottom electrode, of the top electrode, is communicated with the air gap, and is used for ventilating and absorbing moisture; the heating structure is arranged on the side, away from the moisture absorption layer, of the capacitor structure, and the heating structure is used for heating the capacitor structure and the moisture absorption layer. The MEMS chip provided by the invention has higher detection precision when being applied to gas detection.

Description

Technical Field

[0001] The present application relates to the technical field of gas detection, and more specifically, to a MEMS chip and a gas sensor. Background Art

[0002] With the development of science and technology, people are paying more and more attention to the environmental pollution caused by potentially harmful substances, which may affect our physical health, quality of life, life safety and the operation of industrial processes. This has led to a significant increase in the research of miniature and low-cost gas detection devices.

[0003] At present, there are many types of gas detection equipment based on different detection mechanisms, mainly including catalytic, electrochemical, metal oxide semiconductor MOS, selective gas adsorption capacitive, optical / infrared, surface acoustic wave, thermal conduction and other detection principles containing active sensitive materials.

[0004] Among them, selective gas adsorption capacitive detection equipment mostly uses dielectric materials with selective gas adsorption characteristics, which makes the product have the advantages of high sensitivity, fast response, low power consumption, and easy miniaturization. However, it has great humidity cross-sensitivity, resulting in low accuracy of the detection equipment.

[0005] Based on this, it is urgent to design a gas detection device with higher precision. Summary of the invention

[0006] One object of the present application is to provide a new technical solution for a MEMS chip and a gas sensor to at least solve one of the background technical problems.

[0007] According to a first aspect of the present application, a MEMS chip is provided, comprising:

[0008] A capacitor structure, the capacitor structure comprising a top electrode and a bottom electrode arranged at an interval, and an air gap is formed between the top electrode and the bottom electrode;

[0009] A moisture absorbing layer, the moisture absorbing layer is arranged on a side of the top electrode away from the bottom electrode and is connected to the air gap, and the moisture absorbing layer is used for air permeability and moisture absorption;

[0010] A heating structure is provided on a side of the capacitor structure away from the hygroscopic layer, and is used to heat the capacitor structure and the hygroscopic layer.

[0011] Optionally, the heating structure comprises a heating device, an upper insulating layer and a lower insulating layer;

[0012] The upper insulating layer is arranged on a side of the capacitor structure away from the hygroscopic layer, the lower insulating layer is located 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.

[0013] Optionally, the heating structure further includes a heat-conducting layer, and the heat-conducting layer covers the capacitor structure, so that the temperature of the heating device can be conducted to the capacitor structure.

[0014] Optionally, it further includes a substrate and a heat insulation structure, wherein 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.

[0015] Optionally, it further includes a substrate, the substrate is arranged on a side of the heating structure away from the capacitor structure, and the substrate includes a first substrate and a second substrate spaced apart and arranged outside the first substrate;

[0016] 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 extend beyond the first substrate.

[0017] Optionally, 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 via a plurality of connecting beams.

[0018] Optionally, the heating structure further includes a temperature sensor, which is disposed between the upper insulating layer and the lower insulating layer and is used to measure the temperature of the capacitor structure.

[0019] Optionally, the capacitor structure further comprises a support layer, wherein the support layer is disposed between the top electrode and the moisture absorption layer;

[0020] 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 ratio of the size of the through holes to the thickness of the support layer is less than 1 / 2.

[0021] Optionally, the capacitor structure further includes an isolation member, which is disposed in the air gap and has two ends connected to the top electrode and the bottom electrode, respectively.

[0022] Optionally, the moisture absorbing layer is made of polymer, ceramic, metal oxide, nanomaterial or porous material.

[0023] According to a second aspect of the present application, a gas sensor is provided, comprising the MEMS chip described in the first aspect.

[0024] Optionally, it also includes a substrate, a packaging shell and an ASIC chip;

[0025] The packaging shell is arranged on the substrate and forms a containing cavity with the substrate. The packaging shell is provided with a vent hole connected to the containing cavity. The MEMS chip and the ASIC chip are both arranged on the substrate and located in the containing cavity.

[0026] According to one embodiment of the present application, a hygroscopic layer is provided on one side of the capacitor structure, and the hygroscopic layer is connected to the air gap between the top electrode and the bottom electrode, and a heating structure is provided on the other side of the capacitor structure. When the MEMS chip is used for gas detection, the gas in the hygroscopic layer and the air gap can be dehydrated through the heating structure, thereby avoiding the influence of humidity on gas detection and improving the detection accuracy.

[0027] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0029] Figure 1 This is one of the structural schematic diagrams of the MEMS chip provided in this application.

[0030] Figure 2 This is the second structural schematic diagram of the MEMS chip provided in this application.

[0031] Figure 3 yes Figure 2 One of the top views.

[0032] Figure 4 yes Figure 2 The second top view.

[0033] Figure 5 This is the third structural schematic diagram of the MEMS chip provided in this application.

[0034] Figure 6 yes Figure 5 Top view of the .

[0035] Figure 7 This is the fourth structural schematic diagram of the MEMS chip provided in this application.

[0036] Figure 8 yes Figure 7 Top view of the .

[0037] Fig. 9 This is a diagram of the detection principle steps of the MEMS chip provided in this application.

[0038] Fig.10 yes Fig. 9 The corresponding timing waveform diagram.

[0039] Fig.11 It is a schematic diagram of the structure of a gas sensor provided in this application.

[0040] Description of reference numerals:

[0041] 100. MEMS chip; 1. Hygroscopic layer; 2. Capacitor structure; 21. Top electrode; 22. Bottom electrode; 23. Air gap; 24. Support layer; 25. Through hole; 26. Isolator; 3. Heating structure; 31. Heating device; 32. Upper insulating layer; 33. Lower insulating layer; 34. Heat conducting layer; 4. Substrate; 41. First substrate; 42. Second substrate; 43. Connecting beam; 5. Heat insulation structure; 9. Pad;

[0042] 200, substrate; 300, packaging shell; 301, vent; 400, ASIC chip. DETAILED DESCRIPTION

[0043] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0044] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application, its application, or uses.

[0045] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

[0046] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0047] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0048] In practical applications, gas sensors can identify or detect toxic and flammable chemicals in different environments to ensure environmental safety. Among them, capacitive gas sensors usually use dielectric materials with selective gas adsorption characteristics, based on the slight differences in the dielectric constants of various gases, especially the higher the refrigeration efficiency, the larger the dielectric constant of the refrigerant gas, which will cause the capacitance of the high dielectric constant gas in the air to increase, but the large amount of gas content in the air is not stable, especially the water vapor that has a greater impact on the dielectric constant. Therefore, the MEMS chip provided in this application mainly improves the detection accuracy of the MEMS chip from the aspect of eliminating environmental humidity.

[0049] like Figures 1 to 10 As shown, according to the first aspect of the present application, a MEMS (Micro-Electro-Mechanical Systems) chip 100 is provided, comprising: a capacitor structure 2, a hygroscopic layer 1 and a heating structure 3; the capacitor structure 2 comprises a top electrode 21 and a bottom electrode 22 which are spaced apart, and an air gap 23 is formed between the top electrode 21 and the bottom electrode 22; the hygroscopic layer 1 is arranged on a side of the top electrode 21 away from the bottom electrode 22, and is connected to the air gap 23, and the hygroscopic layer 1 is used for air permeability and moisture absorption; the heating structure 3 is arranged on a side of the capacitor structure 2 away from the hygroscopic layer 1, and the heating structure 3 is used for heating the capacitor structure 2 and the hygroscopic layer 1.

[0050] Specifically, in the present embodiment, the MEMS chip 100 adopts the form of a capacitor structure 2 with a hygroscopic layer 1 and a heating structure 3 respectively arranged on both sides, so that when it is applied to gas detection, the capacitor structure 2 and the hygroscopic layer 1 can be heated to a dehydration temperature (e.g., 150°C to 200°C) by the heating structure 3, and the heating is continued to dehydrate the air gap 23 and the hygroscopic layer 1 in the capacitor structure 2. After the hygroscopic layer 1 is completely dehydrated, the capacitor structure 2 can be cooled to a set temperature, and multiple capacitance tests can be performed, and then through repeated multiple tests, according to the formula C=ε r ·ε0·A / d (where ε r is the relative dielectric constant, ε0 is the vacuum dielectric constant, A is the area of ​​the flat electrode, and d is the air gap 23. Here ε0, A, and d are all constants. r The vacuum dielectric constant ε0 of the gas is determined by the type, content and environment of the gas, and then the specific type of the gas is determined. Figures 9 and 10 .

[0051] Among them, the hygroscopic layer 1 can be made of a hygroscopic film layer with a thickness of 1um to 25um, and the material can be selected from polymers, ceramics, metal oxides, nanometers or porous materials that are easy to absorb water vapor (hereinafter referred to as the hygroscopic layer 1). The above materials have good air permeability and the film layer is thin, so that the air permeability response time is about less than 1ms, and 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-sized capillary system in the material, which is usually much slower. For example, taking 10um thick PI (polyimide) and 0.2um airgap (air gap) as an example, when both sides absorb moisture at the same time, the time required to reach saturation at room temperature and pressure may be as long as 10s or more, and the amount of water absorbed in the film at saturation can reach 0.5-3wt% (weight ratio to solid PI), which is 2-3 orders of magnitude higher than the saturated water vapor in the air.

[0052] Based on this, since the moisture absorption process of the hygroscopic layer 1 is relatively slow, it can be considered that the moisture absorption process has just begun, but the ventilation process has been completed, that is, there is no water vapor in the hygroscopic layer 1, and the humidity and gas components inside and outside the hygroscopic layer 1 have reached equilibrium. At this time, the vacuum dielectric constant of the gas detected 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 capacitance can be carried out after the capacitor structure 2 is cooled to the set temperature, and the influence of temperature is eliminated at the same time, further improving the accuracy of the detection. In addition, the hygroscopic layer 1 in the present application is connected to the air gap 23 of the capacitor structure 2, which is also convenient for the gas in the air gap 23 and the gas outside the MEMS structure to convect with each other to reach a state of equilibrium.

[0053] Furthermore, in the above structure, the top electrode 21 can be made of 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 be made of low stress doped polysilicon, metal tungsten, tantalum nitride and other materials, 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 of the air gap 23) is selected to be 0.05um~2um. In addition, a heat conducting structure and a substrate 4 can be set on one side of the heating structure 3 to transfer heating and processing to the capacitor structure 2 and the hygroscopic layer 1. The heat conducting structure can achieve uniformity of temperature transfer. In one embodiment, the heat conducting structure can be implemented by thinning the substrate 4 to simplify the MEMS structure.

[0054] Alternatively, if Figure 1 , Figure 2 , Figure 5 as well as Figure 7As shown, 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 capacitor structure 2 away from the hygroscopic layer 1, and the lower insulating layer 33 is located on the side of the upper insulating layer 32 away from the capacitor structure 2, and the heating device 31 is arranged between the upper insulating layer 32 and the lower insulating layer 33.

[0055] Specifically, in this embodiment, the two sides of the heating structure 3 are electrically insulated from the upper and lower devices through the upper insulating layer 32 and the lower insulating layer 33 to avoid short circuit between the heating device 31 and the conductive structure, so as to improve the reliability of the heating device 31 for heating the capacitor structure 2 and the hygroscopic layer 1. Among them, the heating device 31 can be a resistive heater or a thermistor, 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 properties, and the thickness can be set at 0.1um to 0.5um to meet the design requirements.

[0056] Optionally, refer to Figure 1 , Figure 2 , Figure 5 as well as Figure 7 The heating structure 3 also includes 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.

[0057] Specifically, a temperature sensor may be provided 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 control the working state of the heating structure 3 and determine the detection timing of the capacitor, thereby further improving the detection accuracy of the MEMS chip 100. The temperature sensor, the capacitor structure and the heating device may be connected to external devices through the pads 9 provided on the substrate or the upper insulating layer.

[0058] Alternatively, if Figure 7 As shown, the heating structure 3 further includes 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 .

[0059] Specifically, in practical applications, a heat-conducting layer 34 may be provided on the upper or lower side of the heating device 31, so that the temperature heated by the heating device 31 can be uniformly transferred to the capacitor structure 2, and even to the hygroscopic layer 1, to achieve a dehydration effect on the hygroscopic layer 1. The heat-conducting layer 34 covers the capacitor structure 2, which 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 transferred to various locations of the capacitor structure 2, and further uniformly transferred from the capacitor structure 2 to the hygroscopic layer 1, so that the dehydration speed of each location of the hygroscopic layer 1 is similar, thereby improving the detection accuracy of the capacitor.

[0060] In one embodiment, the heat conducting layer 34 may be embedded in the lower insulating layer 33 at a position corresponding to the capacitor structure 2 to reduce the overall thickness of the heating structure 3. The heat conducting layer 34 may be a highly doped low stress polysilicon thin film heat conducting layer 34 with high thermal conductivity. For example, the doping concentration is 10 20 / cm 3 Above, tensile stress 0 ~ 50MPa, thickness 0.5um ~ 5um, to maintain temperature uniformity.

[0061] Alternatively, if Figure 7 As shown, the MEMS chip 100 further includes a substrate 4 and a heat insulation structure 5 . The substrate 4 is disposed on a side of the heating structure 3 away from the capacitor structure 2 , and the heat insulation structure 5 is disposed between the heating structure 3 and the substrate 4 .

[0062] Specifically, in this embodiment, a substrate 4 is also provided on the lower side of the heating structure 3 to play a certain role in the entire MEMS chip 100, so as to facilitate its assembly with other devices. Among them, 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 transfer effect on the temperature of the heating structure 3, in order to avoid temperature loss, a heat insulation structure 5 is provided between the heat conductive layer 34 and the substrate 4, so that most of the heating temperature of the heating structure 3 is transferred to the capacitor structure 2 and the moisture absorption layer 1, avoiding its transfer to the substrate 4, thereby reducing the energy consumption of the heating structure 3.

[0063] In one embodiment, the thermal insulation structure 5 has a thermal insulation surface layer in contact with the heat-conducting structure and a plurality of columnar structures connected to the substrate 4. The periphery of the heating structure 3 is sealed and connected to the periphery of the substrate 4 to form a vacuum sealed cavity. The thermal insulation surface layer and the substrate 4 are connected and supported at multiple points through the columnar structure in the vacuum sealed cavity. This form can ensure that the heating temperature of the heating device 31 is transferred to the capacitor structure 2 to achieve thermal resistance, power consumption and response speed requirements that meet the performance requirements.

[0064] Alternatively, if Figures 1 to 6 As shown, the MEMS chip 100 also includes a substrate 4, which is arranged on a 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 spaced apart on the outside of 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 to the first substrate 41 through the heating structure 3, and the heating device 31 does not extend beyond the first substrate 41.

[0065] Specifically, in this embodiment, refer to Figure 3, the first substrate 41 is used as the heat-conducting layer 34 of the heating structure, the structure of the heat-conducting layer 34 is omitted, the heating structure 3 is simplified, and the second substrate 42 plays a certain supporting role. Among them, the first substrate 41 covers the capacitor structure 2 to ensure that the heating temperature of the heating structure 3 can be evenly transferred to the capacitor structure 2, and the interval between the first substrate 41 and the second substrate 42 can prevent the heating temperature of the heating structure 3 from being transferred to the second substrate 42. At the same time, 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 where the first substrate 41 is located, reducing the energy consumption of the heating structure 3.

[0066] In the above embodiments, reference Figure 4 In order to further prevent the heating temperature of the heating device 31 from being transferred to the second substrate 42, the portion of the heating structure 3 used to connect the first substrate 41 and the second substrate 42 can be designed in the form of multiple connecting beams 43. For example, the square capacitor structure 2 can use four connecting beams 43 to connect the first substrate 41 and the second substrate 42. The specific design can be based on the specific structure, and the present application does not impose any restrictions on this.

[0067] Optionally, refer to Figure 2 , Figures 4 to 6 As shown, the thickness of the first substrate 41 is smaller than the thickness of the second substrate 42 , and the second substrate 42 is connected to the first substrate 41 via a plurality of connecting beams 43 .

[0068] Specifically, in this 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 capacitor structure 2 while ensuring the uniformity of the temperature of the capacitor structure 2. The thickness of the first substrate 41 can be selected from 1um to 20um, for example, 10um.

[0069] In one embodiment, if Figure 6 As shown, the first substrate 41 and the second substrate 42 are both made of silicon or polycrystalline silicon, and the first substrate 41 and the second substrate 42 are connected in the form of multiple connecting beams 43. The connecting beams 43 may be a part of the heating structure 3, or may be connected by multiple connecting beams 43 made of the same material as the first substrate 41 and the second substrate 42. Among them, the use of silicon or polycrystalline silicon 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.

[0070] Alternatively, if Figure 1 , Figure 2 , Figure 5 and Figure 7As shown, the capacitor structure 2 also includes a supporting layer 24, which is arranged between the top electrode 21 and the hygroscopic layer 1; a plurality of through holes 25 connecting the hygroscopic layer 1 and the air gap 23 are arranged on the top electrode 21 and the supporting layer 24, and the size of the through hole 25 is less than 1 / 2 of the thickness of the supporting layer 24.

[0071] Specifically, in this embodiment, the support layer 24 in the capacitor structure 2 can be used to support and connect the hygroscopic layer 1 and the top electrode 21 of the capacitor structure 2, and multiple through holes 25 are used to connect the hygroscopic layer 1 and the air gap 23 of the capacitor structure 2, so that the gas in the external environment can flow from the hygroscopic layer 1 to the air gap 23, and the gas in the air gap 23 can also flow through the hygroscopic layer 1 through the through holes 25 to the outside of the MEMS chip 100, so as to detect the gas in the external environment and ensure the safety of the environmental gas. Among them, the size of the through hole 25 and the thickness of the support layer 24 are designed to be less than 1 / 2, so as to ensure that the dielectric effect of the medium / environment thereon on the capacitor structure 2 can be ignored, so as to ensure the accuracy of the detection.

[0072] In the above embodiment, the support layer 24 can be made of low-stress high-silicon nitride material with high mechanical strength and thermal conductivity to ensure structural strength and the temperature of the capacitor structure 2 can be quickly transferred to the moisture absorption layer 1. The thickness of the support layer 24 is selected to be 0.5um to 2um, and the aperture of the through hole 25 is selected to be 0.1um to 1um.

[0073] Alternatively, if Figure 1 , Figure 2 , Figure 5 and Figure 7 As shown, the capacitor structure 2 further includes an isolation member 26 . The isolation member 26 is disposed in the air gap 23 , and two ends of the isolation member 26 are respectively connected to the top electrode 21 and the bottom electrode 22 .

[0074] Specifically, in this 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 to ensure the stability of the capacitor structure 2. The spacers 26 can be supported by low-stress silicon nitride or silicon oxide, and the thickness thereof is selected to match the air gap 23 and be 0.3um to 1um.

[0075] According to the second aspect of the present application, Figures 9 to 11 As shown, a gas sensor is provided, comprising the MEMS chip 100 of the first aspect.

[0076] Specifically, Fig.11As shown, the gas sensor provided in this embodiment includes the MEMS chip 100 of the first aspect. Based on the fact that the MEMS chip 100 has a dehumidification function and is small in mass and volume, the gas sensor can remove the influence of humidity on the detection accuracy during detection, thereby improving the detection accuracy of the gas sensor and miniaturizing the volume. This gas sensor can be used to detect the leakage of toxic gases in the environment, such as the leakage of refrigerant in air conditioners, to ensure the safety of the environment.

[0077] Alternatively, if Fig.11 As shown, the gas sensor also includes 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 receiving cavity with the substrate 200, and a vent hole 301 connected to the receiving cavity is provided on the packaging shell 300, and the MEMS chip 100 and the ASIC chip 400 are both arranged on the substrate 200 and located in the receiving cavity.

[0078] Specifically, the gas sensor is integrated with the MEMS chip 100 by providing a substrate 200, a packaging shell 300 and an ASIC chip 400, thereby realizing the requirements of accurate detection and miniaturization of the gas sensor, so that the gas sensor can be applied to more electronic devices or environments.

[0079] This embodiment provides a method for a gas sensor to detect ambient gas, such as Fig. 9 and Fig.10 As shown: before time point T0, the capacitor structure 2 is heated by the heating structure 3, and the temperature sensor can be used to measure the temperature, so that the temperature reaches a dehydration high temperature, such as 150°C to 200°C, and the high temperature is maintained until time point T1. Among them, T1 is greater than the thermal response time constant of the capacitor structure 2, such as the thermal response constant of the capacitor structure 2 is 0.05s to 0.5s, and T1 is 0.5s to 5s.

[0080] At time point T1, the capacitor structure 2 begins to cool down to the set detection temperature, such as 50°C. This is time point T2. At this time, 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 begun, but the ventilation process has been completed, that is, there is no water vapor in the moisture absorption layer 1, and the humidity and gas components inside and outside the moisture absorption layer 1 have reached equilibrium.

[0081] At time point T3, the moisture absorption process reaches 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 membrane) has not yet formed an effective "contact" with the moisture absorption / diffusion of the outer layer. If the diffusion coefficient of water vapor in the membrane is D, then √D·(T3-T2)<(0.1~0.5)·membrane thickness, which roughly corresponds to the amount of water absorbed by the inner layer of the membrane from the cavity is at least the saturated water absorption weight ratio of the membrane*membrane thickness / 10. For the moisture absorption layer 1 of PI material, it is about 0.05~0.3wt%*PI density*membrane thickness>700g / m 3 *Film thickness.

[0082] On the other hand, if the Airgap:film thickness of the hygroscopic layer 1 is 0.2:10, the weight ratio of water vapor to air at 50% RH at room temperature and pressure is about 1.25wt%, that is, the total amount of water vapor in the cavity does not exceed 1.25wt%*1184g / m 3 *Airgap~0.30g / m 3 * The membrane thickness is much lower than the amount of water vapor that the inner membrane can absorb from the air gap 23, that is, the water vapor in the air gap 23 will be "sucked dry" by the membrane to a relative humidity RH<0.02%. This roughly corresponds to a detection accuracy of about 20-30ppm of refrigerant gas R290 or R32, which basically meets the requirements for leakage detection of such emerging low GWP (Global Warming Potential) and low ODP (Ozone Depletion Potential) refrigerants.

[0083] Immediately after T3, the capacitance of the capacitor structure 2 is detected, and the detection is completed at T4. T4 should be much smaller than T∞, that is, the moisture absorption saturation time. In addition, the test can be repeated multiple times between T3 and T4, and the output signal of the test circuit shall be converged. That is, one detection cycle includes heating for dehumidification, cooling for drying the cavity (air gap 23), and detecting capacitance changes, and the total time is approximately 0.5 to 10 seconds. Taking the conventional output of a detection signal every 30 seconds as an example, the average power can be much lower than 0.2mW, which can meet most applications.

[0084] The above detection process is a dynamic dehumidification technology, that is, at the time point T0 before each gas detection, the capacitor structure 2 is first heated to a sufficiently high temperature and maintained at a constant temperature to achieve complete dehydration (T1), and then quickly cooled to room temperature or the set detection temperature. At this moment (time point T2), the absolute moisture content in the air in the cavity and in the ambient air is roughly normal (such as 300K, 50% RH, the air contains about 1.23wt% water vapor), and each gas component has reached uniformity inside and outside through the hygroscopic layer 1. Waiting for enough time to T3, the moisture absorption has not yet reached saturation, that is, the inner layer (close to the cavity) of the hygroscopic film is still in the state of absorbing limited moisture in the cavity (causing the amount of water vapor in the air in the cavity to drop rapidly by 2 to 3 orders of magnitude), and before the water vapor absorbed by the outer layer of the hygroscopic film diffuses to the bottom layer (T∞, such as 10 seconds), the gas detection under the constant temperature and dehumidification detection state is carried out (before T4), which can completely eliminate the influence of ambient humidity and temperature at the same time, so as to achieve the purpose of improving the detection accuracy.

[0085] The above embodiments focus on the differences between the various embodiments. As long as the different optimization features between the various embodiments are not contradictory, they can be combined to form a better embodiment. Considering the simplicity of the text, they will not be repeated here.

[0086] Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are only for illustration, not for limiting the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A MEMS chip, characterized in that: include: A capacitor structure, the capacitor structure comprising a top electrode and a bottom electrode arranged at an interval, and an air gap is formed between the top electrode and the bottom electrode; A moisture absorbing layer, the moisture absorbing layer is arranged on a side of the top electrode away from the bottom electrode and is connected to the air gap, and the moisture absorbing layer is used for air permeability and moisture absorption; A heating structure is provided on a side of the capacitor structure away from the hygroscopic layer, and is used to heat the capacitor structure and the hygroscopic layer.

2. The MEMS chip according to claim 1, characterized in that: The heating structure comprises a heating device, an upper insulating layer and a lower insulating layer; The upper insulating layer is arranged on a side of the capacitor structure away from the hygroscopic layer, the lower insulating layer is located 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.

3. The MEMS chip according to claim 2, characterized in that: The heating structure further comprises a heat-conducting layer, and the heat-conducting layer covers the capacitor structure so that the temperature of the heating device can be conducted to the capacitor structure.

4. The MEMS chip according to claim 3, characterized in that: It also includes 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.

5. The MEMS chip according to claim 2, characterized in that: It also includes a substrate, which is arranged on a side of the heating structure away from the capacitor structure, and includes a first substrate and a second substrate spaced apart and arranged outside the first substrate; 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 extend beyond the first substrate.

6. The MEMS chip according to claim 5, characterized in that: The thickness of the first substrate is smaller than that of the second substrate, and the second substrate is connected to the first substrate via a plurality of connection beams.

7. The MEMS chip according to claim 2, characterized in that: The heating structure further includes a temperature sensor, which is disposed between the upper insulating layer and the lower insulating layer and is used to measure the temperature of the capacitor structure.

8. The MEMS chip according to claim 1, characterized in that: The capacitor structure further comprises a support layer, wherein the support layer is disposed between the top electrode and the moisture absorbing layer; 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 ratio of the size of the through holes to the thickness of the support layer is less than 1 / 2.

9. The MEMS chip according to claim 7, characterized in that: The capacitor structure further includes an isolation member, which is disposed in the air gap and has two ends connected to the top electrode and the bottom electrode respectively.

10. The MEMS chip according to claim 1, characterized in that: The moisture absorbing layer is made of polymer, ceramic, metal oxide, nano material or porous material.

11. A gas sensor, characterized in that: A MEMS chip comprising any one of claims 1-10.

12. The gas sensor according to claim 11, characterized in that: It also includes a substrate, a packaging shell and an ASIC chip; The packaging shell is arranged on the substrate and forms a containing cavity with the substrate. The packaging shell is provided with a vent hole connected to the containing cavity. The MEMS chip and the ASIC chip are both arranged on the substrate and located in the containing cavity.

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