Liquid-based CMOS MEMS micro-thermal convection accelerometer

Abstract

This invention relates to the use of Rayleigh number-based... a A compact, liquid-based micro thermal convective accelerometer (MTCA) was developed and optimized. The MTCA was fabricated using CMOS MEMS technology. To ensure waterproofing, an insulating layer, such as a conformal parylene C coating, was employed. The device's performance was evaluated based on sensitivity, response time, and noise. Both theoretical and experimental results indicate high R0. a The value of the fluid can improve the performance of MTCA. Based on R a The model demonstrates its predictive advantage over simple linear models, allowing for the selection of an appropriate fluid to improve sensitivity and balance the linear range of the device. In some cases, alcohol can be chosen as the liquid for MTCA, which, compared to air-based MTCA, increases sensitivity by two orders of magnitude and reduces the detection limit by one order of magnitude.

Description

Technical Field

[0001] This invention generally relates to micro thermal convective accelerometers (MTCA), and more specifically, to micro thermal convective accelerometers that use liquid as the working fluid. Background Technology

[0002] Accelerometers are used in various devices and systems to measure acceleration, including that caused by gravity, impact, rotation, vibration, etc. In an accelerometer, a proof mass is used in conjunction with a spring. The measurement of spring compression during an acceleration event, measured while the proof mass is being pushed, can be correlated with the acceleration experienced by the proof mass.

[0003] Thermal accelerometers are devices that measure acceleration using the principle of thermal convection. In MEMS-based thermal accelerometers, a small heater heats the fluid (gas or liquid), while a pair of symmetrically arranged temperature sensors measure the temperature difference caused by the heat flow from the heater and the input acceleration. The Rayleigh number, a dimensionless number in fluid mechanics and heat transfer, is the ratio of natural convection to heat diffusion and can be rearranged to the dimensionless input acceleration of the thermal accelerometer. By eliminating the traditional mass block, thermal accelerometers can be made more resistant to shock and vibration. Thermal accelerometers also offer other advantages such as resistance to stiction and hysteresis. Due to their small size and the use of thermal convection in the fluid during operation, thermal accelerometers are often referred to as "micro thermal convection accelerometers" (MTCA).

[0004] However, thermal accelerometers may lack the acceleration sensitivity and frequency response of traditional accelerometers, thus limiting their application in some systems requiring high sensitivity. Therefore, there is a need in the art for thermal accelerometers with enhanced sensitivity and faster frequency response. This invention addresses this need. Summary of the Invention

[0005] This invention provides a MEMS thermal accelerometer based on standard CMOS technology on a silicon wafer. By using CMOS MEMS technology, the overall accelerometer size can be reduced, and it can be integrated with CMOS devices, which can be used in conjunction with the accelerometer. The accelerometer has a cavity with a waterproof coating formed thereon. A resistive microheater is suspended above the cavity, and the resistive microheater includes a waterproof coating formed thereon. At least two temperature detectors are suspended above the cavity, which is located upstream of the resistive microheater. The at least two temperature detectors include a waterproof coating formed thereon.

[0006] At least two temperature detectors are suspended above a cavity located downstream of a resistive microheater. Each temperature detector includes a waterproof coating formed thereon. A waterproof cap is positioned above the cavity, the resistive microheater, the at least two upstream temperature detectors, and the at least two downstream temperature detectors, and is configured to enclose convective liquid within it. Attached Figure Description

[0007] Figure 1 This is a top view of an accelerometer according to one embodiment;

[0008] Figure 2 yes Figure 1 Side view of the accelerometer;

[0009] Figure 3A It shows the method for creating Figure 1 The process of using an accelerometer;

[0010] Figure 3B A prior art accelerometer with a single temperature detector is shown;

[0011] Figure 3C yes Figure 1 A perspective view of the accelerometer;

[0012] Figure 4 yes Figure 1 A schematic diagram illustrating the operation of an accelerometer;

[0013] Figure 5 It is based on the output curve of the Rayleigh number;

[0014] Figure 6 It is the predicted output for nine fluids;

[0015] Figure 7 It is a theoretical analysis of the output of three types of fluids;

[0016] Figure 8 It is a graph of the accelerometer output analyzed from multiple different locations of the temperature detector;

[0017] Figure 9 This is a schematic diagram of the CV heater power supply and reading circuit;

[0018] Figure 10 It is a comparison between single-detector and dual-detector accelerometers;

[0019] Figure 11 It is a graph of accelerated life testing of the waterproof coating on the accelerometer;

[0020] Figures 12A-12C The results of the burn test (12A) and safe operating temperature determination (12B) are shown, as well as the temperature of the coated heater (12C).

[0021] Figure 13 It is a comparison of three working fluids;

[0022] Figure 14 It is an acceleration test of different working fluids;

[0023] Figure 15 The response time characteristics of three working fluids are shown.

[0024] Figure 16 Noise analysis for three working fluids is shown. Detailed Implementation

[0025] Traditional thermal accelerometers use air as the working fluid. However, as mentioned above, conventional air-based thermal accelerometers lack the sensitivity required for commercial applications. Therefore, this invention identifies the use of a liquid as the working fluid, combined with the accelerometer described and explained in the following paragraphs, to provide a thermal accelerometer with higher sensitivity. This is determined by the theoretical model of the thermal accelerometer.

[0026] A. Theoretical modeling of MTCA (Micro-thermal convection accelerometer)

[0027] A novel one-dimensional (1D) model is proposed, which uses, for example... Figure 5 The key parameters shown are used to predict the characteristics of a MEMS-based thermal convection accelerometer by considering the circular flow field and linear temperature distribution within a closed chamber. This model is expressed as the following second-order ordinary differential equation (ODE):

[0028] Formula (1):

[0029]

[0030] Where α i T is the input acceleration; a and T h ν represents the boundary temperatures of the enclosed chamber and the heater, respectively; β and ν are the thermal expansion coefficient and kinetic viscosity coefficient of the working fluid, respectively. f and k s , respectively, are the thermal conductivity of the working fluid and the thin film; H and h are the temperature and the top and bottom boundaries of the circulating flow; t is the film thickness; C p This is the thermal capacity of the working fluid. For further analysis, the normalized output ΔT was calculated. * (ΔT) * =ΔT / ΔT h ), which is a dimensionless function of input parameters (related to normalized acceleration and thermal properties), ϕ=R a As shown in equation (2):

[0031]

[0032] The Rayleigh number is a dimensionless number describing the ratio of free convection to thermal diffusion. A larger value indicates stronger free convection, and as shown in equation (3), higher sensitivity at the same input acceleration:

[0033]

[0034] Based on previous conclusions, when the Rayleigh number exceeds a critical value (R... ac When the input acceleration α = 3000, the behavior of the micro-thermal convection accelerometer tends to be nonlinear. Therefore, using a linear model to predict the performance of the micro-thermal convection accelerometer will be inaccurate. It can be seen from equations (2) and (3) that the input acceleration α i Both the thermal properties of the fluid and the fluid's thermal properties affect the Rayleigh number. A comparison of the nine fluids is summarized in Table 1.

[0035] Table I: Summary of thermal properties of nine fluids

[25] and corresponding Rayleigh numbers (ΔT) h =300K).

[0036] Analysis based on a compact model can predict the performance of a thermal accelerometer, such as... Figure 6As shown. Figure 6 This indicates that the Rayleigh number can serve as a reliable predictor for selecting fluid types to provide better performance. However, due to the saturation effect, at the critical value R... ac Subsequently, the relationship between the output value and the Rayleigh number becomes non-linear, which means that for fluids with high Rayleigh numbers, using a linear model to predict performance across the entire measurement range is not accurate.

[0037] Based on this finding, using liquids as the working fluid provides a higher Rayleigh number, which means that the sensitivity of the accelerometer can be significantly improved. To improve the performance of the accelerometer, a compact model was used to analyze the performance of three fluids: one gas (air) and two liquids (water and alcohol). Table II lists the normalized Rayleigh numbers (Ra*) for these three fluids. The predicted performance based on these three types of fluids is listed below. Figure 7 middle. Figure 7 The results show that water and alcohol provide higher output values, but due to nonlinear behavior, when acceleration exceeds 25 m / s², the output values ​​are lower. 2 At that time, the output value of alcohol tends to saturate.

[0038] Table II. Normalized Rayleigh numbers for air, water, and alcohol. R a * =R a / R a,空气 This represents the normalized Rayleigh number at a superheated temperature of 80 K.

[0039] B. Design of the thermal accelerometer

[0040] Based on the above analysis, this invention provides a thermal accelerometer that uses a liquid as the heating fluid, where the temperature distribution is related to the acceleration. To use a liquid instead of a gas, a new waterproof accelerometer design is needed to prevent short circuits between device components and liquid leakage. Figure 1 This is a top view of a CMOS-based MEMS thermal accelerometer 100 according to one embodiment. As used herein, the term "CMOS-based MEMS" refers to a MEMS (micro-electromechanical system) device built in a CMOS (complementary metal oxide semiconductor) fabrication platform provided by a wafer foundry (such as TSMC), examples of which are described below. By using CMOS-based MEMS technology, the overall accelerometer can be made smaller, and it can be integrated with CMOS devices (which can be used in conjunction with the accelerometer).

[0041] like Figure 1as well as Figure 2 As shown in the cross-sectional view, the accelerometer 100 includes various components suspended above the cavity 110. In one aspect, the cavity may be fabricated by micromachining, typically by etching a silicon or polysilicon layer 120. The accelerometer cavity 110 has a waterproof coating 122 formed thereon. The waterproof coating 122 may be selected from polymers, such as para-xylylene polymers or chlorinated poly(para-xylylene) polymers (e.g., PARYLENE C®). Other waterproof polymers, such as acrylics, silicones, and urethanes, may also be used. In particular, conformal coatings are preferred.

[0042] A resistive microheater 150 is suspended above the cavity. As will be discussed in the manufacturing details below, a series of beams 160 are formed of a silicon oxide layer that extends above the cavity. Typically, these beams are micromachined from a CMOS blank (which is the same CMOS blank used to form the cavity). Various accelerometer components are formed on these beams in layers. The resistive microheater can be a polycrystalline silicon microheater or a resistive thin-film metal microheater. The resistive microheater includes a waterproof coating 152 formed thereon. The waterproof coating 152 may be the same as or different from the coating used for the accelerometer cavity.

[0043] At least two upstream temperature detectors 130 are suspended above cavity 110, which is located upstream of resistive microheater 150. Figure 1 As shown, each temperature detector 132, 134 is equidistantly positioned from the resistive microheater 150. Temperature detectors 132, 134 include a waterproof coating 136 formed thereon, which may be made of the aforementioned polymer. In embodiments of the invention, the temperature detectors can be implemented using at least two measurement process types: thermistor-type or thermopile-type CMOS processes. That is, the temperature detector can be a thermistor-type temperature detector or a thermopile temperature detector.

[0044] At least two downstream temperature detectors 140 are suspended above cavity 110, which is located downstream of resistive microheater 150. Figure 1 As shown, each temperature detector 142, 144 is equidistant from the resistive microheater 150. Temperature detectors 142, 144 include a waterproof coating 146 formed thereon, which may be made of the aforementioned polymer. All temperature detectors may be thin-film metal temperature detectors or polycrystalline silicon temperature detectors.

[0045] A waterproof cover 200 is disposed above the cavity 110, the resistive microheater 150, at least two upstream temperature detectors 130, and at least two downstream temperature detectors 140. The waterproof cover may be made of a waterproof polymer with sufficient rigidity to protect the accelerometer. Exemplary polymers include, but are not limited to, polycarbonate, polymethyl methacrylate, polystyrene, or polyvinyl chloride.

[0046] Each of the resistive microheater 150 and temperature detectors 130, 140 is connected to its respective pad. Bonding pads 310 may be disposed on the substrate 300, and each of them is connected to circuitry on the PCB via corresponding aluminum wires 137 / 138 / 147 / 148 / 154 / 155, which are also covered with a waterproof coating. Metal bonding lines 310 provide interconnection between the bonding pads and one or more printed conductors.

[0047] Because a CMOS foundry is used as the manufacturing platform, the ambient temperature compensation circuit can be mounted on the substrate and integrated into the thermal accelerometer. Alternatively, the frequency response compensation circuit can be mounted on the substrate and integrated into the thermal accelerometer.

[0048] C. Manufacturing method of accelerometer

[0049] Figure 3A A series of processes for manufacturing the accelerometer of this invention are described. For this liquid-based MTCA, the device is fabricated using AMS 0.35 micrometer (μm) 2P4M CMOS manufacturing technology (or other foundry processes such as TSMC 0.18 micrometer 1P6M CMOS, UMC 0.18 micrometer 1P6M CMOS, etc.). The term "2P4M" is used to denote two polysilicon ("P") layers and four metal ("M") layers. AMS refers to the semiconductor manufacturing company ams ORSAM AG. The sensor size is chosen to be 600 micrometers. * 600 micrometers (width) * (Length). Since size is related to sensitivity, the dimensions of various integral devices and cavities can be selected based on the required sensitivity of the accelerometer. For example... Figure 4 As shown, the key parameters of this MTCA include the sensor size (L), heater width (W), and temperature detector position (D). The sensor size is limited by the design area, and the width of the heater 150 is fixed at 75 micrometers. To optimize the detector position, [the following is used]. Figure 8 The compact model shown predicts the optimal location for the temperature detector (D / L = 0.55). The width of the temperature detector bridge is determined to be 68 micrometers.

[0050] In this embodiment, aluminum (3.3e) with a high temperature resistivity (TCR) is selected. -3 (0.9e) is used as a temperature sensing material because it is higher than that of polycrystalline silicon (0.9e). -3 / K). However, polysilicon can be used in other devices depending on the accelerometer application.

[0051] Figure 3B A conventional single-temperature detector design is illustrated. In contrast, this invention provides a novel dual-temperature detector configuration. Figure 3C As mentioned above, the device is designed to have a DD (Dual Detectors) structure.

[0052] according to Figure 3A The process shown describes the fabrication of an accelerometer chip using AMS 0.35-micron CMOS MEMS process technology. The initial CMOS layers are shown in 3A(i). They comprise a silicon substrate 120 with an aluminum layer 172 and a polycrystalline silicon layer 174. To realize a single-crystal useful device, the following post-CMOS process is performed. Figure 3A In (ii), the bridge / beam area is defined through an oxide etching step. Using Figure 3A The DRIE etching step in (iii) is used to etch silicon trenches. Following the DRIE etching step is an isotropic silicon etching (XeF2) step to separate the silicon substrate. The sensor chip is then mounted into a machined cavity in the PCB board 300. Figure 2 Following this, wire bonding and coating with a 2-micron conformal waterproof polymer (e.g., PARYLENE-C) are performed to ensure reliable waterproof performance of the encapsulated MCTA (Figure 3). Finally, the working fluid is sealed within the PMMA cap 200 ( Figure 2 ).

[0053] D. Operation of the accelerometer

[0054] Figure 4 schematically shown Figure 1 and Figure 2 The operation of the accelerometer. As mentioned above, the micro-thermal accelerometer consists of three suspension beams 160 ( Figure 2It consists of a central resistive microheater 150 and two temperature detectors 130 and 140 (upper and lower detectors) symmetrically arranged relative to the central microheater, with the central resistive microheater 150 mounted on the suspension beam. The operating temperature of the microheater is T. h Two symmetrical detectors can sense T respectively. u and T d The local temperature. Without acceleration, the temperature distribution T(x) of the film in the x-direction is symmetrical. With acceleration, due to buoyancy, the input acceleration a... i This will create a circulating flow pattern within the cavity, thereby altering the previously symmetrical temperature distribution within the cavity. Subsequently, the temperature difference output between the two temperature detectors (ΔT=T) will be recorded. d -T u The temperature detector can be monitored. It is powered in constant-voltage (CV) mode, and the detector is... Figure 9 The dual-output method shown is used for allocation. The output value V is compared to that of a traditional single-detector design. out_SD In comparison, the output value V out_DD The following formula can be used to calculate:

[0055]

[0056] Where α is the temperature coefficient of resistance; Vs is the supply voltage of the Wheatstone bridge.

[0057] E. Long-term behavior of waterproof coating

[0058] In one embodiment, Parylene-C is selected as the waterproof material. Accelerometers coated with Parylene-C are expected to have long-term reliability. To predict the long-term performance of the coated accelerometer, micro-thermal convection accelerometers can be subjected to test conditions (stress, strain, temperature, voltage, vibration rate, pressure, etc.) exceeding their normal operating conditions, enabling them to detect any errors and potential failure modes within a short period. For the waterproof coating, accelerated life testing based on thermal cycling is used. Therefore, the degradation rate of the Parylene-C coating material properties increases exponentially with temperature, typically described by the Arrhenius equation. Thus, the test time t for the coating's MTCA is... test and estimated lifespan t work The relationship between them can be predicted as follows:

[0059]

[0060] The coated thermal accelerometer was baked in an oven at 100°C for 4 hours. A waterproof test was then performed, and no short circuit was detected in the resistance measurements. Furthermore, the accelerometer still provided the same output values ​​as before heat treatment, and no significant changes or malfunctions were found in the Parylene-C coated unit. Therefore, as Figure 11 The accelerated life test results demonstrate that the conformal Parylene-C coating has a service life of over 9 years at a normal operating temperature of 20°C.

[0061] To determine the maximum operating temperature of the Parylene-C coating, a burn test was performed. Figure 12A The test confirmed that the conformal coating can operate safely below 200°C. Figure 12B This temperature is higher than the boiling point of water or alcohol. Furthermore, the conformal Parylene-C coating has different thermal properties than silicon oxide, which will cause variations in the temperature of the microheater at the same power consumption. The heater temperature was then characterized under conditions with and without the Parylene-C coating and with different supply currents. Figure 12C This indicates that, at the same power consumption, a sensor with a Parylene-C coating will have an average temperature drop of 15%.

[0062] Example: Experimental analysis of a liquid-based accelerometer

[0063] Three working fluids were tested, including air, water, and alcohol. Figure 13 The results show that alcohol, with its higher Rayleigh number, significantly improves sensitivity (43.8 mV / g), followed by water (7.1 mV / g). An air-based accelerometer with a heater temperature (Th) of 80 °C only achieves a sensitivity of 28 μV / g, which can be increased to 1002 μV / g by increasing Th to 430 °C. Furthermore, Figure 14 This indicates that working fluids with high Ra (e.g., alcohol) will result in significant nonlinear behavior and a small detection range, which is very consistent with the predictions of the compact model.

[0064] In addition to sensitivity characterization, response time was also tested. Fluids with lower density and greater thermal diffusivity are advantageous as working media for higher frequency responses. Based on the thermal properties listed in Table III, alcohol exhibits higher sensitivity, but due to its lower diffusivity, it has a lower frequency response.

[0065] Table III: Comparison of Thermal Properties of Three Fluids

[0066]

[0067] Characterizing response time is crucial for evaluating the performance of liquid-based MTCA. For example... Figure 15 As shown, among these three types of fluids, alcohol has the longest response time (235 ms), followed by water (111 ms) and air (16 ms), which means that when choosing a suitable working fluid, a trade-off should be made between sensitivity and bandwidth.

[0068] In addition, noise is tested to check the minimum detectable acceleration, such as Figure 16 As shown, water exhibits the highest noise spectral density, followed by alcohol and air. After normalizing the noise values ​​(noise value / sensitivity), the minimum detectable acceleration (MDA) for alcohol is 61.9 μg, followed by air (757 μg) and water (916 μg). These comparisons are summarized in Table IV, which indicates that, compared to air-based accelerometers, the accelerometer of this invention improves the normalized sensitivity (3344 μV / g / mW) by two orders of magnitude and the minimum detectable acceleration (61.9 μg) by one order of magnitude.

[0069] Table IV: Comparison of cryogenic convection accelerometers S = Sensitivity, P = Power Consumption, FR = Frequency Response.

[0070] As used herein, for ease of description, spatially related terms such as “below,” “under,” “lower part,” “above,” “upper,” “lower,” “left,” “right,” etc., are used to describe the relationship between a component or feature and another component or feature shown in the figures. In addition to the orientations shown in the figures, spatially related terms are intended to cover different orientations of the apparatus in use or operation. The apparatus may be oriented in other ways (rotated 90 degrees or otherwise), and the spatially related descriptors used herein may also be used for the corresponding interpretations. It should be understood that when one component is “connected” or “coupled” to another component, the component may be directly connected to or coupled to the other component, or there may be an intermediate component.

[0071] As used herein, the terms “approximately,” “substantially,” “essentially,” and “about” are used to describe and explain a small variation. When used in conjunction with an event or situation, the term can refer to the exact occurrence of the event or situation, or the approximate occurrence of the event or situation. As with any given value or range used herein, the term “about” typically refers to ±10%, ±5%, ±1%, or ±0.5% of a given value or range. A range may be indicated herein as from one endpoint to another or between two endpoints. Unless otherwise specified, all ranges disclosed in this disclosure include endpoints. The term “substantially coplanar” can refer to two surfaces disposed along the same plane within a few micrometers (μm), for example, within 10 μm, 5 μm, 1 μm, or 0.5 μm along the same plane. When referring to “substantially” identical numerical values ​​or characteristics, the term can refer to values ​​within a range of ±10%, ±5%, ±1%, or ±0.5% of the average value.

[0072] The foregoing briefly describes several embodiments and detailed features of this disclosure. The embodiments described in this disclosure can readily serve as the basis for designing or modifying other processes and structures for achieving the same or similar purposes and / or obtaining the same or similar advantages introduced in the embodiments of this disclosure. Such equivalent constructions do not depart from the spirit and scope of this disclosure, and various changes, substitutions, and modifications can be made without departing from the spirit and scope of this disclosure.

Claims

1. A CMOS-based MEMS thermal accelerometer, characterized in that, include: The cavity is covered with a waterproof coating. The first suspension beam, the second suspension beam, and the third suspension beam are formed by etching the same silicon oxide layer to define the beam region and extend above the cavity, wherein the first suspension beam is located between the second suspension beam and the third suspension beam; A resistive microheater is formed on the first suspension beam and suspended above the cavity. The resistive microheater includes a waterproof coating formed thereon, wherein the waterproof coating of the resistive microheater covers at least a portion of the surface of the resistive microheater and the first suspension beam. At least two upstream temperature detectors are formed on the second suspension beam and suspended above the cavity, and the at least two upstream temperature detectors are located upstream of the resistive microheater. The at least two upstream temperature detectors include a waterproof coating formed thereon, wherein the waterproof coating of the at least two upstream temperature detectors covers at least a portion of the surface of the at least two upstream temperature detectors and the second suspension beam, wherein each of the at least two upstream temperature detectors is equidistant from the resistive microheater. At least two downstream temperature detectors are formed on the third suspension beam and suspended above the cavity, and the at least two downstream temperature detectors are located downstream of the resistive microheater. The at least two downstream temperature detectors include a waterproof coating formed thereon, wherein the waterproof coating of the at least two downstream temperature detectors covers at least a portion of the surface of the at least two downstream temperature detectors and the third suspension beam, wherein each of the at least two downstream temperature detectors is equidistant from the resistive microheater. A waterproof cover is disposed above the cavity, the first suspension beam, the second suspension beam, the third suspension beam, the resistive microheater, the at least two upstream temperature detectors, and the at least two downstream temperature detectors, the waterproof cover being configured to enclose convective liquid therein.

2. The CMOS-based MEMS thermal accelerometer according to claim 1, characterized in that, The cavity is a silicon or polycrystalline silicon cavity.

3. The CMOS-based MEMS thermal accelerometer according to claim 1, characterized in that, The two downstream temperature detectors are selected from aluminum or polycrystalline silicon temperature detectors.

4. The CMOS-based MEMS thermal accelerometer according to claim 1, characterized in that, The two upstream temperature detectors are selected from aluminum or polycrystalline silicon temperature detectors.

5. The CMOS-based MEMS thermal accelerometer according to claim 1, characterized in that, The resistive microheater mentioned above is a polycrystalline silicon resistive microheater.

6. The CMOS-based MEMS thermal accelerometer according to claim 1, characterized in that, The cavity is coupled to the substrate.

7. The CMOS-based MEMS thermal accelerometer according to claim 6, characterized in that, It also includes an ambient temperature compensation circuit, which is disposed on the substrate and integrated with the thermal accelerometer.

8. The CMOS-based MEMS thermal accelerometer according to claim 6, characterized in that, It also includes a frequency response compensation circuit, which is disposed on the substrate and integrated with the thermal accelerometer.

9. The CMOS-based MEMS thermal accelerometer according to claim 1, characterized in that, The waterproof coating mentioned therein is a polymer coating.

10. The CMOS-based MEMS thermal accelerometer according to claim 9, characterized in that, The polymer coating is selected from one or more of the group consisting of p-xylene polymers, chlorinated poly(p-xylene), polyurethane, acrylic acid, or silicone.

11. The CMOS-based MEMS thermal accelerometer according to claim 1, characterized in that, The convective liquid mentioned therein is water.

12. The CMOS-based MEMS thermal accelerometer according to claim 1, characterized in that, The convective liquid mentioned therein is alcohol.

13. The CMOS-based MEMS thermal accelerometer according to claim 1, characterized in that, The ratio of the position of the temperature detector to the width of the thermal accelerometer is determined by a curve of a compact model, wherein the compact model is determined by at least one property of the convective liquid, and the property of the convective liquid includes at least its normalized Rayleigh number.

14. The CMOS-based MEMS thermal accelerometer according to claim 1, characterized in that, The selection of the convective fluid is determined based on at least the normalized Rayleigh number of multiple candidate convective fluids.

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