MEMS gas sensor based on weakly coupled aln thin film resonator

Abstract

The application discloses a MEMS gas sensor based on a weakly coupled AlN thin film resonator and belongs to the technical field of microelectronic mechanical systems. The gas sensor comprises a glass base, the front surface of the glass base is provided with a plurality of groups of capacitor plates, an AlN thin film resonator array is suspended on the glass base through the capacitor plates, the AlN thin film resonator array is composed of at least four resonator units, and the resonator units are connected through coupling beams. The MEMS gas sensor is configured to realize synchronous quantitative measurement of a plurality of gas concentrations by detecting the change of the vibration amplitude ratio of each resonator unit. The application has the advantages of multi-parameter synchronous detection, strong anti-interference capability, high sensitivity and good stability and is suitable for gas sensing measurement in a complex environment.

Description

Technical Field

[0001] This invention relates to the field of gas sensors and microelectromechanical systems, and particularly to a MEMS gas sensor based on a weakly coupled AlN thin-film resonator. Background Technology

[0002] Microelectromechanical systems (MEMS) technology integrates micromechanical structures with electronic circuits, offering advantages such as small size, low power consumption, and mass production capabilities. It is widely used in environmental monitoring, healthcare, and industrial control. Gas sensors, as an important branch of MEMS, play a crucial role in applications such as air quality monitoring and early warning of flammable and explosive gases.

[0003] Most common MEMS gas sensors are based on sensing mechanisms such as metal oxides and electrochemistry, detecting gases by changes in electrical or optical parameters caused by adsorption. However, these sensors generally suffer from high cross-sensitivity, significant susceptibility to temperature and humidity fluctuations, and poor stability, making it difficult to achieve simultaneous and differentiated measurement of multiple gas components.

[0004] In recent years, MEMS gas sensors based on the resonance principle have attracted widespread attention due to their high sensitivity, fast response, and good stability. Among them, weakly coupled resonator systems can convert external disturbances into changes in the output amplitude ratio through mechanisms such as modal localization, and have the potential to suppress common-mode interference to a certain extent.

[0005] However, existing weakly coupled resonator structures are mostly focused on single-parameter detection or frequency-based detection, resulting in relatively simple system configurations. They generally face challenges such as difficulty in integrating sensitive materials, weak multi-target gas identification capabilities, low modal coupling efficiency, and significant signal crosstalk. Especially in achieving simultaneous and highly selective detection of multiple gases, existing structures still exhibit significant deficiencies in anti-interference capabilities, stability, and signal consistency, limiting their practical application under complex operating conditions. Summary of the Invention

[0006] Purpose of the invention: To address the above problems, this invention provides a MEMS gas sensor based on a weakly coupled AlN thin-film resonator, enabling a novel MEMS gas sensor structure for simultaneous and highly stable detection of multiple gas components, thus meeting the demand for higher performance gas sensing.

[0007] Technical solution: A MEMS gas sensor based on a weakly coupled AlN thin-film resonator, comprising:

[0008] A glass base, the front of which is provided with multiple sets of capacitor plates;

[0009] An AlN thin-film resonator array is suspended above a glass base via the capacitor plate. The AlN thin-film resonator array consists of at least four resonator units, each of which is located at one of the four vertices of a square. Adjacent resonator units are connected by coupling beams to form a square symmetrical layout with the array center as the center of symmetry.

[0010] In this embodiment, among at least four resonator units, at least two resonator units have gas-sensitive materials selectively deposited on their front sides for different target gases, and at least one resonator unit serves as a reference unit for which the gas-sensitive material is not deposited. The gas-sensitive material and the reference unit together constitute a differential measurement structure.

[0011] The MEMS gas sensor is configured to achieve synchronous quantitative measurement of the concentration of multiple gases by detecting changes in the vibration amplitude ratio of each resonator unit.

[0012] Furthermore, the capacitor plate is composed of a first electrode group and a second electrode group facing each other. The first electrode group is disposed on the front side of the glass base, and the second electrode group is disposed on the back side of the AlN thin film resonator array.

[0013] Furthermore, both the first electrode group and the second electrode group include multiple sub-electrode groups, and the total number of sub-electrode groups is twice the number of resonator units. Each sub-electrode group consists of four triangular capacitor plates, two of which are driving electrodes and two are detection electrodes. The driving electrodes and the detection electrodes are alternately distributed to form a centrally symmetrical structure.

[0014] Furthermore, T-shaped anchor points are used as fixed anchor points at the four corners of the resonator unit to connect the resonator unit to the glass base.

[0015] Furthermore, the triangular capacitor plate is a metal capacitor, and is connected to the external interface circuit and phase-locked loop circuit by connecting the triangular capacitor plate with leads.

[0016] Furthermore, the method for simultaneous quantitative measurement of multiple gas concentrations using the aforementioned MEMS gas sensor includes:

[0017] The external interface circuit and phase-locked loop circuit apply AC excitation signals to the driving electrode through leads, and utilize the inverse piezoelectric effect of AlN thin film to drive the AlN thin film resonator array to vibrate near the resonant frequency;

[0018] The target gas is adsorbed by the gas-sensitive material, which changes the equivalent mass of the corresponding resonator unit, causing its resonant frequency to shift and disturbing the vibration state of the weakly coupled resonant system.

[0019] The vibration amplitude of each resonator unit is acquired through the detection electrodes, and the amplitude ratio offset is obtained with reference unit as a benchmark.

[0020] Based on the amplitude ratio offset, multi-channel decoupling calculations are performed to obtain the concentration of the target gas to be measured.

[0021] Furthermore, the four resonator units are constructed as follows:

[0022] The polyimide hydrophilic film on the surface of the first resonator unit has a strong adsorption of water molecules. After the water molecules are adsorbed, the equivalent mass of the resonator will increase, causing the resonant frequency to drop and forming a detectable mass load disturbance.

[0023] The palladium-doped single-walled carbon nanotube film on the surface of the second resonator unit exhibits selective adsorption and catalytic response characteristics to methane molecules. After adsorbing methane, a stable mass change occurs, causing a shift in the resonant frequency.

[0024] Amine functionalization of the surface of the third resonator unit The thin film can undergo a reversible chemical reaction with carbon dioxide through amine groups, resulting in a significant change in mass loading during adsorption. It also shows no obvious response to background gases such as nitrogen and oxygen, thus avoiding cross-interference.

[0025] The fourth resonator unit is a reference unit and does not deposit gas-sensitive materials;

[0026] The mass change caused by gas adsorption generates vibrational disturbances in the weakly coupled resonant system. The amplitude signals of each unit are collected by the detection electrodes, and the amplitude ratio offset is obtained with the reference unit as the benchmark. Then, the disturbance signals of different gases are solved by the multi-channel decoupling algorithm, and finally the synchronous quantitative detection of the concentrations of the three gases is achieved.

[0027] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0028] 1. This invention achieves simultaneous high-precision detection of the concentrations of three gases—water vapor, methane, and carbon dioxide—through a combination design of four resonator units and differentiated sensitive materials, effectively solving the problem of cross-interference in multi-component gas measurement.

[0029] 2. By introducing a fourth resonator unit without sensitive materials as a built-in control group and combining it with a weak coupling resonance mechanism, this invention can effectively suppress common-mode interference such as changes in ambient temperature and humidity and mechanical vibration, and significantly improve the stability and anti-interference capability of the sensor.

[0030] 3. The sensor of this invention adopts a signal transmission method that couples an AlN thin film resonator with a capacitor plate, which combines the high sensitivity of piezoelectric materials with the reliability of non-contact signal transmission. The overall structure is robust and suitable for complex industrial and environmental monitoring applications.

[0031] 4. This invention utilizes micromachining technology for fabrication, exhibiting excellent process compatibility and scalability, and providing an effective path for the development of MEMS gas sensors towards multi-parameter, high-performance, and low-cost directions. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the overall mechanical structure of the present invention;

[0033] Figure 2 This is a front view of the resonator unit of the present invention;

[0034] Figure 3 This is a schematic diagram of the back electrode assembly of the resonator unit of the present invention;

[0035] Figure 4 This is a schematic diagram of the glass base electrode assembly of the present invention;

[0036] Figure 5 This is a schematic diagram of the first sub-electrode group of the present invention;

[0037] Figure 6 This is a schematic diagram of the fifth sub-electrode group and its leads of the present invention;

[0038] Figure 7 This is a graph showing the effect of gas concentration on the resonant amplitude ratio according to the present invention.

[0039] Figure 8 This is a graph showing the sensitivity of the sensor in this invention.

[0040] Figure 9 The graph shows the amplitude-frequency response curves for different gas concentrations.

[0041] Explanation of reference numerals in the attached figures: 1-1: First resonator unit; 1-2: Second resonator unit; 1-3: Third resonator unit; 1-4: Fourth resonator unit; 2: Electrode group; 2-1: First sub-electrode group; 2-1-1: First driving electrode; 2-1-3: Second driving electrode; 2-1-2: First detection electrode; 2-1-4: Second detection electrode; 2-2: Second sub-electrode group; 2-3: Third sub-electrode group; 2-4: Fourth sub-electrode group; 2-5: Fifth sub-electrode group; 2-5-1: Fourth driving electrode; 2-5-3: Third driving electrode; 2-5- 2: Third detection electrode; 2-5-4: Fourth detection electrode; 2-5-7: First drive signal lead; 2-5-5: Second drive signal lead; 2-5-6: First detection signal lead; 2-5-8: Second detection signal lead; 2-6: Sixth sub-electrode group; 2-7: Seventh sub-electrode group; 2-8: Eighth sub-electrode group; 3-1: First coupling beam; 3-2: Second coupling beam; 3-3: Third coupling beam; 3-4: Fourth coupling beam; 4-1: Hydrophilic material; 4-2: Methane-loving material; 4-3: Carbon dioxide-loving material; 5: Glass base. Detailed Implementation

[0042] For the purpose of further detailed description of the embodiments of the present invention below in conjunction with the accompanying drawings and examples, it should be understood that the specific embodiments described herein are merely illustrative of the embodiments of the present invention and are not intended to limit the embodiments of the present invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the embodiments of the present invention are shown in the drawings, and not all structures.

[0043] In the following description, specific details such as target system architecture and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of this application with unnecessary detail.

[0044] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0045] Furthermore, in the description of this application and the appended claims, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0046] This invention provides a MEMS gas sensor based on a weakly coupled AlN thin-film resonator, comprising: a glass base, wherein multiple sets of capacitor plates are provided on the front side of the glass base; an AlN (aluminum nitride) thin-film resonator array, which is suspended above the glass base by the capacitor plates, the AlN thin-film resonator array being composed of at least four resonator units, and the resonator units are connected by coupling beams to form a weak coupling.

[0047] In this embodiment, among at least four resonator units, at least two resonator units have gas-sensitive materials selectively deposited on their front sides for different target gases, and at least one resonator unit serves as a reference unit without deposited gas-sensitive materials. The gas-sensitive materials and the reference unit together constitute a differential measurement structure.

[0048] The MEMS gas sensor is configured to achieve synchronous quantitative measurement of the concentration of multiple gases by detecting changes in the vibration amplitude ratio of each resonator unit.

[0049] In one example, the AlN thin-film resonator array includes four resonator units, which are connected by coupling beams to form a weak coupling, forming a square symmetrical layout. It is integrated with the resonator and has a thickness of 10 nm.

[0050] like Figure 1 and Figure 2 As shown, Figure 1 and Figure 2 All views are top views. The four resonator units are designated as first resonator unit 1-1, second resonator unit 1-2, third resonator unit 1-3, and fourth resonator unit 1-4. The four resonator units are interconnected by coupling beams to form a square symmetrical layout. The first resonator unit 1-1 is connected to the second resonator unit 1-2 via the first coupling beam 3-1, and to the fourth resonator unit 1-4 via the fourth coupling beam 3-4. The second resonator unit 1-2 is connected to the third resonator unit 1-3 via the second coupling beam 3-2, and the third resonator unit 1-3 is connected to the fourth resonator unit 1-4 via the third coupling beam 3-3. This symmetrical coupling structure is used to enhance the mechanical stability of the entire resonator array and to achieve efficient transmission and coupling of vibration modes.

[0051] Furthermore, the capacitor plates are provided with electrode groups 2, which are formed by the first electrode group and the second electrode group being matched and aligned. The first electrode group is located on the front side of the glass base 5, and the second electrode group is located on the back side of the AlN thin film resonator array.

[0052] The first electrode group and the second electrode group are directly aligned and matched to form parallel capacitor plates, with an electrode spacing of 10 mm. This allows the loading of drive signals and the extraction of detection signals.

[0053] Furthermore, both the first and second electrode groups include multiple sub-electrode groups, with the total number of sub-electrode groups being twice the number of resonator units. Each sub-electrode group consists of four triangular capacitor plates, with two serving as driving electrodes and two as detection electrodes. The driving and detection electrodes are alternately distributed, forming a centrally symmetrical structure. This electrode arrangement is used to achieve a uniform distribution of the electric field, reduce crosstalk between the driving and detection signals, and improve the signal-to-noise ratio and measurement accuracy of the entire sensor system.

[0054] In one example, combined Figure 3 As shown, Figure 3 The top view shows that the AlN thin film resonator array has a second electrode group on its back side, including a first sub-electrode group 2-1 on the back side of the first resonator unit 1-1, a second sub-electrode group 2-2 on the back side of the second resonator unit 1-2, a third sub-electrode group 2-3 on the back side of the third resonator unit 1-3, and a fourth sub-electrode group 2-4 on the back side of the fourth resonator unit 1-4.

[0055] like Figure 4 As shown, Figure 4 The top view shows that the front of the glass base 5 has four sets of capacitor plates arranged in a rectangular array, namely the fifth sub-electrode group 2-5, the sixth sub-electrode group 2-6, the seventh sub-electrode group 2-7 and the eighth sub-electrode group 2-8.

[0056] These eight sub-electrode groups have identical structures. Each sub-electrode group consists of four triangular capacitor plates, two of which are driving electrodes and two are detection electrodes. The driving electrodes and detection electrodes are arranged alternately to form a centrally symmetrical structure. This electrode arrangement is used to achieve a uniform distribution of the electric field, reduce crosstalk between the driving and detection signals, and improve the signal-to-noise ratio and measurement accuracy of the entire sensor system.

[0057] In particular, in this embodiment, the driving electrode and the detection electrode have the same structure and the same material, both using a chromium / gold composite film layer, wherein the chromium thickness is 30nm and the gold thickness is 20nm.

[0058] Furthermore, the AlN thin-film resonator array is fabricated using micromachining technology. Its back-side triangular capacitor plate group and the capacitor group on the glass base 5 are paired to form a capacitor plate, thereby loading the driving signal and extracting the detection signal. Specifically, the first sub-electrode group 2-1 and the fifth sub-electrode group 2-5 are paired; the second sub-electrode group 2-2 and the eighth sub-electrode group 2-8 are paired; the third sub-electrode group 2-3 and the seventh sub-electrode group 2-7 are paired; and the fourth sub-electrode group 2-4 and the sixth sub-electrode group 2-6 are paired.

[0059] The eight sub-electrode groups have identical structures and the capacitor pairing method of each pair of electrode groups is exactly the same. Specifically, take the capacitor pairing of the first sub-electrode group 2-1 and the fifth sub-electrode group 2-5 as an example.

[0060] Combination Figure 5 As shown, Figure 5 The first sub-electrode group 2-1 is shown in a bottom view. It includes a first driving electrode 2-1-1, a second driving electrode 2-1-3, a first detection electrode 2-1-2, and a second detection electrode 2-1-4.

[0061] Combination Figure 6 As shown, Figure 6 In a top view, the fifth sub-electrode group 2-5 includes a third driving electrode 2-5-3, a fourth driving electrode 2-5-1, a third detection electrode 2-5-2, and a fourth detection electrode 2-5-4; wherein the first driving electrode 2-1-1 is capacitively matched with the third driving electrode 2-5-3, and the second driving electrode 2-1-3 is capacitively matched with the fourth driving electrode 2-5-1; the first detection electrode 2-1-2 is capacitively matched with the third detection electrode 2-5-2, and the second detection electrode 2-1-4 is capacitively matched with the fourth detection electrode 2-5-4, thereby loading a driving signal and extracting a detection signal.

[0062] In one example, different gas-sensitive materials are deposited on the front surfaces of the first, second, and third resonator units, which can be designed according to the user's needs. Here, we take hydrophilic material 4-1, methane-sensitive material 4-2, and carbon dioxide-sensitive material 4-3 as examples. The front surface of the first resonator unit 1-1 is deposited with hydrophilic material 4-1, the front surface of the second resonator unit 1-2 is deposited with methane-sensitive material 4-2, the front surface of the third resonator unit 1-3 is deposited with carbon dioxide-sensitive material 4-3, and the fourth resonator unit 1-4 serves as a control group, with no gas-sensitive material deposited on its front surface. Its vibration response is used to provide an environmental reference signal to eliminate the influence of common-mode interference from temperature, humidity, and mechanical vibration on the measurement results.

[0063] Among them, hydrophilic material 4-1, methane gas-loving material 4-2, and carbon dioxide gas-loving material 4-3 are deposited on the front side of the corresponding resonator unit through electro-spraying, in-situ thin film growth, and EHD spraying technology, respectively. This is to ensure a firm bond and uniform film formation between each gas-sensitive material and the resonator surface, and to maintain its gas adsorption selectivity and sensitivity characteristics, thereby ensuring the reliability and consistency of the sensor's response to the target gas.

[0064] In one example, the hydrophilic material 4-1 on the upper layer of the first resonator unit 1-1 is formed by electro-spraying, the methane-loving gas material 4-2 on the upper layer of the second resonator unit 1-2 is formed by in-situ thin film growth, the carbon dioxide-loving gas material 4-3 on the upper layer of the third resonator unit 1-3 is formed by EHD spraying technology, and the fourth resonator unit 1-4 serves as a control group, without depositing any gas-sensitive material. Its vibration response is used to provide an environmental reference signal to eliminate the influence of common-mode interference from temperature, humidity, and mechanical vibration on the measurement results.

[0065] When the MEMS gas sensor is placed in the target environment, the specific gas-sensitive material on the AlN thin film resonator adsorbs target molecules, thereby causing a change in the equivalent mass of the corresponding resonator unit, which in turn changes the vibration amplitude ratio of the entire weakly coupled system. By detecting the shift of the amplitude ratio of the corresponding resonator unit relative to the control group reference, the concentrations of water vapor, methane and carbon dioxide in the environment can be measured simultaneously and with high precision.

[0066] The four corners of the resonator unit are fixed with T-shaped anchor points, which connect the resonator unit to the glass base. Using T-shaped anchor points at the four corners minimizes resonator losses.

[0067] Furthermore, the triangular capacitor plates are metal capacitors, and are connected to external interface circuits and phase-locked loop circuits via leads, thereby enabling the input of drive signals and the output of detection signals.

[0068] The fifth, sixth, seventh, and eighth sub-electrode groups on the surface of the glass base 5 are connected to the external interface circuit and the phase-locked loop circuit via leads in the same way. Taking the fifth sub-electrode group 2-5 as an example, the third driving electrode 2-5-3 on the fifth sub-electrode group 2-5 is connected to the metal electrode via the first driving signal lead 2-5-7, and the fourth driving electrode 2-5-1 is connected to the metal electrode via the second driving signal lead 2-5-5, thereby connecting to the external interface circuit and the phase-locked loop circuit. The third detection electrode 2-5-2 on the fifth sub-electrode group 2-5 is connected to the metal electrode via the first detection signal lead 2-5-6, and the fourth detection electrode 2-5-4 is connected to the metal electrode via the second detection signal lead 2-5-8, thereby connecting to the external interface circuit and the phase-locked loop circuit.

[0069] In actual operation, the external interface circuit and phase-locked loop circuit connect the drive signal leads on the glass base to the metal electrodes to apply an AC excitation signal. Utilizing the inverse piezoelectric effect of the AlN thin film, the AC excitation signal drives the entire AlN resonator thin film array to vibrate near its resonant frequency via the drive electrodes in the electrode group. When the gas sensor is placed in the environment of the gas to be measured, the hydrophilic, methane-loving, and carbon dioxide-loving sensitive materials deposited on the front of the first, second, and third resonator units respectively adsorb the corresponding target gas molecules, causing an increase in the equivalent mass of the corresponding resonator unit, thereby causing a shift in its resonant frequency. This disturbs the vibration state of the original weakly coupled resonant system, manifested as a change in the vibration amplitude ratio of each resonator unit. By utilizing the piezoelectric effect of the AlN thin film and using the detection electrodes in the electrode group to detect the shift in the vibration amplitude ratio of the first, second, and third resonator units relative to the fourth control group resonator unit in real time, the concentrations of water vapor, methane, and carbon dioxide in the environment can be measured simultaneously and with high precision.

[0070] Specifically, based on the simplified mechanical dynamics model of the weakly coupled resonant system and Newton's laws, the simplified equations of motion for the mass blocks of the first, second, third, and fourth resonator units are as follows:

[0071] ;

[0072] In the formula, , , , This represents the equivalent mass, equivalent stiffness, displacement, and driving force of each resonator unit mass block. This represents the acceleration of the mass blocks in each resonant unit. , This indicates the coupling stiffness between the two resonator units.

[0073] The above equations of motion can be simplified to the following matrix:

[0074] ;

[0075] in, This represents the velocity vector of each resonant unit mass block. Let represent the mass matrix, stiffness matrix, driving force matrix, and displacement matrix of the weakly coupled resonant system, respectively, and we have:

[0076] ;

[0077] ;

[0078] ;

[0079] ;

[0080] in, Indicates no external disturbance The dimensionless eigenvectors of the first mode reflect the proportional relationship of the vibration amplitudes of each resonator element. The time complex exponential factor represents the simple harmonic motion, characterizing the phase and amplitude changes of the resonator element as it undergoes simple harmonic motion over time.

[0081] Under free vibration conditions, the solution to a weakly coupled resonant system can be transformed into solving the eigenvalues ​​and eigenvectors of the following dimensionless equation, expressed as:

[0082] ;

[0083] in, Under the condition of no external disturbance The dimensionless eigenvalues ​​of the first mode satisfy the relation , The resonant frequency, Under the condition of no external disturbance The dimensionless eigenvectors of the first mode reflect the proportional relationship of the vibration amplitudes of each resonator unit.

[0084] As can be seen from the dimensionless equations above, the eigenvalues ​​and eigenvectors of the system both depend on the parameters of the mass matrix and stiffness matrix. Given the equivalent stiffness of the resonator element... and coupling stiffness Under the premise of (predetermined through micromachining technology), theoretically, it is possible to analyze weakly coupled resonant systems. By analyzing the eigenvalues ​​and eigenvectors, the change in the equivalent mass of each resonator unit can be deduced, thereby achieving high-precision synchronous sensing of multiple parameters such as water vapor, methane, and carbon dioxide concentrations.

[0085] Furthermore, when mass disturbances are introduced into the system, solving the system's characteristic equations reveals that due to the high system complexity and the mutual coupling of the four mass variables, neither eigenvalues ​​nor eigenvectors can be obtained with explicit analytical solutions. Therefore, a clear correspondence between stiffness disturbances and system dynamic parameters cannot be derived. However, signal decoupling methods commonly used in multidimensional force sensors can be applied to solve for the measured signal. Commonly used decoupling algorithms include those based on solving the generalized inverse matrix, those based on backpropagation (BP) neural networks, and those based on genetic algorithms to optimize BP neural networks.

[0086] In the field of decoupling algorithms for multidimensional force sensors, the decoupling method based on solving the generalized inverse matrix has become the most widely used decoupling algorithm due to its simplicity and ease of implementation. This example mainly draws on this algorithm.

[0087] The static decoupling method based on solving the generalized inverse matrix essentially still falls under the category of linear decoupling. This method ensures the minimization of overall error within the full-scale range, thereby guaranteeing measurement accuracy. The specific operation process is as follows: Multiple acceleration values ​​are selected for calibration within the range. First, the load is applied starting from zero, gradually increasing according to the range points until a positive full-scale value is reached. Then, the load is gradually unloaded until it returns to zero. Next, starting from zero, the load is gradually increased until the value corresponding to the negative full-scale range is reached. Finally, the unloading operation is performed in a gradually decreasing manner until the data value returns to zero. This process is repeated multiple times to ensure the accuracy of the test.

[0088] The assumed multi-degree-of-freedom weakly coupled resonant sensor has a total of four channels, i.e., four signals of the parameters to be measured. and Then the relationship between the amplitude ratio vector of the sensor and the signal of the parameter to be measured can be expressed as:

[0089] ;

[0090] ;

[0091] in, It was calibrated through experiments. Matrix, its elements It is a constant used to describe the mapping relationship between the system input (gas concentration) and output (amplitude ratio).

[0092] according to The calibration matrix can be obtained. ,in The output vector is the amplitude ratio. The gas concentration input vector is used, and the two are calibrated using a calibration matrix. Establish a linear relationship to obtain the calibration matrix. Then, calculate the calibration matrix. After obtaining the generalized inverse matrix, the coefficient matrix can be obtained. That is, the input force / torque vector of the dual-axis accelerometer sensor:

[0093] ;

[0094] in, This is the multi-channel amplitude ratio output vector of the sensor.

[0095] coefficient matrix The diagonal elements reflect the correspondence between the input and output of each channel, while the off-diagonal elements characterize the degree of mutual interference between different channels. This leads to... The concentration vector of the multi-component gas to be measured reflects the concentration values ​​of each target gas.

[0096] like Figure 7 As shown, the curves illustrating the influence of gas concentration on the resonant amplitude ratio are presented. The horizontal axis represents gas concentration, and the vertical axis represents the amplitude ratio of the resonant unit. The figure includes three response curves corresponding to water vapor, methane, and carbon dioxide, respectively. The results show a good linear relationship between each gas concentration and the amplitude ratio of the corresponding resonant unit, with minimal cross-interference between different curves. This indicates that the sensor described in this invention has good gas selectivity and discrimination ability, verifying the effectiveness of the differential structure and weak coupling mechanism in multi-gas synchronous detection.

[0097] like Figure 8 The figure shows the sensitivity curves of the sensor of the present invention, reflecting its response sensitivity to different gases. The horizontal axis of the curve represents gas concentration, and the vertical axis represents sensitivity. As can be seen from the figure, the sensor exhibits high sensitivity to water vapor, methane, and carbon dioxide, with particularly significant responses in the low concentration range, and maintains a stable sensitivity trend throughout the detection range. This result indicates that the sensor of the present invention possesses reliable quantitative gas detection capabilities over a wide concentration range, making it suitable for practical environmental monitoring applications.

[0098] like Figure 9 As shown, a cluster of amplitude-frequency response curves of the sensor under different gas concentrations is presented. The horizontal axis represents frequency, and the vertical axis represents amplitude or amplitude ratio. Each set of curves corresponds to the frequency response change of a certain gas as the concentration increases. It can be observed that as the gas concentration increases, the resonance peak shifts towards lower frequencies, and the curve shape remains consistent, without modal distortion. This indicates that gas adsorption mainly affects the vibration characteristics of the system by changing the equivalent mass of the resonant unit, further supporting the detection principle based on amplitude ratio changes, and confirming that the sensor is structurally stable and has a reliable response during gas detection.

[0099] The MEMS gas sensor based on a weakly coupled AlN thin-film resonator provided by this invention has many specific methods and approaches for implementing this technical solution. The above description is only a preferred embodiment of this invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A MEMS gas sensor based on a weakly coupled AlN thin-film resonator, characterized in that, include: A glass base, the front of which is provided with multiple sets of capacitor plates; An AlN thin-film resonator array is suspended above a glass base via the capacitor plate. The AlN thin-film resonator array consists of four resonator units, each of which is located at one of the four vertices of a square. Adjacent resonator units are connected by coupling beams to form a square symmetrical layout with the array center as the center of symmetry. In the four resonator units, at least two resonator units have gas-sensitive materials selectively deposited on their front sides for different target gases, and at least one resonator unit serves as a reference unit for which the gas-sensitive material is not deposited. The gas-sensitive material and the reference unit together form a differential measurement structure. The MEMS gas sensor is configured to achieve synchronous quantitative measurement of the concentration of multiple gases by detecting changes in the vibration amplitude ratio of each resonator unit. The capacitor plate is composed of a first electrode group and a second electrode group facing each other. The first electrode group is disposed on the front side of the glass base, and the second electrode group is disposed on the back side of the AlN thin film resonator array. Both the first electrode group and the second electrode group include multiple sub-electrode groups, and the total number of the sub-electrode groups is twice the number of the resonator units. Each sub-electrode group is composed of four triangular capacitor plates. Of the four triangular capacitor plates, two are driving electrodes and two are detection electrodes. The driving electrodes and the detection electrodes are distributed alternately to form a centrally symmetrical structure.

2. The MEMS gas sensor according to claim 1, characterized in that, The four corners of the resonator unit are fixed with T-shaped anchor points, which connect the resonator unit to the glass base.

3. The MEMS gas sensor according to claim 1, characterized in that, The triangular capacitor plates are metal capacitors, which are connected to an external interface circuit and a phase-locked loop circuit via leads.

4. The MEMS gas sensor according to claim 3, characterized in that, Simultaneous quantitative measurement of multiple gas concentrations, including the following methods: The external interface circuit and phase-locked loop circuit apply AC excitation signals to the driving electrode through leads, and utilize the inverse piezoelectric effect of AlN thin film to drive the AlN thin film resonator array to vibrate near the resonant frequency; The target gas is adsorbed by the gas-sensitive material, which changes the equivalent mass of the corresponding resonator unit, causing its resonant frequency to shift and disturbing the vibration state of the weakly coupled resonant system. The vibration amplitude of each resonator unit is acquired through the detection electrodes, and the amplitude ratio offset is obtained with reference unit as a benchmark. Based on the amplitude ratio offset, multi-channel decoupling calculations are performed to obtain the concentration of the target gas to be measured.

5. The MEMS gas sensor according to claim 4, characterized in that, The equations of motion for each resonator unit mass block are: ； In the formula, , , , This represents the equivalent mass, equivalent stiffness, displacement, and driving force of each resonator unit mass block. This represents the acceleration of the mass blocks in each resonant unit. , This indicates the coupling stiffness between two resonator units.

6. The MEMS gas sensor according to claim 5, characterized in that, The equations of motion are simplified to the following matrix: ； in, This represents the velocity vector of each resonant unit mass block. Let represent the mass matrix, stiffness matrix, driving force matrix, and displacement matrix of the weakly coupled resonant system, respectively, and we have: ； ； ； ； in, Indicates no external disturbance The dimensionless eigenvectors of the first mode reflect the proportional relationship of the vibration amplitudes of each resonator element. The time complex exponential factor represents the simple harmonic motion, characterizing the phase and amplitude changes of the resonator element as it undergoes simple harmonic motion over time.

7. The MEMS gas sensor according to claim 6, characterized in that, In the case of free vibration, the solution of the weakly coupled resonant system is transformed into solving the eigenvalues ​​and eigenvectors of the following dimensionless equation: ； in, Under the condition of no external disturbance The dimensionless eigenvalues ​​of the first mode satisfy the relation , The resonant frequency is determined by analyzing the weakly coupled resonant system. By analyzing the eigenvalues ​​and eigenvectors, we can inversely deduce the change in the equivalent mass of each resonator unit.

8. The MEMS gas sensor according to claim 6, characterized in that, The four resonator units are constructed as follows: The polyimide hydrophilic film on the surface of the first resonator unit has a strong adsorption capacity for water molecules. After the water molecules are adsorbed, the equivalent mass of the resonator increases and the resonant frequency decreases, forming a detectable mass load disturbance. The palladium-doped single-walled carbon nanotube film on the surface of the second resonator unit exhibits selective adsorption and catalytic response characteristics to methane molecules. After adsorbing methane, a mass change occurs, causing a shift in the resonant frequency. Amine functionalization of the surface of the third resonator unit The thin film undergoes a reversible chemical reaction with carbon dioxide through amine groups, the mass loading changes during the adsorption process, and it is unresponsive to nitrogen and oxygen background gases; The fourth resonator unit is a reference unit and does not deposit gas-sensitive materials; The mass change caused by gas adsorption generates vibrational disturbances in the weakly coupled resonant system. The amplitude signals of each unit are collected by the detection electrodes, and the amplitude ratio offset is obtained with the reference unit as the benchmark. Then, the multi-channel decoupling algorithm is used to solve the disturbance signals of different gases, so as to realize the synchronous quantitative detection of the concentration of three gases.

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