A multi-modal gas humidity sensor and a control method and a preparation method thereof

Abstract

The application relates to the technical field of micro-electro-mechanical system sensors, in particular to a multi-modal gas humidity sensor and a control method and a preparation method thereof, the sensor comprising a monolithic integrated sensing unit, a multi-modal switching switch matrix, a driving and detecting circuit, a measurement and control system, a wireless communication module and an upper computer, the output end of the driving and detecting circuit is electrically connected with the signal input end of the measurement and control system, the signal output end of the monolithic integrated sensing unit is electrically connected with the input end of the multi-modal switching switch matrix, and the output end of the multi-modal switching switch matrix is electrically connected with the input end of the driving and detecting circuit, the CMUT and the IDE monolithic integration are realized through wafer bonding and single peeling process, the switching matrix is used to realize three detection mode switching and feature slope anti-wet interference discrimination, the monolithic integrated sensing unit is constructed by connecting the CMUT and the IDE in parallel, the collaborative response of the mass load effect and the dielectric capacitance effect is realized, and the detection sensitivity is improved.

Description

Technical Field

[0001] This invention relates to the field of microelectromechanical systems (MEMS) sensor technology, and in particular to a multimodal gas humidity sensor and its control and fabrication methods. Background Technology

[0002] Gas sensing technology plays an irreplaceable role in environmental monitoring, industrial process control, medical and health care, and aerospace. The performance of gas sensors directly affects the detection accuracy and operating efficiency of related industries. Traditional gas sensors are mainly divided into metal oxide semiconductor, electrochemical, optical and bulk resonant types, but all have obvious limitations. For example, resistive sensors require high temperature operation, have high power consumption and poor selectivity, and electrochemical sensors have lifespan limited by electrolytes, making it difficult to meet miniaturization requirements.

[0003] With the development of Micro-Electro-Mechanical Systems (MEMS) technology, MEMS-based micro-nano sensors have become ideal choices for portable devices due to their advantages of miniaturization, low power consumption, and high consistency. Capacitive micromechanical ultrasonic transducers (CMUTs), as novel MEMS resonant sensors, have attracted much attention in the field of gas sensing. However, existing CMUT sensors still face core technological bottlenecks: First, relying on a single mass adsorption mechanism, they lack sufficient sensitivity for detecting extremely low concentrations of gas or substances with changing dielectric properties. Second, they cannot distinguish between target gas and water vapor interference in high humidity environments, and are prone to mechanical saturation under high gas concentrations, limiting the dynamic detection range. Third, they lack fault tolerance mechanisms; a single point of failure can lead to system paralysis. Fourth, the use of hybrid... When using integrated methods, the large package size and parasitic effects introduced by the bonding wires attenuate high-frequency signals, failing to meet the miniaturization and low parasitic requirements of high-performance sensors. In addition, conventional MEMS sensors also face the contradiction of balancing high sensitivity and high quality factor (Q value). To improve adsorption sensitivity, a thicker sensitive film layer needs to be modified, but this introduces significant mechanical losses and viscoelastic effects, leading to a sharp drop in Q value and deteriorating frequency stability and detection accuracy. At the same time, traditional resonators and electrical detection units are incompatible with each other, making it difficult to achieve monolithic integration using standard MEMS processes and interdigitated electrodes (IDE), further limiting the development of sensor integration and arraying. At present, a multimodal gas and humidity sensor and its control and fabrication methods are needed. Summary of the Invention

[0004] To address the limitations of existing air humidity sensors in terms of limited dynamic detection range and lack of fault tolerance mechanisms, this invention provides a multimodal air humidity sensor, its control method, and its fabrication method.

[0005] In a first aspect, the present invention provides a multimodal gas humidity sensor, which adopts the following technical solution: A multimodal air humidity sensor, comprising: Power supply and bias module, monolithic integrated sensing unit, multi-mode switching matrix, drive and detection circuit, STM32 measurement and control system, wireless communication module and host computer; The signal output terminal of the monolithic integrated sensing unit is electrically connected to the input terminal of the multimode switching matrix, the output terminal of the multimode switching matrix is ​​electrically connected to the input terminal of the driving and detection circuit, and the output terminal of the driving and detection circuit is electrically connected to the signal input terminal of the STM32 measurement and control system. The control output terminal of the STM32 measurement and control system is electrically connected to the control input terminal of the multi-mode switching matrix, and is used to control the on / off state of the multi-mode switching matrix to realize the detection mode switching. The STM32 measurement and control system is bidirectionally connected to the host computer through the wireless communication module to realize data transmission and command interaction. The power supply and bias module is used to provide power support.

[0006] Furthermore, the monolithic integrated sensing unit includes a silicon substrate, a silicon nitride insulating structure layer, an IDE interdigitated electrode region, and a CMUT array region; The silicon nitride insulating structure layer is deposited on the upper surface of the silicon substrate, and the IDE interdigitated electrode region and the CMUT array region are respectively disposed on the upper surface of the silicon nitride insulating structure layer along the length direction of the silicon substrate, thereby realizing monolithic integration; The IDE interdigitated electrode area includes a left busbar, a right busbar, a first pad, a second pad, and two sets of metal fingers. The first pad is fixedly connected to the left busbar. The left busbar is connected to a set of metal fingers extending horizontally to the right. The second pad is fixedly connected to the right busbar. The right busbar is connected to another set of metal fingers extending horizontally to the left. The two sets of metal fingers interlock and have a gap. The gap is the area for sensitive thin film deposition and edge electric field interaction.

[0007] Furthermore, the CMUT array region includes The system comprises a circular micro-element, a surface metal interconnect network, signal pads, and a common pad. The circular micro-element is arranged in an array, and each circular micro-element corresponds to the effective vibration region of a CMUT diaphragm. The upper electrodes of all circular micro-elements are connected to the signal pads through the surface metal interconnect network. The signal pads serve as the positive terminals of the acoustic branches. The substrates of all circular micro-elements are led out to the common pads through vias. The common pads serve as the system common reference ground. The signal pads and the first pads are led out independently at the chip physical level, where N is a positive integer.

[0008] Furthermore, the monolithic integrated sensing unit also includes an electromechanical series branch, a parallel branch, and an additional series resistor. ; The electromechanical series branch is a resistor. ,inductance and capacitors The resistor is composed of The damping effect of the CMUT diaphragm is characterized to reflect sensor energy loss and affect the quality factor; the capacitance... The inductance characterizes the equivalent elastic capacitance of the CMUT diaphragm. Characterizing the equivalent inertia of the CMUT diaphragm; The parallel branch is the static capacitor of the CMUT. With IDE capacitors Composition, total equivalent parallel capacitance satisfy The static capacitor The intrinsic static capacitance of the CMUT is calculated from the electrode area, gap, and dielectric constant. The IDE capacitance is... The capacitance value is positively correlated with the dielectric constant caused by the moisture absorption of the sensitive membrane; The additional series resistor Used to correct energy dissipation that is unrelated to diaphragm motion caused by manufacturing tolerances.

[0009] Furthermore, the multi-mode switching matrix includes multiple sets of low on-resistance analog switches, each set of analog switches being controlled by the GPIO level of the STM32 measurement and control system; The input terminals of the multimode switching matrix include a CMUT signal input terminal and an IDE signal input terminal. The CMUT signal input terminal is electrically connected to the signal pad, and the IDE signal input terminal is electrically connected to the first pad. The output terminal of the multi-mode switching matrix includes an oscillation circuit connection terminal and a phase-sensitive detector circuit connection terminal. The multiple sets of analog switches include an impedance channel switch, an oscillation channel switch, and a parallel node switch. The circuit topology is dynamically reconstructed by combining the on and off states of the three sets of switches.

[0010] Furthermore, the driving and detection circuit includes an oscillation circuit and a phase-sensitive detection circuit. The oscillation circuit includes a two-stage cascaded operational amplifier, a buffer, and a positive phase-shift compensation network. The first-stage operational amplifier is a FET-input type operational amplifier used for initial signal pickup and amplification. The second-stage operational amplifier is a clamping amplifier used for signal gain and output amplitude limiting. The buffer is used to enhance driving capability and isolate load effects. The positive phase-shift compensation network is used to correct loop phase delay. The phase-sensitive detection circuit is used to demodulate the impedance change of the IDE interdigitated electrode region into an analog voltage signal.

[0011] Secondly, a control method for a multimodal air humidity sensor includes: The system initializes and operates stably in a standard clean air environment for a preset time. It then collects the frequency signal output from the Colpitts oscillator circuit, calculates the average frequency value, and sets it as the clean air reference frequency. ; Preset parameters and physical model definitions are used to preset the detection start threshold in the non-volatile memory of the STM32 measurement and control system. Resonance saturation threshold Characteristic slope K, target gas characteristic slope and the slope of humidity interference characteristics ; The multi-mode switching matrix is ​​controlled to enter mode three, and the CMUT and IDE electrical circuits are connected in parallel to the oscillation circuit to acquire the current frequency measurement value. And calculate the total frequency offset, and then compare the total frequency offset with the detection start threshold. Determine the triggering environmental disturbance; When environmental disturbance identification is triggered, a fast timing scan is initiated, switching to mode one and mode two to collect capacitance changes respectively. With the change in resonant frequency The characteristic slope K and the preset reference slope are used to distinguish between humidity interference and target gas. When identifying a target gas, the amount of change in resonant frequency is used as a basis. With resonant saturation threshold Depending on the relationship, you can choose to call the concentration value output from Mode 3 data or switch to Mode 1 extended detection range; During mode one detection, the gas concentration value is calculated based on the collected capacitance change. The concentration value is monitored in real time, and when it falls below the safety threshold, the system switches back to mode three and continuously monitors in a loop.

[0012] Furthermore, when the first mode is the IDE independent detection mode, the impedance channel switch of the multimode switching matrix is ​​closed, the oscillation channel switch and the parallel node switch are open, the IDE unit signal is routed to the phase-sensitive detection circuit, and the CMUT unit is in an electrically floating or shielded state. When the second mode is the CMUT independent detection mode, the oscillation channel switch of the multi-mode switching matrix is ​​closed, the impedance channel switch and the parallel node switch are open, the CMUT unit signal is routed to the Colpitts oscillation circuit, and the IDE unit is in an open circuit state. When the third mode is the parallel collaborative detection mode, the parallel node switch of the multi-mode switching switch matrix and the oscillation channel switch are closed, the impedance channel switch is open, and the IDE unit and the CMUT unit are electrically connected in parallel and then connected to the Colpitts oscillation circuit.

[0013] Furthermore, the calculation of the total frequency offset is performed based on electromechanical series branches, parallel branches, and additional series resistance, including: The total impedance of the monolithic integrated sensing unit This is a series-parallel combination of electromechanical series branches and parallel branches, where the impedance of the electromechanical series branch is... satisfy ; When in detection mode, the total impedance is determined. The imaginary part of the equation is zero to determine the parallel resonance point, and the resonant frequency is calculated based on this parallel resonance point. The resonant frequency The calculation formula is: , in, The damping equivalent resistance of the CMUT diaphragm is given. The imaginary unit is used to characterize the phase relationship between voltage and current in an AC circuit. Angular frequency, The equivalent inertial inductance of the CMUT diaphragm. The equivalent elastic capacitance of the CMUT diaphragm; The total frequency offset Current frequency measurement value Relative to clean reference frequency The offset satisfies And the total frequency offset The frequency shift caused by the mass effect and the frequency shift caused by the capacitance effect are linearly superimposed, and the mass effect is mediated by the inductance in the electromechanical series branch. The change in capacitance is characterized by the capacitance effect through the IDE capacitor in the parallel branch. The change in quantity is represented.

[0014] Thirdly, a method for fabricating a multimodal air humidity sensor includes: S1. Substrate and thin film preparation: Low-resistivity single-crystal silicon wafers are selected as the top wafer and bottom wafer, respectively. A silicon nitride layer is deposited on the surface of the top wafer as the CMUT diaphragm, and a silicon dioxide layer is grown on the surface of the bottom wafer as an insulating and sacrificial layer. S2. Cavity etching and surface treatment: an array of cavity structures is etched in the silicon dioxide layer of the substrate, and the surface of the top substrate is chemically and mechanically polished. S3. Cleaning and bonding: After cleaning and activating the upper and lower silicon wafers, direct bonding of silicon nitride and silicon dioxide is performed and high-temperature annealing is carried out. S4. Diaphragm release and via fabrication: Remove the nitride layer on the back of the top wafer and wet-etch the silicon substrate of the top wafer to release the silicon nitride diaphragm. Prepare the via for the bottom electrode on the upper film surface. S5. Electrode forming and monolithic integration: Deposit a metal layer in a designated area and simultaneously form the CMUT top electrode, common ground electrode, and positive and negative interdigitated electrodes of the IDE through a stripping process, so as to achieve independent lead-out of each electrode port. S6. Device calibration: Calibrate the detection start threshold, resonance saturation threshold, characteristic slope of target gas and humidity interference, and capacitance and concentration sensitivity coefficient in IDE mode under standard clean air environment, and store them in the non-volatile memory of STM32.

[0015] In summary, the present invention has the following beneficial technical effects: 1. This invention constructs a monolithic integrated sensing unit with parallel coupling of CMUT and IDE, and combines it with a modified equivalent circuit model to achieve a synergistic response of mass load effect and dielectric capacitance effect, so that the frequency offset satisfies the linear superposition relationship. It significantly improves the detection sensitivity without increasing the thickness of the sensitive film, while maintaining the high quality factor (Q value) and frequency stability of the device, effectively solving the technical contradiction of the difficulty in achieving high sensitivity and high Q value in traditional sensors.

[0016] 2. This invention constructs three modes—IDE independent detection, CMUT independent detection, and parallel collaborative detection—through a multi-modal switching matrix. Combined with a signal intelligent identification mechanism based on characteristic slope differences, it accurately eliminates water vapor interference signals in high-humidity environments, avoiding false alarms. Furthermore, through automatic mode switching, it achieves dynamic range expansion from trace warning to high-concentration tracking. At the same time, relying on the three-modal redundancy design, it endows the system with fault tolerance capabilities, preventing single-point failures from causing system paralysis, and comprehensively improving the sensor's environmental adaptability, anti-interference ability, and operational reliability.

[0017] 3. This invention adopts a monolithic integration fabrication process based on wafer bonding and substrate transfer. The electrode structures of CMUT and IDE are formed simultaneously through a single metal deposition and stripping process, which breaks through the bottleneck of traditional bulk resonators that are difficult to integrate at high density. It eliminates the parasitic effects introduced by wire bonding in hybrid integration, significantly reduces the sensor packaging volume, meets the application requirements of sensor miniaturization and arraying, and is compatible with standard MEMS processes, making it suitable for large-scale mass production.

[0018] 4. This invention achieves real-time transmission, parsing, and display of detection data, as well as flexible switching control of detection modes, through the coordinated operation of the STM32 measurement and control system, wireless communication module, and host computer. At the same time, the control method ensures the automation and intelligence of the detection process through preset parameters and dynamic identification logic. It is easy to operate and has high detection accuracy, and is suitable for gas and humidity sensitive detection scenarios in multiple fields such as environmental monitoring, industrial process control, and medical health. Attached Figure Description

[0019] Figure 1 This is a top view schematic diagram of the CMUT–IDE parallel structure of a multimodal air-humidity sensor according to an embodiment of the present invention.

[0020] Figure 2 This is a circuit model diagram of the CMUT and interdigitated electrodes in parallel according to an embodiment of the present invention.

[0021] Figure 3 These are impedance amplitude-frequency response curves under different Cp conditions according to embodiments of the present invention.

[0022] Figure 4 These are impedance amplitude-frequency response curves under different Ls conditions according to embodiments of the present invention.

[0023] Figure 5 This is an impedance amplitude-frequency response curve under different Ls and Cp conditions according to an embodiment of the present invention.

[0024] Figure 6 This is a diagram of a multimodal sensor system architecture based on parallel connection of CMUT and IDE according to an embodiment of the present invention.

[0025] Figure 7 This is a flowchart illustrating the fabrication process of the CMUT–IDE parallel structure according to an embodiment of the present invention. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the accompanying drawings.

[0027] Example 1 Reference Figure 1 This embodiment of a multimodal humidity sensor includes: This embodiment discloses a multimodal humidity sensor, specifically employing a reconfigurable resonant structure with a capacitive micromechanical ultrasonic transducer (CMUT) and interdigitated electrodes (IDE) coupled in parallel. The sensor includes a power supply and bias module, a monolithic integrated sensing unit, a multimodal switching matrix, a drive and detection circuit, an STM32 measurement and control system, a wireless communication module, and a host computer. The power supply and bias module is electrically connected to the monolithic integrated sensing unit, the multimodal switching matrix, the drive and detection circuit, the STM32 measurement and control system, and the wireless communication module, providing stable DC power and potential reference to each module. The signal output terminal of the monolithic integrated sensing unit is electrically connected to the input terminal of the multimodal switching matrix, used to transmit the detected humidity. Gas or humidity-related signals are transmitted to the switch matrix; the output of the multi-mode switching switch matrix is ​​electrically connected to the input of the drive and detection circuit to achieve directional routing of the detection signal; the output of the drive and detection circuit is electrically connected to the signal input of the STM32 measurement and control system to transmit the processed electrical signal to the measurement and control core; the control output of the STM32 measurement and control system is electrically connected to the control input of the multi-mode switching switch matrix, and the on / off state of the switch matrix is ​​controlled by GPIO level signals to achieve detection mode switching; the STM32 measurement and control system has bidirectional communication connection with the wireless communication module, and the wireless communication module has bidirectional communication connection with the host computer system to complete data transmission and command interaction, and realize visualization of detection results and manual mode control.

[0028] Specifically, like Figure 1 As shown in the top view of the CMUT-IDE parallel integrated sensor of the present invention, the planar topology of the device is illustrated. The overall layout is spatially divided into an electrical sensing region on the left and an acoustic sensing region on the right. Both are supported by the same silicon substrate and are jointly fabricated on the surface of a silicon nitride insulating layer to achieve monolithic integration. The left side is the IDE interdigitated electrode region, where metal fingers are directly deposited on the surface of the silicon nitride insulating layer, forming a comb-like structure composed of two sets of interlaced, parallel extending fingers. Specifically, the first pad, indicated by reference numeral 3, connects to the left busbar, and its extended fingers extend horizontally to the right; the second pad, indicated by reference numeral 4, connects to the right busbar, and its extended fingers extend horizontally to the left, forming a tight cross-interlocking structure with the former. The tiny gaps between the fingers are the key areas for sensitive thin film deposition and edge electric field interaction.

[0029] The right side is the CMUT array area, which consists of N×N (can be designed according to actual impedance matching requirements) circular micro-elements arranged in a tightly packed array. This example uses... Figure 1Taking the 3×3 array shown as an example, each circular unit represents the effective vibration area of ​​a CMUT diaphragm. The upper electrodes of all units are connected to the signal pad (CMUT upper electrode) shown by label 1 through a surface metal interconnect network, serving as the positive electrode of the acoustic branch. The substrates of all units are led out through vias to the common pad (CMUT lower electrode) shown by label 2, serving as the common reference ground of the system. In this design, label 1 (CMUT signal terminal) and label 3 (IDE signal terminal) are kept in an independent lead-out state at the chip physical level, providing a flexible hardware interface for subsequent multi-mode switching to achieve independent detection or parallel collaborative detection through external circuits.

[0030] Based on the monolithic integrated structure, in order to further reveal its high-sensitivity sensing mechanism from a theoretical perspective, a modified Butterworth-VanDyke (BVD) equivalent circuit model was established, such as... Figure 2 As shown, this model accurately characterizes the physical behavior of the CMUT and IDE connected in parallel at the electrical level. Its circuit topology mainly consists of the following three parts: 1. Electromechanical series branch: , , This branch describes the mechanical properties of the CMUT diaphragm. The damping effect of the CMUT diaphragm reflects the energy loss of the sensor. The main factor affecting the quality factor Q is that current technologies typically require depositing a thick polymer sensitive film on the diaphragm surface to improve sensitivity, which significantly increases the risk of malfunction. This leads to a deterioration in the Q-value. However, this invention utilizes parallel IDE to introduce dielectric response, eliminating the need for thick film deposition in the CMUT diaphragm. This effectively avoids mechanical energy dissipation caused by viscoelasticity, ensuring the system maintains extremely low... It works under the premise of high Q value and high Q value. The equivalent elastic capacitance of the CMUT diaphragm is determined by the diaphragm's geometry, Young's modulus of the material, and film thickness. It is a crucial parameter determining the CMUT's inherent resonant frequency. However, in the application of this invention, since the CMUT diaphragm does not have a sensitive film deposited and operates in a small signal range, its stiffness does not change significantly with humidity or gas adsorption. It can be considered constant during the detection process. Representing the equivalent inertia, this inductance is related to the diaphragm's mass and motion inertia, indicating the diaphragm's motion inductance. It is the response generated when the diaphragm moves, and the inductance value changes as the diaphragm's motion increases. Gas adsorption or changes in interface mass can cause perturbations in the effective mass, which are the main sources of frequency variation in this invention.

[0031] 2. Parallel Branch: The parallel branch is the static capacitor of the CMUT. With IDE capacitors Together, the total equivalent parallel capacitance can be expressed as: .in, The intrinsic static capacitance of the CMUT, determined by the electrode area, gap, and dielectric constant, is one of the important parameters determining the parallel resonant frequency. Its specific expression is: ,in, The vacuum permittivity, The relative permittivity of the medium (usually air or vacuum) between the electrodes of the CMUT. This represents the area of ​​the upper and lower electrodes facing each other. The distance between the two electrodes is the gap width. Since no sensitive film is deposited in the CMUT region of this invention, the structural stiffness and electrode geometry remain stable. It does not change significantly during humidity or gas adsorption and can be considered a constant quantity. The IDE capacitor's value changes with the dielectric constant due to moisture absorption by the sensitive film. It is the primary capacitance variable for frequency tuning in this invention. The IDE consists of two sets of interlaced, parallel-extending metal fingers forming a comb-like structure. These two sets of fingers are connected to different electrodes (the first pad labeled 3 and the second pad labeled 4), forming an alternating "emitter-receiver" structure. When a stable voltage is applied between the two sets of fingers, a uniform edge electric field is formed between the fingers and on the surface, covering the entire sensitive film deposition area. The capacitance value of the IDE... The core calculation formula is determined by the length, width, spacing, metal thickness, and dielectric properties of the sensitive film, and is jointly derived from the factors including the length, width, spacing, metal thickness, and dielectric properties of the finger strips. ,in, denoted as ρ, where N is the relative permittivity of the sensing membrane, L is the number of finger pairs, L is the length of a single finger, and g is the finger spacing. For the finger strip width, in this embodiment, the sensitive film (such as polyimide) is deposited on the gaps and surface of the IDE finger strip, and it is directly within the range of the edge electric field. Therefore, the dielectric constant of the sensitive film is... The core variable affecting the CP capacitance value is the geometric parameters such as the length, width, and spacing of the finger strips, which remain fixed after the fabrication is completed and will not change with environmental changes.

[0032] 3. Additional Series Resistance: Manufacturing tolerances (such as minute unevenness in cavity depth, interconnect resistance, edge leakage, etc.) introduce energy dissipation unrelated to diaphragm motion. The ideal BVD model cannot describe such non-motion losses. Therefore, an additional series resistance is introduced into the equivalent model. Make corrections. It mainly affects the peak value and bandwidth of the amplitude-frequency curve, and can be considered an approximate constant under stable process conditions. Total impedance Represented as a series-parallel combination of electromechanical branches and parallel capacitor branches, the mathematical expression is: , , When the system reaches the parallel resonance point, the imaginary part of the total impedance is zero, and the resonant frequency is... It can be calculated using the following formula: ,in, The damping equivalent resistance of the CMUT diaphragm is given. The imaginary unit is used to characterize the phase relationship between voltage and current in an AC circuit. Angular frequency, The equivalent inertial inductance of the CMUT diaphragm. The formula shows that the equivalent elastic capacitance of the CMUT diaphragm is given by the frequency... It is closely related to the mass effect and capacitance effect, increasing or This will lead to Reduced. Under small perturbations, the frequency shift can be described by a linearized formula. The amount of frequency shift. It is mainly caused by the combined effects of mass effect and capacitance effect.

[0033] Frequency shift and and The relationship between the changes can be expressed as: The first term represents the effect of mass on frequency, i.e. The resulting frequency shift; the second term represents the effect of capacitance on frequency, i.e. The effect of changes in on frequency. When considering only mass loading, the frequency shift is mainly due to ... control: When only capacitance change is considered, the frequency shift is mainly due to control: From a theoretical perspective, the CMUT-IDE parallel architecture of this invention can achieve a synergistic response of mass load effect and dielectric capacitance effect, and the frequency shift caused by the two satisfies a linear superposition relationship.

[0034] To further verify the accuracy of the aforementioned frequency response theoretical derivation, this invention conducted LTspice simulation analysis based on the modified BVD model, as follows: Figure 3 As shown, by applying a constant amplitude AC current source to the port, the curve of the port impedance amplitude |Z| versus frequency is obtained by scanning, and the frequency corresponding to the impedance peak is selected as the parallel resonant characteristic frequency used in this invention. Simulations first verify the response characteristics of a single variable: when only the IDE capacitance is changed... In this case, the resonant peak of the impedance amplitude-frequency curve remains sharp, and the peak height is basically unchanged from the half-power bandwidth. As the frequency increases, the system's quality factor (Q value) does not decrease; the peak impedance position gradually shifts towards lower frequencies, exhibiting characteristic frequency pairings. The monotonically linear decreasing relationship, with each 2.5pF capacitance increment causing a frequency shift of approximately 3.3kHz, verifies the capacitive effect of parallel capacitance changes on the characteristic frequency; this is further demonstrated by changing only the electromechanical inductance. In such cases Figure 4 As shown, each curve maintains a single peak, but the peak frequency varies with... The increase is clearly shifted towards lower frequencies, each 0.5... The inductance increment caused a significant frequency shift of approximately 30 kHz, consistent with... The relationship reflects the mass effect caused by mass loading. Furthermore, when simultaneously applied to… and When applying small changes, such as Figure 5 As shown, the simulation results indicate that the characteristic frequency shift under each combination of operating conditions is related to the corresponding single-mode frequency shift. Offset and only The sum of the offsets is consistent; for example, under the parameter conditions selected in this embodiment, we can obtain... Approximately 3.3kHz Approximately 30kHz, while the total frequency shift during the disturbance is... Approximately 33.3 kHz, and This is consistent. The response of the parallel resonant characteristic frequency to the capacitance and mass effects satisfies a first-order linear superposition relationship. This dual-mechanism synergistic response mechanism enables the superposition enhancement of the frequency signal to weak environmental changes, thereby breaking through the sensitivity limit of traditional single-mechanism sensors in micro-detection.

[0035] To apply the highly sensitive sensor chip to practical monitoring scenarios, a complete hardware circuit and control system were further constructed. For example... Figure 6 As shown, the monolithic integrated sensor system based on parallel connection of CMUT and IDE implemented in this invention mainly consists of a power supply and bias module, a monolithic integrated sensing unit, a multi-mode switching matrix, a drive and detection circuit, an STM32 measurement and control system, a wireless communication module, and a host computer system.

[0036] In this system, the power supply and bias module first provides a stable DC bias voltage to the CMUT sensor, while simultaneously providing a common ground (GND) potential reference to the IDE sensor. This DC bias voltage enables the CMUT vibrating diaphragm to undergo static pre-deformation, thereby placing the CMUT in a linear operating state capable of electromechanical conversion.

[0037] The sensing unit uses the monolithic integrated chip described in this invention. Unlike traditional discrete devices, this embodiment integrates a CMUT unit and an IDE unit simultaneously on the same substrate. The CMUT unit acquires acoustic parameters by detecting changes in the adsorption mass of the target gas on the sensitive film layer based on the mass loading effect; the IDE unit acquires the dielectric parameters of the gas by detecting changes in the dielectric properties or impedance of the gas after adsorption by the sensitive material using the edge electric field effect.

[0038] The multimode switching matrix serves as the core physical unit for system signal routing and topology reconstruction. Its inputs are connected to the signal electrodes of the CMUT unit and the IDE unit, respectively, while its outputs are connected to the Colpitts oscillator circuit and the phase-sensitive detector circuit, respectively. This matrix integrates multiple sets of low-on-resistance analog switches controlled by STM32 GPIO levels. By combining the on / off states of these switches, dynamic topology reconstruction is achieved. When the control signal command is Mode 1 (IDE independent detection), the STM32 controls the impedance channel switch inside the switching matrix to close, while simultaneously controlling the oscillation channel switch and the parallel node switch to open. At this time, the signal from the IDE unit is independently routed to the downstream phase-sensitive detector circuit, while the CMUT unit is electrically floating or shielded. The system is physically constructed as a pure capacitor or impedance detection loop, achieving directional acquisition of environmental dielectric parameters and avoiding load interference from acoustic devices. When the control signal command is Mode 2 (CMUT independent detection), the STM32 controls the oscillation channel switch inside the switching matrix to close, and simultaneously... When the control impedance channel switch and parallel node switch are open, the signal from the CMUT unit is independently routed to the Colpitts oscillator circuit above, and the IDE unit is in an open-circuit state. The system is physically constructed as a single acoustic resonant circuit. The CMUT mainly experiences frequency shift due to the mass loading effect caused by the adsorption of the target gas, thus achieving directional acquisition of acoustic parameters. When the control signal command is mode three (parallel cooperative detection), the parallel node switch and oscillator channel switch inside the STM32 control switch matrix are closed simultaneously, while the impedance channel switch is open. At this time, the IDE unit and the CMUT unit are electrically connected in parallel inside the matrix and connected to the Colpitts oscillator circuit as a whole load. Under this topology, the dielectric change sensed by the IDE is converted into a variable capacitance, which is directly superimposed on the resonant circuit of the CMUT, constructing a unified resonant system with multi-mechanism coupling. This connection method enables the capacitance effect of the IDE and the mass loading effect of the CMUT to achieve a cooperative response at the physical level. The output frequency shift is a linear superposition of the two effects, thereby significantly improving the detection sensitivity.

[0039] This system further solves the problem of a single sensing unit's physical damage or failure causing the entire monitoring system to completely collapse through software logic. Simultaneously, it can acquire dielectric or acoustic parameters according to the application scenario to meet the monitoring needs of specific physical quantities. In actual operation, the STM32 measurement and control system has real-time status monitoring logic. If no frequency output is detected in the oscillation circuit in collaborative mode or CMUT independent mode, the system will automatically determine that the CMUT unit has failed due to thin-film rupture or circuit short circuit, and immediately trigger a fault interrupt service, forcibly disconnecting the CMUT-related signal path and switching the system to mode one, continuing to monitor changes in environmental dielectric parameters using the IDE unit, thereby maintaining basic environmental sensing capabilities. Similarly, if the IDE branch fails, the system can lock into mode two and continue operating. This strategy of mutual backup and automatic isolation, combined with the system's directional parameter acquisition function based on monitoring task requirements, ensures that even in the extreme case of physical damage to the core sensing element, the entire monitoring system will not completely collapse, thus guaranteeing the system's high reliability.

[0040] The oscillation circuit is based on a Colpitts oscillation topology and drives the CMUT to resonate through two cascaded operational amplifier stages. The first stage uses a high-performance FET-input operational amplifier, the ADA4627, for initial signal pickup and amplification. The second stage uses a clamping amplifier, the OPA699, which not only provides signal gain but also limits the output amplitude using its input clamping characteristics, strictly limiting the output voltage range to -0.3V to 3.3V. The amplified and shaped signal is then fed into a BUF602 buffer to enhance driving capability and isolate load effects. Furthermore, a positive phase shift compensation network is integrated into the circuit to correct loop phase delay, ensuring the system strictly adheres to the Barkhausen stability criterion and achieves real-time locking of the resonant frequency. For IDE detection, a phase-sensitive detector circuit is configured in the lower path to accurately convert the capacitance change of the IDE into an analog voltage signal. The circuit mainly consists of a cascaded transimpedance amplifier (TIA), an analog multiplier, and a low-pass filter. First, the weak AC current generated by the change in dielectric constant of the IDE is fed into a transimpedance amplifier (e.g., AD8605) to complete the linear conversion of current to voltage and signal buffering. Then, the converted voltage signal enters the synchronous demodulation stage and performs analog multiplication with a reference signal of the same frequency, shifting the signal carrying capacitance information to the DC baseband. Finally, the high-frequency carrier component is filtered out by an active low-pass filter (LPF), and a DC voltage signal with an amplitude that is linearly related to the IDE capacitance value is output for the back-end ADC to acquire and demodulate the impedance change into an analog voltage signal.

[0041] The STM32 measurement and control system uses an STM32F4 or G4 series microcontroller configured as an external counter. It calculates the real-time frequency data of the CMUT by precisely counting the rising edges of the Colpitts oscillator circuit output signal; simultaneously, it uses an internal ADC to acquire the voltage signal from the phase-sensitive detector circuit. This design leverages the high-speed processing capabilities of the microcontroller to ensure the system responds quickly to changes in sensor signals.

[0042] The wireless communication module uses an industrial-grade Bluetooth module (BLE, such as HC-08 or equivalent) to establish a transparent data transmission link between the MCU and the host computer via an asynchronous serial interface (UART). The module's TX / RX pins are mapped to the PA10 / PA9 pins of the STM32, and the communication baud rate is configured to 115200bps to ensure efficient and stable data transmission.

[0043] The host computer system is developed based on the PyQt framework and features real-time data display and mode control functions. This host computer can display frequency waveforms and impedance change curves separately, and allows users to interactively select between "independent detection" and "cooperative detection" modes. The host computer transmits mode switching commands to the STM32 microcontroller via a wireless transmission module. The STM32 then parses the commands and controls the switching matrix. Furthermore, the host computer software has a built-in data parsing module that converts the received raw data into measured physical quantity values ​​in real time and displays them, thus enabling the measurement and display of multiple physical quantities.

[0044] Example 2 The difference between this embodiment and Embodiment 1 is that this embodiment provides a control method for a multimodal air humidity sensor; Step S1: System initialization. The STM32 measurement and control system completes self-tests of each hardware module, runs stably for a preset time in a standard clean air environment, acquires the frequency signal output by the Colpitts oscillator circuit, calculates the average frequency value, and sets it as the clean air reference frequency. ; Step S2: Before executing the algorithm, the system presets the following key parameters in the MCU's non-volatile memory based on the factory calibration data: Detection start threshold ( ): Under standard clean air conditions (i.e., in an environment where the target gas is absent), the system exhibits modal three-time frequency fluctuations. The value (i.e., 3 times the standard deviation) defines the minimum effective signal strength of the system. Frequency fluctuations below this value are considered background interference and will not trigger subsequent processing.

[0045] Resonant saturation threshold ( ): The upper limit of the frequency offset that the CMUT maintains in maintaining linear mass response characteristics. When the frequency shift amplitude detected in real time exceeds this value, it indicates that the mass load on the vibrating diaphragm surface has exceeded its effective dynamic range, and the sensor is about to enter the nonlinear response region or faces the risk of vibration stoppage.

[0046] Characteristic slope (K): defined as the amount of capacitance change detected by the interdigitated electrodes. The resonant frequency offset detected by the micromechanical ultrasonic transducer (CMUT) The ratio between ) is .

[0047] Target gas characteristic slope ( This is for volatile organic compounds (VOCs) that are the target of detection. Because gas molecules are typically large, adsorption causes a significant shift in the resonant frequency of the CMUT. Its relative permittivity is usually low ( The amount of capacitance change caused by the IDE. Relatively weak.

[0048] Humidity interference characteristic slope ( Regarding water molecules, due to their extremely high relative permittivity (…), The capacitance change it causes is extremely large relative to the frequency shift caused by its mass, therefore .

[0049] Step S3: Corresponding to mode three, the MCU controls the analog switch matrix to close all channels, connects the CMUT and IDE electrical circuits in parallel to the oscillation circuit, and monitors the total frequency offset in real time. ,in This is the current measurement value. It is the clean reference frequency at system initialization. This formula is used to extract the frequency shift amplitude relative to the initial state and eliminates the influence of positive and negative signs.

[0050] Step S4: If This indicates that the current frequency shift amplitude has not exceeded the system's inherent frequency fluctuation limit. The system determines that it is in a background environment without the target gas and remains silent. This indicates that the frequency shift amplitude has significantly exceeded the background interference level, and it is determined that a suspected physical field disturbance has occurred in the environment. Since a single mixed frequency value cannot distinguish whether the disturbance originates from the adsorption of real VOCs gases or from the adsorption of water molecules under high humidity, the MCU immediately suspends the current reading and automatically jumps to step S5.

[0051] Step S5: Physical configuration switching. The STM32 measurement and control system starts a fast timing scan (e.g., within a 200ms window), switches to mode one (IDE independent), connects to the phase-sensitive detection circuit, and acquires the capacitance change caused by the change in dielectric properties. Switch to Mode 2 (CMUT independent), connect to the oscillation circuit, and collect the change in resonant frequency. .

[0052] Step S6: Calculate the current feature slope: Based on the real-time calculated K value and the preset reference slope Based on the comparison results, the system automatically executes the following branch logic: Branch A (determined to be humidity interference): Logic: If the calculated K value is large, it is close to the reference characteristic value of water. If the problem is determined to be caused by humidity interference, the signal shielding logic is executed, the alarm is not triggered, and the process returns to step S3.

[0053] Physical meaning: Although water molecule adsorption also causes a frequency shift, the high dielectric constant of water ( The capacitance change caused by it is much greater than the frequency shift under the same mass, exhibiting typical dielectric response-dominated characteristics.

[0054] Action: The MCU determines that the current signal source is invalid water vapor, automatically executes the signal shielding logic, does not trigger an alarm, and automatically returns to scenario one to continue monitoring, thus fundamentally solving the problem of frequent false alarms by traditional quality sensors in rainy or humid environments.

[0055] Branch B (identified as target gas VOCs): Logic: If the K value falls within the characteristic range of the target VOCs .

[0056] Physical meaning: The signal exhibits typical mass load-dominated characteristics, which are consistent with the physical properties of the target organic gas. It is confirmed as a valid target gas signal, and step S7 is executed.

[0057] Step S7: If This indicates that the concentration is within the safe linear range. To obtain the highest accuracy, the MCU calls the highest-precision mode three data output to determine the final VOCs concentration. Scenario 2 (High Concentration Outbreak Warning): If detected... Rapidly climbed and approached This indicates that the VOC concentration is extremely high and the CMUT is about to saturate. To prevent data loss or device overload, proceed to step S8.

[0058] Step S8: The STM32 measurement and control system controls the multi-mode switching matrix to switch to mode one, closing only the IDE channel and disconnecting the CMUT channel, connecting the IDE to the phase-sensitive detection circuit, and acquiring the real-time capacitance change. Through formula ,in, This indicates the final output gas concentration value. This represents the real-time change in IDE capacitance. This represents the capacitance-concentration sensitivity coefficient (in pF / ppm) under the preset IDE mode. This coefficient is obtained from the factory calibration and stored in the MCU of the STM32 measurement and control system.

[0059] Step S9: Real-time monitoring Value, when When the temperature drops below the safety threshold, automatically switch back to mode three and return to step S3.

[0060] In addition, the STM32 measurement and control system monitors the working status of the CMUT unit and the IDE unit in real time. If no frequency output is detected in the oscillation circuit in the cooperative mode or CMUT independent mode, the CMUT unit is determined to be faulty, and the relevant signal path of the CMUT is immediately disconnected and switched to mode one. If an IDE branch fault is detected, the system locks in mode two and continues to work. Mode three is a parallel cooperative detection mode. The parallel node switch and oscillation channel switch of the multi-mode switching matrix are closed, and the impedance channel switch is open. The IDE unit and the CMUT unit are electrically connected in parallel inside the matrix and connected to the Colpitts oscillation circuit as a whole load. Mode one is an IDE independent detection mode. The impedance channel switch of the multi-mode switching matrix is ​​closed, and the oscillation channel switch and parallel node switch are open. The signal route of the IDE unit is routed to the phase-sensitive detector circuit, and the CMUT unit is in an electrically floating or shielded state. Mode two is a CMUT independent detection mode. The oscillation channel switch of the multi-mode switching matrix is ​​closed, and the impedance channel switch and parallel node switch are open. The signal of the unit is routed to the Colpitts oscillator circuit. The IDE unit is in an open circuit state, and the scan window for fast timing scanning is 200ms.

[0061] Example 3 This embodiment provides a method for fabricating a multimodal air humidity sensor; To achieve high-performance monolithic integration, this invention proposes a fabrication method compatible with standard MEMS processes, employing methods such as... Figure 7The fabrication process is shown below. First, two wafers with a diameter of 100 mm, a resistivity of 0.001–0.005 Ω·cm, and a crystal orientation of [missing information] are selected. <100> Low-resistivity single-crystal silicon wafers were used as the top and bottom wafers, respectively; a silicon nitride layer with a thickness of approximately 600 nm was deposited on the surface of the top wafer using a low-pressure chemical vapor deposition (LPCVD) process. Figure 7 a), subsequently used as a diaphragm; a silicon dioxide layer with a thickness of approximately 500 nm is grown on the surface of the film using a thermal oxidation process ( Figure 7 (b) serves as an insulating and sacrificial layer. Subsequently, an array of cavity structures is etched into the substrate oxide layer using photolithography and reactive ion etching (RIE), and the upper surface is subjected to chemical mechanical polishing (CMP) to reduce its surface roughness to the sub-nanometer level to meet bonding requirements (corresponding to...). Figure 7 c). Next, to ensure a clean bonding interface, the upper and lower silicon wafers were sequentially cleaned in RCA1 and RCA2 solutions for 5 minutes each, followed by another RCA1 cleaning and a 10-minute oxygen plasma activation treatment. After cleaning, silicon nitride-silicon dioxide direct bonding (Fusion Bonding) was performed under a vacuum environment with a pressure of approximately 2500N for 20 minutes, followed by annealing at 1100°C for 1 hour to form strong covalent bonds and seal the cavity (corresponding to...). Figure 7 d). After bonding, the nitride layer on the back side of the top wafer is removed by RIE. Then, the top wafer bulk silicon is selectively wet-etched using tetramethylammonium hydroxide (TMAH) solution until etching stops at the silicon nitride layer at the bonding interface, thus completely removing the top wafer silicon substrate and releasing the suspended silicon nitride diaphragm structure (corresponding to...). Figure 7 e). Then, through photolithography and RIE processes, windows are created on the upper film surface, etching through the silicon nitride and silicon dioxide layers to precisely expose the underlying low-resistivity silicon substrate, forming vias for the bottom electrodes (corresponding to...). Figure 7 f). Finally, the crucial electrode forming and monolithic integration steps are performed. In the diaphragm region, via region, and IDE region, 20nm chromium (Cr) and 80nm aluminum (Al) metal layers are sequentially deposited using electron beam evaporation. Excess metal is removed using a single lift-off process, simultaneously forming the CMUT upper electrode (labeled 1), common ground electrode (labeled 2), and the positive and negative interdigitated electrodes of the IDE (labeled 3 and 4). Figure 7 g). It should be noted that, Figure 7The CMUT electrode (labeled 1) consists of four metal blocks. The three metal blocks on the right are precisely aligned and positioned above the center of the vibrating cavity, serving as the main working electrodes. The leftmost metal block in this group is placed in the non-suspended area, specifically as a wire bonding pad. In the actual planar layout design, these metal units covering different vibrating cavities are electrically connected via interconnecting wires, collectively forming the positive electrode of the CMUT acoustic branch. Simultaneously, the finger electrodes in the IDE region are deposited on the same silicon nitride insulating layer surface. Thus, based on wafer bonding and substrate transfer technology, the CMUT and IDE are synchronously constructed on the same substrate. This process simultaneously forms the electrode structures of two sensors through a single metal deposition and lift-off step, with each port maintaining independent lead-out. This monolithic integration scheme not only overcomes the physical bottleneck of large size and difficulty in high-density integration of traditional bulk resonators (such as QCMs) and eliminates parasitic interference introduced by wire bonding in hybrid integration, but also perfectly meets the application requirements of sensor miniaturization and arraying.

[0062] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A multimodal air humidity sensor, characterized in that, include: Power supply and bias module, monolithic integrated sensing unit, multi-mode switching matrix, drive and detection circuit, STM32 measurement and control system, wireless communication module and host computer; The signal output terminal of the monolithic integrated sensing unit is electrically connected to the input terminal of the multimode switching matrix, the output terminal of the multimode switching matrix is ​​electrically connected to the input terminal of the driving and detection circuit, and the output terminal of the driving and detection circuit is electrically connected to the signal input terminal of the STM32 measurement and control system. The control output terminal of the STM32 measurement and control system is electrically connected to the control input terminal of the multi-mode switching matrix, and is used to control the on / off state of the multi-mode switching matrix to realize the detection mode switching. The STM32 measurement and control system is bidirectionally connected to the host computer through the wireless communication module to realize data transmission and command interaction. The power supply and bias module is used to provide power support.

2. The multimodal air humidity sensor according to claim 1, characterized in that, The monolithic integrated sensing unit includes a silicon substrate, a silicon nitride insulating structure layer, an IDE interdigitated electrode region, and a CMUT array region. The silicon nitride insulating structure layer is deposited on the upper surface of the silicon substrate, and the IDE interdigitated electrode region and the CMUT array region are respectively disposed on the upper surface of the silicon nitride insulating structure layer along the length direction of the silicon substrate, thereby realizing monolithic integration; The IDE interdigitated electrode area includes a left busbar, a right busbar, a first pad, a second pad, and two sets of metal fingers. The first pad is fixedly connected to the left busbar. The left busbar is connected to a set of metal fingers extending horizontally to the right. The second pad is fixedly connected to the right busbar. The right busbar is connected to another set of metal fingers extending horizontally to the left. The two sets of metal fingers interlock and have a gap. The gap is the area for sensitive thin film deposition and edge electric field interaction.

3. A multimodal air humidity sensor according to claim 2, characterized in that, The CMUT array area includes The system comprises a circular micro-element, a surface metal interconnect network, signal pads, and a common pad. The circular micro-element is arranged in an array, and each circular micro-element corresponds to the effective vibration region of a CMUT diaphragm. The upper electrodes of all circular micro-elements are connected to the signal pads through the surface metal interconnect network. The signal pads serve as the positive terminals of the acoustic branches. The substrates of all circular micro-elements are led out to the common pads through vias. The common pads serve as the system common reference ground. The signal pads and the first pads are led out independently at the chip physical level, where N is a positive integer.

4. A multimodal air humidity sensor according to claim 2, characterized in that, The monolithic integrated sensing unit also includes an electromechanical series branch, a parallel branch, and an additional series resistor. ; The electromechanical series branch is a resistor. ,inductance and capacitors The resistor is composed of The damping effect of the CMUT diaphragm is characterized to reflect sensor energy loss and affect the quality factor; the capacitance... The inductance characterizes the equivalent elastic capacitance of the CMUT diaphragm. Characterizing the equivalent inertia of the CMUT diaphragm; The parallel branch is the static capacitor of the CMUT. With IDE capacitors Composition, total equivalent parallel capacitance satisfy The static capacitor The intrinsic static capacitance of the CMUT is calculated from the electrode area, gap, and dielectric constant. The IDE capacitance is... The capacitance value is positively correlated with the dielectric constant caused by the moisture absorption of the sensitive membrane; The additional series resistor Used to correct energy dissipation that is unrelated to diaphragm motion caused by manufacturing tolerances.

5. A multimodal air humidity sensor according to claim 1, characterized in that, The multi-mode switching matrix includes multiple groups of low on-resistance analog switches, and each group of analog switches is controlled by the GPIO level of the STM32 measurement and control system. The input terminals of the multimode switching matrix include a CMUT signal input terminal and an IDE signal input terminal. The CMUT signal input terminal is electrically connected to the signal pad, and the IDE signal input terminal is electrically connected to the first pad. The output terminal of the multi-mode switching matrix includes an oscillation circuit connection terminal and a phase-sensitive detector circuit connection terminal. The multiple sets of analog switches include an impedance channel switch, an oscillation channel switch, and a parallel node switch. The circuit topology is dynamically reconstructed by combining the on and off states of the three sets of switches.

6. A multimodal air humidity sensor according to claim 1, characterized in that, The driving and detection circuit includes an oscillation circuit and a phase-sensitive detection circuit. The oscillation circuit includes two cascaded operational amplifiers, a buffer, and a positive phase-shift compensation network. The first-stage operational amplifier is a FET-input type operational amplifier used for initial signal pickup and amplification. The second-stage operational amplifier is a clamping amplifier used for signal gain and output amplitude limiting. The buffer is used to enhance driving capability and isolate load effects. The positive phase shift compensation network is used to correct loop phase delay. The phase-sensitive detector circuit is used to demodulate the impedance change of the IDE interdigitated electrode region into an analog voltage signal.

7. A control method for a multimodal air humidity sensor, based on the multimodal air humidity sensor according to claim 1, characterized in that, include: The system is initialized by acquiring the frequency signal output from the Corbitz oscillator circuit in a standard air environment and calculating the average frequency value as the clean reference frequency. Preset parameters and physical model definitions: Preset detection start threshold, resonance saturation threshold, characteristic slope, target gas characteristic slope, and humidity interference characteristic slope in the non-volatile memory of the STM32 measurement and control system; The multi-mode switching matrix is ​​controlled to enter mode three, and the CMUT and IDE electrical circuits are connected in parallel to the oscillation circuit to acquire the current frequency measurement value. And calculate the total frequency offset, and then compare the total frequency offset with the detection start threshold. Determine the triggering environmental disturbance; When environmental disturbance identification is triggered, a fast timing scan is initiated, switching to mode one and mode two to collect capacitance changes respectively. With the change in resonant frequency The characteristic slope K and the preset reference slope are used to distinguish between humidity interference and target gas. When identifying a target gas, the amount of change in resonant frequency is used as a basis. With resonant saturation threshold Depending on the relationship, you can choose to call the concentration value output from Mode 3 data or switch to Mode 1 extended detection range; During mode one detection, the gas concentration value is calculated based on the collected capacitance change. The concentration value is monitored in real time, and when it falls below the safety threshold, the system switches back to mode three and continuously monitors in a loop.

8. The control method for a multimodal air humidity sensor according to claim 7, characterized in that, When the first mode is the IDE independent detection mode, the impedance channel switch of the multi-mode switching matrix is ​​closed, the oscillation channel switch and the parallel node switch are open, the IDE unit signal is routed to the phase-sensitive detection circuit, and the CMUT unit is in an electrically floating or shielded state. When the second mode is the CMUT independent detection mode, the oscillation channel switch of the multi-mode switching matrix is ​​closed, the impedance channel switch and the parallel node switch are open, the CMUT unit signal is routed to the Colpitts oscillation circuit, and the IDE unit is in an open circuit state. When the third mode is the parallel collaborative detection mode, the parallel node switch of the multi-mode switching switch matrix and the oscillation channel switch are closed, the impedance channel switch is open, and the IDE unit and the CMUT unit are electrically connected in parallel and then connected to the Colpitts oscillation circuit.

9. The control method for a multimodal air humidity sensor according to claim 7, characterized in that, The calculation of the total frequency offset is performed based on electromechanical series branches, parallel branches, and additional series resistance, including: The total impedance of the monolithic integrated sensing unit This is a series-parallel combination of electromechanical series branches and parallel branches, where the impedance of the electromechanical series branch is... satisfy ; When in detection mode, the total impedance is determined. The imaginary part of the equation is zero to determine the parallel resonance point, and the resonant frequency is calculated based on this parallel resonance point. The resonant frequency The calculation formula is: ， in, Let be the damping equivalent resistance of the CMUT diaphragm. The imaginary unit is used to characterize the phase relationship between voltage and current in an AC circuit. Angular frequency, The equivalent inertial inductance of the CMUT diaphragm. The equivalent elastic capacitance of the CMUT diaphragm; The total frequency offset Current frequency measurement value Relative to clean reference frequency The offset satisfies And the total frequency offset The frequency shift caused by the mass effect and the frequency shift caused by the capacitance effect are linearly superimposed, and the mass effect is mediated by the inductance in the electromechanical series branch. The change in capacitance is characterized by the capacitance effect through the IDE capacitor in the parallel branch. The change in quantity is represented.

10. A method for fabricating a multimodal air humidity sensor, characterized in that, include: S1. Substrate and thin film preparation: Low-resistivity single-crystal silicon wafers are selected as the top wafer and bottom wafer, respectively. A silicon nitride layer is deposited on the surface of the top wafer as the CMUT diaphragm, and a silicon dioxide layer is grown on the surface of the bottom wafer as an insulating and sacrificial layer. S2. Cavity etching and surface treatment: an array of cavity structures is etched in the silicon dioxide layer of the substrate, and the surface of the top substrate is chemically and mechanically polished. S3. Cleaning and bonding: After cleaning and activating the upper and lower silicon wafers, direct bonding of silicon nitride and silicon dioxide is performed and high-temperature annealing is carried out. S4. Diaphragm release and via fabrication: Remove the nitride layer on the back of the top wafer and wet-etch the silicon substrate of the top wafer to release the silicon nitride diaphragm. Prepare the via for the bottom electrode on the upper film surface. S5. Electrode forming and monolithic integration: Deposit a metal layer in a designated area and simultaneously form the CMUT upper electrode, common ground electrode and IDE positive and negative interdigitated electrodes through a stripping process, so as to achieve independent lead-out of each electrode port; S6. Device calibration: Calibrate the detection start threshold, resonance saturation threshold, characteristic slope of target gas and humidity interference, and capacitance and concentration sensitivity coefficient in IDE mode under standard clean air environment, and store them in the non-volatile memory of STM32.

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