A piezoelectric MEMS gas switch device

Abstract

This application relates to the fields of microelectromechanical systems (MEMS) and piezoelectric sensors, specifically disclosing a piezoelectric MEMS gas switch device. The device includes a substrate and a combined cantilever beam membrane structure disposed above the substrate's back cavity. The combined cantilever beam membrane structure consists of a central hexagonal membrane and six petal-shaped cantilever beam membranes evenly distributed around it. Each membrane has a structural layer, a bottom electrode layer, a piezoelectric thin film layer, and a top electrode layer. The piezoelectric thin film layer forms a zoned gradient array of holes and has controlled residual tensile stress. When a small change in air pressure generated by breathing airflow acts on the membrane structure, the membrane flexes and deforms, outputting an electrical signal through the piezoelectric effect. The signal characteristics distinguish between inhalation and exhalation states, thereby controlling the on / off state of the nebulized gas. This application has advantages such as high sensitivity, small size, low power consumption, and high integration capability, making it suitable for intelligent medical nebulization control systems.

Description

Technical Field

[0001] This application relates to the fields of microelectromechanical systems and piezoelectric sensors, and in particular to a piezoelectric MEMS gas switch device. Background Technology

[0002] Nebulized drug delivery is a common clinical treatment for respiratory diseases. It transforms liquid medications into fine aerosol particles, allowing the drugs to be directly deposited in the airways and alveoli, thus achieving highly efficient local drug delivery. With the rise of home healthcare and wearable health management models, higher demands are being placed on the miniaturization, intelligence, and patient compliance of nebulization devices.

[0003] Currently, commercially available portable nebulizers mainly employ continuous spraying or timed spraying with a fixed duty cycle. These control methods do not consider individual differences in patients' respiratory rhythms, continuing to deliver nebulized airflow even during the exhalation phase. This approach presents at least two problems: firstly, it wastes medication and increases treatment costs; secondly, the combined effect of exhalation and nebulized airflow impacting the upper respiratory tract can easily induce coughing reflexes and laryngeal irritation, affecting both treatment comfort and safety.

[0004] To address these issues, researchers have attempted to introduce a respiratory synchronization triggering mechanism into nebulization systems. This involves detecting the inspiratory initiation signal and releasing nebulized gas only during the inspiratory phase. The core of this function lies in the respiratory state sensing unit. Existing solutions mostly rely on external flow sensors (such as hot-wire or differential pressure flow meters) or miniature pressure sensors (such as piezoresistive or capacitive MEMS pressure chips) to collect changes in airway pressure or flow. However, these sensors exhibit several limitations in practical applications: First, hot-wire or differential pressure sensors typically require long flow channels or Venturi structures, resulting in a large size that is difficult to embed in space-constrained adhesive or wearable nebulization patches; second, some sensors have long response times, leading to trigger delays.

[0005] From the perspective of micro-nano manufacturing technology development trends, sensing elements based on micro-electro-mechanical systems (MEMS) have demonstrated advantages in high sensitivity, small size, and low power consumption in fields such as acceleration, pressure, and gas concentration detection. However, there is still a lack of mature solutions for dedicated MEMS devices for respiratory pressure detection.

[0006] In summary, existing medical nebulizers have a technological gap in respiratory synchronization control. There is a lack of a miniaturized, low-power, highly sensitive MEMS respiratory sensing device with direct driving capability. This device needs to be able to identify minute pressure changes during the exhalation and inhalation phases in real time. This requires the sensitive structure to have a high resolution response to micro-pressure and to meet the application requirements of wearable or adhesive nebulizer devices. Summary of the Invention

[0007] To improve the problems of drug waste and patient coughing discomfort caused by the lack of real-time respiratory status sensing in existing medical nebulizers, and to solve the problems of insufficient sensitivity of existing sensors and difficulty in integration into wearable devices, this application provides a piezoelectric MEMS gas switch device.

[0008] The piezoelectric MEMS gas switching device provided in this application adopts the following technical solution: A piezoelectric MEMS gas switching device includes a substrate and a combined cantilever beam membrane structure; A back cavity is formed on the substrate; The combined cantilever beam membrane structure is disposed above the back cavity. The combined cantilever beam membrane structure includes a central regular hexagonal membrane and six petal-shaped cantilever beam membranes evenly distributed around the central regular hexagonal membrane. The center of the central regular hexagonal membrane is fixed, and its edges are suspended and free. The outer edges of the petal-shaped cantilever beam membranes are fixed, and their inner edges are suspended and free. Both the central hexagonal diaphragm and the petal-shaped cantilever beam diaphragm include, from bottom to top, a structural layer, a bottom electrode layer, a piezoelectric thin film layer, and a top electrode layer.

[0009] Furthermore, the piezoelectric thin film layer is formed with a pore array arranged in a partitioned gradient, the pore array being at least one of a hexagonal honeycomb array or a linear array.

[0010] Furthermore, the pores of the central hexagonal membrane adopt a first pore density and a first pore diameter, wherein the first pore density is a low pore density and the first pore diameter is a small pore diameter; The pores in the main body area of ​​the petal-shaped cantilever beam membrane adopt a second pore density and a second pore diameter, wherein the second pore density is greater than the first pore density and the second pore diameter is greater than the first pore diameter; The pores in the free edge region of the petal-shaped cantilever beam membrane adopt a third pore density and a third pore diameter, wherein the third pore density is greater than the second pore density and the third pore diameter is smaller than the second pore diameter.

[0011] Furthermore, the piezoelectric thin film layer has a controlled residual tensile stress, which causes the piezoelectric thin film layer to be in a prestressed state below and close to the buckling critical stress in the working state.

[0012] Furthermore, the ratio of the diameter of the central hexagonal diaphragm to the diameter of the back cavity is 0.4-0.6.

[0013] Furthermore, the central hexagonal diaphragm is led out with an independent electrode, and the electrodes of the six petal-shaped cantilever beam diaphragms are connected in a differential parallel group.

[0014] Furthermore, the six petal-shaped cantilever beam diaphragms are divided into a first sensitive group and a second sensitive group. The first sensitive group includes three petal-shaped cantilever beam diaphragms arranged alternately in the circumferential direction, and the second sensitive group includes the remaining three petal-shaped cantilever beam diaphragms arranged alternately in the circumferential direction. The wiring directions of the top and bottom electrodes of each petal-shaped cantilever diaphragm in the same sensitive group are set according to the polarity of the charge generated under the same air pressure, so that the effective pressure signals of each petal-shaped cantilever diaphragm in the same sensitive group are kept in phase and connected in parallel, so that the piezoelectric charges generated by multiple petal-shaped cantilever diaphragms in the same sensitive group are superimposed.

[0015] Furthermore, it also includes a signal processing circuit, the signal processing circuit comprising: The pressure summation channel is used to weight and sum the output signals of the central hexagonal diaphragm, the first sensitive group, and the second sensitive group to superimpose the in-phase piezoelectric signal caused by the respiratory pressure difference. The flow differential channel is used to perform differential processing on the output signals of the first sensitive group and the second sensitive group to extract airflow direction information and cancel interference.

[0016] This application also provides a breathing state recognition and control method based on the above-mentioned piezoelectric MEMS gas switching device, including the following steps: The central hexagonal diaphragm responds to the average air pressure and overall pressure difference acting on the device surface, and outputs a central channel electrical signal. The six petal-shaped cantilever beam diaphragms respond to local pressure gradients and changes in airflow direction, and output the first and second sensitive group electrical signals after being grouped and connected in parallel in phase. The central channel electrical signal, the first sensitive group electrical signal, and the second sensitive group electrical signal are respectively input into a charge amplifier circuit for gain matching amplification. The amplified three signals are weighted and summed to obtain a pressure sum signal. The first sensitive group electrical signal and the second sensitive group electrical signal are differentially processed to obtain a flow direction differential signal. The current respiratory state is determined based on the polarity of the pressure summation signal, and the amplitude change of the flow direction differential signal is used to assist in determining the respiratory state and counteract interference. Based on the respiratory status assessment, a corresponding nebulizer on / off control signal is generated to release nebulized gas during inhalation and shut off nebulized gas during exhalation.

[0017] This application also provides a medical atomization system, including the above-mentioned piezoelectric MEMS gas switching device.

[0018] In summary, this application includes at least one of the following beneficial technical effects: 1. This application employs a composite sensitive structure combining a central hexagonal diaphragm with six peripheral petal-shaped cantilever beam diaphragms, forming a central-ring synergistic force-bearing system. The central hexagonal diaphragm possesses sixfold rotational symmetry, reducing the device's dependence on airflow direction and enabling stable mechanical responses from breathing airflows from different directions. The six peripheral petal-shaped cantilever beam diaphragms each constitute an independent low-stiffness sensitive unit. Compared to traditional cantilever beams with uniform width, these units can generate greater free-end displacement and concentrate mechanical strain at the root of the cantilever beam, the electrode-covered area, and around the holes, thereby increasing the effective strain and charge output within the piezoelectric layer. The central hexagonal diaphragm and the peripheral petal-shaped cantilever beam diaphragms are functionally complementary, dividing the pressure-bearing area into multiple independently bendable flexible units. This reduces the additional stiffness of the complete diaphragm due to in-plane constraints, increasing the number of high-strain regions while maintaining a large effective pressure-bearing area. This achieves a highly sensitive response to minute changes in respiratory pressure, effectively improving the reliability of inspiratory and expiratory state recognition.

[0019] 2. This application introduces a zoned gradient arrangement of pore array structure into the piezoelectric thin film layer. Specifically, the central hexagonal membrane region employs a low pore density and small pore size arrangement to ensure structural stability and signal output consistency. The main body region of the petal-shaped cantilever beam membrane uses a medium pore density honeycomb array to improve local flexibility. The edge region of the petal-shaped cantilever beam membrane further increases the pore density to reduce the overall equivalent bending stiffness. Through this zoned gradient design, spatially controllable adjustment of the membrane structure's equivalent stiffness and local stress enhancement are achieved. This allows the device to still produce significant deformation response and electrical signal output under low-frequency, low-pressure-difference airflow conditions generated by breathing, significantly improving the detection capability of weak breathing pressure.

[0020] 3. This application introduces controlled residual tensile stress into the piezoelectric thin film layer, placing it in a prestressed state below and close to the buckling critical stress. Under this prestressed state, the equivalent piezoelectric coefficient of the piezoelectric thin film is significantly improved, and the mechanical deformation of the diaphragm under air pressure is effectively amplified, thereby improving the mechanical energy to electrical energy conversion efficiency. This enables the device to detect changes in breathing state with higher sensitivity while maintaining operational stability.

[0021] 4. This application employs an electrode configuration with an independent electrode lead-out of a central hexagonal diaphragm and six peripheral petal-shaped cantilever beam diaphragms connected in a differential parallel configuration. The independent lead-out of the central hexagonal diaphragm avoids the dilution of output voltage caused by increased total equivalent capacitance when directly connected in parallel with the peripheral petal-shaped cantilever beam diaphragms. The peripheral petal-shaped cantilever beam diaphragms are divided into a first sensitive group and a second sensitive group. The electrode wiring direction of each diaphragm within the same sensitive group is set according to charge polarity, ensuring that the effective pressure signal remains in phase and is connected in parallel. This achieves the superposition of piezoelectric charges, increasing the total charge output. Simultaneously, the superposition rate of random noise within each group is lower than the linear superposition rate of the effective signal, effectively improving the signal-to-noise ratio. By constructing a pressure summation channel and a flow direction differential channel, both the superposition and enhancement of the respiratory pressure differential signal are achieved, and differential cancellation of temperature drift, encapsulation stress, and common-mode interference is achieved, further improving the accuracy and anti-interference capability of respiratory state recognition.

[0022] 5. The piezoelectric MEMS gas switch device provided in this application can be easily integrated into the breathing channel of a nebulizer mask. By detecting the patient's inhalation and exhalation states in real time and directly controlling the output and shutdown of the nebulized gas, it achieves an intelligent respiratory synchronization triggering function of releasing the drug mist during the inhalation phase and shutting off the spray during the exhalation phase. This control method effectively avoids the drug waste problem caused by the continuous output of nebulized gas during the exhalation phase in existing continuous spray or timed spray methods. At the same time, it eliminates the reverse impact of the nebulized airflow on the patient's airway during the exhalation phase, significantly reducing the risk of coughing and respiratory discomfort, and improving the safety and comfort of nebulization therapy.

[0023] 6. This application utilizes MEMS micro-nano fabrication technology, resulting in a small overall device size and compact structure. It enables mass production at the wafer level, offering excellent process compatibility and cost advantages. Furthermore, the piezoelectric sensing unit boasts extremely low power consumption, and the sensing structure and drive control can be functionally integrated at the device level, eliminating the need for bulky external flow or pressure sensors. This meets the application requirements of wearable or adhesive medical nebulizers. Attached Figure Description

[0024] Figure 1 This is a structural diagram of a piezoelectric MEMS gas switch device according to an embodiment of this application, wherein (a) is a three-dimensional structural diagram and (b) is a cross-sectional view; Figure 2 This is a schematic diagram of the electrical connections of the piezoelectric MEMS gas switching device according to an embodiment of this application; Figure 3 It is the equivalent piezoelectric coefficient d 33 Trend of prestress in piezoelectric thin film materials; Figure 4This is a schematic diagram of the breathing trigger principle of the piezoelectric MEMS gas switch device in the embodiment of this application, where (a) is the resting state, (b) is the inhalation state, and (c) is the exhalation state. Figure 5 This is a simulation diagram of the received voltage of the piezoelectric MEMS gas switch device according to the embodiment of this application changing with the exhaled air pressure at the human breathing frequency (taking 0.5Hz as an example); Figure 6 This is a simulation diagram of the received voltage of the piezoelectric MEMS gas switch device according to the embodiment of this application changing with the inhalation pressure at the human breathing frequency (taking 0.5Hz as an example); Figure 7 This is a simulation diagram showing the change in received voltage with exhaled air pressure of a conventional cantilever beam structure of the same size as the piezoelectric MEMS gas switch device in the embodiments of this application at the human breathing frequency (taking 0.5Hz as an example); Figure 8 This is a simulation diagram showing the change in received voltage with inhalation pressure of a conventional cantilever beam structure of the same size as the piezoelectric MEMS gas switch device in the embodiments of this application at the human breathing frequency (taking 0.5Hz as an example); Figure 9 This is a diagram illustrating the application of a piezoelectric MEMS gas switching device in a medical atomization scenario, according to an embodiment of this application.

[0025] Reference numerals: 1. Substrate; 2. Back cavity; 3. Support pillar; 4. Oxide layer; 5. Structural layer; 6. Bottom electrode layer; 7. Piezoelectric thin film layer; 8. Top electrode layer; 9. Encapsulation layer; 10. Central hexagonal film; 11. Petal-shaped cantilever beam film. Detailed Implementation

[0026] The following is in conjunction with the appendix Figure 1-9 This application will be described in further detail.

[0027] This application discloses a piezoelectric MEMS gas switching device. (Refer to...) Figure 1 The piezoelectric MEMS gas switch device includes a substrate 1 and a combined cantilever beam membrane structure; wherein, the substrate 1 is made of silicon or silicon-on-cavity insulator, a cylindrical back cavity 2 is formed on the substrate 1, and the combined cantilever beam membrane structure is disposed above the back cavity 2.

[0028] Reference Figure 1 In (a), the combined cantilever beam membrane structure includes a central hexagonal membrane 10 and six petal-shaped cantilever beam membranes 11 evenly distributed around the central hexagonal membrane 10. The center of the central hexagonal membrane 10 is fixed to the support column 3 in the center of the substrate 1, and the edge of the central hexagonal membrane 10 is in a suspended and free state. The outer edge (arc-shaped edge) of the petal-shaped cantilever beam membrane 11 is fixed to the edge of the back cavity 2, and the inner edge (polygonal edge) of the petal-shaped cantilever beam membrane 11 is in a suspended and free state.

[0029] Reference Figure 1 In (b), both the central hexagonal diaphragm 10 and the petal-shaped cantilever diaphragm 11 include, from bottom to top, an oxide layer 4, a structural layer 5, a bottom electrode layer 6, a piezoelectric thin film layer 7, a top electrode layer 8, and an encapsulation layer 9. The oxide layer 4 is made of silicon dioxide, the structural layer 5 is made of silicon, the top electrode layer 8 and the bottom electrode layer 6 are made of molybdenum or aluminum, and the piezoelectric thin film layer 7 is made of any one of aluminum nitride, scandium-doped aluminum nitride, lead zirconate titanate piezoelectric ceramic, lithium niobate, or lithium tantalate. The encapsulation layer 9 is made of a flexible hydrophobic material, including thermoplastic polyurethane or polydimethylsiloxane. The thickness of each layer can be adjusted according to the actual sensitivity and processing requirements.

[0030] In this embodiment, the piezoelectric MEMS gas switch device can be a single-crystal structure or a dual-crystal structure. A single-crystal structure refers to a combined cantilever beam membrane structure with only one piezoelectric thin film layer 7; a dual-crystal structure refers to a combined cantilever beam membrane structure with two piezoelectric thin film layers 7. The dual-crystal structure has higher piezoelectric charge output capability and greater bending deformation amplitude, making it suitable for applications with higher sensitivity requirements.

[0031] The ratio of the diameter of the central hexagonal diaphragm 10 to the diameter of the back cavity 2 is set to 0.4-0.6. This ratio range ensures that the central hexagonal diaphragm 10 has sufficient effective pressure-bearing area to collect respiratory pressure signals, while reserving sufficient deformation space for the peripheral petal-shaped cantilever diaphragm 11, allowing it to bend fully under pressure without excessive constraint from the edge of the back cavity 2. When this ratio is below 0.4, the area of ​​the central hexagonal diaphragm 10 is too small, resulting in insufficient output signal from the main sensing unit. When this ratio is above 0.6, the usable deformation area of ​​the peripheral petal-shaped cantilever diaphragm 11 is excessively compressed, reducing the flexibility enhancement effect of the peripheral channel. By limiting the diameter ratio within the above-mentioned preferred range, a coordinated match is achieved in the spatial layout of the central main sensing unit and the peripheral enhancement unit, optimizing the overall pressure-deformation conversion efficiency of the device.

[0032] Reference Figure 1 In (a), the piezoelectric thin film layer 7 has a pore array arranged in a zoned gradient, the pore array being at least one of a hexagonal honeycomb array or a linear array. The pore density and pore size of the pore array exhibit a zoned gradient distribution on the combined cantilever beam membrane structure, specifically: The holes in the central hexagonal diaphragm 10 adopt a first pore density and a first pore diameter, with the first pore density being low and the first pore diameter being small. The arrangement of low pore density and small pore diameter ensures the structural integrity and rigidity of the central region, enabling the main sensing unit to maintain stable vibration modes and consistent signal output under repeated air pressure.

[0033] The pores in the main area of ​​the petal-shaped cantilever diaphragm 11 employ a second pore density and a second pore diameter, with the second pore density being greater than the first pore density and the second pore diameter being greater than the first pore diameter. The arrangement of medium pore density and large pore diameter effectively reduces the equivalent bending stiffness of the cantilever beam, enabling the diaphragm to generate greater flexural displacement under the same breathing pressure and improving the overall response amplitude of the peripheral channel.

[0034] The pores in the free-side edge region of the petal-shaped cantilever beam diaphragm 11 employ a third pore density and a third pore diameter, with the third pore density being greater than the second pore density and the third pore diameter being smaller than the second pore diameter. Further increasing the pore density and decreasing the pore diameter in the edge region reduces local stiffness while maintaining charge collection efficiency, resulting in stronger strain concentration at the root of the cantilever beam and further enhancing the device's response sensitivity to low-pressure conditions.

[0035] Through the above-mentioned partitioned gradient perforation design, the spatial controllable adjustment of the equivalent stiffness of the membrane structure is achieved. Without sacrificing structural reliability, the effective deformation area is increased and the piezoelectric strain conversion efficiency is improved, enabling the device to generate detectable electrical signal output for weak breathing pressure changes, thus expanding the detection lower limit.

[0036] Furthermore, the piezoelectric thin film layer 7 possesses controlled residual tensile stress, which causes the piezoelectric thin film layer 7 to be in a prestressed state below and close to the buckling critical stress under operating conditions. This prestressed state significantly reduces the equivalent bending stiffness of the film, allowing the same magnitude of air pressure change to induce a larger film deformation, while simultaneously increasing the equivalent piezoelectric coefficient d of the piezoelectric material. 33 This enhances the conversion efficiency of mechanical deformation into electrical signals. In addition, by controlling the residual tensile stress below the buckling critical stress, the thin film is effectively prevented from entering a buckling instability state, ensuring that the device maintains good repeatability and reliability under long-term repeated breathing pressure.

[0037] The piezoelectric coefficient y was determined experimentally. d33 By fitting formulas for the elastic constant N(x) and dielectric loss D(x) with stress x, the equivalent piezoelectric constant d is derived. 33 It is positively correlated with stress x.

[0038]

[0039]

[0040] Figure 3 It shows the equivalent piezoelectric constant d 33 By observing the changing trend of the prestress of the piezoelectric thin film, and applying controllable tensile stress during the device fabrication process, the device can achieve higher electromechanical conversion capabilities.

[0041] This application employs a composite sensing structure combining a central hexagonal diaphragm 10 with six peripheral petal-shaped cantilever beam diaphragms 11. The improved pressure sensitivity primarily stems from the expansion of the pressure-bearing area, reduction of equivalent stiffness, strain concentration, and the synergistic output of multiple sensing units. When a small pressure difference generated by the breathing airflow acts on the device surface, the central hexagonal diaphragm 10 can collect the gas pressure using its larger effective pressure-bearing area and undergo radial bending deformation around the central support region, resulting in significant bending strain around the central fixed region and at the edges of the hexagon. The hexagonal structure possesses sixfold rotational symmetry, reducing the device's dependence on the airflow direction and allowing breathing airflows from different directions to generate a relatively stable mechanical response on the central hexagonal diaphragm 10.

[0042] The six petal-shaped cantilever beam membranes 11 on the periphery each constitute an independent low-stiffness sensitive unit. The fixed side of the petal-shaped cantilever beam is connected to the support area, while the free side extends towards the central area. Its gradually changing profile along its length and the array of partitioned holes on it can reduce the equivalent bending stiffness of the cantilever beam. When the same air pressure is applied to the petal-shaped cantilever beam, compared with a conventional cantilever beam with uniform width, the petal-shaped structure can generate a larger free end displacement and concentrate mechanical strain at the root of the cantilever beam, the electrode-covered area, and around the holes, thereby increasing the effective strain and charge output within the piezoelectric layer.

[0043] The central hexagonal diaphragm 10 and the six peripheral petal-shaped cantilever diaphragms 11 are functionally complementary. The central hexagonal diaphragm 10 primarily responds to the average air pressure and overall pressure difference acting on the device surface, while the peripheral petal-shaped cantilever diaphragms 11 exhibit a more pronounced response to local pressure gradients, differences in airflow distribution, and changes in flow direction. Compared to a single, intact diaphragm, the composite structure provided in this embodiment divides the pressure-bearing area into multiple independently bendable flexible units, reducing the additional stiffness caused by in-plane constraints in a single diaphragm, and increasing the number of high-strain regions while maintaining a large effective pressure-bearing area.

[0044] Reference Figure 2 The central hexagonal diaphragm uses an independent electrode output, which can avoid the dilution of the output voltage of the central hexagonal diaphragm 10 due to the increase in total equivalent capacitance after it is directly connected in parallel with the six petal-shaped cantilever beam diaphragms on the periphery.

[0045] Reference Figure 2The electrodes of the six petal-shaped cantilever beam diaphragms are connected in a differential parallel configuration. Due to the typical third-order circumferential mode in a six-fold rotationally symmetric structure, an antisymmetric mode with a specific circumferential order will appear in the resonant modes of the six petal-shaped cantilever beam diaphragms on the periphery of this device. Therefore, the six petal-shaped cantilever beam diaphragms are divided into a first sensitive group and a second sensitive group. The first sensitive group includes three petal-shaped cantilever beam diaphragms arranged alternately along the circumference (i.e., the 1st, 3rd, and 5th circumferentially), and the second sensitive group includes the remaining three petal-shaped cantilever beam diaphragms arranged alternately along the circumference (i.e., the 2nd, 4th, and 6th circumferentially). The wiring direction of the top and bottom electrodes of each petal-shaped cantilever beam diaphragm within the same sensitive group is set according to the charge polarity generated under the same air pressure, ensuring that the effective pressure signals of each petal-shaped cantilever beam diaphragm within the same sensitive group remain in phase and are connected in parallel. The output charge Q of the first and second sensitive groups... A and Q B They are respectively: Q A =Q1+Q3+Q5 Q B =Q2+Q4+Q6 Q1, Q3, and Q5 are the output charges of the three petal-shaped cantilever beam membranes in the first sensitive group, and Q2, Q4, and Q6 are the output charges of the three petal-shaped cantilever beam membranes in the second sensitive group.

[0046] Therefore, the piezoelectric charges generated by multiple petal-shaped cantilever diaphragms within the same sensitive group superimpose with each other, increasing the total charge output of the peripheral channel. The growth rate of independent random noise within each petal-shaped cantilever diaphragm is typically lower than the linear superposition rate of the effective signal; therefore, parallel aggregation can also improve the effective signal-to-noise ratio of the peripheral sensitive channel.

[0047] The central channel and the peripheral channels (including the first and second sensitive groups) can be connected to charge amplifier circuits with different feedback capacitors or gains, so that the central hexagonal diaphragm, the first sensitive group and the second sensitive group can be gain matched according to their respective charge output amplitudes, thereby fully preserving the high sensitivity response of the central hexagonal diaphragm to small average air pressures.

[0048] Furthermore, the signal processing circuit includes a pressure summation channel and a flow direction differential channel.

[0049] The pressure summation channel is used to perform a weighted summation of the output signals from the central hexagonal diaphragm, the first sensitive group, and the second sensitive group, to obtain: V Sigma =G c V c +G A V A +GB V B Among them, V Sigma V is the total output voltage. C V A and V B The output voltages of the center channel, the first sensitive group, and the second sensitive group are respectively, G C G A and G B This is the corresponding gain coefficient. This summation channel is used to superimpose the in-phase piezoelectric signal caused by the breathing pressure difference, thereby improving the detection amplitude of the device for minute pressure changes.

[0050] The differential channel is used to perform differential processing on the output signals of the first sensitive group and the second sensitive group to obtain: V Delta =G d (V A -V B ) Among them, V Delta For differential voltage, G d This is the differential gain coefficient.

[0051] When the airflow is unevenly distributed on the device surface or has a specific flow direction, the pressure and bending degree of the petal-shaped cantilever beam diaphragm at different positions are different. The differential channel can extract the spatial asymmetry response to help determine the airflow direction and breathing state. For temperature drift, packaging stress, substrate vibration and circuit common-mode interference that act on two peripheral sensitive groups at the same time, differential processing can partially cancel them out, thereby reducing equivalent noise and zero drift.

[0052] The piezoelectric MEMS gas switch device provided in this embodiment recognizes the human breathing state based on the piezoelectric effect. Its working principle is as follows: Figure 4 As shown, when a person is inhaling, the device surface is subjected to negative pressure, driving the central hexagonal diaphragm and the six peripheral petal-shaped cantilever beam diaphragms to flex and deform. The piezoelectric thin film layer, due to the combined effects of stretching and bending, generates a strain distribution in a specific direction, outputting a corresponding piezoelectric potential signal between the top and bottom electrodes. When a person is exhaling, the MEMS membrane structure is subjected to positive pressure, causing the diaphragms to flex and deform in the opposite direction. The strain state in the piezoelectric thin film layer changes in the opposite direction, altering the piezoelectric polarization direction and charge distribution, thus generating a potential signal between the electrodes with opposite polarity and amplitude compared to the inhalation state. Because the forces acting on the diaphragms are opposite during inhalation and exhalation, the strain responses generated by the central hexagonal diaphragm and the peripheral petal-shaped cantilever beam diaphragms under the piezoelectric effect are significantly different, and the output signals from each electrode have distinguishable characteristics in terms of polarity, amplitude, and phase.

[0053] Based on the aforementioned signal differences, this embodiment employs an optimized electrical connection method: the central hexagonal diaphragm is led out with independent electrodes and amplified independently; the six peripheral petal-shaped cantilever beam diaphragms are divided into two groups for in-phase parallel connection and differential processing; finally, multi-channel weighted fusion effectively avoids capacitive load and signal cancellation problems between different sensitive areas. On this basis, the signal processing circuit constructs a pressure summation channel and a flow direction differential channel. Utilizing the opposite pressure effects generated by exhalation and inhalation, the polarity of the output signal from the pressure summation channel is reversed. The control unit, by combining the polarity and amplitude of the pressure summation signal with the changes in the peripheral differential signals, can significantly improve the distinguishability between inhalation, exhalation, and external mechanical disturbances. Thus, this embodiment not only achieves piezoelectric charge superposition enhancement through in-phase parallel connection but also comprehensively improves the effective output sensitivity, signal-to-noise ratio, and reliability of respiratory state recognition through independent amplification of the central channel, peripheral group differential processing, and multi-channel weighted fusion.

[0054] Figure 5 and Figure 6 These are simulation diagrams showing the changes in received voltage of the piezoelectric MEMS gas switch device according to the embodiments of this application under human breathing frequency (taking 0.5Hz as an example) as a function of exhaled or inhaled air pressure; Figure 7 and Figure 8 The figures show simulations of the received voltage of a conventional cantilever beam structure of the same size as the piezoelectric MEMS gas switch device in this application, under human breathing frequency (0.5Hz as an example), as a function of exhalation or inhalation pressure. The results show that within the low-frequency airflow pressure range corresponding to human breathing (typically in the range of several Pa to tens of Pa), the output voltage of the device in this embodiment exhibits a good near-linear relationship with the applied air pressure, demonstrating high linearity and stability, and higher sensitivity than the conventional cantilever beam structure. Therefore, this embodiment can not only accurately identify human inhalation and exhalation states but also further distinguish changes in airflow intensity during breathing, achieving refined perception of different breathing states. This excellent air pressure sensitivity and linear output characteristic provide a reliable foundation for its application in medical nebulization control systems, enabling it to realize intelligent nebulization gas switch functions based on real-time control of breathing states, thereby significantly improving the safety and comfort of nebulization therapy.

[0055] like Figure 9 As shown, the piezoelectric MEMS gas switch device provided in this embodiment is used in a medical nebulization system, installed within the breathing channel of the nebulizer mask, to monitor the patient's breathing status in real time. The system also includes a nebulizer and a control unit. The nebulizer converts liquid medication into aerosol particles and delivers them to the patient's breathing area through the nebulizer mask.

[0056] The breathing state recognition and control method based on the above-mentioned piezoelectric MEMS gas switching device includes the following steps: When the patient is inhaling, the external airflow enters the mask and applies negative pressure to the combined cantilever beam membrane structure, causing the central hexagonal membrane and the six outer petal-shaped cantilever beam membranes to flex and deform. When the patient is exhaling, the pressure inside the mask increases, and the combined cantilever beam membrane structure is subjected to positive pressure, causing the central hexagonal membrane and the six outer petal-shaped cantilever beam membranes to flex and deform in the opposite direction.

[0057] The central hexagonal diaphragm responds to the average air pressure and overall pressure difference acting on the device surface, outputting a central channel electrical signal.

[0058] The six petal-shaped cantilever beam diaphragms respond to local pressure gradients and changes in airflow direction, and output the first and second sensitive group electrical signals after being grouped and connected in parallel.

[0059] The center channel electrical signal, the first sensitive group electrical signal, and the second sensitive group electrical signal are respectively input into the charge amplifier circuit for gain matching amplification.

[0060] The amplified three signals are weighted and summed to obtain the pressure sum signal. The first and second sensitive group electrical signals are differentially processed to obtain the flow direction differential signal.

[0061] The current respiratory state is determined by the polarity of the pressure summation signal, and the amplitude change of the flow direction differential signal is used to further determine the respiratory state and counteract interference.

[0062] The control unit generates a corresponding nebulizer on / off control signal based on the breathing state judgment result, so that the nebulizer is turned on and the nebulized gas is released during the inhalation state; and the nebulizer is turned off and the nebulized gas is turned off during the exhalation state, so as to avoid the continuous output of nebulized gas during the exhalation phase.

[0063] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A piezoelectric MEMS gas switching device, characterized in that: Includes substrates and combined cantilever beam membrane structures; A back cavity is formed on the substrate; The combined cantilever beam membrane structure is disposed above the back cavity. The combined cantilever beam membrane structure includes a central regular hexagonal membrane and six petal-shaped cantilever beam membranes evenly distributed around the central regular hexagonal membrane. The center of the central regular hexagonal membrane is fixed, and its edges are suspended and free. The outer edges of the petal-shaped cantilever beam membranes are fixed, and their inner edges are suspended and free. Both the central hexagonal diaphragm and the petal-shaped cantilever beam diaphragm include, from bottom to top, a structural layer, a bottom electrode layer, a piezoelectric thin film layer, and a top electrode layer.

2. The piezoelectric MEMS gas switching device according to claim 1, characterized in that: The piezoelectric thin film layer is formed with a pore array arranged in a partitioned gradient, and the pore array is at least one of a hexagonal honeycomb array or a linear array.

3. The piezoelectric MEMS gas switching device according to claim 2, characterized in that: The pores of the central hexagonal membrane adopt a first pore density and a first pore diameter, wherein the first pore density is a low pore density and the first pore diameter is a small pore diameter; The pores in the main body area of ​​the petal-shaped cantilever beam membrane adopt a second pore density and a second pore diameter, wherein the second pore density is greater than the first pore density and the second pore diameter is greater than the first pore diameter; The pores in the free edge region of the petal-shaped cantilever beam membrane adopt a third pore density and a third pore diameter, wherein the third pore density is greater than the second pore density and the third pore diameter is smaller than the second pore diameter.

4. The piezoelectric MEMS gas switching device according to claim 1, characterized in that: The piezoelectric thin film layer has a controlled residual tensile stress, which causes the piezoelectric thin film layer to be in a prestressed state below and close to the buckling critical stress in the working state.

5. The piezoelectric MEMS gas switching device according to claim 1, characterized in that: The ratio of the diameter of the central hexagonal diaphragm to the diameter of the back cavity is 0.4-0.

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6. The piezoelectric MEMS gas switching device according to claim 1, characterized in that: The central hexagonal diaphragm is led out with an independent electrode, and the electrodes of the six petal-shaped cantilever beam diaphragms are connected in a differential parallel group.

7. A piezoelectric MEMS gas switching device according to claim 6, characterized in that: The six petal-shaped cantilever beam diaphragms are divided into a first sensitive group and a second sensitive group. The first sensitive group includes three petal-shaped cantilever beam diaphragms that are alternately arranged in the circumferential direction, and the second sensitive group includes the remaining three petal-shaped cantilever beam diaphragms that are alternately arranged in the circumferential direction. The wiring directions of the top and bottom electrodes of each petal-shaped cantilever diaphragm in the same sensitive group are set according to the polarity of the charge generated under the same air pressure, so that the effective pressure signals of each petal-shaped cantilever diaphragm in the same sensitive group are kept in phase and connected in parallel, so that the piezoelectric charges generated by multiple petal-shaped cantilever diaphragms in the same sensitive group are superimposed.

8. A piezoelectric MEMS gas switching device according to claim 7, characterized in that: It also includes a signal processing circuit, which includes: The pressure summation channel is used to weight and sum the output signals of the central hexagonal diaphragm, the first sensitive group, and the second sensitive group to superimpose the in-phase piezoelectric signal caused by the respiratory pressure difference. The flow differential channel is used to perform differential processing on the output signals of the first sensitive group and the second sensitive group to extract airflow direction information and cancel interference.

9. A breathing state recognition and control method based on the piezoelectric MEMS gas switching device according to any one of claims 1-8, characterized in that: Includes the following steps: The central hexagonal diaphragm responds to the average air pressure and overall pressure difference acting on the device surface, and outputs a central channel electrical signal. The six petal-shaped cantilever beam diaphragms respond to local pressure gradients and changes in airflow direction, and output the first and second sensitive group electrical signals after being grouped and connected in parallel in phase. The central channel electrical signal, the first sensitive group electrical signal, and the second sensitive group electrical signal are respectively input into a charge amplifier circuit for gain matching amplification. The amplified three signals are weighted and summed to obtain a pressure sum signal. The first sensitive group electrical signal and the second sensitive group electrical signal are differentially processed to obtain a flow direction differential signal. The current respiratory state is determined based on the polarity of the pressure summation signal, and the amplitude change of the flow direction differential signal is used to assist in determining the respiratory state and counteract interference. Based on the respiratory status assessment, a corresponding nebulizer on / off control signal is generated to release nebulized gas during inhalation and shut off nebulized gas during exhalation.

10. A medical nebulization system, characterized in that: Includes the piezoelectric MEMS gas switching device according to any one of claims 1-8.

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