An overload or interference signal release and sensitivity enhancement design method of a hydrophone discrete beam membrane fusion sound sensitive chip

Abstract

This invention discloses a method for overload or interference signal release and discrete capacitor enhancement design of a hydrophone discrete beam-diaphragm fusion acoustic sensing chip. A flat diaphragm fabricated on a C-shaped silicon cup substrate is divided into multiple sub-beam diaphragms, which together form a circular flat diaphragm with micron-level gaps between each sub-beam diaphragm. Each sub-beam diaphragm has a piezoelectric sensing membrane and a detection capacitor electrode, with the detection capacitors on each sub-beam diaphragm connected in series. This invention addresses how to enhance the original sensitivity of a sensor chip within the limited dimensions of a MEMS sensitive structure, while simultaneously improving the sensor's overload resistance and environmental adaptability. The hydrophone discrete beam-diaphragm fusion acoustic sensing chip is used to sense underwater sound pressure and other signals, enabling the fabrication of sound pressure hydrophones. This chip can also be used to design and fabricate sensors for displacement, differential pressure, flow rate, velocity, particle vibration, and corresponding parameters in air.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology, specifically MEMS acoustic sensors, and relates to a design method for overload or interference signal release and sensitivity enhancement of discrete capacitors based on a hydrophone discrete beam-diaphragm fusion acoustic sensitive chip structure. Background Technology

[0002] Aluminum nitride (ALN) is a group III-V wide-bandgap semiconductor material. Aluminum nitride thin films are excellent piezoelectric materials due to their high temperature resistance, chemical stability, good insulation, and good thermal conductivity. Aluminum nitride thin films have attracted widespread attention because of their bidirectional electromechanical actuation properties and their ability to be fabricated using reactive sputtering. Compared to traditional piezoelectric ceramics and zinc oxide (ZnO), aluminum nitride thin films offer significant advantages in sensor miniaturization and stability. While ALN piezoelectric materials have a relatively low piezoelectric coefficient, their low dielectric constant results in a high FOM (Form Factor of Measurement) value. Furthermore, aluminum nitride thin films exhibit process compatibility with MEMS, enabling mass production, which further enhances their appeal. In recent years, international and domestic research has focused on various sensor technologies using aluminum nitride thin films, including PMUT (Programmable Detection Unit) and radio frequency trace detection. The United States, in particular, has achieved several technological breakthroughs in near-zero power radio frequency and acoustic sensor technologies, while China has also made significant progress in PMUT and high-precision biological detection.

[0003] Micro-Electro-Mechanical Systems (MEMS) are high-tech electromechanical devices that integrate microelectronics and mechanical engineering. Operating within the micrometer range, they are characterized by miniaturization (small size, light weight) and the ability to be integrated and mass-produced. Richard et al. proposed an aluminum nitride piezoelectric micromechanical ultrasonic transducer, leveraging the compatibility of aluminum nitride with CMOS processes, demonstrating that aluminum nitride improves the signal-to-noise ratio compared to piezoelectric ceramics. Xu Jinghui's team proposed a MEMS ultra-low frequency hydrophone using aluminum nitride piezoelectric materials, operating at 10-100Hz with a sound pressure sensitivity of -182dB, achieving high sound pressure sensitivity for MEMS piezoelectric hydrophones. Li Chuanyu's team at the Chinese Academy of Sciences proposed an ultra-thin silicon substrate aluminum nitride Lamb wave piezoelectric resonator. Their designed Lamb wave resonator enables high-precision trace detection, and research indicates that the aluminum nitride Lamb wave sensor possesses advantages such as high chemical stability, CMOS compatibility, and high-temperature resistance. This demonstrates that aluminum nitride thin films can play an advantageous role in various types of sensor technologies. With the development of various unmanned platform technologies, more diverse sensor technologies that can be integrated can support unmanned platforms to obtain intelligent autonomous capabilities. However, this also places higher demands on the environmental adaptability and stability of sensors. Therefore, conducting research on sensitivity enhancement methods and environmental tolerance technologies for novel acoustic pressure sensor technologies based on aluminum nitride thin film materials is of great significance for improving the original sensitivity and environmental adaptability of sensors.

[0004] The technical team led by Pu Shengchun from Harbin Engineering University, in collaboration with the technical team from the 49th Research Institute of China Electronics Technology Group Corporation (CETC), combined the novel aluminum nitride MEMS sensitive material with acoustic sensor technology. They conducted research on acoustic sensitive structures, MEMS mechanical sensitive structures, and the coupling of force-sensitive and piezoelectric sensitive characteristics, and designed an aluminum nitride MEMS acoustic test chip, achieving good verification results. Summary of the Invention

[0005] This invention proposes a design method for overload or interference signal release and discrete capacitance enhancement of a hydrophone discrete beam-diaphragm fusion acoustic sensitive chip, which solves the problem of how to enhance the original sensitivity of the sensor sensitive chip within the limited size of the MEMS sensitive structure, and also improve the sensor's environmental adaptability and overload resistance.

[0006] This invention is achieved through the following technical solution:

[0007] A hydrophone discrete beam-diaphragm fused acoustic sensitive chip structure, the acoustic sensitive chip structure includes a C-shaped silicon cup base 1 and a flat diaphragm 2 fabricated on the C-shaped silicon cup base. The flat diaphragm 2 fabricated on the C-shaped silicon cup base is divided into multiple sub-beam diaphragms 3. The multiple sub-beam diaphragms 3 together form a circular flat diaphragm. There are micron-level gaps 4 between each sub-beam diaphragm 3.

[0008] Each of the sub-beam membranes 3 has a piezoelectric sensitive layer 3-11 and detection electrodes distributed on both sides of the piezoelectric sensitive layer 3-11, namely, the upper electrode 3-10 and the lower electrode 3-12 forming a detection capacitor. The detection capacitors on each of the sub-beam membranes 3 are connected in series through the upper electrode 3-10 and the lower electrode 3-12 of the adjacent sub-beam membrane.

[0009] A discrete beam-diaphragm fused acoustic sensitive chip structure for hydrophones, wherein the piezoelectric sensitive material layer is any piezoelectric sensitive material.

[0010] A method for automatically releasing overload signals or interference in a discrete beam-membrane fused acoustic sensitive chip structure for a hydrophone. The method specifically involves automatically releasing overload signals or interference and automatically restoring the normal sensitive structure and sensitive characteristics through the design of the discrete beam-membrane fused acoustic sensitive chip structure. When the sound pressure signal in the water medium is within the detection sound pressure range P designed for the sensitive chip, the discrete beam-membrane fused acoustic sensitive chip presents an overall flat membrane structure due to the existence of gap damping, and the sensitive mode is a flat membrane sensitive mode.

[0011] When there is a signal or interference in the water medium that exceeds twice the designed sound pressure range P, the large overload signal or interference is a dynamic signal that acts on the flat diaphragm, causing the diaphragm to be compressed and generate stress and strain distribution. The stress and deflection are greatest at the center of the diaphragm. As the amplitude of the overload or interference sound pressure signal increases, the increase in the deflection at the center of the diaphragm will cause the diaphragm to split along the gap, increasing the distance between the sub-beam diaphragms. The closer to the center, the larger the gap. At this time, the original flat diaphragm structure is dispersed into N sub-beam diaphragms 3. At this time, the hydrophone's acoustic sensing structure can be equivalent to multiple cantilever beam sensing structures. The hydrophone's acoustic sensing chip presents a cantilever beam sensing mode. The detection capacitor electrode is designed in the corresponding stress change sensitive area of ​​each sub-beam diaphragm to detect the stress change on the beam and convert it into an electrical signal output. When the external overload signal or interference disappears, each sub-beam diaphragm will return to its initial position. Since the gap between the sub-beam diaphragms is very small, under the action of damping force, the sensing structure returns to the flat diaphragm structure and can continue to sensitively detect signals that are no greater than twice the designed sound pressure range P.

[0012] An automatic overload signal or interference release method for a hydrophone discrete beam-diaphragm fused acoustic sensitive chip structure is disclosed. The method comprises a peripherally fixed circular flat diaphragm formed by the fusion of sub-beam membranes and its sensing mode. The thickness of the circular flat diaphragm is denoted as h, and the radius of the thin film region is denoted as R. Stress-strain analysis is performed. To avoid nonlinearity, the following two assumptions are made in the calculations of the following formulas:

[0013] (1) Assume that the pressure p is applied uniformly to the surface of the flat diaphragm;

[0014] (2) Apply the small deflection theory, that is, the maximum deflection of the flat diaphragm is no more than 1 / 3 of the film thickness;

[0015] Under the above assumptions, radial stress

[0016]

[0017] Tangential stress

[0018]

[0019] radial strain

[0020]

[0021] Tangential strain

[0022]

[0023] Through the formula for calculating radial strain, when When the radial strain is equal to 0;

[0024] The deflection of the flat diaphragm is:

[0025]

[0026] According to formula (1-5), the maximum deflection occurs at the center of the circular diaphragm where r = 0, and the maximum deflection is:

[0027]

[0028] The approximate formula for the natural frequency of a flat diaphragm is:

[0029]

[0030] Where: k----stiffness of the elastic sensing element;

[0031] m----Equivalent vibrational mass of a circular flat diaphragm;

[0032] Substituting the mass m of the circular flat diaphragm and the stiffness of the diaphragm structure into equation (1-7), and simplifying, we can obtain the natural frequency of the flat diaphragm as follows:

[0033]

[0034] In the above formulas: E---elastic modulus of thin circular flat diaphragm; μ----Poisson's ratio of thin circular flat diaphragm; h----diaphragm thickness; R----diaphragm radius; r----radius of any part of the diaphragm; ρ----density of diaphragm material.

[0035] An automatic overload signal or interference release method for a hydrophone discrete beam-diaphragm fused acoustic sensitive chip structure is disclosed. Under the action of overload signal or interference, the sub-beam diaphragm approximates an equal-strength beam, exhibiting an equal-strength beam sensitive mode. Let the fixed end width of the beam be b, the beam length be l, the beam thickness be h, and the distance from a certain cross-section along the beam length direction to the point of force application be x. Then, the maximum stress at the cross-section is...

[0036]

[0037] Make

[0038]

[0039] Then it can be found

[0040]

[0041] In the formula b x The beam width at the location corresponding to the x-value;

[0042] The strain values ​​at each point of a beam of equal strength are

[0043]

[0044] Maximum deflection ω at the free end of a beam of equal strength max for

[0045]

[0046] It is the deflection at the free end of a cantilever beam with a uniform cross-section. times;

[0047] Based on equation (2-5), we can derive...

[0048]

[0049] In the formula, the coefficient k is the ratio of load to deflection, i.e., stiffness;

[0050] The lowest natural frequency f0 of a beam of equal strength is

[0051]

[0052] or

[0053] A discrete capacitor enhancement design method for a hydrophone discrete beam-membrane fused acoustic sensitive chip structure involves fabricating a piezoelectric sensitive material layer on the discrete beam-membrane fused acoustic sensitive chip structure, and fabricating an upper electrode layer and a lower electrode layer on the upper and lower sides of the piezoelectric sensitive material layer to form a sensitive detection capacitor; each of the sub-beam membranes 3 is a discrete capacitor, and the discrete capacitors are connected in series; N discrete capacitors are connected in series to form the total detection capacitance of the chip.

[0054] A discrete capacitor sensitization design method for a hydrophone discrete beam-diaphragm fused acoustic sensitive chip structure is characterized by a discrete capacitor series connection structure and method. Each sub-beam diaphragm 3 has a lower electrode 3-12 of the discrete capacitor led out from the outside of the arc-shaped electrode and connected to a process via 3-4. The process via 3-4 of the lower electrode of the discrete capacitor is electrically connected to the upper electrode 3-10 of the discrete capacitor on the adjacent sub-beam diaphragm 3. The multiple sub-beam diaphragms 3 have the same structure. The upper electrode of the first discrete capacitor is led out to the output pad on the hydrophone discrete beam-diaphragm fused acoustic sensitive chip structure through a lead wire. The lower electrode of the last discrete capacitor is led out to the upper electrode surface through a process via point and then connected to the lower electrode output pad on the hydrophone discrete beam-diaphragm fused acoustic sensitive chip structure through a wire. The two electrodes of the series-connected total capacitor are led out through the upper and lower electrode pads.

[0055] A discrete capacitor sensitization design method for a discrete beam-diaphragm fusion acoustic sensitive chip in a hydrophone, wherein each discrete capacitor includes an upper electrode 3-10, a piezoelectric sensitive layer 3-11, and a lower electrode 3-12, and the upper electrode 3-10, the piezoelectric sensitive layer 3-11, the lower electrode 3-12, and the flat diaphragm 2 are stacked sequentially from top to bottom.

[0056] A discrete capacitance enhancement design method for a discrete beam-membrane fused sensing chip in a hydrophone, based on the principle of MEMS discrete capacitance enhancement, where the total capacitance of the discrete beam-membrane fused acoustic sensing chip in the hydrophone is set as C. The voltage output by capacitor C is then:

[0057] v0=Q / C (3-1)

[0058] Discretize the total capacitance C into N sub-capacitors I; the capacitance of each sub-capacitor I is approximately C / N. Connect the N sub-capacitors I in series, and let the total capacitance after series connection be C', with the capacitance of each sub-capacitor I being C / N. Then, according to the formula for capacitor series connection...

[0059]

[0060] Because C1 = C2 = ... = C n =C / N, then:

[0061]

[0062] Let the distributed capacitance in the equivalent circuit be Cp, and the input capacitance of the preamplifier circuit be Cin. After N sub-capacitors are connected in series, the total input capacitance of the preamplifier circuit is:

[0063]

[0064] Based on the definition of capacitance, V = Q / C, the charge generated by each sub-capacitor I is approximately Q / N, thus the output voltage of the circuit is:

[0065]

[0066] Output voltage value V' of a single capacitive sensor:

[0067]

[0068] Comparing the output voltages obtained from the two different circuits, the voltage gain expression is as follows:

[0069]

[0070] To obtain the optimal number of discrete values, the extreme values ​​of the voltage gain are calculated. To find the optimal number of discrete elements; simplifying the equation yields:

[0071]

[0072] Substituting equation (3-8) into the voltage gain expression, we obtain the following relationship between the maximum gain and the number of discrete capacitors:

[0073]

[0074] A method for implementing a double-sided etching process for a discrete beam-diaphragm fused acoustic sensitive chip structure in a hydrophone, the method comprising the following steps:

[0075] Step 1: Photolithography is performed on the front side of the silicon substrate, followed by deep trench etching to a depth of h to create the gaps in the discrete beam-film fusion sensitive chip structure.

[0076] Step 2: After filling the deep trench in Step 1 with sacrificial material, a bottom electrode layer is fabricated by magnetron sputtering of molybdenum, and then the bottom electrode is patterned.

[0077] Step 3: Fabricate an aluminum nitride piezoelectric sensing material layer on the molybdenum electrode;

[0078] Step 4: Fabricate the upper electrode on the aluminum nitride piezoelectric sensitive material layer, and pattern the upper electrode by photolithography to bring out the electrode and complete the front process;

[0079] Step 5: Backplane photolithography, forming a back cavity through dry etching, with the etching depth being the total silicon wafer thickness minus h, ultimately ensuring that the thickness of the fused beam film meets the design requirements.

[0080] The beneficial effects of this invention are:

[0081] This invention proposes a design and implementation method for a MEMS hydrophone discrete beam-diaphragm fusion acoustic sensing chip overload or interference signal release and discrete capacitor sensitization design structure.

[0082] This invention can improve the original sensitivity of the sensing chip, as well as the sensor's environmental adaptability and overload resistance, within the limited size of the MEMS sensing structure.

[0083] This invention breaks through the conventional circular electrode design method. By using discrete electrode design, the piezoelectric sensitive detection capacitor in the sensitive area is discretized into N detection sub-capacitors. The signal extraction and output design is formed by connecting multiple discrete sub-capacitors in series, which achieves the effect of enhanced sensitivity and defines the design range related to the input capacitance and distributed capacitance.

[0084] The overload release method of the present invention uses sensitive mode switching technology to achieve high-sensitivity detection of small signals and detection and interference removal of high overload signals.

[0085] The sensitive chip of this invention has a high sensitivity detection capability for small sound pressure signals.

[0086] The sensitive chip of the present invention has the ability to withstand large sound pressure signal overload and the ability to detect and extract large sound pressure signals, thus having a wide dynamic detection range.

[0087] The sensitive chip of this invention has the ability to resist large interferences and the adaptive capability of a wide dynamic range. Attached Figure Description

[0088] Appendix Figure 1 This is a schematic diagram of the structure of the present invention.

[0089] Appendix Figure 2 This is a schematic diagram of the electrode and wiring relationship of the present invention, wherein (a) is a conventional continuous circumferential electrode and (b) is a discrete electrode.

[0090] Appendix Figure 3 This is a schematic diagram of the discrete beam-film fusion sensitive film chip process structure of the present invention, wherein (a) is a front view and (b) is a dimension marking diagram.

[0091] Appendix Figure 4 This is a schematic diagram of the etching process of the present invention.

[0092] Appendix Figure 5 This is a schematic cross-sectional view of the peripheral fixed flat diaphragm model of the present invention.

[0093] Appendix Figure 6 This is a stress distribution curve of the peripherally fixed circular flat diaphragm model of the present invention.

[0094] Appendix Figure 7 Here is the equivalent circuit diagram of the sensitive detection capacitor of the present invention, wherein (a) is the equivalent circuit diagram of the discrete capacitor sensor circuit and (b) is the equivalent circuit diagram of the single continuous capacitor sensor circuit.

[0095] Appendix Figure 8 This is a schematic diagram of the equal strength beam model of the present invention. Detailed Implementation

[0096] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0097] A hydrophone discrete beam-diaphragm fused acoustic sensitive chip structure, the acoustic sensitive chip structure includes a C-shaped silicon cup base 1 and a flat diaphragm 2 fabricated on the C-shaped silicon cup base. The flat diaphragm 2 fabricated on the C-shaped silicon cup base is divided into multiple sub-beam diaphragms 3. The multiple sub-beam diaphragms 3 together form a circular flat diaphragm. There are micron-level gaps 4 between each sub-beam diaphragm 3.

[0098] Each of the sub-beam membranes 3 has a piezoelectric sensitive layer 3-11 and detection electrodes distributed on both sides of the piezoelectric sensitive layer 3-11 to form an upper electrode 3-10 and a lower electrode 3-12. The upper electrode 3-10 on each of the sub-beam membranes 3 and the lower electrode 3-12 of the adjacent sub-beam membrane are connected to realize the series connection of the detection capacitor.

[0099] The continuous circumferential electrode is uniformly discretized into m (m=15 in this example) discrete electrodes to form m sensitive sub-capacitors. The discretized sub-capacitor electrodes are connected in series, that is, the lower electrode on the first sub-beam film is connected to the upper electrode on the second sub-beam film through the process via point, and so on. Finally, the entire sensitive capacitor connected in series is led out through the electrodes from the upper electrode of the first electrode and the lower electrode of the mth electrode.

[0100] Furthermore, the overload release method specifically involves the fact that, since the acoustic signal to be detected is very weak, the design of the hydrophone's acoustic sensitive chip needs to minimize the thickness of the thin film to make the sensitive chip very sensitive. However, when there is a large signal or interference, the sensitive film structure will be subjected to a large overload, which will lead to damage to the sensitive film structure.

[0101] The discrete beam-membrane fusion acoustic sensor chip structure design automatically releases overload signals or interference and can automatically restore the normal sensitive structure and sensitive characteristics: When the sound pressure signal in the water medium is within the detection sound pressure range P of the sensor chip design, the discrete beam-membrane fusion sensor chip exhibits a flat membrane structure due to the existence of gap damping. That is, the damping is proportional to the velocity gradient on the gap. The smaller the gap, the greater the damping, which can be expressed by the following formula:

[0102]

[0103] Where x and y represent the x-axis and y-axis coordinates, f represents the damping force, and μ' is the damping coefficient. The velocity gradient along the x-axis

[0104] The sensitive mode is the flat diaphragm sensitive mode, which obeys the first-order flat diaphragm mechanical theory and stress and strain distribution characteristics. At this time, the sound pressure sensor (hydrophone) designed and manufactured by the discrete beam-diaphragm fusion acoustic sensitive chip can detect the sound pressure signal normally and effectively.

[0105] When there is a signal or interference in the water medium that exceeds twice the designed sound pressure range P, the large overload signal or interference is a dynamic signal that acts on the flat diaphragm, causing the flat diaphragm to be compressed and generate stress and strain distribution according to the first-order flat diaphragm mechanics theory. According to the stress distribution curve given before the referenced formula (1-1 to 1-4), it can be seen that the stress and deflection are the largest at the center of the diaphragm. As the amplitude of the overload or interference sound pressure signal increases, the increase in the deflection at the center of the diaphragm will cause the diaphragm to split along the gap, increasing the distance between the sub-diaphragms. The closer to the center, the larger the gap. At this time, the original flat diaphragm structure is dispersed into N sub-beam diaphragms 3. At this time, the hydrophone acoustic sensing structure can be equivalent to multiple cantilever beam sensing structures. At this time, the hydrophone acoustic sensing chip presents a cantilever beam sensing mode; it obeys the elastic beam mechanics theory and presents the corresponding stress and strain distribution law on the beam. The detection capacitor electrode is designed in the corresponding stress change sensitive area of ​​each sub-beam diaphragm to detect the stress change on the beam and convert it into an electrical signal output. That is, the sound pressure or interference is converted through stress, i.e., the deformation of the beam is released. When the external overload signal or interference disappears, each sub-beam membrane will return to its initial position. Since the gap between the sub-beam membranes is very small, according to formula (1-0), under the action of damping force, the sensitive structure will return to the flat membrane structure and can continue to sensitively detect signals that are no more than twice the designed sound pressure range P.

[0106] Furthermore, the overload release method specifically involves a flat membrane mechanically sensitive structure formed by the fusion of discrete beam membranes, and a peripherally fixed circular flat membrane sensitive mode formed by the fusion of sub-beam membranes. Let the thickness of the prototype flat membrane be h, and the radius of the thin film region be R. Stress-strain analysis is performed. To avoid nonlinearity, the following two assumptions are made in the calculations of the following formulas:

[0107] (1) Assume that the pressure p is applied uniformly to the surface of the flat diaphragm;

[0108] (2) Apply the small deflection theory, that is, the maximum deflection of the flat diaphragm is no more than 1 / 3 of the film thickness;

[0109] Under the above assumptions, radial stress

[0110]

[0111] Tangential stress

[0112]

[0113] radial strain

[0114]

[0115] Tangential strain

[0116]

[0117] It can be seen from the formula for calculating radial strain that when When the radial strain is equal to 0;

[0118] The stress distribution curves of the peripherally fixed circular flat diaphragm, plotted according to formulas (1-1) and (1-2), are shown below. Figure 6 As shown.

[0119] The deflection of the flat sheet is:

[0120]

[0121] According to formula (1-5), the maximum deflection occurs at the center of the circular diaphragm where r = 0, and the maximum deflection is:

[0122]

[0123] The approximate formula for the natural frequency of a flat diaphragm is:

[0124]

[0125] Where: k----stiffness of the elastic sensing element, in N / m;

[0126] m----Equivalent vibrational mass of a circular flat diaphragm, in kg;

[0127] Substituting the disk mass *m* and the stiffness of the single-crystal silicon into equation (1-7), and simplifying, we obtain the natural frequency of the flat diaphragm as:

[0128]

[0129] In the above formulas: E---elastic modulus of thin circular flat diaphragm; μ----Poisson's ratio of thin circular flat diaphragm; h----diaphragm thickness; R----diaphragm radius; r----radius of any part of the diaphragm; ρ----density of diaphragm material.

[0130] Furthermore, the overload release method specifically involves the sub-beam membrane approximating an equal-strength beam sensitive mode under overload signal or interference, which can be calculated and analyzed using an equal-strength beam model: Let the fixed end width of the beam be b, the beam length be l, the beam thickness be h, and the distance from a certain section along the beam length direction to the point of force application be x. Then the maximum stress at the section is...

[0131]

[0132] Make

[0133]

[0134] Then we can find

[0135]

[0136] In the formula b x The beam width at the location corresponding to the x-value;

[0137] The strain values ​​at each point of a beam of equal strength are

[0138]

[0139] Maximum deflection ω at the free end of a beam of equal strength max for

[0140]

[0141] It is the deflection at the free end of a cantilever beam with a uniform cross-section. times;

[0142] Based on equation (2-5), we can derive...

[0143]

[0144] In the formula, the coefficient k is the ratio of load to deflection, i.e., stiffness;

[0145] The lowest natural frequency f0 of a beam of equal strength is

[0146] or

[0147]

[0148] A discrete capacitor sensitization design method for a discrete beam-membrane fused acoustic sensitive chip structure in a hydrophone is disclosed. The method involves designing the electrodes of the discrete capacitors, i.e., the structure and electrical connection method of the electrodes. A piezoelectric sensitive material layer is fabricated on the discrete beam-membrane fused acoustic sensitive chip structure. Upper and lower electrode layers are fabricated on the upper and lower sides of the piezoelectric sensitive material layer, respectively, forming a sensitive detection capacitor. Each sub-beam membrane 3 is a discrete capacitor, and the discrete capacitors are connected in series. N discrete capacitors are connected in series to form the total detection capacitance of the chip.

[0149] Furthermore, each of the sub-beam membranes 3 has a process via connection point 3-4 for the lower electrode of the discrete capacitor led out on the outside of the arc-shaped electrode. The lower electrode 3-12 of the discrete capacitor is electrically connected to the upper electrode 3-11 of the discrete capacitor on the adjacent sub-beam membrane 3 through the process via connection point 3-4. The multiple sub-beam membranes 3 have the same structure. The upper electrode 3-11 of the first discrete capacitor is led out to the output pad on the hydrophone discrete beam membrane fusion acoustic sensitive chip structure through a lead wire. The lower electrode 3-12 of the last discrete capacitor is led out to the upper electrode surface through a process via point, and then connected to the lower electrode output pad on the hydrophone discrete beam membrane fusion acoustic sensitive chip structure through a connection wire. The two electrodes of the total capacitor after series connection are led out through the upper and lower electrode pads.

[0150] Furthermore, each discrete capacitor includes an upper electrode 3-10, a piezoelectric sensitive layer 3-11, and a lower electrode 3-12, which are stacked sequentially from top to bottom; each discrete capacitor is located on a C-shaped silicon cup base 1, which contains a silicon dioxide cutoff layer 5.

[0151] Furthermore, based on the principle of discrete capacitance enhancement in MEMS, the designs of discrete electrode sensing chips and single electrode sensing chips are as follows: Figure 2 As shown, if the total capacitance of the discrete beam-diaphragm fused acoustic sensor chip in the hydrophone is C, then the voltage output by capacitor C is:

[0152] v0=Q / C (3-1)

[0153] Discretize the total capacitance C into N sub-capacitors I; the capacitance of each sub-capacitor I is approximately C / N. Connect the N sub-capacitors I in series, and let the total capacitance after series connection be C', with the capacitance of each sub-capacitor I being C / N. Then, according to the formula for capacitor series connection...

[0154]

[0155] Because C1 = C2 = ... = C n =C / N, then:

[0156]

[0157] Let the distributed capacitance in the equivalent circuit be Cp, and the input capacitance of the preamplifier circuit be Cin. After N sub-capacitors are connected in series, the total input capacitance of the preamplifier circuit is:

[0158]

[0159] Based on the definition of capacitance, V = Q * C, the charge generated by each sub-capacitor I is approximately Q / N (note: this approximation is due to the loss of some area caused by the capacitor spacing). Therefore, the output voltage of the circuit is:

[0160]

[0161] Output voltage value V' of a single capacitive sensor:

[0162]

[0163] Comparing the output voltages obtained from the two different circuits, the voltage gain expression is as follows:

[0164]

[0165] As can be seen from the voltage gain expression, the gain obtained by discretizing capacitor C and connecting sub-capacitors in series is closely related to the number of discretized capacitors N. To obtain the optimal number of discretized capacitors, the extreme value of the voltage gain is calculated. To find the optimal number of discrete elements; simplifying the equation yields:

[0166]

[0167] Substituting equation (3-8) into the voltage gain expression, we obtain the following relationship between the maximum gain and the number of discrete capacitors:

[0168]

[0169] A method for implementing a double-sided etching process for a discrete beam-diaphragm fused acoustic sensor chip in a hydrophone, the method comprising the following steps:

[0170] Step 1: Photolithography is performed on the front side of the silicon substrate, followed by deep trench etching with an etching thickness of h to create the gaps in the discrete beam-film fusion sensitive chip structure.

[0171] Step 2: After filling the deep trench in Step 1 with sacrificial material, a bottom electrode layer is fabricated by magnetron sputtering of molybdenum, and then the bottom electrode is patterned.

[0172] Step 3: Fabricate an aluminum nitride piezoelectric sensing material layer on the molybdenum electrode;

[0173] Step 4: Fabricate the upper electrode on the aluminum nitride piezoelectric sensitive material layer, and pattern the upper electrode by photolithography to bring out the electrode and complete the front process;

[0174] Step 5: Backplane photolithography, forming a back cavity through dry etching, with the etching depth being the total silicon wafer thickness minus h, ultimately ensuring that the thickness of the fused beam film meets the design requirements.

[0175] Furthermore, the piezoelectric sensitive material layer can be any piezoelectric sensitive material, preferably aluminum nitride piezoelectric material. All such technologies that use piezoelectric sensitive materials are within the scope of protection of this patent.

[0176] Novel hydrophone discrete beam-diaphragm fused acoustic sensor chip structure, such as Figure 1 As shown, the novel hydrophone discrete beam-diaphragm fusion acoustic sensitive chip is composed of m (m=15) fan-shaped sub-beam membranes fixed on a base to form a flat membrane structure. There are gaps of 5 to 10 micrometers between the sub-beam membranes. The membrane is a discontinuous membrane.

Claims

1. A method for automatically releasing overload signals or interference in a hydrophone with a discrete beam-diaphragm fused acoustic sensitive chip structure, characterized in that, The release method is specifically designed to automatically release overload signals or interference and automatically restore normal sensitive structure and sensitive characteristics through the discrete beam-membrane fusion acoustic sensitive chip structure design: when the sound pressure signal in the water medium is within the detection sound pressure range P of the sensitive chip design, the discrete beam-membrane fusion acoustic sensitive chip presents a flat membrane structure as a whole due to the existence of gap damping, and the sensitive mode is the flat membrane sensitive mode. When there is a signal or interference in the water medium that is more than twice the designed sound pressure range P, the large overload signal or interference is a dynamic signal that acts on the flat diaphragm, causing the flat diaphragm to be compressed and generate stress and strain distribution. The stress and deflection are the largest at the center of the diaphragm. As the amplitude of the overload or interference sound pressure signal increases, the increase in the deflection at the center of the diaphragm will cause the diaphragm to split along the gap, increasing the distance between the sub-beam diaphragms. The closer to the center, the larger the gap. At this time, the original flat diaphragm structure is dispersed into N sub-beam diaphragms (3). At this time, the hydrophone sound-sensitive structure can be equivalent to multiple cantilever beam sensitive structures. At this time, the hydrophone sound-sensitive chip presents a cantilever beam sensitive mode. The detection capacitor electrode is designed in the corresponding stress change sensitive area of ​​each sub-beam diaphragm to detect the stress change on the beam and convert it into an electrical signal output. When the external overload signal or interference disappears, each sub-beam diaphragm will return to its initial position. Since the gap between the sub-beam diaphragms is very small, under the action of the damping force, the sensitive structure returns to the flat diaphragm structure and can continue to sensitively detect signals that are no more than twice the designed sound pressure range P. The acoustic sensitive chip structure includes a C-shaped silicon cup base (1) and a flat film (2) fabricated on the C-shaped silicon cup base. The flat film (2) fabricated on the C-shaped silicon cup base is divided into multiple sub-beam films (3). The multiple sub-beam films (3) together form a circular flat film. There are micron-level gaps (4) between each sub-beam film (3). Each of the sub-beam membranes (3) has a piezoelectric sensitive layer (3-11) and detection electrodes distributed on both sides of the piezoelectric sensitive layer (3-11), namely, the upper electrode (3-10) and the lower electrode (3-12) form a detection capacitor. The detection capacitor on each of the sub-beam membranes (3) is connected in series through the upper electrode (3-10) and the lower electrode (3-12) of the adjacent sub-beam membrane.

2. The method for automatically releasing overload signals or interference in a hydrophone discrete beam-diaphragm fused acoustic sensitive chip structure according to claim 1, characterized in that, The piezoelectric sensitive layer (3-11) is made of any piezoelectric sensitive material that is compatible with MEMS processes.

3. The method for automatically releasing overload signals or interference in a hydrophone discrete beam-diaphragm fused acoustic sensitive chip structure according to claim 1, characterized in that, A peripherally fixed circular flat diaphragm formed by the fusion of sub-beam membranes and its sensitive modes are analyzed. The thickness of the circular flat diaphragm is denoted as h, and the radius of the thin film region is denoted as R. Stress-strain analysis is performed. To avoid nonlinearity, the following two assumptions are made in the calculations of the following formulas: (1) Assume that the pressure p is applied uniformly to the surface of the flat diaphragm; (2) Apply the small deflection theory, that is, the maximum deflection of the flat diaphragm is no more than 1 / 3 of the film thickness; Under the above assumptions, radial stress (1-1) Tangential stress (1-2) radial strain (1-3) Tangential strain (1-4) Through the formula for calculating radial strain, when When the radial strain is equal to 0; The deflection of the flat diaphragm is: (1-5) According to formula (1-5), the maximum deflection occurs at the center of the circular diaphragm at r=0, and the maximum deflection is: (1-6) The approximate formula for the natural frequency of a flat diaphragm is: (1-7) Where: k----stiffness of the elastic sensing element; m----Equivalent vibrational mass of a circular flat diaphragm; Substituting the mass m of the circular flat diaphragm and the stiffness of the diaphragm structure into equation (1-7), and simplifying, we can obtain the natural frequency of the flat diaphragm as: (1-8) In the above formulas: E --- the elastic modulus of a thin circular flat diaphragm; ----Poisson's ratio of a thin, circular flat diaphragm; h----diaphragm thickness; R----diaphragm radius; r----radius of any part of the diaphragm; ----Density of the diaphragm material.

4. The method for automatically releasing overload signals or interference in a hydrophone discrete beam-diaphragm fused acoustic sensitive chip structure according to claim 1, characterized in that, Under overload signals or interference, the sub-beam membrane approximates a beam of equal strength, exhibiting a beam-sensitive mode. Let the width of the fixed end of the beam be *b*, and the beam length be *l*. Given a beam with thickness h and a cross-section along its length from the point of application of the force to distance x, find the maximum stress at that cross-section. （2-1） Make （2-2） Then it can be found （2-3） In the formula To and The corresponding beam width; The strain values ​​at each point of a beam of equal strength are （2-4） Maximum deflection at the free end of a beam of equal strength for （2-5） It is the deflection at the free end of a cantilever beam with a uniform cross-section. times; Derived from equation (2-5) （2-6） In the formula, the coefficient k is the ratio of load to deflection, i.e., stiffness; Lowest natural frequency of beams of equal strength for （2-7） or (2-8).

5. A discrete capacitance enhancement design method for a hydrophone discrete beam-diaphragm fused acoustic sensitive chip structure, characterized in that, The discrete capacitor enhancement design method is based on the hydrophone discrete beam diaphragm fusion acoustic sensitive chip structure in the automatic overload signal or interference release method of the hydrophone discrete beam diaphragm fusion acoustic sensitive chip structure of claim 1. A piezoelectric sensitive material layer is fabricated on the discrete beam diaphragm fusion acoustic sensitive chip structure. An upper electrode layer and a lower electrode layer are fabricated on the upper and lower sides of the piezoelectric sensitive material layer to form a sensitive detection capacitor. Each sub-beam diaphragm (3) is a discrete capacitor, and the discrete capacitors are connected in series. N discrete capacitors are connected in series to form the total detection capacitor of the chip.

6. The discrete capacitance enhancement design method for a hydrophone discrete beam-diaphragm fused acoustic sensitive chip structure according to claim 5, characterized in that, Discrete capacitor series connection structure and method: Each sub-beam membrane (3) has a discrete capacitor lower electrode (3-12) led out from the outside of the arc electrode and connected to the process via (3-4). The process via (3-4) of the lower electrode of the discrete capacitor is electrically connected to the upper electrode (3-10) of the discrete capacitor on the adjacent sub-beam membrane (3). The multiple sub-beam membranes (3) have the same structure. The upper electrode of the first discrete capacitor is led out to the output pad on the hydrophone discrete beam membrane fusion acoustic sensitive chip structure through the lead wire. The lower electrode of the last discrete capacitor is led out to the upper electrode surface through the process via point and then connected to the lower electrode output pad on the hydrophone discrete beam membrane fusion acoustic sensitive chip structure through the connection wire. The two electrodes of the series total capacitor are led out through the upper and lower electrode pads.

7. The discrete capacitance enhancement design method for a hydrophone discrete beam-diaphragm fused acoustic sensitive chip structure according to claim 5, characterized in that, Each discrete capacitor includes an upper electrode (3-10), a piezoelectric sensitive layer (3-11), and a lower electrode (3-12), which are stacked sequentially from top to bottom.

8. The discrete capacitance enhancement design method for a hydrophone discrete beam-diaphragm fused acoustic sensitive chip structure according to claim 5, characterized in that, MEMS Capacitor Discrete Sensitivity Enhancement Principle: If the total capacitance of the discrete beam-diaphragm fused acoustic sensor chip in a hydrophone is C, then the voltage output by capacitor C is: （3-1） Discretize the total capacitance C into N sub-capacitors I; the capacitance of each sub-capacitor I is approximately C / N. Connect the N sub-capacitors I in series, and let the total capacitance after series connection be C', with the capacitance of each sub-capacitor I being C / N. Then, according to the formula for capacitor series connection... （3-2） because, ,but: （3-3） Let the distributed capacitance in the equivalent circuit be Cp, and the input capacitance of the preamplifier circuit be Cin. After N sub-capacitors are connected in series, the total input capacitance of the preamplifier circuit is: （3-4） Then, according to the definition of capacitance The charge generated by each sub-capacitor I is Q / N, resulting in the circuit's output voltage as: （3-5） Output voltage value of a single capacitive sensor : （3-6） Comparing the output voltages obtained from the two different circuits, the voltage gain expression is as follows: （3-7） To obtain the optimal number of discrete values, the extreme values ​​of the voltage gain are calculated. To find the optimal number of discrete elements; simplify equation (3-7) to obtain: （3-8） Substituting equation (3-8) into the voltage gain expression, we obtain the following relationship between the maximum gain and the number of discrete capacitors: （3-9）。 9. A method for implementing a double-sided etching process for a discrete beam-diaphragm fused acoustic sensitive chip structure in a hydrophone, characterized in that, The process implementation method is based on the hydrophone discrete beam-membrane fused acoustic sensitive chip structure in the automatic overload signal or interference release method of the hydrophone discrete beam-membrane fused acoustic sensitive chip structure of claim 1. The process implementation method includes the following steps: Step 1: Photolithography is performed on the front side of the silicon substrate, followed by deep trench etching to a depth of h to create the gaps in the discrete beam-film fusion sensitive chip structure. Step 2: After filling the deep trench in Step 1 with sacrificial material, a bottom electrode layer is fabricated by magnetron sputtering of molybdenum, and then the bottom electrode is patterned. Step 3: Fabricate an aluminum nitride piezoelectric sensing material layer on the molybdenum electrode; Step 4: Fabricate the upper electrode on the aluminum nitride piezoelectric sensitive material layer, and pattern the upper electrode by photolithography to bring out the electrode and complete the front process; Step 5: Backplane photolithography, forming a back cavity through dry etching, with the etching depth being the total silicon wafer thickness minus h, ultimately ensuring that the thickness of the fused beam film meets the design requirements.

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