Ultrasonic transducer with double-layer vibrating diaphragm, manufacturing method and electronic equipment

Abstract

The invention discloses an ultrasonic transducer with double vibrating diaphragms, a manufacturing method and electronic equipment, the ultrasonic transducer comprises a substrate with a concave cavity, a supporting layer is arranged in the opening direction of the concave cavity, a first vibrating diaphragm is arranged below the supporting layer, and the first vibrating diaphragm is of a first sandwich structure; a second vibrating diaphragm is arranged on the supporting layer, and the second vibrating diaphragm is of a second sandwich structure; the first sandwich structure and the second sandwich structure respectively comprise a bottom electrode, a piezoelectric layer and a top electrode. According to the ultrasonic transducer with the double-layer vibrating diaphragm, the manufacturing method and the electronic equipment provided by the invention, higher amplitude can be provided, the power of the ultrasonic transducer is stronger, the provided boost is higher, and the sensitivity is higher under the same voltage.

Description

TECHNICAL FIELD

[0001] The present application relates to a piezoelectric micro-electro-mechanical system (MEMS) ultrasonic transducer and a manufacturing method, in particular to an ultrasonic transducer with a double diaphragm and a manufacturing method and an electronic device. BACKGROUND

[0002] The piezoelectric micro-electro-mechanical system (MEMS) ultrasonic transducer has the advantages of easy mass production, compatibility with CMOS (Complementary Metal-Oxide Semiconductor), and other advantages that traditional ultrasonic transducers cannot have. However, the current development of the piezoelectric MEMS ultrasonic transducer has encountered the problem of difficulty in obtaining high sensitivity.

[0003] The current piezoelectric MEMS ultrasonic transducer needs to achieve the following goals:

[0004] 1. Higher output sound pressure level with smaller driving voltage;

[0005] 2. Higher output sound pressure level with smaller driving power.

[0006] Some solutions to this problem have been proposed previously, such as mechanically decoupling the complete diaphragm into a multi-petal structure to obtain higher degrees of freedom, or using a four-side cantilever beam to drive the center diaphragm to achieve piston vibration mode. These solutions have good results in improving vibration displacement, but in essence, they all sacrifice the forward resonance frequency as a trade-off. However, the resonance frequency is one of the design indicators and often cannot be arbitrarily selected. Existing solutions are a trade-off between sensitivity and resonance frequency, often sacrificing one for the other.

[0007] The current piezoelectric MEMS ultrasonic transducer has the following problems:

[0008] 1. Sensitivity and resonance frequency are traded off, there is no unified evaluation standard and formula to ensure both sensitivity and resonance frequency.

[0009] 2. The diaphragm of the MEMS ultrasonic transducer is relatively thin, and the equivalent mechanical stiffness is low, which is prone to breakage during use, especially under impact, and the device reliability is low.

[0010] 3. The sensitivity of MEMS ultrasonic transducers is not only related to the planar structure design, but also to the thickness of the membrane layer. The unoptimized thickness of the piezoelectric layer and the thickness ratio of the piezoelectric layer to other membrane layers are one of the main reasons for the low sensitivity of MEMS transducers made of piezoelectric films. On the other hand, the manufacturing method of piezoelectric MEMS transducers will also limit the range of selectable film thickness. For example, piezoelectric (MEMS) transducers based on cavity SOI have requirements for the minimum thickness of the diaphragm, such as greater than 1 micron. However, a thicker diaphragm thickness will reduce the sensitivity of the transducer.

[0011] Therefore, the problems existing in the prior art need to be further improved and developed. Summary of the Invention

[0012] (1) Purpose of the invention: In order to solve the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide an ultrasonic transducer with a double-layer diaphragm that can improve the acoustic performance of the ultrasonic transducer.

[0013] (2) Technical solution: In order to solve the above technical problems, the present technical solution provides a double-layer diaphragm ultrasonic transducer, comprising a substrate with a concave cavity, wherein a supporting layer is arranged in the opening direction of the concave cavity, a first diaphragm is arranged below the supporting layer, and the first diaphragm is a first sandwich structure; a second diaphragm is arranged above the supporting layer, and the second diaphragm is a second sandwich structure; the first sandwich structure and the second sandwich structure respectively include a bottom electrode, a piezoelectric layer, and a top electrode, and the material of the piezoelectric layer is PZT.

[0014] In the double-layer diaphragm ultrasonic transducer, the material of the supporting layer is silicon or silicon nitride.

[0015] The ultrasonic transducer with a double-layer diaphragm, wherein the thickness of the bottom electrodes corresponding to the first sandwich structure and the second sandwich structure is the same, the thickness of the piezoelectric layers corresponding to the first sandwich structure and the second sandwich structure is the same, and the thickness of the top electrodes corresponding to the first sandwich structure and the second sandwich structure is the same.

[0016] The ultrasonic transducer with a double-layer diaphragm, wherein the second sandwich structure is sequentially covered with a circular bottom electrode, a circular piezoelectric layer, and a circular top electrode starting from the support layer from bottom to top;

[0017] In the first sandwich structure, starting from the support layer, a circular bottom electrode, a circular piezoelectric layer and a circular top electrode are sequentially covered from top to bottom.

[0018] The double-layer diaphragm ultrasonic transducer, wherein the bottom electrode has a composite material layer structure, and the composite material layer structure is zirconium oxide, platinum, SRO or titanium, platinum, and a buffer layer from bottom to top, wherein zirconium oxide or titanium acts as a seed layer.

[0019] The ultrasonic transducer of the double-layer diaphragm, wherein the top electrode is a same-layer process material, and the same-layer process material comprises metal materials of molybdenum, platinum, magnesium, aluminum, ruthenium, titanium, iridium, osmium, silver, gold, copper, tungsten, and alloys or composite layers of the metals.

[0020] The ultrasonic transducer of the double-layer diaphragm, wherein an isolation layer is arranged at the upper surface and the edge of the second sandwich structure piezoelectric layer.

[0021] The ultrasonic transducer of the double-layer diaphragm, wherein the isolation layer is a local area at the upper surface and the edge of the piezoelectric layer, or a ring-shaped area around the center of the second sandwich structure.

[0022] The ultrasonic transducer of the double-layer diaphragm, wherein the isolation layer is a continuous step shape, comprising steps from high to low, a first layer of steps covering the lower piezoelectric layer edge, a second layer of steps covering the edge of the bottom electrode, and a third layer of steps covering the edge of the connection between the support layer and the bottom electrode.

[0023] The ultrasonic transducer of the double-layer diaphragm, wherein the material of the isolation layer comprises air, vacuum, or a dielectric material, and the dielectric material comprises silicon oxide, silicon nitride.

[0024] The ultrasonic transducer of the double-layer diaphragm, wherein the cavity has a plurality of channels extending in the direction of the opening of the cavity, and the support layer has through holes matched with the channels, and the through holes are in communication with the channels.

[0025] The ultrasonic transducer of the double-layer diaphragm, wherein the upper surface of the support layer is flat, and the support layer completely wraps the end surface of the piezoelectric layer and the top electrode and the bottom electrode below the support layer. The ultrasonic transducer of the double-layer diaphragm, wherein an optimization value FOM value representing the acoustic performance of the piezoelectric micro-electro-mechanical system ultrasonic transducer is arranged, and the optimization value FOM value is calculated according to the following formula:

[0026]

[0027] wherein γ is the specific heat capacity ratio of air; P0 is the atmospheric pressure; S is the diaphragm area; E P is the Young's modulus of the piezoelectric material; d 31 is the piezoelectric coefficient of the piezoelectric material; U is the driving voltage; V 711 is the simulated ear volume; p P is the density of the piezoelectric material; p n is the density of the support layer; t p is the total thickness of the two piezoelectric layers; t n is the thickness of the support layer.

[0028] The ultrasonic transducer of the dual-layer diaphragm, wherein the log of the figure of merit FOM value represents a sound pressure level at a certain resonant frequency:

[0029] log(FOM) = 20*log 10 (P*f).

[0030] The ultrasonic transducer of the dual-layer diaphragm, wherein the log of the figure of merit FOM value is greater than 105.

[0031] The ultrasonic transducer of the dual-layer diaphragm, wherein the piezoelectric layer thickness of the first or second diaphragm is less than 0.5 microns.

[0032] The ultrasonic transducer of the dual-layer diaphragm, wherein the log of the figure of merit FOM value is greater than 110.

[0033] The ultrasonic transducer of the dual-layer diaphragm, wherein the piezoelectric layer thickness of the first or second diaphragm is less than 0.5 microns.

[0034] The ultrasonic transducer of the dual-layer diaphragm, wherein the log of the figure of merit FOM value is greater than 112.

[0035] The ultrasonic transducer of the dual-layer diaphragm, wherein the piezoelectric layer thickness of the first or second diaphragm is less than 0.3 microns.

[0036] The ultrasonic transducer of the dual-layer diaphragm, wherein the ratio of the support layer thickness to the total thickness of the two piezoelectric layers is 50%-120%.

[0037] The ultrasonic transducer of the dual-layer diaphragm, wherein the ratio of the support layer thickness to the total thickness of the two piezoelectric layers is 60%-100%.

[0038] The ultrasonic transducer of the dual-layer diaphragm, wherein the piezoelectric layer thickness of the first or second diaphragm is greater than 0.3 microns and less than 0.8 microns, and the support layer thickness is greater than 0.2 microns and less than 0.6 microns.

[0039] The ultrasonic transducer of the dual-layer diaphragm, wherein the piezoelectric layer thickness of the first or second diaphragm is less than 0.3 microns, and the support layer thickness is greater than 0.05 microns and less than 0.3 microns.

[0040] A method for manufacturing an ultrasonic transducer of a dual-layer diaphragm, comprising the following steps:

[0041] Step one, forming a concave cavity in the substrate, filling a sacrificial layer in the concave cavity, the sacrificial layer is flush with the upper surface of the substrate;

[0042] Step two, sequentially depositing a top electrode, a piezoelectric layer and a bottom electrode of the first diaphragm from bottom to top on the surface of the substrate by a deposition process to form a first sandwich structure;

[0043] Step three, covering a support layer on the upper part of the first sandwich structure of the first diaphragm and the substrate by a deposition process;

[0044] Step four, depositing a second diaphragm on the surface of the support layer, the second diaphragm comprising a bottom electrode, a piezoelectric layer and a top electrode deposited in sequence.

[0045] The method for manufacturing the ultrasonic transducer of the double-layer diaphragm, wherein,

[0046] The step two further comprises the following steps: patterning the metal layers where the top electrode, the piezoelectric layer and the bottom electrode of the first diaphragm into a circular shape, the circular top electrode, the circular piezoelectric layer and the circular bottom electrode having the same center.

[0047] The method for manufacturing the ultrasonic transducer of the double-layer diaphragm, wherein, the step three further comprises the following steps:

[0048] The support layer is made flat by a planarization process.

[0049] The method for manufacturing the ultrasonic transducer of the double-layer diaphragm, wherein, the step four further comprises the following steps:

[0050] The metal layers where the bottom electrode, the piezoelectric layer and the top electrode of the second diaphragm are patterned into a circular shape by a patterning process, the circular top electrode, the circular piezoelectric layer and the circular bottom electrode having the same center.

[0051] The method for manufacturing the ultrasonic transducer of the double-layer diaphragm, wherein, the step four further comprises the following steps:

[0052] An isolation layer is covered on the surface of the right end part of the piezoelectric layer of the second diaphragm, a small amount of the upper surface and the sidewall of the bottom electrode exposed below the right end of the piezoelectric layer, and part of the surface of the support layer on the right side of the bottom electrode by a deposition and patterning process.

[0053] The method for manufacturing the ultrasonic transducer of the double-layer diaphragm, wherein, the step four further comprises the following steps:

[0054] The isolation layer is made of a material that can be dissolved in the etching environment, and the isolation layer is removed by the releasing process to form a gap in the position originally filled with the isolation layer at the lower part of the extension of the top electrode in the second diaphragm.

[0055] The method for manufacturing the ultrasonic transducer of the double-layer diaphragm, wherein, the step four further comprises the following steps:

[0056] A cavity is formed in the substrate by removing the sacrificial layer using a gaseous or liquid etching environment.

[0057] An electronic device comprising a processor, a memory, a communication interface and a communication bus, the processor, the memory and the communication interface accomplish the communication among each other through the communication bus, the processor is connected to the double-layer diaphragm ultrasonic transducer of any one.

[0058] (Three) beneficial effects: the double-layer diaphragm ultrasonic transducer and the manufacturing method and the electronic device provided by the application can provide higher amplitude, stronger power of the ultrasonic transducer, higher boost, and higher sensitivity under the same voltage. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 is the merit figure of the ultrasonic transducer of the double-layer diaphragm of the application changing the thickness of PZT layer (piezoelectric layer) and silicon (support layer);

[0060] Figure 2 is the trend graph of calculating the merit and equivalent stiffness when the thickness of PZT in the ultrasonic transducer of the double-layer diaphragm of the application is 0.1 microns and the thickness of silicon is changed;

[0061] Figure 3 is the trend graph of calculating the merit and equivalent stiffness when the thickness of PZT in the ultrasonic transducer of the double-layer diaphragm of the application is 0.5 microns and the thickness of silicon is changed;

[0062] Figure 4 is the trend graph of calculating the merit and equivalent stiffness when the thickness of PZT in the ultrasonic transducer of the double-layer diaphragm of the application is 1 micron and the thickness of silicon is changed;

[0063] Figure 5 is the merit figure of the ultrasonic transducer of the double-layer diaphragm of the application changing the thickness of PZT layer (piezoelectric layer) and silicon nitride (support layer);

[0064] Figure 6 is the trend graph of calculating the merit and equivalent stiffness when the thickness of PZT layer in the ultrasonic transducer of the double-layer diaphragm of the application is 0.1 microns and the thickness of silicon nitride is changed;

[0065] Figure 7 is the trend graph of calculating the merit and equivalent stiffness when the thickness of PZT layer in the ultrasonic transducer of the double-layer diaphragm of the application is 0.5 microns and the thickness of silicon nitride is changed;

[0066] Figure 8 is the trend graph of calculating the merit and equivalent stiffness when the thickness of PZT layer in the ultrasonic transducer of the double-layer diaphragm of the application is 1 micron and the thickness of silicon nitride is changed;

[0067] Figure 9is a schematic diagram of a top view of an ultrasonic transducer of the double-layer diaphragm of the present invention;

[0068] Figure 10 is a schematic diagram of a top view of an ultrasonic transducer of the double-layer diaphragm of the present invention with a ring-shaped isolation layer;

[0069] Figure 11 is a schematic diagram of a cross-sectional view of an ultrasonic transducer of the double-layer diaphragm of the present invention;

[0070] Figure 12 is a schematic diagram of a cross-sectional view of an ultrasonic transducer of the double-layer diaphragm of the present invention;

[0071] Figure 13 is a schematic diagram of a cross-sectional view of an ultrasonic transducer of the double-layer diaphragm of the present invention;

[0072] Figure 14 is a schematic diagram of a cross-sectional view of an ultrasonic transducer of the double-layer diaphragm of the present invention;

[0073] Figure 15 is a schematic diagram of a cross-sectional view of an ultrasonic transducer of the double-layer diaphragm of the present invention;

[0074] Figure 16 is a schematic diagram of a cross-sectional view of an ultrasonic transducer of the double-layer diaphragm of the present invention;

[0075] Figure 17 is a schematic diagram of a cross-sectional view of an ultrasonic transducer of the double-layer diaphragm of the present invention;

[0076] Figure 18 is a schematic diagram of a cross-sectional view of an ultrasonic transducer of the double-layer diaphragm of the present invention;

[0077] Figure 19 is a schematic diagram of a cross-sectional view of an ultrasonic transducer of the double-layer diaphragm of the present invention;

[0078] Figure 20 is a schematic diagram of a cross-sectional view of an ultrasonic transducer of the double-layer diaphragm of the present invention;

[0079] Figure 21 is a schematic diagram of a cross-sectional view of an ultrasonic transducer of the double-layer diaphragm of the present invention;

[0080] Figure 22 is a schematic diagram of a cross-sectional view of an ultrasonic transducer of the double-layer diaphragm of the present invention;

[0081] Figure 23 is a schematic diagram of a cross-sectional view of an ultrasonic transducer of the double-layer diaphragm of the present invention;

[0082] Figure 24It is the manufacturing method of the double-layer diaphragm piezoelectric micro-electro-mechanical system ultrasonic transducer of the present application, and is the effect diagram of step 112;

[0083] Figure 25 It is the manufacturing method of the double-layer diaphragm ultrasonic transducer of the present application, and is the effect diagram of step 113;

[0084] Figure 26 It is the structural schematic diagram of the electronic device with the double-layer diaphragm ultrasonic transducer of the present application. DETAILED DESCRIPTION

[0085] The present application will be further described below in conjunction with preferred embodiments, and more details are set forth in the following description in order to fully understand the present application, however, the present application can be implemented in various other ways different from the description, and the person skilled in the art can make similar generalization and deduction according to the actual application without departing from the connotation of the present application, therefore, the protection scope of the present application should not be limited by the content of the specific embodiments.

[0086] The accompanying drawings are schematic diagrams of the embodiments of the present application, and it should be noted that the drawings are only examples, and are not drawn according to the condition of the same scale, and should not be used as a limitation to the actual protection scope of the present application.

[0087] The present application proposes an ultrasonic transducer with a double-layer diaphragm, the piezoelectric layer of the ultrasonic transducer adopts a PZT (lead zirconate titanate piezoelectric ceramics) film, and the thickness of the piezoelectric layer is selected to be optimal, and the ratio of the thickness of the support layer to the total thickness of the two piezoelectric layers is 50%-120%, further, the ratio of the thickness of the support layer to the total thickness of the two piezoelectric layers is preferably 60%-100%. The sound pressure sensitivity of the ultrasonic transducer can be improved, and the reliability of the device can be improved. Especially when the thickness of the piezoelectric layer is small, selecting a reasonable thickness of the support layer can greatly improve the performance and reliability of the device. Preferably, the thicknesses of the bottom electrode, the piezoelectric layer and the top electrode corresponding to the double-layer diaphragm of the present application are the same, that is, the thicknesses of the bottom electrodes corresponding to the first sandwich structure and the second sandwich structure are the same, the thicknesses of the piezoelectric layers corresponding to the first sandwich structure and the second sandwich structure are the same, and the thicknesses of the top electrodes corresponding to the first sandwich structure and the second sandwich structure are the same. In the second sandwich structure, from the bottom to the top, the bottom electrode, the piezoelectric layer and the top electrode are sequentially covered; in the first sandwich structure, from the top to the bottom, the bottom electrode, the piezoelectric layer and the top electrode are sequentially covered.

[0088] The present application defines a figure of merit (FOM) representing the acoustic pressure sensitivity and the output acoustic pressure of an ultrasonic transducer, the larger the FOM, the better the acoustic performance of the ultrasonic transducer, the FOM is related to the thickness of the piezoelectric layer and the thickness of the support layer. The FOM is described as formula (1):

[0089]

[0090] Where, γ - the specific heat capacity of air; P0 - atmospheric pressure; S - the diaphragm area; E P - Young's modulus of the piezoelectric material; d 31 - piezoelectric coefficient of the piezoelectric material; U - driving voltage; V 711 - the volume of the simulated ear; ρ P - the density of the piezoelectric material; ρ n - the density of the support layer; t p - the total thickness of the two piezoelectric layers; t n - the thickness of the support layer.

[0091] The material of the piezoelectric layer of the present application includes single crystal or polycrystalline PZT, and doped PZT.

[0092] The present application can take the logarithm of the figure of merit FOM, representing the sound pressure level at a certain resonance frequency, as shown in formula (2):

[0093] log(FOM) = 20*log 10 (P*f) formula (2)

[0094] The sensitivity P (the output acoustic pressure under unit voltage excitation and unit area) and the resonance frequency f both affect the acoustic pressure sensitivity and the output acoustic pressure performance of the ultrasonic transducer, and their product can be used to evaluate the overall performance of the acoustic pressure sensitivity and the output acoustic pressure of an ultrasonic transducer. Therefore, the product of the sensitivity P and the first-order resonance frequency f of the diaphragm of the ultrasonic transducer is defined as the figure of merit FOM of the ultrasonic transducer.

[0095] The double-layer diaphragm ultrasonic transducer of the present application limits the size of the thickness of the piezoelectric layer of the ultrasonic transducer, so that the piezoelectric micro-electro-mechanical system ultrasonic transducer outputs larger sound pressure level at unit voltage excitation, unit area, and fixed resonance frequency, that is, it has larger area-normalized output acoustic pressure efficiency under the premise of fixed resonance frequency.

[0096] The first preferred embodiment of the double-layer diaphragm ultrasonic transducer of the present application determines the thickness of the piezoelectric layer and the thickness of the support layer, and uses silicon as the support layer. The thickness of silicon can be determined by the FOM value formula, and the thickness of the piezoelectric layer and the support layer can be changed, that is, Figure 1 the thickness of the PZT layer and the silicon layer.

[0097] Preferably, the piezoelectric layer of the present application is a PZT layer, and when the material of the support layer is silicon, the optimal value is calculated by changing the thickness of the piezoelectric layer and the support layer. When the thickness of the piezoelectric layer is less than 0.8 microns, the optimal value increases significantly. In another preferred embodiment, when the thickness of the piezoelectric layer is less than 0.5 microns, the optimal value further increases. Therefore, the thickness of the piezoelectric layer of the present application is preferably less than 0.8 microns; or the thickness of the piezoelectric layer is less than 0.5 microns.

[0098] In order to make the performance of the ultrasonic transducer device better, a certain thickness range can be obtained according to the optimal value, such as Figure 1 In the present application, the log(FOM) is preferably greater than 105; further, the log(FOM) is preferably greater than 110; further, the log(FOM) is preferably greater than 112.

[0099] From Figure 1 It can be seen that the optimal value FOM of the thickness of the piezoelectric layer PZT is less than 0.8 microns is greater than the optimal value FOM of the thickness of the piezoelectric layer PZT layer is greater than 0.8 microns. On the other hand, when the thickness of the piezoelectric layer PZT is less than 0.8 microns, the preferred embodiment of the thickness of silicon can improve the optimal value FOM to a certain extent, and when the thickness of the piezoelectric layer PZT is greater than 0.8 microns, the change of the thickness of the support layer, that is, the thickness of silicon, has little effect on the FOM value. Therefore, the thickness of the piezoelectric layer of the diaphragm of the ultrasonic transducer of the present application is preferably less than 0.8 microns.

[0100] From Figure 1 It can be seen that the optimal value FOM of the thickness of the piezoelectric layer PZT is less than 0.5 microns is greater than the FOM of the thickness of the PZT is greater than 0.5 microns; on the other hand, when the thickness of the piezoelectric layer PZT is less than 0.5 microns, the influence degree of the thickness of the support layer, that is, the thickness of silicon, on improving the optimal value FOM is greater than the influence degree of the change of the thickness of silicon when the thickness of the piezoelectric layer PZT is greater than 0.5 microns. Therefore, the thickness of the piezoelectric layer of the diaphragm of the ultrasonic transducer of the present application is preferably less than 0.5 microns.

[0101] The present application takes the thickness of the piezoelectric layer PZT as 0.1, 0.5, 1 microns respectively, changes the thickness of silicon, calculates the optimal value FOM and the equivalent stiffness, as shown in Figure 2 , Figure 3 and Figure 4 .

[0102] From Figure 2 , Figure 3 and Figure 4 It can be seen that by selecting an appropriate range of silicon thickness, the performance of the ultrasonic transducer can be improved, and due to the significant increase in the equivalent stiffness of the device, not only the manufacturing difficulty can be reduced, but also the reliability of the device can be improved.

[0103] The present application can improve the performance of the ultrasonic transducer when the thickness of the PZT layer is less than 0.3 microns (e.g. Figure 2 The present application can improve the performance of the ultrasonic transducer when the thickness of the PZT layer is less than 0.3 microns (e.g. Figure 3 The present application can improve the performance of the ultrasonic transducer when the thickness of the PZT layer is less than 0.3 microns (e.g. Figure 4 The present application can improve the performance of the ultrasonic transducer when the thickness of the PZT layer is less than 0.3 microns (e.g.

[0104] From Figure 2 , Figure 3 and Figure 4 , it can be seen that the thinner the thickness of the piezoelectric layer, the greater the merit of the ultrasonic transducer, and the thinner the thickness of the piezoelectric layer, the greater the impact of the thickness of the silicon layer on the performance of the ultrasonic transducer, and reasonable selection of the thickness of the silicon support layer can greatly improve the performance.

[0105] The second preferred embodiment of the present application for determining the thickness of the piezoelectric layer and the thickness of the support layer is an ultrasonic transducer with a double-layer diaphragm, which uses silicon nitride as the support layer. The thickness of the silicon nitride can be determined by the merit FOM formula of the ultrasonic transducer. By changing the thickness of the PZT layer and the silicon nitride, the following results are obtained. Figure 5

[0106] To make the performance of the ultrasonic transducer better, a certain thickness range can be obtained according to the merit, and the preferred merit value corresponding to the thickness of the PZT layer and the silicon nitride is shown in the shadow range in Figure 5 , preferably, log(FOM) is greater than 105; further, preferably, log(FOM) is greater than 110.

[0107] From the above Figure 5 , it can be seen that the merit FOM value of the PZT layer with a thickness less than 0.8 microns is greater than the merit FOM value of the PZT layer with a thickness greater than 0.8 microns; on the other hand, reasonable selection of the thickness of the silicon nitride can improve the merit FOM value to a certain extent when the thickness of the PZT layer is less than 0.8 microns, while the change of the thickness of the silicon nitride has little effect on the FOM value when the thickness of the PZT layer is greater than 0.8 microns. Therefore, the present application preferably has a PZT layer thickness of less than 0.8 microns for the ultrasonic transducer.

[0108] From the above Figure 5 ​It can be seen from the table that the FOM value of the PZT layer with a thickness less than 0.5 microns is greater than the FOM value of the PZT layer with a thickness greater than 0.5 microns; on the other hand, the reasonable selection of the thickness of the silicon nitride layer has a greater impact on the FOM value when the thickness of the PZT layer is less than 0.5 microns than when the thickness of the PZT layer is greater than 0.5 microns. Therefore, the thickness of the piezoelectric layer of the diaphragm of the ultrasonic transducer, that is, the thickness of the PZT layer, is preferably less than 0.5 microns.

[0109] The present application calculates the figure of merit FOM value and the equivalent stiffness when the thickness of the PZT layer is 0.1, 0.5 and 1 microns respectively and the thickness of the silicon nitride layer is changed, as shown in Figure 6 、 Figure 7 and Figure 8 .

[0110] It can be seen from Figure 6 、 Figure 7 and Figure 8 that the performance of the ultrasonic transducer can be improved by selecting an appropriate range of the thickness of the silicon nitride layer, and at the same time, due to the significant increase in the equivalent stiffness of the device, not only the manufacturing difficulty can be reduced, but also the reliability of the device can be improved. When the thickness of the PZT layer is less than 0.3 microns, as shown in Figure 6 , the performance of the ultrasonic transducer can be improved by selecting the thickness of the silicon nitride layer in the range of 0.05 microns to 0.3 microns. When the thickness of the PZT layer is greater than 0.3 microns and less than 0.8 microns, as shown in Figure 7 , the performance of the ultrasonic transducer can be improved by selecting the thickness of the silicon nitride layer in the range of 0.2 microns to 0.6 microns. When the thickness of the PZT layer is greater than 0.8 microns, as shown in Figure 8 , the performance of the ultrasonic transducer is poor, and the influence of the thickness of the silicon nitride layer on the performance of the ultrasonic transducer is further reduced.

[0111] It can be seen from Figure 6 、 Figure 7 and Figure 8 that the thinner the piezoelectric layer, the greater the figure of merit of the ultrasonic transducer, and the thinner the PZT layer, the greater the impact of the selection of the thickness of the silicon nitride layer on the performance of the ultrasonic transducer, and the reasonable selection of the thickness of the silicon nitride support layer can greatly improve the performance.

[0112] The ultrasonic transducer with double-layer diaphragm provided by the application can effectively improve the quasi-steady response sound pressure level of the ultrasonic transducer without changing the resonance frequency. By setting the piezoelectric layer thickness of the ultrasonic transducer to be less than 0.8 microns, preferably less than 0.5 microns, the ultrasonic transducer has a high figure of merit, and has good sound pressure sensitivity and output sound pressure performance. Preferably, when the piezoelectric layer thickness is greater than 0.3 microns and less than 0.8 microns, the support layer thickness ranges from greater than 0.2 microns to less than 0.6 microns; when the piezoelectric layer thickness is less than 0.3 microns, the support layer thickness ranges from greater than 0.05 microns to less than 0.3 microns, which can improve the output sound pressure of the ultrasonic transducer and improve the reliability of the device. By setting the piezoelectric layer thickness and the support layer thickness of the ultrasonic transducer, the output sound pressure level and sensitivity of the ultrasonic transducer are improved, the efficiency of the output sound pressure is improved, the reliability and manufacturing consistency of the ultrasonic transducer are improved, and the high-frequency response is better than many existing solutions, that is, the full-bandwidth response is better.

[0113] The ultrasonic transducer with double-layer diaphragm provided by the application can effectively improve the quasi-steady response sound pressure level of the ultrasonic transducer without changing the resonance frequency. By setting the piezoelectric layer thickness of the ultrasonic transducer to be less than 0.8 microns, preferably less than 0.5 microns, the ultrasonic transducer has a high figure of merit, and has good sound pressure sensitivity and output sound pressure performance. Preferably, when the piezoelectric layer thickness is greater than 0.3 microns and less than 0.8 microns, the support layer thickness ranges from greater than 0.2 microns to less than 0.6 microns; when the piezoelectric layer thickness is less than 0.3 microns, the support layer thickness ranges from greater than 0.05 microns to less than 0.3 microns, which can improve the output sound pressure of the ultrasonic transducer and improve the reliability of the device. By setting the piezoelectric layer thickness and the support layer thickness of the ultrasonic transducer, the output sound pressure level and sensitivity of the ultrasonic transducer are improved, the efficiency of the output sound pressure is improved, the reliability and manufacturing consistency of the ultrasonic transducer are improved, and the high-frequency response is better than many existing solutions, that is, the full-bandwidth response is better. Figure 9 、 Figure 10 and Figure 11 The ultrasonic transducer with double-layer diaphragm provided by the application can effectively improve the quasi-steady response sound pressure level of the ultrasonic transducer without changing the resonance frequency. By setting the piezoelectric layer thickness of the ultrasonic transducer to be less than 0.8 microns, preferably less than 0.5 microns, the ultrasonic transducer has a high figure of merit, and has good sound pressure sensitivity and output sound pressure performance. Preferably, when the piezoelectric layer thickness is greater than 0.3 microns and less than 0.8 microns, the support layer thickness ranges from greater than 0.2 microns to less than 0.6 microns; when the piezoelectric layer thickness is less than 0.3 microns, the support layer thickness ranges from greater than 0.05 microns to less than 0.3 microns, which can improve the output sound pressure of the ultrasonic transducer and improve the reliability of the device. By setting the piezoelectric layer thickness and the support layer thickness of the ultrasonic transducer, the output sound pressure level and sensitivity of the ultrasonic transducer are improved, the efficiency of the output sound pressure is improved, the reliability and manufacturing consistency of the ultrasonic transducer are improved, and the high-frequency response is better than many existing solutions, that is, the full-bandwidth response is better.

[0114] The first sandwich structure of the first diaphragm is wrapped by the support layer, and the second sandwich structure of the second diaphragm is arranged on the upper surface of the support layer. The first sandwich structure includes a bottom electrode B100, a piezoelectric layer P100, and a top electrode T100, and the second sandwich structure includes a bottom electrode B200, a piezoelectric layer P200, and a top electrode T200. The material of the support layer F200 can be selected from silicon, silicon nitride, and silicon oxide.

[0115] In the first sandwich structure, the circular bottom electrode B100 is arranged below the support layer, the circular piezoelectric layer P100 is arranged above the circular bottom electrode B100, the piezoelectric layer P100 is circular in the top view and is substantially concentric with the bottom electrode B100. The edge of the piezoelectric layer P100 extends to the outside of the edge of the recess SP100, and extends outward in the diameter direction of the center of the bottom electrode B100 by a small amount or is substantially aligned. The material of the piezoelectric layer P100 can be selected from lead zirconate titanate (PZT) or doped lead zirconate titanate.

[0116] The top electrode T100 is circular in plan view and is substantially concentric with the piezoelectric layer B100 and the bottom electrode P100, the radius of the top electrode T100 is greater than the radius of the piezoelectric layer B100, and extends outwardly in the diameter direction of the center of the circle relative to the edge of the piezoelectric layer P100 by a small amount, or is substantially aligned.

[0117] The bottom electrode B200 has a composite layer structure, which from bottom to top is Figure 10 zirconium oxide, platinum, SRO or titanium, platinum, a buffer layer, wherein the zirconium oxide or titanium acts as a seed layer.

[0118] The in-situ process material of the top electrode T200 includes but is not limited to metal materials such as molybdenum, platinum, magnesium, aluminum, ruthenium, titanium, iridium, osmium, silver, gold, copper, tungsten, etc., and alloys or composite layers of the metals.

[0119] The first sandwich structure is led out by the top motor T100 on the left side in combination with the metal layer M110 through the through hole C100, and is led out by the bottom motor B100 on the left side in combination with the metal layer M120 through the through hole C110. The second sandwich structure is led out by the top motor T200 and the bottom motor B200 leading-out sections located on both sides of the second sandwich structure.

[0120] The surface of the support layer F200 is covered with a second sandwich structure, which has a circular bottom electrode B200, the edge of which extends outwardly from the edge of the cavity SP100 by a small amount, which can be greater than 2 microns and less than 10 microns. The piezoelectric layer P200 is covered on the bottom electrode B200. The support layer F200 can be made of materials such as silicon, silicon nitride, and silicon oxide.

[0121] The bottom electrode B200 is made of in-situ process material and has a composite layer structure, which from bottom to top is Figure 9 or Figure 10 zirconium oxide, platinum, SRO or titanium, platinum, a buffer layer, wherein the zirconium oxide or titanium acts as a seed layer.

[0122] The piezoelectric layer P200 is covered on the bottom electrode B200, and the piezoelectric layer P200 is circular in plan view and is substantially concentric with the bottom electrode B200. The edge of the piezoelectric layer P200 also extends outwardly from the edge of the cavity SP100, and is recessed inwardly relative to the edge of the bottom electrode B200 by a small amount, which can be less than 0.5 microns and greater than 5 microns, or is substantially aligned. The material of the piezoelectric layer P200 can be selected from lead zirconate titanate (PZT) or doped lead zirconate titanate.

[0123] The present invention covers the piezoelectric layer P200 with a top electrode T200. The top electrode T200 is Figure 9 The top electrode T200 is circular and substantially concentric with the piezoelectric layer B200 and the bottom electrode P200. Furthermore, the radius of the top electrode T200 is significantly smaller than that of the piezoelectric layer B200, resulting in the top electrode T200 occupying approximately 40%-60% of the area of ​​the piezoelectric layer B200. The top electrode T200 is made of a single-layer process material. Single-layer process materials include, but are not limited to, metal materials such as molybdenum, platinum, magnesium, aluminum, ruthenium, titanium, iridium, osmium, silver, gold, copper, and tungsten, as well as alloys or composite layers of these metals.

[0124] The second sandwich structure of the second diaphragm of the present invention is provided with an isolation layer L200, such as Figure 11 As shown, the right end portion of the surface of the piezoelectric layer P200, a small amount of the upper surface and side wall of the bottom electrode B200 exposed below the right end of the piezoelectric layer P200, and a portion of the surface of the support layer F200 located on the right side of the bottom electrode B200 are covered with an isolation layer L200. Preferably, the isolation layer L200 described in the present invention is in the form of continuous steps, with steps from high to bottom. The first step covers the edge of the piezoelectric layer P200 below it, the second step covers the edge of the bottom electrode B200, and the third step covers the edge of the connection between the support layer F200 and the bottom electrode B200.

[0125] The isolation layer L200 is a local area covering the edge of the piezoelectric layer, or an annular area surrounding the center of the second sandwich structure.

[0126] The present invention provides an isolation layer L200 on the upper surface and edge of the piezoelectric layer P200 of the second sandwich structure. The isolation layer L200 is a localized area on the upper surface and edge of the piezoelectric layer P200, or an annular area surrounding the center of the second sandwich structure. The functions of the isolation layer L200 include:

[0127] 1. The isolation layer weakens the electric field formed between the piezoelectric layer P200 and the bottom electrode B200 thereunder, thereby reducing energy loss caused by coupling;

[0128] Second, the isolation layer electrically isolates the right lead end of the top motor T200 and the right edge of the bottom electrode B200 in the second sandwich structure;

[0129] Third, the isolation layer is set to be a complete ring, which can make the structure near the effective acoustic area have strong isotropy, thereby helping to improve the sound field distribution.

[0130] The piezoelectric layer P200 does not need to cross the edge of the bottom electrode B200, so the piezoelectric layer P200 does not bend, which is beneficial to improve the performance and reliability of the device. The material of the isolation layer L200 can be air, vacuum or dielectric material, such as silicon oxide, silicon nitride, etc.

[0131] The recessed cavity SP100 is embedded in the upper surface of the substrate S100, and the recessed cavity SP100 also has several channels extending in the opening direction of the recessed cavity. For example, the present application can provide four channels SP110, SP120, SP130 and SP140. The support layer F200 has four through holes R100, R110, R120, R130, which respectively communicate the channels SP110, SP120, SP130, SP140 with the outside. The through holes communicate with the channels, and are used to release the filling material in the recessed cavity SP100 in a gaseous or liquid environment in the later stage of the process. The filling material includes an etchant. The gaseous and liquid etching environment is usually composed of a fluorine-containing etchant, such as gaseous hydrogen fluoride or a solution of hydrogen fluoride.

[0132] The present application Figure 9 In the first preferred embodiment of the double-layer diaphragm ultrasonic transducer, the effective acoustic area is determined by the area of the top electrode T200, that is, the circular area of the top electrode T200 defines the effective acoustic area.

[0133] The upper surface of the support layer F200 of the double-layer diaphragm is flat, which can ensure the flatness of the electrode layer and the piezoelectric film deposited on the support layer F200 subsequently, that is, the bottom electrode, the piezoelectric layer and the top electrode are flat, which maximally eliminates the film defects introduced by the bending of the electrode layer and the piezoelectric film, thereby ensuring the integrity and reliability of the boundary conditions of the vibration structure. At the same time, the support layer F200 completely wraps the end surface of the piezoelectric layer P100 and its electrodes T100 and B100 below the support layer: because the stress at the root of the diaphragm, that is, the end surface of the piezoelectric layer P100 and its electrodes T100 and B100, is the largest when the diaphragm vibrates to produce sound, and the electrical failure and mechanical failure of the piezoelectric layer and the electrode layer often occur at the end surface, the support layer F200 completely surrounds and covers to provide greater mechanical support and electrical isolation, and the negative effects of stress concentration and end surface effects can be greatly reduced.

[0134] The manufacturing method of the double-layer diaphragm ultrasonic transducer of the present application comprises the following steps:

[0135] Step one, forming a recessed cavity in the substrate, and filling a sacrificial layer in the recessed cavity, the sacrificial layer being flush with the upper surface of the substrate;

[0136] Step two, sequentially depositing a top electrode, a piezoelectric layer and a bottom electrode of the first diaphragm from bottom to top on the surface of the substrate by a deposition process to form a first sandwich structure;

[0137] Step three, covering a support layer on the upper part of the first sandwich structure of the first diaphragm and the substrate by a deposition process;

[0138] Step four, depositing a second diaphragm on the surface of the support layer, the second diaphragm comprising a bottom electrode, a piezoelectric layer and a top electrode deposited in sequence.

[0139] The material of the piezoelectric layer is PZT, and the material of the support layer is silicon or silicon nitride.

[0140] The manufacturing method of the ultrasonic transducer with the double-layer diaphragm comprises the following steps:

[0141] Step 100, forming a cavity SP100 in a substrate S100 by a mask patterning and deep etching process, as shown in Figure 12 .

[0142] Step 101, filling a sacrificial layer F100 in the cavity SP100 by a deposition process, and making the sacrificial layer F100 substantially flush with the upper surface of the substrate S100 by a planarization process, as shown in Figure 13 .

[0143] Step 102, sequentially depositing a first diaphragm on the surface of the substrate S100, the first diaphragm being a first sandwich structure comprising a bottom electrode B100, a piezoelectric layer P100 and a top electrode T100, and the bottom electrode B100 and the top electrode T100 respectively using a respective metal layer.

[0144] The metal layer where the bottom electrode B100 is located is actually composed of multiple layers of materials, from bottom to top, the materials are zirconium oxide, platinum, SRO or titanium, platinum, a buffer layer in sequence, wherein the zirconium oxide or titanium acts as a seed layer.

[0145] The material of the piezoelectric layer P100 is lead zirconate titanate (PZT) or doped lead zirconate titanate.

[0146] The material of the metal layer where the top electrode T100 is located can be selected but is not limited to molybdenum, platinum, magnesium, aluminum, ruthenium, titanium, iridium, osmium, silver, gold, copper, tungsten, etc., and alloys or composite layers of the metals, as shown in Figure 14 .

[0147] Step 103, by means of a patterning process, the metal layer where the top electrode T100 of the first diaphragm is located is processed into the top electrode T100, which is circular in plan view. The top electrode T100 also has an extension on its left side, which extends across the left side edge of the cavity SP100 and covers part of the surface of the piezoelectric film located on the left side of the edge of the cavity SP100, as shown in Figure 15 .

[0148] Step 104, by means of an etching process, the piezoelectric layer P100 is patterned, after which the edge of the piezoelectric layer P100 is inwardly recessed, circular in plan view, and the circular edge extends a small distance, which can be greater than 2 microns and less than 10 microns, outside the edge of the cavity SP100. The piezoelectric layer P100 also has an extension on its left side, which is covered under the extension of the top electrode T100, and the left side edge of the piezoelectric layer P100 extension and the left side edge of the top electrode T100 extension are substantially aligned, and the left side edge of the left side extension of the top electrode T100 is recessed to the right side relative to the left edge of the piezoelectric layer P100 by a certain amount, which can be greater than 10 microns and less than 30 microns, as shown in Figure 16 .

[0149] Step 105, by means of an etching process, the metal layer where the bottom electrode B100 is located is further patterned to form a bottom electrode B100 that is circular in plan view, and the edge of the bottom electrode B100 is substantially aligned with the edge of the piezoelectric layer P100, and the bottom electrode B100 is substantially concentric with the circular top electrode T100 and the circular piezoelectric layer P100. The area of the circular top electrode T100 is about 40%-60% of the area of the circular bottom electrode B100, as shown in Figure 17 .

[0150] Step 106, a support layer F200 is deposited on the upper part of the first sandwich structure of the first diaphragm and the substrate S100 by deposition, and the support layer F200 is planarized by a planarization process, as shown in Figure 18 .

[0151] Step 107, a second diaphragm is deposited on the surface of the support layer F200, which includes a metal layer where the bottom electrode B200 is located and a piezoelectric layer P200 deposited in sequence. The metal layer is actually composed of multiple layers of material, from bottom to top, the materials are zirconium oxide, platinum, SRO or titanium, platinum, a buffer layer, in which zirconium oxide or titanium serves as a seed layer. The piezoelectric layer P200 is made of lead zirconate titanate (PZT) or doped lead zirconate titanate, as shown in Figure 19 .

[0152] Step 108, the piezoelectric layer P200 is patterned by etching process, after patterning, the edge of the piezoelectric layer P200 is inwardly indented, in the top view, it is a circle, and the circular edge crosses a small distance outside the edge of the cavity SP100, which can be greater than 2 microns and less than 10 microns. The metal layer where the bottom electrode B200 is located is also patterned by etching process, forming a circular bottom electrode B200, wherein the edge of the bottom electrode B200 is substantially aligned with the edge of the piezoelectric layer P200, or slightly larger than the edge of the piezoelectric layer P200, which can be greater than 0.5 microns and less than 5 microns. In addition, the bottom electrode B200 also has an extension on the left side, and the left side edge of the extension is indented to the right side relative to the left side edge of the extension of the top electrode T100, as shown in Figure 20 .

[0153] Step 109, by deposition and patterning process, the right end surface of the piezoelectric layer P200, a small amount of the upper surface and sidewall of the bottom electrode B200 exposed under the right end of the piezoelectric layer P200, and part of the surface of the support layer F200 located to the right of the bottom electrode B200 are covered with an isolation layer L200, as shown in Figure 21 .

[0154] Step 110, by deposition and patterning process, the top electrode T200 of the second sandwich structure of the second diaphragm is made, which is circular in the top view, and is substantially concentric with the circular piezoelectric layer P200 and the circular bottom electrode B200 below it, and the area of the top electrode T200 is about 40%-60% of the bottom electrode B200; the top electrode T200 also has an extension on the right side, part of which covers the upper surface and sidewall of the isolation layer L100, and further extends to the right and covers part of the surface of the support layer F200 located to the right of the isolation layer L200. The material of the extremely extended portion of the isolation layer T200 can be selected from but not limited to molybdenum, platinum, magnesium, aluminum, ruthenium, titanium, iridium, osmium, silver, gold, copper, tungsten, etc., and alloys or composite layers of the metals, as shown in Figure 22 .

[0155] Step 111, by patterning and etching process, through holes C100 and C110 are made in the support layer F200 located above the extended ends of the top electrode T100 and the bottom electrode B100, as shown in Figure 23 .

[0156] Step 112, by deposition and patterning process, metal layers M100 and M130 are made on the surface of the extended ends of the bottom electrode B200 and the top electrode T200 respectively; metal layers M110 and M120 are formed on the bottom, sidewall and part of the support layer surface around the through holes C100 and C110, as shown in Figure 24 .

[0157] Step 113, the sacrificial layer F100 is removed by a releasing process (e.g. using gaseous or liquid etching environment) to form a cavity SP100 in the substrate S100. It is worth noting that the isolation layer L200 can be made of a material that can be dissolved by the above-mentioned etching environment, so that the isolation layer L200 can be removed together by the releasing process, and a gap is formed in the position originally filled with the isolation layer L200 under the extended portion of the top electrode T200, as shown in Figure 25

[0158] The present application also includes an electronic device comprising the technical features of any of the above embodiments of the dual-layer diaphragm ultrasonic transducer (PMUT), as shown in Figure 26

[0159] The processor 1002, the communications interface 1004, and the memory 1006 communicate with each other through the communications bus 1008.

[0160] The communications interface 1004 is configured to communicate with network elements of other devices, such as clients or other servers.

[0161] The processor 1002 is configured to execute the program 1010. Specifically, the program 1010 can include program codes including computer operation instructions.

[0162] The processor 1002 can be a central processing unit (CPU), or an application specific integrated circuit (ASIC), or one or more integrated circuits configured to implement embodiments of the present application. The one or more processors included in the terminal can be processors of the same type, such as one or more CPUs; or processors of different types, such as one or more CPUs and one or more ASICs.

[0163] The memory 1006 is configured to store the program 1010. The memory 1006 can include a high-speed RAM memory, and can also include a non-volatile memory, such as at least one disk memory.

[0164] The dual-layer diaphragm ultrasonic transducer (PMUT) is also a preferred embodiment of any dual-layer diaphragm ultrasonic transducer in the embodiments of the present application.

[0165] ​​The above is the description of the preferred embodiments of the present application, which can help the skilled in the art to more fully understand the technical solutions of the present application. However, these embodiments are only illustrative, and the specific implementation of the present application should not be limited to the description of these embodiments. For those skilled in the art to which the present application belongs, without departing from the concept of the present application, a number of simple deductions and transformations can be made, which should be considered as falling within the protection scope of the present application.

Claims

1. An ultrasonic transducer of the double-layer diaphragm type comprising a substrate with a recessed cavity, characterized in that, The support layer is arranged in the opening direction of the cavity, a first diaphragm is arranged below the support layer, and the first diaphragm is a first sandwich structure; a second diaphragm is arranged above the support layer, and the second diaphragm is a second sandwich structure; the first sandwich structure and the second sandwich structure each include a bottom electrode, a piezoelectric layer, and a top electrode, and the material of the piezoelectric layer is PZT.

2. The dual-layer diaphragm ultrasonic transducer of claim 1, wherein, The material of the support layer is silicon or silicon nitride.

3. The dual-layer diaphragm ultrasonic transducer of claim 1, wherein, The thicknesses of the corresponding bottom electrodes of the first sandwich structure and the second sandwich structure are the same, the thicknesses of the corresponding piezoelectric layers of the first sandwich structure and the second sandwich structure are the same, and the thicknesses of the corresponding top electrodes of the first sandwich structure and the second sandwich structure are the same.

4. The dual-layer diaphragm ultrasonic transducer of claim 1, wherein, In the second sandwich structure, a circular bottom electrode, a circular piezoelectric layer, and a circular top electrode are sequentially arranged from bottom to top starting from the support layer. In the first sandwich structure, a circular bottom electrode, a circular piezoelectric layer, and a circular top electrode are sequentially arranged from top to bottom starting from the support layer.

5. The dual-layer diaphragm ultrasonic transducer of claim 1, wherein, The bottom electrode has a composite layer structure, which sequentially includes zirconium oxide, platinum, SRO or titanium, platinum, and a buffer layer from bottom to top, wherein the zirconium oxide or titanium serves as a seed layer.

6. The dual-layer diaphragm ultrasonic transducer of claim 1, wherein, The top electrode is a same-layer process material, and the same-layer process material includes metal materials such as molybdenum, platinum, magnesium, aluminum, ruthenium, titanium, iridium, osmium, silver, gold, copper, tungsten, and alloys or composite layers of the metal materials.

7. The dual-layer diaphragm ultrasonic transducer of claim 1, wherein, An isolation layer is arranged on the upper surface and the edge of the piezoelectric layer of the second sandwich structure.

8. The dual-layer diaphragm ultrasonic transducer of claim 7, wherein, The isolation layer is a local area on the upper surface and the edge of the piezoelectric layer, or a ring-shaped area around the center of the second sandwich structure.

9. The dual-layer diaphragm ultrasonic transducer of claim 7, wherein, The isolation layer is a continuous step structure, including steps from high to low, a first layer of steps covering the lower edge of the piezoelectric layer, a second layer of steps covering the edge of the bottom electrode, and a third layer of steps covering the edge of the connection between the support layer and the bottom electrode.

10. The dual-layer diaphragm ultrasonic transducer of claim 9, wherein, The material of the isolation layer includes air, vacuum, or a dielectric material, and the dielectric material includes silicon oxide and silicon nitride.

11. The dual-layer diaphragm ultrasonic transducer of claim 1, wherein, The cavity has a plurality of channels extending in the opening direction of the cavity, and the support layer has through holes matched with the channels, and the through holes are in communication with the channels.

12. The dual-layer diaphragm ultrasonic transducer of claim 1, wherein, The upper surface of the support layer is flat, and the support layer completely wraps the end surfaces of the piezoelectric layer, the top electrode, and the bottom electrode below the support layer.

13. The dual-layer diaphragm ultrasonic transducer of claim 2, wherein, An FOM value representing the acoustic performance of the piezoelectric micro-electro-mechanical system ultrasonic transducer is provided, and the FOM value is calculated according to the following formula: Where, cp - specific heat capacity of air; P0 - atmospheric pressure; S - diaphragm area; E P - Young's modulus of piezoelectric material; d 31 - piezoelectric coefficient of piezoelectric material; U - driving voltage; V 711 - simulated ear volume; p P - density of piezoelectric material; p n - density of support layer; t p - total thickness of two piezoelectric layers; t n - thickness of support layer.

14. The dual-layer diaphragm ultrasonic transducer of claim 13, wherein, The FOM value is logarithmized to represent the sound pressure level under a certain resonant frequency: log(FOM) = 20*log 10 (P*f).

15. The dual-layer diaphragm ultrasonic transducer of claim 14, wherein, The logarithm log(FOM) of the FOM value is greater than 105.

16. The dual-layer diaphragm ultrasonic transducer of claim 15, wherein, The thickness of the piezoelectric layer is less than 0.8 microns.

17. The dual-layer diaphragm ultrasonic transducer of claim 14, wherein, The logarithm log(FOM) of the FOM value is greater than 110.

18. The dual-layer diaphragm ultrasonic transducer of claim 17, wherein, The thickness of the piezoelectric layer of the first diaphragm or the second diaphragm is less than 0.5 microns.

19. The double-layer diaphragm ultrasonic transducer according to claim 14, characterized in that: The logarithm log(FOM) of the FOM value is greater than 112.

20. The dual-layer diaphragm ultrasonic transducer of claim 19, wherein, The thickness of the piezoelectric layer of the first diaphragm or the second diaphragm is less than 0.3 microns.

21. The dual-layer diaphragm ultrasonic transducer of claim 1, wherein, The ratio of the thickness of the support layer to the total thickness of the two piezoelectric layers is 50%-120%.

22. The dual-layer diaphragm ultrasonic transducer of claim 1, wherein, The ratio of the thickness of the support layer to the total thickness of the two piezoelectric layers is 60%-100%.

23. The dual-layer diaphragm ultrasonic transducer of claim 1, wherein, The piezoelectric layer of the first or second diaphragm has a thickness greater than 0.3 microns and less than 0.8 microns, and the support layer has a thickness greater than 0.2 microns and less than 0.6 microns.

24. The dual-layer diaphragm ultrasonic transducer of claim 1, wherein, The piezoelectric layer of the first or second diaphragm has a thickness less than 0.3 microns, and the support layer has a thickness greater than 0.05 microns and less than 0.3 microns.

25. A method for manufacturing a dual-diaphragm ultrasonic transducer, comprising the following steps: Step 1: forming a cavity in a substrate, and filling a sacrificial layer in the cavity, the sacrificial layer being flush with the upper surface of the substrate; Step 2: sequentially depositing, from bottom to top, a top electrode, a piezoelectric layer, and a bottom electrode of a first diaphragm on the surface of the substrate to form a first sandwich structure; Step 3: covering the upper part of the first sandwich structure of the first diaphragm and the substrate with a support layer by a deposition process; Step 4: depositing a second diaphragm on the surface of the support layer, the second diaphragm comprising a bottom electrode, a piezoelectric layer, and a top electrode sequentially deposited.

26. The method for manufacturing a dual-diaphragm ultrasonic transducer according to claim 25, wherein: the step 2 further comprises the following steps: patterning the metal layers of the top electrode, the piezoelectric layer, and the bottom electrode of the first diaphragm into a circular shape, the circular top electrode, the circular piezoelectric layer, and the circular bottom electrode having a common center.

27. The method of manufacturing a dual-layer diaphragm ultrasonic transducer of claim 25, wherein, the step 3 further comprises the following steps: making the support layer flat by a planarization process.

28. The method of manufacturing a dual-layer diaphragm ultrasonic transducer of claim 25, wherein, the step 4 further comprises the following steps: patterning the metal layers of the bottom electrode, the piezoelectric layer, and the top electrode of the second diaphragm into a circular shape by a patterning process, the circular top electrode, the circular piezoelectric layer, and the circular bottom electrode having a common center.

29. The method of manufacturing a dual-layer diaphragm ultrasonic transducer of claim 25, wherein, the step 4 further comprises the following steps: covering the right end part of the surface of the piezoelectric layer of the second diaphragm, a small amount of the upper surface and the sidewall of the bottom electrode exposed below the right end of the piezoelectric layer, and part of the surface of the support layer on the right side of the bottom electrode with an isolation layer by a deposition and patterning process.

30. The method of manufacturing a dual-layer diaphragm ultrasonic transducer of claim 29, wherein, the step 4 further comprises the following steps: the isolation layer is made of a material that can be dissolved in an etching environment, and the isolation layer is removed by a releasing process to form a gap in the position where the lower part of the extension of the top electrode of the second diaphragm was originally filled with the isolation layer.

31. The method of manufacturing a dual-layer diaphragm ultrasonic transducer of claim 25, wherein, the step 4 further comprises the following steps: removing the sacrificial layer by a releasing process using a gaseous or liquid etching environment to form a cavity in the substrate.

32. An electronic device, comprising: a processor, a memory, a communication interface, and a communication bus, the processor, the memory, and the communication interface completing communication with each other through the communication bus, and the processor being connected to the dual-diaphragm ultrasonic transducer of any one of claims 1-24.

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