Micromechanical piezoelectric ultrasonic transducer

Abstract

The invention relates to the technical field of microelectronic devices, in particular to a micromechanical piezoelectric ultrasonic transducer which comprises a substrate, a composite insulating layer, a bottom electrode, a piezoelectric layer and a top electrode. The composite insulating layer comprises a stress compensation combination layer; the stress compensation combined layer comprises a first stress compensation layer and a second stress compensation layer which are deposited in a laminated manner; the thermal expansion coefficient of the first stress compensation layer is lower than that of the substrate, and the thermal expansion coefficient of the second stress compensation layer is higher than that of the substrate. Through the stress compensation of the composite insulating layer, the stress influence can be effectively reduced, the warping of the film layer is avoided, and the reliability and consistency of the device are improved.

Description

Technical Field

[0001] The present application relates to the technical field of microelectronic devices, and in particular to a micromechanical piezoelectric ultrasonic transducer. Background Art

[0002] In the field of micromachined piezoelectric ultrasonic transducers (PMUTs), traditional devices generally use a composite layered structure design of a top electrode, a piezoelectric layer, and a bottom electrode to achieve the conversion of electrical-mechanical-acoustic energy. The substrate is made of silicon, glass, or polymer materials, and is usually a few microns thick, serving as the mechanical support base of the device. Its stiffness directly affects the resonant frequency of the transducer. For example, a silicon substrate with a high elastic modulus can improve structural stability but limit the vibration amplitude. The piezoelectric layer is usually a thin film of aluminum nitride or lead zirconate titanate with a thickness of 0.5-5μm. Under the action of an alternating voltage, an inverse piezoelectric effect is generated, inducing bending vibration of the structure.

[0003] Due to the difference in thermal expansion coefficients between the substrate and piezoelectric layers, residual stress accumulates during high-temperature processes such as annealing and deposition. Thicker piezoelectric layers further increase this residual stress, leading to severe film warping, which in turn can cause a shift in the device's resonant frequency and even structural delamination, compromising device reliability and consistency. Summary of the Invention

[0004] The purpose of this application is to provide a micromechanical piezoelectric ultrasonic transducer, which effectively reduces the stress effect, avoids film warping, and improves the reliability and consistency of the device through stress compensation of the composite insulating layer.

[0005] The embodiment of the present application is implemented as follows:

[0006] An embodiment of the present application provides a micromechanical piezoelectric ultrasonic transducer, comprising a substrate and a composite insulating layer, a bottom electrode, a piezoelectric layer, and a top electrode sequentially stacked on the substrate; the composite insulating layer comprises a stress-compensating composite layer; the stress-compensating composite layer comprises a first stress-compensating layer and a second stress-compensating layer deposited in a stacked manner; the thermal expansion coefficient of the first stress-compensating layer is lower than the thermal expansion coefficient of the substrate, and the thermal expansion coefficient of the second stress-compensating layer is higher than the thermal expansion coefficient of the substrate.

[0007] As an optional implementation manner, the composite insulating layer includes a plurality of groups of the stress-compensating combination layers; and the first stress-compensating layers and the second stress-compensating layers are alternately stacked between two adjacent groups of the stress-compensating combination layers.

[0008] As an optional implementation, the composite insulating layer further includes an interface insulating layer deposited on the substrate; and at least one group of the stress-compensating combination layers is disposed on the interface insulating layer.

[0009] As an optional embodiment, the composite insulating layer further includes an acoustic matching layer deposited on the stress-compensating composite layer.

[0010] As an optional embodiment, the acoustic matching layer includes an aluminum nitride layer and a porous silicon oxide layer sequentially stacked on the stress compensation composite layer; the densities of the substrate, the aluminum nitride layer and the porous silicon oxide layer gradually decrease.

[0011] As an optional embodiment, the bottom electrode, piezoelectric layer and top electrode form a diaphragm; the surface of the diaphragm facing away from the substrate is divided into a middle area and an edge area circumferentially surrounding the middle area; a thickness reinforcement structure is provided in the edge area to increase the thickness of the diaphragm edge.

[0012] As an optional embodiment, the thickness reinforcement structure includes an annular structure circumferentially surrounding the central area; or, the thickness reinforcement structure includes a plurality of strip-shaped structures arranged at intervals and extending circumferentially.

[0013] As an optional implementation manner, the projected area of ​​the edge region on the substrate is 10-30% of the projected area of ​​the diaphragm on the substrate.

[0014] As an optional embodiment, the piezoelectric layer includes a scandium-doped piezoelectric layer; the scandium doping concentration of the scandium-doped piezoelectric layer increases linearly from the side close to the top electrode to the side close to the bottom electrode; or, the scandium doping concentration of the scandium-doped piezoelectric layer decreases linearly from the side close to the top electrode to the side close to the bottom electrode; or, the scandium doping concentration of the scandium-doped piezoelectric layer increases linearly from the two side surfaces close to the top electrode and the bottom electrode to the middle of the scandium-doped piezoelectric layer.

[0015] As an optional implementation, there are at least two piezoelectric layers; an intermediate electrode layer is provided between adjacent piezoelectric layers; and a piezoelectric buffer layer is provided in each piezoelectric layer.

[0016] The beneficial effects of the embodiments of the present application include:

[0017] The present embodiment can reduce residual stress accumulation. By precisely controlling the thickness ratio of the first and second stress-compensating layers, the tensile and compressive stresses caused by differences in thermal expansion coefficients can be effectively balanced, thereby reducing the net residual stress in the entire structure. This helps prevent film warping and ensures the flatness and stability of the device structure.

[0018] The embodiments of the present application can improve the consistency of the resonant frequency, which reduces the structural deformation caused by residual stress. In particular, for the piezoelectric layer, this means a more stable vibration mode and a more consistent resonant frequency. This configuration can effectively improve the control accuracy of the piezoelectric ultrasonic transducer.

[0019] The embodiments of the present application can enhance device reliability and consistency by alleviating stress concentration, reducing the risk of stress-induced structural delamination, and improving the overall mechanical strength and durability of the device. Furthermore, this also means more consistent product quality can be achieved during the manufacturing process because the stress impact on each unit is minimized.

[0020] In addition, the embodiments of the present application also optimize the electrical-mechanical-acoustic conversion efficiency. Through effective stress management, it not only helps to maintain the integrity of the device structure, but also indirectly promotes the efficient conversion of the piezoelectric effect. That is, under the action of alternating voltage, the piezoelectric layer can more effectively produce the inverse piezoelectric effect, induce the expected bending vibration, and thus improve the overall energy conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 This is one of the structural schematic diagrams of the micromachined piezoelectric ultrasonic transducer according to an embodiment of the present application;

[0023] Figure 2 This is a schematic structural diagram of the composite insulating layer of the micromachined piezoelectric ultrasonic transducer according to an embodiment of the present application;

[0024] Figure 3 This is the second structural diagram of the micromechanical piezoelectric ultrasonic transducer according to an embodiment of the present application.

[0025] Icon: 100-substrate; 101-composite insulating layer; 102-bottom electrode; 103-piezoelectric layer; 104-top electrode; 105-stress compensation combination layer; 106-first stress compensation layer; 107-second stress compensation layer; 108-interface insulating layer; 109-acoustic matching layer; 110-aluminum nitride layer; 111-porous silicon oxide layer; 112-middle region; 113-edge region; 114-thickness reinforcement structure. DETAILED DESCRIPTION

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0027] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without creative work are within the scope of protection of the present application.

[0028] It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings. In addition, the terms "first," "second," "third," etc. are used only to distinguish the descriptions and are not to be understood as indicating or implying relative importance.

[0029] It should also be noted that, in the description of this application, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0030] In the field of micromachined piezoelectric ultrasonic transducers (PMUTs), traditional devices generally adopt a composite layered structure design of a top electrode 104, a piezoelectric layer 103, and a bottom electrode 102 to achieve the conversion of electrical-mechanical-acoustic energy. The substrate 100 is made of silicon, glass, or polymer materials, and is usually a few microns thick, serving as the mechanical support base of the device. Its stiffness directly affects the resonant frequency of the transducer. For example, a silicon substrate 100 with a high elastic modulus can improve structural stability, but it will limit the vibration amplitude. The piezoelectric layer 103 is usually an aluminum nitride or lead zirconate titanate film with a thickness of 0.5-5μm. Under the action of alternating voltage, an inverse piezoelectric effect is generated, inducing structural bending vibration.

[0031] Due to the difference in thermal expansion coefficients between substrate 100 and piezoelectric layer 103, residual stress accumulates during high-temperature processes such as annealing and deposition. When the piezoelectric layer 103 is thicker, the residual stress increases further, leading to severe film warping, which in turn can cause a shift in the device's resonant frequency and even structural delamination, resulting in poor device reliability and consistency.

[0032] To solve the above technical problems, an embodiment of the present application provides a micromechanical piezoelectric ultrasonic transducer.

[0033] Reference Figure 1 、 Figure 2As shown, an embodiment of the present application provides a micromechanical piezoelectric ultrasonic transducer, including a substrate 100 and a composite insulating layer 101, a bottom electrode 102, a piezoelectric layer 103 and a top electrode 104 stacked in sequence on the substrate 100; the composite insulating layer 101 includes a stress compensation combination layer 105; the stress compensation combination layer 105 includes a first stress compensation layer 106 and a second stress compensation layer 107 deposited in a stacked manner; the thermal expansion coefficient of the first stress compensation layer 106 is lower than the thermal expansion coefficient of the substrate 100, and when the temperature is cooled, the first stress compensation layer 106 can generate a tensile stress perpendicular to the substrate 100; the thermal expansion coefficient of the second stress compensation layer 107 is higher than the thermal expansion coefficient of the substrate 100, and when the temperature is cooled, the second stress compensation layer 107 can generate a compressive stress opposite to the tensile stress.

[0034] It should be noted that the first stress compensation layer 106 may be made of silicon dioxide, and the second stress compensation layer 107 may be made of aluminum nitride. The stress compensation composite layer 105 acts as a stress buffer layer to isolate direct stress coupling between the substrate 100 and the piezoelectric layer 103 .

[0035] The present embodiment can reduce residual stress accumulation. By precisely controlling the thickness ratio of the first stress-compensating layer 106 and the second stress-compensating layer 107, the tensile and compressive stresses caused by the difference in thermal expansion coefficients can be effectively balanced, thereby reducing the net residual stress in the entire structure. This helps prevent film warping and ensures the flatness and stability of the device structure.

[0036] It should be noted that the thickness ratio of the first stress compensation layer 106 and the second stress compensation layer 107 can be set by those skilled in the art as needed, and is not particularly limited thereto.

[0037] The embodiments of the present application can improve the consistency of the resonant frequency, which reduces the structural deformation caused by residual stress, especially for the piezoelectric layer 103. This means a more stable vibration mode and a more consistent resonant frequency. The above configuration can effectively improve the control accuracy of the piezoelectric ultrasonic transducer.

[0038] The embodiments of the present application can enhance device reliability and consistency by alleviating stress concentration, reducing the risk of stress-induced structural delamination, and improving the overall mechanical strength and durability of the device. Furthermore, this also means more consistent product quality can be achieved during the manufacturing process because the stress impact on each unit is minimized.

[0039] In addition, the embodiment of the present application also optimizes the electrical-mechanical-acoustic conversion efficiency. Through effective stress management, it not only helps to maintain the integrity of the device structure, but also indirectly promotes the efficient conversion of the piezoelectric effect. That is, under the action of alternating voltage, the piezoelectric layer 103 can more effectively generate the inverse piezoelectric effect, induce the expected bending vibration, and thus improve the overall energy conversion efficiency.

[0040] Reference Figure 2 As shown, as an optional embodiment, the composite insulating layer 101 includes multiple groups of stress-compensating combination layers 105 ; first stress-compensating layers 106 and second stress-compensating layers 107 are alternately stacked between two adjacent groups of stress-compensating combination layers 105 .

[0041] Furthermore, the embodiment of the present application provides multiple groups of stress compensation combination layers 105 , each group consisting of a first stress compensation layer 106 and a second stress compensation layer 107 , forming a multi-layer structure.

[0042] It's important to note that by increasing the number of stress-compensating layers and employing an alternating stacking approach, stress distribution can be more precisely controlled at the microscale. This helps to better offset internal stresses caused by differences in thermal expansion coefficients, thereby reducing the risk of deformation of the overall structure. The multilayered structure provides stronger mechanical support, allowing the entire device to remain stable even in the face of large temperature fluctuations or external pressure.

[0043] It should be noted that the alternating stacking of the first stress-compensating layer 106 and the second stress-compensating layer 107 can enhance the flexibility of the manufacturing process. This design allows for flexible adjustment of the thickness and number of layers according to specific material properties and application scenarios to meet different performance requirements.

[0044] In addition, the embodiments of the present application can improve the durability and reliability of the device by effectively alleviating the stress concentration phenomenon, reducing the probability of failure modes such as delamination and cracking caused by stress accumulation, and improving the overall durability and reliability of the device.

[0045] Reference Figure 2 As shown, as an optional embodiment, the composite insulating layer 101 further includes an interface insulating layer 108 deposited on the substrate 100 ; and at least one set of stress compensation combination layers 105 is disposed on the interface insulating layer 108 .

[0046] It should be noted that, in the embodiment of the present application, an interface insulating layer 108 is first deposited on the substrate 100 , and then at least one or more stress compensation combination layers 105 including a first stress compensation layer 106 and a second stress compensation layer 107 are arranged thereon.

[0047] The interface insulating layer 108 of the embodiment of the present application has the following effects:

[0048] The interface insulating layer 108 of the embodiment of the present application can effectively fill the microscopic defects or uneven areas on the surface of the substrate 100, providing a smoother and more uniform foundation for subsequent layers, which helps to improve the consistency and reliability of the entire structure.

[0049] The interfacial insulating layer 108 of the present embodiment acts as an electrical isolation layer, effectively blocking direct contact between the bottom electrode 102 and the substrate 100, thereby avoiding potential leakage paths. This not only reduces leakage current and improves energy efficiency, but also enhances the long-term stability of the device.

[0050] By filling and covering defects on the surface of substrate 100, the present embodiment makes the layered surface smoother. Therefore, interfacial insulating layer 108 reduces electric field concentration points, thereby increasing the breakdown field strength of the overall structure. This means that the device can operate at higher voltages without electrical breakdown, increasing the safe range of operation.

[0051] A smooth and defect-free bottom layer helps improve the deposition quality of upper layer materials (such as the stress-compensating composite layer 105, the bottom electrode 102, the piezoelectric layer 103, and the top electrode 104). High-quality deposition ensures good adhesion between layers, reduces the risk of delamination, and enhances the mechanical strength of the entire device.

[0052] Since the dielectric constant of the interface insulating layer 108 is controllable, the parasitic capacitance between the electrode and the piezoelectric layer 103 can be adjusted by selecting the appropriate material and thickness. Appropriate parasitic capacitance helps reduce signal loss and distortion, thereby improving the transmission efficiency and accuracy of high-frequency signals.

[0053] It can be seen that the composite insulating layer 101 of the embodiment of the present application not only serves as a stress adjustment layer, but also significantly reduces leakage current by blocking the leakage path between the bottom electrode 102 and the substrate 100. Its controllable dielectric constant can adjust the parasitic capacitance between the electrode and the piezoelectric layer 103 to improve the high-frequency signal transmission efficiency.

[0054] In summary, the composite insulating layer 101, including the interfacial insulating layer 108, enables the embodiments of the present application to not only effectively manage internal device stress but also significantly improve electrical performance, particularly in terms of reducing leakage current, increasing breakdown field strength, and optimizing parasitic capacitance. These improvements are crucial for improving the operating efficiency, reliability, and high-frequency performance of PMUT devices, making them suitable for high-precision ultrasonic applications.

[0055] Reference Figure 2As shown, as an optional embodiment, the composite insulating layer 101 further includes an acoustic matching layer 109 deposited on the stress-compensating composite layer 105. The acoustic matching layer 109 includes an aluminum nitride layer 110 and a porous silicon oxide layer 111 stacked sequentially on the stress-compensating composite layer 105; the densities of the substrate 100, the aluminum nitride layer 110, and the porous silicon oxide layer 111 gradually decrease.

[0056] Furthermore, in the embodiment of the present application, an acoustic matching layer 109 is deposited on the stress compensation composite layer 105 . The acoustic matching layer 109 is composed of an aluminum nitride layer 110 and a porous silicon oxide layer 111 stacked in sequence.

[0057] It should be noted that the aluminum nitride layer 110 is a low-density aluminum nitride material. By adjusting the density gradient between the layers, the density is gradually reduced from the substrate 100 to the working medium. For example, the substrate 100 is a silicon substrate 100, and its density is 2.33 g / cm 3 Gradually change to 1.8 g / cm 3 , making the acoustic impedance transition smooth. Among them, the low-density aluminum nitride material has a density lower than the standard aluminum nitride of 3.26g / cm 3 , to cooperate with the subsequent porous silicon oxide layer 111 to form a density gradient.

[0058] It's important to explain that when sound waves pass from one medium to another with a significantly different acoustic impedance, reflection and transmission occur at the interface. The greater the reflection loss, the lower the energy transfer efficiency. Therefore, if the acoustic impedance difference between the two media is significant, most of the sound energy will be reflected back to the source, resulting in energy loss and signal attenuation.

[0059] The embodiment of the present application uses the above-mentioned design to gradually transition from the high-density solid substrate 100 to the low-density working medium, forming a continuous and smooth acoustic impedance change path. This acoustic gradient structure can significantly reduce interface reflections and improve the penetration efficiency of sound waves. Due to its lower density and sound velocity, the porous silicon oxide layer 111 has an acoustic impedance close to that of common media such as air. Therefore, when the sound wave reaches the porous silicon oxide layer 111, the amount of sound wave reflected back to the transducer is significantly reduced due to the reduced acoustic impedance difference, thereby improving the efficiency of sound energy transmission.

[0060] It should be noted that effective acoustic impedance matching not only reduces reflection loss but also improves overall energy conversion efficiency. Therefore, the embodiments of the present application can convert more electrical energy into acoustic energy and effectively transmit it, while also improving the efficiency of acoustic energy conversion into electrical energy, thereby enhancing the quality and strength of the signal received by the device.

[0061] Further explanation: In the embodiments of the present application, the acoustic matching layer 109 can enhance the sensitivity of the PMUT device by reducing reflection loss and improving energy transmission efficiency. This is particularly important for applications requiring high-precision detection, such as medical imaging and non-destructive testing.

[0062] Reference Figure 3 As shown, as an optional embodiment, the bottom electrode 102, the piezoelectric layer 103, and the top electrode 104 form a diaphragm. The surface of the diaphragm facing away from the substrate 100 is divided into a central region 112 and an edge region 113 circumferentially surrounding the central region 112. A thickness reinforcement structure 114 is provided in the edge region 113 to increase the thickness of the diaphragm edge. The thickness reinforcement structure 114 includes an annular structure circumferentially surrounding the central region 112; alternatively, the thickness reinforcement structure 114 includes a plurality of strip-shaped structures arranged at intervals and extending circumferentially.

[0063] It should be noted that existing technologies exhibit a conflict between frequency and sensitivity control, with the resonant frequency and sensitivity exhibiting a strong coupling relationship. This is primarily due to the fact that the physical properties of both are subject to the control of multiple variables, such as the thickness of the piezoelectric layer 103. Specifically, while increasing the thickness of the piezoelectric layer 103 can significantly enhance sensitivity by enhancing the mechanical strain amplification effect, it also increases the overall stiffness of the device, forcing a shift in the resonant frequency. Conversely, thinning the piezoelectric layer 103 to improve high-frequency response, the electromechanical conversion efficiency decreases sharply due to the reduction in the effective driving volume of the piezoelectric material. This inherent contradiction makes it difficult for traditional structures to meet the stringent sensitivity requirements of high-frequency applications. For example, medical ultrasound imaging requires both high-frequency resolution and high receiver sensitivity, while industrial non-destructive testing faces the dual challenges of high-frequency penetration and the ability to detect weak defect echoes. Furthermore, this strong coupling restricts the device's adaptability in multimodal and broadband scenarios, forcing system designers to compromise between performance parameters and severely limiting the potential of PMUTs in precision testing and high-resolution imaging.

[0064] It should be noted that the middle area 112 can be understood as the effective working area of ​​the diaphragm.

[0065] By adding a thickness reinforcement structure 114 to the diaphragm edge, the present embodiment enhances the rigidity of the entire diaphragm without significantly changing the mechanical properties of the central region 112. This means that the overall resonant frequency of the device can be adjusted by adjusting the thickness of the edge region 113 without affecting the sensitivity of the central region 112.

[0066] In this way, even if the thickness of the piezoelectric layer 103 is maintained or reduced to improve the sensitivity, the resonant frequency can be controlled by adjusting the rigidity of the edge region 113, thereby breaking the strong coupling relationship between frequency and sensitivity in traditional designs.

[0067] The embodiments of the present application can improve high-frequency response capability and sensitivity:

[0068] While ensuring a sufficiently high resonant frequency, the electromechanical conversion efficiency of the piezoelectric layer 103 can be maintained or even improved, because there is no need to significantly increase the thickness of the piezoelectric layer 103 to compensate for the performance degradation caused by lowering the resonant frequency.

[0069] For application scenarios such as medical ultrasound imaging and industrial non-destructive testing that require both high resolution and high sensitivity, the design of the embodiment of the present application can provide a more effective solution.

[0070] The embodiments of the present application can enhance multimodal adaptability and broadband operation capabilities:

[0071] By effectively separating frequency and sensitivity, the PMUT can operate efficiently across a wider frequency range, adapting to diverse application scenarios. This embodiment eliminates the need for system designers to compromise between performance parameters, allowing them to flexibly adjust the diaphragm design based on specific applications, thereby maximizing the potential of the PMUT.

[0072] In addition, the embodiments of the present application can improve long-term stability and reliability:

[0073] The increased thickness of the reinforcement structure 114 not only facilitates frequency tuning, but also improves the overall strength of the diaphragm, reduces the risk of fatigue damage due to long-term vibration, and extends the service life of the device.

[0074] As an optional implementation manner, the projected area of ​​the edge region 113 on the substrate 100 is 10-30% of the projected area of ​​the diaphragm on the substrate 100 .

[0075] The material of the thickness reinforcement structure 114 can be silicon dioxide, or metal materials such as aluminum and copper.

[0076] As an optional embodiment, the piezoelectric layer 103 includes a scandium-doped piezoelectric layer 103; the scandium doping concentration of the scandium-doped piezoelectric layer 103 linearly increases from the side close to the top electrode 104 to the side close to the bottom electrode 102; or, the scandium doping concentration of the scandium-doped piezoelectric layer 103 linearly decreases from the side close to the top electrode 104 to the side close to the bottom electrode 102; or, the scandium doping concentration of the scandium-doped piezoelectric layer 103 linearly increases from the two side surfaces close to the top electrode 104 and the bottom electrode 102 to the middle of the scandium-doped piezoelectric layer 103.

[0077] For example, the scandium doping concentration of the scandium-doped piezoelectric layer 103 increases linearly from 0 to 20% from the side close to the top electrode 104 to the side close to the bottom electrode 102. The piezoelectric layer 103 may be made of aluminum nitride.

[0078] By adjusting the scandium doping concentration, the present embodiment can form a piezoelectric coefficient gradient within the piezoelectric layer 103. This helps to more evenly distribute the electric field intensity at the interface, thereby improving the overall energy conversion efficiency and potentially enhancing the sensitivity and response speed of the device.

[0079] In the embodiments of the present application, scandium doping can adjust the thermal expansion coefficient of the piezoelectric material to be closer to that of the silicon substrate 100. This means that when the temperature changes, the difference in thermal expansion between the two is reduced, effectively suppressing cracking that may occur during thermal cycling and maintaining the high-temperature stability of the device.

[0080] In addition, the gradient of scandium doping concentration not only affects the thermal expansion coefficient, but also helps balance internal stress, reduces structural damage caused by thermal expansion mismatch, and further improves the reliability and service life of the device.

[0081] In addition, it should be noted that scandium doping can also adjust the dielectric constant of the piezoelectric layer 103, which is very important for reducing the parasitic capacitance between the electrode and the piezoelectric layer 103. Lower parasitic capacitance means less energy loss, especially under high-frequency operation, which helps improve signal transmission efficiency and overall device performance.

[0082] Combining the above advantages, especially by reducing parasitic capacitance and optimizing energy conversion efficiency, this design significantly improves the responsiveness of PMUT in high-frequency applications, making it suitable for scenarios requiring high precision and fast response, such as medical ultrasound imaging and industrial non-destructive testing.

[0083] As an optional implementation, there are at least two piezoelectric layers 103 ; an intermediate electrode layer is provided between adjacent piezoelectric layers 103 ; and a piezoelectric buffer layer is provided in each piezoelectric layer 103 .

[0084] The embodiments of the present application can reduce interface stress, improve stress distribution, and enhance the overall performance of the device through the piezoelectric buffer layer.

[0085] It should be noted that the presence of the intermediate electrode layer allows for independent control of each piezoelectric layer 103. This means that the operating state of each layer can be adjusted as needed, enabling more complex drive modes and higher electromechanical conversion efficiency. When all piezoelectric layers 103 work together, the overall output power and sensitivity can be enhanced by precisely controlling the phase and amplitude of each layer.

[0086] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A micro-machined piezoelectric ultrasonic transducer, characterized in that: The invention comprises a substrate (100) and a composite insulating layer (101), a bottom electrode (102), a piezoelectric layer (103) and a top electrode (104) sequentially stacked on the substrate (100); the composite insulating layer (101) comprises a stress compensation composite layer (105); the stress compensation composite layer (105) comprises a first stress compensation layer (106) and a second stress compensation layer (107) deposited in a stacked manner; the thermal expansion coefficient of the first stress compensation layer (106) is lower than the thermal expansion coefficient of the substrate (100), and the thermal expansion coefficient of the second stress compensation layer (107) is higher than the thermal expansion coefficient of the substrate (100).

2. The micromechanical piezoelectric ultrasonic transducer according to claim 1, characterized in that: The composite insulating layer (101) comprises a plurality of groups of stress compensation combination layers (105); the first stress compensation layers (106) and the second stress compensation layers (107) are alternately stacked between two adjacent groups of stress compensation combination layers (105).

3. The micromechanical piezoelectric ultrasonic transducer according to claim 1, characterized in that: The composite insulating layer (101) further comprises an interface insulating layer (108) deposited on the substrate (100); at least one group of stress compensation combination layers (105) is arranged on the interface insulating layer (108).

4. The micromechanical piezoelectric ultrasonic transducer according to claim 1, characterized in that: The composite insulating layer (101) further comprises an acoustic matching layer (109) deposited on the stress-compensating composite layer (105).

5. The micromechanical piezoelectric ultrasonic transducer according to claim 4, characterized in that: The acoustic matching layer (109) comprises an aluminum nitride layer (110) and a porous silicon oxide layer (111) sequentially stacked on the stress compensation composite layer (105); the densities of the substrate (100), the aluminum nitride layer (110) and the porous silicon oxide layer (111) gradually decrease.

6. The micromechanical piezoelectric ultrasonic transducer according to any one of claims 1 to 5, characterized in that: The bottom electrode (102), the piezoelectric layer (103) and the top electrode (104) form a diaphragm; the surface of the diaphragm facing away from the substrate (100) is divided into a middle area (112) and an edge area (113) circumferentially surrounding the middle area (112); the edge area (113) is provided with a thickness reinforcement structure (114) so ​​that the thickness of the edge of the diaphragm is increased.

7. The micromechanical piezoelectric ultrasonic transducer according to claim 6, characterized in that: The thickness reinforcement structure (114) includes an annular structural member circumferentially surrounding the middle region (112); or, the thickness reinforcement structure (114) includes a plurality of strip-shaped structural members arranged at intervals and extending circumferentially.

8. The micromechanical piezoelectric ultrasonic transducer according to claim 6, characterized in that: The projection area of ​​the edge region (113) on the substrate (100) is 10-30% of the projection area of ​​the diaphragm on the substrate (100).

9. The micromechanical piezoelectric ultrasonic transducer according to any one of claims 1 to 5, characterized in that: The piezoelectric layer (103) includes a scandium-doped piezoelectric layer (103); the scandium doping concentration of the scandium-doped piezoelectric layer (103) increases linearly from the side close to the top electrode (104) to the side close to the bottom electrode (102); or, the scandium doping concentration of the scandium-doped piezoelectric layer (103) decreases linearly from the side close to the top electrode (104) to the side close to the bottom electrode (102); or, the scandium doping concentration of the scandium-doped piezoelectric layer (103) increases linearly from the two side surfaces close to the top electrode (104) and the bottom electrode (102) to the middle of the scandium-doped piezoelectric layer (103).

10. The micromachined piezoelectric ultrasonic transducer according to any one of claims 1 to 5, characterized in that: There are at least two piezoelectric layers (103); an intermediate electrode layer is provided between adjacent piezoelectric layers (103); and a piezoelectric buffer layer is provided in each piezoelectric layer (103).

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