A piezoelectric ultrasonic transducer and a method of manufacturing the same

Abstract

The present application relates to the technical field of semiconductor process, and especially relates to a piezoelectric ultrasonic transducer and a preparation method thereof, which comprises a substrate, a piezoelectric layer formed on the front surface of the substrate, a back cavity formed by penetrating the substrate, a structure layer formed on the surface of the piezoelectric layer, the thickness of the structure layer being greater than the thickness of the piezoelectric film in the piezoelectric layer, and an anti-leakage sound layer arranged on the surface of the structure layer; a through groove is formed along the edge of the diaphragm, so that the diaphragm forms an external structure outside the diaphragm area and an internal structure in the diaphragm area, and the external structure and the internal structure are connected through a cantilever beam formed in the through groove. The preparation method comprises the following steps: preparing the substrate; growing the piezoelectric layer; etching the piezoelectric layer; growing the structure layer; etching the structure layer; and etching the substrate to form the back cavity. The present application uses silicon oxide as the structure layer, which can effectively reduce the resonant frequency; the cantilever beam can convert the PMUT from the Gaussian mode to the piston-like mode to improve the sensitivity, and can also provide good support.

Description

Technical Field

[0001] This invention relates to the field of semiconductor processing technology for piezoelectric ultrasonic transducers, and particularly to a piezoelectric ultrasonic transducer and its preparation method. Background Technology

[0002] An ultrasonic sensor is a sensor that converts ultrasonic signals into other energy signals (usually electrical signals). Ultrasonic waves are mechanical waves with vibration frequencies higher than 20 kHz. They are characterized by high frequency, short wavelength, minimal diffraction, and, most importantly, good directionality, enabling them to propagate directionally as rays. Ultrasonic waves have a strong penetrating ability in liquids and solids, especially in solids that are opaque to sunlight. When ultrasonic waves encounter impurities or interfaces, they produce significant reflections, forming reflected echoes. When they encounter moving objects, they produce the Doppler effect. Ultrasonic sensors are widely used in industry, defense, and biomedicine.

[0003] In existing technologies, low-frequency ultrasonic sensors are required for long-distance measurement, monitoring, and information transmission using ultrasound. Therefore, low-frequency MEMS chip devices have a large market. However, traditional piezoelectric MEMS chips are composed of stacked SOI substrates with back cavities and piezoelectric layers. The top silicon in the SOI substrate acts as a structural layer and serves as the neutral plane. Silicon has a high Young's modulus and high process stress, which leads to a high resonant frequency, which is not conducive to the production design and manufacturing of low-frequency devices. On this basis, the transducer diaphragm does not receive good support during vibration. The traditional Gaussian mode has a large displacement in the middle and a small displacement at the edges, resulting in low sound pressure.

[0004] Patent document with application number 202310177503.5 discloses a piezoelectric micromechanical ultrasonic transducer and its fabrication method. The piezoelectric micromechanical ultrasonic transducer includes: a substrate having a first surface and a second surface opposite to each other, and a cavity formed from the first surface to the interior of the substrate; a barrier layer including a first barrier layer on the first surface and a second barrier layer on the second surface; and a piezoelectric unit located on the side of the second barrier layer away from the substrate, the piezoelectric unit including a lower electrode, a piezoelectric layer and an upper electrode stacked sequentially; wherein the upper electrode is a patterned electrode structure, and the orthographic projection of the pattern of the upper electrode on the substrate is a dual-electrode circle, hexagon, octagon, circle, multi-diaphragm triangle or multi-diaphragm rectangle.

[0005] The proposed solution demonstrates that by patterning the upper electrode as described above, the detection sensitivity of the piezoelectric micromechanical ultrasonic transducer can be improved, meeting the application requirements for underwater target detection and imaging. However, the solution also has several drawbacks: using the top silicon in the SOI substrate as a structural layer to assume the function of the neutral plane presents challenges for the production design and manufacturing of low-frequency devices, and results in poor ultrasonic transducer sensitivity.

[0006] In summary, this application proposes a piezoelectric ultrasonic transducer and its fabrication method to solve the aforementioned problems. Summary of the Invention

[0007] To address the aforementioned problems, the present invention aims to propose a piezoelectric ultrasonic transducer and its fabrication method. By using a structural layer instead of the traditional top silicon, the resonant frequency can be effectively reduced. The cantilever beam structure can convert the piezoelectric ultrasonic transducer (PMUT) from a Gaussian mode to a piston-like mode to improve sensitivity. While providing good support, it enables the piezoelectric ultrasonic transducer to maintain good performance under vibration and impact.

[0008] The objective of this invention can be achieved through the following technical solution: a piezoelectric ultrasonic transducer, comprising a substrate having a front side and a back side, a piezoelectric layer formed on the front side of the substrate, a back cavity extending through the piezoelectric layer on the back side of the substrate, a structural layer formed on the surface of the piezoelectric layer, the piezoelectric layer and the structural layer within the longitudinal projection area of ​​the back cavity serving as a diaphragm, the thickness of the structural layer being greater than the thickness of the piezoelectric film in the piezoelectric layer, such that the neutral plane is located within the lateral projection area of ​​the structural layer;

[0009] Among them, the piezoelectric layer and structural layer within the longitudinal projection area of ​​the back cavity are diaphragms. A through groove is opened along the edge of the diaphragm to form an external structure outside the diaphragm area and an internal structure within the diaphragm area. The external structure and the internal structure are connected by a cantilever beam formed in the through groove.

[0010] The neutral plane is located in the structural layer, replacing the traditional top silicon, resulting in lower process stress and effectively reducing the resonant frequency, which is beneficial for the production design and manufacturing of low-frequency devices. The external and internal structures are connected by a cantilever beam formed within the through slot, which provides good support for the transducer diaphragm during vibration, improving the performance of the piezoelectric ultrasonic transducer.

[0011] As a further embodiment of the present invention, a soundproof layer for covering the through groove is formed on the surface of the structural layer.

[0012] By attaching a polymer film to the top of the piezoelectric ultrasonic transducer (PMUT), sound leakage can be effectively prevented.

[0013] As a further embodiment of the present invention, the cantilever beam is provided in a plurality of units, and the plurality of cantilever beams are arranged in a circular array inside the through groove.

[0014] As a further embodiment of the present invention, in the cross-section of the cantilever beam, the opposite sides of the cantilever beam are all arc-shaped or V-shaped.

[0015] As a further aspect of the present invention:

[0016] A cantilever beam has opposite sides that are either inwardly curved or outwardly curved.

[0017] A cantilever beam has either an inner V-shape or an outer V-shape on opposite sides.

[0018] The cantilever beam has arc-shaped and V-shaped surfaces on its two outer sides, which can better convert the piezoelectric ultrasonic transducer (PMUT) from Gaussian mode to piston-like mode to improve sensitivity. It also has good stability and rigidity, which can provide good support and enable the piezoelectric ultrasonic transducer to maintain good performance under vibration and impact.

[0019] As a further embodiment of the present invention, the material of the structural layer is silicon oxide.

[0020] As a further embodiment of the present invention, the structural layer is a two-layer structure or a three-layer structure in which silicon nitride and silicon oxide are alternately stacked.

[0021] By employing the aforementioned structural layer, the neutral plane is located within the lateral projection area of ​​the structural layer. Utilizing the low Young's modulus and low process stress of silicon oxide / silicon nitride, the resonant frequency can be effectively reduced, which is beneficial for the design and manufacturing of low-frequency devices.

[0022] A method for fabricating the above-mentioned piezoelectric ultrasonic transducer, the method comprising the following steps:

[0023] S1. Prepare a substrate with a front side and a back side. Grow a piezoelectric layer on the front side of the substrate.

[0024] S2. Etch the piezoelectric layer to pattern it;

[0025] S3. Grow a structural layer on the surface of the patterned piezoelectric layer;

[0026] S4. Etch the structural layer to pattern the structural layer;

[0027] S5. Etch through the substrate to form a back cavity;

[0028] The thickness of the structural layer is greater than the thickness of the piezoelectric film in the piezoelectric layer, so that the neutral surface is located within the lateral projected area of ​​the structural layer.

[0029] Among them, the piezoelectric layer and structural layer within the longitudinal projection range of the back cavity are diaphragms. The diaphragms are etched to form through grooves along the edges, thereby forming an external structure outside the diaphragm region and an internal structure within the diaphragm region. The external structure and the internal structure are connected by a cantilever beam formed by etching the diaphragm within the through grooves.

[0030] By using the above processing method, the neutral plane is moved up, the process stress is low, and the resonant frequency can be effectively reduced. At the same time, the cantilever beam structure allows the piezoelectric ultrasonic transducer (PMUT) to be converted from the Gaussian mode to a piston-like mode, improving the sensitivity. It also has good stability and rigidity, which can provide good support, enabling the piezoelectric ultrasonic transducer to maintain good performance under vibration and impact.

[0031] As a further embodiment of the present invention: after the structural layer in S4 is patterned, a sound leakage prevention layer is grown on the surface of the structural layer, and the sound leakage prevention layer is made of a polymer film.

[0032] As a further embodiment of the present invention: the back cavity is formed by etching through the substrate in step S5, including the following steps:

[0033] S5-1, the back side of the substrate is etched by DRIE dry etching, and the substrate retains 5-15% thickness after DRIE dry etching;

[0034] S5-2, the back side of the substrate is etched through using a wet process to completely penetrate the remaining 5-15% thickness of the substrate, forming a back cavity.

[0035] By combining the above-mentioned dry and wet processes, the yield rate can be improved.

[0036] The beneficial effects of this invention are:

[0037] 1. The piezoelectric ultrasonic transducer and its fabrication method of the present invention use silicon oxide / silicon nitride as the structural layer, and the neutral plane is raised to the structural layer to replace the traditional top silicon. Silicon oxide / silicon nitride has low Young's modulus and low process stress, which can effectively reduce the resonant frequency and is beneficial to the design and manufacturing of low frequency devices.

[0038] 2. The present invention creates a through groove along the edge of the diaphragm, forming an external structure outside the diaphragm region and an internal structure within the diaphragm region. The external and internal structures are connected by a cantilever beam formed in the through groove, which can provide good support for the transducer diaphragm during vibration and improve the performance of the piezoelectric ultrasonic transducer.

[0039] 3. The cantilever beam of the present invention has an arc-shaped surface and a V-shaped surface on its two outer sides, which can enable the cantilever beam to convert the piezoelectric ultrasonic transducer (PMUT) from the Gaussian mode to the piston-like mode to improve the sensitivity. It also has good stability and rigidity, which can provide good support and enable the piezoelectric ultrasonic transducer to maintain good performance under vibration and impact.

[0040] 4. In this invention, a sound leakage prevention layer is grown on the surface of the structural layer. The sound leakage prevention layer is made of polymer film. The polymer film can be used for a long time in a very wide temperature range and has excellent electrical insulation properties and outstanding mechanical strength. It can be perfectly matched with the piezoelectric ultrasonic transducer (PMUT). The polymer film is attached to the top of the PMUT and can effectively prevent sound leakage.

[0041] 5. The piezoelectric ultrasonic transducer fabrication method proposed in this invention, compared with the traditional fabrication process, first grows a piezoelectric layer and patterns it, then grows a structural layer on the surface of the piezoelectric layer, and then patterns the structural layer. The patterning steps of the piezoelectric layer and the structural layer are independent and do not interfere with each other. The piezoelectric layer does not need to generate unnecessary hollowing due to the patterning of the structural layer, thus ensuring the integrity of the piezoelectric layer to the greatest extent. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the structure of a piezoelectric ultrasonic transducer proposed in this embodiment;

[0043] Figure 2 for Figure 1 Exploded view of the structure;

[0044] Figure 3 for Figure 1 Front view;

[0045] Figure 4 for Figure 1 Top view;

[0046] Figure 5 for Figure 1 A bottom view;

[0047] Figure 6 for Figure 1 A schematic diagram of the structure of one embodiment;

[0048] Figures 7-11 This is a schematic diagram of the preparation method proposed in this embodiment.

[0049] In the attached diagram:

[0050] 1. Substrate;

[0051] 2. Piezoelectric layer; 21. Bottom electrode; 22. Piezoelectric thin film; 23. Top electrode;

[0052] 3. Structural layer; 31. First structural layer; 32. Second structural layer; 33. Third structural layer; 3a. External structure; 3b. Internal structure; 3c. Cantilever beam;

[0053] 4. Soundproof layer. Detailed Implementation

[0054] Embodiments of the present invention are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar symbols denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0055] Example 1:

[0056] Please see Figure 1 and Figure 3 The piezoelectric ultrasonic transducer proposed in this embodiment includes a substrate 1, a piezoelectric layer 2, and a structural layer 3 stacked sequentially.

[0057] like Figure 2 As shown, substrate 1 has a front side and a back side. A back cavity is formed through substrate 1 from the back side. The piezoelectric layer 2 and structural layer 3 within the longitudinal projection range of the back cavity are diaphragms. The back cavity provides space for the diaphragm to vibrate.

[0058] Optionally, substrate 1 is a silicon wafer substrate 1, which replaces SOI substrate 1 to reduce costs.

[0059] The piezoelectric layer 2 includes a bottom electrode 21, a piezoelectric film 22 and a top electrode 23 sequentially stacked on the surface of the substrate 1. The thickness of the structural layer 3 is greater than the thickness of the piezoelectric film 22, so that the neutral plane is located within the lateral projection area of ​​the structural layer 3.

[0060] The material of structural layer 3 can be silicon oxide, which has a lower Young's modulus than silicon.

[0061] Optionally, the structural layer 3 includes a first structural layer 31 and a second structural layer 32, wherein the thickness of the second structural layer 32 is much greater than the thickness of the first structural layer 31. Preferably, the material of the first structural layer 31 is silicon nitride (Si3N4), and the material of the second structural layer 32 is silicon oxide (SiO2). Optionally, when the material of the first structural layer 31 is silicon oxide, the material of the second structural layer 32 is silicon nitride.

[0062] Preferably, the structural layer 3 includes a first structural layer 31, a second structural layer 32, and a third structural layer 33, wherein the thickness of the second structural layer 32 is significantly greater than the thickness of the first structural layer 31 and / or the third structural layer 33. Preferably, the first structural layer 31 is made of silicon nitride (Si3N4), the second structural layer 32 is made of silicon oxide (SiO2), and the third structural layer 33 is made of silicon nitride. Optionally, when the first structural layer 31 is made of silicon oxide, the second structural layer 32 is made of silicon nitride, and the third structural layer 33 is made of silicon oxide.

[0063] The main structure of the above three-layer structure 3 is the second structural layer 32. The second structural layer 32 mainly undertakes the function of adjusting the neutral plane of the chip. The device performance is mainly determined by the material and thickness of the second structural layer 32. The first structural layer 31 mainly improves the adhesion of the intermediate layer and improves the film quality. The third structural layer 33 increases the flexibility of the structural layer 3. The three-layer structure is more stable and reliable, and improves the yield.

[0064] In this embodiment, silicon oxide / silicon nitride is used instead of silicon as the material of structural layer 3. Silicon oxide / silicon nitride has a low Young's modulus and low process stress, which can effectively reduce the resonant frequency and is beneficial to the design and manufacturing of low-frequency devices.

[0065] Furthermore, the piezoelectric layer 2 and structural layer 3 within the longitudinal projection area of ​​the back cavity serve as a diaphragm. A through groove is formed along the edge of the diaphragm to form an external structure 3a outside the diaphragm region and an internal structure 3b within the diaphragm region. The external structure 3a and the internal structure 3b are connected by a cantilever beam 3c formed within the through groove.

[0066] Example 2:

[0067] Based on Example 1, multiple through slots are formed along the edge of the diaphragm, and adjacent through slots are connected by cantilever beams 3c, for example... Figure 4 or Figure 5 The six through slots shown form six cantilever beams 3c; the cantilever beams 3c are arranged in a ring array inside the through slots.

[0068] Optional, such as Figure 4 or Figure 5 As shown, in the cross-section of cantilever beam 3c, a set of opposite sides of cantilever beam 3c are all V-shaped. The V-shape can be... Figure 4 a or Figure 5 The inner V-shape shown in diagram a (roughly an inverted rhombus), or as... Figure 4 b or Figure 5 The outer V-shape (approximately rhomboid) shown in b makes the two outer surfaces of a cantilever beam 3c either inner V-faces (approximately inverted rhomboid surfaces) or outer V-faces (approximately rhomboid surfaces).

[0069] Optionally, in the cross-section of the cantilever beam 3c, a set of opposite sides of the cantilever beam 3c are all arc-shaped (not shown in the figure). The arc shape can be an inner arc or an outer arc, so that the two outer surfaces of a cantilever beam 3c are inner arc surfaces or outer arc surfaces.

[0070] By using the aforementioned cantilever beam 3c with an outer surface that is curved or V-shaped, the piezoelectric ultrasonic transducer (PMUT) can be converted from the Gaussian mode to the piston mode to improve sensitivity. At the same time, the curved and V-shaped surfaces have good stability and rigidity, which can provide good support, enabling the PMUT to maintain good performance under vibration and impact.

[0071] Example 3:

[0072] Based on Example 1 or 2, such as Figure 6 As shown, a sound-proof layer 4 for covering the through groove is formed on the surface of the structural layer 3. The sound-proof layer 4 is made of a polymer film.

[0073] The polymer membrane can be used for a long time over a very wide temperature range and has excellent electrical insulation properties and outstanding mechanical strength, making it a perfect match for PMUT. At the same time, the polymer membrane is attached to the top of PMUT to effectively prevent sound leakage.

[0074] Example 4:

[0075] Regarding the piezoelectric ultrasonic transducers of Examples 1-3, this example discloses a method for fabricating the above-mentioned piezoelectric ultrasonic transducers, the steps of which include:

[0076] Please see Figure 7 S1, Prepare substrate 1, substrate 1 has a front side and a back side, and grow a piezoelectric layer 2 on the front side of substrate 1, specifically including:

[0077] S1-1, a bottom electrode 21 is sputtered and grown on the front side of substrate 1;

[0078] S1-2, a piezoelectric thin film 22 is sputtered and grown on the surface of the bottom electrode 21;

[0079] S1-3, top electrode 23 is sputtered and grown on the surface of piezoelectric thin film 22.

[0080] Please see Figure 8 S2, Etching piezoelectric layer 2 to pattern piezoelectric layer 2, specifically including:

[0081] S2-1, The top electrode 23 is patterned by etching the top electrode 23 using the IBE dry etching method;

[0082] S2-2, wet etching is used to pattern the piezoelectric thin film 22;

[0083] S2-3, the bottom electrode 21 is patterned by using the IBE dry etching method.

[0084] Please see Figure 9 S3, using PECVD process to deposit structural layer 3 on the surface of piezoelectric layer 2, the thickness of structural layer 3 is greater than the thickness of piezoelectric film 22, so that the neutral plane is located within the lateral projection area of ​​structural layer 3.

[0085] Please see Figure 10 S4, etch structure layer 3 to pattern structure layer 3.

[0086] Optionally, a sound leakage prevention layer 4 is grown on the surface of the structural layer 3, and the sound leakage prevention layer 4 is a polymer film (polymer).

[0087] The polymer membrane can be used for a long time over a very wide temperature range and has excellent electrical insulation properties and outstanding mechanical strength, making it a perfect match for PMUT. At the same time, the polymer membrane is attached to the top of PMUT to effectively prevent sound leakage.

[0088] Please see Figure 11 S5, etching through the back of substrate 1 to form a back cavity. The piezoelectric layer 2 and structural layer 3 within the longitudinal projection area of ​​the back cavity serve as the diaphragm, and the back cavity provides space for the diaphragm to vibrate.

[0089] Optionally, when using the above process, several through-grooves are generated along the edge of the diaphragm by patterning the piezoelectric layer 2 and the structural layer 3, forming an external structure 3a outside the diaphragm region and an internal structure 3b within the diaphragm region. The external structure 3a and the internal structure 3b are connected by several cantilever beams 3c formed in the through-grooves, and the cantilever beams 3c are arranged in a ring array inside the through-grooves.

[0090] like Figure 4 or Figure 5 As shown in the cross-section of the formed cantilever beam 3c, a set of opposite sides of the cantilever beam 3c are all arc-shaped or V-shaped, so that the two outer surfaces of a cantilever beam 3c are arc-shaped or V-shaped surfaces.

[0091] The cantilever beam 3c with an arc or V-shaped surface generated by the above process can convert the piezoelectric ultrasonic transducer (PMUT) from the Gaussian mode to the piston mode to improve sensitivity. At the same time, the arc and V-shaped surfaces have good stability and rigidity, which can provide good support and enable the PMUT to maintain good performance under vibration and impact.

[0092] The fabrication method of the piezoelectric ultrasonic transducer (PMUT) proposed in this embodiment, compared with the traditional fabrication process, first grows a piezoelectric layer 2 and patterns it, then grows a structural layer 3 on the surface of the piezoelectric layer 2, and then patterns the structural layer 3. Therefore, the patterning steps of the piezoelectric layer 2 and the structural layer 3 are independent and do not interfere with each other. The piezoelectric layer 2 does not need to produce unnecessary hollowing due to the patterning of the structural layer 3, thus ensuring the integrity of the piezoelectric layer 2 to the greatest extent.

[0093] Example 5:

[0094] As a preferred embodiment of Example 4, further, when creating the back cavity process, a dry etching process can be used to etch a portion of the substrate 1 from the back side of the substrate 1, and then a wet etching process can be used to etch through the back cavity of the substrate 1, specifically including:

[0095] S5-1, DIRE etching is performed on the back side of substrate 1. This process does not penetrate substrate 1, as IBE etching would damage the piezoelectric layer 2. Therefore, substrate 1 will retain 5-15% of its thickness after DIRE etching.

[0096] S5-2, the back side of substrate 1 is etched by wet etching process, completely penetrating the remaining 5-15% thickness of substrate 1 to form a U-shaped support structure and a back cavity.

[0097] This fabrication method is for piezoelectric MEMS chips based on silicon wafer substrate 1. Since the buried oxide layer serves as a cutoff line during the etching of SOI substrate 1, a back cavity can be formed by penetrating the buried oxide layer. Pure dry etching may damage the piezoelectric layer 2. In order to improve the yield, a dry etching process is used to etch part of the silicon wafer substrate 1, and then a wet process is used to etch through the remaining part. The wet process will not affect the piezoelectric layer 2.

[0098] Example 6:

[0099] As a preferred embodiment of Example 4 or 5, when etching the structural layer 3 to pattern the structural layer 3, the diaphragm region of the structural layer 3 is formed to have a pattern consistent with the diaphragm region of the piezoelectric thin film 22.

[0100] Optionally, structural layer 3 may be a two-layer or three-layer structure with alternating layers of silicon nitride and silicon oxide.

[0101] Optionally, when the structural layer 3 adopts a structure of a first structural layer 31, a second structural layer 32, and a third structural layer 33, the materials of the first structural layer 31 and the third structural layer 33 are silicon nitride, the material of the second structural layer 32 is silicon oxide, and the thickness of the second structural layer 32 is much greater than the thickness of the first structural layer 31 and / or the third structural layer 33.

[0102] The structure of the above-mentioned structural layer 3 allows the neutral plane to be located within the lateral projection area of ​​structural layer 3. The low Young's modulus and low process stress of silicon oxide can be utilized to effectively reduce the resonant frequency, which is beneficial to the design and manufacturing of low-frequency devices.

[0103] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0104] It should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0105] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0106] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0107] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

Claims

1. A piezoelectric ultrasonic transducer, comprising a substrate (1) having opposing front and back sides, wherein a piezoelectric layer (2) is formed on the front side of the substrate (1), characterized in that: The back of the substrate (1) has a cavity extending through the piezoelectric layer (2), and a structural layer (3) is formed on the surface of the piezoelectric layer (2). The piezoelectric layer (2) and the structural layer (3) within the longitudinal projection area of ​​the back cavity are diaphragms. The thickness of the structural layer (3) is greater than the thickness of the piezoelectric thin film (22) in the piezoelectric layer (2), so that the neutral plane is located within the lateral projection area of ​​the structural layer (3). Among them, the piezoelectric layer (2) and structural layer (3) within the longitudinal projection area of ​​the back cavity are diaphragms. A through groove is opened along the edge of the diaphragm to form an external structure (3a) outside the diaphragm area and an internal structure (3b) within the diaphragm area. The external structure (3a) and the internal structure (3b) are connected by a cantilever beam (3c) formed in the through groove. The cantilever beam (3c) is provided in several forms, and the cantilever beams (3c) are arranged in a ring array inside the through groove; A cantilever beam (3c) has opposite sides that are either inner or outer arc-shaped; or a cantilever beam (3c) has opposite sides that are either inner or outer V-shaped. The material of the structural layer (3) is silicon oxide.

2. The piezoelectric ultrasonic transducer according to claim 1, characterized in that, A soundproof layer (4) is formed on the surface of the structural layer (3) to cover the through groove.

3. A method for preparing a piezoelectric ultrasonic transducer according to any one of claims 1 to 2, characterized in that, The preparation method includes the following steps: S1. Prepare a substrate (1). The substrate (1) has a front side and a back side. A piezoelectric layer (2) is grown on the front side of the substrate (1). S2. Etch the piezoelectric layer (2) to pattern the piezoelectric layer (2); S3. A structural layer (3) is grown on the surface of the patterned piezoelectric layer (2). S4. Etch the structural layer (3) to pattern the structural layer (3); S5. Through etching the substrate (1), a back cavity is formed; The thickness of the structural layer (3) is greater than the thickness of the piezoelectric film (22) in the piezoelectric layer (2), so that the neutral surface is located within the lateral projection area of ​​the structural layer (3); Among them, the piezoelectric layer (2) and structural layer (3) within the longitudinal projection range of the back cavity are diaphragms. The diaphragm forms a through groove along the edge due to etching, thereby forming an external structure (3a) outside the diaphragm region and an internal structure (3b) within the diaphragm region. The external structure (3a) and the internal structure (3b) are connected by a cantilever beam (3c) formed by etching the diaphragm in the through groove.

4. The preparation method according to claim 3, characterized in that, After the structural layer (3) in S4 is patterned, a sound leakage prevention layer (4) is grown on the surface of the structural layer (3). The sound leakage prevention layer (4) is made of polymer film.

5. The preparation method according to claim 3, characterized in that, The S5 process involves etching through the substrate (1) to form a back cavity, including the following steps: S5-1, the back side of the substrate (1) is etched by DRIE dry etching, and the substrate (1) retains a thickness of 5-15% after DRIE dry etching; S5-2, the back side of the substrate (1) is further etched by wet process to completely penetrate the remaining 5-15% thickness of the substrate (1) to form a back cavity.

Images