Piezoelectric mems ultrasonic transducer with imitated langas and preparation method thereof

Abstract

The application provides a piezoelectric MEMS ultrasonic transducer simulating a Langevin vibrator and a preparation method thereof, which comprises, from bottom to top, a first silicon layer, a first electrode layer, a piezoelectric layer, a second electrode layer and a second silicon layer; wherein: a plurality of array units are arranged on the first silicon layer, the array units are separated by grooves, the grooves penetrate the piezoelectric layer and the second electrode layer, and the second electrode layer is divided into a plurality of second electrode layer units by the grooves; the second silicon layer comprises a plurality of stepped protruding structures, and the protruding structures are respectively located on the second electrode layer units; the protruding structure comprises coaxially arranged upper and lower second silicon layers, and the upper second silicon layer is away from the second electrode layer unit; and the area of the upper second silicon layer is smaller than that of the lower second silicon layer. 33 The piezoelectric MEMS ultrasonic transducer of the application can be used in small-size high-precision occasions such as intracardiac blood vessel imaging and fingerprint identification.

Description

Technical Field

[0001] This invention relates to the field of MEMS ultrasonic transducer technology, specifically to a piezoelectric MEMS ultrasonic transducer that mimics a Langevin oscillator and its fabrication method. Background Technology

[0002] Ultrasound is increasingly used in industrial and biomedical fields, including non-destructive evaluation, ultrasound-driven systems, medical imaging, therapeutic ultrasound, and particle and cell manipulation. Ultrasound can be excited using many different methods, including piezoelectricity, magnetostriction, and photoacoustics. Among these, piezoelectricity is the most common and widely used. Traditional piezoelectric ultrasonic transducers (Langevin ultrasonic transducers) typically consist of a piezoelectric material layer, a thin, highly conductive electrode layer in the middle (e.g., Au or Pt), and usually an adhesion layer (e.g., Cr or Ti) connected to a wire. This traditional ultrasonic transducer utilizes the longitudinal vibration mode (d) of the piezoelectric material. 33 (Vibration modes). However, the Langevin ultrasonic transducer is too large, which greatly limits its application in many situations.

[0003] With the rapid development of microelectromechanical systems (MEMS) technology, micromechanical ultrasonic transducers based on capacitive (cMUT) and piezoelectric (pMUT) technologies can significantly reduce device size and be used in various complex, high-resolution applications. Their low power consumption and better acoustic impedance matching media also broaden their application scenarios. Generally, cMUTs have a high electromechanical coupling coefficient, but they suffer from drawbacks such as limited vertical deformation, nonlinear driving effects, and high DC bias voltage. With advancements in piezoelectric material technology, pMUTs are gradually becoming an alternative to cMUTs. Currently, the most widely used piezoelectric thin film materials are lead zirconium titanate (PZT) and aluminum nitride (AlN). Compared to AlN, PZT has better piezoelectric properties, so it is often used in applications requiring high-performance devices.

[0004] A search of existing technologies revealed the following:

[0005] Chao Wang, Zheyao Wang, et al., authored "A Micromachined Piezoelectric Ultrasonic Transducer Operating in d" in the IEEE SENSORS JOURNAL. 33 "Mode Using Square Interdigital Electrodes" reports a working method in d 33 In the pMUT mode, the top electrode uses a square interdigitated electrode. In-plane polarization and the interdigitated electrode enable the pMUT to operate in d... 33In this mode, PZT converts ultrasonically pressure-induced in-plane stress into in-plane directional charge; the square interdigitated electrodes fully utilize the film stress to improve device sensitivity and increase device capacitance. The pMUT is optimized by changing the size of the square interdigitated electrodes rather than the thickness of the PZT film. This operation is performed in d... 33 Modal pMUTs have a large ultrasonic transmitting / receiving area, making them suitable for ultrasonic applications requiring high directivity.

[0006] Yuri Kusano, Itaru Ishii, et al. published "High-SPL Air-Coupled Piezoelectric Micromachined Ultrasonic Transducers Based on 36% ScAlN Thin-Film" in IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, reporting a high-performance pMUT based on a 36% scandium-doped aluminum nitride (ScAlN) thin film. This pMUT has a piezoelectric coefficient twice that of AlN, achieves a sound pressure level of 105 dB at 10 cm at an operating frequency of 100 kHz, and exhibits only 30 dB attenuation over a 2 m range.

[0007] S Sadeghpour, M Kraft, et al., in the Journal of Micromechanics and Microengineering, wrote "Design and fabrication strategy for an efficient leadzirconate titanate based piezoelectric micromachined ultrasound transducer," which introduces the design and fabrication method of pMUT based on PZT thin film to improve the performance of pMUT. They used finite element simulation and analytical equation methods to study the influence of the optimal thickness of piezoelectric ceramic, electrode radius, and residual stress on the resonant frequency of piezoelectric ceramic.

[0008] In summary, most of the piezoelectric MEMS ultrasonic transducers reported so far employ d... 31 Vibration modes, and due to process limitations, the thickness of the piezoelectric film is difficult to increase, resulting in significant limitations on sound pressure level and directivity, for d 33 Modal modulation can currently only be achieved using interdigitated electrodes. No piezoelectric MEMS ultrasonic transducers have been reported that simultaneously possess advantages such as small size, thick-film fabrication, and enhanced sound pressure output through matching layers. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the purpose of this invention is to provide a piezoelectric MEMS ultrasonic transducer that mimics the Langevin oscillator and its fabrication method.

[0010] According to one aspect of the present invention, a piezoelectric MEMS ultrasonic transducer incorporating a Langevin oscillator is provided, the piezoelectric MEMS ultrasonic transducer comprising, from bottom to top, a first silicon layer, a first electrode layer, a piezoelectric layer, a second electrode layer, and a second silicon layer; wherein:

[0011] The first silicon layer has a plurality of array units, which are separated by trenches. The trenches penetrate the piezoelectric layer and the second electrode layer, and the second electrode layer is divided into a plurality of second electrode layer units by the trenches.

[0012] The second silicon layer includes a plurality of stepped protrusions, which are respectively located on the second electrode layer unit;

[0013] The protrusion structure includes an upper second silicon layer and a lower second silicon layer coaxially arranged, wherein the upper second silicon layer is far away from the second electrode layer unit; the area of ​​the upper second silicon layer is smaller than the area of ​​the lower second silicon layer.

[0014] Furthermore, the arrangement of the plurality of array units is a rectangular array or a circular array.

[0015] Furthermore, the upper second silicon layer and the lower second silicon layer have the same thickness, which is half the thickness of the second silicon layer.

[0016] Furthermore, the piezoelectric MEMS ultrasonic transducer also includes leads for leading out the first electrode layer and the second electrode layer of each array unit.

[0017] According to a second aspect of the present invention, a method for fabricating the above-described Langevin-inspired piezoelectric MEMS ultrasonic transducer is provided, the method comprising:

[0018] Two double-polished silicon wafers are provided, wherein the thickness of the second silicon wafer is greater than the thickness of the first silicon wafer;

[0019] A first metal layer is formed on one side of the first silicon wafer, and a second metal layer is formed on one side of the second silicon wafer;

[0020] A piezoelectric material sheet is provided, and both sides of the piezoelectric material sheet are respectively bonded to the first metal layer and the second metal layer;

[0021] An oxide layer or a metal layer is deposited on the side of the second silicon wafer away from the piezoelectric material sheet, and a pattern is formed by photolithography. Then the oxide layer or metal layer is etched as a first hard mask.

[0022] After the pattern is formed by photolithography, the second silicon wafer is etched using deep silicon etching, and the etching stops when half the thickness of the second silicon wafer is reached.

[0023] After the photoresist is washed away, the remaining silicon layer of the second silicon wafer is etched using the first hard mask deep silicon etching. The etching is stopped after the second metal layer is reached.

[0024] A second hard mask is provided, the second hard mask is bonded to the second metal layer, and the second hard mask is used to etch away the second metal layer.

[0025] The piezoelectric material layer is etched away to expose the first metal layer, forming multiple array units on the first silicon wafer, thus obtaining a piezoelectric MEMS ultrasonic transducer that mimics the Langevin oscillator.

[0026] Furthermore, the thickness of the two double-polished silicon wafers is determined based on the sound velocity of the material and the required resonant frequency.

[0027] Furthermore, the deep silicon etching of the second silicon wafer includes a pattern of either circles or polygons.

[0028] Furthermore, the second hard mask is formed by laser cutting, the material of the second hard mask is PI tape, and the shape of the second hard mask is square.

[0029] Furthermore, the etching of the piezoelectric material layer includes etching the piezoelectric material layer by means of ion beam etching or wet etching.

[0030] Furthermore, the first metal layer serves as the first electrode layer of the ultrasonic transducer, and the second metal layer serves as the second electrode layer of the ultrasonic transducer. After exposing the first metal layer, the method further includes: using a wire bonding machine to lead out the first electrode layer and the second electrode layer of each array unit to facilitate signal excitation and acquisition.

[0031] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0032] This invention utilizes MEMS technology to enable operation in d 33 The size of the ultrasonic transducer for vibration modes has been reduced to the micrometer level, realizing the miniaturization of the traditional Langevin ultrasonic transducer. This greatly improves the performance of the piezoelectric MEMS ultrasonic transducer, which can be used in applications such as ultrasonic imaging, non-destructive testing, and high-precision ranging. Attached Figure Description

[0033] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0034] Figure 1 This is a schematic diagram of the structure of a piezoelectric MEMS ultrasonic transducer that mimics the Langevin oscillator in one embodiment of the present invention;

[0035] Figure 2 This is a side view schematic diagram of a piezoelectric MEMS ultrasonic transducer that mimics the Langevin oscillator in one embodiment of the present invention;

[0036] Figure 3 This is a top view schematic diagram of a piezoelectric MEMS ultrasonic transducer that mimics the Langevin oscillator in one embodiment of the present invention;

[0037] Figure 4 This is a flowchart illustrating the fabrication method of a piezoelectric MEMS ultrasonic transducer mimicking a Langevin oscillator in one embodiment of the present invention.

[0038] In the figure: 1 is the second silicon layer, 2 is the second electrode layer, 3 is the piezoelectric layer, 4 is the first electrode layer, and 5 is the first silicon layer. Detailed Implementation

[0039] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0040] With the development of electronic devices, piezoelectric MEMS ultrasonic transducers with higher sound pressure levels and better directivity have become an inevitable trend. Therefore, this invention provides a piezoelectric MEMS ultrasonic transducer that mimics the Langevin oscillator, referring to... Figure 1-3 The piezoelectric MEMS ultrasonic transducer includes, from bottom to top, a first silicon layer 5, a first electrode layer 4, a piezoelectric layer 3, a second electrode layer 2, and a second silicon layer 1. The first silicon layer 5 has multiple array units separated by trenches that penetrate the piezoelectric layer 3 and the second electrode layer 2. The second electrode layer 2 is divided into multiple second electrode layer units by the trenches. The second silicon layer 1 includes multiple stepped protrusions, the number of which is equal to the number of array units. The protrusions are located on the second electrode layer units. Each protrusion includes an upper second silicon layer and a lower second silicon layer coaxially arranged, with the upper second silicon layer located away from the second electrode layer units. The area of ​​the upper second silicon layer is smaller than that of the lower second silicon layer, forming a unique horn-shaped piezoelectric MEMS ultrasonic transducer.

[0041] In some implementations, since the energy of a single array unit (array element) is insufficient, multiple array units can provide more energy or realize functions such as phased arrays, thereby enabling more applications. The arrangement shape of multiple array units is a rectangular array or a ring array. Specifically, a ring array refers to multiple array units first arranged into a first circle, and then arranged in a progressive manner towards the interior of the first circle with a slightly smaller radius to form a concentric second circle, and so on, until the center of the circle is reached to form an array.

[0042] In some implementations, the upper second silicon layer and the lower second silicon layer have the same thickness, which is half the thickness of the second silicon layer 1. Equal thickness is beneficial for matching acoustic impedance.

[0043] In some embodiments, the piezoelectric MEMS ultrasonic transducer in this invention further includes leads for leading out the first electrode layer 4 and the second electrode layer 2 of each array unit.

[0044] Compared with traditional piezoelectric MEMS ultrasonic transducers, the piezoelectric MEMS ultrasonic transducer in this embodiment of the invention has the advantage of small size and excellent ultrasonic performance.

[0045] Another embodiment of the present invention also provides a method for fabricating the above-mentioned piezoelectric MEMS ultrasonic transducer with a Langevin-like oscillator, the method comprising:

[0046] S1. Two double-polished silicon wafers are provided, wherein the thickness of the second silicon wafer is greater than the thickness of the first silicon wafer;

[0047] S2. A first metal layer is formed on one side of the first silicon wafer, and a second metal layer is formed on one side of the second silicon wafer;

[0048] S3. Provide a piezoelectric material sheet as a piezoelectric material layer (piezoelectric layer), and bond both sides of the piezoelectric material sheet to the first metal layer and the second metal layer respectively to form a piezoelectric wafer;

[0049] S4. Deposit an oxide layer or a metal layer on the side of the second silicon wafer away from the piezoelectric material sheet, and form a pattern by photolithography, and then etch the oxide layer or metal layer as the first hard mask.

[0050] S5. After the photolithography pattern is formed, the second silicon wafer is etched using deep silicon etching. Etching is stopped when the second silicon wafer reaches half its thickness.

[0051] S6. After washing away the photoresist, use the first hard mask to etch the remaining silicon layer of the second silicon wafer. After etching to the second metal layer, stop etching to form an array.

[0052] S7. Provide a second hard mask, attach the second hard mask to the second metal layer, and use the second hard mask to etch away the second metal layer.

[0053] S8. Etch away the piezoelectric material layer to expose the first metal layer for wiring, forming multiple array units on the first silicon wafer to obtain a piezoelectric MEMS ultrasonic transducer that mimics the Langevin oscillator.

[0054] This invention reduces the size of an ultrasonic transducer operating in the d33 vibration mode to the micrometer level using MEMS technology, achieving miniaturization of the traditional Langevin ultrasonic transducer. This greatly improves the performance of the piezoelectric MEMS ultrasonic transducer, which can be used in applications such as ultrasonic imaging, non-destructive testing, and high-precision ranging.

[0055] In some embodiments, in S1, a double-polished silicon wafer is used as the substrate, and the thickness of the two double-polished silicon wafers is determined according to the sound velocity of the material and the required resonant frequency. Preferably, two double-polished silicon wafers with strictly controlled thickness are selected, where the thickness of one wafer is twice the thickness of the other wafer; for example, the thicknesses of the two double-polished silicon wafers are 200 μm and 400 μm, respectively. In other embodiments, the thickness of the two wafers can be adjusted according to the sound velocity of the material and the required resonant frequency, and is not limited to a two-times-thickness relationship. The substrate material includes, but is not limited to, rigid substrates such as Si, SiC, ITO glass, gallium arsenide, and aluminum nitride ceramic sheets, and flexible substrates such as PDMS and PI. When using substrates of other materials, ion beam etching can be used for etching.

[0056] In some embodiments, in S2, the metals sputtered on the first metal layer and the second metal layer are metal materials with good conductivity and suitable for use as electrodes, including but not limited to Au, Pt, Cu and Al.

[0057] In some embodiments, in S3, the piezoelectric material sheet uses a piezoelectric material, including but not limited to PZT piezoelectric ceramics, ZnO, AlN, PMN-PT, PVDF, etc.; the thickness of the piezoelectric material sheet is 100 μm. Compared with the MEMS process in the prior art, the method in this embodiment of the invention realizes the preparation of a thick film in a piezoelectric MEMS ultrasonic transducer, and the thickness of the piezoelectric material sheet can be adjusted according to the resonant frequency required for the actual application. The two sputtered silicon wafers and the piezoelectric material sheet are bonded together using conductive silver paste.

[0058] In some implementations, in S4, since photoresist cannot be used as a mask for the second deep silicon etch, a hard mask needs to be prepared in advance. An oxide layer or metal layer is deposited on the thicker side of the silicon wafer, i.e., the second silicon wafer, using plasma-enhanced chemical vapor deposition (PECVD) as a hard mask. The thickness of the oxide layer or metal layer is mainly determined by the deep silicon etching process. Generally, etching 200µm of Si requires about 3µm of silicon oxide. If it is a metal layer, it does not need to be too thick, usually a few hundred nm is sufficient. The pattern is formed by photolithography, and then the oxide layer or metal layer is etched by reactive ion etching to serve as the first hard mask.

[0059] In some embodiments, etching stops at half the thickness of the second silicon wafer in step S5 to create a horn-like shape, thereby improving sound transmission efficiency. Equal thickness facilitates acoustic impedance matching. The deep silicon etching pattern can be any of circular or polygonal shapes, such as rectangles, triangles, or other polygonal shapes. Of course, in other embodiments, other shapes of deep silicon etching patterns can be used for easier arrangement, as long as they achieve the same function as in the embodiments of this invention.

[0060] The diameter or side length of the array unit is related to the resonant frequency. The number of array units is determined according to the specific application scenario and size. In some embodiments, in S6, the array units are arranged in a rectangular array with a quantity of 5*5 arrays. The diameter or side length of the array units in the array is 500μm. In other embodiments, the number of rectangular arrays and the diameter or side length of the array units in the array can be arbitrarily adjusted according to the required resonant frequency. A ring array can also be used, as long as the same function as in the embodiments of the present invention can be achieved.

[0061] In some embodiments, in S7, the second hard mask is formed by laser cutting. The material of the second hard mask is a high-temperature resistant material, such as PI tape. The pattern of the second hard mask needs to be able to etch the underlying first metal layer and piezoelectric material layer. Preferably, the pattern of the second hard mask is square.

[0062] In some embodiments, etching away the piezoelectric material layer in S8 includes etching away the piezoelectric material layer by means of ion beam etching or wet etching.

[0063] The first metal layer serves as the first electrode layer of the ultrasonic transducer, and the second metal layer serves as the second electrode layer of the ultrasonic transducer. In some embodiments, after exposing the first metal layer, the method further includes: leading out the first electrode layer and the second electrode layer of each array unit through a wire bonding machine to facilitate signal excitation and acquisition.

[0064] This invention first employs MEMS technology to fabricate a top hard mask, i.e., the first hard mask, as a mask for step etching. Next, a horn shape for the top silicon wafer, i.e., the second silicon wafer, is formed through two-step deep silicon etching. The first deep silicon etching uses photoresist as a mask for patterning, etching down to the top electrode layer, i.e., the second metal layer. The second deep silicon etching uses the top hard mask as a mask. Finally, a patterned PI thick tape is laser-cut as the second hard mask, and the top electrode layer is etched using an ion beam. Wet etching or ion beam etching of the piezoelectric material layer exposes the bottom electrode layer, i.e., the first metal layer. This invention mimics the Langevin oscillator structure to achieve a unique horn structure fabrication, realizing the fabrication of a thick film in a piezoelectric MEMS ultrasonic transducer. Furthermore, unlike the d31 vibration mode of traditional piezoelectric MEMS ultrasonic transducers, where the piezoelectric sheet typically vibrates vertically with its two sides as anchor points, this invention restricts the vertical vibration direction, allowing the piezoelectric sheet to only generate a longitudinal vibration mode, thus achieving a d33 vibration mode mimicking the Langevin oscillator. This piezoelectric MEMS ultrasonic transducer, which mimics the Langevin oscillator, can be used in small-size, high-precision applications such as intracardiac vascular imaging and fingerprint recognition. The micrometer-sized device can be made into a single unit or multiple units according to the application scenario. For example, in cardiovascular imaging, the device can be integrated onto a cardiac catheter to achieve intracardiac ultrasound imaging; in fingerprint recognition, the small size of the device makes integration possible, allowing it to be integrated into smartphones or other smart devices to achieve ultrasonic fingerprint recognition.

[0065] In one specific embodiment, such as Figure 4 As shown, the fabrication process of the piezoelectric MEMS ultrasonic transducer inspired by Langevin oscillators can be divided into 6 steps, which are described in detail below:

[0066] Step 1, such as Figure 4 As shown in (a), metal layers are first sputtered on two silicon wafers of different thicknesses as the top electrode layer (i.e., the second electrode layer) and the bottom electrode layer (i.e., the first electrode layer). Then, the silicon wafers are bonded to both sides of the piezoelectric material wafer with conductive silver paste, with the metal layers facing the piezoelectric material wafer.

[0067] In a preferred embodiment, the metal of the top electrode layer and the bottom electrode layer is Au, and the thickness is 300 nm.

[0068] As a preferred embodiment, the piezoelectric material sheet is a PZT piezoelectric ceramic sheet with a thickness of 100 μm.

[0069] In a preferred embodiment, the thicknesses of the two silicon wafers are 400μm and 200μm, respectively, wherein the 400μm silicon wafer is the top silicon layer, i.e., the second silicon layer, and the 200μm silicon wafer is the bottom silicon layer, i.e., the first silicon layer.

[0070] Step 2, as follows Figure 4As shown in (b), a metal layer or oxide layer is deposited on the top silicon layer, and then a 5 μm photoresist is coated on the metal layer or oxide layer. The process involves pre-baking for 90 s, exposure for 45 s, development for 50 s, rinsing with deionized water for 30 s, drying with nitrogen, and post-baking for 12 min to etch away the metal layer or oxide layer. The remaining metal layer or oxide layer is used as the first hard mask for subsequent etching.

[0071] In a preferred embodiment, the metal layer or oxide layer is SiO2; the thickness of the metal layer or oxide layer is 5 μm.

[0072] In a preferred embodiment, the metal layer or oxide layer is etched into a 5*5 array, the array unit is a circle with a diameter of 250μm, and the spacing between the array units, i.e., the trench size between the array units, is 1000μm.

[0073] Step 3, as follows Figure 4 As shown in (c), a 5μm layer of photoresist is coated on the top silicon layer, pre-baked for 90s, exposed for 45s, developed for 50s, rinsed with deionized water for 30s, dried with nitrogen, and post-baked for 12min. The top silicon layer is then etched with deep silicon until the second metal layer on the second silicon layer is exposed, at which point the deep silicon etching is stopped.

[0074] In a preferred embodiment, the top silicon layer etching pattern is an array of 5*5 arrays, with array elements being circles with a diameter of 500μm and an array element spacing of 1000μm.

[0075] Step 4, as Figure 4 As shown in (d), the SiO2 layer formed in the second step is used as the first hard mask for deep silicon etching. The etching depth is detected by a profilometer during etching.

[0076] As a preferred embodiment, the etching depth of deep silicon etching is 200 μm.

[0077] Step 5, as Figure 4 As shown in (e), a second hard mask, cut by laser, is bonded to the top silicon layer, and the second metal layer is etched by an ion beam to form the pattern of the top electrode.

[0078] As a preferred embodiment, the second hard mask material for laser cutting is thick PI tape;

[0079] In a preferred embodiment, in order to etch the underlying first metal layer and piezoelectric material layer through the second hard mask, the pattern of the hard mask is a square of 700μm*700μm.

[0080] Step 6, as Figure 4As shown in (f), after the fifth step of ion beam etching, the PZT piezoelectric layer is wet-etched to expose the bottom electrode layer for wire bonding. The wafer is immersed in the prepared etching solution for etching, and a magnetic stirrer is used to stir the etching solution to improve etching uniformity and speed. Then, the etched wafer is immersed in the prepared HNO3 solution for 3 minutes. Finally, it is immersed in deionized water for a few minutes to clean and remove surface impurities. Nitrogen gas is blown off and vacuum dried.

[0081] As a preferred embodiment, the mask for wet etching is still the PI thick tape hard mask from step five.

[0082] In a preferred embodiment, after the preparation steps are completed, the top and bottom electrodes of each array element are led out using a wire bonding machine to facilitate signal excitation and acquisition.

[0083] As a preferred embodiment, after the lead wire is completed, a 2μm thick layer of the biocompatible material Parylene-N film is deposited, which also has the effect of matching the acoustic impedance of specific scenarios and specific materials.

[0084] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention. The above preferred features can be used in any combination without conflict.

Claims

1. A piezoelectric MEMS ultrasonic transducer emulating a Langevin vibrator, characterized in that, The piezoelectric MEMS ultrasonic transducer comprises a first silicon layer, a first electrode layer, a piezoelectric layer, a second electrode layer and a second silicon layer arranged from bottom to top. The first silicon layer is provided with a plurality of array units, and the array units are separated by grooves. The second silicon layer comprises a plurality of stepped convex structures, and the convex structures are respectively located on the second electrode layer units. The convex structure comprises an upper second silicon layer and a lower second silicon layer arranged coaxially.

2. The piezoelectric MEMS ultrasonic transducer of claim 1, wherein, The upper second silicon layer is away from the second electrode layer unit.

3. The piezoelectric MEMS ultrasonic transducer of claim 1, wherein, The area of the upper second silicon layer is smaller than the area of the lower second silicon layer, forming a horn structure piezoelectric MEMS ultrasonic transducer.

4. A method of manufacturing a piezoelectric MEMS ultrasonic transducer according to any one of claims 1 to 3, characterized in that, The array units are arranged in a rectangular array or a circular array. The piezoelectric MEMS ultrasonic transducer further comprises a lead wire for leading out the first electrode layer and the second electrode layer of each array unit. The piezoelectric MEMS ultrasonic transducer comprises: Two double-polished silicon wafers are provided, wherein the thickness of the second silicon wafer is greater than the thickness of the first silicon wafer. A first metal layer is formed on one side of the first silicon wafer, and a second metal layer is formed on one side of the second silicon wafer. A piezoelectric material sheet is provided, and the two sides of the piezoelectric material sheet are bonded to the first metal layer and the second metal layer respectively. An oxide layer or a metal layer is deposited on the side of the second silicon wafer away from the piezoelectric material sheet, and a pattern is formed by photolithography, and then the oxide layer or the metal layer is etched as a first hard mask. After the pattern is formed by photolithography, the second silicon wafer is deep silicon etched, and the etching is stopped when the second silicon wafer is etched to half of its thickness. After the photoresist is washed away, the first hard mask is used to deep silicon etch the remaining silicon layer of the second silicon wafer, and the etching is stopped after the second metal layer is etched.

5. The method of claim 4, wherein the piezoelectric MEMS ultrasonic transducer is a replica of a Langevin transducer. A second hard mask is provided, and the second hard mask is bonded to the second metal layer, and the second metal layer is etched away using the second hard mask.

6. The method of claim 4, wherein the piezoelectric MEMS ultrasonic transducer is a replica of a Langevin transducer. The piezoelectric material layer is etched away, thereby exposing the first metal layer, forming a plurality of array units on the first silicon wafer, and obtaining a piezoelectric MEMS ultrasonic transducer.

7. The method of claim 4, wherein the piezoelectric MEMS ultrasonic transducer is a replica of a Langevin transducer. The thickness of the two double-polished silicon wafers is determined according to the speed of sound of the material and the required resonance frequency.

8. The method of claim 4, wherein the piezoelectric MEMS ultrasonic transducer is a replica of a Langevin transducer. The deep silicon etching of the second silicon wafer comprises any one of a circular shape and a polygonal shape.

9. The method of claim 4, wherein the piezoelectric MEMS ultrasonic transducer is a replica of a Langevin transducer. The second hard mask is formed by laser cutting, the material of the second hard mask is PI tape, and the pattern of the second hard mask is a square. The etching of the piezoelectric material layer comprises ion beam etching or wet etching. After the first metal layer is exposed, the first electrode layer and the second electrode layer of each array unit are led out by a wire bonding machine for signal excitation and collection.

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