Ultrasonic transducer with short waveguide structure and method of manufacture, ultrasonic testing apparatus

Abstract

The application discloses an ultrasonic transducer with a short waveguide structure, a manufacturing method thereof and an ultrasonic detection device. The manufacturing method comprises the following steps: providing a first substrate, including a first supporting layer and a first device layer formed on the surface of the first supporting layer; patterning the first device layer to form an opening through the first device layer; providing a second substrate, including a second supporting layer and a second device layer on the second supporting layer; bonding the second device layer to the surface of the first device layer towards the first substrate; removing the second supporting layer to form a piezoelectric sensing unit on the side of the second device layer away from the first device layer, and the piezoelectric sensing unit is located opposite to the opening; and removing the first supporting layer to expose the opening, which serves as a waveguide. The manufacturing method can form an ultrasonic transducer with a short waveguide structure, is suitable for large-scale manufacturing of flexible ultrasonic transducers, and improves the performance of the ultrasonic transducer.

Description

Technical Field

[0001] This application relates to the field of piezoelectric sensing technology, specifically to an ultrasonic transducer with a short waveguide structure, its manufacturing method, and an ultrasonic testing device. Background Technology

[0002] Ultrasonic imaging technology has advantages such as being radiation-free and capable of real-time imaging. It can be used to observe the structure under test by emitting and receiving ultrasonic waves through an ultrasonic probe.

[0003] Because ultrasound waves can only transmit with low loss in solids or liquids, it is essential to ensure there are no air gaps between the probe and the surface being measured. For flexible structures (such as human organs and tissues), air gaps can be eliminated by applying coupling gel and pressing the probe when using conventional probes for ultrasound imaging; however, this approach may cause patient discomfort. Furthermore, due to the complex geometry of human joints and similar areas, imaging these areas with conventional probes is difficult, often requiring radiographic imaging, which makes rapid, timely, and real-time detection challenging. Flexible wearable devices can comfortably conform to the human body and enable long-term online monitoring, thus attracting significant attention from researchers. Compared to traditional ultrasound sensors, flexible ultrasound sensors may avoid or reduce tissue compression, improving patient comfort. They can also effectively conform to joints and other areas for efficient ultrasound imaging, enabling rapid and real-time imaging and expanding the range of medical imaging methods. Wearable sensors typically need to fit snugly against the human body, requiring a certain degree of structural flexibility. Conventional rigid probes usually necessitate the addition of a flexible coupling layer and / or the application of pressure to achieve complete contact with the surface being measured. This can lead to signal attenuation and discomfort. Using flexible ultrasonic transducers can effectively conform to the surface being measured, which is significant for improving the signal-to-noise ratio and achieving a seamless wearing experience.

[0004] Ultrasonic transducer arrays can acquire more structural information by adjusting the emitted sound field. Therefore, processing one-dimensional or two-dimensional arrays is very important for improving imaging effects. At present, research on flexible devices is mostly based on the combination of flexible substrates and discrete ultrasonic units to form ultrasonic unit arrays. It is difficult to ensure consistency in large-scale production, and the acoustic emission effect of the devices is not good. The signals between the various ultrasonic units are prone to crosstalk, which cannot be effectively applied to flexible devices. The imaging effect needs to be further improved. Summary of the Invention

[0005] In view of this, this application provides an ultrasonic transducer with a short waveguide structure, a manufacturing method thereon, and an ultrasonic testing device to solve the problem of poor imaging effect of existing ultrasonic transducers.

[0006] This application provides a method for manufacturing an ultrasonic transducer with a short waveguide structure, comprising: providing a first substrate, the first substrate including a first support layer and a first device layer formed on the surface of the first support layer; patterning the first device layer to form an opening penetrating the first device layer; providing a second substrate, the second substrate including a second support layer and a second device layer located on the second support layer; bonding the second device layer to the surface of the first device layer with the second device layer facing the first substrate; removing the second support layer to form a piezoelectric sensing unit on the side of the second device layer away from the first device layer, the piezoelectric sensing unit being positioned opposite the opening; and removing the first support layer to expose the opening, the opening serving as a waveguide.

[0007] Optionally, it also includes filling the opening with a waveguide medium.

[0008] Optionally, the manufacturing method further includes: after forming the piezoelectric sensing unit and before removing the first support layer, forming a passivation layer covering the piezoelectric sensing unit; forming a through hole located in the passivation layer, filling the through hole with conductive material to form a conductive pillar, the conductive pillar being electrically connected to the piezoelectric sensing unit.

[0009] Optionally, the method for forming the piezoelectric sensing unit includes: sequentially stacking a bottom electrode material layer, a functional thin film layer, and a top electrode material layer from the second device layer outwards; sequentially patterning the top electrode material layer, the functional thin film layer, and the bottom electrode material layer to form a bottom electrode, a functional thin film, and a top electrode stacked sequentially from the second device layer outwards, wherein the bottom electrode extends outwards from the piezoelectric sensing unit; and simultaneously forming the bottom electrode by patterning the bottom electrode material layer, forming a connection electrode located on the same layer as the bottom electrode; the method for forming a through-hole located in the passivation layer and filling the through-hole with conductive material to form a conductive pillar includes: forming a first through-hole and a second through-hole penetrating the passivation layer, wherein a portion of the bottom electrode is exposed at the bottom of the first through-hole, and a portion of the connection electrode is exposed at the bottom of the second through-hole; filling the first through-hole and the second through-hole with conductive material to form a first conductive pillar electrically connected to the bottom electrode and a second conductive pillar electrically connected to the connection electrode; simultaneously fixing the tops of the first conductive pillar and the second conductive pillar to the circuit layer, wherein both the first conductive pillar and the second conductive pillar are electrically connected to the circuit layer.

[0010] Optionally, the first through hole and the second through hole are symmetrically distributed around the piezoelectric sensing unit, and the tops of the first conductive pillar and the second conductive pillar are higher than the top of the passivation layer; after the tops of the first conductive pillar and the second conductive pillar are fixed to the surface of the circuit layer, a cavity is formed between the circuit layer and the passivation layer.

[0011] Optionally, the second support layer includes: a second substrate layer and a second dielectric layer located on the surface of the second substrate layer; during the removal of the second support layer, only the second substrate layer is removed; the piezoelectric sensing unit is formed on the surface of the second dielectric layer; or, the manufacturing method further includes: after removing the second support layer, forming a second dielectric layer on the surface of the second device layer, and then forming the piezoelectric sensing unit on the surface of the second dielectric layer.

[0012] Optionally, a plurality of arrayed openings are formed in the first device layer, and a plurality of arrayed piezoelectric sensing units are formed on the surface of the second dielectric layer, wherein each piezoelectric sensing unit corresponds to one of the openings; and / or, both the first substrate and the second substrate are SOI wafers, and both the first device layer and the second device layer are the top semiconductor layers of the SOI wafers; and / or, the thickness of the first device layer is less than or equal to 100 micrometers, and the thickness of the second device layer is less than or equal to 100 micrometers.

[0013] Optionally, the circuit layer includes a flexible substrate and electrical connection lines or functional circuits formed on / inside the flexible substrate.

[0014] This application also provides an ultrasonic transducer with a short waveguide structure, comprising: a first device layer with an opening penetrating the first device layer; an isolation layer located on one side surface of the first device layer, the isolation layer closing one end of the opening; a second device layer located on the surface of the isolation layer; and a piezoelectric sensing unit located on the side of the second device layer opposite to the first device layer, the piezoelectric sensing unit being positioned opposite the opening.

[0015] Optionally, the opening is filled with a waveguide medium; and / or, a second dielectric layer is formed on the surface of the second device layer opposite to the first device layer, and the piezoelectric sensing unit is located on the surface of the second dielectric layer.

[0016] Optionally, it further includes: a passivation layer located on the second device layer and covering the piezoelectric sensing unit, and a conductive pillar penetrating the passivation layer, the conductive pillar being electrically connected to the piezoelectric sensing unit; the top of the conductive pillar being bonded to a circuit layer, and the conductive pillar being electrically connected to the circuit layer.

[0017] Optionally, the conductive pillars are symmetrically distributed around the piezoelectric sensing unit, and the top of the conductive pillars is higher than the top of the passivation layer; the top of the conductive pillars is bonded to the surface of the circuit layer, so that a cavity is formed between the circuit layer and the passivation layer.

[0018] Optionally, the cavity is filled with a buffer medium.

[0019] Optionally, the piezoelectric sensing unit includes: a bottom electrode, a functional thin film, and a top electrode stacked sequentially from the second device layer outwards, with the bottom electrode extending outwards from the piezoelectric sensing unit; the ultrasonic transducer further includes: a connecting electrode located on the same layer as the bottom electrode, the connecting electrode being electrically connected to the top electrode; the conductive pillar includes a first conductive pillar and a second conductive pillar, the bottom of the first conductive pillar being connected to the bottom electrode extending outwards from the piezoelectric sensing unit, and the bottom of the second conductive pillar being connected to the connecting electrode.

[0020] Optionally, the circuit layer includes: a flexible substrate, and electrical connection lines or functional circuits formed on and / or inside the flexible substrate.

[0021] Optionally, the first device layer has a plurality of arrayed openings, and the second device layer has a plurality of arrayed piezoelectric sensing units, each piezoelectric sensing unit corresponding to one of the openings; and / or, the first device layer and the second device layer are both top semiconductor layers of an SOI wafer; and / or, the thickness of the first device layer is less than or equal to 100 micrometers, and the thickness of the second device layer is less than or equal to 100 micrometers.

[0022] Embodiments of this application also provide an ultrasonic testing device, comprising: an ultrasonic transducer manufactured using any of the manufacturing methods described above; or, comprising an ultrasonic transducer as described in any of the preceding claims.

[0023] The ultrasonic transducer manufactured by the method described in this application incorporates a waveguide structure into its design, effectively improving acoustic emission and reducing crosstalk between units. During manufacturing, an opening is formed through a single etching process, serving as a short waveguide. This simple and unique short waveguide structure enhances acoustic emission efficiency, reduces crosstalk between units, and allows direct contact with the human body surface without damaging the piezoelectric sensing unit. This transducer can be fabricated using ultra-thin SOI wafers, meeting the requirements of flexible arrays. It can be mass-produced using integrated circuit technology, ensuring consistency during large-scale production. Applied to flexible wearable devices, it facilitates long-term real-time monitoring of superficial organs or functions as a tactile sensor and actuator. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figures 1 to 12 This is a schematic diagram of the formation process of an ultrasonic transducer according to an embodiment of this application;

[0026] Figure 13 This is a schematic diagram of the structure of an ultrasonic transducer according to an embodiment of this application. Detailed Implementation

[0027] Current research on flexible devices is mostly based on the combination of flexible substrates and discrete ultrasonic units. This design cannot take advantage of the yield control, complex wiring and large-scale production of integrated circuit technology. Introducing waveguide structures into the design of ultrasonic transducers can effectively improve the acoustic emission effect of the device and reduce crosstalk between units. However, the inventors have found that this technology is currently mainly for non-flexible transducers. At the same time, the waveguide structure has a large depth-to-width ratio, which has certain disadvantages in terms of processing and filling. In addition, the large waveguide length makes it easy to be damaged.

[0028] Based on this, embodiments of this application provide an ultrasonic transducer manufactured on a large scale using integrated circuit technology. The device has a special short waveguide structure, which improves the acoustic emission efficiency of the device, reduces crosstalk between units, and allows direct contact with the human body surface without damaging the vibrating units. Furthermore, the ultrasonic transducer can be a flexible structure for long-term real-time monitoring of superficial human organs, or function as a tactile sensor and actuator. This transducer can be fabricated using ultra-thin silicon wafers, thus meeting the requirements of flexible arrays.

[0029] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In the absence of conflict, the following embodiments and their technical features can be combined with each other.

[0030] Please refer to Figures 1 to 12 This is a schematic diagram of the manufacturing process of an ultrasonic transducer with a short waveguide structure according to an embodiment of the present invention.

[0031] Please refer to Figure 1 A first substrate 100 is provided, the first substrate 100 including a first support layer and a first device layer 103 formed on the surface of the first support layer.

[0032] The first device layer 103 can be made of semiconductor material to ensure compatibility with semiconductor processes and facilitate large-scale manufacturing. In other embodiments, the material of the first device layer 103 is not limited.

[0033] The thickness of the first device layer 103 determines the waveguide length of the final ultrasonic transducer. A suitable thickness of the first device layer 103 can be selected based on the designed waveguide length. Other parameters of the first device layer 103 are not limited.

[0034] Preferably, the thickness of the first device layer 103 is low. In the absence of the first support layer, the first device layer 103, due to its small thickness, possesses flexible characteristics such as being able to be rolled up and twisted, thus forming a flexible ultrasonic transducer with a short waveguide. Preferably, the thickness of the first device layer 103 is less than or equal to 100 micrometers, for example, in the range of 10 μm to 100 μm. During subsequent manufacturing processes, the first support layer provides mechanical support to the first device layer 103.

[0035] In this embodiment, the first support layer of the first substrate 100 includes a first substrate layer 101 and a first dielectric layer 102 located on the surface of the first substrate layer 101. Specifically, in this embodiment, the first substrate 100 is a silicon-on-insulator (SOI) wafer, the first substrate layer 101 is a silicon substrate layer, the first dielectric layer 102 is a buried oxide layer, and the first device layer 103 is a top semiconductor layer, i.e., a thin silicon layer on top. In other embodiments, the first substrate 100 may also be other semiconductor material structures with a similar sandwich structure. The thickness of the top silicon layer of an SOI wafer is typically 10 μm to 100 μm, exhibiting flexibility.

[0036] In some embodiments, an existing SOI wafer can be directly used as the first substrate 100. In other embodiments, buried oxide implantation can be performed directly on single-crystal silicon to form an insulating layer within the single-crystal silicon wafer to form the first substrate 100. Directly using a semiconductor material layer as the first substrate 100 is more compatible with subsequent integrated circuit manufacturing processes.

[0037] In some embodiments, the surface of the first substrate 100 may be subjected to thermal oxidation treatment before subsequent processes are performed.

[0038] In some implementations, the first device layer 103 may be an intrinsic material layer or have a low doping concentration. This is not limited here. Those skilled in the art can perform appropriate pretreatment on the first device layer 103 according to actual needs.

[0039] In other embodiments, the first substrate layer 101 may also be other rigid substrate materials, the first dielectric layer 102 may also be an adhesion layer, and the first device layer 103 may be a semiconductor material layer such as a silicon layer or a germanium silicon layer. The first device layer 103 is adhered to the first substrate layer 101 through the first dielectric layer 102, and the first substrate layer 101 provides mechanical support to provide sufficient mechanical strength during subsequent processes.

[0040] In other embodiments, the first support layer may also be a single-layer structure.

[0041] Please refer to Figure 2 The first device layer 103 is graphically visualized to form an opening 113 penetrating the first device layer 103.

[0042] The first device layer 103 is etched, with the first support layer as the etching stop layer, to form the opening 113, which exposes the first dielectric layer 102 inside the first support layer.

[0043] In this embodiment, the sidewall of the opening 113 is perpendicular to the surface of the first substrate 100, and the opening shape is circular. In other embodiments, the opening shape of the opening 113 can also be various shapes such as polygonal, rectangular, semi-circular, etc.; the sidewall of the opening 113 can also be various morphologies such as inclined sidewall, arc-shaped sidewall, or stepped sidewall. The sidewall morphology, opening shape, and other parameters of the opening 113 can be set according to the final waveguide parameter requirements, and are not limited here.

[0044] The first device layer 103 is relatively thin, resulting in a small depth-to-width ratio of the opening 113, and the etching process for forming the opening 113 is simple.

[0045] Please refer to Figure 3 A second substrate 200 is provided, the second substrate including a second support layer and a second device layer 203 located on the second support layer.

[0046] The material of the second device layer 203 can be a semiconductor material to ensure compatibility with semiconductor processes and facilitate large-scale manufacturing. In other embodiments, the material of the second device layer 203 is not limited.

[0047] The thickness of the second device layer 203 determines the resonant frequency of the final ultrasonic transducer. A suitable thickness for the second device layer 203 can be selected based on the design requirements for the resonant frequency. Other parameters of the second device layer 203 are not limited.

[0048] Preferably, the second device layer 203 has a low thickness. In the absence of the second support layer, the second device layer 203, due to its small thickness, possesses flexible characteristics such as being able to be rolled up and twisted, thus forming a flexible ultrasonic transducer with a short waveguide. Preferably, the thickness of the second device layer 203 is less than or equal to 100 micrometers, for example, in the range of 10 μm to 100 μm. During subsequent manufacturing processes, the second support layer provides mechanical support to the second device layer 203.

[0049] In this embodiment, the second support layer of the second substrate 200 includes a second substrate layer 201 and a second dielectric layer 202 located on the surface of the second substrate layer 201. Specifically, in this embodiment, the second substrate 200 is a silicon-on-insulator (SOI) wafer, the second substrate layer 201 is a silicon substrate layer, the second dielectric layer 202 is a buried oxide layer, and the second device layer 203 is the top semiconductor layer, i.e., the top thin silicon layer. In other embodiments, the second substrate 200 may also be other semiconductor material structures with a similar sandwich structure. The thickness of the top silicon layer of an SOI wafer is typically 10 μm to 100 μm, exhibiting flexibility.

[0050] In some embodiments, an existing SOI wafer can be directly used as the second substrate 200. In other embodiments, buried oxide implantation can be performed directly on the single-crystal silicon to form an insulating layer within the single-crystal silicon wafer to form the second substrate 200. Directly using a semiconductor material layer as the second substrate 200 is more compatible with subsequent integrated circuit manufacturing processes.

[0051] Similar to the structure of the first substrate 100, the second device layer 203 can be an intrinsic material layer or have a low doping concentration, which is not limited here. Those skilled in the art can perform appropriate pretreatment on the second device layer 203 according to actual needs.

[0052] In other embodiments, the second substrate layer 201 may also be other rigid substrate materials, the second dielectric layer 202 may also be an adhesion layer, and the second device layer 203 may be a semiconductor material layer such as a silicon layer or a germanium silicon layer. The second device layer 203 is adhered to the second substrate layer 201 through the second dielectric layer 202, and the second substrate layer 201 provides mechanical support to provide sufficient mechanical strength during subsequent processes.

[0053] In other embodiments, the second support layer may also be a single-layer structure.

[0054] Please refer to Figure 4 An isolation layer 301 is formed on the surface of the second device layer 203.

[0055] The isolation layer 301 can be made of an insulating dielectric material, such as silicon oxide, silicon nitride, or silicon oxynitride. The isolation layer 301 serves as an isolation layer between the first device layer 103 and the second device layer 203, and also acts as a bonding layer between the second device layer 203 and the first device layer 103, improving bonding stability. Furthermore, in some embodiments, the isolation layer 301 can also be stressed, acting as a stress buffer to prevent warping or other deformation problems in the morphology of the first device layer 103 and the second device layer 203 due to internal stress after the removal of the first and second support layers in subsequent processes, thus affecting the reliability of the final device.

[0056] In this embodiment, the material of the isolation layer 301 is silicon oxide, and a furnace tube thermal oxidation process is used. The isolation layer 301 is formed on the surface of both the second device layer 203 and the second substrate layer 201.

[0057] In other embodiments, a deposition process may be used to form the isolation layer 301 only on the surface of the second device layer 203.

[0058] Please refer to Figure 5 The second device layer 203 is oriented toward the first substrate 100 and bonded to the surface of the first device layer 103 through the isolation layer 301.

[0059] The second substrate 200 is bonded to the first substrate 100 by a bonding process, and appropriate bonding process parameters are selected according to the material of the bonding interface.

[0060] In this embodiment, the bonding interface is the contact surface between the isolation layer 301 and the first device layer 103, and the materials of the two are silicon oxide and silicon, respectively. Therefore, a silicon oxide-silicon bonding process is adopted.

[0061] In some embodiments, it may be unnecessary to form the isolation layer 301 on the surface of the second device layer 203, and instead the surfaces of the second device layer 203 and the second device layer 103 may be directly bonded using a silicon-silicon bonding process.

[0062] In some embodiments, an isolation layer may be formed on the surface of the first device layer 103 to bond the second device layer 203 to the isolation layer on the surface of the first device layer 103. Alternatively, the isolation layer may be formed on both the surface of the first device layer 103 and the surface of the second device layer 203 to form an isolation layer-isolation layer bonding interface.

[0063] Please refer to Figure 6 Remove the second support layer.

[0064] The second support layer is removed by one or a combination of processes such as dry etching, wet etching, and chemical mechanical polishing.

[0065] In this embodiment, during the removal of the second support layer, only the second substrate layer 201 is removed, while the second dielectric layer 202 is retained. Specifically, using the second dielectric layer 202 as a stop layer, the second substrate layer 201 and its surface isolation layer 301 are removed through mechanical thinning and chemical polishing, exposing the surface of the second dielectric layer 202, which greatly reduces the thickness of the device. The remaining second device layer 203 and its surface second dielectric layer 202 are relatively thin and have flexible characteristics. The remaining second dielectric layer 202 can serve as an isolation dielectric layer between the subsequently formed piezoelectric sensing unit and the second device layer 203.

[0066] In other embodiments, the second support layer may be completely removed. Before forming the piezoelectric sensing unit, an isolation dielectric layer is first formed on the surface of the second device layer 203, and then the piezoelectric sensing unit is formed on the surface of the isolation dielectric layer.

[0067] In other embodiments, the piezoelectric sensing unit can also be formed directly on the surface of the second device layer 203.

[0068] Please refer to Figure 7 A piezoelectric sensing unit 400 is formed on the side of the second device layer 203 away from the first device layer 103, and the position of the piezoelectric sensing unit is opposite to the position of the opening 113.

[0069] In this embodiment, the piezoelectric sensing unit 400 is formed on the surface of the second dielectric layer 202. The piezoelectric sensing unit 400 includes a bottom electrode 401, a functional thin film 402, and a top electrode 403 stacked sequentially from the second device layer 203 outwards. The bottom electrode 401 and the top electrode 402 can be made of conductive metal materials such as Pt, Au, and Cu. The functional thin film 402 can be made of a piezoelectric sensing material, which can be an organic piezoelectric thin film or an inorganic piezoelectric thin film; wherein the inorganic piezoelectric thin film can include: aluminum nitride (AlN) piezoelectric thin film, zinc oxide (ZnO) piezoelectric thin film, or lead zirconate titanate (PZT) piezoelectric thin film, etc.; the organic piezoelectric thin film can include: polyvinyl fluoride (PVF) piezoelectric thin film or polyvinylidene fluoride (PVDF) piezoelectric thin film, etc. The bottom electrode 401 extends outwards from the piezoelectric sensing unit 400 to provide a contact area for forming an outward electrical connection.

[0070] After sequentially depositing a bottom electrode material layer, a functional thin film material layer, and a top electrode material layer on the surface of the second dielectric layer 202, each material layer is patterned to form the bottom electrode 401, the functional thin film 402, and the top electrode 403 of the piezoelectric sensing unit 400. In this embodiment, while patterning the bottom electrode material layer to form the bottom electrode 401, a connecting electrode 404 located on the same layer as the bottom electrode 401 is also formed. The top electrode 403 is electrically connected to the connecting electrode 404. Preferably, the regions of the connecting electrode 404 and the bottom electrode 401 extending outward from the piezoelectric sensing unit are located on both sides of the piezoelectric sensing unit 400, respectively, to facilitate the subsequent formation of conductive pillars on both sides of the piezoelectric sensing unit 400.

[0071] The piezoelectric sensing unit 400 is positioned opposite the opening 113. Preferably, the piezoelectric sensing unit 400 is directly opposite the opening 113, and the orthographic projection of the functional thin film 402 in the direction towards the opening is located within the region of the opening 113. In other embodiments, the projections of the functional thin film 402 and the opening 113 in the direction perpendicular to the first device layer 103 at least partially overlap. The opening 113 serves as a waveguide, allowing ultrasonic waves generated by the vibration of the piezoelectric sensing unit 400 to be emitted outwards via the opening 113, and external ultrasonic waves to be transmitted to the piezoelectric sensing unit 400 via the opening 113. The opening 113, acting as a waveguide, improves both ultrasonic wave transmission and reception efficiency.

[0072] In some embodiments, a plurality of arrayed openings 113 may be formed within the first substrate 100. Correspondingly, a plurality of arrayed piezoelectric sensing units are formed on the second device layer 203 at positions opposite to each opening 113, thereby constituting a piezoelectric sensing unit array. Each piezoelectric sensing unit can be separated from each other, or they can be electrically connected. For example, there can be an electrical connection between the bottom electrodes of each piezoelectric sensing unit: all of them can be electrically connected; or they can be arranged in rows or columns, with the bottom electrodes of each row or column of sensing units electrically connected, and the rows or columns being independent of each other; or, there can also be an electrical connection between the top electrodes of each piezoelectric sensing unit: all of them can be electrically connected; or they can be arranged in rows or columns. Since each piezoelectric sensing unit corresponds to one opening 113, signal crosstalk between the piezoelectric sensing units can be reduced.

[0073] The multiple openings 113 formed in the first device layer 103 can all have the same shape and size, or different opening shapes and sizes can be designed for different regions to adjust the waveguide parameters of different regions.

[0074] In this embodiment, after forming the piezoelectric sensing unit 400, a passivation layer 410 is further formed covering the piezoelectric sensing unit 400. The passivation layer 410 completely covers the piezoelectric sensing unit 400 and the entire surface of the second dielectric layer 202.

[0075] In other embodiments, the passivation layer 410 may also expose the top electrode 403 to facilitate the formation of an electrical connection with the top electrode 403 in subsequent processes.

[0076] The passivation layer 410 can be made of insulating dielectric materials such as silicon oxide and silicon nitride, which serve as electrical isolation and protection.

[0077] Subsequently, the first support layer can be removed to expose the opening 113, forming an ultrasonic transducer. The opening 113 serves as the waveguide of the ultrasonic transducer, playing a role in beamforming and shielding interference for the transmission and reception of ultrasonic waves.

[0078] Furthermore, in this embodiment, an electrical connection structure with the piezoelectric sensing unit 400 is further formed before the first support layer is removed.

[0079] Please refer to Figure 8 A through-hole is formed penetrating the passivation layer 410; the through-hole is filled with conductive material to form a conductive pillar electrically connected to the piezoelectric sensing unit.

[0080] Specifically, in this embodiment, a first through-hole and a second through-hole are formed on both sides of the piezoelectric sensing unit. The bottom of the first through-hole exposes the extension area of ​​the bottom electrode 401, and the bottom of the second through-hole exposes the connecting electrode 404. Then, through processing techniques such as electroplating, a conductive material is formed that fills the first through-hole, the second through-hole, and covers the surface of the passivation layer 410. The conductive material is patterned to form a first conductive pillar 411 located in the first through-hole and a second conductive pillar 412 located in the second through-hole. The bottom of the first conductive pillar 411 is connected to the bottom electrode 401, and the bottom of the second conductive pillar 412 is connected to the connecting electrode 404. The connecting electrode 404 is electrically connected to the top electrode 403.

[0081] Since the bottom electrode 401 and the connecting electrode 404 are located on the same layer, the first through-hole and the second through-hole have the same depth. This allows for simultaneous formation of both through-holes in a single etching process, reducing manufacturing complexity. Because the top electrode 403 has a limited size, directly forming through-holes on it would require precise alignment. Using the connecting electrode 404 as the lead-out electrode of the top electrode 403 allows for a larger connecting electrode 404, reducing the alignment accuracy requirements for the second through-hole and further simplifying the manufacturing process.

[0082] In other embodiments, it may be unnecessary to form the connecting electrode 404, and a second through hole may be formed directly on the top electrode 403 to form a conductive post directly connected to the top electrode 403.

[0083] In this embodiment, the tops of the first conductive pillar 411 and the second conductive pillar 412 are both higher than the top of the passivation layer 410.

[0084] Please refer to Figure 9 This is a top view schematic diagram of the first conductive post 411 and the second conductive post 412 formed in one embodiment.

[0085] Figure 9 To illustrate the relative positions of the various parts, only some of the material layers are shown, and this is not a strictly top-view diagram of the structure.

[0086] like Figure 9 As shown, in this embodiment, a plurality of piezoelectric sensing units (represented by functional thin films 401) are formed on the second device layer 203. In this embodiment, the functional thin film 401 of the piezoelectric sensing unit is circular. The first conductive post 411 and the second conductive post 412 are located on both sides of the piezoelectric sensing unit and are symmetrically distributed. Furthermore, in this embodiment, the cross-sections of the first conductive post 411 and the second conductive post 412 are both arc-shaped and located on the same circumference.

[0087] In other embodiments, the first conductive post 411 and the second conductive post 412 may also be cylinders or polygonal prisms, with corresponding cross-sections of circles, polygons, etc.

[0088] In other embodiments, the cross-sections of the first conductive post 411 and the second conductive post 412 are preferably elongated, arc-shaped, or other shapes, so that the side wall areas of the first conductive post 411 and the second conductive post 412 are large, which can form a cylindrical cavity around the piezoelectric sensing unit, which is beneficial to improving the efficiency of the ultrasonic transducer.

[0089] Please refer to Figure 10The top of the conductive post is bonded to a circuit layer 500, and the conductive post is electrically connected to the circuit layer 500.

[0090] The circuit layer 500 can be a circuit board or a dedicated integrated circuit chip, etc. The surface of the circuit layer 500 has connection pads 501, which can be used to fix the first conductive post 411 and the second conductive post 412 to the corresponding connection pads 501 on the circuit layer 500 through metal bonding, soldering, or other methods. The connection pads 501 can be solder pads, metal bumps, etc. The circuit layer 500 contains connection lines or functional circuits, and the connection pads 501 are connected to the connection lines or functional circuits inside the circuit layer 500.

[0091] The circuit layer 500 is supported by the first conductive pillar 411 and the second conductive pillar 412, and a cavity 502 is formed between the circuit layer 500 and the passivation layer 410, which serves as a cavity to provide vibration space for the piezoelectric sensing unit.

[0092] In some embodiments, the circuit layer 500 is a circuit board with internal electrical connection lines. The first conductive post 411 and the second conductive post 412 electrically lead out the top electrode 403 and the bottom electrode 401 of the piezoelectric sensing unit 400 and electrically connect them to the circuit layer 500 to achieve signal transmission. In some embodiments, the distribution of electrical connection lines within the circuit layer 500 can also achieve a redistribution of the electrical pins of the piezoelectric sensing unit 400. The circuit layer 500 can also be connected to a processor, control unit, etc., to realize the processing of sensing signals and the transmission of control signals.

[0093] In other embodiments, a functional circuit is formed within the circuit layer 500, which can be an analog or logic circuit. In one embodiment, the circuit layer 500 is an ASIC chip. The circuit layer 500 is connected to the piezoelectric sensing unit 400 through the first conductive post 411 and the second conductive post 412. The circuit layer 500 can directly send control signals to the piezoelectric sensing unit 400 and perform calculations and processing on the sensing signals generated by the piezoelectric sensing unit 400, which can effectively reduce the size of the ultrasonic transducer and is more suitable for application in small electronic devices, such as wearable devices.

[0094] In this embodiment, the circuit layer 500 includes a flexible substrate and electrical connection lines or functional circuits formed on the surface, inside, or both the surface and inside of the flexible substrate. The circuit layer 500 also possesses flexibility, resulting in a flexible overall structure for the final ultrasonic transducer, allowing for better conformity to the object being measured during sensing and detection. For example, the circuit layer 500 can be a flexible printed circuit board (FPCB) or a flexible CMOS circuit layer. The flexible CMOS circuit layer includes a flexible substrate and a CMOS circuit formed on the flexible substrate. The CMOS circuit can be an analog and / or logic circuit, such as an ASIC circuit.

[0095] After fixing the first conductive post 411 and the second conductive post 412 to the circuit layer 500, a buffer medium can be further filled into the cavity 502. In some embodiments, the gas in the cavity 502, such as air, is used directly as the buffer medium; in other embodiments, the cavity 502 can be filled with a flexible dielectric material such as a colloid or polydimethylsiloxane (PDMS). By filling the cavity 502 with a buffer medium, on the one hand, it can play an adhesive role, strengthening the connection reliability between the circuit layer 500 and the conductive post; on the other hand, by adjusting the elastic parameters of the buffer medium, such as Young's modulus and density, the operating frequency and other parameter characteristics of the ultrasonic transducer can be adjusted.

[0096] Please refer to Figure 11 Remove the first support layer to expose the opening 113, which serves as a waveguide.

[0097] In this implementation, Figure 10 After the structure shown is flipped, the first substrate layer 101 and the first dielectric layer 102 are removed by mechanical thinning and chemical polishing, exposing the first device layer 103 and the opening 113 formed in the first device layer 103. During the operation of the ultrasonic transducer, the opening 113 faces the object being tested. The opening 113 acts as a waveguide for ultrasonic signals, playing a role in beamforming the transmitted or received ultrasonic signals, which can improve the acoustic emission efficiency of the device, reduce crosstalk between units, and improve the transduction efficiency of the ultrasonic transducer. Furthermore, each piezoelectric sensing unit 400 corresponds one-to-one with the opening 113 and has an independent waveguide structure, which can reduce signal crosstalk between units and improve the detection accuracy of the ultrasonic transducer when used for ultrasonic testing.

[0098] Since the thickness of the first device layer 103 is small and the thickness of the opening 113 is small, the structure can be formed by etching with a small aspect ratio. The processing technology is simple. As a waveguide, the length is short, which can reduce signal transmission loss and is not easily damaged.

[0099] The opening 113 can remain unfilled, with the gas inside the opening serving as the waveguide medium. In other embodiments, to further improve the waveguide's performance, the opening 113 can be further filled with a waveguide medium.

[0100] Please refer to Figure 12 The opening is filled with waveguide medium 1131.

[0101] The waveguide medium 1131 is preferably an acoustic impedance matching material, which can be polydimethylsiloxane (PDMS), colloid or other flexible material. The waveguide parameters, such as dispersion characteristics, loss, field distribution, etc., can be adjusted by adjusting the elastic parameters of the waveguide medium, such as Young's modulus, density, etc., thereby adjusting the performance parameters of the ultrasonic transducer.

[0102] When the ultrasonic transducer is used for human ultrasound detection, the waveguide medium generally needs to be biocompatible with the human body and have an acoustic impedance close to that of the human body.

[0103] In other embodiments, the waveguide parameters can be altered by adjusting the shape of the opening. For example, a resonant cavity can be formed by limiting the depth of the opening, i.e., the length of the short waveguide, and the resonant cavity can be used to output pressure or measure external pressure, thereby enabling the ultrasonic transducer to function as a tactile sensor-actuator.

[0104] Please refer to Figure 13 This is a schematic diagram of an ultrasonic transducer with a horn-shaped waveguide according to an embodiment of the present invention. In this embodiment, the opening formed in the first device layer 103 has inclined sidewalls and a certain opening angle. The overall cross-section has an expanding trend, that is, the size of one end facing the piezoelectric sensing unit is smaller than the size of the other end, forming a horn shape. The larger side is used to face the object being detected, thereby expanding the sound field of the emitted and received ultrasonic waves.

[0105] In other embodiments, the opening may have other shapes, such as stepped, etc., which are not limited here.

[0106] The above-described method for forming ultrasonic transducers allows for the large-scale fabrication of ultrasonic transducers using integrated circuit technology. These transducers can be fabricated using ultra-thin device layers, thus meeting the requirements of flexible arrays. This enables the formation of flexible ultrasonic transducers for long-term real-time monitoring of superficial human organs, or for use as tactile sensors and actuators. Furthermore, this ultrasonic transducer features a special short waveguide structure. This structure improves the acoustic emission efficiency of the device, reduces crosstalk between units, and, located between the object under test and the piezoelectric sensing unit, directly contacts the object. During the detection process, the short waveguide structure acts as a buffer and protector, preventing damage to the piezoelectric sensing unit.

[0107] An embodiment of this application also provides an ultrasonic transducer with a short waveguide structure.

[0108] Please refer to Figure 11 This is a schematic diagram of the structure of an ultrasonic transducer according to an embodiment of the present invention.

[0109] In this embodiment, the ultrasonic transducer includes: a first device layer 103 with an opening 113 penetrating through the first device layer 103; an isolation layer 301 located on one side surface of the first device layer 103, the isolation layer 301 closing one end of the opening 113; a second device layer 203 located on the surface of the isolation layer 301; and a piezoelectric sensing unit 400 located on the side of the second device layer 203 facing away from the first device layer 103, the piezoelectric sensing unit 400 being positioned opposite to the opening 113.

[0110] The materials of the first device layer 103 and the second device layer 203 can be semiconductor materials to ensure compatibility with semiconductor processes and facilitate large-scale manufacturing. In other embodiments, the materials of the first device layer 103 and the second device layer 203 are not limited.

[0111] The thickness of the first device layer 103 determines the waveguide length of the final ultrasonic transducer. A suitable thickness of the first device layer 103 can be selected based on the designed waveguide length. Other parameters of the first device layer 103 are not limited.

[0112] Preferably, the first device layer 103 and the second device layer 203 have a low thickness and flexible characteristics such as being able to be rolled up and twisted, so that the ultrasonic transducer has flexible characteristics and can be used in wearable devices, etc. Preferably, the thickness of the first device layer 103 and the second device layer 203 is less than or equal to 100 micrometers, for example, in the range of 10 μm to 100 μm.

[0113] Preferably, the first device layer 103 and the second device layer 203 can be the top semiconductor layer of a silicon-on-insulator (SOI) wafer, obtained by removing the substrate layer and buried oxide layer of the SOI wafer.

[0114] The first device layer 103 and the second device layer 203 can be intrinsic material layers or have a low doping concentration, which is not limited here. Those skilled in the art can perform appropriate pretreatment on the first device layer 103 and the second device layer 203 according to actual needs.

[0115] In this embodiment, the sidewall of the opening 113 is perpendicular to the surface of the first device layer 103, and the opening shape is circular. In other embodiments, the opening shape of the opening 113 can also be polygonal, rectangular, semi-circular, or other shapes; the sidewall of the opening 113 can also be inclined, arc-shaped, or stepped, or other shapes. The sidewall morphology, opening shape, and other parameters of the opening 113 can be set according to the final waveguide parameter requirements, and are not limited here.

[0116] The isolation layer 301 can be made of an insulating dielectric material, such as silicon oxide, silicon nitride, or silicon oxynitride. The isolation layer 301 serves as an isolation layer between the first device layer 103 and the second device layer 203, and also acts as a bonding layer between the second device layer 203 and the first device layer 103, improving bonding stability. Furthermore, in some embodiments, the isolation layer 301 can also be stressed, acting as a stress buffer to prevent warping or other deformation problems in the morphology of the first device layer 103 and the second device layer 203 due to internal stress after the removal of the first and second support layers in subsequent processes, thus affecting the reliability of the final device.

[0117] In this embodiment, the piezoelectric sensing unit 400 includes a bottom electrode 401, a functional thin film 402 and a top electrode 403 stacked sequentially from the second device layer 203 outwards, and the bottom electrode 401 extends outwards from the piezoelectric sensing unit 400.

[0118] In this embodiment, the surface of the second device layer 203 also has a second dielectric layer 202, and the piezoelectric sensing unit 400 is formed on the surface of the second dielectric layer 202.

[0119] In this embodiment, Figure 11The diagram shows only a single piezoelectric sensing unit and its corresponding single opening 113. In some embodiments, multiple arrayed openings 113 may be formed within the first substrate 100. Correspondingly, multiple arrayed piezoelectric sensing units are formed on the second device layer 203 at positions opposite to each opening 113, thereby constituting a piezoelectric sensing unit array. Each piezoelectric sensing unit can be separated from the others, or they can be electrically connected. For example, there can be an electrical connection between the bottom electrodes of each piezoelectric sensing unit; or, there can be an electrical connection between the top electrodes of each piezoelectric sensing unit. Since each piezoelectric sensing unit corresponds to one opening 113, signal crosstalk between the piezoelectric sensing units can be reduced. Furthermore, the multiple openings 113 formed within the first device layer 103 can all have the same morphology and size, or different opening morphologies and sizes can be designed for different regions to adjust the waveguide parameters of different regions.

[0120] In this embodiment, in addition to the bottom electrode 401, the surface of the second dielectric layer 202 also has a connecting electrode 404 located on the same layer as the bottom electrode 401, and the connecting electrode 404 is electrically connected to the top electrode 403.

[0121] The ultrasonic transducer further includes: a passivation layer 410 located on the second device layer 203 and covering the piezoelectric sensing unit 400, and a conductive post penetrating the passivation layer 410, the conductive post being electrically connected to the piezoelectric sensing unit 400; the top of the conductive post being fixedly connected to a circuit layer 500, and the conductive post being electrically connected to the circuit layer 500.

[0122] Specifically, in this embodiment, the conductive post includes a first conductive post 411 and a second conductive post 412 located on both sides of the piezoelectric sensing unit 400. The bottom of the first conductive post 411 is connected to the extension area of ​​the bottom electrode 401, and one end of the second conductive post 412 is connected to the connecting electrode 404, thereby realizing the electrical connection between the upper and lower electrodes of the piezoelectric sensing unit.

[0123] Preferably, the first conductive post 411 and the second conductive post 412 are symmetrically distributed around the piezoelectric sensing unit 400. Further, the tops of the first conductive post 411 and the second conductive post 412 are higher than the top of the passivation layer 410; the tops of the conductive posts are bonded to the surface of the circuit layer 500, forming a cavity 502 between the circuit layer 500 and the passivation layer 410, serving as a cavity to provide vibration space for the piezoelectric sensing unit.

[0124] Preferably, the cavity 502 may be filled with a buffer medium, such as a flexible medium like colloid or PDMS. On the one hand, this can act as an adhesive, enhancing the reliability of the connection between the circuit layer 500 and the conductive pillars. On the other hand, the operating frequency and other parameters of the ultrasonic transducer can be adjusted by adjusting the elastic parameters of the buffer medium, such as Young's modulus and density.

[0125] The circuit layer 500 can be a circuit board or a dedicated integrated circuit chip, etc. The surface of the circuit layer 500 has connection pads 501, which can be used to fix the first conductive post 411 and the second conductive post 412 to the corresponding connection pads 501 on the circuit layer 500 through metal bonding, soldering, or other methods. The connection pads 501 can be solder pads, metal bumps, etc. The circuit layer 500 contains connection lines or functional circuits, and the connection pads 501 are connected to the connection lines or functional circuits inside the circuit layer 500.

[0126] In some embodiments, the circuit layer 500 is a circuit board with internal electrical connection lines. The first conductive post 411 and the second conductive post 412 electrically lead out the top electrode 403 and the bottom electrode 401 of the piezoelectric sensing unit 400 and electrically connect them to the circuit layer 500 to achieve signal transmission. In some embodiments, the distribution of electrical connection lines within the circuit layer 500 can also achieve a redistribution of the electrical pins of the piezoelectric sensing unit 400. The circuit layer 500 can also be connected to a processor, control unit, etc., to realize the processing of sensing signals and the transmission of control signals.

[0127] In other embodiments, a functional circuit is formed within the circuit layer 500, which can be an analog or logic circuit. In one embodiment, the circuit layer 500 is an ASIC chip. The circuit layer 500 is connected to the piezoelectric sensing unit 400 through the first conductive post 411 and the second conductive post 412. The circuit layer 500 can directly send control signals to the piezoelectric sensing unit 400 and perform calculations and processing on the sensing signals generated by the piezoelectric sensing unit 400, which can effectively reduce the size of the ultrasonic transducer and is more suitable for application in small electronic devices, such as wearable devices.

[0128] In this embodiment, the circuit layer 500 includes a flexible substrate and electrical connection lines or functional circuits formed on the surface, inside, or both the surface and inside of the flexible substrate. The circuit layer 500 also possesses flexibility, resulting in a flexible overall structure for the final ultrasonic transducer, allowing for better conformity to the object being measured during sensing and detection. For example, the circuit layer 500 can be a flexible printed circuit board (FPCB) or a flexible CMOS circuit layer. The flexible CMOS circuit layer includes a flexible substrate and a CMOS circuit formed on the flexible substrate. The CMOS circuit can be an analog and / or logic circuit, such as an ASIC circuit.

[0129] Please refer to Figure 12 This is a schematic diagram of an ultrasonic transducer according to another embodiment of the present invention. In this embodiment, the opening is filled with waveguide medium 1131.

[0130] The waveguide medium 1131 is preferably an acoustic impedance matching material, which can be polydimethylsiloxane (PDMS), colloid or other flexible material. The waveguide parameters, such as dispersion characteristics, loss, field distribution, etc., can be adjusted by adjusting the elastic parameters of the waveguide medium, such as Young's modulus, density, etc., thereby adjusting the performance parameters of the ultrasonic transducer.

[0131] When the ultrasonic transducer is used for human ultrasound detection, the waveguide medium generally needs to be biocompatible with the human body and have an acoustic impedance close to that of the human body.

[0132] In other embodiments, the waveguide parameters can be altered by adjusting the shape of the opening. For example, a resonant cavity can be formed by limiting the depth of the opening, i.e., the length of the short waveguide, and the resonant cavity can be used to output pressure or measure external pressure, thereby enabling the ultrasonic transducer to function as a tactile sensor-actuator.

[0133] Please refer to Figure 13 This is a schematic diagram of the structure of an ultrasonic transducer according to another embodiment of the present invention. In this embodiment, the opening formed in the first device layer 103 has inclined sidewalls and a certain opening angle. The overall cross-section has an expanding trend, that is, the size of one end facing the piezoelectric sensing unit is smaller than the size of the other end, forming a horn shape. The larger side is used to face the object being detected, thereby expanding the sound field of the emitted and received ultrasonic waves.

[0134] Ultrasonic transducers also feature a special short waveguide structure, which can improve the acoustic emission efficiency of the device and reduce crosstalk between units. This structure can be fabricated using ultra-thin device layers to meet the requirements of flexible arrays, thereby forming flexible ultrasonic transducers for long-term real-time detection of superficial human organs or for use as tactile sensors and actuators. Furthermore, the short waveguide structure can effectively increase the frequency of flexible devices.

[0135] Embodiments of the present invention also provide an ultrasonic testing device, comprising: an ultrasonic transducer manufactured using the manufacturing method described in any of the above embodiments; or, comprising the ultrasonic transducer described in any of the above embodiments. The ultrasonic transducer has flexible characteristics and can be used as a probe for ultrasonic testing, or integrated into a wearable device, and is particularly suitable for testing flexible structures.

[0136] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, such as the combination of technical features between embodiments, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for manufacturing an ultrasonic transducer with a short waveguide structure, characterized in that, include: A first substrate is provided, the first substrate including a first support layer and a first device layer formed on the surface of the first support layer; The first device layer is graphically represented to form an opening that penetrates the first device layer; A second substrate is provided, the second substrate including a second support layer and a second device layer located on the second support layer; The second device layer is oriented toward the first substrate and bonded to the surface of the first device layer; Remove the second support layer and form a piezoelectric sensing unit on the side of the second device layer away from the first device layer, with the piezoelectric sensing unit positioned opposite the opening. Remove the first support layer to expose the opening, which serves as a waveguide; The opening is filled with waveguide medium.

2. The method for manufacturing an ultrasonic transducer according to claim 1, characterized in that, The manufacturing method further includes: after forming the piezoelectric sensing unit and before removing the first support layer, forming a passivation layer covering the piezoelectric sensing unit; forming a through hole located in the passivation layer, filling the through hole with conductive material to form a conductive pillar, the conductive pillar being electrically connected to the piezoelectric sensing unit.

3. The method for manufacturing an ultrasonic transducer according to claim 2, characterized in that, The method of forming the piezoelectric sensing unit includes: A bottom electrode material layer, a functional thin film layer, and a top electrode material layer are stacked sequentially from the second device layer outwards; the top electrode material layer, the functional thin film layer, and the bottom electrode material layer are patterned sequentially to form a bottom electrode, a functional thin film, and a top electrode stacked sequentially from the second device layer outwards, with the bottom electrode extending outwards from the piezoelectric sensing unit; and, while patterning the bottom electrode material layer to form the bottom electrode, a connecting electrode located on the same layer as the bottom electrode is formed; The method for forming a through-hole located within the passivation layer and filling the through-hole with conductive material to form a conductive pillar includes: forming a first through-hole and a second through-hole penetrating the passivation layer, wherein a portion of the bottom electrode is exposed at the bottom of the first through-hole and a portion of the connection electrode is exposed at the bottom of the second through-hole; filling the first through-hole and the second through-hole with conductive material to form a first conductive pillar electrically connected to the bottom electrode and a second conductive pillar electrically connected to the connection electrode; and simultaneously fixing the tops of the first conductive pillar and the second conductive pillar to the circuit layer, wherein both the first conductive pillar and the second conductive pillar are electrically connected to the circuit layer.

4. The method for manufacturing an ultrasonic transducer according to claim 3, characterized in that, The first and second through holes are symmetrically distributed around the piezoelectric sensing unit, and the tops of the first and second conductive pillars are higher than the top of the passivation layer; after the tops of the first and second conductive pillars are fixed to the surface of the circuit layer, a cavity is formed between the circuit layer and the passivation layer.

5. The method for manufacturing an ultrasonic transducer according to claim 1, characterized in that, The second support layer includes: a second substrate layer and a second dielectric layer located on the surface of the second substrate layer; during the removal of the second support layer, only the second substrate layer is removed; the piezoelectric sensing unit is formed on the surface of the second dielectric layer; or, The manufacturing method further includes: after removing the second support layer, forming a second dielectric layer on the surface of the second device layer, and then forming the piezoelectric sensing unit on the surface of the second dielectric layer.

6. The method for manufacturing an ultrasonic transducer according to claim 5, characterized in that, Multiple arrayed openings are formed in the first device layer, and multiple arrayed piezoelectric sensing units are formed on the surface of the second dielectric layer, wherein each piezoelectric sensing unit corresponds to one of the openings. And / or, both the first substrate and the second substrate are SOI wafers, and both the first device layer and the second device layer are the top semiconductor layers of the SOI wafer; And / or, the thickness of the first device layer is less than or equal to 100 micrometers, and the thickness of the second device layer is less than or equal to 100 micrometers.

7. The method for manufacturing an ultrasonic transducer according to claim 3, characterized in that, The circuit layer includes a flexible substrate and electrical connection lines or functional circuits formed on / inside the surface of the flexible substrate.

8. An ultrasonic transducer with a short waveguide structure, characterized in that, It is manufactured by the ultrasonic transducer manufacturing method according to any one of claims 1-7.

9. An ultrasonic testing device, characterized in that, include: An ultrasonic transducer manufactured using the manufacturing method as described in any one of claims 1 to 7; Alternatively, the ultrasonic transducer as described in claim 8.

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