Ultrasound transducer, method of manufacture and multi-modal wearable monitoring device

Abstract

The application provides a method for preparing an ultrasonic transducer for transparent rigid piezoelectric material. The method first cuts from the piezoelectric layer side of the piezoelectric wafer with a transparent matching layer, leaving a certain thin layer without cutting through completely, to provide overall mechanical support and ensure that the array elements are arranged at a predetermined interval. Then, a transparent organic elastic material is injected into the array element gap, and the support after solidification further fixes the array element position to realize precise bonding of high-density array elements and flexible circuit electrodes. In the subsequent cutting through of the remaining thin layer, the array elements are effectively supported by the transparent elastic material and are not easily damaged, thereby significantly improving the process reliability and array element yield. The method effectively protects the brittle piezoelectric material and supports the manufacture of high-density, large-array flexible arrays. The obtained device realizes high flexibility with the aid of the transparent elastic material in the array element gap and the flexible circuit; and high sensitivity ultrasonic performance is obtained through the design of the double-layer matching layer and the backing.

Description

Technical Field

[0001] This application relates to the field of wearable technology, and in particular to an ultrasonic transducer, its preparation method, and a multimodal wearable monitoring device. Background Technology

[0002] In the field of wearable health monitoring, developing flexible patch-type devices capable of long-term, continuous, and non-invasive acquisition of deep tissue structure, function, and molecular information of the human body is a key development direction for achieving proactive health management, dynamic monitoring of disease progression, and precise tracking of the rehabilitation process. The development of flexible patches that integrate sound and light in a multimodal manner is considered an ideal technological route to achieve this goal.

[0003] The current best technical solution employs a compact integrated design (coaxial, same field of view) of optical sensing units and transparent ultrasonic transducer arrays, which is the core solution for realizing high-performance acousto-optic fusion multimodal devices. This solution effectively improves imaging quality and efficiency by significantly shortening the light / acoustic propagation path, eliminating unilluminated areas, reducing light-acoustic alignment errors, and minimizing data redundancy. Building upon this solution, developing a flexible ultrasonic transducer array with high transparency is a key step in advancing this technology towards a more compact, precise, portable, multifunctional, and truly wearable form.

[0004] However, existing ultrasonic array technology faces severe challenges: (1) Material and morphological limitations. Traditional rigid, opaque ultrasonic arrays cannot conform to the curved surface of the human body, and are prone to unstable acoustic coupling and motion artifacts due to body surface movement, and seriously block or interfere with the optical channel, failing to meet the requirements of comfort, stability and optical compatibility for long-term continuous monitoring. (2) Performance limitations of flexible arrays. The element density of existing flexible ultrasonic arrays is insufficient (the element spacing is generally too large), making it difficult to meet the requirements of high-resolution beamforming and limiting the imaging resolution. (3) Bottleneck in the fabrication of high-survival-rate, high-density transparent flexible arrays. Due to the significant differences in physical / mechanical properties between rigid piezoelectric materials and flexible circuits, as well as the high-density integration scale, it is extremely challenging to establish a high-precision, high-reliability electrical interconnection between the two with one-to-one channel correspondence.

[0005] Therefore, overcoming the bottlenecks in acoustic-optical fusion flexible patch technology urgently requires: developing high-density, high-survival-rate, multi-channel transparent flexible ultrasonic transducer arrays, and simultaneously overcoming challenges in the collaborative design of high-transparency heterogeneous material systems, innovative structural design and stretchable interconnection schemes, high-precision fabrication processes, and stable and reliable flexible packaging technology. Summary of the Invention

[0006] In view of this, the present invention provides an ultrasonic transducer, a preparation method, and a multimodal wearable monitoring device, so as to provide an ultrasonic transducer with high density, high survival rate, and multiple channels.

[0007] To solve the above problems, this application adopts the following technical solution: One objective of this application is to provide a method for manufacturing an ultrasonic transducer, comprising the following steps: A first transparent electrode layer and a second transparent electrode layer are formed on the upper and lower surfaces of the transparent piezoelectric material layer, respectively. A transparent matching layer is formed on the upper surface of the first transparent electrode layer; The transparent piezoelectric wafer is cut from one side of the transparent piezoelectric material layer according to a preset linear array element spacing. wear Alternatively, most of the transparent piezoelectric material layer can be cut off, leaving a thin layer containing a transparent matching layer that is not cut or not cut through, thereby forming an array of transparent piezoelectric wafers that are still connected through the thin layer; An organic transparent elastic material is filled between each individual element in the transparent piezoelectric wafer; The positive and negative electrodes of the flexible circuit layer are bonded to the positive and negative electrodes of the transparent piezoelectric wafer; The remaining thin layer with the transparent matching layer is cut from one side of the matching layer according to the preset linear array element spacing, and it is ensured that the thin layer is completely cut through to form an array unit composed of multiple independent transparent piezoelectric wafer piezoelectric transducers. The gaps between the cut thin layers are filled with an organic transparent elastic material; The ultrasonic transducer is obtained by bonding a transparent flexible backing layer to the lower surface of the flexible circuit layer.

[0008] In some embodiments, the following step is also included: polishing the surface of the transparent piezoelectric material layer to form the polished transparent piezoelectric material layer.

[0009] In some embodiments, the method further includes the following steps: chamfering one wide edge of the polished transparent piezoelectric material layer and forming an electrode edging on this side to interconnect the upper and lower surface electrodes so that subsequent processes can lead the positive and negative electrodes to this side together.

[0010] In some embodiments, in the step of polishing the surface of the transparent piezoelectric material layer to form the polished transparent piezoelectric material layer, the transparent piezoelectric material layer includes lithium niobate crystal, transparent piezoelectric ceramic, or single crystal.

[0011] In some embodiments, in the step of forming a first transparent electrode layer and a second transparent electrode layer on the upper and lower surfaces of the transparent piezoelectric material layer, the first transparent electrode layer and the second transparent electrode layer include transparent electrodes, the transparent electrodes including oxide transparent electrodes, ultrathin metal mesh / nanowires or transparent conductive films, the oxide transparent electrodes including ITO, FTO or AZO, the ultrathin metal mesh / nanowires including silver nanowires or copper nanowires, and the transparent conductive film including PET with TCO.

[0012] In some embodiments, in the step of forming a transparent matching layer on the upper surface of the first transparent electrode layer, the transparent matching layer is a bilayer structure. The material of the transparent matching layer includes a transparent inorganic material with high acoustic impedance and a transparent polymer with low acoustic impedance. The transparent inorganic material includes quartz glass or colorless optical glass, and the transparent polymer includes epoxy resin, polymethyl methacrylate resin, polystyrene, parylene, polyurethane, transparent polyurethane, and dimethylsiloxane.

[0013] In some embodiments, the transparent piezoelectric wafer is cut from one side of the transparent piezoelectric material layer according to a preset linear array element spacing, cutting through or removing most of the transparent piezoelectric material layer, leaving a thin layer containing the transparent matching layer uncut or not cut through, thereby forming an array of transparent piezoelectric wafers still connected by the thin layer; including: before cutting the array elements, a high-precision dicing machine is used to perform a shallow pre-cut, the direction of which is perpendicular to the subsequent array element cut and close to the electrode edge side, to achieve separation of the positive and negative electrodes.

[0014] In some embodiments, the organic transparent elastic material includes PDMS, 732 glass glue, 734 glass glue, and 705 silicone rubber; the adhesive used for bonding includes epoxy resin and acrylic resin.

[0015] In some embodiments, in the step of bonding a transparent flexible backing layer to the lower surface of the flexible circuit layer to obtain the ultrasonic transducer, the transparent backing layer is a single-layer structure, and the material of the transparent backing layer includes a transparent organic polymer, such as silicone, polydimethylsiloxane (PDMS), or polyurethane elastomer. In some embodiments, the substrate material of the flexible circuit layer includes transparent polyimide (PI) or transparent PET, and the electrodes of the flexible circuit layer include metal electrodes or transparent electrodes. The flexible circuit layer can be bonded to the conductive channels of the electrode layers of independent array elements through one or more circuits; each circuit can adopt a single-layer or multi-layer electrode layer structure.

[0016] The second objective of this application is to provide an ultrasonic transducer, comprising: Transparent piezoelectric material layer; A first transparent electrode layer is formed on the upper surface of the transparent piezoelectric material layer; A second transparent electrode layer is formed on the lower surface of the transparent piezoelectric material layer; A transparent matching layer formed on the upper surface of the first transparent electrode layer; A transparent piezoelectric wafer is cut from one side of a transparent piezoelectric material layer according to a predetermined linear array element spacing, cutting through or removing most of the transparent piezoelectric material layer, leaving a thin layer containing a transparent matching layer uncut or partially cut, thereby forming an array of transparent piezoelectric wafers still connected by this thin layer. An organic transparent elastic material is then filled between the elements in the transparent piezoelectric wafer.

[0017] A flexible circuit layer is formed by bonding the positive and negative electrodes of the flexible circuit layer to the positive and negative electrodes of the transparent piezoelectric wafer. A transparent ultrasonic transducer is constructed by cutting the residual thin layer with a transparent matching layer from one side of the matching layer according to a preset linear array element spacing, ensuring that the thin layer is completely cut through, to form an array unit composed of multiple independent transparent piezoelectric crystal piezoelectric transducers; organic transparent elastic material is filled in the gap between the thin layer cut through the transparent piezoelectric crystal and the corresponding transparent piezoelectric transducer. A transparent flexible backing layer is bonded to the lower surface of the flexible circuit layer.

[0018] The third objective of this application is to provide a multimodal wearable monitoring device, including the aforementioned ultrasonic transducer.

[0019] The present application adopts the above technical solution, and its beneficial effects are as follows: The ultrasonic transducer fabrication method provided in this application first cuts a piezoelectric wafer with a transparent matching layer from one side of the piezoelectric layer, leaving a thin layer intact without completely cutting through it. This provides overall mechanical support and ensures that the array elements are arranged at a preset spacing. Then, a transparent organic elastic material is poured into the gaps between the array elements. The solidified material further fixes the array element positions, achieving precise bonding between the high-density array elements and flexible circuit electrodes. In the subsequent cutting through of the remaining thin layer, the array elements are effectively supported by the transparent elastic material, making them less susceptible to damage, thus significantly improving process reliability and array element yield. This method effectively protects the brittle piezoelectric material and supports the fabrication of high-density, large-array-number flexible arrays. Combined with a double matching layer and backing, it ensures high-sensitivity ultrasonic performance. Furthermore, the transparency of the entire material system allows the ultrasonic channel and optical channel to be completely coaxial and in the same field of view, without obstruction or blind spots, perfectly supporting the real-time fusion of ultrasonic imaging, photoacoustic imaging, and optical imaging (such as optical coherence tomography).

[0020] The multimodal wearable monitoring device provided in this application includes an ultrasonic transducer that can arrange optical sensors behind a flexible ultrasonic array to achieve a coaxial design, so that the emission angles of the two can be completely overlapped, avoiding the occurrence of blind spots and improving imaging quality, thereby supporting real-time multimodal imaging of ultrasound / photoacoustics / optics; the flexible substrate achieves conformal fit with the curved surface of the human body, improving coupling stability and reducing motion artifacts; the array can integrate various optical sensors, while achieving miniaturization, wearability and multifunctional integration. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application or the prior art will be briefly introduced below. Obviously, the 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.

[0022] Figure 1 This is a flowchart illustrating the steps of the method for preparing the ultrasonic transducer provided in Embodiment 1 of this application.

[0023] Figure 2 This is a schematic diagram of the ultrasonic transducer provided in Embodiment 2 of the present invention; Figure 3 This is a three-dimensional structural schematic diagram of the ultrasonic transducer provided in Embodiment 2 of the present invention; Figure 4 This is a schematic diagram of the first cutting process of the ultrasonic transducer provided in Embodiment 2 of the present invention; Figure 5 This is a schematic diagram of the electrode layer of the ultrasonic transducer provided in Embodiment 2 of the present invention; Figure 6 This is a schematic diagram of the second cutting process of the ultrasonic transducer provided in Embodiment 2 of the present invention. Detailed Implementation

[0024] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. In the description of this application, it should be understood that the terms "upper", "lower", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified. To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0025] Example 1 Please see Figure 1 The present application provides a flowchart of a method for fabricating an ultrasonic transducer, including steps S10 to S80. The specific implementation of each step is described in detail below.

[0026] Step S10: A first transparent electrode layer and a second transparent electrode layer are formed on the upper and lower surfaces of the transparent piezoelectric material layer, respectively.

[0027] In this embodiment, the following step is also included: polishing the surface of the transparent piezoelectric material layer to form the polished transparent piezoelectric material layer.

[0028] As can be understood, this embodiment performs gradient polishing on the surface of the transparent piezoelectric material layer (such as lithium niobate or relaxor ferroelectric single crystal), using diamond polishing paste with particle sizes decreasing sequentially from 7 micrometers to 0.25 micrometers. This process aims to eliminate macroscopic scratches and obtain an optically smooth surface. This is fundamental to achieving high optical transparency and ensuring the quality of subsequent thin-film electrodes.

[0029] Furthermore, it also includes the following steps: chamfering and electrode edge wrapping on one wide side of the polished transparent piezoelectric material layer.

[0030] It is understandable that the sides of the transparent piezoelectric material layer are chamfered and electrode edging is applied. Electrode edging interconnects the upper and lower surface electrodes so that subsequent processes can bring the positive and negative electrodes together to this side.

[0031] Furthermore, in this embodiment, magnetron sputtering technology is used to prepare a first transparent electrode layer and a second transparent electrode layer on the upper and lower surfaces of the polished transparent piezoelectric material layer. Magnetron sputtering can form uniform, dense, strongly adhered, and highly conductive nanoscale thin films.

[0032] In this embodiment, the first transparent electrode layer and the second transparent electrode layer include transparent electrodes, which include oxide transparent electrodes, ultrathin metal mesh / nanowires or transparent conductive films. The oxide transparent electrodes include ITO, FTO or AZO, the ultrathin metal mesh / nanowires include silver nanowires or copper nanowires, and the transparent conductive film includes PET with TCO.

[0033] In this embodiment, the thickness of the transparent electrode is 100 nm, achieving the best balance between ensuring sufficient conductivity (low resistance) and high optical transmittance.

[0034] Step S20: A transparent matching layer is formed on the upper surface of the first transparent electrode layer. The transparent piezoelectric wafer is cut from one side of the transparent piezoelectric material layer according to a preset linear array element spacing, cutting through or removing most of the transparent piezoelectric material layer, leaving a thin layer containing the transparent matching layer uncut or not cut through, thereby forming an array of several transparent piezoelectric wafers still connected by the thin layer.

[0035] In this embodiment, the transparent matching layer has a double-layer structure. The material of the transparent matching layer includes a transparent inorganic material with high acoustic impedance and a transparent polymer with low acoustic impedance. The transparent inorganic material includes quartz glass or colorless optical glass, and the transparent polymer includes epoxy resin, polymethyl methacrylate resin, polystyrene, parylene, polyurethane, transparent polyurethane, and dimethylsiloxane.

[0036] Specifically, a quartz glass sheet is adhered to the upper surface of the first transparent electrode layer as a first transparent matching layer, using epoxy resin as an adhesive. Epoxy resin is then poured over the first matching layer as a second transparent matching layer, and the layers are ground and polished to the required thickness.

[0037] It is understood that in this embodiment, a transparent matching layer is prepared on the upper surface of the first transparent electrode layer by precision coating (such as spin coating) or lamination process. The transparent matching layer has a two-layer structure. Typically, the first layer (closely attached to the electrode) is made of a transparent inorganic material with high acoustic impedance (such as quartz glass), and the second layer is made of a transparent polymer with low acoustic impedance (such as PDMS or epoxy resin) to achieve broadband acoustic matching.

[0038] Specifically, both layers are precisely ground to a quarter-wavelength thickness (calculated based on the material's sound velocity and the transducer's center frequency). This is a classic application of acoustic impedance matching theory, which aims to gradually change the acoustic impedance through a multi-layered structure to minimize sound wave reflection at the interface between the piezoelectric material and the propagation medium (such as water or tissue), thereby significantly improving the forward transmission efficiency and receiving sensitivity of ultrasonic waves.

[0039] Furthermore, the transparent piezoelectric wafers are cut from one side of the transparent piezoelectric material layer according to a preset linear array element spacing, cutting through or removing most of the transparent piezoelectric material layer, leaving a thin layer containing the transparent matching layer uncut or partially cut, thereby forming an array of transparent piezoelectric wafers still connected by this thin layer. This includes: before cutting the array elements, using a high-precision dicing machine to perform a shallow pre-cut, the direction of which is perpendicular to the subsequent array element cuts and close to the electrode edging side, to achieve separation of the positive and negative electrodes.

[0040] In this embodiment, a high-precision diamond dicing machine cutting system is used to cut the stacked structure according to a preset linear array element spacing (typically on the order of half a wavelength to achieve high density). The core of process control is to precisely control the cutting depth, ensuring that most of the transparent piezoelectric material layer is cut through or removed, but stopping in front of the transparent matching layer without damaging the matching layer structure. This ensures that the elements maintain precise relative positions and mechanical stability in subsequent processing, greatly improving process yield and array survival rate.

[0041] This dicing process divides a continuous piezoelectric layer into multiple electrically independent arrays of transparent piezoelectric wafers. After dicing, each wafer becomes an independent electrical functional unit, but all units remain physically connected through a complete matching layer above, providing stability for subsequent operations.

[0042] It is understandable that a high-precision dicing machine is used to perform a shallow pre-cut before cutting the array elements to separate the positive and negative electrodes, so that the positive and negative electrodes are on the same side, which facilitates subsequent bonding with flexible circuits.

[0043] It is understood that this embodiment achieves high-density electrical isolation of the array, which is the basis for electronic scanning and beamforming. Maintaining the integrity of the matching layer is crucial, as it provides overall mechanical support and ensures that the array elements are arranged at preset intervals.

[0044] Step S30: Fill the spaces between each individual element in the transparent piezoelectric wafer with an organic transparent elastic material.

[0045] In this embodiment, liquid organic transparent elastic materials (such as PDMS, 732 glass glue, 734 glass glue, and 705 silicone rubber) are filled into all the gaps between the transparent piezoelectric wafers cut in the above steps by dispensing, scraping, or vacuum encapsulation. Subsequently, thermosetting or UV curing is performed to solidify the elastomer.

[0046] It is understandable that immediately filling after cutting "bundles" the independent and fragile piezoelectric wafers into a robust monolithic module, greatly enhancing their resistance to mechanical stress (such as alignment pressure) and vibration in subsequent processes. This provides a flat and stable substrate for the precise alignment and bonding of subsequent flexible circuits, significantly improving process yield and element survival rate, and solving the industry problem of brittle piezoelectric materials being easily broken in subsequent flexible integration. The elastomer itself also acts as an acoustic isolation material, suppressing mechanical (acoustic) crosstalk between elements.

[0047] Step S40: Attach the positive and negative electrodes of the flexible circuit layer to the positive and negative electrodes of the transparent piezoelectric wafer.

[0048] In this embodiment, the flexible circuit layer can be fabricated by using photolithography or printing processes to create conductive channels corresponding to the piezoelectric array pattern on a transparent flexible substrate (such as PI or PET). The electrodes can be made of metal (Cu) or transparent materials. The substrate material of the flexible circuit layer includes polyimide (PI) or transparent PET, and the electrodes of the flexible circuit layer include metal electrodes or transparent electrodes. The flexible circuit layer can be bonded to the conductive channels of the electrode layers of individual array elements through one or more circuits; each circuit can employ a single-layer or multi-layer electrode layer structure.

[0049] In this embodiment, anisotropic conductive adhesive (ACF) or non-conductive transparent epoxy resin is used to align and thermo-bond the positive and negative electrode pads on the flexible circuit layer with the positive and negative electrodes on the corresponding transparent piezoelectric material layer.

[0050] This step, as we understand it, enables the electrical interconnection of each independent piezoelectric element with the external control system. Performed under the support of a cured elastomer, the bonding process is stable and highly accurate, avoiding connection failures caused by substrate movement or element displacement, thus achieving reliable electrical connections for high-density arrays. The introduction of flexible circuitry gives the device overall bendability. The multi-channel design supports independent element addressing and driving.

[0051] Step S50: Cut the remaining thin layer with the transparent matching layer from one side of the matching layer according to the preset linear array element spacing, and ensure that the thin layer is completely cut through to form an array unit composed of multiple independent transparent piezoelectric wafer piezoelectric transducers.

[0052] In this embodiment, a precision cutting device is used again to cut the thin layer containing the transparent matching layer along the exact same element pattern as in step S30. The cutting depth needs to be precisely controlled this time to ensure that the entire thin layer is cut through, but only slightly cuts into the surface of the underlying solidified organic elastic filler material, so as not to damage the underlying piezoelectric wafer.

[0053] It should be noted that this cutting process divides the originally continuous acoustic matching layer into independent units, each corresponding to a piezoelectric chip below. Thus, each element is not only electrically independent but also completely acoustically isolated.

[0054] It is understood that in this embodiment, the acoustic waves (surface waves) transmitted between array elements through the matching layer are completely cut off, greatly reducing acoustic crosstalk, which is crucial for obtaining high-resolution ultrasound images. The cutting is performed after circuit bonding, avoiding damage to fragile electrical connection points caused by cutting stress.

[0055] Step S60: Fill the gaps in the cut thin layers with an organic transparent elastic material; In this embodiment, an organic transparent elastic material (which can be the same as the organic transparent elastic material described in the previous step) is filled into the gaps between the transparent matching layer units formed by cutting, and then cured. This step fills the gaps created after the matching layer is cut, making the upper surface of the device smooth and continuous. It works together with the underlying elastomer filled in the previous step to completely encapsulate the entire array structure (piezoelectric wafer, matching layer) in an elastic medium.

[0056] It is understood that this embodiment provides additional mechanical protection and forms a smooth acoustic wave emitting / receiving surface, which facilitates coupling with human skin. This further enhances the acoustic isolation between array elements and the structural integrity of the entire device.

[0057] Step S70: Adhere the transparent flexible backing layer to the lower surface of the flexible circuit layer to obtain the ultrasonic transducer.

[0058] Specifically, on the lower surface of the flexible circuit layer (i.e. the side facing away from the piezoelectric array element), a layer of transparent flexible backing material (such as PDMS or transparent elastic polyurethane) is applied by coating lamination or adhesive (such as transparent epoxy resin).

[0059] Furthermore, the transparent backing layer has a single-layer structure, and the material of the transparent backing layer includes organic polymers, such as silicone, polydimethylsiloxane (PDMS), and polyurethane elastomer.

[0060] This step understandably completes the final encapsulation of the device. The backing layer acts as an acoustic damping layer, absorbing backward-propagating ultrasound waves and shortening pulse length; it also serves as a mechanical protective layer, sealing and protecting the flexible circuitry. This improves the ultrasonic axial resolution and ensures the device's durability and biocompatibility. Its flexibility and transparency maintain the overall characteristics of the device.

[0061] The method for fabricating an ultrasonic transducer provided in this application first involves cutting a piezoelectric wafer with a transparent matching layer from one side of the piezoelectric layer, leaving a thin layer intact without completely cutting through it. This provides overall mechanical support and ensures that the array elements are arranged at a preset spacing. Then, a transparent organic elastic material is infused into the gaps between the array elements. The solidified material further fixes the position of the array elements, achieving precise bonding between the high-density array elements and flexible circuit electrodes. During the subsequent cutting through of the remaining thin layer, the array elements are effectively supported by the transparent elastic material, making them less susceptible to damage. This significantly improves process reliability and array element yield, thereby greatly enhancing process reliability and array element survival rate. It fundamentally protects the brittle piezoelectric material, making it possible to manufacture high-density, large-array-number flexible arrays. Furthermore, the combination of a double matching layer ensures high-sensitivity ultrasonic performance. In addition, the transparency of the entire material system allows the ultrasonic channel and optical channel to be completely coaxial and in the same field of view, without obstruction or blind spots, perfectly supporting the real-time fusion of ultrasonic imaging, photoacoustic imaging, and optical imaging (such as optical coherence tomography).

[0062] Example 2 Please see Figure 2 and Figure 3 Here is a schematic diagram of the ultrasonic transducer structure provided in this embodiment, including: Transparent piezoelectric material layer 10.

[0063] In this embodiment, the transparent piezoelectric material layer 10 is formed from lithium niobate (LiNbO3), lithium tantalate (LiTaO3) and its doped / relaxed ferroelectric single crystals, transparent piezoelectric ceramics (including PMN-PT, PIN-PMN-PT ceramics with specific components, which are made transparent through special processes) or piezoelectric polymers (including PVDF and its copolymers).

[0064] In this embodiment, the method further includes polishing the surface of the transparent piezoelectric material layer to form the polished transparent piezoelectric material layer.

[0065] As can be understood, this embodiment performs gradient polishing on the surface of the transparent piezoelectric material layer (such as lithium niobate or relaxor ferroelectric single crystal), using diamond polishing paste with particle sizes decreasing sequentially from 7 micrometers to 0.25 micrometers. This process aims to eliminate macroscopic scratches and obtain an optically smooth surface. This is fundamental to achieving high optical transparency and ensuring the quality of subsequent thin-film electrodes.

[0066] Furthermore, it also includes the following step: polishing one wide edge of the transparent piezoelectric material layer. Perform chamfering and electrode edge wrapping.

[0067] It is understandable that chamfering and electrode edging are applied to the sides of the transparent piezoelectric material layer to interconnect the upper and lower surface electrodes, so that the positive and negative electrodes can be brought together to this side in subsequent processes.

[0068] A first transparent electrode layer 20 is formed on the upper surface of the transparent piezoelectric material layer, and a second transparent electrode layer 30 is formed on the lower surface of the transparent piezoelectric material layer.

[0069] In this embodiment, the first transparent electrode layer and the second transparent electrode layer include transparent electrodes, which include oxide transparent electrodes, ultrathin metal mesh / nanowires or transparent conductive films. The oxide transparent electrodes include ITO, FTO or AZO, the ultrathin metal mesh / nanowires include silver nanowires or copper nanowires, and the transparent conductive film includes PET with TCO.

[0070] In this embodiment, the thickness of the transparent electrode is 100 nm, achieving the best balance between ensuring sufficient conductivity (low resistance) and high optical transmittance.

[0071] A transparent matching layer 40 is formed on the upper surface of the first transparent electrode layer 20.

[0072] In this embodiment, the transparent matching layer has a double-layer structure. The material of the transparent matching layer includes a transparent inorganic material with high acoustic impedance and a transparent polymer with low acoustic impedance. The transparent inorganic material includes quartz glass or colorless optical glass, and the transparent polymer includes epoxy resin, polymethyl methacrylate resin, polystyrene, parylene, polyurethane, transparent polyurethane, and dimethylsiloxane.

[0073] Specifically, a quartz glass sheet is adhered to the upper surface of the first transparent electrode layer as a first transparent matching layer, using epoxy resin as an adhesive. Epoxy resin is then poured over the first matching layer as a second transparent matching layer, and the layers are ground and polished to the required thickness.

[0074] It is understood that in this embodiment, a transparent matching layer is prepared on the upper surface of the first transparent electrode layer by precision coating (such as spin coating) or lamination process. The transparent matching layer has a two-layer structure. Typically, the first layer (closely attached to the electrode) is made of a transparent inorganic material with high acoustic impedance (such as quartz glass), and the second layer is made of a transparent polymer with low acoustic impedance (such as spin-coated PDMS or epoxy resin) to achieve broadband acoustic matching.

[0075] Specifically, both layers are precisely ground to a quarter-wavelength thickness (calculated based on the material's sound velocity and the transducer's center frequency). This is a classic application of acoustic impedance matching theory, which aims to gradually change the acoustic impedance through a multi-layered structure to minimize sound wave reflection at the interface between the piezoelectric material and the propagation medium (such as water or tissue), thereby significantly improving the forward transmission efficiency and receiving sensitivity of ultrasonic waves.

[0076] A transparent piezoelectric wafer is formed by cutting the transparent piezoelectric material layer according to a preset linear array element spacing, ensuring that only the transparent piezoelectric material layer is cut through, so as to form an array unit composed of several transparent piezoelectric wafers, with each independent element in the transparent piezoelectric wafer filled with an organic transparent elastic material.

[0077] Please see Figure 4 In this embodiment, a high-precision diamond dicing machine cutting system is used to cut the stacked structure according to a preset linear array element spacing (typically on the order of half a wavelength to achieve high density). The core of process control is to precisely control the cutting depth, cutting through or removing most of the transparent piezoelectric material layer, leaving the thin layer containing the transparent matching layer uncut or partially cut. Figure 5 Without damaging the matching layer, a transparent piezoelectric wafer array is formed, consisting of several wafers still connected through the thin layer. This dicing process divides a continuous piezoelectric layer into multiple electrically independent arrays of transparent piezoelectric wafers. After dicing, each wafer becomes an independent electrical functional unit, but all units remain physically connected through a complete matching layer above, providing stability for subsequent operations.

[0078] It is understood that this embodiment achieves high-density electrical isolation of the array, which is the basis for electronic scanning and beamforming. Maintaining the integrity of the matching layer is crucial, providing overall mechanical support and ensuring that the array elements are arranged at preset intervals.

[0079] In this embodiment, liquid organic transparent elastic materials (such as PDMS, 732 glass glue, 734 glass glue, and 705 silicone rubber) are filled into all the gaps between the transparent piezoelectric wafers cut in the above steps by dispensing, scraping, or vacuum encapsulation. Subsequently, thermosetting or UV curing is performed to solidify the elastomer.

[0080] It is understandable that immediately filling after cutting "bundles" the independent and fragile piezoelectric wafers into a robust monolithic module, greatly enhancing their resistance to mechanical stress (such as alignment pressure) and vibration in subsequent processes. This provides a flat and stable substrate for the precise alignment and bonding of subsequent flexible circuits, significantly improving process yield and element survival rate, and solving the industry problem of brittle piezoelectric materials being easily broken in subsequent flexible integration. The elastomer itself also acts as an acoustic isolation material, suppressing mechanical (acoustic) crosstalk between elements.

[0081] A flexible circuit layer 50 is provided, with its positive and negative electrodes bonded to the positive and negative electrodes of the transparent piezoelectric wafer.

[0082] In this embodiment, the flexible circuit layer can be fabricated by using photolithography or printing processes to create conductive channels corresponding to the piezoelectric element pattern on a transparent flexible substrate (such as PI or PET). The electrodes can be made of metal (Cu) or transparent materials. The substrate material of the flexible circuit layer includes transparent polyimide (PI) or transparent PET, and the electrodes of the flexible circuit layer include metal electrodes or transparent electrodes. The flexible circuit layer can be bonded to the conductive channels of the electrode layers of individual elements through one or more circuits; each circuit can employ a single-layer or multi-layer electrode layer structure.

[0083] In this embodiment, anisotropic conductive adhesive (ACF) or non-conductive transparent epoxy resin is used to align and thermo-bond the positive and negative electrode pads on the flexible circuit layer with the corresponding positive and negative electrodes on the transparent piezoelectric layer.

[0084] It is understood that in this embodiment, the prepared, precisely arranged array elements (still attached to the temporary substrate) are precisely aligned and reliably bonded to the pre-prepared transparent multi-channel flexible circuit (FPC), achieving high-precision and high-reliability electrical interconnection between each array element and the corresponding channel of the flexible circuit. The temporary support substrate is removed after bonding.

[0085] This allows for the electrical interconnection of each independent piezoelectric element with the external control system. Supported by a cured elastomer, the bonding process is stable and highly accurate, preventing connection failures due to substrate movement or element displacement, thus achieving reliable electrical connections for high-density arrays. The introduction of flexible circuitry gives the device overall bendability. The multi-channel design supports independent element addressing and driving.

[0086] A transparent piezoelectric transducer, wherein the transparent matching layer is cut and cut through the thin layer containing the transparent matching layer according to a preset linear array element spacing to form an array composed of several transparent piezoelectric elements, and the space between the transparent piezoelectric wafer and the corresponding transparent piezoelectric transducer is filled with an organic transparent elastic material.

[0087] Please see Figure 6 In this embodiment, a precision cutting device is used again to cut the thin layer containing the transparent matching layer along the exact same element pattern as described above. The cutting depth needs to be precisely controlled to ensure that the entire thin layer is cut through, but only slightly cuts into the surface of the underlying solidified organic elastic filler material, without damaging the underlying piezoelectric wafer.

[0088] It should be noted that this cutting process divides the originally continuous acoustic matching layer into independent units, each corresponding to a piezoelectric chip below. Thus, each element is not only electrically independent but also completely acoustically isolated.

[0089] It is understood that in this embodiment, the acoustic waves (surface waves) transmitted between array elements through the matching layer are completely cut off, greatly reducing acoustic crosstalk, which is crucial for obtaining high-resolution ultrasound images. The cutting is performed after circuit bonding, avoiding damage to fragile electrical connection points caused by cutting stress.

[0090] In this embodiment, an organic transparent elastic material is filled into the gaps between the transparent matching layer units formed by cutting, and then cured. This step fills the voids created after the matching layer is cut, making the upper surface of the device smooth and continuous. It works together with the underlying elastomer filled in the previous step to completely encapsulate the entire array structure (piezoelectric wafer, matching layer) in an elastic medium.

[0091] It is understood that this embodiment provides additional mechanical protection and forms a smooth acoustic wave emitting / receiving surface, which facilitates coupling with human skin. This further enhances the acoustic isolation between array elements and the structural integrity of the entire device.

[0092] A transparent flexible backing layer 60 is bonded to the lower surface of the flexible circuit layer.

[0093] Specifically, on the lower surface of the flexible circuit layer (i.e. the side facing away from the piezoelectric array element), a layer of transparent flexible backing material (such as flexible PDMS or transparent polyurethane) is applied by coating lamination or adhesive (such as transparent epoxy resin).

[0094] Furthermore, the transparent backing layer has a single-layer structure, and the material of the transparent backing layer includes organic polymers, such as silicone, polydimethylsiloxane (PDMS), and polyurethane elastomer.

[0095] Understandably, the backing layer acts as an acoustic damping layer, absorbing backward-propagating ultrasonic waves and shortening the pulse length; simultaneously, it serves as a mechanical protective layer, sealing and protecting the flexible circuitry. This improves the ultrasonic axial resolution and ensures the device's durability and biocompatibility. Its flexibility and transparency maintain the overall characteristics of the device.

[0096] It should be noted that the ultrasonic transducer provided in this embodiment adopts a stacked structure of "transparent acoustic matching layer - transparent piezoelectric layer (including transparent electrodes) - transparent flexible circuit layer - transparent flexible backing layer". It mainly relies on the transparent flexible circuit (FPC) substrate (including PET, PEN, transparent PI, etc.) to provide overall mechanical flexibility and bendability. The gaps between the array elements are filled with transparent elastic silicone, allowing for minute relative displacements between the elements, further absorbing stress, enhancing overall flexibility, preventing breakage, and maintaining acoustic isolation and optical transparency between the elements; the high transparency of the array is achieved by using a combination of multiple transparent materials.

[0097] It is understood that the ultrasonic transducer provided in this embodiment includes multiple independent transparent piezoelectric transducer elements arranged in a two-dimensional or one-dimensional array; the center spacing of the elements satisfies the following: the spacing of linear array elements is less than λ; the spacing of area array elements is less than λ / 2 (λ is the operating wavelength); a transparent flexible circuit layer (FPC) contains independent conductive channels corresponding to the number of array elements; the array elements are electrically interconnected with the corresponding conductive channels on the transparent flexible circuit layer through epoxy resin.

[0098] It is understandable that, since the center spacing of the linear array is less than λ (working wavelength) and the center spacing of the area array is less than λ / 2, the requirements for beamforming are met, thus achieving high-resolution imaging.

[0099] The ultrasonic transducer provided in this application fills the gaps between array elements with an organic transparent elastic material. Utilizing the mechanical support provided by this material after curing, it protects the brittle piezoelectric wafer from damage during subsequent flexible circuit bonding and matching layer cutting, thereby significantly improving process reliability and array element survival rate. This fundamentally protects the brittle piezoelectric material, making it possible to manufacture high-density, large-array-number flexible arrays. Furthermore, the step-by-step isolation of electrical and acoustic components, combined with a double-layer matching layer and backing, ensures low crosstalk, high sensitivity, and wide bandwidth ultrasonic performance. In addition, the transparency of the entire material system allows the ultrasonic and optical channels to be completely coaxial and in the same field of view, without obstruction or blind spots, perfectly supporting the real-time fusion of ultrasonic imaging, photoacoustic imaging, and optical imaging (such as optical coherence tomography).

[0100] Example 3 Embodiment 3 of this application also provides a multimodal wearable monitoring device, including the ultrasonic transducer mentioned above.

[0101] It also includes various optical devices arranged on the back side of the transparent flexible ultrasonic transducer array, including photodetectors, optical sensors, and semiconductor lasers. The device is constructed in the form of a flexible patch, which allows the optical sensors to be arranged behind the flexible ultrasonic array, achieving a coaxial design so that the emission angles of the two can be completely overlapped, avoiding the occurrence of blind spots, improving imaging quality, and thus supporting real-time multimodal imaging of ultrasound / photoacoustics / optics. The flexible substrate enables conformal fitting with the curved surface of the human body, improving coupling stability and reducing motion artifacts. The array can integrate various optical sensors, while achieving miniaturization, wearability, and multifunctional integration, making it suitable for various wearable monitoring scenarios.

[0102] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A method of making an ultrasonic transducer, characterized by, Includes the following steps: A first transparent electrode layer and a second transparent electrode layer are formed on the upper and lower surfaces of the transparent piezoelectric material layer, respectively. A transparent matching layer is formed on the upper surface of the first transparent electrode layer. The transparent piezoelectric wafer is cut from one side of the transparent piezoelectric material layer according to a preset linear array element spacing, cutting through or removing most of the transparent piezoelectric material layer, leaving a thin layer containing the transparent matching layer uncut or not cut through, thereby forming an array of several transparent piezoelectric wafers still connected by the thin layer. Organic transparent elastic material is filled between the elements in the transparent piezoelectric wafer; The positive and negative electrodes of the flexible circuit layer are bonded to the positive and negative electrodes of the transparent piezoelectric wafer; The remaining thin layer with the transparent matching layer is cut from one side of the matching layer according to the preset linear array element spacing, and the thin layer is completely cut through to form an array unit composed of multiple independent transparent piezoelectric wafer piezoelectric transducers. The gaps between the cut thin layers are filled with an organic transparent elastic material; The ultrasonic transducer is obtained by bonding a transparent flexible backing layer to the lower surface of the flexible circuit layer.

2. The method of claim 1, wherein the piezoelectric layer is formed by a method selected from the group consisting of a sputtering method, a sol-gel method, a chemical vapor deposition method, and a physical vapor deposition method. It also includes the following step: polishing the surface of the transparent piezoelectric material layer to form the polished transparent piezoelectric material layer.

3. The method for preparing an ultrasonic transducer as described in claim 2, characterized in that, It also includes the following steps: chamfering one wide edge of the polished transparent piezoelectric material layer, and making an electrode edging on this side to interconnect the upper and lower surface electrodes so that the positive and negative electrodes can be led to this side in subsequent processes.

4. The method for preparing an ultrasonic transducer as described in claim 2, characterized in that, In the step of polishing the surface of the transparent piezoelectric material layer to form the polished transparent piezoelectric material layer, the transparent piezoelectric material layer includes lithium niobate crystal, transparent piezoelectric ceramic or single crystal.

5. The method for preparing an ultrasonic transducer as described in claim 1, characterized in that, In the step of forming a first transparent electrode layer and a second transparent electrode layer on the upper and lower surfaces of the transparent piezoelectric material layer, the first transparent electrode layer and the second transparent electrode layer include transparent electrodes. The transparent electrodes include oxide transparent electrodes, ultrathin metal mesh / nanowires or transparent conductive films. The oxide transparent electrodes include ITO, FTO or AZO. The ultrathin metal mesh / nanowires include silver nanowires or copper nanowires. The transparent conductive film includes PET with TCO.

6. The method for preparing an ultrasonic transducer as described in claim 1, characterized in that, In the step of forming a transparent matching layer on the upper surface of the first transparent electrode layer, the transparent matching layer is a double-layer structure. The material of the transparent matching layer includes a transparent inorganic material with high acoustic impedance and a transparent polymer with low acoustic impedance. The transparent inorganic material includes quartz glass or colorless optical glass, and the transparent polymer includes epoxy resin, polymethyl methacrylate resin, polystyrene, parylene, polyurethane, transparent polyurethane, and dimethylsiloxane.

7. The method for preparing an ultrasonic transducer as described in claim 1, characterized in that... The transparent piezoelectric wafer is cut from one side of the transparent piezoelectric material layer according to a preset linear array element spacing, cutting through or removing most of the transparent piezoelectric material layer, leaving a thin layer containing the transparent matching layer uncut or not cut through, thereby forming a transparent piezoelectric wafer array consisting of several wafers still connected by the thin layer; including: before cutting the array elements, a high-precision dicing machine is used to perform a shallow pre-cut, the direction of which is perpendicular to the subsequent array element cut and close to the electrode edge side, to achieve separation of the positive and negative electrodes.

8. The method for preparing an ultrasonic transducer as described in claim 1, characterized in that, The organic transparent elastic material includes PDMS, 732 glass glue, 734 glass glue and 705 silicone rubber; the adhesive used for bonding includes epoxy resin and acrylic resin.

9. The method for preparing an ultrasonic transducer as described in claim 1, characterized in that, In the step of bonding the transparent flexible backing layer to the lower surface of the flexible circuit layer to obtain the ultrasonic transducer, the transparent backing layer is a single-layer structure, and the material of the transparent backing layer includes a flexible transparent organic polymer, including silicone, polydimethylsiloxane (PDMS), and polyurethane elastomer.

10. The method for preparing an ultrasonic transducer as described in claim 1, characterized in that, The substrate material of the flexible circuit layer includes transparent polyimide (PI) or transparent PET. The electrodes of the flexible circuit layer include metal electrodes or transparent electrodes. The flexible circuit layer can be bonded to the conductive channels of the electrode layers of independent array elements through one or more sets of circuits. Each set of circuits can adopt a single-layer or multi-layer electrode layer structure.

11. An ultrasonic transducer, characterized in that, include: Transparent piezoelectric material layer; A first transparent electrode layer is formed on the upper surface of the transparent piezoelectric material layer; A second transparent electrode layer is formed on the lower surface of the transparent piezoelectric material layer; A transparent matching layer formed on the upper surface of the first transparent electrode layer; A transparent piezoelectric wafer is formed by cutting it from one side of the transparent piezoelectric material layer according to a preset linear array element spacing, cutting through or removing most of the transparent piezoelectric material layer, leaving a thin layer containing a transparent matching layer uncut or partially cut, thereby forming an array of transparent piezoelectric wafers still connected by this thin layer; before cutting the array elements, a shallow pre-cut is performed using a high-precision dicing machine, the direction of which is perpendicular to the subsequent array element cuts and close to the electrode edge side, to achieve separation of the positive and negative electrodes. The gaps between each array element are filled with an organic transparent elastic material; A flexible circuit layer, the positive and negative electrodes of which are bonded to the positive and negative electrodes of the transparent piezoelectric wafer; A transparent piezoelectric transducer is formed by cutting the thin layer with a transparent matching layer from one side of the matching layer according to a preset linear array element spacing, and ensuring that the thin layer is completely cut through, so as to form an array unit composed of multiple independent transparent piezoelectric wafer piezoelectric transducers, and filling the gaps in the cut thin layer with organic transparent elastic material. A transparent flexible backing layer is bonded to the lower surface of the flexible circuit layer.

12. A multimodal wearable monitoring device, characterized in that, Includes the ultrasonic transducer as described in claim 11.

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