Dual-electrode piezoelectric film ultrasonic transducer and array coupling method thereof

Abstract

The present invention relates to the field of electronic materials and devices, specifically to a two-electrode piezoelectric thin-film ultrasonic transducer and an array coupling method thereof. The two-electrode piezoelectric thin-film ultrasonic transducer comprises a structural layer, a floating electric field control layer, a piezoelectric layer, and an electrode assembly, arranged in sequence. The floating electric field control layer is configured without an external electrical interface, and a longitudinal series electric field path is formed between the floating electric field control layer and the electrode assembly. The electrode assembly comprises a central electrode, configured as a drive signal input or a receiving signal output terminal; and an outer ring electrode, coaxially spaced from the central electrode, configured as a reference ground terminal. The purpose of the invention is to address the technical issues of complex wiring and control circuits and high process costs associated with two-electrode PMUTs.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic materials and devices, and in particular to a dual-electrode piezoelectric thin film ultrasonic transducer and an array coupling method thereof. Background Art

[0002] A PMUT (piezoelectric micromachined ultrasonic transducer) is a miniature device that uses the direct and inverse piezoelectric effects to transmit and receive acoustic waves. Due to its miniaturization, high performance, and low power consumption, PMUT devices are widely used in medical ultrasound imaging, sensors, acoustic communications, industrial testing, and other fields.

[0003] The traditional single-electrode PMUT only excites half of the diaphragm during transmission and only receives the charge generated by half of the diaphragm during reception. Therefore, its sensitivity is insufficient, making it difficult to efficiently capture weak ultrasonic signals, limiting its application in high-frequency, high-precision scenarios. To solve this problem, some researchers have proposed a dual-electrode PMUT. This technology designs a reverse potential area on the surface of the diaphragm and uses the superposition effect of the reverse electric field to enhance the strain of the piezoelectric layer. In theory, it can simultaneously improve the transmission power and receiving sensitivity. However, the traditional dual-electrode structure requires a separate lower electrode and uses two pairs of differential structures to control the transmission and reception functions respectively, resulting in complex wiring and high process difficulty. In particular, array devices are often required in actual ultrasonic detection. The complex wiring and circuit control hardware costs of the traditional dual-electrode seriously limit its practical application. Summary of the Invention

[0004] In order to solve the technical problems of complex wiring and control circuits of dual-electrode PMUTs and high process costs, the present invention provides a dual-electrode piezoelectric thin film ultrasonic transducer and an array coupling method thereof. The technical solutions adopted are as follows:

[0005] The technical solution of the first aspect of the present invention provides a dual-electrode piezoelectric thin film ultrasonic transducer, comprising a structural layer, a floating electric field regulation layer, a piezoelectric layer, and an electrode assembly arranged in sequence, wherein the floating electric field regulation layer is configured without an external electrical interface, and a longitudinal series electric field path is formed between the floating electric field regulation layer and the electrode assembly; the electrode assembly comprises:

[0006] a central electrode configured as a driving signal input or a receiving signal output;

[0007] The outer ring electrode is coaxially arranged with the central electrode and spaced apart from each other, and is configured as a reference ground terminal.

[0008] Furthermore, the central electrode is a circular or annular structure, and the distance between the central electrode and the outer ring electrode is at least 5 μm.

[0009] Furthermore, it also includes a supporting layer, which is configured as a substrate. The structural layer is arranged on the supporting layer through a micromachining process. The structural layer is a suspended membrane structure and is configured with a back cavity.

[0010] Furthermore, the floating electric field regulation layer is formed by depositing a metal layer by magnetron sputtering and is in contact with the piezoelectric layer, and the piezoelectric layer is made of lithium niobate or aluminum nitride.

[0011] Furthermore, in the transmitting mode, a unipolar driving voltage is applied to the central electrode, and in the receiving mode, an output signal is processed by a single-ended amplifier circuit.

[0012] Furthermore, the outer ring electrode is connected in parallel to the outer ring electrodes of adjacent transducer units to a common reference ground through a surface metallization process.

[0013] Furthermore, the central electrode is configured to have an area equal to that of the outer ring electrode.

[0014] The technical solution of the second aspect of the present invention provides a dual-electrode piezoelectric thin film ultrasonic transducer array coupling method, using the dual-electrode piezoelectric thin film ultrasonic transducer described in the technical solution of the first aspect of the present invention, the method comprising:

[0015] forming a structural layer on the support layer through a micromachining process;

[0016] depositing a floating electric field regulation layer on the structural layer, and depositing a piezoelectric layer above the floating electric field regulation layer;

[0017] Patterning the piezoelectric layer to form a multi-channel array layout;

[0018] Performing groove isolation on the floating electric field regulation layer of each channel, wherein the groove is used to block the electrical connection between the floating electric field regulation layers of adjacent channels;

[0019] Depositing a passivation layer to fill the groove area and performing surface planarization;

[0020] Electrode assemblies for each channel are formed on the passivation layer and electrically connected.

[0021] Furthermore, electrode assemblies of each channel are formed on the passivation layer and electrically connected, including:

[0022] Depositing a metal layer on the passivation layer by magnetron sputtering, and forming the central electrode, outer ring electrode and connection points of each channel by a patterning process;

[0023] The outer ring electrodes of each channel are connected in parallel to a unified reference ground through the connection points, and the central electrode of each channel is independently led out.

[0024] Furthermore, the groove passes through the floating electric field regulating layer, and the thickness of the passivation layer matches the depth of the groove.

[0025] The present invention has the following beneficial effects:

[0026] The dual-electrode piezoelectric thin film ultrasonic transducer provided by the present invention designs a surface dual-electrode structure of a central electrode and an outer ring electrode, configures the floating electric field control layer to have no external electrical interface, configures the central electrode as a driving signal input or receiving signal output terminal, and configures the outer ring electrode as a reference ground terminal. Only the central electrode and the outer ring electrode are required to realize the transmission and reception functions of ultrasonic waves; compared with the traditional dual-electrode PMUT, the positive and negative driving circuits of the traditional dual-electrode PMUT are reduced to one, and the differential signal is changed to a single-ended signal, which significantly reduces the number of interfaces and wiring complexity; in the transmitting mode, the unipolar driving voltage directly acts on the central electrode, and in the receiving mode, the single-ended signal processing does not require a differential amplifier circuit, thereby reducing the hardware cost of the driving and detection circuits while retaining the high sensitivity advantage of the dual-electrode structure.

[0027] On the other hand, the dual-electrode piezoelectric thin film ultrasonic transducer array coupling method provided by the present invention physically blocks the charge leakage path of adjacent channels by isolating the floating electric field control layer of each channel through grooves and filling the passivation layer, thereby solving the signal crosstalk problem caused by the shared bottom electrode of the multi-channel array. The surface electrode assembly simplifies the complex differential wiring of the traditional dual-electrode array into single-ended signal control by uniformly grounding the outer ring electrode and independently leading the center electrode, significantly reducing the number of leads and process complexity. While ensuring the independent operation of multiple channels, this method maintains the sensitivity of dual-electrode transmission and reception, and reduces the complexity of the driving circuit and detection circuit of the array device and the hardware cost to half of the traditional solution. It is suitable for the preparation of large-scale high-density ultrasonic transducer arrays. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 A schematic cross-sectional view of a dual-electrode piezoelectric thin film ultrasonic transducer provided by one embodiment of the present invention;

[0030] Figure 2 A top view of a dual-electrode piezoelectric thin film ultrasonic transducer provided by one embodiment of the present invention;

[0031] Figure 3 A schematic diagram showing comparison of electrode impedances of a dual-electrode piezoelectric thin film ultrasonic transducer provided by one embodiment of the present invention;

[0032] Figure 4 A schematic diagram of a portion of the structure of a dual-electrode piezoelectric thin film ultrasonic transducer provided by one embodiment of the present invention;

[0033] Figure 5 A wiring diagram of a transmitting mode of a dual-electrode piezoelectric thin film ultrasonic transducer provided by one embodiment of the present invention;

[0034] Figure 6 A wiring diagram of a receiving mode of a dual-electrode piezoelectric thin film ultrasonic transducer provided by one embodiment of the present invention;

[0035] Figure 7 A schematic diagram showing a comparative test of electrode receiving performance of a dual-electrode piezoelectric thin film ultrasonic transducer provided by one embodiment of the present invention;

[0036] Figure 8 A flow chart of a method for coupling a dual-electrode piezoelectric thin film ultrasonic transducer array provided by one embodiment of the present invention;

[0037] Figure 9 A schematic diagram of patterning a piezoelectric layer provided by one embodiment of the present invention;

[0038] Figure 10 A schematic diagram of a groove provided by one embodiment of the present invention;

[0039] Figure 11 A schematic diagram of a passivation layer deposition process according to an embodiment of the present invention;

[0040] Figure 12 A schematic diagram of electrode assembly deposition provided by one embodiment of the present invention;

[0041] Figure 13 A schematic diagram of a back cavity provided by an embodiment of the present invention;

[0042] Icon: 1-support layer, 2-structural layer, 3-floating electric field control layer, 4-piezoelectric layer, 5-center electrode, 6-outer ring electrode, 7-connection point, 8-groove, 9-passivation layer. DETAILED DESCRIPTION

[0043] To further illustrate the technical means and effectiveness of the present invention in achieving its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, describes in detail the specific implementation, structure, features, and effectiveness of a dual-electrode piezoelectric thin film ultrasonic transducer and its array coupling method proposed in accordance with the present invention. In the following description, different references to "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0044] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0045] The specific scheme of a dual-electrode piezoelectric thin film ultrasonic transducer and its array coupling method provided by the present invention is described in detail below with reference to the accompanying drawings.

[0046] Currently, conventional dual-electrode PMUTs utilize the superposition effect of opposite electric fields to improve transmit power and receive sensitivity by designing two regions with opposite potentials. However, the inventors discovered in actual use that conventional dual-electrode structures require etching to expose the bottom metal layer and separately lead out the lower electrode. For a single-channel dual-electrode PMUT, three external interfaces—Vin+, Vin-, and GND—are required. For an n-channel array device, n Vin+ and n Vin- interfaces are required, along with one GND interface, for a total of 2*n+1 interfaces. Conventional single-electrode PMUTs only require n+1 interfaces. While the conventional dual-electrode PMUT structure offers improved performance, the number of pins and lead complexity have increased by approximately 100%. Furthermore, for the device's transceiver control, conventional dual-electrode PMUTs require separate, phase-opposite drive signals applied to the inner and outer electrodes in transmit mode, while receive mode requires synchronous acquisition of the dual-electrode charges and processing via a differential amplifier. The use of two pairs of differential structures to control transmit and receive functions increases the process difficulty and device control circuit complexity. Especially for the dual-electrode PMUT array, the complex wiring, number of pins and lead complexity of the traditional dual-electrode PMUT are about twice that of the conventional single-electrode structure. The driving and detection circuit complexity and hardware cost of the transceiver circuit have also doubled, which seriously limits its practical application.

[0047] See also Figure 1 and Figure 2 , which shows a cross-sectional structural diagram and a top view of a dual-electrode piezoelectric thin film ultrasonic transducer provided by an embodiment of the present invention, wherein the dual-electrode piezoelectric thin film ultrasonic transducer comprises: a structural layer 2, a floating electric field control layer 3, a piezoelectric layer 4 and an electrode assembly arranged in sequence, wherein the floating electric field control layer 3 is configured to have no external electrical interface, and a longitudinal series electric field path is formed between the floating electric field control layer 3 and the electrode assembly; the electrode assembly comprises: a central electrode 5, configured as a driving signal input or receiving signal output terminal; an outer ring electrode 6, arranged coaxially and spaced apart from the central electrode 5, and configured as a reference ground terminal.

[0048] Specifically, a floating electric field control layer 3, a piezoelectric layer 4 and an electrode assembly are sequentially arranged on the top of the structural layer 2, and a support layer 1 configured as a substrate is further provided at the bottom of the structural layer 2. The structural layer 2 is arranged on the support layer 1 through a micromachining process. The structural layer 2 is a suspended thin film structure and is configured with a back cavity; the support layer 1 can be made of silicon-based or low-stress materials, such as SiO2 or Si, and a circular or annular suspended thin film structure is formed as the structural layer 2 through a micromachining process. After the structural layer 2 is patterned, a back cavity is etched at the bottom of the structural layer 2; micromachining technology specifically refers to precision technologies used in the field of semiconductor and micro-electromechanical system manufacturing, including photolithography, etching, thin film deposition and other technologies; in the production of dual-electrode PMUT, photolithography is used to accurately transfer patterns and determine the shapes of each electrode. The shape, position, and size of the layer materials are determined. Etching is used to remove material from specific areas to form a suspended membrane structure, a back cavity, and to pattern each functional layer. Thin film deposition techniques such as magnetron sputtering are used to grow functional thin films, such as the composite metal layer and piezoelectric layer 4 of the floating electric field control layer 3, to ensure that each layer has corresponding mechanical and electrical properties. The floating electric field control layer 3 serves as a mechanical support and electric field control layer. Magnetron sputtering equipment can be used to sequentially sputter and deposit Ti and Pt target materials on the surface of the suspended membrane structure layer 2 to form a Ti / Pt composite metal layer as the floating electric field control layer 3, ensuring that the layer thickness is uniform and there are no external electrical connections. The floating electric field control layer 3 has no external electrical interface and is only coupled to the surface electrode assembly through a longitudinal electric field path. On the floating electric field control layer 3, the piezoelectric layer 4 is grown and patterned by methods such as chemical solution deposition or physical vapor deposition. Then, the photolithography and sputtering processes are used again to produce the central electrode 5 and the outer ring electrode 6 on the surface of the piezoelectric layer 4. After the production of each layer is completed, the entire dual-electrode PMUT is packaged and performance tested.

[0049] In actual operation, in transmit mode, a unipolar drive voltage is applied to the central electrode 5. Due to the presence of the floating electric field control layer 3, a longitudinal series electric field is formed. This electric field drives the piezoelectric layer 4 to vibrate. Due to the inverse piezoelectric effect, electrical energy is converted into mechanical energy, generating ultrasonic waves that are emitted outward. In receive mode, external ultrasonic waves act on the piezoelectric layer 4, causing it to vibrate. Due to the direct piezoelectric effect, the piezoelectric layer 4 generates an electrical signal, which is output through the central electrode 5. The outer ring electrode 6 acts as a reference ground to provide a stable reference potential for the signal, thereby achieving effective reception of the ultrasonic signal.

[0050] See Figure 3 、 Figure 4 、 Figure 5 、 Figure 6As shown in the figure, SIG represents the signal, 2VPP represents the peak voltage, V0 represents the sensor output, and Vout represents the amplifier output. In order to verify the feasibility of the dual-electrode PMUT without the need to lead out the bottom electrode, the impedance simulation of the dual-electrode PMUT was carried out using finite element simulation software. Lithium niobate material was used as the piezoelectric layer 4, and three impedance values ​​were calculated respectively: R1 is the impedance of the floating electric field control layer 3, R2 is the impedance of the outer ring electrode 6, and R3 is the impedance of the center electrode 5. The specific connections of R1, R2, and R3 are shown in the figure. Figure 3 As shown in the figure, after simulation, the relationship between the three impedance values ​​is: R1 and R2 are of the same magnitude, and R3 is 3 orders of magnitude higher. The following is a specific explanation using the parameters in Table 1 as an example, as shown in Table 1:

[0051]

[0052] Table 1: Finite element software device impedance simulation parameter settings

[0053] Finite element simulation shows that R1 is 80KΩ, R2 is 100KΩ, and R3 is 78MΩ; see Figure 5 In emission mode, only a peak-to-peak voltage equivalent to that of a conventional dual-electrode structure needs to be applied between the inner and outer electrodes, without the need to generate an additional drive signal with opposite phase. Due to the extremely large R3, the electric field forms a series path along the vertical direction through the bottom floating electric field control layer 3. When the inner and outer ring electrodes 6 have equal areas, they are completely equivalent to the reverse potential drive of a conventional structure, achieving a vibration output efficiency comparable to that of a conventional dual-electrode structure. Figure 6 In the receiving mode, through a reverse amplification circuit, the central electrode 5 is connected to the amplifier input terminal, and the outer ring electrode 6 is connected to the reference ground, so that the received signal can be amplified without the need for differential amplification. The high transverse impedance forces the signal to be obtained through the series longitudinal electric field formed by the bottom floating electric field control layer 3. Due to the reverse force characteristics of the inner and outer diaphragms, the final potential difference is the sum of the absolute values ​​of the longitudinal potentials of the inner and outer electrodes, thereby amplifying the received signal. It can be understood that this embodiment has successfully verified the feasibility of the dual-electrode PMUT without the need to lead out the bottom electrode through finite element simulation. From the analysis results of the impedance characteristics, it can be seen that the specific impedance relationship enables the dual-electrode PMUT to achieve similar or even better performance than the conventional dual-electrode structure in the transmitting and receiving modes with a simplified driving and signal processing method. In the transmitting mode, the simplified driving method avoids the complex generation of phase-opposite driving signals; in the receiving mode, single-ended signal processing replaces differential amplification, reducing circuit complexity. This shows that the dual-electrode PMUT provided in this embodiment effectively simplifies the device structure and control method by optimizing the electrode structure and utilizing a unique electric field path while ensuring the core performance of the ultrasonic transducer, providing a more efficient and low-cost solution for the design and manufacture of ultrasonic transducers.

[0054] To verify the feasibility of not leading out the bottom electrode and the effectiveness of the new dual-electrode PMUT in changing from three-electrode control to two-electrode control, while also confirming that it retains the advantage of double sensitivity of the dual-electrode structure, the following tests were conducted:

[0055] This embodiment tests the new dual-electrode PMUT in three working modes: single outer ring electrode 6, single center electrode 5, and dual electrode. In different modes, appropriate excitation signals are applied to simulate the actual working scene of the ultrasonic transducer; using appropriate measurement equipment, the voltage variation data of the device output signal in different modes is collected over time, such as Figure 7 The waveform shown, Figure 7 The horizontal axis represents time, reflecting the change of the signal over time; the vertical axis represents voltage, showing the voltage amplitude of the device output signal at different time points. The collected data is then processed to calculate the peak value Vpp of the signal in each mode, which is 7.2 for the single outer ring electrode 6, 5.9 for the single center electrode 5, and 13.3 for the dual electrode. From the test results of the embodiment and the data in the figure, it can be seen that the new dual-electrode PMUT successfully achieves a control method without extracting the bottom electrode and using a dual-electrode method. The peak Vpp (13.3) obtained in the dual-electrode mode is approximately equal to the sum of the Vpp of the single outer ring electrode 6 (7.2) and the single center electrode 5 (5.9). This shows that the new dual-electrode PMUT retains the double sensitivity advantage of the dual-electrode structure compared to the single-electrode structure while simplifying the control method. The dual-electrode PMUT provided in the embodiment effectively reduces the difficulty of device control without affecting the core performance sensitivity of the ultrasonic transducer, providing a more convenient and efficient solution for the integration and use of ultrasonic transducers in practical applications.

[0056] In summary, the dual-electrode piezoelectric thin film ultrasonic transducer provided in this embodiment, by designing the surface dual-electrode structure of the central electrode 5 and the outer ring electrode 6, configures the floating electric field control layer 3 to have no external electrical interface, configures the central electrode 5 as the driving signal input or receiving signal output end, and configures the outer ring electrode 6 as the reference ground end, and only requires the central electrode 5 and the outer ring electrode 6 to realize the ultrasonic transmission and reception functions; compared with the traditional dual-electrode PMUT, the positive and negative driving circuits of the traditional dual-electrode PMUT are reduced to one, and the differential signal is changed to a single-ended signal, which significantly reduces the number of interfaces and wiring complexity; in the transmitting mode, the unipolar driving voltage directly acts on the central electrode 5, and in the receiving mode, the single-ended signal processing does not require a differential amplifier circuit, thereby reducing the hardware cost of the driving and detection circuits, while retaining the high sensitivity advantage of the dual-electrode structure.

[0057] Preferably, the central electrode 5 is a circular or annular structure, and the spacing between the central electrode 5 and the outer ring electrode 6 is at least 5 μm. The outer ring electrode 6 is connected in parallel to the outer ring electrode 6 of the adjacent transducer unit to a unified reference ground through a surface metallization process, and the central electrode 5 is configured to have an area equal to that of the outer ring electrode 6. This embodiment effectively reduces the capacitive coupling effect between the electrodes and reduces signal crosstalk by adopting a coaxial layout of the circular or annular central electrode 5 and the outer ring electrode 6, and strictly maintaining a spacing of no less than 5 μm between the two. The outer ring electrode 6 is connected in parallel to a unified reference ground through a surface metallization process, ensuring that the potential of each unit is consistent, which can simplify the wiring complexity of the array device. The equal area design of the central electrode 5 and the outer ring electrode 6 optimizes the symmetry of the electric field distribution. The electrode traces of the central electrode 5 and the outer ring electrode 6 are filled with insulating material to avoid the risk of short circuit between the electrodes. This solution improves the reliability of the device while maintaining the high sensitivity of the dual-electrode system, and is suitable for large-scale integration and complex signal control scenarios of high-density ultrasound arrays.

[0058] Preferably, the floating electric field control layer 3 is formed by depositing a metal layer by magnetron sputtering and is in contact with the piezoelectric layer 4, and the piezoelectric layer 4 is made of lithium niobate or aluminum nitride material; specifically, using magnetron sputtering equipment, the cleaned substrate with the structural layer 2 is placed in a suitable position in the sputtering chamber; then the metal target is installed, and the sputtering chamber is evacuated to achieve a high vacuum environment; and then by applying electric and magnetic fields, the target atoms are sputtered out under the action of plasma and deposited on the surface of the structural layer 2 on the substrate, to obtain a metal layer of the required thickness and quality as the floating electric field control layer 3; taking aluminum nitride as the piezoelectric material as an example, the piezoelectric layer 4 can be grown by magnetron sputtering or vapor deposition; in this embodiment, the floating electric field control layer 3 prepared by magnetron sputtering can accurately control the thickness and uniformity of the film, so that it can effectively play a mechanical support and electric field control role, and is in close contact with the piezoelectric layer 4 to ensure efficient transmission of the electric field. Lithium niobate or aluminum nitride is selected as the material of the piezoelectric layer 4 to fully utilize its good piezoelectric properties, ensure that the ultrasonic transducer efficiently realizes the mutual conversion of electrical energy and mechanical energy, and improves the sensitivity and stability of ultrasonic transmission and reception. The piezoelectric layer 4 can also be made of other types of piezoelectric materials such as lead zirconate titanate.

[0059] Preferably, in the transmitting mode, a unipolar driving voltage is applied to the central electrode 5, and in the receiving mode, the output signal is processed by a single-ended amplifier circuit; specifically, in the transmitting mode, a single-channel high-voltage amplifier is used to directly apply a unipolar AC driving voltage with a preset peak value to the central electrode 5, the outer ring electrode 6 is grounded, and an equivalent reverse electric field is formed through the longitudinal series path of the floating electric field control layer 3, thereby exciting the piezoelectric layer 4 to generate symmetrical vibration; in the receiving mode, the central electrode 5 is directly connected to the input end of the low-noise reverse amplifier, and the outer ring electrode 6 is used as a reference ground. The high input impedance is used to match the high impedance characteristics of the piezoelectric induced charge to directly amplify the single-ended signal generated by the diaphragm deformation, and an RC low-pass filter network can also be integrated at the front end of the amplifier to suppress high-frequency noise; shielded routing is used to reduce crosstalk between channels and ensure signal fidelity; this embodiment reduces the positive and negative driving circuits of the traditional dual electrode to a single-channel control through the simplified architecture of unipolar drive and single-ended signal processing, and at the same time utilizes the longitudinal electric field coupling mechanism of the floating electric field control layer 3 to achieve vibration efficiency and receiving sensitivity equivalent to the traditional dual electrode. In transmit mode, a unilaterally driven electric field excites symmetrical vibrations through a longitudinal path, avoiding complex differential routing. In receive mode, a single-ended amplifier circuit directly extracts the charge signal, maintaining a high signal-to-noise ratio without the need for differential amplification. This solution significantly reduces hardware complexity and cost while retaining the performance advantages of dual electrodes, providing a solution for large-scale integration and low-power applications of high-density ultrasound arrays.

[0060] As mentioned above, the dual-electrode piezoelectric thin film ultrasonic transducer proposed in the technical solution of the first aspect of the present invention significantly reduces the difficulty of preparing the dual-electrode piezoelectric thin film ultrasonic transducer and the complexity of controlling the transmission and reception mode by simplifying the electrode configuration, while effectively reducing the number of wiring layers and process costs. However, when constructing a large multi-channel array, if the same design strategy as that of a single dual-electrode piezoelectric thin film ultrasonic transducer is adopted, that is, the outer ring electrodes 6 of all channels are uniformly connected to the reference ground, a charge leakage problem will occur; adjacent channels will form a closed loop through a path such as: "A channel outer ring electrode → floating electric field control layer → B channel outer ring electrode → A channel outer ring electrode". When channel A is in working state and channel B is in inactive state, the loop will generate a parasitic potential difference between the outer ring electrodes 6 of the two channels, causing the effective charge generated by the outer ring electrode 6 of channel A to leak to the outer ring electrode 6 of channel B through the floating electric field control layer 3. Especially when there are multiple non-working channels in the array, this charge leakage path will show a multi-node parallel characteristic, and ultimately the potential accumulated in the outer ring of the working channel will be completely offset by the multiple idle channel shunt paths, resulting in the failure of the differential signal extraction mechanism of the dual-electrode structure. To solve this problem, we proposed a dual-electrode piezoelectric thin film ultrasonic transducer array coupling method; for details, please refer to Figures 8 to 13, which shows a method flow chart and schematic diagram of each step of a dual-electrode piezoelectric thin film ultrasonic transducer array coupling method provided by an embodiment of the present invention, wherein the method includes:

[0061] Step S1: forming a structural layer 2 on the support layer 1 by a micromachining process; specifically, growing a low-stress SiO2 thin film layer as the structural layer 2 on the silicon-based support layer 1 by a chemical vapor deposition process;

[0062] Step S2: depositing a floating electric field control layer 3 on the structural layer 2, and depositing a piezoelectric layer 4 above the floating electric field control layer 3; specifically, using a magnetron sputtering process to deposit a Ti / Pt composite metal layer as the floating electric field control layer 3 on the surface of the suspended thin film layer without leading to an external interface; and depositing a lithium niobate (LiNbO3) or aluminum nitride (AlN) piezoelectric film on the floating electric field control layer 3 by pulsed laser deposition or reactive magnetron sputtering.

[0063] Step S3: Patterning the piezoelectric layer 4 to form a multi-channel array layout; specifically, patterning is performed by reactive ion etching (RIE) to release the film boundary to form the multi-channel array layout; after the patterning, a circular or annular back cavity structure is formed at the bottom of the structural layer 2 by photolithography and anisotropic dry etching processes;

[0064] Step S4: Grooving 8 is performed on the floating electric field control layer 3 of each channel to isolate the floating electric field control layer 3. The groove 8 is used to block the electrical connection between the floating electric field control layers 3 of adjacent channels. Specifically, the floating electric field control layer 3 of each channel is physically grooved 8 using deep reactive ion etching (DRIE) or focused ion beam (FIB) technology. The groove 8 deeply penetrates the metal layer to ensure that the floating electric field control layers 3 of adjacent channels are completely isolated and the charge leakage path is blocked.

[0065] Step S5: Deposit a passivation layer 9 to fill the groove 8 area and perform surface flattening. Specifically, since the grooves 8 are isolated between different channels and wiring is impossible, this embodiment adopts the method of depositing and filling the passivation layer 9 to achieve a unified connection of the outer ring electrode 6 between the channels to the reference ground. The groove 8 passes through the floating electric field control layer 3, and the thickness of the passivation layer 9 matches the depth of the groove 8. The SiO2 or SiN passivation layer 9 can be filled in the groove 8 area through a plasma enhanced chemical vapor deposition process, with a thickness matching the depth of the groove 8, and then chemical mechanical polishing is performed to achieve surface flattening, providing a continuous substrate for subsequent electrode deposition.

[0066] Step S6: forming electrode assemblies of each channel on the passivation layer 9 and electrically connecting them; specifically, depositing a surface metal layer by magnetron sputtering and constructing an electrode assembly and a connection point 7 by graphical means, and connecting the outer ring electrodes 6 of different channels together; wherein the connection point 7 includes a common outer ring electrode 6 connection point and a central electrode 5 connection point of different channels, and the outer ring electrodes 6 of each channel are connected in parallel to a unified reference ground connection point, requiring only one common grounding interface; the central electrode 5 of each channel is independently led out to the corresponding signal connection point.

[0067] This embodiment eliminates the closed loop formed by the above-mentioned "A channel outer ring electrode → floating electric field control layer → B channel outer ring electrode → A channel outer ring electrode" path by etching and isolating the floating electric field control layer 3 between different channels, thereby avoiding the potential consumption of the working channel by the non-working channel; taking the 16-channel array structure as an example, the conventional dual-electrode structure requires 16 inner electrode connection points, 16 outer electrode connection points and 1 bottom ground electrode lead-out connection point, a total of 33 connection points. However, since the array device formed by this patent does not need to lead out the outer ring of each channel separately, but connects all the outer ring electrodes 6 together to form a reference ground electrode, only 16 center electrode 5 connection points and 1 reference ground connection point are required, reducing the wiring complexity by 50%.

[0068] The dual-electrode piezoelectric thin film ultrasonic transducer array coupling method provided in this embodiment isolates the floating electric field control layer 3 of each channel by engraving 8 and filling the passivation layer 9, thereby physically blocking the charge leakage path of adjacent channels and solving the signal crosstalk problem caused by the shared bottom electrode of the multi-channel array. The surface electrode assembly simplifies the complex differential wiring of the traditional dual-electrode array into single-ended signal control by uniformly grounding the outer ring electrode 6 and independently leading the center electrode 5, significantly reducing the number of leads and process complexity. While ensuring the independent operation of multiple channels, this method maintains the sensitivity of dual-electrode transmission and reception, and reduces the complexity of the driving circuit and detection circuit of the array device and the hardware cost to half of the traditional solution. It is suitable for the preparation of large-scale high-density ultrasonic transducer arrays.

[0069] Preferably, forming electrode assemblies of each channel on the passivation layer 9 and electrically connecting them includes:

[0070] Step S61: depositing a metal layer on the passivation layer 9 by magnetron sputtering, and forming the central electrode 5, outer ring electrode 6 and connection point 7 of each channel by a patterning process; specifically, a high-conductivity metal layer is uniformly deposited on the surface of the passivation layer 9 by a magnetron sputtering process; then, the pattern of the central electrode 5, outer ring electrode 6 and connection point 7 is defined on the metal layer by a photolithography process, and excess metal is removed by wet etching or dry etching to form a precise electrode gap (≥5μm) and connection point 7 structure; finally, SiO2 or SiN insulating medium is filled in the electrode trace between the central electrode 5 and the outer ring electrode 6 to avoid short circuit between the electrodes.

[0071] Step S62: The outer ring electrodes 6 of each channel are connected in parallel to a unified reference ground through the connection point 7, and the center electrode 5 of each channel is independently led out; specifically, the outer ring electrodes 6 of each channel are connected to a unified reference ground pad through surface metal leads, and the lead design can adopt a serpentine or radial layout to minimize parasitic inductance and ensure potential consistency; the center electrode 5 of each channel is connected to the corresponding signal pad through an independent metal trace, and the trace path is realized by opening windows or cross-layer through holes in the passivation layer 9 to avoid signal crosstalk between channels; finally, the connection point area is chemically mechanically polished to ensure that the surface is flattened and then encapsulated with a protective layer to prevent oxidation or mechanical damage; this embodiment constructs an electrode assembly through magnetron sputtering and graphic processing, combined with a wiring strategy of unified grounding of the outer ring electrode 6 and independent lead-out of the center electrode 5, to simplify the complex differential wiring of the traditional dual-electrode array into single-ended signal control, significantly reducing the number of connection points 7 and process complexity; this solution greatly reduces hardware cost and wiring difficulty while maintaining the high sensitivity of the dual electrodes.

[0072] In summary, the dual-electrode piezoelectric thin film ultrasonic transducer and its array coupling method provided by the present invention, in the dual-electrode PMUT monomer design, adopts a surface dual-electrode architecture, abandons the bottom electrode lead-out, and only uses the center electrode 5 and the outer ring electrode 6 to realize ultrasonic transmission and reception, simplifying the complex driving circuit of the traditional dual-electrode, converting the differential signal into a single-ended signal processing, greatly reducing the device control difficulty, wiring complexity and hardware cost, while retaining the high sensitivity advantage of the dual-electrode structure over the single-electrode structure; at the dual-electrode PMUT array coupling method level, to address the key problem of charge leakage in the multi-channel array, a unique process of isolating the floating electric field control layer 3 between channels by grooves 8 and depositing a passivation layer 9 is adopted, effectively blocking the charge leakage path, avoiding the potential consumption of the non-working channel on the working channel, ensuring that each channel operates independently and stably, and maintaining the high sensitivity characteristics of the dual electrode. This design also greatly simplifies the wiring, reduces the number of connection points 7, reduces the process complexity and cost, and significantly improves the integration and reliability of the array. Overall, this technical solution takes into account both the performance improvement of transducer units and the large-scale application needs of arrays. It has broad application prospects in fields that are highly dependent on ultrasonic transducer technology, such as medical ultrasound imaging, industrial non-destructive testing, and acoustic communications.

[0073] It should be noted that the order in which the embodiments of the present invention are described above is for illustrative purposes only and does not necessarily represent the superiority or inferiority of the embodiments. The processes depicted in the accompanying drawings do not necessarily require the specific order or sequential order shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0074] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

Claims

1. A dual-electrode piezoelectric thin film ultrasonic transducer, characterized in that: The invention comprises a structural layer, a floating electric field regulation layer, a piezoelectric layer and an electrode assembly arranged in sequence, wherein the floating electric field regulation layer is configured to have no external electrical interface, and a longitudinal series electric field path is formed between the floating electric field regulation layer and the electrode assembly; the electrode assembly comprises: a central electrode configured as a driving signal input or a receiving signal output; an outer ring electrode, coaxially arranged with the central electrode and spaced apart, configured as a reference ground terminal; The floating electric field regulation layer is formed by depositing a metal layer by magnetron sputtering and is in contact with the piezoelectric layer, and the piezoelectric layer is made of lithium niobate or aluminum nitride; It also includes a supporting layer, which is configured as a substrate. The structural layer is arranged on the supporting layer through a micromachining process. The structural layer is a suspended membrane structure and is configured with a back cavity.

2. The dual-electrode piezoelectric thin film ultrasonic transducer according to claim 1, wherein: The central electrode is a circular or annular structure, and the distance between the central electrode and the outer ring electrode is at least 5 μm.

3. The dual-electrode piezoelectric thin film ultrasonic transducer according to claim 1, wherein: In the transmitting mode, a unipolar driving voltage is applied to the central electrode, and in the receiving mode, an output signal is processed by a single-ended amplifier circuit.

4. The dual-electrode piezoelectric thin film ultrasonic transducer according to claim 1, wherein: The outer ring electrode is connected in parallel to the outer ring electrodes of adjacent transducer units to a unified reference ground through a surface metallization process.

5. The dual-electrode piezoelectric thin film ultrasonic transducer according to any one of claims 1 to 4, characterized in that: The central electrode is configured to have an area equal to that of the outer ring electrodes.

6. A dual-electrode piezoelectric thin film ultrasonic transducer array coupling method, characterized in that: Using the dual-electrode piezoelectric thin film ultrasonic transducer according to any one of claims 1 to 5, the method comprises: forming a structural layer on the support layer through a micromachining process; depositing a floating electric field regulation layer on the structural layer, and depositing a piezoelectric layer above the floating electric field regulation layer; Patterning the piezoelectric layer to form a multi-channel array layout; Performing groove isolation on the floating electric field regulation layer of each channel, wherein the groove is used to block the electrical connection between the floating electric field regulation layers of adjacent channels; Depositing a passivation layer to fill the groove area and performing surface planarization; Electrode assemblies for each channel are formed on the passivation layer and electrically connected.

7. The dual-electrode piezoelectric thin film ultrasonic transducer array coupling method according to claim 6, characterized in that: The electrode components of each channel are formed on the passivation layer and electrically connected, including: Depositing a metal layer on the passivation layer by magnetron sputtering, and forming the central electrode, outer ring electrode and connection points of each channel by a patterning process; The outer ring electrodes of each channel are connected in parallel to a unified reference ground through the connection points, and the central electrode of each channel is independently led out.

8. The dual-electrode piezoelectric thin film ultrasonic transducer array coupling method according to claim 6, wherein: The groove passes through the floating electric field regulating layer, and the thickness of the passivation layer matches the depth of the groove.

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