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

Abstract

The invention relates to the technical field of electronic materials and devices, in particular to a dual-electrode piezoelectric film ultrasonic transducer and an array coupling method thereof.The dual-electrode piezoelectric film ultrasonic transducer comprises a structural layer, a floating electric field regulation and control layer, a piezoelectric layer and an electrode assembly which are sequentially arranged, and the floating electric field regulation and control layer is configured to be free of an external electrical interface; a longitudinal series electric field path is formed between the floating electric field regulation and control layer and the electrode assembly; the electrode assembly includes: a central electrode configured as a driving signal input or receiving signal output; and the outer ring electrode and the central electrode are coaxially arranged at intervals, and the outer ring electrode is configured as a reference ground end. The objective of the invention is to solve the technical problems of complex wiring and control circuit and high process cost of a dual-electrode PMUT.

Description

Technical Field

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

[0002] A PMUT (piezoelectric micromachined ultrasonic transducer) is a microdevice that utilizes the direct and inverse piezoelectric effects to achieve acoustic wave transmission and reception. Due to its advantages such as miniaturization, high efficiency, and low power consumption, PMUT devices are widely used in fields such as medical ultrasonic imaging, sensors, acoustic communication, and industrial inspection.

[0003] In a traditional single-electrode structure PMUT, only half of the diaphragm area is excited during transmission, and only the charges generated by half of the diaphragm area are received during reception. Therefore, the sensitivity is insufficient, making it difficult to efficiently capture weak ultrasonic signals, which limits its application in high-frequency and high-precision scenarios. To solve this problem, some researchers have proposed a dual-electrode structure PMUT. This technology enhances the piezoelectric layer strain by designing a reverse potential region on the diaphragm surface and utilizing the superposition effect of the reverse electric field. In theory, it can synchronously improve the transmission power and reception sensitivity. However, the traditional dual-electrode structure requires a separate lower electrode to be led out and two pairs of differential structures to control the transmission and reception functions respectively, resulting in complex wiring and high process difficulty. Especially in actual ultrasonic detection, array devices are often required. The complex wiring and circuit control hardware cost of the traditional dual-electrode severely limit its practical application. Summary of the Invention

[0004] To solve the technical problems of complex wiring and control circuit and high process cost of the dual-electrode PMUT, the present invention provides a dual-electrode piezoelectric thin-film ultrasonic transducer and its array coupling method. The specific technical solutions adopted are as follows: The technical solution of the first aspect of the present invention provides a dual-electrode piezoelectric thin-film ultrasonic transducer, which includes a structure layer, a floating electric field regulation layer, a piezoelectric layer, and an electrode assembly arranged in sequence. 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 includes: A central electrode, configured as a driving signal input or receiving signal output terminal; An outer ring electrode, coaxially and spaced apart from the central electrode, configured as a reference ground terminal.

[0005] Further, the central electrode is in a circular or annular structure, and the distance between the central electrode and the outer ring electrode is at least 5 μm.

[0006] Further, it further includes a support layer, the support layer is configured as a substrate, the structure layer is disposed on the support layer through a microfabrication process, and the structure layer is a suspended thin-film structure and is configured with a back cavity.

[0007] Further, the floating electric field regulation layer is formed by magnetron sputtering to deposit a metal layer and is in contact with the piezoelectric layer, and the piezoelectric layer is made of lithium niobate or aluminum nitride material.

[0008] Further, in the emission mode, a unipolar driving voltage is applied to the central electrode, and in the reception mode, the output signal is processed by a single-ended amplifier circuit.

[0009] Further, the outer ring electrodes are connected in parallel to a unified reference ground through a surface metallization process with the outer ring electrodes of adjacent transducer units.

[0010] Further, the central electrode is configured to have an area equal to that of the outer ring electrode.

[0011] The technical solution of the second aspect of the present invention provides a coupling method for a dual-electrode piezoelectric thin film ultrasonic transducer array, adopting the dual-electrode piezoelectric thin film ultrasonic transducer of the technical solution of the first aspect of the present invention. The method includes: Form a structural layer on the support layer through a microfabrication process; Deposit a floating electric field regulation layer on the structural layer, and deposit a piezoelectric layer above the floating electric field regulation layer; Perform patterning on the piezoelectric layer to form a multi-channel array layout; Perform grooving isolation on the floating electric field regulation layer of each channel, and the groove is used to block the electrical connection between the floating electric field regulation layers of adjacent channels; Deposit a passivation layer to fill the groove area and perform surface planarization treatment; Form electrode assemblies for each channel on the passivation layer and perform electrical connection.

[0012] Further, forming electrode assemblies for each channel on the passivation layer and performing electrical connection includes: Deposit a metal layer on the passivation layer by magnetron sputtering, and form the central electrode, outer ring electrode and connection point of each channel through a patterning process; Connect the outer ring electrodes of each channel in parallel to a unified reference ground through the connection point, and independently lead out the central electrode of each channel.

[0013] Further, the groove penetrates through the floating electric field regulation layer, and the thickness of the passivation layer matches the depth of the groove.

[0014] The present invention has the following beneficial effects: The dual-electrode piezoelectric thin-film ultrasonic transducer provided by the present invention, through the design of the surface dual-electrode structure of the central electrode and the outer-ring electrode, configures the floating electric field regulation layer without an external electrical interface, configures the central electrode as the driving signal input or the receiving signal output terminal, and configures the outer-ring electrode as the reference ground terminal. Only the central electrode and the outer-ring electrode are required to achieve the functions of ultrasonic transmission and reception. Compared with the traditional dual-electrode PMUT, the positive and negative two-way driving circuits of the traditional dual-electrode PMUT are reduced to one, and the differential signal is changed to a single-ended signal, significantly reducing the number of interfaces and the wiring complexity. In the transmission mode, the unipolar driving voltage directly acts on the central electrode, and in the reception 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.

[0015] On the other hand, the dual-electrode piezoelectric thin-film ultrasonic transducer array coupling method provided by the present invention solves the problem of signal crosstalk caused by the shared bottom electrode in the multi-channel array by grooving to isolate the floating electric field regulation layers of each channel and filling the passivation layer to physically block the charge leakage path between adjacent channels. The surface electrode assembly simplifies the complex differential wiring of the traditional dual-electrode array into single-ended signal control by grounding the outer-ring electrodes uniformly and independently leading out the central electrodes, significantly reducing the number of leads and the process complexity. While ensuring the independent operation of multiple channels, this method maintains the dual-electrode transceiver sensitivity, and reduces the complexity and hardware cost of the driving circuit and detection circuit of the array device to half of the traditional solution, which is suitable for the preparation of large-scale high-density ultrasonic transducer arrays. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0017] Figure 1 It is a schematic cross-sectional structure diagram of a dual-electrode piezoelectric thin-film ultrasonic transducer provided by an embodiment of the present invention; Figure 2 It is a top view of a dual-electrode piezoelectric thin-film ultrasonic transducer provided by an embodiment of the present invention; Figure 3 It is a schematic diagram of the electrode impedance comparison of a dual-electrode piezoelectric thin-film ultrasonic transducer provided by an embodiment of the present invention; Figure 4 It is a partial structure diagram of a dual-electrode piezoelectric thin-film ultrasonic transducer provided by an embodiment of the present invention; Figure 5Schematic wiring diagram of the emission mode of the double - electrode piezoelectric thin - film ultrasonic transducer provided by an embodiment of the present invention; Figure 6 Schematic wiring diagram of the reception mode of the double - electrode piezoelectric thin - film ultrasonic transducer provided by an embodiment of the present invention; Figure 7 Schematic diagram of the electrode reception performance comparison test of the double - electrode piezoelectric thin - film ultrasonic transducer provided by an embodiment of the present invention; Figure 8 Method flowchart of the array coupling method of the double - electrode piezoelectric thin - film ultrasonic transducer provided by an embodiment of the present invention; Figure 9 Schematic diagram of the piezoelectric layer patterning provided by an embodiment of the present invention; Figure 10 Schematic diagram of the grooving provided by an embodiment of the present invention; Figure 11 Schematic diagram of the passivation layer deposition provided by an embodiment of the present invention; Figure 12 Schematic diagram of the electrode assembly deposition provided by an embodiment of the present invention; Figure 13 Schematic diagram of the back - cavity patterning provided by an embodiment of the present invention; Icons: 1 - support layer, 2 - structural layer, 3 - floating - electric - field regulation layer, 4 - piezoelectric layer, 5 - central electrode, 6 - outer - ring electrode, 7 - connection point, 8 - grooving, 9 - passivation layer. Detailed implementation manners

[0018] In order to further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following, in combination with the accompanying drawings and preferred embodiments, details the specific implementation manners, structures, features, and effects of a double - electrode piezoelectric thin - film ultrasonic transducer and its array coupling method proposed according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs.

[0020] The following specifically describes the specific solutions of a double - electrode piezoelectric thin - film ultrasonic transducer and its array coupling method provided by the present invention with reference to the accompanying drawings.

[0021] At present, traditional double - electrode - structure PMUTs improve the emission power and reception sensitivity by designing two regions with opposite electric potentials and utilizing the superposition effect of reverse electric fields. However, the inventor found in actual applications that the traditional double - electrode structure requires etching to expose the bottom metal layer and separately lead out the lower electrode. For a single - channel double - electrode PMUT, a total of 3 external interfaces, namely Vin +, Vin -, and GND, are required; for an n - channel array device, n Vin + and n Vin - interfaces are each required, and another 1 GND interface is needed, totaling 2*n + 1 interfaces, while a conventional single - electrode PMUT only requires n + 1 interfaces. Although the traditional double - electrode PMUT structure has improved performance, the number of pins and the complexity of the leads have increased by about 1 times. At the same time, in terms of the transceiver control of the device, in the emission mode, drive signals with opposite phases need to be separately applied to the inner electrode and the outer electrode, and in the reception mode, the charges of the double electrodes need to be synchronously collected and processed by a differential amplifier. Since two pairs of differential structures are used to control the emission and reception functions, the process difficulty and the complexity of the device control circuit are increased. Especially for a double - electrode PMUT array, the complex wiring, the number of pins, and the complexity of the leads of the traditional double - electrode PMUT are about 2 times that of the conventional single - electrode structure, and the complexity and hardware cost of the drive and detection circuits of the transceiver circuit also double, severely limiting its practical application.

[0022] Please refer to Figure 1 and Figure 2 , which shows a schematic cross - sectional structure diagram and a top - view diagram of a double - electrode piezoelectric thin - film ultrasonic transducer provided by an embodiment of the present invention. The double - electrode piezoelectric thin - film ultrasonic transducer includes: a structure layer 2, a floating - electric - field regulation layer 3, a piezoelectric layer 4, and an electrode assembly arranged in sequence. The floating - electric - field regulation layer 3 is configured without an external electrical interface, and a longitudinal series - electric - field path is formed between the floating - electric - field regulation layer 3 and the electrode assembly. The electrode assembly includes: a central electrode 5, configured as a drive - signal input or a reception - signal output terminal; an outer - ring electrode 6, coaxially and spaced apart from the central electrode 5, configured as a reference - ground terminal.

[0023] Specifically, a floating electric field regulation layer 3, a piezoelectric layer 4, and an electrode assembly are sequentially disposed on the top of the structural layer 2. A support layer 1 configured as a substrate is further provided at the bottom of the structural layer 2. The structural layer 2 is disposed on the support layer 1 through a microfabrication 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 a silicon-based or low-stress material, such as SiO2 or Si, and a circular or annular suspended thin film structure is formed as the structural layer 2 through a microfabrication process. After the structural layer 2 is subjected to patterning, a back cavity is etched at the bottom of the structural layer 2. The microfabrication process specifically refers to precise technologies applied in the fields of semiconductor and microelectromechanical system manufacturing, including technologies such as photolithography, etching, and thin film deposition. In the fabrication of a dual-electrode PMUT, photolithography is used to accurately transfer patterns to determine the shape, position, and size of each layer of material. Etching is used to remove materials in specific areas to form a suspended thin film structure, a back cavity, and to pattern each functional layer. Thin film deposition technologies such as magnetron sputtering are used to grow functional thin films, such as the composite metal layer of the floating electric field regulation layer 3 and the piezoelectric layer 4, to ensure that each layer has corresponding mechanical and electrical properties. The floating electric field regulation layer 3, as a mechanical support and electric field regulation layer, can use a magnetron sputtering device to sequentially sputter-deposit Ti and Pt targets on the surface of the suspended thin film structure layer 2 to form a Ti / Pt composite metal layer as the floating electric field regulation layer 3, ensuring that the thickness of this layer is uniform and there is no external electrical connection lead-out. The floating electric field regulation layer 3 is not provided with an external electrical interface and is only coupled to the surface electrode assembly through a longitudinal electric field path. On the floating electric field regulation layer 3, the piezoelectric layer 4 is grown and patterned by methods such as chemical solution deposition or physical vapor deposition. Then, the central electrode 5 and the outer ring electrode 6 are fabricated on the surface of the piezoelectric layer 4 by using photolithography and sputtering processes again. After the fabrication of each layer is completed, the entire dual-electrode PMUT is subjected to packaging treatment and performance testing.

[0024] In actual operation, in the emission mode, a unipolar driving voltage is applied to the central electrode 5. Due to the presence of the floating electric field regulation layer 3, a longitudinal series electric field is formed. This electric field drives the piezoelectric layer 4 to vibrate. According to the inverse piezoelectric effect, electrical energy is converted into mechanical energy to generate ultrasonic waves and emit them outward. In the receiving mode, external ultrasonic waves act on the piezoelectric layer 4, causing the piezoelectric layer 4 to vibrate. Based on the direct piezoelectric effect, the piezoelectric layer 4 generates an electrical signal, and this signal is output through the central electrode 5. The outer ring electrode 6 serves as a reference ground to provide a stable reference potential for the signal, thereby realizing the effective reception of ultrasonic signals.

[0025] Please refer to Figure 3 、 Figure 4 、 Figure 5 、 Figure 6As shown, where SIG represents the signal, 2VPP represents the peak voltage, V0 represents the sensor output, and Vout represents the amplifier output; in this embodiment, in order to verify the feasibility of the double-electrode PMUT without leading out the bottom electrode, impedance simulation of the double-electrode PMUT was carried out using finite element simulation software. Lithium niobate material was used as the piezoelectric layer 4 to calculate three impedance values respectively: R1 is the impedance of the floating electric field regulation layer 3, R2 is the impedance of the outer ring electrode 6, and R3 is the impedance of the central electrode 5; the specific connection of R1, R2, and R3 is as Figure 3 shown; after simulation, the magnitude relationship between the three impedance values is: R1 and R2 are of the same order of magnitude, and R3 is 3 orders of magnitude higher. The following takes the parameters in Table 1 as an example for specific description. As shown in Table 1:

[0026] Table 1: Parameter settings for impedance simulation of finite element software devices After finite element simulation, R1 is 80 KΩ, R2 is 100 KΩ, and R3 is 78 MΩ; see Figure 5 , in the transmission mode, only a peak-to-peak voltage equivalent to that of a conventional double electrode needs to be applied between the inner and outer electrodes, and there is no need to additionally generate a driving signal with a reverse phase. Since R3 is extremely large, the electric field forms a series connection path longitudinally through the bottom floating electric field regulation layer 3. When the areas of the inner and outer ring electrodes 6 are equal, it is completely equivalent to the reverse potential driving of the conventional structure, achieving a vibration output efficiency equivalent to that of the conventional double electrode; see Figure 6 , in the receiving mode, through a reverse amplifier circuit, the central electrode 5 is connected to the input end of the amplifier, and the outer ring electrode 6 is connected to the reference ground, and the amplification of the received signal can be achieved without using the differential amplification method. The high transverse impedance forces the signal to be obtained through the series longitudinal electric field formed by the bottom floating electric field regulation layer 3. Due to the reverse force characteristics of the inner and outer vibration membranes, the final potential difference is the sum of the absolute values of the longitudinal potentials of the inner and outer electrodes, realizing the amplification of the received signal; it can be understood that in this embodiment, through finite element simulation, the feasibility of the double-electrode PMUT without leading out the bottom electrode was successfully verified. From the analysis results of the impedance characteristics, the specific impedance relationship enables the double-electrode PMUT to achieve similar or even better performance than the conventional double-electrode structure in the transmission and receiving modes with a simplified driving and signal processing method. In the transmission mode, the simplified driving method avoids the generation of complex driving signals with opposite phases; in the receiving mode, single-ended signal processing replaces differential amplification, reducing the circuit complexity. It shows that the double-electrode PMUT provided in this embodiment, while ensuring the core performance of the ultrasonic transducer, effectively simplifies the device structure and control method by optimizing the electrode structure and utilizing the unique electric field path, providing a more efficient and low-cost solution for the design and manufacture of ultrasonic transducers.

[0027] To verify the feasibility of not leading out the bottom electrode and the effectiveness of changing the three - electrode control to dual - electrode control for the new dual - electrode PMUT, and at the same time confirm that it retains the double - sensitivity advantage of the dual - electrode structure, the following test verifications were carried out: In this embodiment, the new dual - electrode PMUT in three working modes of single outer - ring electrode 6, single center electrode 5, and dual - electrode was tested. Under different modes, appropriate excitation signals were applied to simulate the actual working scenario of the ultrasonic transducer; with appropriate measuring equipment, the voltage - time - varying data of the output signals of the device under different modes were collected, such as Figure 7 the waveform shown, Figure 7 where the abscissa represents time, reflecting the change process of the signal over time; the ordinate represents voltage, showing the voltage amplitude of the output signal of the device at different time points; and then the collected data were processed to calculate the peak value Vpp of the signal in each mode, obtaining 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 has successfully achieved not leading out the bottom electrode and adopting the control method of dual - electrode. The peak Vpp (13.3) in the dual - electrode mode obtained by the test 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), which indicates that the new dual - electrode PMUT simplifies the control method while retaining the double - sensitivity advantage of the dual - electrode structure compared with the single - electrode structure. Through the dual - electrode PMUT provided in the embodiment, without affecting the core performance sensitivity of the ultrasonic transducer, the control difficulty of the device is effectively reduced, providing a more convenient and efficient solution for the integration and use of the ultrasonic transducer in practical applications.

[0028] In summary, for the dual - electrode piezoelectric thin - film ultrasonic transducer provided in this embodiment, by designing the surface dual - electrode structure of the center electrode 5 and the outer - ring electrode 6, configuring the floating - electric - field regulation layer 3 without an external electrical interface, configuring the center electrode 5 as the drive - signal input or receive - signal output terminal, and the outer - ring electrode 6 as the reference - ground terminal, the functions of ultrasonic wave transmission and reception can be realized only with the center electrode 5 and the outer - ring electrode 6; compared with the traditional dual - electrode PMUT, the positive and negative two - way drive circuits of the traditional dual - electrode PMUT are reduced to 1 path, and the differential signal is changed to a single - ended signal, significantly reducing the number of interfaces and the wiring complexity; in the transmission mode, the unipolar drive voltage directly acts on the center electrode 5, and in the reception mode, the single - ended signal processing does not require a differential amplifier circuit, thereby reducing the hardware cost of the drive and detection circuits while retaining the high - sensitivity advantage of the dual - electrode structure.

[0029] Preferably, the central electrode 5 has a circular or annular structure, and the distance 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 a unified reference ground with the outer ring electrodes 6 of adjacent transducer units through a surface metallization process, and the central electrode 5 is configured to have the same area as the outer ring electrode 6; in this embodiment, by adopting a coaxial layout of the circular or annular central electrode 5 and the outer ring electrode 6 and strictly maintaining the distance between the two not less than 5 μm, the capacitive coupling effect between the electrodes is effectively reduced, and signal crosstalk is reduced; the outer ring electrode 6 is connected in parallel to a unified reference ground through a surface metallization process to ensure that the potentials of each unit are 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, and an insulating material is filled at the electrode traces of the central electrode 5 and the outer ring electrode 6 to avoid the risk of short circuit between the electrodes. This solution improves the device reliability while maintaining the high sensitivity of the double electrodes, and is suitable for large-scale integration and complex signal control scenarios of high-density ultrasonic arrays.

[0030] Preferably, the floating electric field control layer 3 is formed by magnetron sputtering to deposit a metal layer 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 a magnetron sputtering device, the substrate with the structural layer 2 cleaned is placed at a suitable position in the sputtering chamber; then a metal target is installed, and the sputtering chamber is evacuated to a high vacuum environment; furthermore, by applying an electric field and a magnetic field, 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 with 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 chemical vapor deposition; in this embodiment, the floating electric field control layer 3 prepared by magnetron sputtering can accurately control the film thickness and uniformity, enabling it to effectively play the roles of mechanical support and electric field control, and being in close contact with the piezoelectric layer 4 to ensure efficient electric field transmission. Selecting lithium niobate or aluminum nitride as the material of the piezoelectric layer 4 makes full use of their good piezoelectric properties to ensure that the ultrasonic transducer efficiently realizes the mutual conversion between electrical energy and mechanical energy, and improves the sensitivity and stability of ultrasonic emission and reception. The piezoelectric layer 4 can also adopt other types of piezoelectric materials such as lead zirconate titanate.

[0031] Preferably, a unipolar driving voltage is applied to the central electrode 5 in the transmitting mode, and the output signal is processed by a single-ended amplifier circuit in the receiving mode; 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 connection path of the floating electric field control layer 3 to stimulate the piezoelectric layer 4 to generate symmetric vibration; in the receiving mode, the central electrode 5 is directly connected to the input end of a low-noise reverse amplifier, the outer ring electrode 6 is used as a reference ground, and the high input impedance is used to match the high-impedance characteristic of the piezoelectrically induced charge to directly amplify the single-ended signal generated by the diaphragm deformation. An RC low-pass filter network can also be integrated at the front end of the amplifier to suppress high-frequency noise; shielded traces are used to reduce crosstalk between channels and ensure signal fidelity; in this embodiment, through the simplified architecture of unipolar driving and single-ended signal processing, the positive and negative two-channel driving circuits of the traditional double electrodes are reduced to a single-channel control. At the same time, the longitudinal electric field coupling mechanism of the floating electric field control layer 3 is used to achieve the same vibration efficiency and receiving sensitivity as the traditional double electrodes. In the transmitting mode, the single-sided driving electric field stimulates symmetric vibration through the longitudinal path, avoiding complex differential wiring; in the receiving mode, the single-ended amplifier circuit directly extracts the charge signal, and a high signal-to-noise ratio can be maintained without differential amplification. This solution significantly reduces the hardware complexity and cost, while retaining the performance advantages of the double electrodes, providing a solution for the large-scale integration and low-power consumption application of high-density ultrasonic arrays.

[0032] As described above, the double-electrode piezoelectric thin-film ultrasonic transducer proposed in the technical solution of the first aspect of the present invention significantly reduces the preparation difficulty and the complexity of the transceiver mode control of the double-electrode piezoelectric thin-film ultrasonic transducer by simplifying the electrode configuration, and at the same time effectively reduces the number of wiring layers and the process cost. However, when constructing a multi-channel large-scale array, if the same design strategy as that of a single double-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 "outer ring electrode of channel A → floating electric field control layer → outer ring electrode of channel B → outer ring electrode of channel A". When channel A is in the working state and channel B is in the non-activated state, this loop will generate a parasitic potential difference between the outer ring electrodes 6 of the two channels, resulting in the effective charge generated by the outer ring electrode 6 of channel A leaking 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 exhibit a multi-node parallel characteristic, and finally the potential accumulated on the outer ring of the working channel will be completely offset by the shunt paths of multiple idle channels, resulting in the failure of the differential signal extraction mechanism of the double-electrode structure. To solve this problem, we propose a coupling method for a double-electrode piezoelectric thin-film ultrasonic transducer array; for details, please refer to Figures 8 to 13As shown, it shows a method flow chart of a method for coupling a dual - electrode piezoelectric thin - film ultrasonic transducer array provided by an embodiment of the present invention and schematic diagrams of each step. The method includes: Step S1: Form a structural layer 2 on a support layer 1 through a micro - machining process. Specifically, grow a low - stress SiO2 thin - film layer as the structural layer 2 on a silicon - based support layer 1 through chemical vapor deposition. Step S2: Deposit a floating - field control layer 3 on the structural layer 2 and deposit a piezoelectric layer 4 above the floating - field control layer 3. Specifically, deposit a Ti / Pt composite metal layer as the floating - field control layer 3 on the surface of the suspended thin - film layer by magnetron sputtering without leading out an external interface; deposit a lithium niobate (LiNbO3) or aluminum nitride (AlN) piezoelectric thin - film on the floating - field control layer 3 by pulsed laser deposition or reactive magnetron sputtering. Step S3: Pattern the piezoelectric layer 4 to form a multi - channel array layout. Specifically, perform patterning by reactive ion etching (RIE) to release the film boundary to form a multi - channel array layout; after patterning, form a circular or annular back - cavity structure at the bottom of the structural layer 2 through photolithography and anisotropic dry - etching processes. Step S4: Groove 8 isolate the floating - field control layer 3 of each channel. The groove 8 is used to block the electrical connection of the floating - field control layer 3 between adjacent channels. Specifically, use deep reactive ion etching (DRIE) or focused ion beam (FIB) technology to physically groove 8 the floating - field control layer 3 of each channel. The depth of the groove 8 penetrates the metal layer to ensure complete isolation of the floating - field control layer 3 between adjacent channels and block the charge leakage path. Step S5: Deposit a passivation layer 9 to fill the groove 8 area and perform surface planarization. Specifically, since grooving 8 isolation between different channels makes wiring impossible, in this embodiment, the passivation layer 9 deposition and filling method is used to achieve the unified connection of the outer - ring electrodes 6 between channels to the reference ground. The groove 8 penetrates the floating - 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 by plasma - enhanced chemical vapor deposition, with a thickness matching the depth of the groove 8, and then chemical - mechanical polishing is performed to achieve surface planarization, providing a continuous substrate for subsequent electrode deposition. Step S6: Form electrode assemblies for each channel on the passivation layer 9 and perform electrical connection. Specifically, deposit a surface metal layer by magnetron sputtering and construct electrode assemblies and connection points 7 through patterning, and connect the outer - ring electrodes 6 of different channels together; among them, the connection point 7 includes a common outer - ring electrode 6 connection point and a central - electrode 5 connection point for different channels. Connect the outer - ring electrodes 6 of each channel in parallel to the unified reference - ground connection point, and only one common - grounding interface is required; the central electrodes 5 of each channel are independently led out to the corresponding signal connection points.

[0033] In this embodiment, by etching and isolating the floating electric field control layer 3 between different channels, the closed loop formed by the path of "outer ring electrode of channel A → floating electric field control layer → outer ring electrode of channel B → outer ring electrode of channel A" is eliminated, avoiding the potential consumption of the non-working channel on the 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 connection point led out by the bottom ground electrode, a total of 33 connection points. However, in this patent, since the formed array device does not need to separately lead out the outer ring of each channel, but connects all the outer ring electrodes 6 together to form a reference ground electrode, only 16 central electrode 5 connection points and 1 reference ground connection point are required, reducing the wiring complexity by 50%.

[0034] The dual-electrode piezoelectric thin-film ultrasonic transducer array coupling method provided in this embodiment physically blocks the charge leakage path between adjacent channels by grooving 8 to isolate the floating electric field control layer 3 of each channel and filling the passivation layer 9, solving the problem of signal crosstalk caused by sharing the bottom electrode in 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 grounding the outer ring electrode 6 uniformly and leading out the central electrode 5 independently, significantly reducing the number of leads and the process complexity. While ensuring the independent operation of multiple channels, this method maintains the dual-electrode transceiver sensitivity, and reduces the complexity of the driving circuit, detection circuit, and hardware cost of the array device to half of the traditional solution, being applicable to the preparation of large-scale high-density ultrasonic transducer arrays.

[0035] Preferably, forming and electrically connecting the electrode assemblies of each channel on the passivation layer 9 includes: Step S61: Deposit a metal layer on the passivation layer 9 by magnetron sputtering, and form the central electrode 5, outer ring electrode 6, and connection point 7 of each channel through a patterning process; specifically, uniformly deposit a highly conductive metal layer on the surface of the passivation layer 9 by using the magnetron sputtering process; then define the patterns of the central electrode 5, outer ring electrode 6, and connection point 7 on the metal layer through the photolithography process, and use wet etching or dry etching to remove the excess metal to form precise electrode gaps (≥5μm) and connection point 7 structures; finally, fill the electrode trace between the central electrode 5 and the outer ring electrode 6 with SiO2 or SiN insulating medium to avoid short circuit between electrodes.

[0036] Step S62: Connect the outer ring electrodes 6 of each channel in parallel to a unified reference ground through the connection point 7, and independently lead out the central electrode 5 of each channel; specifically, connect the outer ring electrodes 6 of each channel to a unified reference ground pad through surface metal leads. The lead design can adopt a serpentine or radial layout to minimize parasitic inductance and ensure potential consistency; the central electrode 5 of each channel is connected to the corresponding signal pad through an independent metal trace. The trace path is realized by opening a window in the passivation layer 9 or a via across layers to avoid signal crosstalk between channels; finally, perform chemical mechanical polishing on the connection point area to ensure surface planarization and then encapsulate the protective layer to prevent oxidation or mechanical damage; in this embodiment, the electrode assembly is constructed by magnetron sputtering and patterning processes. Combining the wiring strategy of unifying the ground connection of the outer ring electrode 6 and independently leading out the central electrode 5 simplifies the complex differential wiring of the traditional dual-electrode array into single-ended signal control, significantly reducing the number of connection points 7 and the process complexity; while maintaining the high sensitivity of the dual electrodes, this solution greatly reduces the hardware cost and wiring difficulty.

[0037] In summary, for the dual-electrode piezoelectric thin-film ultrasonic transducer and its array coupling method provided by the present invention, in the design of the dual-electrode PMUT monomer, through the surface dual-electrode structure, the bottom electrode lead-out is abandoned, and only the central electrode 5 and the outer ring electrode 6 are used to realize ultrasonic transmission and reception, simplifying the complex drive circuit of the traditional dual electrodes, converting the differential signal into 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 compared to the single-electrode structure; in terms of the dual-electrode PMUT array coupling method, aiming at the key problem of charge leakage in the multi-channel array, a unique process of grooving 8 in the floating electric field control layer 3 between channels for isolation and depositing the passivation layer 9 for filling is adopted, effectively blocking the charge leakage path, avoiding the potential consumption of the non-working channels on the working channels, ensuring the independent and stable operation of each channel, and maintaining the high-sensitivity characteristics of the dual electrodes. 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 improvement of the transducer monomer performance and the requirements of large-scale array applications, and has broad application prospects in fields highly dependent on ultrasonic transducer technology such as medical ultrasonic imaging, industrial non-destructive testing, and acoustic communication.

[0038] It should be noted that: the above sequence of embodiments of the present invention is only for description and does not represent the superiority or inferiority of the embodiments. The processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0039] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other, and each embodiment focuses on the differences from other embodiments.

Claims

1. Dual-electrode piezoelectric thin-film ultrasonic transducer, characterized in that, It includes a structural layer, a floating electric field regulation layer, a piezoelectric layer, and an electrode assembly arranged in sequence. 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 includes: A central electrode configured as a drive signal input or a received signal output terminal; An outer ring electrode coaxially and spaced apart from the central electrode, configured as a reference ground terminal.

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

3. The double-electrode piezoelectric thin-film ultrasonic transducer according to claim 1, wherein It further includes a support layer configured as a substrate. The structural layer is provided on the support layer through a microfabrication process. The structural layer is a suspended thin film structure and is configured with a back cavity.

4. The double-electrode piezoelectric thin-film ultrasonic transducer according to claim 1, wherein, The floating electric field regulation layer is formed by magnetron sputtering to deposit a metal layer and is in contact with the piezoelectric layer. The piezoelectric layer is made of lithium niobate or aluminum nitride material.

5. The double-electrode piezoelectric thin-film ultrasonic transducer according to claim 1, wherein In the emission mode, a unipolar drive voltage is applied to the central electrode, and in the reception mode, the output signal is processed through a single-ended amplifier circuit.

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

7. The dual-electrode piezoelectric thin-film ultrasonic transducer according to any one of claims 1 to 6, characterized in that, The central electrode is configured to have the same area as the outer ring electrode.

8. Method for coupling a dual-electrode piezoelectric thin-film ultrasonic transducer array, characterized in that, Using the dual-electrode piezoelectric thin film ultrasonic transducer according to any one of claims 1 to 7, the method includes: Forming a structural layer on the support layer through a microfabrication process; Depositing a floating electric field regulation layer on the structural layer and depositing a piezoelectric layer above the floating electric field regulation layer; Performing patterning on the piezoelectric layer to form a multi-channel array layout; Grooving and isolating the floating electric field regulation layer of each channel. 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 grooved area and performing surface planarization; Forming the electrode assemblies of each channel on the passivation layer and performing electrical connection.

9. The method for coupling a dual-electrode piezoelectric thin film ultrasonic transducer array according to claim 8, wherein, Forming the electrode assemblies of each channel on the passivation layer and performing electrical connection, 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 through a patterning process; Connecting the outer ring electrodes of each channel in parallel to a unified reference ground through the connection points and independently leading out the central electrodes of each channel.

10. The dual-electrode piezoelectric thin-film ultrasonic transducer array coupling method according to claim 8, characterized in that The groove penetrates the floating electric field regulation layer, and the thickness of the passivation layer matches the depth of the groove.

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