Flexible PMUTs with bending and torsional deformation functions and preparation method thereof

Abstract

The present invention discloses a flexible PMUT with bending and torsional deformation functions and a preparation method thereof. The device comprises a flexible substrate and a plurality of transducer units disposed on the flexible substrate. Each transducer unit is independent of each other. Specifically, the structural layer, flexible lower electrode, lower piezoelectric layer, flexible intermediate electrode, upper piezoelectric layer, and flexible upper electrode of each unit are independent of each other. Each transducer unit is connected only by flexible materials. When the device is bent, stretched, or twisted, the flexible material is stretched or compressed, resulting in a large deformation, while the piezoelectric layer and structural layer of each unit hardly deform, and the upper piezoelectric layer, lower piezoelectric layer, and structural layer will not break. Thus, the overall high flexibility and stretchability of the device are achieved while ensuring that the performance of each PMUT unit is not affected. The flexible PMUTs of the present invention can be manufactured using a full MEMS process, which can achieve the production of PMUTs with bending and torsional functions while ensuring high sensitivity and unit density of the device.

Description

Technical Field

[0001] The present invention relates to flexible electronics and MEMS ultrasonic transducer technology, and in particular to flexible PMUTs with bending and torsional deformation functions and a preparation method thereof. Background Art

[0002] Ultrasonic waves have the advantages of being non-invasive, highly penetrating, and having good directivity, and are therefore widely used in imaging and medical treatment, biological testing, industrial production, consumer electronics, and other fields. Currently, ultrasonic transducers are mostly based on bulk PZT materials, which have disadvantages such as large size, impedance mismatch with biological tissue, and difficulty in array preparation. In contrast, MEMS ultrasonic transducers have been widely used in many fields due to their small size, large bandwidth, and ease of integration with ICs. Piezoelectric micromachined ultrasonic transducers (PMUTs) are one of the important research directions of MEMS ultrasonic transducers. They have low power consumption, stable performance, and reliable preparation process, and have attracted a lot of research attention. They are currently used in ultrasonic medical treatment, consumer electronics, automotive engineering and other fields.

[0003] In recent years, with the rapid increase in demand for ultrasonic transducer technology that can better adapt to the irregular topography of the detection surface and has excellent flexibility in fields such as ultrasonic bio-detection, human health monitoring, smart factories, and biomimetic robots, flexible PMUTs ultrasonic transducers that can achieve bending, stretching, and torsional deformation functions have become an important development direction. For example, when an ultrasonic sensor is installed on the surface of a biological body, it needs to be able to adhere well and adapt to the irregular topography of the surface to avoid air gaps that affect detection accuracy; when the ultrasonic sensor is attached to the human wrist for blood pressure and heart rate detection, human movement will cause the transducer to frequently stretch and bend; when the transducer is attached to the skin above the brachial artery or carotid artery, human movement will also cause the transducer to undergo significant torsional deformation; when the ultrasonic transducer is attached to the surface of a soft robot, the transducer will undergo various forms of deformation such as bending, stretching, and torsion as the robot moves. However, the current PMUTs structure is mainly based on rigid materials such as silicon and glass, which makes it difficult to achieve bending, stretching and torsional deformation to meet the ultrasonic detection needs in the above situations. Therefore, there is an urgent need for the development of flexible PMUTs sensors that can achieve bending and torsional deformation functions.

[0004] Currently, in order to realize the production of flexible PMUTs ultrasonic transducers, some researchers fill flexible materials between array elements to make the entire ultrasonic transducer array flexible. However, the device production process often does not fully adopt MEMS technology and the electrode connection between each unit is difficult, making it difficult to mass-produce ultrasonic arrays with dense array elements, making it difficult to improve the performance of the sensor. Other researchers use flexible piezoelectric materials such as PVDF to make completely flexible ultrasonic transducers. Although this method allows the device to maintain a high degree of flexibility, the piezoelectric coefficient of the flexible piezoelectric material is low, which limits the performance of the device. Some researchers also make rigid piezoelectric layers and structural layers on a flexible substrate. Since the piezoelectric layer and structural layer are thin, the overall structure of the device has a certain degree of bendability. However, since the rigid structural layer and piezoelectric layer are not stretchable, the device cannot achieve tensile and torsional deformation.

[0005] In summary, although existing research has made some progress in the design and preparation of flexible PMUTs, it is still difficult to achieve micromachining technology for PMUTs two-dimensional transducer arrays that takes into account high unit density, high transceiver performance, high flexibility and stretchability. Summary of the Invention

[0006] To solve the above technical difficulties, the present invention proposes a flexible PMUTs with bending and torsional deformation functions and a preparation method thereof. The flexible PMUTs of the present invention can be manufactured using a full MEMS process, which can achieve the production of PMUTs with bending and torsional functions while ensuring the high sensitivity and unit density of the device.

[0007] The technical solution adopted in the present invention is as follows:

[0008] A flexible PMUTs with bending and torsional deformation functions includes a flexible substrate and a plurality of transducer units arranged on the flexible substrate, each transducer unit including a flexible support, a structural layer, a flexible lower electrode, a lower piezoelectric layer, a flexible intermediate electrode, an upper piezoelectric layer, and a flexible upper electrode. The flexible support is arranged on the flexible substrate, the structural layer is arranged at the upper end of the flexible support, and a vacuum cavity is sealed between the structural layer, the flexible support, and the flexible substrate; the lower piezoelectric layer is arranged on the upper surface of the structural layer, the flexible lower electrode is arranged on the upper surface of the structural layer, and the flexible lower electrode is embedded in the lower surface of the lower piezoelectric layer; the upper piezoelectric layer is arranged on the upper surface of the lower piezoelectric layer, the flexible intermediate electrode is in a ring shape, the flexible intermediate electrode is arranged on the upper surface of the lower piezoelectric layer, and the flexible intermediate electrode is embedded in the lower surface of the upper piezoelectric layer, and the flexible upper electrode is arranged on the upper surface of the upper piezoelectric layer; the flexible upper electrode is electrically connected to the flexible lower electrode;

[0009] The flexible support is shared between adjacent transducer units, and upper electrode electrical connections are provided between the flexible upper electrodes of all transducer units; and middle electrode electrical connections are provided between the flexible middle electrodes of all transducer units.

[0010] Preferably, in each transducer unit, the flexible upper electrode, the upper piezoelectric layer, the lower piezoelectric layer, the flexible lower electrode, the structural layer, and the cavity have the same shape, the flexible middle electrode and the cavity have the same lateral dimensions, the flexible upper electrode and the flexible lower electrode have the same lateral dimensions, and the lateral dimensions of the flexible upper electrode and the flexible lower electrode are larger than the lateral dimensions of the flexible middle electrode and the cavity; the lateral dimension of the upper piezoelectric layer is larger than the lower piezoelectric layer and the structural layer, the lateral dimensions of the lower piezoelectric layer and the structural layer are the same, and the lateral dimensions of the upper piezoelectric layer, the lower piezoelectric layer, and the structural layer are larger than the lateral dimensions of the flexible upper electrode and the flexible lower electrode; the axes of the flexible upper electrode, the upper piezoelectric layer, the flexible middle electrode, the lower piezoelectric layer, the flexible lower electrode, the structural layer, and the cavity are coaxial.

[0011] Preferably, the cross-sectional shapes of the flexible upper electrode, the upper piezoelectric layer, the lower piezoelectric layer, the flexible lower electrode, the structural layer and the cavity are all circular.

[0012] Preferably, in each transducer unit, a conductive channel is provided through the flexible upper electrode, the upper piezoelectric layer and the lower piezoelectric layer, the conductive channel is located outside the outer edge of the flexible middle electrode, the upper end of the conductive channel is connected to the flexible upper electrode, and the lower end of the conductive channel is connected to the flexible lower electrode, and the conductive channel is filled with flexible conductive material.

[0013] Preferably, the upper surface of the flexible support is provided with a groove between adjacent transducer units, the upper electrode electrical connection and the middle electrode electrical connection are both arranged in the groove, and an electrical connection isolation layer is provided between the upper electrode electrical connection and the middle electrode electrical connection.

[0014] Preferably, the material of the flexible upper electrode is indium tin oxide flexible conductive material, the material of the flexible middle electrode is indium tin oxide flexible conductive material, the material of the flexible lower electrode is indium tin oxide flexible conductive material, the material of the upper electrode electrical connection is indium tin oxide flexible conductive material, and the material of the lower electrode electrical connection is indium tin oxide flexible conductive material; the material of the upper piezoelectric layer is AlN, ZnO or PZT, and the material of the lower piezoelectric layer is AlN, ZnO or PZT; the material of the structural layer is Si3N4, SiO2 or SiC; the material of the electrical connection isolation layer is PDMS, Ecoflex, PI or PET; the material of the flexible pillar is photoresist or BCB; the material of the flexible substrate is PDMS, photoresist, BCB, PET or PI.

[0015] Preferably, the flexible substrate and the flexible pillar adopt an integrated structure, and the flexible pillar is the remaining flexible substrate located around the cavity after a cavity is machined on the upper surface of the flexible substrate.

[0016] Preferably, the plurality of transducer units are distributed on the flexible substrate in a matrix form.

[0017] The method for preparing the flexible PMUTs with bending and torsional deformation functions of the present invention comprises the following steps:

[0018] S1, preparing a flexible layer on the surface of a rigid substrate (such as a glass substrate);

[0019] S2, etching the upper surface of the flexible layer to form a cavity, and the remaining flexible layer serves as a flexible support and a flexible substrate;

[0020] S3, bonding the single crystal silicon wafer having a silicon dioxide layer on the top layer to the upper surface of the flexible pillar under a vacuum environment, sealing the cavity, and the silicon dioxide layer covering the upper surface of the flexible pillar during bonding;

[0021] S4, removing the single crystal silicon layer on the single crystal silicon wafer and retaining the silicon dioxide layer;

[0022] S5, preparing a flexible lower electrode layer on the upper surface of the silicon dioxide layer, and performing photolithography and etching on the flexible lower electrode layer to form a patterned flexible lower electrode;

[0023] S6, depositing a piezoelectric layer on the surface of the silicon dioxide layer and the flexible lower electrode;

[0024] S7, photolithography and etching of the piezoelectric layer and the silicon dioxide layer, where the etching stops at the surface of the flexible substrate to form a structural layer and a lower piezoelectric layer;

[0025] S8, sputtering a flexible intermediate electrode layer on the flexible substrate and the lower piezoelectric layer, photolithography, and etching the flexible intermediate electrode layer to form a patterned annular flexible intermediate electrode and electrically connect the flexible intermediate electrode;

[0026] S9, performing photolithography and deposition to form a mask on the flexible substrate and the lower piezoelectric layer, spin-coating a flexible insulating material layer on the flexible substrate, photolithography and etching the flexible insulating material layer to form an electrical connection isolation layer, and removing the mask;

[0027] S10, depositing a piezoelectric material layer on the electrical connection isolation layer and the flexible intermediate electrode, and photolithography and etching the piezoelectric material layer to form an upper piezoelectric layer;

[0028] S11, photolithography and etching of the upper piezoelectric layer and the lower piezoelectric layer to form a conductive channel;

[0029] S12, sputtering a flexible electrode layer on the upper piezoelectric layer and the electrical connection isolation layer, and filling the conductive channel with the material of the flexible electrode layer, and then photolithography and etching the flexible electrode layer to form a patterned flexible upper electrode and an electrical connection between the flexible upper electrode and the flexible upper electrode;

[0030] S13, removing the rigid substrate to obtain the flexible PMUTs with bending and torsional deformation functions.

[0031] Preferably, when the upper surface of the flexible support is provided with grooves between adjacent transducer units:

[0032] In the above S7, when the piezoelectric layer and the silicon dioxide layer are photolithographically and etched, the etching stops at the surface of the flexible substrate, and then the upper surface of the flexible substrate is processed to form the groove, and then S8 is performed.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The flexible PMUTs with bending and torsional deformation functions of the present invention have flexible pillars and flexible substrates, and each transducer unit is independent of each other, specifically, the structural layer, flexible lower electrode, lower piezoelectric layer, flexible middle electrode, upper piezoelectric layer and flexible upper electrode of each unit are independent of each other, and each transducer unit is connected only by flexible materials. When the device is bent, stretched and twisted, the flexible material is stretched or compressed, resulting in a large deformation, while the piezoelectric layer and structural layer of each unit are almost not deformed, and the upper piezoelectric layer, lower piezoelectric layer and structural layer will not be broken, thereby achieving high flexibility and stretchability of the device as a whole while ensuring that the performance of each PMUTs unit is not affected; the present invention has two piezoelectric layers, an upper piezoelectric layer and a lower piezoelectric layer. Compared with the conventional PMUTs structure with one piezoelectric layer and one structural layer, the structural layer It is replaced by a piezoelectric layer. When the flexible upper electrode and the flexible lower electrode are grounded and AC excitation is applied to the flexible middle electrode, the upper and lower piezoelectric layers will shrink or stretch in opposite radial directions respectively, so that the displacement of the piezoelectric layer increases, and the transducer has greater sensitivity. The present invention has a ring-shaped flexible middle electrode. When vibrating, compared with the conventional PMUTs structure, the edge displacement of the piezoelectric layer can be increased, so that the entire piezoelectric layer tends to piston vibration, the average vibration displacement of the piezoelectric layer is increased, and the performance of the flexible PMUTs is improved. The present invention has a vacuum cavity, so that when the piezoelectric layer and the structural layer vibrate, the energy is only transmitted to the other side of the cavity, reducing energy loss. In summary, the PMUTs of the present invention effectively improve the ultrasonic transmission and reception performance while realizing the bending and torsional deformation functions, and based on the MEMS manufacturing process, it can realize mass production of high-density ultrasonic arrays.

[0035] Furthermore, the upper surface of the flexible pillar is provided with grooves between adjacent transducer units, and the grooves can further reduce the connection parts between the flexible pillars shared by adjacent transducer units, thereby improving the flexibility of the entire flexible PMUTs. At the same time, the present invention has an electrical connection isolation layer, which separates the electrical connection of the upper electrode from the electrical connection of the middle electrode, thereby realizing the electrical connection of each unit and realizing the preparation of a high filling density array based on MEMS technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram (cross-sectional view) of the flexible PMUTs structure with bending and torsional deformation functions of the present invention;

[0037] Figure 2 For the present invention Figure 1 Schematic diagram of the top view of the flexible PMUTs with bending and torsional deformation functions according to the embodiment shown.

[0038] Figure 3 For the present invention Figure 1 Schematic diagram of the tensile deformation structure of flexible PMUTs with bending and torsional deformation functions in the embodiment shown.

[0039] Figure 4 For the present invention Figure 1 Schematic diagram of the bending deformation structure of flexible PMUTs with bending and torsional deformation functions in the embodiment shown.

[0040] Figure 5 For the present invention Figure 1 Schematic diagram of the torsional deformation structure of flexible PMUTs with bending and torsional deformation functions in the embodiment shown.

[0041] Figure 6 This is a schematic diagram (cross-sectional view) of the first variation structure of the flexible PMUTs with bending and torsional deformation functions of the present invention.

[0042] Figure 7 Schematic diagram (cross-sectional view) of the second variation structure of the flexible PMUTs with bending and torsional deformation functions of the present invention.

[0043] Figure 8 For the present invention Figure 1 FIG. 1 is a flow chart of a process for preparing flexible PMUTs with bending and torsional deformation functions according to an embodiment of the present invention.

[0044] In the figure: 1-flexible upper electrode; 2-conductive channel; 3-upper piezoelectric layer; 4-flexible middle electrode; 5-lower piezoelectric layer; 6-flexible lower electrode; 7-structural layer; 8-upper electrode electrical connection; 9-electrical connection isolation layer; 10-middle electrode electrical connection; 11-flexible pillar; 12-cavity; 13-flexible substrate; 14-glass substrate; 15-SU-8 photoresist layer; 16-single crystal silicon wafer; 17-silicon dioxide layer; 18-AlN layer; 19-groove. DETAILED DESCRIPTION

[0045] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and embodiments:

[0046] Reference Figure 1 、 Figure 2 、 Figure 6-Figure 8The flexible PMUTs with bending and torsional deformation functions of the present invention include a flexible substrate 13 and a plurality of transducer units arranged on the flexible substrate 13, each transducer unit including a flexible pillar 11, a structural layer 7, a flexible lower electrode 6, a lower piezoelectric layer 5, a flexible intermediate electrode 4, an upper piezoelectric layer 3 and a flexible upper electrode 1. The flexible pillar 11 is arranged on the flexible substrate 13, the structural layer 7 is arranged at the upper end of the flexible pillar 11, and a vacuum cavity 12 is sealed between the structural layer 7, the flexible pillar 11 and the flexible substrate 13; the lower piezoelectric layer 5 is arranged on the upper surface of the structural layer 7, the flexible lower electrode 6 is arranged on the upper surface of the structural layer 7 and the flexible lower electrode 6 is embedded in the lower surface of the lower piezoelectric layer 5; the upper piezoelectric layer 3 is arranged on the upper surface of the lower piezoelectric layer 5, the flexible intermediate electrode 4 is in a ring shape, the flexible intermediate electrode 4 is arranged on the upper surface of the lower piezoelectric layer 5 and the flexible intermediate electrode 4 is embedded in the lower surface of the upper piezoelectric layer 3, and the flexible upper electrode 1 is arranged on the upper surface of the upper piezoelectric layer 3; the flexible upper electrode 1 is electrically connected to the flexible lower electrode 6;

[0047] The flexible support 11 is shared between adjacent transducer units. An upper electrode electrical connection 8 is provided between the flexible upper electrodes 1 of all transducer units; and an intermediate electrode electrical connection 10 is provided between the flexible intermediate electrodes 4 of all transducer units.

[0048] The flexible intermediate electrode 4 adopts an annular electrode. The purpose is to make the displacement of the edge area of ​​the upper piezoelectric layer 3 and the lower piezoelectric layer 5 larger when the piezoelectric layer vibrates, so that the piezoelectric layer is closer to the piston vibration and has a larger average displacement, thereby improving the performance of the device. The lateral dimensions of the inner and outer circles of the annular electrode need to fully consider the impact on the vibration displacement of the piezoelectric layer. The purpose of setting the two piezoelectric layers of the upper piezoelectric layer 3 and the lower piezoelectric layer 5 is: when the flexible upper electrode 1 and the flexible lower electrode 6 are grounded and the flexible intermediate electrode 4 applies AC excitation, the upper piezoelectric layer 3 and the lower piezoelectric layer 5 will shrink or stretch in opposite radial directions respectively, so that the axial displacement of the piezoelectric layer is greatly improved, thereby improving the sensitivity of the device. The selection of the thickness and lateral dimensions of the upper and lower piezoelectric layers should fully consider the impact on the resonant frequency of the device. The interior of the cavity 12 is vacuum. The purpose of using a vacuum cavity is that when the upper piezoelectric layer 3 and the lower piezoelectric layer 5 vibrate, the sound wave only propagates to the side with the medium, and does not propagate into the cavity 12, thereby reducing the energy loss of the device and avoiding the noise interference caused by the reflection of the sound wave in the cavity 12.

[0049] Combine Figure 2-Figure 5The cross-sectional shapes of the flexible upper electrode 1, upper piezoelectric layer 3, lower piezoelectric layer 5, flexible lower electrode 6, structural layer 7, and cavity 12 are all circular. In each transducer unit, the flexible upper electrode 1, upper piezoelectric layer 3, lower piezoelectric layer 5, flexible lower electrode 6, structural layer 7, and cavity 12 are of the same shape. The lateral dimensions of the flexible intermediate electrode 4 and cavity 12 are the same. The lateral dimensions of the flexible upper electrode 1 and flexible lower electrode 6 are the same. The lateral dimensions of the flexible upper electrode 1 and flexible lower electrode 6 are larger than those of the flexible intermediate electrode 4 and cavity 12. The lateral dimensions of the upper piezoelectric layer 3 are larger than those of the lower piezoelectric layer 5 and structural layer 7. The lateral dimensions of the lower piezoelectric layer 5 and structural layer 7 are larger than those of the flexible upper electrode 1 and flexible lower electrode 6. The axes of the flexible upper electrode 1, upper piezoelectric layer 3, flexible intermediate electrode 4, lower piezoelectric layer 5, flexible lower electrode 6, structural layer 7, and cavity 12 are coaxial. The lateral dimension of the structural layer 7 needs to be larger than the lateral dimension of the cavity 12 to ensure the sealing of the cavity; the thickness of the structural layer 7 should be as small as possible while ensuring the bonding quality to avoid adverse effects on the sensitivity of the device.

[0050] In the present invention, the flexible upper electrode 1 and the flexible lower electrode 6 in each transducer unit are electrically connected in the following manner: a conductive channel 2 is provided through the flexible upper electrode 1, the upper piezoelectric layer 3 and the lower piezoelectric layer 5. The conductive channel 2 is located outside the outer edge of the flexible middle electrode 4. The upper end of the conductive channel 2 is connected to the flexible upper electrode 1, and the lower end of the conductive channel 2 is connected to the flexible lower electrode 6. The conductive channel 2 is filled with a flexible conductive material.

[0051] In the above scheme of the present invention, the upper electrode electrical connection 8 and the intermediate electrode electrical connection 10 can adopt different paths or the same path; when the same path is adopted, the upper electrode electrical connection 8 is stacked above the intermediate electrode electrical connection 10, and an electrical connection isolation layer 9 is provided between the upper electrode electrical connection 8 and the intermediate electrode electrical connection 10.

[0052] As another variant structure of the present invention, Figure 6 As shown, the upper surface of the flexible support 11 is provided with grooves 19 between adjacent transducer units. The upper electrode electrical connection 8 and the middle electrode electrical connection 10 are both disposed within the grooves 19, with an electrical connection isolation layer 9 disposed between the upper electrode electrical connection 8 and the middle electrode electrical connection 10. The purpose of the grooves 19 is to further enhance the flexibility of the entire PMUT, thereby improving the device's ability to undergo tensile, bending, and torsional deformation. The width of the grooves 19 should fully consider their impact on the bonding strength between the structural layer 7 and the flexible support 11, as well as their impact on the deformation of the piezoelectric layer and the structural layer 7.

[0053] In the above-mentioned solution of the present invention, the materials of each structure are selected as follows: the material of the flexible upper electrode 1 is a flexible conductive material of indium tin oxide, the material of the flexible middle electrode 4 is a flexible conductive material of indium tin oxide, the material of the flexible lower electrode 6 is a flexible conductive material of indium tin oxide, the material of the upper electrode electrical connection 8 is a flexible conductive material of indium tin oxide, and the material of the lower electrode electrical connection is a flexible conductive material of indium tin oxide; the material of the upper piezoelectric layer 3 is AlN, ZnO or PZT, and the material of the lower piezoelectric layer 5 is AlN, ZnO or PZT; the material of the structural layer 7 is made of a rigid insulating material such as Si3N4, SiO2 or SiC, which is easy to bond with materials such as SU-8 photoresist; the material of the electrical connection isolation layer 9 is a flexible insulating material such as PDMS, Ecoflex, PI or PET. The purpose of using the insulating material is to separate the upper electrode electrical connection 8 from the middle electrode electrical connection 10 to prevent them from being conductive; the purpose of using the flexible material is to not affect the relative movement between the units and ensure the flexibility of the device; the thickness of the electrical connection isolation layer 9 should be as small as possible while ensuring the insulation between the upper and lower electrodes to avoid affecting the flexibility of the device. The flexible pillar 11 is made of insulating flexible materials such as photoresist or BCB; the flexible substrate 13 is made of insulating flexible materials such as PDMS, photoresist, BCB, PET or PI. The purpose of using flexible materials for the flexible pillar 11 and the flexible substrate 13 is to make the device stretchable and prevent the device from breaking during stretching, bending, and twisting. Another purpose of using insulating flexible materials such as SU-8 photoresist or BCB for the flexible pillar 11 and the flexible substrate 13 is to facilitate bonding with the structural layer 7 through a bonding process. In the present invention, the flexible upper electrode 1, the flexible middle electrode 4, the upper electrode electrical connection 8, and the middle electrode electrical connection 10 are made of flexible conductive materials such as ITO that are compatible with MEMS technology. The purpose of using flexible conductive materials is to make the electrical connections between the units stretchable to a certain extent and prevent them from breaking due to bending and twisting of the device. The thickness of the flexible upper electrode 1, the flexible middle electrode 4, the upper electrode electrical connection 8, and the middle electrode electrical connection 10 should be as small as possible while ensuring conductivity to improve their stretchability and avoid affecting the resonant frequency of the device.

[0054] Figure 3 、 Figure 4 、 Figure 5 These are schematic diagrams of the application modes of stretching, bending and torsional deformation of flexible PMUTs with bending and torsional deformation functions. It can be seen that the PMUTs device can be well implemented under different deformation conditions.

[0055] As another variant structure of the present invention, Figure 1 and Figure 6As shown, the flexible substrate 13 and the flexible support 11 of the present invention can adopt an integrated structure. In this case, the flexible support 11 is the remaining flexible substrate 13 located around the cavity 12 after the cavity 12 is processed on the upper surface of the flexible substrate 13. Figure 7 As shown, the flexible substrate 13 and the flexible support 11 can also adopt a split structure. In this case, the flexible substrate 13 and the flexible support 11 are generally made of different materials, or are processed through different processes during preparation. The present invention does not make special limitations, and researchers can design and process according to actual conditions.

[0056] See also Figure 3-Figure 5 In the present invention, several transducer units of the flexible PMUTs with bending and torsional deformation functions are distributed in a matrix form on the flexible substrate 13. The specific distribution form of the transducer units can also be flexibly selected according to actual needs, and can be distributed in various shapes such as circular and polygonal shapes. The present invention will no longer limit this.

[0057] The present invention is Figure 1 As an example, the structure of the flexible PMUTs shown in the figure is combined with Figure 8 The preparation process of the flexible PMUTs of this structure is introduced as follows. Figure 3-Figure 5 The transducer units shown are arranged in an array of flexible PMUTs. The process includes the following steps:

[0058] (1) Take a glass substrate 14 and spin-coat a SU-8 photoresist layer 15 on the surface;

[0059] (2) Photolithography and etching of the SU-8 photoresist layer 15 to form a plurality of cavities 12 distributed in a row on the SU-8 photoresist layer 15, and the remaining SU-8 photoresist layer 15 serves as the PMUTs flexible support 11 and the flexible substrate 13;

[0060] (3) forming a silicon dioxide layer 17 on the upper surface of the cleaned single crystal silicon wafer 16 by a dry or wet oxidation method;

[0061] (4) bonding the top silicon dioxide layer 17 of the single crystal silicon wafer 16 to the upper surface of the flexible support 11 under a vacuum environment. The silicon dioxide layer 17, the flexible support 11 and the flexible substrate 13 seal the corresponding area of ​​the cavity 12 to form a sealed, vacuum cavity 12;

[0062] (5) Thinning the single crystal silicon wafer 16 by mechanical chemical polishing, and then etching away the remaining single crystal silicon layer by wet or dry etching, with the etching stopping at the silicon dioxide layer 17;

[0063] (6) depositing or spin-coating an ITO layer on the silicon dioxide layer 17 and performing photolithography and etching to form a patterned flexible lower electrode 6;

[0064] (7) Depositing AlN or ZnO on the surface of the silicon dioxide layer 17 and the flexible lower electrode 6 to form a piezoelectric layer;

[0065] (8) Photolithography and etching of the piezoelectric layer and the silicon dioxide layer 17, with the etching stopping at the surface of the flexible support 11, to form the structural layer 7 and the lower piezoelectric layer 5;

[0066] (9) ITO is prepared on the flexible pillar 11 and the lower piezoelectric layer 5 by a magnetron sputtering process and then photolithographically and etched to form a patterned flexible intermediate electrode 4 and a flexible intermediate electrode electrical connection 10, and the flexible intermediate electrode 4 and the flexible intermediate electrode electrical connection 10 are connected through an electrical connection on the step sidewall;

[0067] (10) On the flexible pillar 11 and the lower piezoelectric layer 5, photolithography and deposition are performed to form a silicon dioxide mask, and then PI is spin-coated on the flexible pillar 11 and the lower piezoelectric layer 5 and photolithography and etching are performed to form an electrical connection isolation layer 9, and then the silicon dioxide mask is removed by wet etching;

[0068] (11) Depositing AlN or ZnO on the electrical connection isolation layer 9 and the flexible intermediate electrode 4 and performing photolithography and etching to form an upper piezoelectric layer 3;

[0069] (12) Photolithography patterns the shape of the conductive channel, dry or wet etching the upper piezoelectric layer 3 and the lower piezoelectric layer 5, and stopping the etching at the flexible lower electrode 6 to form the conductive channel 2;

[0070] (13) ITO is prepared on the upper piezoelectric layer 3 and the electrical connection isolation layer 9 by a magnetron sputtering process and then photolithographically and etched to form a patterned flexible upper electrode 1 and a flexible upper electrode electrical connection 8, and the flexible upper electrode 1 and the flexible upper electrode electrical connection 8 are connected to each other through an electrical connection on the step sidewall;

[0071] (14) The glass substrate 14 is peeled off to complete the preparation.

[0072] In summary, it can be seen that the present invention utilizes a flexible substrate, a flexible support, and independent transducer units to realize the bending, stretching, and twisting functions of the MEMS ultrasonic transducer; utilizes a double-layer piezoelectric layer and annular electrodes to improve the device's electromechanical coupling coefficient, sensitivity, and other performance; utilizes a vacuum cavity to reduce the transducer's energy loss and improve device performance; utilizes an electrical connection isolation layer to isolate the electrical connection between the upper electrode and the middle electrode, thereby realizing electrical connection between the various units of the flexible PMUTs; and utilizes MEMS technology to realize the preparation of miniaturized, high-density two-dimensional flexible ultrasonic transducers.

[0073] The above is only one embodiment of the present invention, not all or the only embodiment. Any equivalent transformation of the technical solution of the present invention made by ordinary technicians in this field after reading the specification of the present invention is covered by the claims of the present invention.

Claims

1. A flexible PMUTs with bending and torsional deformation functions, characterized in that: The invention comprises a flexible substrate (13) and a plurality of transducer units arranged on the flexible substrate (13), each transducer unit comprising a flexible support (11), a structural layer (7), a flexible lower electrode (6), a lower piezoelectric layer (5), a flexible intermediate electrode (4), an upper piezoelectric layer (3) and a flexible upper electrode (1), the flexible support (11) being arranged on the flexible substrate (13), the structural layer (7) being arranged at the upper end of the flexible support (11), and a vacuum cavity (12) being formed by sealing between the structural layer (7), the flexible support (11) and the flexible substrate (13); the lower piezoelectric layer ( 5) is arranged on the upper surface of the structural layer (7), the flexible lower electrode (6) is arranged on the upper surface of the structural layer (7) and the flexible lower electrode (6) is embedded in the lower surface of the lower piezoelectric layer (5); the upper piezoelectric layer (3) is arranged on the upper surface of the lower piezoelectric layer (5), the flexible intermediate electrode (4) is in the shape of a ring, the flexible intermediate electrode (4) is arranged on the upper surface of the lower piezoelectric layer (5) and the flexible intermediate electrode (4) is embedded in the lower surface of the upper piezoelectric layer (3), and the flexible upper electrode (1) is arranged on the upper surface of the upper piezoelectric layer (3); the flexible upper electrode (1) is electrically connected to the flexible lower electrode (6); The flexible support (11) is shared between adjacent transducer units, and an upper electrode electrical connection (8) is provided between the flexible upper electrodes (1) of all transducer units; and an intermediate electrode electrical connection (10) is provided between the flexible intermediate electrodes (4) of all transducer units.

2. The flexible PMUTs with bending and torsional deformation functions according to claim 1, characterized in that: In each transducer unit, the flexible upper electrode (1), the upper piezoelectric layer (3), the lower piezoelectric layer (5), the flexible lower electrode (6), the structural layer (7), and the cavity (12) have the same shape, the flexible middle electrode (4) and the cavity (12) have the same lateral dimensions, the flexible upper electrode (1) and the flexible lower electrode (6) have the same lateral dimensions, and the lateral dimensions of the flexible upper electrode (1) and the flexible lower electrode (6) are larger than the lateral dimensions of the flexible middle electrode (4) and the cavity (12); the upper piezoelectric layer (3) The lateral dimensions of the upper piezoelectric layer (3), the lower piezoelectric layer (5), and the structural layer (7) are larger than the lateral dimensions of the lower piezoelectric layer (5) and the structural layer (7); the lateral dimensions of the upper piezoelectric layer (3), the lower piezoelectric layer (5), and the structural layer (7) are the same; the lateral dimensions of the upper piezoelectric layer (3), the lower piezoelectric layer (5), and the structural layer (7) are larger than the lateral dimensions of the flexible upper electrode (1) and the flexible lower electrode (6); and the axes of the flexible upper electrode (1), the upper piezoelectric layer (3), the flexible intermediate electrode (4), the lower piezoelectric layer (5), the flexible lower electrode (6), the structural layer (7), and the cavity (12) are coaxial.

3. The flexible PMUTs with bending and torsional deformation functions according to claim 2, characterized in that: The cross-sectional shapes of the flexible upper electrode (1), the upper piezoelectric layer (3), the lower piezoelectric layer (5), the flexible lower electrode (6), the structural layer (7) and the cavity (12) are all circular.

4. The flexible PMUTs with bending and torsional deformation functions according to claim 1, characterized in that: In each transducer unit, a conductive channel (2) is provided through the flexible upper electrode (1), the upper piezoelectric layer (3) and the lower piezoelectric layer (5), wherein the conductive channel (2) is located outside the outer edge of the flexible middle electrode (4), the upper end of the conductive channel (2) is connected to the flexible upper electrode (1), and the lower end of the conductive channel (2) is connected to the flexible lower electrode (6), and the conductive channel (2) is filled with a flexible conductive material.

5. The flexible PMUTs with bending and torsional deformation functions according to claim 1, characterized in that: The upper surface of the flexible support (11) is provided with a groove (19) between adjacent transducer units, the upper electrode electrical connection (8) and the middle electrode electrical connection (10) are both arranged in the groove (19), and an electrical connection isolation layer (9) is provided between the upper electrode electrical connection (8) and the middle electrode electrical connection (10); the material of the electrical connection isolation layer (9) is PDMS, Ecoflex, PI or PET.

6. The flexible PMUTs with bending and torsional deformation functions according to claim 1, characterized in that: The material of the flexible upper electrode (1) is indium tin oxide flexible conductive material, the material of the flexible middle electrode (4) is indium tin oxide flexible conductive material, the material of the flexible lower electrode (6) is indium tin oxide flexible conductive material, the material of the upper electrode electrical connection (8) is indium tin oxide flexible conductive material, and the material of the lower electrode electrical connection is indium tin oxide flexible conductive material; the material of the upper piezoelectric layer (3) is AlN, ZnO or PZT, and the material of the lower piezoelectric layer (5) is AlN, ZnO or PZT; the material of the structural layer (7) is Si3N4, SiO2 or SiC; the material of the flexible pillar (11) is photoresist or BCB; the material of the flexible substrate (13) is PDMS, photoresist, BCB, PET or PI.

7. The flexible PMUTs with bending and torsional deformation functions according to claim 1 or 6, characterized in that: The flexible substrate (13) and the flexible pillar (11) adopt an integrated structure, and the flexible pillar (11) is the remaining flexible substrate (13) located around the cavity (12) after the cavity (12) is machined on the upper surface of the flexible substrate (13).

8. The flexible PMUTs with bending and torsional deformation functions according to claim 1, characterized in that: A plurality of transducer units are distributed on the flexible substrate (13) in a matrix form.

9. The method for preparing flexible PMUTs with bending and torsional deformation functions according to any one of claims 1 to 8, characterized in that: The steps include: S1, preparing a flexible layer on the surface of a rigid substrate; S2, etching the upper surface of the flexible layer to form a cavity (12), and the remaining flexible layer serves as a flexible support (11) and a flexible substrate (13); S3, bonding a single crystal silicon wafer (16) having a silicon dioxide layer (17) on the top silicon layer to the upper surface of the flexible pillar (11) under a vacuum environment, sealing the cavity (12), and during bonding, the silicon dioxide layer (17) covers the upper surface of the flexible pillar (11); S4, removing the single crystal silicon layer on the single crystal silicon wafer (16), and retaining the silicon dioxide layer (17); S5, preparing a flexible lower electrode layer on the upper surface of the silicon dioxide layer (17), and performing photolithography and etching on the flexible lower electrode layer to form a patterned flexible lower electrode (6); S6, depositing a piezoelectric layer on the surface of the silicon dioxide layer (17) and the flexible lower electrode (6); S7, photolithography and etching of the piezoelectric layer and the silicon dioxide layer (17), where the etching stops at the surface of the flexible substrate (13), to form a structural layer (7) and a lower piezoelectric layer (5); S8, sputtering a flexible intermediate electrode layer on the flexible substrate (13) and the lower piezoelectric layer (5), photolithography, and etching the flexible intermediate electrode layer to form a patterned annular flexible intermediate electrode (4) and a flexible intermediate electrode electrical connection (10); S9, photolithography and deposition to form a mask on the flexible substrate (13) and the lower piezoelectric layer (5), spin-coating a flexible insulating material layer on the flexible substrate (13), photolithography and etching the flexible insulating material layer to form an electrical connection isolation layer (9), and removing the mask; S10, depositing a piezoelectric material layer on the electrical connection isolation layer (9) and the flexible intermediate electrode (4), and photolithography and etching the piezoelectric material layer to form an upper piezoelectric layer (3); S11, photolithography and etching of the upper piezoelectric layer (3) and the lower piezoelectric layer (5) to form a conductive channel (2); S12, sputtering a flexible electrode layer on the upper piezoelectric layer (3) and the electrical connection isolation layer (9), and filling the conductive channel (2) with the material of the flexible electrode layer, and then photolithography and etching the flexible electrode layer to form a patterned flexible upper electrode (1) and a flexible upper electrode electrical connection (8); S13, removing the rigid substrate to obtain the flexible PMUTs with bending and torsional deformation functions.

10. The method for preparing flexible PMUTs with bending and torsional deformation functions according to claim 9, characterized in that: When the upper surface of the flexible support (11) is provided with grooves (19) between adjacent transducer units: In the above-mentioned S7, when the piezoelectric layer and the silicon dioxide layer (17) are photoetched and etched, the etching stops at the surface of the flexible substrate (13), and then the upper surface of the flexible substrate (13) is processed to form the above-mentioned groove (19), and then S8 is performed.

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