Flexible piezoelectric micromechanical ultrasonic transducer and preparation method and application thereof

Abstract

The invention discloses a flexible piezoelectric micromechanical ultrasonic transducer as well as a preparation method and application thereof. The flexible piezoelectric micromechanical ultrasonic transducer comprises a laminated structure and a flexible coating layer packaging the laminated structure, the laminated structure comprises a flexible substrate, an adhesive layer, a first supporting layer, a second supporting layer, a bottom electrode layer, a piezoelectric layer and a top electrode layer which are sequentially laminated, the first supporting layer is provided with a through cavity structure, and the second supporting layer is provided with a through cavity structure. The first supporting layer and the second supporting layer are both made of epoxy group negative photoresist, and the piezoelectric layer is composed of polyvinylidene fluoride-trifluoroethylene and nano potassium sodium niobate ceramic particles. The flexible piezoelectric micromechanical ultrasonic transducer has the advantages of being high in sensitivity, good in tensile ductility and bendability, capable of flexibly adjusting resonant frequency, easy to array and the like, the preparation method is simple, the production cost is low, batch production is easy, and the flexible piezoelectric micromechanical ultrasonic transducer is suitable for large-scale industrial production and application.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a flexible piezoelectric micromechanical ultrasonic transducer and a preparation method and application thereof. Background Art

[0002] Piezoelectric micromechanical ultrasonic transducer is a microelectromechanical system (MEMS) device used to transmit or receive ultrasonic signals. It has the advantages of small size, low power consumption, low cost, no need for DC bias, and easy arraying. It has been widely used in many portable devices.

[0003] Traditional rigid silicon-based piezoelectric micromechanical ultrasonic transducers are difficult to fit tightly to non-flat and smooth surfaces, and are prone to acoustic impedance mismatch, which affects the accuracy of measurement data and greatly limits their application. Flexible ultrasonic devices have good flexibility and can adapt to different surface shapes and curvatures, thereby improving the accuracy and stability of data applied to non-planar surfaces or complex detection environments (for example, flexible ultrasonic arrays based on row and column addressing can obtain relatively better detection fields and image resolution under specific curvatures). At present, flexible piezoelectric ultrasonic transducers based on thickness vibration are relatively mature, but such transducers often require mechanical cutting, laser cutting, etc. to achieve the preparation of composite piezoelectric materials, which limits the minimum spacing and size of the device and is not conducive to mass production of the device. In addition, the operating frequency of the device depends only on the thickness of the piezoelectric material, which is not conducive to the flexible regulation of the resonant frequency of the device. Therefore, flexible piezoelectric micromechanical ultrasonic transducers that can flexibly regulate the resonant frequency based on the cavity diameter and the diaphragm thickness have good development prospects.

[0004] At present, the design schemes of flexible piezoelectric micromechanical ultrasonic transducers mainly include the following two categories: 1) Island-bridge design: a silicon spring structure is formed by deep silicon etching process, so that the device has the ability to stretch and bend, or a piezoelectric micromechanical ultrasonic transducer based on a rigid substrate (for example, a silicon substrate) is bonded to a flexible substrate by gluing, embossing, etc., so that the device has the ability to bend. In order to ensure the transceiver sensitivity of the device, this type of design usually uses piezoelectric ceramics as the piezoelectric layer, but piezoelectric ceramics and silicon both have the disadvantages of low toughness and lack of ductility. When subjected to stress, the device tends to break in the form of crack extension, which cannot meet the application scenario requirements of small curvature radius; 2) Fully flexible micromechanical ultrasonic transducers prepared based on micro-nano processing technology: This type of device usually has good bending ability, but the tensile performance is very limited. At the same time, the piezoelectric layer uses a single organic piezoelectric material, which is difficult to obtain high sensitivity. It can be seen that the existing flexible piezoelectric micromechanical ultrasonic transducers have obvious defects and are difficult to fully meet the requirements of practical applications.

[0005] Therefore, it is of great significance to develop a flexible piezoelectric micromechanical ultrasonic transducer with high sensitivity, good tensile ductility and bending properties, flexible adjustment of resonant frequency, easy arraying and easy mass production. Summary of the invention

[0006] The object of the present invention is to provide a flexible piezoelectric micromechanical ultrasonic transducer and a preparation method and application thereof.

[0007] The technical solution adopted by the present invention is:

[0008] A flexible piezoelectric micromechanical ultrasonic transducer comprises a stacked structure and a flexible coating layer encapsulating the stacked structure; the stacked structure comprises a flexible substrate, an adhesive layer, a first supporting layer, a second supporting layer, a bottom electrode layer, a piezoelectric layer and a top electrode layer stacked in sequence; the first supporting layer is provided with a through cavity structure; the first supporting layer and the second supporting layer are both made of epoxy-based negative photoresist; the piezoelectric layer comprises polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) and nano potassium sodium niobate ceramic particles.

[0009] Preferably, the flexible coating layer is made of one of silicone rubber and polydimethylsiloxane potting glue.

[0010] Preferably, the silicone rubber is Ecoflex silicone rubber produced by Smooth-On.

[0011] Preferably, the polydimethylsiloxane potting adhesive is SYLGARD 184 from Dow Corning.

[0012] Preferably, the flexible substrate is made of epoxy-based negative photoresist.

[0013] Preferably, the thickness of the flexible substrate is 30 μm to 60 μm.

[0014] Preferably, the adhesive layer is made of photosensitive low-temperature curing flexible epoxy resin adhesive.

[0015] Preferably, the thickness of the adhesive layer is 4 μm to 7 μm.

[0016] Preferably, the photosensitive low-temperature curing flexible epoxy resin adhesive is the photosensitive low-temperature curing epoxy resin adhesive PermiNex 1005 produced by Kayaku Corporation.

[0017] Preferably, the thickness of the first supporting layer is 50 μm to 80 μm.

[0018] Preferably, the second supporting layer has a thickness of 5 μm to 10 μm.

[0019] Preferably, the surfaces of the second supporting layer and the first supporting layer corresponding to the through-cavity structures are further provided with protruding structures.

[0020] Preferably, the protrusion structure is cylindrical, with a diameter of 20 μm to 80 μm and a height of 30 μm to 40 μm.

[0021] Preferably, the number of the protrusion structures is one or more.

[0022] Preferably, the bottom electrode layer is composed of at least one of Au, Cr, Ag and Ti.

[0023] Preferably, the bottom electrode layer has a thickness of 200 nm to 500 nm.

[0024] Preferably, the area of ​​the bottom electrode layer is not less than the opening area of ​​the penetrating cavity structure of the first supporting layer.

[0025] Preferably, the top electrode layer is composed of at least one of Au, Cr, Ag and Ti.

[0026] Preferably, the thickness of the top electrode layer is 200 nm to 500 nm.

[0027] Preferably, the top electrode layer comprises a plurality of contacts arranged in an array, and adjacent contacts are connected by a double-path serpentine wire.

[0028] Preferably, the area of ​​the top electrode layer is 60% to 80% of the opening area of ​​the first support layer penetrating the cavity structure.

[0029] Preferably, the through cavity structure is cylindrical, with a diameter of 90 μm to 110 μm.

[0030] Preferably, the epoxy-based negative photoresist is one of epoxy-based negative photoresist SU-8 2005 produced by Suzhou Zhongxin Qiheng Scientific Instrument Co., Ltd. and epoxy-based negative photoresist SU-8 2025 produced by Suzhou Zhongxin Qiheng Scientific Instrument Co., Ltd.

[0031] Preferably, the mass ratio of the polyvinylidene fluoride-trifluoroethylene to the nano potassium sodium niobate ceramic particles is 1.5 to 3.0:1.

[0032] Preferably, the polyvinylidene fluoride-trifluoroethylene is from Arkema FC 20.

[0033] Preferably, the particle size of the nano potassium sodium niobate ceramic particles is 300nm to 500nm.

[0034] Preferably, the piezoelectric layer has a thickness of 1 μm to 4 μm.

[0035] Preferably, the piezoelectric layer is provided with a through hole for leading a wire from the bottom electrode layer to the same side of the top electrode layer.

[0036] A method for preparing the flexible piezoelectric micromechanical ultrasonic transducer as described above comprises the following steps:

[0037] 1) depositing a sacrificial layer material on a single side of a rigid substrate by magnetron sputtering to form a first sacrificial layer;

[0038] 2) depositing electrode material on a partial surface area of ​​the first sacrificial layer by an evaporation process to form a top electrode layer;

[0039] 3) coating the piezoelectric material on the surface of the first sacrificial layer and the top electrode layer by spin coating to form a piezoelectric layer;

[0040] 4) depositing electrode material on a portion of the surface of the piezoelectric layer using an evaporation process to form a bottom electrode layer;

[0041] 5) annealing the device obtained in step 4);

[0042] 6) coating the support layer material on the surface of the piezoelectric layer and the bottom electrode layer by spin coating to form a second support layer;

[0043] 7) coating a support layer material on a partial surface area of ​​the second support layer by spin coating to form a first support layer;

[0044] 8) coating a sacrificial layer material on one side of another rigid substrate by spin coating to form a second sacrificial layer;

[0045] 9) coating the surface of the second sacrificial layer with a flexible substrate material by spin coating to form a flexible substrate;

[0046] 10) bonding the first supporting layer and the flexible substrate with an adhesive to form an adhesive layer;

[0047] 11) The second sacrificial layer is dissolved by a solvent, and the corresponding rigid substrate is removed. The device is then fixed in a mold with the flexible substrate facing downward and kept at a certain distance from the bottom of the mold. The coating material is then injected until the portion below the first sacrificial layer of the device is immersed, and then cured. The first sacrificial layer is then dissolved by a solvent, and the corresponding rigid substrate is removed. The coating material is then coated on the surface of the piezoelectric layer and the top electrode layer by spraying, and then cured to form a flexible coating layer, thereby obtaining a flexible piezoelectric micromechanical ultrasonic transducer.

[0048] Preferably, the rigid substrate in step 1) is one of a glass substrate, a silicon substrate and a quartz substrate.

[0049] Preferably, the sacrificial layer material in step 1) is aluminum.

[0050] Preferably, in step 8), the rigid substrate is one of a glass substrate, a sapphire substrate and a quartz substrate.

[0051] Preferably, the sacrificial layer material in step 8) is a negative photoresist.

[0052] An ultrasonic device comprises the above-mentioned flexible piezoelectric micromechanical ultrasonic transducer.

[0053] Preferably, the ultrasonic device comprises a plurality of flexible piezoelectric micromechanical ultrasonic transducers, and the flexible piezoelectric micromechanical ultrasonic transducers are electrically connected to each other through the top electrode layer and the bottom electrode layer connected in parallel, and the connecting wires are all double-path serpentine wires. The redundant design of the serpentine wire is adopted to realize the interconnection, and while maintaining the electrical connection, an island-bridge structure is formed between the transducer units, which increases the stretchability and flexibility of the device, reduces the local stress concentration when an external force acts, and improves the overall durability of the device.

[0054] Preferably, the ultrasonic device is one of a portable ultrasonic imaging device, an active tactile generating device, and a wearable vital sign monitoring device.

[0055] The working principle of the flexible piezoelectric micromechanical ultrasonic transducer of the present invention is as follows: when the transducer works in the transmitting mode, a pulse excitation voltage signal is applied to the top electrode layer, the bottom electrode layer is grounded, the piezoelectric layer vibrates with the frequency of the pulse excitation signal, and the electrical energy is converted into mechanical energy based on the inverse piezoelectric effect to achieve the transmission of the ultrasonic signal; when the transducer works in the receiving mode, the incident ultrasonic signal causes the piezoelectric layer to vibrate, and the mechanical energy is converted into electrical energy based on the positive piezoelectric effect, and the signal is extracted and amplified by signal conditioning circuits such as charge amplifiers, voltage amplifiers, and transimpedance amplifiers to achieve the reception and preprocessing of the ultrasonic signal.

[0056] The beneficial effects of the present invention are as follows: the flexible piezoelectric micromechanical ultrasonic transducer of the present invention has the advantages of high sensitivity, good tensile ductility and bending, flexible adjustment of resonant frequency, and easy arraying, and its preparation method is simple, the production cost is low, and it is easy to mass produce, and is suitable for large-scale industrial production and application.

[0057] Specifically:

[0058] 1) The flexible piezoelectric micromechanical ultrasonic transducer of the present invention adopts a flexible coating layer, which gives the transducer greater tensile ductility and bendability, and can effectively relieve and disperse the stress applied to the transducer structural unit, and adopts a first support layer and a second support layer made of an epoxy negative photoresist with high mechanical strength and chemical corrosion resistance, which gives the first support layer and the second support layer a certain bending ability, reducing the risk of fracture. When the transducer is subjected to a large compressive / tensile stress, the rigid support structure (the first support layer and the second support layer) will not produce excessive deformation, thereby avoiding the resonance frequency and the transceiver sensitivity from being greatly offset due to the external force, thereby affecting the normal performance of the device;

[0059] 2) The piezoelectric layer in the flexible piezoelectric micromechanical ultrasonic transducer of the present invention adopts a 0-3 type piezoelectric composite material, which can improve the piezoelectric performance of the piezoelectric layer. The nano potassium sodium niobate ceramic particles therein can improve the electromechanical coupling coefficient of the piezoelectric layer, which not only effectively improves the sensitivity of the piezoelectric layer, but also ensures the flexibility and bending ability of the piezoelectric layer;

[0060] 3) The present invention adopts a reverse micro-nano processing technology to prepare a flexible piezoelectric micromechanical ultrasonic transducer, which is compatible with the preparation process of piezoelectric materials that require high-temperature annealing, thereby avoiding the influence of high temperature on other structures. In addition, the epoxy-based negative photoresist used can form a high aspect ratio structural pattern by spin coating lithography, so the structural height can be controlled by controlling its viscosity and spin coating speed to achieve flexible control of the resonant frequency, and reduce the production cost, which is convenient for mass production and preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is a schematic structural diagram of the flexible piezoelectric micromechanical ultrasonic transducer of the present invention.

[0062] Figure 2 It is a structural schematic diagram (top view) of the lateral stretching process of the top electrode layer in the flexible piezoelectric micromechanical ultrasonic transducer of the present invention.

[0063] Explanation of the accompanying drawings: 10, flexible covering layer; 20, flexible substrate; 30, adhesive layer; 40, first supporting layer; 50, second supporting layer; 60, bottom electrode layer; 70, piezoelectric layer; 701, polyvinylidene fluoride-trifluoroethylene; 702, nano potassium sodium niobate ceramic particles; 80, top electrode layer; 801, contact; 802, serpentine winding wire.

[0064] Figure 3 This is the normalized sound pressure-frequency curve of the flexible piezoelectric micromechanical ultrasonic transducer of Example 1.

[0065] Figure 4 This is the normalized sound pressure-frequency curve of the flexible piezoelectric micromechanical ultrasonic transducer of Example 2.

[0066] Figure 5 This is the sound pressure-frequency curve of the flexible piezoelectric micromechanical ultrasonic transducer of Example 3 at 1 mm in the axial sound field. DETAILED DESCRIPTION

[0067] The present invention will be further explained and illustrated below in conjunction with specific embodiments.

[0068] Embodiment 1:

[0069] A flexible piezoelectric micromechanical ultrasonic transducer (schematic diagram as shown in Figure 1 As shown), it consists of a stacked structure and a flexible covering layer 10 that encapsulates the stacked structure; the flexible covering layer 10 is made of Ecoflex silicone rubber from Smooth-On; the stacked structure consists of a flexible substrate 20, an adhesive layer 30, a first supporting layer 40, a second supporting layer 50, a bottom electrode layer 60, a piezoelectric layer 70 and a top electrode layer 80 that are stacked in sequence from bottom to top;

[0070] The flexible substrate 20 is made of epoxy negative photoresist SU-8 2025 from Suzhou SMIC Qiheng Scientific Instrument Co., Ltd., with a thickness of 50 μm;

[0071] The adhesive layer 30 is made of Kayaku's photosensitive low-temperature curing epoxy resin adhesive PermiNex 1005, with a thickness of 5 μm;

[0072] The first supporting layer 40 is provided with a through cavity structure, which is cylindrical and has a diameter of 110 μm / 106 μm / 102 μm / 98 μm / 94 μm / 90 μm;

[0073] The first support layer 40 is made of epoxy negative photoresist SU-82025 from Suzhou SMIC Qiheng Scientific Instrument Co., Ltd., with a thickness of 50 μm;

[0074] The second support layer 50 is made of epoxy negative photoresist SU-82005 from Suzhou SMIC Qiheng Scientific Instrument Co., Ltd., with a thickness of 5 μm;

[0075] The bottom electrode layer 60 is made of Au-Cr alloy and has a thickness of 400 nm. The area of ​​the bottom electrode layer 60 is equal to the opening area of ​​the first support layer 40 that penetrates the cavity structure.

[0076] The piezoelectric layer 70 is made of polyvinylidene fluoride-trifluoroethylene 701 (Arkema FC 20, the molar ratio of vinylidene fluoride units to trifluoroethylene units is 4:1) and nano potassium sodium niobate ceramic particles 702 (particle size is 300nm-500nm) are composed in a mass ratio of 3:1, and the thickness is 2μm;

[0077] The top electrode layer 80 includes a plurality of contacts 801 arranged in an array, and adjacent contacts 801 are connected by two-way serpentine wires 802 (the schematic diagram of the structure of the top electrode layer during the lateral stretching process is shown in FIG. Figure 2 As shown; top view); the top electrode layer 80 is made of Au-Cr alloy and has a thickness of 400nm; the area of ​​the top electrode layer 80 is 70% of the opening area of ​​the first support layer 40 that penetrates the cavity structure.

[0078] Depend on Figure 2 It can be seen that: when the top electrode layer is stretched and deformed, the serpentine winding wire can adapt to the deformation well, effectively disperse the force, reduce the concentration of local stress, and prevent the transducer cavity structure from producing excessive deformation within a certain stretching range, thereby improving the flexibility and durability of the entire device.

[0079] The preparation method of the above-mentioned flexible piezoelectric micromechanical ultrasonic transducer is as follows:

[0080] 1) taking a glass substrate, ultrasonically cleaning it with acetone, ethanol and deionized water in sequence, drying it, and then depositing an aluminum film with a thickness of 1 μm on one side of the glass substrate by magnetron sputtering to form a first sacrificial layer;

[0081] 2) Spin-coating the stripped photoresist on the surface of the first sacrificial layer, and then performing heat baking and exposure development to form a top electrode layer preparation area, and then rinsing with deionized water and drying with a nitrogen gun, and then using an evaporation process to deposit a 400nm thick Au-Cr alloy film on the top electrode layer preparation area, and then immersing in acetone to remove the photoresist to form a top electrode layer;

[0082] 3) 3-aminopropyltriethoxysilane is coated on the surface of the first sacrificial layer and the top electrode layer (to improve the adhesion of the piezoelectric layer on the electrode), and then the piezoelectric material (polyvinylidene fluoride-trifluoroethylene with a mass fraction of 15%, nano potassium sodium niobate ceramic particles with a mass fraction of 5%, and a solvent of N,N-dimethylformamide) is coated on the surface of the first sacrificial layer and the top electrode layer by spin coating, and then placed on a hot plate at 70°C for 15 minutes, and then the photoresist is stripped by spin coating, and then heat-baked and exposed and developed, and then rinsed with deionized water and blown dry with a nitrogen gun, and then patterned by RIE etching (to reduce crosstalk between transducer units and reserve a through hole for leading the wire from the bottom electrode layer to the same side of the top electrode layer), the etching gas is O2, C4F8 and Ar, the etching power is 100W, and a piezoelectric layer with a thickness of 2μm is formed;

[0083] 4) Spin-coating the stripped photoresist on the surface of the piezoelectric layer, and then performing heat baking and exposure development to form a bottom electrode layer preparation area, and then rinsing with deionized water and drying with a nitrogen gun, and then using a vapor deposition process to deposit a 400nm thick Au-Cr alloy film on the bottom electrode layer preparation area, and then immersing in acetone to remove the photoresist to form a bottom electrode layer;

[0084] 5) placing the device obtained in step 4) in a vacuum environment and annealing at 130° C. for 60 min (to improve the crystallinity of the piezoelectric composite material, induce phase transition, increase the β-phase content of the piezoelectric film in the organic polymer, and enhance the interface bonding strength between the top / bottom electrode layer and the piezoelectric layer), then naturally cooling to room temperature, and polarizing the piezoelectric layer by corona polarization at 80° C. (to preferentially orient the dipoles and further improve the piezoelectric performance), with a polarization voltage of 2 kV for 20 min;

[0085] 6) Spin coating the surface of the piezoelectric layer and the bottom electrode layer with epoxy negative photoresist SU-8 2005 produced by Suzhou Zhongxin Qiheng Scientific Instrument Co., Ltd., and then heat baking, exposure, development and hardening the film, and then rinse with deionized water and blow dry with a nitrogen gun to form a second support layer with a thickness of 5 μm;

[0086] 7) Spin coating the epoxy negative photoresist SU-8 2025 produced by Suzhou Zhongxin Qiheng Scientific Instrument Co., Ltd. on the surface of the second support layer, and then heat baking, exposure, development and hardening the film, and then rinsing with deionized water and drying with a nitrogen gun to form a first support layer with a thickness of 50 μm;

[0087] 8) taking a glass substrate, ultrasonically cleaning it with acetone, ethanol and deionized water in sequence, drying it, and then coating a negative photoresist with a thickness of 3 μm on one side of the glass substrate by spin coating to form a second sacrificial layer;

[0088] 9) Spin coating the surface of the second sacrificial layer with epoxy negative photoresist SU-8 2025 produced by Suzhou Zhongxin Qiheng Scientific Instrument Co., Ltd., and then heat-baking, exposure, development and hardening the film, and then rinsing with deionized water and drying with a nitrogen gun to form a flexible substrate with a thickness of 50 μm;

[0089] 10) Adhere the first support layer and the flexible substrate using Kayaku's photosensitive low-temperature curing epoxy resin adhesive PermiNex 1005, and then perform heat baking, exposure development and heat curing to form an adhesive layer with a thickness of 5 μm;

[0090] 11) Acetone was used to dissolve the second sacrificial layer, and the corresponding glass substrate was removed. The device was then rinsed with deionized water and dried with a nitrogen gun. The device was then bombarded with oxygen plasma for 120 seconds (to make the sample have better hydrophilicity). The device was then fixed in a mold with the flexible substrate facing down and kept a certain distance from the bottom of the mold. Ecoflex silicone rubber was then injected until the part below the first sacrificial layer of the device was submerged, and then allowed to stand and cure at room temperature. The first sacrificial layer was then dissolved with a phosphoric acid solution with a mass fraction of 85%, and the corresponding glass substrate was removed. Ecoflex silicone rubber with a thickness of 10 μm was then coated on the surface of the piezoelectric layer and the top electrode layer by spraying, and then allowed to stand and cure at room temperature to form a flexible coating layer, thereby obtaining a flexible piezoelectric micromechanical ultrasonic transducer.

[0091] The normalized sound pressure-frequency curves of the flexible piezoelectric micromechanical ultrasonic transducers of this embodiment (six types of transducers, the diameters R1 penetrating the cavity structure are denoted as a to f from small to large) are as follows: Figure 3 shown.

[0092] Depend on Figure 3 It can be seen that: as the diameter of the through-cavity structure changes, the resonant frequency of the flexible piezoelectric micromechanical ultrasonic transducer with the maximum transmitted sound pressure changes significantly.

[0093] Embodiment 2:

[0094] A flexible piezoelectric micromechanical ultrasonic transducer, wherein the thickness of the second supporting layer is 5μm / 6μm / 7μm / 8μm / 9μm / 10μm, the diameter R1 of the through-cavity structure is 110μm, and the rest is exactly the same as the flexible piezoelectric micromechanical ultrasonic transducer of Example 1.

[0095] The normalized sound pressure-frequency curves of the flexible piezoelectric micromechanical ultrasonic transducers of this embodiment (six types of transducers, the thickness R2 of the second supporting layer is denoted as a to f from small to large) are as follows: Figure 4 shown.

[0096] Depend on Figure 4 It can be seen that: as the thickness of the second supporting layer changes, the resonant frequency of the flexible piezoelectric micromechanical ultrasonic transducer with the maximum transmitted sound pressure changes significantly.

[0097] Embodiment 3:

[0098] A flexible piezoelectric micromechanical ultrasonic transducer, wherein a cylindrical protrusion is arranged at the center of the surface of the second supporting layer (the surface corresponding to the through-cavity structure of the first supporting layer) (the size specifications of the cylindrical protrusion are diameter 50μm×height 40μm / diameter 60μm×height 30μm / diameter 80μm×height 40μm; the composition of the cylindrical protrusion is the same as that of the second supporting layer), the diameter R1 of the through-cavity structure is 110μm, and the rest is exactly the same as the flexible piezoelectric micromechanical ultrasonic transducer of Example 1.

[0099] The sound pressure-frequency curve of the flexible piezoelectric micromechanical ultrasonic transducer of this embodiment (three types of transducers, the cylindrical protrusions are denoted as a to c in order of volume from small to large) at 1 mm in the axial sound field is as follows: Figure 5 (The flexible piezoelectric micromechanical ultrasonic transducer in Example 1 with a through-cavity structure diameter R1 of 110 μm and no additional protrusion structure is used as a control; R3 represents the diameter of the cylindrical protrusion, and H represents the height of the cylindrical protrusion).

[0100] Depend on Figure 5 It can be seen that by selecting the appropriate size of the cylindrical protrusion and making the device perform piston-like motion, the sensitivity of the device can be further improved without reducing the resonant frequency.

[0101] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A flexible piezoelectric micromechanical ultrasonic transducer, characterized in that: The invention relates to a flexible coating layer comprising a stacked structure and an encapsulating stacked structure; the stacked structure comprises a flexible substrate, an adhesive layer, a first supporting layer, a second supporting layer, a bottom electrode layer, a piezoelectric layer and a top electrode layer which are stacked in sequence; the first supporting layer is provided with a through cavity structure; the first supporting layer and the second supporting layer are both made of epoxy-based negative photoresist; the piezoelectric layer comprises polyvinylidene fluoride-trifluoroethylene and nano-potassium sodium niobate ceramic particles.

2. The flexible piezoelectric micromechanical ultrasonic transducer according to claim 1, characterized in that: The flexible coating layer comprises one of silicone rubber and polydimethylsiloxane potting glue; the flexible substrate is made of epoxy-based negative photoresist; and the adhesive layer is made of photosensitive low-temperature curing flexible epoxy resin glue.

3. The flexible piezoelectric micromechanical ultrasonic transducer according to claim 1, characterized in that: The through cavity structure is cylindrical, and has a diameter of 90 μm to 110 μm.

4. The flexible piezoelectric micromechanical ultrasonic transducer according to claim 1, characterized in that: The thickness of the first supporting layer is 50 μm to 80 μm; the thickness of the second supporting layer is 5 μm to 10 μm.

5. The flexible piezoelectric micromechanical ultrasonic transducer according to claim 1, characterized in that: The composition of the bottom electrode layer includes at least one of Au, Cr, Ag, and Ti; the thickness of the bottom electrode layer is 200nm to 500nm; the composition of the top electrode layer includes at least one of Au, Cr, Ag, and Ti; the thickness of the top electrode layer is 200nm to 500nm.

6. The flexible piezoelectric micromechanical ultrasonic transducer according to claim 1, characterized in that: The mass ratio of the polyvinylidene fluoride-trifluoroethylene to the nano potassium sodium niobate ceramic particles is 1.5-3.0:1; the particle size of the nano potassium sodium niobate ceramic particles is 300nm-500nm.

7. The flexible piezoelectric micromechanical ultrasonic transducer according to claim 1, characterized in that: The thickness of the piezoelectric layer is 1 μm to 4 μm.

8. The flexible piezoelectric micromechanical ultrasonic transducer according to any one of claims 1 to 7, characterized in that: The surfaces of the second supporting layer and the first supporting layer corresponding to the through-cavity structures are also provided with protruding structures.

9. A method for preparing a flexible piezoelectric micromechanical ultrasonic transducer according to any one of claims 1 to 8, characterized in that: The following steps are involved: 1) depositing a sacrificial layer material on a single side of a rigid substrate by magnetron sputtering to form a first sacrificial layer; 2) depositing electrode material on a partial surface area of ​​the first sacrificial layer by an evaporation process to form a top electrode layer; 3) coating the piezoelectric material on the surface of the first sacrificial layer and the top electrode layer by spin coating to form a piezoelectric layer; 4) depositing electrode material on a portion of the surface of the piezoelectric layer using an evaporation process to form a bottom electrode layer; 5) annealing the device obtained in step 4); 6) coating the support layer material on the surface of the piezoelectric layer and the bottom electrode layer by spin coating to form a second support layer; 7) coating a support layer material on a partial surface area of ​​the second support layer by spin coating to form a first support layer; 8) coating a sacrificial layer material on one side of another rigid substrate by spin coating to form a second sacrificial layer; 9) coating the surface of the second sacrificial layer with a flexible substrate material by spin coating to form a flexible substrate; 10) bonding the first supporting layer and the flexible substrate with an adhesive to form an adhesive layer; 11) The second sacrificial layer is dissolved by a solvent, and the corresponding rigid substrate is removed. The device is then fixed in a mold with the flexible substrate facing downward and kept at a certain distance from the bottom of the mold. The coating material is then injected until the portion below the first sacrificial layer of the device is immersed, and then cured. The first sacrificial layer is then dissolved by a solvent, and the corresponding rigid substrate is removed. The coating material is then coated on the surface of the piezoelectric layer and the top electrode layer by spraying, and then cured to form a flexible coating layer, thereby obtaining a flexible piezoelectric micromechanical ultrasonic transducer.

10. An ultrasonic device, characterized in that: The flexible piezoelectric micromechanical ultrasonic transducer comprises any one of claims 1 to 8.

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