Piezoelectric film pressure sensor and self-assembly preparation method thereof

Abstract

The invention provides a piezoelectric film pressure sensor and a self-assembly preparation method thereof, and the method comprises the steps: S1, depositing a sacrificial layer on a substrate; s2, depositing a bottom electrode layer on the sacrificial layer; s3, depositing a piezoelectric layer formed by inorganic piezoelectric single crystals on the bottom electrode layer; s4, depositing a top electrode layer in an electrode area of the piezoelectric layer; s5, etching a part of a non-electrode area of the piezoelectric layer to the sacrificial layer to expose the substrate and the end face of the bottom electrode layer to obtain a piezoelectric film; s6, depositing a fixing layer on the piezoelectric film to fix one edge of the piezoelectric film on the substrate; s7, depositing electrode pin layers of the bottom electrode layer and the top electrode layer; and S8, carrying out wet etching to remove the sacrificial layer, washing, drying, and then carrying out polarization processing to obtain the piezoelectric film pressure sensor. The piezoelectric film pressure sensor has good flexibility, a large deformation range and good piezoelectric performance, and the preparation method is simple.

Description

Technical Field

[0001] The invention belongs to the technical field of pressure sensors and relates to a piezoelectric film pressure sensor and a self-assembly preparation method thereof. Background Art

[0002] Pressure sensors can detect pressure signals and convert them into electrical signals according to certain rules. Due to their high sensitivity, fast response, high piezoelectric coefficient and good environmental adaptability, flexible piezoelectric materials play an important role in pressure sensors and are widely used in stress sensing, strain sensing, sound sensing and vibration sensing. In particular, for pressure sensors that sense normal stress / strain, such as press-type tactile sensors and pneumatic pressure monitoring sensors, they require piezoelectric materials to have large deformation capabilities to adapt to various pressure changes and ensure stable operation of the sensor. Therefore, it is particularly urgent to develop flexible piezoelectric sensing materials and pressure sensors with high sensitivity.

[0003] At present, flexible piezoelectric materials mainly include organic piezoelectric polymers and inorganic piezoelectric films. Generally speaking, although organic piezoelectric polymers have high flexibility, their piezoelectric coefficient is low, resulting in poor piezoelectric sensing performance; inorganic piezoelectric films have high piezoelectric performance, but due to their poor flexibility, they deform less under pressure, resulting in poor piezoelectric sensing performance.

[0004] (1) Organic piezoelectric polymers: Polyvinylidene fluoride (PVDF) and its copolymer P(VDF-TrFE) are the most widely used organic piezoelectric materials because they have good flexibility and have the highest piezoelectric properties among existing piezoelectric polymers. However, their piezoelectric coefficient d 33 It is usually less than 30 pC / N, which is much lower than that of inorganic piezoelectric materials; and its glass transition temperature is usually lower than 120 °C, which makes it difficult to use in high temperature environments; it also has a large thermal expansion coefficient, resulting in poor temperature stability of the device. In order to improve the piezoelectric properties of organic piezoelectric polymers, in addition to modifying the material composition, researchers have made them into three-dimensional structures such as folds, micro-domes, and curved surfaces through structural design. The stress / strain applied to these geometric shapes can be amplified, thereby producing a large piezoelectric response. For example, Chinese invention patent CN113043582B discloses a method for improving the piezoelectric response of polymer materials, which makes flexible polymer films form folds to enhance the piezoelectric response. The Chinese patent application with publication number CN108542377A uses an arched PVDF piezoelectric polymer as a pressure-sensitive module. However, this three-dimensional structure usually involves a complex manufacturing process; and the size of such devices is usually at the millimeter or even centimeter level, making it difficult to miniaturize the device.

[0005] (2) Inorganic piezoelectric films: Flexible piezoelectric films can be prepared by directly depositing inorganic piezoelectric films on high-temperature resistant flexible substrates (such as metal foils, mica, etc.). For example, Yeo et al. (Sensors and Actuators A: Physical 273,90-97 (2018)) prepared PZT films on nickel foil substrates, showing good piezoelectric energy collection characteristics. However, since oxide films are usually deposited at relatively high temperatures, these base metal foils are easily oxidized and introduce interface defects; in addition, these oxide films usually exist in the form of polycrystalline and have defects such as grain boundaries. These factors will lead to poor piezoelectric performance of the device. Mica is widely used as a flexible substrate due to its low price, high light transmittance, mechanical flexibility and high temperature resistance. For example, Wang et al. (Nano Energy, 2018, 43: 351–358) prepared PZT films on fluorocrystalline mica substrates by spin coating, and then thinned the mica substrate to 20.0 μm by mechanical thinning. PZT / Mica exhibits good flexibility and mechanical stability, with a curvature radius as low as 2.2 mm, and can remain stable under 40,000 mechanical deformations. The Chinese patent application with publication number CN117881266A proposes growing PZT on a mica substrate with a Pt bottom electrode. The flexible PZT film has a high piezoelectric response, a small relative dielectric constant, and a low leakage current. Zhang et al. (J Mater Sci: MaterElectron (2024) 35:298) reported that the adaptive bending radius of the PZT film (80-200 nm) deposited on thinned mica (~10μm) is about 1.5 mm. However, this inorganic flexible piezoelectric film is still constrained by the mica substrate and has little deformation under pressure, so it has low sensitivity when used for weak mechanical sensing such as tactile perception.

[0006] In addition, thin film self-assembly technology has great potential in the preparation of flexible piezoelectric films with large deformation capabilities. For example, the Chinese patent application with publication number CN116471917A discloses a controllable self-assembly method and device for long strip films, which proposes a double-layer self-curling film based on nickel ferrite / lead zirconate titanate. After the film is separated from the substrate, it can naturally form a three-dimensional scroll. However, since the lattice constant of nickel ferrite is quite different from that of the strontium aluminate sacrificial layer and lead zirconate titanate, lattice defects are easily introduced during the film growth process, which limits the performance of the device. Therefore, it is urgent to propose a new type of piezoelectric film pressure sensor and its self-assembly manufacturing method. Summary of the invention

[0007] In order to solve the above problems of the prior art, the present invention provides a piezoelectric film pressure sensor and a self-assembly preparation method thereof. The piezoelectric film pressure sensor has good flexibility, a large deformation range, good piezoelectric performance, and a simple preparation method.

[0008] The present invention is achieved through the following technical solutions: In a first aspect, the present invention provides a self-assembly preparation method of a piezoelectric film pressure sensor, comprising the following steps: S1, depositing a sacrificial layer on the substrate; S2, depositing a bottom electrode layer on the sacrificial layer; S3, depositing a piezoelectric layer formed of an inorganic piezoelectric single crystal on the bottom electrode layer; wherein the crystal structure of the bottom electrode layer matches the piezoelectric layer, and the lattice constant of the bottom electrode layer is smaller than the lattice constant of the piezoelectric layer; S4, depositing a top electrode layer in the electrode region of the piezoelectric layer; S5, etching part of the non-electrode area of ​​the piezoelectric layer to the sacrificial layer by etching, exposing the end surfaces of the substrate and the bottom electrode layer, and obtaining a piezoelectric film; S6, depositing a fixing layer on the piezoelectric film to fix one edge of the piezoelectric film on the substrate; S7, depositing an electrode lead layer of a bottom electrode layer and a top electrode layer to lead out the bottom electrode layer and the top electrode layer; S8, wet etching the sacrificial layer, washing, drying, and then polarizing to obtain a piezoelectric film pressure sensor.

[0009] Preferably, the bottom electrode layer is Nb-doped SrTiO 3 or SrRuO 3 , the piezoelectric layer is Pb(Zr,Ti)O 3 or PMN-PT.

[0010] Preferably, the substrate is an oxide single crystal substrate.

[0011] Furthermore, the substrate is SrTiO 3 .

[0012] Preferably, the sacrificial layer is CaSr 2 Al 2 O 6 .

[0013] Preferably, the fixed layer is a negative photoresist.

[0014] Preferably, S6 specifically comprises: spin coating negative photoresist on the piezoelectric film, heating and baking to obtain a negative photoresist coating, ultraviolet exposure, heating and baking again, developing in a developer, and then baking to form a patterned fixed layer to fix one edge of the piezoelectric layer on the substrate.

[0015] Preferably, S8 specifically comprises: immersing the sample obtained in S7 into water, so that the sacrificial layer is dissolved by water, and self-assembly of the arched piezoelectric film is achieved as the sacrificial layer is dissolved.

[0016] Furthermore, in S8, the drying is freeze-drying, and the polarization treatment is polarization at 80°C-100°C and 150 kV / cm-200 kV / cm DC electric field for 20-30 minutes.

[0017] In a second aspect, the present invention provides a piezoelectric film pressure sensor obtained by the self-assembly preparation method as described above.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The preparation method of the piezoelectric film pressure sensor of the present invention adopts a lattice constant of the bottom electrode layer that is smaller than the lattice constant of the piezoelectric layer, that is, a strategy of gradually increasing the lattice constant of the film from the bottom to the top layer is adopted, so that the film is strictly epitaxially grown, and the problem of introducing defects in the film growth process caused by the lattice constant of the bottom film being too large is avoided, thereby improving the device performance. Because the lattice constant of the bottom electrode layer is smaller than the lattice constant of the piezoelectric layer, the bottom electrode layer also serves as a stress layer. When the sacrificial layer is wet-etched, due to the lattice mismatch strain gradient between the bottom electrode layer and the piezoelectric layer, the upper piezoelectric layer will be subjected to in-plane compressive stress, and the stress / strain is released when the piezoelectric film is peeled off. Therefore, after the sacrificial layer is removed by wet etching, the planar piezoelectric film will curl downward to self-assemble into an arched piezoelectric film, which can be detached from the substrate and will not break even after repeated pressing, and has better elasticity. Compared with the planar piezoelectric film, the arched piezoelectric film structure design can produce greater deformation under the same pressure, thereby achieving a significant improvement in piezoelectric response. Therefore, the arched piezoelectric film pressure sensor has higher sensitivity when applied to flexible pressure sensing. Compared with the traditional method of improving the performance of piezoelectric devices through structural design, the process of the present invention is simple and can be formed in one step. The length of a single device is only a few hundred microns, and the size can be further reduced, so that the miniaturization of the piezoelectric device unit can be achieved. In addition, the present invention uses inorganic piezoelectric single crystals as the piezoelectric layer. Compared with traditional flexible piezoelectric polymers, the piezoelectric layer formed by inorganic piezoelectric single crystals has a higher piezoelectric coefficient, so that the prepared piezoelectric film pressure sensor has the advantage of strong piezoelectric sensing response. At the same time, compared with traditional flexible pressure sensors based on piezoelectric polymers, the pressure sensor based on inorganic piezoelectric single crystals in the present invention has a wider operating temperature range, up to ~300°C, and good temperature stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 This is a flow chart of the self-assembly preparation method of the piezoelectric film pressure sensor of the present invention.

[0021] Figure 2 These are actual pictures of the piezoelectric film in Example 1 before (a) and after (b) curling.

[0022] Figure 3 This is a comparison diagram of the piezoelectric responses of the planar piezoelectric film and the arched piezoelectric film under pressure in Example 1.

[0023] Figure 4 The sensitivity test results of the arched piezoelectric film sensor unit in Example 1. DETAILED DESCRIPTION

[0024] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0025] It should be noted that the process equipment or devices not specifically specified in the following embodiments are all conventional equipment or devices in the art.

[0026] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0027] The self-assembly preparation method of the piezoelectric film pressure sensor of the present invention comprises the following steps: S1, depositing a sacrificial layer on the substrate; S2, depositing a bottom electrode layer on the sacrificial layer; S3, depositing a piezoelectric layer on the bottom electrode layer; wherein the piezoelectric layer is an inorganic piezoelectric single crystal, the crystal structure of the bottom electrode layer matches the piezoelectric layer, and the lattice constant of the bottom electrode layer is smaller than the lattice constant of the piezoelectric layer; S4, depositing a top electrode layer in the electrode region of the piezoelectric layer; S5, etching part of the non-electrode area of ​​the piezoelectric layer to the sacrificial layer by etching, exposing the end surfaces of the substrate and the bottom electrode layer, and forming a piezoelectric film on the substrate; S6, depositing a fixing layer on the piezoelectric film to fix one edge of the piezoelectric film on the substrate; S7, depositing electrode lead layers of the bottom electrode layer and the top electrode layer to lead out the bottom electrode layer and the top electrode layer; S8, wet etching the sacrificial layer to obtain a piezoelectric film pressure sensor.

[0028] The crystal structure of the bottom electrode layer used in the present invention matches the piezoelectric layer, and the lattice constant is smaller than the lattice constant of the piezoelectric layer, that is, the strategy of gradually increasing the lattice constant of the film from the bottom to the top is adopted, so that the film is strictly epitaxially grown, avoiding the problem of introducing defects in the film growth process caused by the lattice constant of the bottom film being too large, thereby improving the device performance. Because the lattice constant of the bottom electrode layer is smaller than the lattice constant of the piezoelectric layer, the bottom electrode layer also acts as a stress layer; therefore, when the sacrificial layer is wet-etched, due to the lattice mismatch strain gradient between the bottom electrode layer and the piezoelectric layer, the upper piezoelectric layer will be subjected to in-plane compressive stress, and the stress / strain will be released during corrosion and peeling. Therefore, after the sacrificial layer is removed by wet etching, the planar piezoelectric film will curl downward to self-assemble into an arched piezoelectric film. Compared with the planar film device, the arched structure design can produce greater deformation under the same stress, thereby achieving a significant improvement in the piezoelectric response. Therefore, the arched piezoelectric film pressure sensor has higher sensitivity when applied to flexible pressure sensing. Compared with the traditional method of improving the performance of piezoelectric devices through structural design, the process of the present invention is simple and can be formed in one step. A single device is only a few hundred microns in length, and the size can be further reduced, enabling the miniaturization of piezoelectric device units.

[0029] The present invention uses an inorganic piezoelectric single crystal as the piezoelectric layer. Compared with the traditional flexible piezoelectric polymer, the piezoelectric layer formed by the inorganic piezoelectric single crystal has a higher piezoelectric coefficient, so that the prepared piezoelectric film pressure sensor has the advantage of strong piezoelectric sensing response. At the same time, compared with the traditional flexible pressure sensor based on piezoelectric polymer, the pressure sensor based on the inorganic piezoelectric single crystal in the present invention has a wider operating temperature range, up to ~300°C, and good temperature stability.

[0030] When the present invention is implemented, it specifically includes the following steps (such as Figure 1 shown): (1) Cleaning substrates, such as oxide single crystal strontium titanate (SrTiO 3 ), etc., a sacrificial layer, such as calcium-doped strontium aluminate (CaSr) is epitaxially deposited on the substrate by pulsed laser deposition or magnetron sputtering technology. 2 Al 2 O 6 ).

[0031] (2) epitaxially deposit a bottom electrode layer, i.e., an oxide single crystal thin film, such as strontium ruthenate (SrRuO 3 ) or Nb-doped SrTiO 3 The crystal structure of the bottom electrode layer matches the piezoelectric layer, and the lattice constant is smaller than that of the piezoelectric layer. The bottom electrode layer also serves as a stress layer.

[0032] (3) Epitaxial deposition of a piezoelectric layer formed by an inorganic piezoelectric single crystal, such as lead zirconate titanate (Pb(Zr,Ti)O 3 ), lead magnesium niobate-lead titanate (PMN-PT), etc.

[0033] (4) A combination of photolithography and magnetron sputtering is used to deposit a patterned metal film as a top electrode layer, such as Au, Pt, etc., in the electrode region of the piezoelectric layer.

[0034] (5) By combining photolithography, dry etching and other methods, part of the non-electrode area of ​​the piezoelectric layer is etched to the sacrificial layer, exposing the end faces of the substrate and the bottom electrode layer to obtain a piezoelectric film and realize planar device patterning.

[0035] (6) Photolithography a layer of patterned negative photoresist (such as SU8, etc.) to form a fixed layer to fix the end of the piezoelectric film on the substrate.

[0036] (7) Using a combination of photolithography and magnetron sputtering, a patterned electrode pin layer, such as Au, Pt, etc., is deposited on the fixed layer to lead out the bottom electrode layer and the top electrode layer.

[0037] (8) The sacrificial layer is wet-etched. Due to the lattice mismatch strain gradient between the bottom electrode layer and the piezoelectric layer, the lattice constant of the lower bottom electrode layer is smaller and the lattice constant of the upper piezoelectric layer is larger. Therefore, the upper piezoelectric layer will be subjected to in-plane compressive stress. The stress / strain is released during corrosion and peeling. Therefore, after the sacrificial layer is removed by wet etching, the flat film will spontaneously curl into an arched piezoelectric film.

[0038] (9) The substrate and the piezoelectric film are rinsed in deionized water for 2 to 3 times, and the deionized water is removed by freeze drying technology. After further polarization treatment at a higher temperature, a self-assembled arched piezoelectric film pressure sensor can be obtained.

[0039] Example 1: Self-assembled lead zirconate titanate-based flexible piezoelectric film pressure sensor The present invention provides a method based on lead zirconate titanate (Pb(Zr,Ti)O 3 ) The high-sensitivity pressure sensor of the arched piezoelectric film is SrTiO from bottom to top. 3 Substrate, SrRuO 3 Bottom electrode layer, Pb(Zr,Ti)O 3 Piezoelectric layer, Pt top electrode layer, SU8 fixing layer and Pt electrode pin layer.

[0040] The implementation steps of this embodiment are as follows: Step 1: pulsed laser deposition on SrTiO 3 Epitaxial deposition of CaSr on substrate 2 Al 2 O 6 Sacrificial layer.

[0041] (1-1) Pretreatment of substrate: (001) oriented SrTiO 3 The substrate was placed in acetone, alcohol, and deionized water in turn, ultrasonically cleaned for 10 minutes in turn, and blown dry with dry nitrogen. The substrate was then placed in an ultraviolet ozone cleaning machine for 15 minutes to ensure that the substrate surface was clean and dust-free.

[0042] (1-2) Pulsed laser deposition on SrTiO 3 CaSr is deposited on the substrate 2 Al 2 O 6 Sacrificial layer, deposition conditions include: SrTiO 3 The substrate heating temperature was 760 °C, the laser energy was 0.8 W, the laser frequency was 3 Hz, and the working gas was O 2 The oxygen pressure was 15 Pa and the deposition time was 10 min to obtain a CaSr with a thickness of about 20 nm. 2 Al 2 O 6 Sacrificial layer.

[0043] Step 2: pulsed laser deposition on CaSr 2 Al 2 O 6 Epitaxial deposition of SrRuO on the sacrificial layer 3 Bottom electrode layer.

[0044] (2-1) Pulsed laser deposition on CaSr 2 Al 2 O 6 SrRuO is deposited on the sacrificial layer 3 The deposition conditions of the bottom electrode layer include: substrate heating temperature 650 °C, laser energy 0.8 W, laser frequency 5 Hz, working gas O 2The oxygen pressure was 10 Pa and the deposition time was 60 min to obtain a SrRuO layer with a thickness of about 200 nm. 3 Bottom electrode layer.

[0045] (2-2) SrRuO 3 The pseudocubic lattice constant of CaSr is a=3.93 Å. 2 Al 2 O 6 The lattice constant of the sacrificial layer is a=3.907 Å. Therefore, SrRuO 3 Layer can be in CaSr 2 Al 2 O 6 Epitaxial growth on the layer.

[0046] Step 3: Pulsed laser deposition on SrRuO 3 Epitaxial deposition of Pb(Zr,Ti)O on the bottom electrode layer 3 Piezoelectric layer.

[0047] (3-1) Pulsed laser deposition on SrRuO 3 Pb(Zr,Ti)O is deposited on the bottom electrode layer 3 The deposition conditions of the piezoelectric layer include: substrate heating temperature 625 °C, laser energy 0.8 W, laser frequency 5 Hz, working gas O 2 The oxygen pressure was 26 Pa and the deposition time was 60 min to obtain a Pb(Zr,Ti)O layer with a thickness of about 200 nm. 3 Piezoelectric layer.

[0048] (3-2) Pb(Zr,Ti)O 3 The piezoelectric layer has a tetragonal phase structure with lattice constants of a=b=4.017 Å, c=4.139 Å, and SrRuO 3 The pseudocubic lattice constant of Pb(Zr,Ti)O is a=3.93 Å. Since 3.93 Å<4.017 Å, 3 The piezoelectric layer is in SrRuO 3 When grown on the bottom electrode layer, it is subjected to in-plane compressive stress, which provides a strain gradient for the self-assembly of the arched piezoelectric film.

[0049] Step 4: In Pb(Zr,Ti)O 3 A Pt top electrode layer is deposited on the surface of the piezoelectric layer by combining photolithography and magnetron sputtering to construct a surface electrode pattern.

[0050] (4-1) Spin-coat AR-P 3510T positive photoresist by dropping the photoresist on the sample surface and spin-coating at 500 rpm for 10 s and 4000 rpm for 50 s. Dry the sample on a heating table at 120 °C for 5 min, expose it to UV light for 8 s, and develop it in a developer for 60 s to pattern the photoresist.

[0051] (4-2) Deposition of precious metal electrode: A layer of precious metal electrode Pt was deposited on the electrode region of the piezoelectric layer by magnetron sputtering technology. The working gas was Ar gas, the working pressure was 3 mTorr, and the DC sputtering power was 70 W for 400 s to obtain a 20 nm thick Pt top electrode layer. Then, the positive photoresist was removed in acetone to obtain a Pt top electrode layer with a pattern size of 500 μm × 600 μm. Finally, annealing was performed at 400 °C for 5 minutes to make the Pt top electrode layer bonded to Pb(Zr,Ti)O 3 The piezoelectric layer is firmly bonded.

[0052] Step 5: Spin-coat a thick photoresist protective layer and pattern it by ultraviolet exposure. Etch part of the non-electrode area of ​​the piezoelectric layer to the sacrificial layer by ion beam etching, and completely expose the end face of the bottom electrode layer, remove the photoresist, realize planar device patterning, and obtain a piezoelectric film.

[0053] (5-1) Spin-coat AR-P 3220 positive photoresist by dropping the photoresist on the film surface and spin-coating at 500 rpm for 10 s and 2000 rpm for 50 s. Place the sample on a heating table at 100 °C and dry for 2 min. Repeat the operation three times to obtain a photoresist coating of about 30 μm thick. Expose to ultraviolet light to form a patterned protective layer.

[0054] (5-2) Etch part of the non-electrode area of ​​the piezoelectric layer by ion beam etching technology until the sacrificial layer is completely etched away and the end surface of the bottom electrode layer is completely exposed. The etching conditions are: vacuum degree 8×10 -4 Pa, the anode current was 1 A, and the etching was performed for 50 min. The photoresist was then removed in acetone.

[0055] Step six, forming a fixing layer on the surface of the patterned piezoelectric film by photolithography of a negative photoresist (SU8), and fixing one edge of the piezoelectric film on the substrate.

[0056] (6-1) Spin-coat SU8 2002 negative photoresist, drop the negative photoresist on the surface of the piezoelectric film, spin-coat at 500 rpm for 10 s, spin-coat at 4000 rpm for 50 s, place the sample on a heating table at 100 °C for 5 min to dry, obtain a negative photoresist coating of about 2 μm thick, expose to UV light for 15 s, place the sample on a heating table at 100 °C for 5 min, develop in a developer for 60 s, and then place the sample on a heating table at 200 °C for 15 min to form a patterned fixed layer, fixing one edge of the piezoelectric film on the substrate.

[0057] Step seven, deposit the Pt electrode pin layer by combining photolithography and magnetron sputtering, and lead out the top / bottom electrode layer to facilitate subsequent testing.

[0058] (7-1) Spin-coat AR-P 3510T positive photoresist by dropping the photoresist on the sample surface and spin-coating at 500 rpm for 10 s and 4000 rpm for 50 s. Dry the sample on a heating table at 120 °C for 5 min, expose it to UV light for 8 s, and develop it in a developer for 60 s to pattern the photoresist. (7-2) Deposition of precious metal electrode pins: A layer of precious metal Pt electrode pins was deposited on the surface of the fixed layer by magnetron sputtering technology, with Ar gas as the working gas, working pressure of 3 mTorr, DC sputtering power of 70 W for 4000 s, to obtain a 200 nm thick Pt film. The positive photoresist was then removed in acetone to obtain a patterned Pt electrode pin layer.

[0059] Step eight, wet-etching the sacrificial layer to completely remove the sacrificial layer.

[0060] (8-1) Immerse the substrate and piezoelectric film in deionized water to make CaSr 2 Al 2 O 6 The sacrificial layer is dissolved by deionized water at room temperature, thereby releasing the upper piezoelectric film. Due to the lattice mismatch strain gradient between the bottom electrode layer and the piezoelectric layer, the self-assembly of the arched piezoelectric film is finally achieved as the sacrificial layer dissolves, such as Figure 2 shown.

[0061] Step nine, using freeze drying technology to remove deionized water and polarize the piezoelectric device at the same time.

[0062] The piezoelectric film was polarized at 100°C and 200 kV / cm DC electric field for 20 minutes, cooled to room temperature under pressure, and then tested. Compared with flat films, piezoelectric films with arched structures can withstand greater stress / strain and thus produce greater piezoelectric response, such as Figure 3 As shown. The piezoelectric coefficient of the piezoelectric film d33 Up to 120 pC / N, sensitivity up to 0.004Pa (such as Figure 4 As shown), it can work stably at -50~300℃.

[0063] Example 2: Self-assembled PMN-PT based flexible piezoelectric film pressure sensor The high-sensitivity pressure sensor based on PMN-PT arched piezoelectric film provided in this embodiment is composed of SrTiO 3 Substrate, 0.5% Nb-doped SrTiO 3 Bottom electrode layer, PMN-PT piezoelectric layer, Pt top electrode layer, SU8 fixing layer and Pt electrode pin layer.

[0064] The implementation steps of this embodiment are as follows: Step 1: pulsed laser deposition on SrTiO 3 Epitaxial deposition of CaSr on substrate 2 Al 2 O 6 Sacrificial layer.

[0065] (1-1) Pretreatment of substrate: (001) oriented SrTiO 3 The substrate was placed in acetone, alcohol, and deionized water in turn, ultrasonically cleaned for 10 minutes in turn, and blown dry with dry nitrogen. The substrate was then placed in an ultraviolet ozone cleaning machine for 15 minutes to ensure that the substrate surface was clean and dust-free.

[0066] (1-2) Pulsed laser deposition on SrTiO 3 CaSr is deposited on the substrate 2 Al 2 O 6 Sacrificial layer, deposition conditions include: SrTiO 3 The substrate heating temperature was 760 °C, the laser energy was 0.8 W, the laser frequency was 3 Hz, and the working gas was O 2 The oxygen pressure was 15 Pa and the deposition time was 10 min to obtain a CaSr with a thickness of about 20 nm. 2 Al 2 O 6 Sacrificial layer.

[0067] Step 2: pulsed laser deposition on CaSr 2 Al 2 O 6 0.5% Nb-doped SrTiO was epitaxially deposited on the sacrificial layer. 3 Bottom electrode layer.

[0068] (2-1) Pulsed laser deposition on CaSr 2 Al 2 O6 0.5% Nb-doped SrTiO was deposited on the sacrificial layer. 3 The deposition conditions of the bottom electrode layer include: substrate heating temperature 650 °C, laser energy 0.8 W, laser frequency 5 Hz, working gas O 2 The oxygen pressure was 20 Pa and the deposition time was 60 min to obtain a 0.5% Nb-doped SrTiO with a thickness of about 200 nm. 3 Bottom electrode layer.

[0069] (2-2) Cubic phase 0.5% Nb-doped SrTiO 3 The lattice constant of CaSr is a=3.905 Å. 2 Al 2 O 6 The lattice constant of the sacrificial layer is a=3.907 Å. Therefore, 0.5% Nb-doped SrTiO 3 Layer can be in CaSr 2 Al 2 O 6 Epitaxial growth on the layer.

[0070] Step 3: Pulsed laser deposition was used to deposit 0.5% Nb-doped SrTiO 3 The PMN-PT piezoelectric layer is epitaxially deposited on the bottom electrode layer.

[0071] (3-1) Pulsed laser deposition was used to deposit 0.5% Nb-doped SrTiO 3 The PMN-PT piezoelectric layer was deposited on the bottom electrode layer. The deposition conditions included: substrate heating temperature 625 °C, laser energy 0.8 W, laser frequency 5 Hz, working gas O 2 The oxygen pressure was 25 Pa and the deposition time was 60 min, and a PMN-PT piezoelectric layer with a thickness of about 200 nm was obtained.

[0072] (3-2) The PMN-PT piezoelectric layer has a tetragonal structure with a lattice constant of a=b=4.024 Å, while the cubic phase 0.5% Nb-doped SrTiO 3 The lattice constant of PMN-PT is a=3.905 Å. Since 3.905 Å<4.024 Å, the PMN-PT piezoelectric layer is 3 When grown on the bottom electrode layer, it is subjected to in-plane compressive stress, which provides a strain gradient for the self-assembly of the arched piezoelectric film.

[0073] Step 4: Deposit a Pt top electrode layer on the surface of the PMN-PT piezoelectric layer by combining photolithography and magnetron sputtering to construct a surface electrode pattern.

[0074] (4-1) Spin-coat AR-P 3510T positive photoresist by dropping the photoresist on the sample surface and spin-coating at 500 rpm for 10 s and 4000 rpm for 50 s. Dry the sample on a heating table at 120 °C for 5 min, expose it to UV light for 8 s, and develop it in a developer for 60 s to pattern the photoresist.

[0075] (4-2) Deposition of precious metal electrode: A layer of precious metal electrode Pt was deposited on the electrode region of the piezoelectric layer by magnetron sputtering technology. The working gas was Ar gas, the working pressure was 3 mTorr, and the DC sputtering power was 70 W for 400 s to obtain a 20 nm thick Pt top electrode layer. Then, the positive photoresist was removed in acetone to obtain a Pt top electrode layer with a pattern size of 500 μm × 600 μm. Finally, annealing was performed at 400 °C for 5 minutes to firmly bond the Pt top electrode layer to the PMN-PT piezoelectric layer.

[0076] Step 5: Spin-coat a thick photoresist protective layer and pattern it by ultraviolet exposure. Etch part of the non-electrode area of ​​the piezoelectric layer to the sacrificial layer by ion beam etching, and completely expose the end face of the bottom electrode layer, remove the photoresist, realize planar device patterning, and obtain a piezoelectric film.

[0077] (5-1) Spin-coat AR-P 3220 positive photoresist by dropping the photoresist on the film surface and spin-coating at 500 rpm for 10 s and 2000 rpm for 50 s. Place the sample on a heating table at 100 °C and dry for 2 min. Repeat the operation three times to obtain a photoresist coating of about 30 μm thick. Expose to ultraviolet light to form a patterned protective layer.

[0078] (5-2) Etch part of the non-electrode area of ​​the piezoelectric layer by ion beam etching technology until the sacrificial layer is completely etched away and the end surface of the bottom electrode layer is completely exposed. The etching conditions are: vacuum degree 8×10 -4 Pa, the anode current was 1 A, and the etching was about 40 min. The photoresist was then removed in acetone.

[0079] Step six, forming a fixing layer on the surface of the patterned piezoelectric film by photolithography of a negative photoresist (SU8), and fixing one edge of the piezoelectric film on the substrate.

[0080] (6-1) Spin-coat SU8 2002 negative photoresist, drop the negative photoresist on the surface of the piezoelectric film, spin-coat at 500 rpm for 10 s, spin-coat at 4000 rpm for 50 s, place the sample on a heating table at 100 °C for 5 min to dry, obtain a negative photoresist coating of about 2 μm thick, expose to UV light for 15 s, place the sample on a heating table at 100 °C for 5 min, develop in a developer for 60 s, and then place the sample on a heating table at 200 °C for 15 min to form a patterned fixed layer, fixing one edge of the piezoelectric film on the substrate.

[0081] Step seven, deposit the Pt electrode pin layer by combining photolithography and magnetron sputtering, and lead out the top / bottom electrode layer to facilitate subsequent testing.

[0082] (7-1) Spin-coat AR-P 3510T positive photoresist by dropping the photoresist on the sample surface and spin-coating at 500 rpm for 10 s and 4000 rpm for 50 s. Dry the sample on a heating table at 120 °C for 5 min, expose it to UV light for 8 s, and develop it in a developer for 60 s to pattern the photoresist. (7-2) Deposition of precious metal electrode pins: A layer of precious metal Pt electrode pins was deposited on the surface of the fixed layer by magnetron sputtering technology, with Ar gas as the working gas, working pressure of 3 mTorr, DC sputtering power of 70 W for 4000 s, to obtain a 200 nm thick Pt film. The positive photoresist was then removed in acetone to obtain a patterned Pt electrode pin layer.

[0083] Step eight, wet-etching the sacrificial layer to completely remove the sacrificial layer.

[0084] (8-1) Immerse the substrate and piezoelectric film in deionized water to make CaSr 2 Al 2 O 6 The sacrificial layer is dissolved by deionized water at room temperature, thereby releasing the upper piezoelectric film. Due to the lattice mismatch strain gradient between the bottom electrode layer and the piezoelectric layer, the self-assembly of the arched piezoelectric film is finally achieved as the sacrificial layer dissolves, such as Figure 2 shown.

[0085] In step nine, the deionized water is removed by freeze drying technology while polarizing the piezoelectric film.

[0086] The piezoelectric film was polarized at 90°C and 200 kV / cm DC electric field for 20 minutes, cooled to room temperature under pressure, and then tested. Compared with the flat film, the arched piezoelectric film can withstand greater stress / strain and thus produce a greater piezoelectric response. The piezoelectric coefficient of the piezoelectric film is d 33It can reach 200 pC / N, the sensitivity can reach 0.002 Pa, and it can work stably at -50~120℃.

[0087] The advantages of the piezoelectric film pressure sensor of the present invention include: (1) Strong piezoelectric sensing response: Compared with traditional flexible piezoelectric polymers, the inorganic piezoelectric single crystal film of the present invention has a higher piezoelectric coefficient. Compared with planar film devices, the arched structure design can produce greater deformation under the same stress, thereby significantly improving the piezoelectric response. Therefore, the self-curling arched piezoelectric device has higher sensitivity when used in flexible pressure sensing. (2) Wide operating temperature range and good temperature stability: The operating temperature of traditional polymer-based flexible pressure sensors is usually below 120°C. The operating temperature range based on inorganic piezoelectric single crystal film in the present invention is wider, up to ~300°C, and has good temperature stability. (3) Compared with the traditional method of improving the performance of piezoelectric devices through structural design, the process of the present invention is simple and can be formed in one step. The length of a single device is only a few hundred microns, and the size can be further reduced, which can realize the miniaturization of piezoelectric device units.

Claims

1. A self-assembly preparation method of a piezoelectric film pressure sensor, characterized in that: The steps include: S1, depositing a sacrificial layer on the substrate; S2, depositing a bottom electrode layer on the sacrificial layer; S3, depositing a piezoelectric layer formed by an inorganic piezoelectric single crystal on the bottom electrode layer; wherein the crystal structure of the bottom electrode layer matches the piezoelectric layer, and the lattice constant of the bottom electrode layer is smaller than the lattice constant of the piezoelectric layer; S4, depositing a top electrode layer in the electrode region of the piezoelectric layer; S5, etching part of the non-electrode area of ​​the piezoelectric layer to the sacrificial layer by etching, exposing the end surfaces of the substrate and the bottom electrode layer, and obtaining a piezoelectric film; S6, depositing a fixing layer on the piezoelectric film to fix one edge of the piezoelectric film on the substrate; S7, depositing an electrode lead layer of a bottom electrode layer and a top electrode layer to lead out the bottom electrode layer and the top electrode layer; S8, wet etching the sacrificial layer, washing, drying, and then polarizing to obtain a piezoelectric film pressure sensor.

2. The self-assembly preparation method of the piezoelectric film pressure sensor according to claim 1, characterized in that: The bottom electrode layer is Nb-doped SrTiO3 or SrRuO3, and the piezoelectric layer is Pb(Zr,Ti)O3 or PMN-PT.

3. The self-assembly preparation method of the piezoelectric film pressure sensor according to claim 1, characterized in that: The substrate is an oxide single crystal substrate.

4. The self-assembly preparation method of the piezoelectric film pressure sensor according to claim 2, characterized in that: The substrate is SrTiO3.

5. The self-assembly preparation method of the piezoelectric film pressure sensor according to claim 1, characterized in that: The sacrificial layer is CaSr2Al2O6.

6. The self-assembly preparation method of a piezoelectric film pressure sensor according to claim 1, characterized in that: The fixed layer is a negative photoresist.

7. The self-assembly preparation method of a piezoelectric film pressure sensor according to claim 1, characterized in that: S6 specifically includes: spin coating negative photoresist on the piezoelectric film, heating and baking to obtain a negative photoresist coating, ultraviolet exposure, heating and baking again, developing in a developer, and then baking to form a patterned fixed layer to fix one edge of the piezoelectric layer on the substrate.

8. The self-assembly preparation method of a piezoelectric film pressure sensor according to claim 1, characterized in that: S8 is specifically: immersing the sample obtained in S7 into water, so that the sacrificial layer is dissolved by water, and self-assembly of the arched piezoelectric film is achieved as the sacrificial layer is dissolved.

9. The self-assembly preparation method of the piezoelectric film pressure sensor according to claim 8, characterized in that: In S8, the drying is freeze drying, and the polarization treatment is polarization at 80°C-100°C and a DC electric field of 150 kV / cm-200 kV / cm for 20-30 minutes.

10. A piezoelectric film pressure sensor obtained by the self-assembly preparation method according to any one of claims 1 to 9.

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