Piezoelectric device and preparation method thereof

Abstract

The invention provides a piezoelectric device and a preparation method thereof. The piezoelectric device comprises a substrate material layer; the single crystal seed layer is arranged on the substrate material layer, and the single crystal seed layer is made of a six-membered ring structure carbon material; the electrode layer is arranged on the single crystal seed layer; and the single crystal piezoelectric film is arranged on the electrode layer. According to the preparation method of the piezoelectric device, the cost is lower, the material price is lower, the film deposition efficiency is higher, and the crystal structure of the single crystal piezoelectric film is more stable.

Description

Technical Field

[0001] The present application relates to the field of micro electro mechanical systems (MEMS) design, and more specifically, to a piezoelectric device and a method for preparing the same. Background Art

[0002] Micro electro mechanical systems (MEMS) are devices that integrate electronic circuits, sensors or actuators on a semiconductor substrate using technologies such as photolithography, corrosion, thin film deposition, silicon micromachining, non-silicon micromachining and precision machining. MEMS is an independent intelligent system with a system size of several millimeters or even smaller, and its internal structure is generally in the micron or even nanometer level. For example, the size of common MEMS products is generally 3mm×3mm×1.5mm, or even smaller.

[0003] Piezoelectric MEMS refers to a micro-electromechanical system that uses piezoelectric materials as sensors or actuators, that is, a device that combines the piezoelectric effect with MEMS technology. At present, the piezoelectric materials commonly used in piezoelectric MEMS are bulk or easy-to-produce polycrystalline piezoelectric films, while the electrical and mechanical properties of single-crystal piezoelectric films are better than those of polycrystalline piezoelectric films, but the difficulty of preparing them is much higher than that of polycrystalline piezoelectric films. In order to prepare piezoelectric materials with better performance to meet the ever-increasing performance requirements of MEMS devices, how to prepare single-crystal piezoelectric films at a lower cost and higher efficiency has become an urgent problem to be solved. Summary of the invention

[0004] The present application provides a piezoelectric device and a method for preparing the same. The piezoelectric device includes a single-crystal piezoelectric film. The preparation method has lower cost, cheaper materials, higher film deposition efficiency and a more stable crystal structure.

[0005] In a first aspect, an embodiment of the present application provides a piezoelectric device, comprising: a base material layer; a single crystal seed layer, which is arranged on the base material layer, and the single crystal seed layer is composed of a hexacyclic structured carbon material; an electrode layer, which is arranged on the single crystal seed layer; and a single crystal piezoelectric film, which is arranged on the electrode layer.

[0006] In combination with the first aspect, in certain implementations of the first aspect, the six-membered ring structure carbon material is any one of the following: graphene, graphite, or graphene oxide.

[0007] According to the piezoelectric device provided in the embodiment of the present application, the electrode substrate contained therein is cheaper, the chemical properties are more stable and the film deposition rate is faster. The lattice size and lattice orientation of the hexacyclic carbon material are determined, and the lattice orientation is the c-axis orientation of the crystal axis. Then, when a layer of hexacyclic carbon materials such as graphite, graphene or graphene oxide is grown on the substrate as a seed layer, the lattice orientation of the seed layer is not affected by the substrate, or in other words, whether the substrate is single crystal, polycrystalline or amorphous, the seed layer can grow and the lattice orientation is fixed to the c-axis orientation. Therefore, the lattice orientation of the electrode layer and the subsequent growth of the single crystal piezoelectric film is also fixed and more stable. In addition, the processing cost of the carbon material is much lower than the processing cost of the metal or metal oxide, and the cost of the manufacturing equipment for preparing the electrode substrate is also lower. The single crystal piezoelectric film provided in the embodiment of the present application may include AlN film, PZT film, etc.

[0008] In combination with the first aspect, in some implementations of the first aspect, the thickness of the single crystal seed layer is 2 to 100 nm.

[0009] In combination with the first aspect, in some implementations of the first aspect, an oxide film layer is further included, and the oxide film layer is disposed between the electrode layer and the single crystal piezoelectric film.

[0010] In combination with the first aspect, in some implementations of the first aspect, the oxide film layer includes a perovskite oxide film.

[0011] According to the solution provided in the embodiment of the present application, the role of the oxide film layer is to block the piezoelectric material components in the piezoelectric film from diffusing into the electrode layer to prevent the peeling caused by the structural change and reduced adhesion between the electrode layer and the piezoelectric film, such as blocking the diffusion of oxygen atoms in the piezoelectric film. In addition, the oxide film layer can be a conductive oxide with a perovskite structure, and growing a layer of conductive oxide with a perovskite structure on the electrode layer can ensure conductivity.

[0012] In combination with the first aspect, in some implementations of the first aspect, the electrode layer is composed of a single metal layer or a stack of multiple metal layers.

[0013] In combination with the first aspect, in certain implementations of the first aspect, the electrode layer is composed of at least one of the following metals: gold, platinum, palladium, rhodium, iridium or ruthenium.

[0014] In combination with the first aspect, in certain implementations of the first aspect, the base material layer includes any one of the following: an amorphous silicon substrate, a single crystal silicon substrate, or a silicon substrate with an oxide film.

[0015] According to the technical solution provided in the embodiment of the present application, since the lattice orientation of the hexacyclic carbon material seed layer is determined, or the material type of the base material layer does not affect the lattice orientation of the seed layer, the base material layer in the embodiment of the present application can be any substrate material used to grow a thin film.

[0016] In combination with the first aspect, in some implementations of the first aspect, the single crystal piezoelectric film includes a single crystal lead zirconate titanate PZT film.

[0017] In a second aspect, an embodiment of the present application provides an electronic device, comprising the piezoelectric device in the first aspect.

[0018] In a third aspect, an embodiment of the present application provides a method for preparing a piezoelectric device, the method comprising: preparing a base material layer; preparing a single crystal seed layer on the base material layer, the single crystal seed layer being composed of a hexacyclic structured carbon material; preparing an electrode layer on the single crystal seed layer; and depositing a piezoelectric material on the electrode layer to obtain a single crystal piezoelectric film.

[0019] In combination with the third aspect, in certain implementations of the third aspect, the method further includes: preparing an oxide thin film layer on the electrode layer.

[0020] In combination with the third aspect, in certain implementations of the third aspect, the oxide film layer includes a perovskite metal oxide film.

[0021] In combination with the third aspect, in certain implementations of the third aspect, preparing a single crystal seed layer on a base material layer includes: depositing a catalytic metal on the base material layer, the catalytic metal including a metal material naturally oriented on the a-axis or c-axis of the crystal axis; adding a carbon-containing hydrocarbon gas as a carbon source gas, and forming the single crystal seed layer by thermally decomposing the carbon-containing hydrocarbon gas on the catalytic metal.

[0022] In combination with the third aspect, in certain implementations of the third aspect, the catalytic metal includes at least one of cobalt, copper and zirconium.

[0023] In combination with the third aspect, in certain implementations of the third aspect, the carbon-containing hydrocarbon gas is methane.

[0024] In combination with the third aspect, in certain implementations of the third aspect, the six-membered ring structure carbon material is any one of the following: graphene, graphite, or graphene oxide.

[0025] In combination with the third aspect, in certain implementations of the third aspect, the thickness of the single crystal seed layer is 2 to 100 nm.

[0026] In combination with the third aspect, in certain implementations of the third aspect, the electrode layer is composed of a single metal layer or is formed by stacking multiple metal layers.

[0027] In combination with the third aspect, in certain implementations of the third aspect, the electrode layer is composed of at least one of the following metals: gold, platinum, palladium, rhodium, iridium or ruthenium.

[0028] In combination with the third aspect, in certain implementations of the third aspect, the base material layer includes any one of the following: an amorphous silicon substrate, a single crystal silicon substrate, and a silicon substrate with an oxide film. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of a piezoelectric MEMS provided in an embodiment of the present application.

[0030] Figure 2 It is a schematic structural diagram of an electrode substrate provided in an embodiment of the present application.

[0031] Figure 3 It is a schematic structural diagram of an electrode substrate for growing a single-crystal piezoelectric film provided in an embodiment of the present application.

[0032] Figure 4 It is a schematic structural diagram of a piezoelectric MEMS provided in an embodiment of the present application.

[0033] Figure 5 This is a processing flow chart of an electrode substrate provided in an embodiment of the present application.

[0034] Figure 6 It is a process flow chart for generating a single crystal seed layer provided in an embodiment of the present application. DETAILED DESCRIPTION

[0035] The technical solution in this application will be described below in conjunction with the accompanying drawings.

[0036] Micro electro mechanical systems (MEMS) are devices that integrate electronic circuits, sensors or actuators on a semiconductor substrate using technologies such as photolithography, corrosion, thin film deposition, silicon micromachining, non-silicon micromachining and precision machining. MEMS is an independent intelligent system with a system size of several millimeters or even smaller, and its internal structure is generally in the micron or even nanometer level. For example, the size of common MEMS products is generally 3mm×3mm×1.5mm, or even smaller.

[0037] Piezoelectric MEMS or piezoelectric devices are micro-electromechanical systems that use piezoelectric materials as sensors or actuators. Piezoelectric materials refer to a type of single-crystal or polycrystalline solid materials that will have charges on both ends when subjected to pressure. They are important carriers for energy conversion and signal transmission. Piezoelectric materials can produce piezoelectric effect or inverse piezoelectric effect. Among them, the piezoelectric effect means that when certain dielectrics are deformed by external forces in a certain direction, polarization will occur inside them, and opposite positive and negative charges will appear on their two opposite surfaces. When the external force is removed, it will return to an uncharged state. This phenomenon is called the positive piezoelectric effect. When the direction of the force changes, the polarity of the charge also changes. On the contrary, when an electric field is applied in the polarization direction of the dielectric, these dielectrics will also deform. When the electric field is removed, the deformation of the dielectric disappears. This phenomenon is called the inverse piezoelectric effect.

[0038] The principle of the piezoelectric effect is that if pressure is applied to a piezoelectric material, the piezoelectric material will generate a potential difference (called the positive piezoelectric effect), and vice versa, if voltage is applied, mechanical stress will be generated (called the inverse piezoelectric effect). If the pressure is a high-frequency vibration, a high-frequency current will be generated. When a high-frequency electrical signal is applied to a piezoelectric material, a high-frequency acoustic signal (mechanical vibration) will be generated.

[0039] Piezoelectric materials include piezoelectric single crystals, piezoelectric ceramics or piezoelectric films. Piezoelectric single crystals refer to crystals that grow in a long-range orderly manner according to the crystal space lattice, such as quartz crystals, lithium gallate, lithium germanate, titanium germanate, and lithium niobate and lithium tantalate, etc. Piezoelectric ceramics generally refer to piezoelectric polycrystals, which are polycrystals formed by mixing, molding, and high-temperature sintering of raw materials with necessary ingredients, and obtained by the solid-phase reaction between powder particles and the sintering process. Piezoelectric ceramics include barium titanate (BaTiO3, BT), lead zirconate titanate (PbZr x Ti1-xO3, PZT) and so on. Piezoelectric film is formed by atoms or atomic groups being deposited on a substrate by sputtering or sputtering, and its structure can be polycrystalline or even single crystal. Devices made of piezoelectric film only need to deposit a very thin layer of piezoelectric material on the substrate. During the preparation of the film, the film is deposited in a certain orientation, and no polarization orientation and cutting processes are required. Piezoelectric film has the advantages of both piezoelectric single crystal and piezoelectric ceramic, that is, the surface is smooth and dense, easy to manufacture, low price, easy to adjust, and reliable and stable performance. In addition, the performance of piezoelectric devices can be adjusted by adjusting the film thickness, substrate type and electrode form, and piezoelectric MEMS can be planarized and integrated. Piezoelectric films include aluminum nitride (AlN), zinc oxide (ZnO) and PZT series piezoelectric films.

[0040] Figure 1A schematic diagram of a piezoelectric MEMS is shown, wherein the piezoelectric MEMS is a piezoelectric micromachined ultrasonic transducer (PMUT). Figure 1 As shown in the figure, PMUT has the following structure: from top to bottom, it is an upper metal electrode, a piezoelectric film, a lower metal electrode, an elastic layer and a silicon substrate. The upper metal electrode and the lower metal electrode are connected to the same voltage source. The suspended area in the middle of the silicon substrate is a diaphragm. The expansion and compression of the piezoelectric film can drive the deformation of the elastic layer, and the deformation of the elastic layer causes the diaphragm to vibrate up and down uniformly. The emission of ultrasonic waves in PMUT is formed by the uniform up and down vibration of the diaphragm squeezing the air.

[0041] Figure 1 This is just a schematic structure of PMUT. Figure 1 The upper metal electrode of the PMUT shown may also be in other shapes. The metal electrode may be made of metal materials, such as tungsten, molybdenum, titanium, platinum, aluminum, copper, gold, etc. In addition, a seed layer (not shown) for determining the lattice orientation growth of the piezoelectric film may be included between the base material layer and the lower metal electrode. Figure 1 ), Figure 1 The piezoelectric film shown can be grown on the lower metal electrode based on the above seed layer. The above structure will be described in detail later and will not be described here. The material of the piezoelectric film can be the above AlN or PZT. Figure 1 In the structure shown, the upper metal electrode may further include another layer of piezoelectric film and another layer of metal electrode on the piezoelectric film to form a piezoelectric bimorph, which will not be described in detail herein.

[0042] In some embodiments of the present application, having Figure 1 The piezoelectric MEMS of the structure shown may also include a film bulk acoustic resonator (FBAR), a piezoelectric MEMS speaker, a piezoelectric MEMS print head, a piezoelectric sensor, etc. The MEMS in the embodiment of the present application may also include the above-mentioned piezoelectric film element. That is, the piezoelectric MEMS may also be a part or the whole of an electronic device. For example, a product using PMUT may also be a biometric authentication sensor (fingerprint authentication sensor, blood vessel authentication sensor, etc.) or a medical / health care sensor (blood pressure meter, blood vessel imaging sensor), etc.

[0043] Figure 2An electrode substrate for depositing piezoelectric material to form a piezoelectric film is shown. The electrode substrate includes a bottom base material layer 210, a middle seed layer 220, and an uppermost electrode layer 230 or a lower metal electrode. The seed layer 220 is used to determine the crystal orientation growth of the piezoelectric film of the upper structure, and the piezoelectric material is deposited on the surface of the electrode substrate to form a piezoelectric film with a certain crystal orientation. In addition, the seed layer 220 also plays a role in regulating crystal nucleation and adjusting the lattice mismatch. For example, if the piezoelectric film is an AlN film, the seed layer 220 can be a thin layer of AlN. If the piezoelectric film is a PZT film, the seed layer 220 can be a metal such as titanium (Ti), chromium (Cr), titanium oxide (TiO2), or zirconium oxide (ZrO2) and a mixture of zirconium oxide (ZrO2) and oxides of rare earth elements. The rare earth element can be at least one selected from scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu). The rare earth element oxide can be, for example, the oxide of the above-mentioned lanthanum (La) - lanthanum nickelate (LNO). The electrode layer 230 is Figure 1 In the structure shown, the metal electrode is located below the z-axis, and the piezoelectric film is formed on the electrode layer 230 .

[0044] At present, the piezoelectric materials commonly used in piezoelectric MEMS are bulk or easy-to-produce polycrystalline piezoelectric films. For example, the above-mentioned PMUT generally uses polycrystalline PZT piezoelectric films deposited by magnetron sputtering. Polycrystalline piezoelectric films refer to piezoelectric films in which there are different degrees of misorientation between individual microcrystals or small single crystals, and when all microcrystals have the same orientation, the piezoelectric film is a single crystal piezoelectric film. Both polycrystalline piezoelectric films and single crystal piezoelectric films can be grown on Figure 2 The surface of the electrode substrate shown. Any orientation difference between the crystallites will reduce the electromechanical coupling coefficient and thermal conductivity, or in other words, the electrical and mechanical properties of polycrystalline piezoelectric films are inferior to those of single-crystal piezoelectric films. In addition, the surface uniformity of single-crystal piezoelectric films is higher. In order to meet the ever-increasing performance requirements of MEMS devices in the future, it is necessary to replace the piezoelectric material from polycrystalline piezoelectric films to single-crystal piezoelectric films.

[0045] However, the preparation of single-crystal piezoelectric films is much more difficult than that of polycrystalline piezoelectric films. Figure 2Taking the electrode substrate shown in the figure as an example, since a single crystal piezoelectric film needs to be formed, in order for the piezoelectric film to grow in a certain crystal orientation, the seed layer 220, the electrode layer 230 or the base material layer 210 need to be single crystal materials. At present, single crystal piezoelectric films are generally grown on single crystal heterogeneous substrates, such as high-cost single crystal silicon substrates, which results in limited materials that can be used for the base material layer and high costs. Moreover, at present, the processing Figure 2 The process flow of the structure shown is also relatively complex and costly. For example, when preparing a single-crystal AlN film, the setting and adjustment of the chamber pressure, gas flow, sputtering power, and magnetic field process parameters of magnetron sputtering are very complex. When preparing a PZT film, the process cost of magnetron sputtering is relatively high, and the control of the growth environment and process conditions of the PZT film is more complex than that of the magnetron sputtering AlN film. For example, a layer of oxide film needs to be grown on the electrode layer as a buffer layer. The oxide film layer as a buffer layer will be specifically introduced later, and will not be repeated here. For another example, if the piezoelectric film is a single-crystal PZT film, the seed layer 220 needs to be a mixture of zirconium oxide or zirconium oxide and rare earth element oxides. The film deposition process of these materials has many steps and high costs. It can be obtained that in terms of process technology, the process cost of preparing single-crystal piezoelectric films at this stage is relatively high and the process is complex. In addition, due to the shortcomings of the above-mentioned materials and process technologies, the cost of manufacturing equipment for preparing single-crystal piezoelectric films is also relatively high.

[0046] In order to solve the shortcomings of the above materials, process technology and manufacturing equipment, the embodiments of the present application provide an electrode substrate and a processing method thereof for depositing piezoelectric material to form a single crystal piezoelectric film. The electrode substrate is cheaper, has more stable chemical properties and a faster film deposition rate.

[0047] Figure 3 FIG. 2 shows an electrode substrate structure in an embodiment of the present application. Figure 3 As shown in (a) of FIG. 1 , the overall structure of the electrode substrate is Figure 2The electrode substrate shown is the same, the difference is that the seed layer in the embodiment of the present application is a single crystal seed layer 320, and the material selected is a single crystal carbon material, rather than the above-mentioned metal or metal oxide. The thickness of the single crystal seed layer 320 is 2 to 100 nm, preferably 10 to 50 nm. The single crystal carbon material can be a carbon material with a continuous six-membered ring structure such as graphite, graphene or graphene oxide. The reason for using the above carbon material as a seed layer is that: first, carbon materials such as graphite, graphene or graphene oxide are all continuous six-membered ring structures, and their lattice size and lattice orientation are determined, and the lattice orientation is the c-axis orientation of the crystal axis. Then, when a layer of carbon material such as graphite, graphene or graphene oxide is grown on the substrate as a seed layer, the lattice orientation of the seed layer is not affected by the substrate, or in other words, whether the substrate is single crystal, polycrystalline or amorphous, the seed layer can grow and the lattice orientation is fixed to the c-axis orientation. Therefore, the lattice orientation of the electrode layer 330 located above the single crystal seed layer 320 and the subsequently grown single crystal piezoelectric film is also fixed and more stable. Figure 3 The cost of manufacturing equipment for the electrode substrate shown in (a) is also lower. Figure 3 The electrode substrate shown in (a) can be used to prepare the above-mentioned single crystal piezoelectric films such as AlN thin film and PZT thin film.

[0048] As mentioned above, since the lattice orientation of the seed layer is determined and is not affected by the substrate, Figure 3 The base material layer 310 shown in (a) can be an amorphous silicon substrate, a single crystal silicon substrate or a polycrystalline silicon substrate. In other embodiments of the present application, the base material layer 310 can also be a silicon substrate with an oxide film. For example, the raw material of the base material layer is a silicon substrate, and the surface of the silicon substrate close to the single crystal seed layer has silicon dioxide (SiO2) as an adhesion layer with a thickness of about 100nm, which can improve the adhesion between the single crystal seed layer 320 and the silicon substrate. Optionally, the base material layer 310 in the present application can also be an insulating substrate silicon (silicon-on-insulator, SOI), cavity SOI (cavity-SOI, CSOI), or a non-silicon substrate such as silicon carbide (SiC) and sapphire (Al2O3).

[0049] The electrode layer 330 may be composed of a single metal layer or a plurality of metal layers, and the metal constituting the electrode layer may include at least one of gold (Au), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir) or ruthenium (Ru). The thickness of the electrode layer 330 is about 50 to 500 nm, preferably 100 nm.

[0050] Alternatively, if Figure 3As shown in (b), if the single crystal piezoelectric film is a PZT film, the electrode substrate in the embodiment of the present application also includes an oxide film layer 340 disposed on the electrode layer. The oxide film layer 340 is usually a metal oxide having the same lattice structure (perovskite type) as the piezoelectric layer, such as strontium ruthenate (SrRuO3, SRO) or strontium titanate (SrTiO3, STO), etc., with a thickness of about 10 to 50 nm, preferably 20 nm. The role of the oxide film layer is to block the piezoelectric material components in the piezoelectric film from diffusing into the electrode layer 330 to prevent the structural changes between the electrode layer 330 and the piezoelectric film and the peeling caused by the reduction of adhesion, such as blocking the diffusion of oxygen atoms in the piezoelectric film. In addition, SRO and STO themselves are conductive oxides with a perovskite structure, and growing a layer of SRO or STO on the electrode layer can ensure conductivity.

[0051] like Figure 3 As shown in (c) in Figure 3 A piezoelectric material is deposited on the electrode substrate shown in (a) or (b) to finally form a single crystal piezoelectric layer 350 on the electrode substrate. In the embodiment of the present application, in order to prepare a piezoelectric device, an oxide film or a metal material may be further deposited on the single crystal piezoelectric layer 350 to form an electrode layer as an upper electrode (the electrode layer 330 serves as a lower electrode) and an oxide film layer between the upper electrode layer and the single crystal piezoelectric layer 350.

[0052] Optionally, Figure 3 The structure shown may further include other functional layers. For example, in the structure of a PMUT, an elastic material layer may be included between the single crystal seed layer 320 and the base material layer 310 .

[0053] Figure 4 It shows a method based on Figure 3 The piezoelectric device is obtained by using the electrode substrate shown in FIG. Figure 4 As shown in (a), the piezoelectric device obtained based on the electrode substrate may include the electrode substrate in the embodiment of the present application, the single crystal piezoelectric film, and the oxide film layer 460 and the electrode layer (upper electrode layer 470) arranged on the single crystal piezoelectric film. Figure 4 The piezoelectric device shown in (a) can be applied to Figure 1 The PMUT and other electronic devices shown.

[0054] Figure 4 (b) in FIG. 1 shows a specific structural schematic diagram of another piezoelectric device, wherein the piezoelectric device may be a piezoelectric MEMS speaker. Figure 4 Unlike (a) in Figure 1, the specific structure of the piezoelectric MEMS speaker is not a complete layer-by-layer stacking. For ease of display, Figure 4(b) in FIG. 2 omits the oxide film layer. The base material layer can be composed of a silicon substrate such as SOI and silicon dioxide. In addition, the single crystal seed layer 420 and the lower electrode layer 430 are completely stacked layer by layer. The piezoelectric film layer 450 is etched to form a pattern, and the upper electrode layer 470 is grown on the piezoelectric film layer 450 in the form of another pattern. The lead layer 480 is used to lead out the lower electrode layer 430.

[0055] Optionally, in the embodiment of the present application, the piezoelectric device may further include multiple piezoelectric film layers, that is, one or more piezoelectric film layers and electrode layers are grown on the upper electrode layer 470 to form a piezoelectric bimorph, etc. This application will not elaborate on this.

[0056] The embodiment of the present application also shows a method for preparing the above-mentioned electrode substrate. Figure 5 A schematic flow chart showing the manufacturing process of the electrode substrate and the piezoelectric film.

[0057] Step 1: Prepare a base material layer, that is, prepare a base sheet of the electrode substrate.

[0058] As can be seen from the above, in the embodiments of the present application, the base material layer can be an amorphous silicon substrate, a single crystal silicon substrate or a silicon substrate with an oxide film, and can also be a non-silicon substrate such as silicon carbide (SiC) and sapphire (Al2O3). For example, the process of preparing the base material layer can be grinding and double-sided polishing of the silicon wafer, thereby obtaining a silicon substrate with high flatness and good surface finish. For another example, if it is necessary to prepare a silicon substrate with an oxide film, an amorphous silicon substrate or a single crystal silicon substrate can be used as a substrate, and then the silicon substrate can be heated and oxidized or plasma enhanced chemical vapor deposition (PECVD) can be used to epitaxially grow SiO2 on the surface of the silicon substrate, thereby obtaining a silicon substrate with an oxide film. The thickness of the base material layer in step 1 is 300μm to 800μm.

[0059] For example, taking a single crystal silicon wafer as an example, the production process of a single crystal silicon wafer may include steps such as raw material preparation, single crystal growth, cutting and polishing. The specific process of step 1 may include:

[0060] First, raw material preparation is carried out. High-purity silicon can be selected as raw material and finely processed and purified to remove impurities and control purity. High-purity silicon can usually be prepared by chlorination method or silane method.

[0061] Secondly, single crystal growth is performed by placing the purified silicon raw material in a high temperature furnace and gradually melting and crystallizing the silicon raw material into a single crystal by controlling the temperature and atmosphere conditions. Common single crystal growth methods include the Czochralski method and the floating zone method.

[0062] Then, the grown single crystal silicon rods are cut to obtain silicon wafers of the required size. Diamond wire saws are usually used for cutting to ensure the flatness and precise size of the silicon wafers. The cut silicon wafers are then subjected to mechanical grinding and chemical mechanical polishing such as grinders to make the surface of the silicon wafers flat and smooth and meet specific surface quality requirements.

[0063] Then, after polishing, the silicon wafer is thoroughly cleaned to remove the polishing liquid and residue. The polished silicon wafer is then subjected to a rigorous quality inspection, including evaluation of surface flatness, thickness uniformity, crystal structure, etc. As needed, some additional processing steps are performed on the single crystal silicon wafer, such as thinning, doping, oxidation, etc., to meet specific device manufacturing requirements.

[0064] Finally, a processed single crystal silicon wafer is obtained and used as the base material layer in the electrode substrate of the present application.

[0065] Step 2: Prepare a single crystal seed layer on the base material layer.

[0066] In the embodiments of the present application, the single crystal seed layer is composed of single crystal hexacyclic carbon materials such as graphene, graphite or graphene oxide. The embodiments of the present application show various process methods for preparing single crystal seed layers composed of hexacyclic carbon materials. Figure 6 A process for preparing a single crystal seed layer provided in an embodiment of the present application is shown, wherein the process method deposits the single crystal seed layer by a physical vapor deposition (PVD) or chemical vapor evaporation (CVD) method.

[0067] Exemplarily, the basic process of preparing a single crystal seed layer composed of graphene by the CVD method is: put the substrate as the base material layer into a heating furnace, introduce hydrogen and argon or nitrogen to protect and heat to about 1000°C, stabilize the temperature, and maintain it for about 20 minutes; then stop introducing the protective gas, and then introduce the carbon source (such as methane, ethylene or acetylene) gas, about 30 minutes, the reaction is completed; cut off the power supply, turn off the carbon source gas, and then introduce the protective gas to exhaust the carbon source gas, and in the protective gas environment until the tube cools to room temperature, take out the substrate, and obtain the graphene layer deposited on the substrate. The process will be described in detail below.

[0068] like Figure 6As shown in the first step, in the process of preparing a single crystal seed layer composed of graphene by the CVD method, a catalytic metal is needed as an important condition for growing graphene, such as copper, cobalt or alloys such as Co-Ni, Au-Ni, Ni-Mo, etc. The main basis for selecting the catalytic metal is the melting point of the metal, the amount of carbon dissolved, and whether there is a stable metal carbide. These factors determine the growth temperature, growth mechanism and type of carrier gas used for graphene. In addition, the crystal type and crystal orientation of the metal will also affect the growth quality of graphene. The reason for using catalytic metals is the surface catalytic mechanism, that is, when the carbon after the cracking of the carbon source gas at high temperature contacts a specific catalyst metal (such as copper), graphene is formed on the surface, and the sample is protected to inhibit the continued deposition of the film. Therefore, this mechanism makes it easier to form a single layer of graphene. The catalytic metal layer 360 can serve as both a growth substrate and a catalytic effect during the CVD growth of graphene. Furthermore, as Figure 6 As shown in the second step of the present invention, a carbon source gas is added so that the carbon source gas is thermally decomposed on the above-mentioned catalytic metal to form a Figure 6 The single crystal seed layer 320 composed of the hexacyclic carbon material shown in the third step in FIG. In the embodiment of the present application, the carbon source gas can be a carbon-containing hydrocarbon gas, preferably, the carbon-containing hydrocarbon gas can be methane (CH4) or acetylene (C2H2), ethylene (C2H4).

[0069] Optionally, in Figure 6 In the third step, the catalytic metal layer 360 can be retained in the processed piezoelectric MEMS, that is, located between the single crystal seed layer 320 and the base material layer 310, or the single crystal seed layer 320 can be peeled off after the single crystal seed layer 320 is processed, and the catalytic metal layer 360 is removed by chemical etching and other methods, and finally the single crystal seed layer 320 is set on the base material layer 310.

[0070] In the embodiment of the present application, the single crystal seed layer may also be graphite or graphene oxide, so Figure 6 The catalytic metal layer 360 in the embodiment may be a metal material naturally oriented on the a-axis or c-axis of the crystal axis. For example, the catalytic metal may include at least one of cobalt, copper and zirconium.

[0071] The following describes the general process of graphene growth on the catalytic metal layer 360 by taking copper as the catalytic metal and methane as the carbon-containing hydrocarbon gas as an example:

[0072] First, CH4 molecules are adsorbed on the copper surface. Under high temperature, the CH bonds of CH4 molecules break, producing various carbon fragments CH xThe dehydrogenation reaction in this process is related to the catalytic activity of copper. Since the activity of metallic copper is not very strong, the catalytic dehydrogenation process of methane is a strong endothermic reaction. The energy barrier for complete dehydrogenation to produce carbon atoms is very high. Therefore, the cracking of methane molecules is incomplete. Among them, the cracking and dehydrogenation of hydrocarbon gases on the copper surface includes partial dehydrogenation, coupling, and re-dehydrogenation processes. Monodisperse adsorbed carbon atoms will not be formed on the copper surface.

[0073] Then, after the methane molecules are dehydrogenated, the carbon elements on the copper surface aggregate with each other, generate new CC bonds and clusters, and begin to nucleate to form graphene islands.

[0074] Finally, as the number of graphene nuclei on the copper surface increases, the carbon atoms or clusters produced subsequently continue to attach to the nucleation sites, causing the graphene nuclei to gradually grow until they are "stitched" together and eventually connected into a continuous graphene film.

[0075] Optionally, the carbon source gas used in the present application may include solids (such as carbon-containing polymer materials, etc.), liquids (such as anhydrous ethanol, etc.), etc. in addition to carbon-containing hydrocarbon gases, or may include auxiliary gases such as hydrogen, argon and nitrogen mentioned above to reduce wrinkles of the film, increase flatness and reduce the deposition of amorphous carbon.

[0076] Optionally, in an embodiment of the present application, the process for preparing the single crystal seed layer may be to directly coat the graphene solution on the base material layer, and after the graphene solution is dried, a single crystal seed layer composed of graphene is obtained.

[0077] Optionally, in some other embodiments of the present application, the process method for preparing the single crystal seed layer may also be a transfer method, that is, transferring the prepared graphite, graphene or graphene oxide film to the base material layer.

[0078] Exemplarily, the single crystal seed layer can be transferred by wet chemical etching substrate method. For example, the process of transferring graphene film can be as follows: first, a graphene film is processed on a metal substrate, and a certain transfer medium (such as polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS)) is spin-coated on the surface of the graphene film as a supporting layer; then, the metal substrate is corroded in an appropriate chemical solution, and the graphene film is transferred to the target substrate or the substrate material layer in the embodiment of the present application after being cleaned with distilled water, and one side of the graphene film is bonded to the substrate material layer; finally, the supporting layer material on the surface of the graphene is removed by certain means (such as PMMA can be removed by solvent dissolution or high-temperature thermal decomposition, and PDMS can be directly peeled off) to obtain a substrate with a graphene film. Alternatively, the transfer of graphene film can be achieved by using a thermal release tape as a graphene transfer medium. It is characterized in that it has a certain adhesive force at room temperature, and above a specific temperature, the adhesive force drops sharply or even disappears, showing a "thermal release" characteristic.

[0079] Exemplarily, the present application can also transfer the single crystal seed layer by dry transfer method or mechanical stripping method. For example, the dry transfer method can select cross-linking molecules that can form covalent bonds with the single crystal seed layer, so that the adsorption force of the single crystal seed layer and the polymer with cross-linking molecules deposited on the surface is greater than the adsorption force of the single crystal seed layer and the original substrate, thereby achieving the separation of the single crystal seed layer from the original substrate. For another example, the mechanical stripping method can peel off the single crystal seed layer from the original substrate by a certain mechanical force. However, the transfer method needs to ensure that the graphene is structurally intact and undamaged after the transfer, and that the transfer process does not pollute the graphene (including doping, etc.), and it is necessary to ensure that the transfer process is stable and reliable.

[0080] Step 3: Prepare an electrode layer on the single crystal seed layer.

[0081] In an embodiment of the present application, the electrode layer may be composed of a single layer of metal or a multilayer metal stack, such as at least one of gold, platinum, palladium, rhodium, iridium or ruthenium. Step 3 may deposit the crystals of the above metals by PVD or CVD method. The deposition conditions vary depending on the metal material used. Finally, the electrode layer is deposited as a metal single crystal film with a natural orientation as the crystal axis a-axis or c-axis orientation.

[0082] For example, take the deposition of platinum by CVD as an example. The specific steps are as follows: First, prepare the deposition gas, and deliver the platinum-containing substrate (such as platinum tetrahydrogen ammonia solution) to the reaction chamber at a constant flow rate. Secondly, heat the reaction chamber. Heat the reaction device to a suitable reaction temperature (such as 500-700°C). Finally, deposit the film layer, that is, decompose the platinum-containing substrate in the reaction chamber with the deposition gas to generate platinum atoms, and deposit them on the silicon dioxide surface.

[0083] Optionally, when the single crystal piezoelectric film is a PZT piezoelectric film, the processing technology of the present application may further include step 4: preparing an oxide film layer on the electrode layer. In an embodiment of the present application, the oxide film layer may be deposited by PVD, CVD or sol-gel method. The process of step 4 is similar to step 3, both of which are epitaxially growing a single crystal film with an a-axis or c-axis orientation.

[0084] Step 5: Prepare a single crystal piezoelectric layer on the electrode substrate.

[0085] For example, taking PZT piezoelectric film as an example, the available methods include magnetron sputtering (PVD) and sol-gel.

[0086] The magnetron sputtering method usually uses a magnetron sputtering device to bombard the PZT target with charged particles under high vacuum, and crystallizes the PZT piezoelectric film on the electrode substrate;

[0087] The sol-gel method can be performed in the following steps:

[0088] i. Forming a precursor solution of the piezoelectric film by chemical solution deposition, or coating by spin coating. Based on the specific rotation speed and time of the spin coating process, the precursor solution has a desired thickness. The material in the precursor solution of the piezoelectric film can be PZT.

[0089] ii. Drying the precursor solution to form a piezoelectric thin film, for example, heating the precursor solution at 100° C. to 150° C. for about 1 to 10 minutes using a hot plate or an electric furnace. This step can remove organic matter present during the formation of the piezoelectric thin film.

[0090] iii. calcining the piezoelectric film, for example, using a rapid thermal annealing (RTA) process, heating at 500° C.-800° C. for about 1 minute to 10 minutes.

[0091] iv. Repeat the above steps i-iii until a Figure 3 The single crystal piezoelectric layer 350 shown in (c) in FIG. The single crystal piezoelectric layer has a desired thickness, and for example, the thickness is preferably 10 to 50 nm.

[0092] After obtaining the electrode substrate shown in the embodiment of the present application, the piezoelectric material can be deposited on the electrode substrate by sputtering or the various deposition methods mentioned above, and finally a single crystal piezoelectric film is grown. The preparation cost of the electrode substrate shown in the present application is low, or the preparation cost of the single crystal seed layer is lower and the deposition rate is faster. Moreover, the base material layer of the electrode substrate has more optional materials and is not limited to the base materials such as single crystal silicon with higher cost.

[0093] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A piezoelectric device, characterized in that: include: a base material layer; A single crystal seed layer is disposed on the base material layer, and the single crystal seed layer is composed of a hexacyclic carbon material; an electrode layer, disposed on the single crystal seed layer; The single crystal piezoelectric film is arranged on the electrode layer.

2. The piezoelectric device according to claim 1, characterized in that: The six-membered ring structure carbon material is any one of the following: graphene, graphite or graphene oxide.

3. The piezoelectric device according to claim 1 or 2, characterized in that: The thickness of the single crystal seed layer is 2-100 nm.

4. The piezoelectric device according to any one of claims 1 to 3, characterized in that: It also includes an oxide film layer, which is arranged between the electrode layer and the single crystal piezoelectric film.

5. The piezoelectric device according to claim 4, characterized in that: The oxide film layer includes a perovskite-type oxide film.

6. The piezoelectric device according to any one of claims 1 to 5, characterized in that: The electrode layer is formed by a single metal layer or by stacking multiple metal layers.

7. The piezoelectric device according to claim 6, characterized in that: The electrode layer is composed of at least one of the following metals: gold, platinum, palladium, rhodium, iridium or ruthenium.

8. The piezoelectric device according to any one of claims 1 to 7, characterized in that: The base material layer includes any one of the following: an amorphous silicon substrate, a single crystal silicon substrate or a silicon substrate with an oxide film.

9. The piezoelectric device according to any one of claims 1 to 8, characterized in that: The single crystal piezoelectric film includes a single crystal lead zirconate titanate PZT film.

10. An electronic device, characterized in that: The piezoelectric device comprises the piezoelectric device as claimed in any one of claims 1 to 9.

11. A method for preparing a piezoelectric device, characterized in that: include: preparing a base material layer; Preparing a single crystal seed layer on the base material layer, wherein the single crystal seed layer is composed of a hexacyclic carbon material; preparing an electrode layer on the single crystal seed layer; A piezoelectric material is deposited on the electrode layer to obtain a single crystal piezoelectric film.

12. The method according to claim 11, characterized in that Before depositing the piezoelectric material on the electrode layer, the method further comprises: An oxide thin film layer is prepared on the electrode layer.

13. The method according to claim 12, characterized in that The oxide film layer includes a perovskite-type metal oxide film.

14. The method according to any one of claims 11 to 13, characterized in that The step of preparing a single crystal seed layer on the base material layer comprises: Depositing a catalytic metal on the base material layer, wherein the catalytic metal comprises a metal material naturally oriented on the a-axis or c-axis of the crystal axis; A hydrocarbon gas containing carbon is added as a carbon source gas, and the single crystal seed layer is formed by thermally decomposing the hydrocarbon gas containing carbon on the catalytic metal.

15. The method according to claim 14, characterized in that The catalytic metal includes at least one of cobalt, copper and zirconium.

16. The method according to claim 14 or 15, characterized in that The carbon-containing hydrocarbon gas is methane.

17. The method according to any one of claims 11 to 16, characterized in that The six-membered ring structure carbon material is any one of the following: graphene, graphite or graphene oxide.

18. The method according to any one of claims 11 to 17, characterized in that The thickness of the single crystal seed layer is 2-100 nm.

19. The method according to any one of claims 11 to 18, characterized in that The electrode layer is formed by a single metal layer or by stacking multiple metal layers.

20. The method according to claim 19, characterized in that The electrode layer is composed of at least one of the following metals: gold, platinum, palladium, rhodium, iridium or ruthenium.

21. The method according to any one of claims 11 to 20, characterized in that The base material layer includes any one of the following: an amorphous silicon substrate, a single crystal silicon substrate or a silicon substrate with an oxide film.

22. The method according to any one of claims 11 to 21, characterized in that The single crystal piezoelectric film includes a single crystal lead zirconate titanate PZT film.

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