Lead zirconate titanate film and low-temperature preparation method and application thereof

Abstract

The invention relates to the technical field of piezoelectric materials, in particular to a lead zirconate titanate film and a low-temperature preparation method and application thereof.The preparation method comprises the steps that Ti metal serves as a radio frequency target material and is subjected to first sputtering deposition treatment on a substrate, and a Ti adhesion layer is formed; forming a bottom electrode on the Ti adhesion layer; taking PbxZr0. 52Ti0. 48O3 ceramic as a radio frequency target material, carrying out second sputtering deposition treatment on the bottom electrode, and carrying out rapid heat treatment to form a PZT seed layer; and carrying out third sputtering deposition treatment on the PZT seed layer by taking PbxZr0. 52Ti0. 48O3 ceramic as a radio frequency target material, carrying out rapid heat treatment, and repeating the step to form the lead zirconate titanate film. According to the method, the substrate tray is not additionally heated in the process of sputtering and depositing the PZT thin film material, so that the loss and volatilization of PbO are reduced, and the stability of thin film components can be effectively maintained; the PZT seed layer is utilized to provide more crystal nucleuses, so that the uniform crystallization of the PZT film is promoted, the crystallization quality and the electrical property of the PZT film are improved, the grain boundary defect is reduced, and the adhesive force and the stability of the film and the substrate are enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of piezoelectric materials, and in particular to a lead zirconate titanate film and a low-temperature preparation method and application thereof. Background Art

[0002] Piezoelectric materials refer to a series of special materials that can change the charge on the surface under the action of mechanical stress (such as pressure or vibration) and can deform when an electric field is applied to the surface. This effect of mutual conversion of mechanical energy and electrical energy is called (inverse) piezoelectric effect. Commonly used piezoelectric materials include quartz, lead zirconate titanate (PZT), zinc oxide (ZnO), aluminum nitride (AlN) and some polymer materials (such as PVDF, etc.). Among them, PZT stands out from many piezoelectric materials due to its excellent piezoelectric, dielectric and ferroelectric properties. It is widely used in various sensors, actuators and transducers, such as ultrasonic transducer imaging arrays, surface acoustic wave (SAW) devices, energy capture devices, MEMS speakers, MEMS accelerometers, dynamic random access memories (DRAMs), non-volatile random access memories (NVRAMs), etc.

[0003] PZT materials can be divided into two categories according to their size: ceramic materials and thin film materials. Among them, PZT ceramics are formed by mixing and sintering powders, and the proportion of each component can be precisely controlled, so they have a higher piezoelectric coefficient. However, ceramics are bulk materials on a macro scale, with large thickness, small area, and low flux, which makes it difficult to meet the current needs of MEMS sensors and actuators that are becoming increasingly miniaturized and micro-miniaturized. PZT thin film materials are prepared using semiconductor processes, which have the advantages of high integration, high flux, low cost, and easy miniaturization. They are an important development direction of PZT materials in recent years. The mainstream preparation methods of PZT thin films are sol-gel process, pulsed laser deposition (PLD), and magnetron sputtering. However, the existing PZT thin film preparation methods are difficult to prepare PZT thin film materials with good crystallinity, uniform crystal orientation, low internal stress, and high piezoelectric coefficients in high throughput, thus hindering their further application.

[0004] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a lead zirconate titanate film and a low-temperature preparation method and application thereof, aiming to solve the problem that the PZT film prepared by the existing process has large internal stress, resulting in surface damage of the film layer.

[0006] The technical solution of the present invention is as follows:

[0007] A low-temperature preparation method of a lead zirconate titanate film comprises the following steps:

[0008] providing a substrate;

[0009] Performing a first sputtering deposition process on the substrate using Ti metal as a radio frequency target to form a Ti adhesion layer;

[0010] forming a bottom electrode on the Ti adhesion layer;

[0011] Pb x Zr 0.52 Ti 0.48 O3 ceramic is used as a radio frequency target material to perform a second sputtering deposition process on the bottom electrode, and a PZT seed layer is formed by rapid thermal treatment; wherein x is between 1.1 and 1.3;

[0012] Pb x Zr 0.52 Ti 0.48 The third sputtering deposition process is performed on the PZT seed layer using O3 ceramic as a radio frequency target, and after rapid thermal treatment, the third sputtering deposition process and the rapid thermal treatment are repeated to form a lead zirconate titanate film.

[0013] The low-temperature preparation method of lead zirconate titanate film, wherein the substrate includes one of a single crystal silicon wafer with a (100) crystal orientation, a single crystal silicon wafer with a SiO2 layer on the surface with a (100) crystal orientation, and a SOI silicon wafer with a (100) crystal orientation.

[0014] The low-temperature preparation method of lead zirconate titanate film is described, wherein the first sputtering deposition treatment is performed under an inert atmosphere; the air pressure in the chamber of the first sputtering deposition treatment is 0.5mTorr-5mTorr, and the RF power of the first sputtering deposition treatment is 50W-300W.

[0015] The low-temperature preparation method of lead zirconate titanate film, wherein the second sputtering deposition process and the third sputtering deposition process are carried out in a mixed atmosphere of inert gas and oxygen; the gas flow rate of the inert gas is 19sccm-77sccm, and the gas flow rate of the oxygen is 0.4sccm-1sccm.

[0016] The low-temperature preparation method of lead zirconate titanate film, wherein the RF power of the second sputtering deposition process and the third sputtering deposition process is 50W-80W; during the second sputtering deposition process and the third sputtering deposition process, the rotation speed of the tray used to carry the substrate is 6rpm-10rpm.

[0017] The low-temperature preparation method of the lead zirconate titanate film, wherein the heating rate of the rapid thermal treatment is 2.5°C / s-10°C / s; the rapid thermal treatment includes a pre-annealing stage and an annealing stage; the temperature of the pre-annealing stage is 450°C-550°C, and the time of the pre-annealing stage is 60s-120s; the temperature of the annealing stage is 600°C-700°C, and the time of the annealing stage is 2min-15min.

[0018] The low-temperature preparation method of the lead zirconate titanate film, wherein the thickness of the PZT seed layer is 30nm-100nm; after a single third sputtering deposition process, a lead zirconate titanate film of 300nm-600nm is formed on the PZT seed layer.

[0019] The low-temperature preparation method of the lead zirconate titanate film, wherein the thickness of the lead zirconate titanate film is 1 μm-2 μm.

[0020] A lead zirconate titanate film is prepared by a low-temperature preparation method of the lead zirconate titanate film.

[0021] Application of lead zirconate titanate film in micro-electromechanical system.

[0022] Beneficial effects: The present invention provides a lead zirconate titanate film and a low-temperature preparation method and application thereof. The low-temperature preparation method of the lead zirconate titanate film comprises the following steps: providing a substrate; performing a first sputtering deposition process on the substrate using Ti metal as a radio frequency target to form a Ti adhesion layer; forming a bottom electrode on the Ti adhesion layer; x Zr 0.52 Ti 0.48 O3 ceramic is used as a radio frequency target material to perform a second sputtering deposition process on the bottom electrode, and a PZT seed layer is formed after rapid thermal treatment; wherein x is between 1.1 and 1.3; Pb x Zr 0.52 Ti 0.48 O3 ceramic is used as a radio frequency target material to perform a third sputtering deposition process on the PZT seed layer, and after rapid heat treatment, the third sputtering deposition process and the rapid heat treatment are repeated to form a lead zirconate titanate film. The present invention does not additionally heat the substrate tray during the sputtering deposition of the PZT thin film material, which reduces the loss and volatilization of PbO, can effectively maintain the stability of the film components, and at the same time avoids the heating and cooling time of the substrate tray, reduces the preparation time of the PZT film, and optimizes the preparation cost of the PZT thin film material; and, the PZT seed layer is used to provide more crystal nuclei to promote the uniform crystallization of the PZT film, thereby improving the crystallization quality and electrical properties of the PZT film, reducing grain boundary defects, and enhancing the adhesion and stability of the film to the substrate; at the same time, the PZT film prepared by the method has small internal stress and a smooth and flat film surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a diagram of the PZT perovskite crystal structure;

[0024] Figure 2 It is a process flow diagram of a low-temperature preparation method of a lead zirconate titanate thin film of the present invention;

[0025] Figure 3 is a schematic diagram of the structure of the substrate;

[0026] Figure 4 Schematic diagram of the film structure after the bottom electrode is deposited;

[0027] Figure 5 Schematic diagram of the internal structure of the magnetron sputtering chamber;

[0028] Figure 6 It is a schematic diagram of the film structure after the lead zirconate titanate film is deposited;

[0029] Figure 7 It is a schematic diagram of the film structure after the top electrode is deposited and patterned;

[0030] Figure 8 is the XRD characterization diagram of the Pt bottom electrode deposited in Example 1;

[0031] Fig. 9 This is a scanning electron microscope cross-sectional characterization image of the lead zirconate titanate film prepared in Example 1;

[0032] Fig.10 This is the XRD characterization diagram of the lead zirconate titanate film prepared in Example 1;

[0033] Fig.11 This is an optical microscope characterization image of the patterned top electrode in Example 1;

[0034] Fig.12 Schematic diagram of a high internal stress PZT film sample;

[0035] Fig.13 Schematic diagram of the PZT thin film sample after stress release. DETAILED DESCRIPTION

[0036] The present invention provides a lead zirconate titanate film and a low-temperature preparation method and application thereof. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless specifically defined as herein.

[0038] The chemical formula of lead zirconate titanate is Pb(Zr x Ti 1-x )O3, when x is around 0.52, the material is at the critical point of composition and properties, called the morphological phase boundary (MPB). At this point, the PZT material crystal appears a perovskite structure, which has the best piezoelectric and dielectric properties, such as Figure 1 As shown in the figure, it can be attributed to the following two reasons: first, the tetragonal phase and rhombohedral phase coexist at the morphological phase boundary of PZT, which provides a large number of phase boundaries for the material, making it easier for the polarization direction inside PZT to rearrange under the action of the external electric field, thereby enhancing the material's ability to respond to changes in the electric field; second, a monoclinic phase may also appear at the morphological phase boundary, further enhancing the piezoelectric and electrostrictive properties of PZT. Therefore, in order to ensure the best performance, it is crucial to control the Zr / Ti element ratio in the PZT material to 52:48.

[0039] However, the existing methods for preparing PZT thin films make it difficult to prepare PZT thin films with good crystallinity, uniform crystal orientation, low internal stress, and high piezoelectric coefficient in a high throughput manner.

[0040] Based on this, Figure 2 As shown, the present invention provides a low-temperature preparation method of a lead zirconate titanate film, comprising the steps of:

[0041] Step S10: providing a substrate;

[0042] Step S20: performing a first sputtering deposition process on the substrate using Ti metal as a radio frequency target to form a Ti adhesion layer;

[0043] Step S30: forming a bottom electrode on the Ti adhesion layer;

[0044] Step S40: Pb x Zr 0.52 Ti 0.48 O3 ceramic is used as a radio frequency target material to perform a second sputtering deposition process on the bottom electrode, and a PZT seed layer is formed by rapid thermal treatment; wherein x is between 1.1 and 1.3;

[0045] Step S50: Pb x Zr 0.52 Ti 0.48 The third sputtering deposition process is performed on the PZT seed layer using O3 ceramic as a radio frequency target, and after rapid thermal treatment, the third sputtering deposition process and the rapid thermal treatment are repeated to form a lead zirconate titanate film.

[0046] Existing methods require heating the substrate during magnetron sputtering to promote phase change inside the film to improve its crystal quality. In the traditional method of preparing PZT thin film materials using magnetron sputtering, the substrate tray usually needs to be heated and stabilized at 300-600°C, which causes a large amount of PbO in the PZT film to volatilize during the long deposition process, making it difficult to control the film composition; in addition, the vacuum degree in the chamber is high, and the substrate tray at a high temperature cannot effectively exchange heat and cool down, further increasing the volatilization loss of PbO.

[0047] In this embodiment, since the use of multiple rapid thermal processing technologies releases the residual stress accumulated in the growth process of the PZT film and promotes the crystallization of the film, there is no need to heat the substrate tray during the sputtering deposition of the PZT film material. This reduces the loss and volatilization of PbO, can effectively maintain the stability of the film components, and avoids the heating and cooling time of the substrate tray, reduces the preparation time of the PZT film, and optimizes the preparation cost of the PZT film material; and, the PZT seed layer is used to provide more crystal nuclei to promote the uniform crystallization of the PZT film, thereby improving the crystallization quality and electrical properties of the PZT film, reducing grain boundary defects, and enhancing the adhesion and stability of the film to the substrate; at the same time, the PZT film prepared by this method has low internal stress and a smooth and flat film surface.

[0048] Specifically, the present invention directly uses only PZT thin film material as the seed layer, which not only simplifies the processing procedures, but also reduces the potential pollution caused by the introduction of new elements, ensuring the purity of the prepared PZT thin film material. In addition, the multiple RTP technology used in the present invention can not only promote the formation of PZT thin film crystals, but also reduce the component loss caused by the volatilization of PbO at high temperature, effectively maintaining the stability of the film components.

[0049] In some embodiments, Figure 3 As shown, the substrate includes one of a single crystal silicon wafer with a (100) crystal orientation, a single crystal silicon wafer with a SiO2 layer on the surface, and a SOI silicon wafer with a (100) crystal orientation.

[0050] Specifically, different substrates are suitable for different processes, and appropriate processing technology and substrates are selected according to the device structure. For example, for a simple piezoelectric single cantilever beam structure, a (100) crystal orientation single crystal silicon wafer (Si substrate) and a wet etching process can be directly selected for preparation; while a complex cantilever beam or diaphragm with a back cavity structure requires a (100) crystal orientation single crystal silicon wafer or SOI silicon wafer with a SiO2 layer on the surface and a back etching process, in which SiO2 plays the role of stopping etching and releasing the structure.

[0051] Furthermore, the crystal orientation of the substrate will affect the subsequently deposited thin film; first, the surface energy of the single-crystal silicon wafer with a (100) crystal orientation is low, which is conducive to the adhesion of the thin film and can improve the stability and durability during processing and use; secondly, the crystal orientation of the subsequently deposited thin film is closely related to the crystal orientation of the substrate. A bottom electrode with a (111) crystal orientation (preferably a Pt thin film) can be grown on a single-crystal silicon wafer with a (100) crystal orientation, and only then can a PZT piezoelectric thin film with a (001) crystal orientation be grown; finally, single-crystal silicon wafers with a (100) crystal orientation are widely used in the industry, and have a lower price at the same size and specification, which has a cost advantage.

[0052] In some embodiments, the surface of the (100) crystal orientation single crystal silicon wafer has a SiO2 layer, wherein the thickness of the SiO2 layer on the surface is 0.2μm-0.5μm; the SiO2 layer has the function of stopping etching and releasing the structure during processing. Keeping the thickness of the SiO2 layer within 0.2μm-0.5μm can relieve the internal stress caused by PZT, improve the thermal expansion matching between the PZT film and silicon, reduce cracks and defects in the PZT film, and improve its mechanical strength and stability. In addition, the SiO2 layer can also play an insulating role, reduce the leakage current of the device during operation, and improve the performance of the device. However, a SiO2 layer that is too thick or too thin will have problems such as large residual stress and thermal expansion mismatch. In addition, an overly thick insulating layer will cause an increase in parasitic capacitance, form an additional leakage path, and increase dielectric loss. An overly thin insulating layer will not be sufficiently insulating and increase leakage current, which will reduce the electrical performance and energy efficiency of the device.

[0053] In some embodiments, the SOI silicon wafer (Silicon on Insulator, SOI) with a (100) crystal orientation includes a top silicon with a thickness of 0.05μm-10μm and a crystal orientation of (100), a buried oxide layer (SiO2) with a thickness of 0.25μm-2μm, and an insulating substrate silicon with a thickness of 300μm-500μm and a crystal orientation of (100).

[0054] In some embodiments, the step S10 further includes cleaning the substrate, specifically including the steps of: placing the substrate in an acetone solution and ultrasonically cleaning it for 5-10 minutes; then rinsing it with deionized water (DI Water) and placing it in an isopropanol (IPA) solution and ultrasonically cleaning it for 5-10 minutes, then using deionized water to completely clean the surface of the substrate again, and using a nitrogen gun to blow and remove water droplets adhering to the surface of the substrate, and finally placing the substrate on a hot plate at 100-120°C and baking it for 1-2 minutes to dry the substrate, ensuring that the residual water vapor molecules on its surface after entering the vacuum chamber will not destroy the vacuum environment and affect the vacuum degree.

[0055] In some embodiments, the first sputtering deposition process is performed under an inert atmosphere; the pressure in the chamber of the first sputtering deposition process is 0.5mTorr-5mTorr, and the RF power of the first sputtering deposition process is 50W-300W. Controlling the pressure in the chamber of the first sputtering deposition process between 0.5mTorr-5mTorr can make the plasma density low, but the electron temperature and ion energy high, and the mean free path of the sputtered atoms long, so that a dense film with good adhesion and smooth surface can be prepared; and at this power, the film thickness can be accurately controlled, and a Ti adhesion layer with low stress, small defects and dense film layer can be obtained, which can tightly combine the bottom electrode and the substrate.

[0056] In some embodiments, the inert atmosphere includes, but is not limited to, one or more of argon, neon, krypton, and xenon.

[0057] In some embodiments, the thickness of the Ti adhesion layer is between 10 nm and 20 nm. The Ti adhesion layer of this thickness has the effect of improving the adhesion of the Pt thin film on the Si substrate.

[0058] In some embodiments, in step S30, a Pt film is used as a bottom electrode, which specifically includes the steps of: using Pt metal as a DC target to perform sputtering deposition of Pt metal, during which the gas pressure in the chamber is stabilized between 0.5mTorr-5mTorr, and the DC sputtering power is 50W-100W.

[0059] In some embodiments, the schematic diagram of the film structure after the bottom electrode is deposited is as follows: Figure 4 As shown, the thickness of the bottom electrode is 165nm-215nm; the bottom electrode is used for the growth of the PZT film and its electrical control, and the bottom electrode at this thickness has lower resistance, better thermal stability and mechanical stability, and can provide a more uniform grain growth environment for the PZT film; and this thickness can effectively control the deposition time, improve efficiency and reduce costs.

[0060] In this embodiment, Pb is used x Zr 0.52 Ti 0.48 O3 ceramics are used as the target material of magnetron sputtering RF target to sputter and deposit PZT thin film, where x is between 1.1-1.3, and multiple rapid thermal annealing processes (RTP) are used to prepare PZT thin film with a high (001) crystal orientation perovskite phase. The excess of Pb of 10%-30% is to compensate for the loss of Pb volatilized during the sputtering deposition and heat treatment of the thin film material, so as to ensure that the obtained PZT thin film has a precise stoichiometric ratio.

[0061] In some embodiments, in step S40 and step S50, the Pb x Zr 0.52 Ti 0.48 The O3 ceramic (PZT target) is fixed on the RF target position of the magnetron sputtering equipment. Its position in the magnetron sputtering chamber is as follows: Figure 5 As shown, the substrate is located at the top of the magnetron sputtering device, and the RF target position includes a first RF target position parallel to the substrate and two second RF target positions at a certain angle to the substrate; the Pb x Zr 0.52 Ti 0.48 O3 ceramic (PZT target) is fixed at the second RF target position; wherein the target and the substrate form a certain angle to improve sputtering uniformity, optimize deposition rate and film quality, and reduce target loss and plasma damage.

[0062] Specifically, the substrate material (Pt / Ti / substrate) with the bottom electrode deposited is fixed on the substrate tray of the magnetron sputtering equipment, and a nitrogen gun is used to blow away the dust particles on the surface of the substrate to ensure the film quality of the PZT film; after the blowing is completed, it is placed in the vacuum chamber of the magnetron sputtering equipment. In order to deposit high-quality and high-purity PZT thin films, it is necessary to obtain a higher background vacuum before sputtering deposition to prevent contamination by residual gas molecules. In this embodiment, a mechanical pump and a turbomolecular pump cascade system are used to obtain a high vacuum for the vacuum chamber. First, a mechanical pump is used to evacuate the vacuum chamber to obtain a rough vacuum of 1 to 5 Pa, and then a turbomolecular pump and a mechanical pump are cascaded to obtain a 10 -4 ~10 -5 Pa of high vacuum.

[0063] In some embodiments, the second sputtering deposition process and the third sputtering deposition process are performed in a mixed atmosphere of an inert gas and oxygen; the gas flow rate of the inert gas is 19 sccm-77 sccm, and the gas flow rate of the oxygen is 0.4 sccm-1 sccm.

[0064] Specifically, before performing the second sputtering deposition process and the third sputtering deposition process, an inert gas and oxygen O2 are introduced into the vacuum chamber, and a flow meter and a flow valve are used to monitor the gas flow; wherein, the gas flow of the inert gas is 19sccm-77sccm, and the gas flow of the oxygen is 0.4sccm-1sccm; at the same time, the opening size of the gate valve between the molecular pump and the vacuum chamber is controlled to maintain the air pressure in the vacuum chamber at 0.5-0.7Pa.

[0065] In some embodiments, the RF power of the second sputtering deposition process and the third sputtering deposition process is 50W-80W; during the second sputtering deposition process and the third sputtering deposition process, the rotation speed of the tray for carrying the substrate is 6rpm-10rpm. The thickness of the PZT seed layer and the PZT film can be accurately controlled by low power, and a film with low stress, few defects and dense film layer can be obtained; and controlling the rotation speed of the tray can achieve uniform deposition and obtain a film with consistent film thickness.

[0066] In a preferred embodiment, the radio frequency power of the second sputtering deposition process and the third sputtering deposition process is 65W; during the second sputtering deposition process and the third sputtering deposition process, the rotation speed of the tray for carrying the substrate is 8 rpm.

[0067] In some embodiments, the heating rate of the rapid thermal treatment is 2.5°C / s-10°C / s; the rapid thermal treatment includes a pre-annealing stage and an annealing stage; the temperature of the pre-annealing stage is 450°C-550°C, and the time of the pre-annealing stage is 60s-120s; the temperature of the annealing stage is 600°C-700°C, and the time of the annealing stage is 2min-15min. Rapid thermal processing (RTP) can quickly raise the temperature to the annealing temperature, which helps the uniform crystallization of the PZT film and forms a film with an excellent crystal structure; in addition, compared with the traditional annealing process, the rapid thermal processing time is short, which reduces the stress accumulation caused by the different thermal expansion coefficients, can reduce the defect density, and improve the electrical and acoustic properties.

[0068] Specifically, Pb x Zr 0.52 Ti 0.48 After the second sputtering deposition process is performed on the bottom electrode using O3 ceramic as a radio frequency target, a PZT seed layer with a (001) crystal orientation and no surface damage can be obtained through rapid thermal treatment.

[0069] In a preferred embodiment, the heating rate of the rapid thermal treatment is 7°C / s; the rapid thermal treatment includes a pre-annealing stage and an annealing stage; the temperature of the pre-annealing stage is 500°C, and the time of the pre-annealing stage is 100s; the temperature of the annealing stage is 650°C, and the time of the annealing stage is 8min.

[0070] In some embodiments, the thickness of the PZT seed layer is 30nm-100nm; after a single third sputtering deposition process, a 300nm-600nm lead zirconate titanate film is formed on the PZT seed layer. By first depositing PZT with a thickness of 30nm-100nm and then performing rapid heat treatment, a PZT seed layer with a (001) crystal orientation and no surface damage can be obtained; and by performing the third sputtering deposition process and the rapid heat treatment multiple times, the residual internal stress can be effectively released, and after successive deposition, a lead zirconate titanate film of the target thickness is finally obtained. However, if the lead zirconate titanate film is deposited to the target thickness at one time, it is easy to have cracks, voids and other defects due to excessive internal stress.

[0071] In some embodiments, the schematic diagram of the film structure after the lead zirconate titanate film is deposited is as follows: Figure 6 As shown, the thickness of the lead zirconate titanate film is 1μm-2μm. That is, after a single third sputtering deposition process, a 300nm-600nm lead zirconate titanate film is formed on the PZT seed layer, and then after repeating the third sputtering deposition process and the rapid thermal treatment, a lead zirconate titanate film with a total thickness of 1μm-2μm can be formed. Lead zirconate titanate films of this thickness are suitable for use in micro-electromechanical systems (MEMS) piezoelectric devices, while a single deposition of a PZT film of this thickness is prone to defects such as cracks and voids due to excessive internal stress. Therefore, the present invention releases the residual internal stress by first depositing a PZT seed layer and using the RTP process, and provides more crystal nuclei for the deposition of the PZT film, thereby improving the crystallization quality and electrical properties of the film; at the same time, multiple depositions of thin lead zirconate titanate films are used to accumulate a 1μm-2μm thick and highly (001) oriented perovskite phase lead zirconate titanate film, so that the obtained film has low internal stress and a smooth and flat film surface.

[0072] In some embodiments, a metal thin layer with an electrode shape needs to be prepared on the surface of the lead zirconate titanate film so that it can form an electrode pair together with the bottom electrode to drive the PZT piezoelectric layer (i.e., the lead zirconate titanate film) to complete the required function. The schematic diagram of the film structure after the top electrode is deposited and patterned is as shown in FIG. Figure 7As shown. After the step S50, it also includes: forming a top electrode on the lead zirconate titanate film and patterning it; specifically including the steps of: using a spin coater to evenly spin-coat the photoresist on the surface of the lead zirconate titanate film, and then pre-baking on a high-temperature hot plate to initially solidify the photoresist; using a mask exposure machine or a laser direct writing device to expose the photoresist, and transferring the electrode shape pattern to the photoresist by soaking in a developer, and then placing it on a high-temperature hot plate to complete the hardening of the photoresist; using magnetron sputtering technology or electron beam evaporation (E-beam Evaporator) technology to deposit metal on the surface of the PZT piezoelectric material; after the deposition is completed, the PZT piezoelectric material with the top electrode is placed in acetone (Acetone) for ultrasonic cleaning to remove the metal film layer except the required electrode pattern. Finally, it is cleaned with isopropyl alcohol (IPA) and deionized water to obtain a top electrode film with an electrode pattern.

[0073] In some embodiments, the material of the top electrode is selected from platinum, aluminum, and gold; and the thickness of the top electrode is 100nm-200nm.

[0074] In addition, the present invention also provides a lead zirconate titanate film, which is prepared by using a low-temperature preparation method of the lead zirconate titanate film.

[0075] In some embodiments, the PZT film produced by the method has low internal stress and a smooth and flat film surface.

[0076] In addition, the present invention also provides an application of the lead zirconate titanate film in a micro-electromechanical system.

[0077] The following examples are further given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention.

[0078] Example 1

[0079] In this embodiment, a 250nm SiO2 / 500μm (100) Si wafer is used as a substrate to prepare a lead zirconate titanate thin film at low temperature. The specific steps are as follows:

[0080] 1) Use acetone and isopropyl alcohol (IPA) solutions to ultrasonically clean the substrate for 5 to 10 minutes, and use deionized water (DI-water) to clean the substrate surface. After cleaning, use a nitrogen gun to blow away the water droplets adhering to the substrate surface. Finally, place the substrate on a hot plate at 100 to 120°C and dry it for 1 to 2 minutes.

[0081] 2) Magnetron sputtering technology was used to deposit 15nm Ti and 200nm Pt on the surface of the dry substrate. A 3-inch Ti metal target was placed at the RF target position, Ar was used as the sputtering gas, and the background vacuum was 10 -6 ~10 -7 Torr, the working pressure is 3mTorr, the RF power is 300W; the 3-inch Pt metal target is placed in the DC target position, the sputtering gas is Ar, and the background vacuum is 10 -6 ~10 -7 Torr, working pressure is 4mTorr, RF power is 100W. After deposition, XRD equipment is used for characterization, and the results are as follows Figure 8 As shown, the obtained Pt bottom electrode has a (111) crystal orientation.

[0082] 3) 100nm PZT film was deposited on the surface of Pt / Ti / SiO2 / Si substrate using RF magnetron sputtering technology. 1.1 Zr 0.52 Ti 0.48 The ceramic target of O3 component is fixed on the RF target and a mechanical and turbomolecular cascade pump is used to obtain 10 -4 ~10 -5 The background vacuum is 1.377 Pa. The sputtering gases used are Ar and O2, with an Ar flow rate of 19.5 sccm and an O2 flow rate of 0.4 sccm. During sputtering, the working gas pressure is 0.5 Pa, the RF power is 50 W, and the substrate tray speed is set to 8 rpm. The deposited PZT film is subjected to rapid thermal treatment to obtain a PZT seed layer with a thickness of 100 nm; wherein the heating rate is 2.5 ° C / s, the pre-annealing temperature is 500 ° C, the pre-annealing time is 100 s, the annealing temperature is 700 ° C, and the annealing time is 2 min.

[0083] 4) Depositing a 300 nm PZT film using radio frequency magnetron sputtering technology, and obtaining a PZT film with a (001) crystal orientation using RTP technology, the sputtering parameters and RTP parameters being the same as those in step 3).

[0084] 5) Repeat step 4) to obtain a 1 μm PZT thin film.

[0085] Fig. 9 This is a scanning electron microscope (SEM) cross-sectional characterization diagram of the lead zirconate titanate (PZT) film prepared in this embodiment. As can be seen from the figure, the PZT film prepared by this method is relatively dense, with a thickness of about 1 μm and columnar grains. Fig.10 This is the XRD characterization diagram of the 1μm PZT film, which proves that the obtained PZT film has a high degree of (001) crystal orientation and is suitable for MEMS piezoelectric actuators.

[0086] 6) Spin-coat 1-2 μm photoresist on the surface of the obtained PZT film using a spin coater, and pre-bake on a high-temperature hot plate; use a laser direct writing device to expose the photoresist, and transfer the design pattern to the photoresist through a developer, and then place it on a high-temperature hot plate to complete the hard film; use magnetron sputtering technology to deposit 100-200 nm Pt metal on the surface of the PZT piezoelectric material, and the sputtering parameters are the same as step 2); use acetone solution to ultrasonically clean and peel off the top electrode metal (lift-off), and finally use deionized water to clean the top electrode surface to obtain a patterned top electrode film, such as Fig.11 shown.

[0087] The PZT film samples before and after releasing the internal stress are shown in Figure 2. Fig.12 and Fig.13 As shown in the figure, before the internal stress is released, the excessive internal stress will cause defects such as cracks and pits on the surface of the film layer; after the internal stress is released, the surface of the film layer is smooth and flat.

[0088] In summary, the present invention provides a lead zirconate titanate film and a low-temperature preparation method and application thereof. The low-temperature preparation method of the lead zirconate titanate film comprises the following steps: providing a substrate; performing a first sputtering deposition process on the substrate using Ti metal as a radio frequency target to form a Ti adhesion layer; forming a bottom electrode on the Ti adhesion layer; x Zr 0.52 Ti 0.48 O3 ceramic is used as a radio frequency target material to perform a second sputtering deposition process on the bottom electrode, and a PZT seed layer is formed after rapid thermal treatment; wherein x is between 1.1 and 1.3; Pb x Zr 0.52 Ti 0.48 O3 ceramic is used as a radio frequency target material to perform a third sputtering deposition process on the PZT seed layer, and after rapid heat treatment, the third sputtering deposition process and the rapid heat treatment are repeated to form a lead zirconate titanate film. The present invention does not additionally heat the substrate tray during the sputtering deposition of the PZT thin film material, which reduces the loss and volatilization of PbO, can effectively maintain the stability of the film components, and at the same time avoids the heating and cooling time of the substrate tray, reduces the preparation time of the PZT film, and optimizes the preparation cost of the PZT thin film material; and, the PZT seed layer is used to provide more crystal nuclei to promote the uniform crystallization of the PZT film, thereby improving the crystallization quality and electrical properties of the PZT film, reducing grain boundary defects, and enhancing the adhesion and stability of the film to the substrate; at the same time, the PZT film prepared by the method has small internal stress and a smooth and flat film surface.

[0089] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A low-temperature preparation method of lead zirconate titanate thin film, characterized in that: Includes steps: providing a substrate; Performing a first sputtering deposition process on the substrate using Ti metal as a radio frequency target to form a Ti adhesion layer; forming a bottom electrode on the Ti adhesion layer; Pb x Zr 0.52 Ti 0.48 O3 ceramic is used as a radio frequency target material to perform a second sputtering deposition process on the bottom electrode, and a PZT seed layer is formed by rapid thermal treatment; wherein x is between 1.1 and 1.3; Pb x Zr 0.52 Ti 0.48 The third sputtering deposition process is performed on the PZT seed layer using O3 ceramic as a radio frequency target, and after rapid thermal treatment, the third sputtering deposition process and the rapid thermal treatment are repeated to form a lead zirconate titanate film.

2. The low-temperature preparation method of lead zirconate titanate thin film according to claim 1, characterized in that: The substrate comprises one of a single crystal silicon wafer with a (100) crystal orientation, a single crystal silicon wafer with a SiO2 layer on the surface and a SOI silicon wafer with a (100) crystal orientation.

3. The low-temperature preparation method of lead zirconate titanate thin film according to claim 1, characterized in that: The first sputtering deposition process is performed under an inert atmosphere; the gas pressure in the chamber of the first sputtering deposition process is 0.5mTorr-5mTorr, and the radio frequency power of the first sputtering deposition process is 50W-300W.

4. The low-temperature preparation method of lead zirconate titanate thin film according to claim 1, characterized in that: The second sputtering deposition process and the third sputtering deposition process are performed in a mixed atmosphere of an inert gas and oxygen; the gas flow rate of the inert gas is 19 sccm-77 sccm, and the gas flow rate of the oxygen is 0.4 sccm-1 sccm.

5. The low-temperature preparation method of lead zirconate titanate thin film according to claim 1, characterized in that: The radio frequency power of the second sputtering deposition process and the third sputtering deposition process is 50W-80W; during the second sputtering deposition process and the third sputtering deposition process, the rotation speed of the tray for carrying the substrate is 6rpm-10rpm.

6. The low-temperature preparation method of lead zirconate titanate thin film according to claim 1, characterized in that: The heating rate of the rapid thermal treatment is 2.5°C / s-10°C / s; the rapid thermal treatment includes a pre-annealing stage and an annealing stage; the temperature of the pre-annealing stage is 450°C-550°C, and the time of the pre-annealing stage is 60s-120s; the temperature of the annealing stage is 600°C-700°C, and the time of the annealing stage is 2min-15min.

7. The low-temperature preparation method of lead zirconate titanate thin film according to claim 1, characterized in that: The thickness of the PZT seed layer is 30nm-100nm; after a single third sputtering deposition process, a lead zirconate titanate film with a thickness of 300nm-600nm is formed on the PZT seed layer.

8. The low-temperature preparation method of lead zirconate titanate thin film according to claim 1, characterized in that: The lead zirconate titanate film has a thickness of 1 μm-2 μm.

9. A lead zirconate titanate film, characterized in that: The lead zirconate titanate film is prepared by the low-temperature preparation method of the lead zirconate titanate film as described in any one of claims 1 to 8.

10. Use of the lead zirconate titanate film as claimed in claim 9 in a micro-electromechanical system.

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