A lead zirconate titanate thin film and a low-temperature preparation method and application thereof

Abstract

The application 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 comprising the following steps: Ti metal is taken as a radio frequency target material to perform first sputter deposition treatment on a substrate to form a Ti adhesion layer; a bottom electrode is formed on the Ti adhesion layer; Pb x Zr 0.52 Ti 0.48 O3 ceramic is taken as a radio frequency target material to perform second sputter deposition treatment on the bottom electrode, rapid heat treatment is performed, a PZT seed layer is formed; Pb x Zr 0.52 Ti 0.48 O3 ceramic is taken as a radio frequency target material to perform third sputter deposition treatment on the PZT seed layer, rapid heat treatment is performed, the step is repeated, and a lead zirconate titanate film is formed. In the process of sputter deposition of the PZT film material, the substrate tray is not additionally heated, the loss and volatilization of PbO are reduced, the film component stability can be effectively maintained; more crystal nuclei are provided by the PZT seed layer, the uniform crystallization of the PZT film is promoted, the crystallization quality and electrical properties of the PZT film are improved, the crystal boundary defects are reduced, and the adhesion and stability of the film and the substrate are enhanced.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric materials technology, and in particular to a lead zirconate titanate thin film and its low-temperature preparation method and application. Background Technology

[0002] Piezoelectric materials are a series of special materials that can change their surface charge under mechanical stress (such as pressure or vibration) and deform when an electric field is applied to their surface. This effect of interconversion between mechanical energy and electrical energy is called the (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). Among them, PZT stands out from many piezoelectric materials due to its excellent piezoelectric, dielectric, and ferroelectric properties, and is widely used in various sensors, actuators, and transducers, such as ultrasonic transducer imaging arrays, surface acoustic wave (SAW) devices, energy traps, MEMS loudspeakers, MEMS accelerometers, dynamic random access memory (DRAMs), and non-volatile random access memory (NVRAMs).

[0003] PZT materials can be broadly classified into two categories based on size: ceramic materials and thin film materials. PZT ceramics are formed by powder mixing and sintering, allowing for precise control of the component ratios and thus possessing a high piezoelectric coefficient. However, ceramics are macroscopically bulk materials with large thickness, small area, and low throughput, making it difficult to meet the increasingly miniaturized and micro-sized demands of current MEMS sensors and actuators. PZT thin film materials, on the other hand, are fabricated using semiconductor processes, offering advantages such as high integration, high throughput, low cost, and ease of miniaturization, making them a significant development direction for PZT materials in recent years. The mainstream methods for preparing PZT thin films include the sol-gel process, pulsed laser deposition (PLD), and magnetron sputtering. However, existing PZT thin film preparation methods struggle to produce high-throughput PZT thin film materials with good crystallinity, uniform crystal orientation, low internal stress, and a high piezoelectric coefficient, thus hindering their further applications.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a lead zirconate titanate thin film and its low-temperature preparation method and application, aiming to solve the problem that the PZT thin film prepared by the existing process has high internal stress, which leads to the damage of the film surface.

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

[0007] A method for low-temperature preparation of lead zirconate titanate thin films, comprising the following steps:

[0008] Provide substrate;

[0009] Ti metal is used as an RF target and a first sputtering deposition process is performed on the substrate to form a Ti adhesion layer;

[0010] A bottom electrode is formed on the Ti adhesion layer;

[0011] Pb x Zr 0.52 Ti 0.48 O3 ceramic is used as an RF target material and a second sputtering deposition process is performed on the bottom electrode. After rapid thermal treatment, a PZT seed layer is formed; wherein x is between 1.1 and 1.3.

[0012] Pb x Zr 0.52 Ti 0.48 O3 ceramic is used as an RF target material for a third sputtering deposition process on the PZT seed layer. 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 the lead zirconate titanate thin film, wherein the substrate includes one of the following: a (100) oriented single-crystal silicon wafer, a (100) oriented single-crystal silicon wafer with a SiO2 layer on the surface, and a (100) oriented SOI silicon wafer.

[0014] The low-temperature preparation method of the lead zirconate titanate thin film, wherein the first sputtering deposition process is carried out in an inert atmosphere; the chamber pressure of the first sputtering deposition process is 0.5 mTorr-5 mTorr, and the radio frequency power of the first sputtering deposition process is 50 W-300 W.

[0015] The low-temperature preparation method of the lead zirconate titanate thin film, wherein the second sputtering deposition treatment and the third sputtering deposition treatment are carried out in an atmosphere of 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.

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

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

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

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

[0020] A lead zirconate titanate thin film is prepared using a low-temperature preparation method for lead zirconate titanate thin films.

[0021] Application of a lead zirconate titanate thin film in microelectromechanical systems (MEMS).

[0022] Beneficial Effects: This invention provides a lead zirconate titanate thin film, its low-temperature preparation method, and its application. The low-temperature preparation method of the lead zirconate titanate thin film includes 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; and then applying Pb... x Zr 0.52 Ti 0.48 O3 ceramic was used as the RF target and subjected to a second sputtering deposition process on the bottom electrode, followed by rapid thermal treatment to form a PZT seed layer; wherein x is between 1.1 and 1.3; Pb x Zr 0.52 Ti 0.48 O3 ceramic is used as the RF target material for a third sputtering deposition process on the PZT seed layer. This is followed by rapid thermal annealing, and the process is repeated to form a lead zirconate titanate (PZT) thin film. This invention eliminates the need for additional heating of the substrate tray during the sputtering deposition of PZT thin film, reducing PbO loss and volatilization, effectively maintaining film composition stability, and avoiding substrate tray heating and cooling time, thus reducing PZT film preparation time and optimizing PZT film material preparation costs. Furthermore, the PZT seed layer provides more crystal nuclei, promoting uniform crystallization of the PZT film, thereby improving the crystal quality and electrical properties of the PZT film, reducing grain boundary defects, and enhancing the adhesion and stability between the film and the substrate. Simultaneously, the PZT film prepared by this method has low internal stress and a smooth, flat surface. Attached Figure Description

[0023] Figure 1 The crystal structure diagram of PZT perovskite;

[0024] Figure 2 This is a schematic diagram of the process flow for a low-temperature preparation method of lead zirconate titanate thin film according to the present invention.

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

[0026] Figure 4 This is a schematic diagram of the film structure after the bottom electrode has been deposited;

[0027] Figure 5 A schematic diagram of the internal structure of a magnetron sputtering cavity;

[0028] Figure 6 This is a schematic diagram of the film structure after the lead zirconate titanate film has been deposited.

[0029] Figure 7 This is a schematic diagram of the film structure after the top electrode has been deposited and patterned.

[0030] Figure 8 The image shows the XRD characterization of the Pt bottom electrode deposited in Example 1.

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

[0032] Figure 10 The image shows the XRD characterization of the lead zirconate titanate thin film prepared in Example 1.

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

[0034] Figure 12 A schematic diagram of a high-stress PZT thin film sample;

[0035] Figure 13 This is a schematic diagram of a PZT thin film sample after stress relief. Detailed Implementation

[0036] This invention provides a lead zirconate titanate thin film, its low-temperature preparation method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0037] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0038] The chemical formula of lead titanate is Pb(Zr) x Ti 1-x When x is around 0.52, the material is at a critical point in terms of composition and properties, called the morphotropic phase boundary (MPB). At this point, the PZT material crystal exhibits a perovskite structure, possessing optimal piezoelectric and dielectric properties, such as... Figure 1 As shown, this can be mainly attributed to the following two reasons: First, PZT contains both tetragonal and rhombic phases at its phase boundaries, providing a large number of phase boundaries and making it easier for the polarization directions inside PZT to rearrange under the influence of an external electric field, thereby enhancing the material's response to changes in the electric field. Second, a monoclinic phase may also appear at the phase boundaries, further enhancing the piezoelectric and electrostrictive properties of PZT. Therefore, to ensure optimal performance, controlling the Zr / Ti element ratio in PZT material to 52:48 is crucial.

[0039] However, existing methods for preparing PZT thin films are insufficient for high-throughput production of PZT thin films with good crystallinity, uniform crystal orientation, low internal stress, and high voltage coefficient.

[0040] Based on this, such as Figure 2 As shown, the present invention provides a low-temperature preparation method for lead zirconate titanate thin films, comprising the following steps:

[0041] Step S10: Provide a substrate;

[0042] Step S20: Ti metal is used as an RF target and a first sputtering deposition process is performed on the substrate to form a Ti adhesion layer;

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

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

[0045] Step S50: Pb x Zr 0.52 Ti 0.48 O3 ceramic is used as an RF target material for a third sputtering deposition process on the PZT seed layer. 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 transitions within the thin film and improve its crystallinity. In traditional methods for preparing PZT thin films using magnetron sputtering, the substrate tray typically needs to be heated and stabilized at 300-600°C. This causes significant volatilization of PbO within the PZT film during prolonged deposition, making it difficult to control the film composition. Furthermore, the high vacuum within the chamber prevents effective heat exchange and cooling of the substrate tray at high temperatures, further increasing PbO volatilization losses.

[0047] In this embodiment, the use of multiple rapid thermal processing techniques releases the residual stress accumulated during the growth of the PZT film and promotes film crystallization. Therefore, no additional heating of the substrate tray is required during the sputtering deposition of the PZT film material. This reduces the loss and volatilization of PbO, effectively maintains the stability of the film composition, avoids the heating and cooling time of the substrate tray, reduces the PZT film preparation time, and optimizes the preparation cost of the PZT film material. Furthermore, the PZT seed layer provides more crystal nuclei, promoting uniform crystallization of the PZT film, thereby improving the crystal 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, this invention uses only PZT thin film material as the seed layer, which not only simplifies the processing steps but also reduces potential contamination caused by the introduction of new elements, ensuring the purity of the prepared PZT thin film material. Furthermore, the multiple RTP technology used in this invention not only promotes the formation of PZT thin film crystals but also reduces component loss caused by PbO volatilization at high temperatures, effectively maintaining the stability of the film composition.

[0049] In some implementations, such as Figure 3 As shown, the substrate includes one of the following: a (100) oriented monocrystalline silicon wafer, a (100) oriented monocrystalline silicon wafer with a SiO2 layer on the surface, and a (100) oriented SOI silicon wafer.

[0050] Specifically, different substrates are suitable for different processes, and the appropriate processing technology and substrate 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 wet etching process can be directly selected; while for complex cantilever beams or diaphragms with back cavity structures, a (100) crystal orientation single crystal silicon wafer or SOI silicon wafer with SiO2 layer on the surface and back etching process are required, in which SiO2 plays the role of stopping etching and releasing the structure.

[0051] Furthermore, the crystal orientation of the substrate affects the subsequent deposition of the thin film. First, the surface energy of a (100) oriented single-crystal silicon wafer is low, which is conducive to the adhesion of the thin film and can improve the stability and durability during processing and use. Second, the crystal orientation of the subsequently deposited thin film is closely related to the crystal orientation of the substrate. A (111) oriented bottom electrode (preferably a Pt thin film) can be grown on a (100) oriented single-crystal silicon wafer, which is necessary to grow a PZT piezoelectric thin film with a (001) oriented crystal orientation. Finally, (100) oriented single-crystal silicon wafers are widely used in the industry and have a lower price for the same size and specifications, giving them a cost advantage.

[0052] In some embodiments, the (100) oriented single-crystal silicon wafer with a SiO2 layer on its surface has a SiO2 layer thickness of 0.2 μm-0.5 μm. The SiO2 layer serves to stop etching and release the structure during processing. Maintaining the SiO2 layer thickness within the 0.2 μm-0.5 μm range can alleviate 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. Furthermore, the SiO2 layer also acts as an insulator, reducing leakage current during device operation and improving device performance. However, excessively thick or thin SiO2 layers can lead to high residual stress and thermal expansion mismatch. In addition, an excessively thick insulating layer can increase parasitic capacitance, forming additional leakage paths and increasing dielectric loss, while an excessively thin layer lacks sufficient insulation, increasing leakage current. Both of these factors reduce the electrical performance and energy efficiency of the device.

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

[0054] In some embodiments, step S10 further includes cleaning the substrate, specifically including the following steps: placing the substrate in an acetone solution and ultrasonically cleaning it for 5-10 minutes; then rinsing it with deionized water and ultrasonically cleaning it in an isopropanol (IPA) solution for 5-10 minutes; then thoroughly cleaning the substrate surface again with deionized water and using a nitrogen gun to remove water droplets adhering to the substrate surface; 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 residual water vapor molecules on its surface will not disrupt the vacuum environment and affect the vacuum level after entering the vacuum chamber.

[0055] In some embodiments, the first sputtering deposition process is performed under an inert atmosphere; the chamber pressure for the first sputtering deposition process is 0.5 mTorr-5 mTorr, and the radio frequency power for the first sputtering deposition process is 50 W-300 W. Controlling the chamber pressure for the first sputtering deposition process between 0.5 mTorr and 5 mTorr allows for a low plasma density but high electron temperature and ion energy, while also resulting in a longer mean free path of the sputtered atoms. This allows for the fabrication of dense, well-adhesive, and smooth thin films. Furthermore, at this power, the film thickness can be precisely controlled, and a dense Ti adhesion layer with low stress and few defects can be obtained, enabling a tight bond between 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, and this thickness of Ti adhesion layer has the effect of improving the adhesion of Pt film on Si substrate.

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

[0059] In some embodiments, a schematic diagram of the film structure after deposition of the bottom electrode is shown below. Figure 4 As shown, the thickness of the bottom electrode is 165nm-215nm. The bottom electrode is used for the growth of PZT thin films and their electrical control. 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 PZT thin films. Moreover, 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 ceramic was used as the target material for magnetron sputtering RF targets to sputter and deposit PZT thin films, where x was between 1.1 and 1.3. A highly (001) oriented perovskite phase PZT thin film was prepared using a multi-stage rapid thermal annealing (RTP) process. An excess of 10%-30% Pb was added to compensate for Pb volatilization losses during sputtering and heat treatment, ensuring that the resulting PZT thin film had a precise stoichiometric ratio.

[0061] In some embodiments, in steps S40 and 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, and its position in the magnetron sputtering cavity is as follows: Figure 5 As shown, the substrate is located at the top inside the magnetron sputtering equipment, and the radio frequency (RF) target positions include a first RF target position parallel to the substrate and two second RF target positions forming a certain angle with the substrate; the Pb x Zr 0.52 Ti 0.48 O3 ceramic (PZT target) is fixed at the second RF target site; wherein the target and the substrate are at 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 deposited bottom electrode is fixed on the substrate tray of the magnetron sputtering equipment, and dust particles on the substrate surface are blown away using a nitrogen gun to ensure the quality of the PZT film. After blowing, it is placed in the vacuum chamber of the magnetron sputtering equipment. In order to deposit high-quality, high-purity PZT films, a high background vacuum is required before sputtering to prevent contamination by residual gas molecules. In this embodiment, a cascaded system of mechanical pumps and turbomolecular pumps is used to obtain a high vacuum in the vacuum chamber. First, a rough vacuum of 1-5 Pa is obtained in the vacuum chamber using a mechanical pump, and then a cascaded turbomolecular pump and mechanical pump are used to obtain a 10 Pa vacuum. -4 ~10 -5 High vacuum of Pa.

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

[0064] Specifically, before performing the second and third sputtering deposition processes, inert gas and oxygen (O2) are introduced into the vacuum chamber, and the gas flow rate is monitored using a flow meter and a flow valve; wherein, 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; at the same time, the opening size of the gate valve between the molecular pump and the vacuum chamber is controlled to maintain the gas pressure in the vacuum chamber at 0.5-0.7 Pa.

[0065] In some embodiments, the radio frequency power of the second and third sputtering deposition processes is 50W-80W; during the second and third sputtering deposition processes, the tray rotation speed for supporting the substrate is 6rpm-10rpm. By utilizing low power to precisely control the thickness of the PZT seed layer and the PZT film, films with low stress, few defects, and dense film layers can be obtained; while controlling the tray rotation speed enables uniform deposition, resulting in films with consistent 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 used to support the substrate is 8rpm.

[0067] In some embodiments, the heating rate of the rapid heat treatment is 2.5℃ / s-10℃ / s; the rapid heat treatment includes a pre-annealing stage and an annealing stage; the temperature of the pre-annealing stage is 450℃-550℃, and the time of the pre-annealing stage is 60s-120s; the temperature of the annealing stage is 600℃-700℃, and the time of the annealing stage is 2min-15min. Rapid heat treatment (RTP) can quickly raise the temperature to the annealing temperature, which helps to achieve uniform crystallization of PZT films and form films with excellent crystal structures. Furthermore, compared to traditional annealing processes, rapid heat treatment has a shorter time, reduces stress accumulation caused by differences in thermal expansion coefficients, can reduce defect density, and improve electrical and acoustic properties.

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

[0069] In a preferred embodiment, the rapid heat treatment has a heating rate of 7°C / s; the rapid heat 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 lead zirconate titanate film of 300nm-600nm is formed on the PZT seed layer. Depositing a PZT layer of 30nm-100nm thickness followed by rapid thermal treatment can produce a (001) oriented PZT seed layer with no surface damage; while performing the third sputtering deposition process and the rapid thermal treatment multiple times can effectively release residual internal stress, and through successive deposition, a lead zirconate titanate film of the target thickness can finally be obtained. However, if a lead zirconate titanate film of the target thickness is deposited in a single step, it is prone to defects such as cracks and voids due to excessive internal stress.

[0071] In some embodiments, a schematic diagram of the film structure after the deposition of the lead zirconate titanate thin film is shown below. 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 lead zirconate titanate film of 300nm-600nm is formed on the PZT seed layer. Then, by 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 piezoelectric devices of microelectromechanical systems (MEMS), while PZT films of this thickness deposited in a single process are prone to defects such as cracks and voids due to excessive internal stress. Therefore, this invention releases residual internal stress by first depositing a PZT seed layer and using the RTP process, and provides more crystal nuclei for the deposition of PZT thin films, thereby improving the crystal quality and electrical properties of the films. At the same time, it accumulates by depositing thin lead zirconate titanate films of multiple thicknesses to obtain a 1μm-2μm thick perovskite phase lead zirconate titanate film with a high (001) orientation, resulting in a film with 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 with the bottom electrode to drive the PZT piezoelectric layer (i.e., the lead zirconate titanate film) to perform the required function. A schematic diagram of the film structure after depositing the top electrode and patterning is shown below. Figure 7As shown. After step S50, the method further includes: forming and patterning a top electrode on the lead zirconate titanate film; specifically including the following steps: uniformly spin-coating photoresist onto the surface of the lead zirconate titanate film using a spin coater, and then pre-baking the photoresist on a high-temperature hot plate to pre-cur the photoresist; exposing the photoresist using a photomask exposure machine or laser direct writing equipment, and transferring the electrode shape pattern into the photoresist by immersion in a developing solution, and then placing it on a high-temperature hot plate to complete the hardening of the photoresist; depositing metal on the surface of the PZT piezoelectric material using magnetron sputtering or electron beam evaporation; after deposition, ultrasonically cleaning the PZT piezoelectric material with the top electrode in acetone to remove the metal film layer other than the desired electrode pattern. Finally, cleaning with isopropanol (IPA) and deionized water to obtain a top electrode film with electrode pattern.

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

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

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

[0076] In addition, the present invention also provides an application of lead zirconate titanate thin film in microelectromechanical systems.

[0077] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

[0078] Example 1

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

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

[0081] 2) 15nm Ti and 200nm Pt were deposited sequentially on a dry substrate using magnetron sputtering. A 3-inch Ti metal target was placed at the RF target position, and Ar was used as the sputtering gas with a base vacuum of 10... -6 ~10 -7 The operating pressure is 3 mTorr, and the RF power is 300 W. A 3-inch Pt metal target is placed in a DC target position, and Ar is used for sputtering gas. The base vacuum is 10. -6 ~10 -7 The working pressure was 4 mTorr, and the RF power was 100 W. After deposition, the material was characterized using XRD, and the results are as follows: Figure 8 As shown, the obtained Pt bottom electrode has a (111) crystal orientation.

[0082] 3) A 100 nm PZT thin film was deposited on a Pt / Ti / SiO2 / Si substrate using radio frequency magnetron sputtering. (2-inch Pb) 1.1 Zr 0.52 Ti 0.48 An O3-based ceramic target was fixed on a radio frequency target, and a mechanical and turbomolecular cascade pump was used to obtain 10 -4 ~10 -5 The base vacuum was 0.5 Pa. The sputtering gases were 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 pressure was 0.5 Pa, the RF power was 50 W, and the substrate tray rotation speed was set to 8 rpm. The deposited PZT film underwent rapid thermal annealing to obtain a 100 nm thick PZT seed layer; the heating rate was 2.5 °C / s, the pre-annealing temperature was 500 °C, the pre-annealing time was 100 s, the annealing temperature was 700 °C, and the annealing time was 2 min.

[0083] 4) Deposit a 300 nm PZT thin film using radio frequency magnetron sputtering technology, and obtain a PZT thin film with (001) crystal orientation using RTP technology. The sputtering parameters and RTP parameters are the same as in step 3).

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

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

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

[0087] PZT thin film samples before and after stress release are shown below. Figure 12 and Figure 13 As shown, in the sample before the internal stress was released, excessive internal stress would cause defects such as cracks and pits on the surface of the film; while after the internal stress was released, the surface of the film was smooth and flat.

[0088] In summary, this invention provides a lead zirconate titanate thin film, its low-temperature preparation method, and its application. The low-temperature preparation method of the lead zirconate titanate thin film includes the following steps: providing a substrate; performing a first sputtering deposition process on the substrate using Ti metal as an RF target to form a Ti adhesion layer; forming a bottom electrode on the Ti adhesion layer; and then applying Pb... x Zr 0.52 Ti 0.48 O3 ceramic was used as the RF target and subjected to a second sputtering deposition process on the bottom electrode, followed by rapid thermal treatment to form a PZT seed layer; wherein x is between 1.1 and 1.3; Pb x Zr 0.52 Ti 0.48 O3 ceramic is used as the RF target material for a third sputtering deposition process on the PZT seed layer. This is followed by rapid thermal annealing, and the process is repeated to form a lead zirconate titanate (PZT) thin film. This invention eliminates the need for additional heating of the substrate tray during the sputtering deposition of PZT thin film, reducing PbO loss and volatilization, effectively maintaining film composition stability, and avoiding substrate tray heating and cooling time, thus reducing PZT film preparation time and optimizing PZT film material preparation costs. Furthermore, the PZT seed layer provides more crystal nuclei, promoting uniform crystallization of the PZT film, thereby improving the crystal quality and electrical properties of the PZT film, reducing grain boundary defects, and enhancing the adhesion and stability between the film and the substrate. Simultaneously, the PZT film prepared by this method has low internal stress and a smooth, flat surface.

[0089] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for low temperature preparation of lead zirconate titanate thin films, characterized in that, The method comprises the steps of: providing a substrate; carrying out a first sputter deposition process on the substrate by 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 as a radio frequency target material is subjected to a second sputter deposition process on the bottom electrode, and after rapid thermal processing, a PZT seed layer is formed; wherein x is between 1.1 and 1.

3. Pb x Zr 0.52 Ti 0.48 O3 ceramic as a radio frequency target material is subjected to a third sputter deposition process on the PZT seed layer, followed by a rapid thermal process, and the third sputter deposition process and the rapid thermal process are repeated to form a lead zirconate titanate thin film. the temperature rising rate of the rapid thermal process is 2.5℃ / s-10℃ / s; the rapid thermal process comprises a pre-annealing stage and an annealing stage; the temperature of the pre-annealing stage is 450℃-550℃, and the time of the pre-annealing stage is 60s-120s; the temperature of the annealing stage is 600℃-700℃, and the time of the annealing stage is 2min-15min; the thickness of the Ti adhesion layer is between 10nm-20nm; the thickness of the PZT seed layer is 30nm-100nm; a lead zirconate titanate thin film with a thickness of 300nm-600nm is formed on the PZT seed layer after a single third sputter deposition process; the thickness of the lead zirconate titanate thin film is 1μm-2μm.

2. The method of claim 1, wherein the method is carried out at a temperature of 200 °C or less. The substrate comprises one of a (100) crystal direction monocrystalline silicon wafer, a (100) crystal direction monocrystalline silicon wafer with a SiO2 layer on the surface, and a (100) crystal direction SOI silicon wafer.

3. The method of claim 1, wherein the lead zirconate titanate thin film is prepared at a temperature of 300°C or less. The first sputter deposition process is carried out in an inert atmosphere; the chamber internal gas pressure of the first sputter deposition process is 0.5mTorr-5mTorr, and the radio frequency power of the first sputter deposition process is 50W-300W.

4. The method of claim 1, wherein the lead zirconate titanate thin film is prepared at a temperature of 300 °C or less. The second sputter deposition process and the third sputter deposition process are carried out in a mixed atmosphere of inert gas and oxygen; the gas flow of the inert gas is 19sccm-77sccm, and the gas flow of the oxygen is 0.4sccm-1sccm.

5. The method of claim 1, wherein the lead zirconate titanate thin film is prepared at a temperature of 300 °C or less. The radio frequency power of the second sputter deposition process and the third sputter deposition process is 50W-80W; during the second sputter deposition process and the third sputter deposition process, the rotation speed of a tray used for carrying the substrate is 6rpm-10rpm.

6. A lead zirconate titanate film, characterized by, The lead zirconate titanate thin film is prepared by using the low-temperature preparation method of any one of claims 1-5.

7. Application of the lead zirconate titanate thin film of claim 6 in a micro-electro-mechanical system.

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