Method for enhancing piezoelectric property of PZT film through rapid annealing

Abstract

The invention discloses a method for enhancing the piezoelectric property of a PZT film through rapid annealing, which comprises the following steps: 1) in a vacuum environment of a sputtering chamber of magnetron sputtering equipment, depositing a PZT film with a crystal structure on a substrate which is heated to a set temperature by a PZT target material; (2) the PZT film is taken out of a sputtering cavity of the magnetron sputtering equipment and then put into a hearth of a rapid annealing furnace, the hearth of the rapid annealing furnace is vacuumized, the PZT film is annealed in a vacuum environment and then cooled along with the furnace, the annealing temperature is larger than the Curie point of the PZT film, and therefore phase structure reconstruction and ferroelectric domain reorientation of the PZT film are achieved; therefore, the transverse piezoelectric coefficient of the PZT film is improved. According to the method, the PZT film deposited on the substrate is crystallized to form a crystal structure, the PZT film is annealed and heated to the Curie point or above, phase structure reconstruction and ferroelectric domain redistribution of the PZT film are achieved, and the transverse piezoelectric coefficient of the PZT film is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of MEMS technology, and more specifically, relates to a method for rapidly annealing to enhance the piezoelectric properties of PZT thin films. Background Technology

[0002] Current Status of Micro-Electro-Mechanical Systems (MEMS) and Piezoelectric Technology: Micro-Electro-Mechanical Systems (MEMS), as a revolutionary technology that integrates microelectronic circuits and micromechanical structures at the micrometer scale, has become one of the cornerstones of modern information technology.

[0003] With the rapid development of IoT, 5G communication, autonomous driving, and biomedical technologies, the demand for MEMS devices in fields such as optical imaging, ultrasonic detection, RF filtering, and chip-level heat dissipation and cooling is growing exponentially. In MEMS actuation and sensing mechanisms, compared to electrostatic actuation (requiring high voltage and poor linearity) and electrothermal actuation (high power consumption and slow response), piezoelectric actuation is gradually becoming the mainstream technology for high-end MEMS devices due to its high energy density, extremely fast response speed (microsecond level), low power consumption, and excellent electromechanical conversion efficiency.

[0004] Currently, commercially available piezoelectric MEMS devices primarily utilize aluminum nitride (AlN) as the functional thin film. AlN possesses excellent chemical stability, high acoustic velocity, and perfect compatibility with CMOS processes. However, AlN belongs to the wurtzite structure, and its piezoelectric effect mainly originates from the intrinsic polarization of the crystal lattice, lacking ferroelectric domain structures, resulting in a low piezoelectric coefficient. Typically, the piezoelectric coefficient of AlN is only 5 pm / V-6 pm / V, and even with Sc (scandium) doping modification, its performance improvement still has physical limits (usually less than 100 pm / V). Furthermore, during the magnetron sputtering growth of AlN thin films, process fluctuations can easily introduce defects such as nitrogen vacancies, leading to increased leakage current and consequently deteriorating the electrical reliability of the device.

[0005] To meet the demands of high-end MEMS devices for large displacement and high output force, lead zirconate titanate (PZT), a typical perovskite ferroelectric material, has become the recognized best alternative. Unlike AlN, PZT possesses a flippable ferroelectric domain structure. Its enormous piezoelectric response stems not only from the intrinsic contribution of lattice distortion but also primarily from the extrinsic motion of the ferroelectric domain walls under external fields. Therefore, the theoretical piezoelectric coefficient of high-quality PZT films can reach tens of times that of AlN, making it the preferred material for next-generation high-performance piezoelectric MEMS devices.

[0006] Despite the excellent properties of PZT materials, integrating them into thin films on silicon substrates while maintaining the performance of bulk materials is extremely challenging. Currently, the mainstream methods for preparing PZT thin films include sol-gel, pulsed laser deposition (PLD), and magnetron sputtering.

[0007] Sol-gel method: Although the stoichiometric ratio is easy to control, it requires repeated spin coating and high-temperature annealing, which is cumbersome and not suitable for the preparation of large-area thick films. It is also prone to cracking.

[0008] Pulsed laser deposition: Suitable for growing high-quality epitaxial single-crystal thin films, often used in basic research, but due to poor large-area uniformity and the presence of "droplet" defects, it is difficult to meet the mass production requirements of industrial-grade 8-inch or 12-inch wafers.

[0009] Magnetron sputtering is widely recognized as the preferred technology for large-scale production of PZT thin films due to its fast deposition rate, good large-area uniformity, high process repeatability, and moderate cost. However, the performance of PZT thin films prepared by magnetron sputtering is often lower than that of bulk materials. This is because the film is rigidly bound by the substrate, which hinders domain wall movement. More seriously, the piezoelectric properties of PZT thin films are extremely sensitive to residual stress, crystal orientation, and domain structure distribution within the film. During magnetron sputtering, bombardment by high-energy particles, mismatch in thermal expansion coefficients, and lattice mismatch often introduce huge residual stresses into the PZT film.

[0010] Minh D. Nguyen of the University of Twente increased the piezoelectric coefficient to 408 pm / V by controlling the loose grain boundary stress created by pulsed laser deposition. Chen Zuhuang of Harbin Institute of Technology increased the piezoelectric coefficient of PZT films to 585 pm / V using flexible substrate transfer technology. Regarding domain structure manipulation, Wang Yaojin of Nanjing University of Science and Technology increased the piezoelectric coefficient of PZT films to 550 pm / V at multilayer gradient interfaces.

[0011] Current processes only optimize the longitudinal piezoelectric coefficient, but are insufficient for optimizing the transverse piezoelectric coefficient of PZT films prepared by magnetron sputtering. Furthermore, existing post-annealing processes are usually only used to crystallize amorphous PZT films, and there is a lack of a simple, efficient, and significantly improved post-processing control method for PZT films that have already formed a crystalline structure. Summary of the Invention

[0012] To address the above-mentioned deficiencies or improvement needs of existing technologies, this invention provides a method for rapidly annealing to enhance the piezoelectric properties of PZT thin films. This method involves crystallizing the PZT thin film deposited on a substrate to form a crystal structure, and then heating the crystal structure PZT thin film above the Curie point to achieve a redistribution of phases and ferroelectric domains in the PZT thin film, thereby improving the transverse piezoelectric coefficient of the PZT thin film.

[0013] To achieve the above objectives, according to the present invention, a method for rapidly annealing to enhance the piezoelectric properties of PZT thin films is provided, comprising the following steps: 1) In the vacuum environment of the sputtering chamber of the magnetron sputtering equipment, PZT target material is deposited on a substrate heated to a set temperature by magnetron sputtering technology, so that the PZT film crystallizes directly during deposition to form a crystal structure. 2) After removing the PZT thin film from the sputtering chamber of the magnetron sputtering equipment in step 1), place it into the furnace chamber of the rapid annealing furnace. Evacuate the furnace chamber of the rapid annealing furnace to allow the PZT thin film to anneal in a vacuum environment and then cool with the furnace. The annealing temperature is higher than the Curie point of the PZT thin film to achieve phase structure reconstruction and ferroelectric domain reorientation of the PZT thin film, thereby improving the transverse piezoelectric coefficient of the PZT thin film.

[0014] In the vacuum environment of magnetron sputtering, the substrate is heated to a set temperature, allowing the PZT target to directly form a crystalline structure during deposition. This process avoids the grain boundary voids and microcracks caused by volume shrinkage during the amorphous-to-crystalline transition in the traditional "room temperature deposition of amorphous thin films + subsequent annealing and crystallization" process. The deposition process directly forms a dense and complete crystalline framework, providing structural support for improved piezoelectric performance. When the annealing temperature is higher than the Curie point of the PZT film, the PZT film transforms from a ferroelectric phase (tetragonal / rhombohedral phase) to a paraelectric phase (cubic phase), completely releasing the growth stress and thermal mismatch stress accumulated during deposition. Upon cooling, a new phase transition occurs, generating ferroelectric domains. The domain structure is redistributed according to the principle of minimum energy, activating domain wall mobility. This reconstruction not only enhances the intrinsic piezoelectric contribution from lattice distortion but also significantly strengthens the extrinsic piezoelectric contribution dominated by domain wall mobility, ultimately improving the lateral piezoelectric coefficient and meeting the multi-directional driving / sensing requirements of MEMS devices.

[0015] Preferably, the specific steps of step 1) are as follows: 1.1) Place the substrate in the sputtering chamber of the magnetron sputtering equipment and position the substrate below the PZT target, then evacuate the sputtering chamber; 1.2) The substrate is heated to the set temperature using the heating stage of a magnetron sputtering device; 1.3) Open the inlet valve of the magnetron sputtering equipment to allow the process gas to flow into the sputtering chamber, and ensure that the pressure in the sputtering chamber is 0.5 Pa - 1 Pa; wherein, the process gas is a mixture of inert gas and oxygen; 1.4) Deposit a PZT thin film on the substrate that has been heated to the set temperature. After a set time for the PZT thin film to become a crystal structure, stop heating on the heating stage and close the air inlet valve. After waiting for the substrate to cool down, remove the substrate and the PZT thin film on the substrate.

[0016] During the deposition process, the substrate is continuously heated. When the sputtered Pb, Zr, Ti atoms and oxygen atoms reach the substrate surface, the high temperature of the substrate, heated to the set temperature, gives these adsorbed atoms extremely high surface migration energy. This allows the atoms to overcome the potential barrier and migrate to the lattice site with the lowest lattice potential energy to arrange themselves, rather than being randomly stacked.

[0017] The high-temperature environment of the substrate provides sufficient activation energy, promoting the direct nucleation and growth of a thermodynamically more stable perovskite structure. This in-situ crystallization mechanism directly reduces the amorphous layer and defect density at grain boundaries, enabling the PZT film to possess a good crystal framework before entering the subsequent annealing process. This provides a high-quality material basis for the phase and ferroelectric domain redistribution in the subsequent rapid annealing stage, avoiding the risks of severe volume shrinkage and stress cracking caused by complete recrystallization from the amorphous state.

[0018] The pressure within the sputtering chamber is strictly limited to 0.5 Pa–1 Pa, a golden pressure window optimized for PZT materials. If the pressure is too low (<0.5 Pa), the mean free path of the gas molecules is too large, resulting in excessively high kinetic energy carried by sputtered ions and neutral particles upon reaching the substrate. This not only causes backsputtering (i.e., deposited atoms are bounced back) but also physically damages the formed lattice, introducing point defects. If the pressure is too high (greater than 1 Pa), particles undergo excessive gas-phase collisions before reaching the substrate, leading to excessive kinetic energy dissipation (thermalization). Low-energy particles lack migration ability upon reaching the substrate, easily forming a loose, porous structure with prominent columnar grain boundaries. The 0.5 Pa–1 Pa pressure range ensures that the deposited particles retain adequate kinetic energy—enough to compact the PZT film through atomic peening, increasing density, without causing severe lattice damage. This is crucial for obtaining MEMS piezoelectric films with high dielectric breakdown strength and low leakage current.

[0019] As an oxide, PZT suffers from oxygen deficiency during physical sputtering due to its light weight; oxygen is easily removed by the vacuum pump or scattered in the plasma. This oxygen vacancy is a major cause of ferroelectric fatigue and domain pinning. This invention uses a mixture of inert gas and oxygen as the process gas. Introducing oxygen during deposition and performing reactive magnetron sputtering allows for real-time replenishment of oxygen atoms needed for lattice growth. This in-situ oxygen compensation reduces the oxygen vacancy concentration within the PZT film, directly increasing its remanent polarization and making ferroelectric domains more prone to flipping under an electric field, resulting in a higher piezoelectric coefficient on a macroscopic scale.

[0020] Preferably, in step 1.1), the lead zirconate titanate material of the PZT target has the molecular formula Pb. 1.1 Zr x Ti 1-x O3, and x takes values ​​from 0.48 to 0.55; In step 1.2), the substrate is heated to 500°C. o C-650 o C; In step 1.4), the magnetron sputtering power is 200W-300W, the deposition time is 1.5h-2h, and the thickness of the obtained PZT film is 1.5μm-2μm.

[0021] When Zr / Ti is approximately 52 / 48 (i.e. x When x approaches 0.52, the material is in the morphotropic phase boundary (MPB). In this region, both tetragonal (6 polarization directions) and rhombohedral (8 polarization directions) phases coexist within the PZT material. Due to the coexistence of these two phases, the number of permissible polarization directions reaches its maximum (6+8=14). This means that under an external electric field, the energy barrier for ferroelectric domain reorientation is lowest, and polarization reversal is easiest. The dielectric constant and piezoelectric coefficient of PZT reach their peaks near the MPB. Limiting x to the range of 0.48~0.55 is precisely to capture this peak physical effect. If the composition is not locked near the MPB during the deposition stage, even with subsequent annealing, the domain rearrangement ability will be significantly reduced due to the lack of sufficient permissible polarization directions. Therefore, limiting x to 0.48~0.55 is a material science prerequisite for achieving high piezoelectric properties.

[0022] Lead (Pb) is a highly volatile element, and the vapor pressure of its oxide (PbO) increases sharply with increasing temperature. At 500°C... o C-650 o In the high-temperature deposition environment of C, a large number of lead atoms deposited on the substrate will volatilize again. If Pb1Zr is used...x Ti 1-x Using O3 as a standard target, high-temperature deposition leads to severe lead deficiency in PZT films. Lead deficiency directly results in the formation of the pyrochlore phase. The pyrochlore phase is paraelectric, lacks piezoelectricity, and acts as an insulating inclusion, disrupting the continuity of ferroelectric domains. Compared to Pb1Zr... x Ti 1-x The standard target material for O3, the Pb used in this invention 1.1 Zr x Ti 1-x A 10% lead excess in O3 is a precise engineering balance point. If the excess is insufficient, it cannot counteract high-temperature volatilization, leading to lattice defects and pyrochlore phase. If the excess is excessive, the excess lead will precipitate at the grain boundaries in the form of lead oxide, causing a sharp increase in leakage current and reducing the breakdown voltage of the PZT film.

[0023] Pb 1.1 Zr x Ti 1-x O3 excess 10% lead combined with 500 o C-650 o The temperature C is just right so that the excess lead reaching the substrate and the lead volatilized at high temperature reach a dynamic equilibrium.

[0024] The formation of PZT perovskite structures requires overcoming a potential barrier. Below 500 o At temperature C, the thermal energy of the deposited atoms is insufficient to allow them to migrate to the correct lattice positions, easily leading to the formation of an amorphous or metastable pyrochlore phase. 500 o C-650 o The temperature limit of C ensures that deposition and crystallization occur simultaneously, resulting in a dense crystal structure and avoiding the loose and porous problems associated with low-temperature deposition. When the temperature exceeds 650°C... o Lead and titanium in C, PZT readily undergo severe interdiffusion with the bottom electrode (typically Pt or LaNiO3) or the silicon substrate. This forms a low-dielectric-constant interfacial dead layer, significantly reducing the effective driving voltage. Higher deposition temperatures result in greater thermal mismatch stress after cooling to room temperature. Limiting the deposition temperature to 650°C... o Below C, residual tensile stress is effectively controlled, preventing PZT films from cracking or peeling off from the substrate during cooling.

[0025] A magnetron sputtering power of 200W-300W is employed, providing a suitable plasma density. The sputtered particles arrive at the substrate with appropriate kinetic energy, increasing the PZT film density through atomic peening without causing backsputtering damage or substrate overheating due to excessive energy. The deposition rate at this power allows for sufficient diffusion of adsorbed atoms on the surface, facilitating the formation of columnar crystal structures, which in turn enhance the lateral piezoelectric coefficient.

[0026] A deposition time of 1.5h-2h produces a PZT film with a thickness of 1.5μm-2μm, which is moderate. If the deposition time is too short, the PZT film will be too thin, resulting in insufficient driving force and a high risk of leakage. If the deposition time is too long, the PZT film will be too thick, the grains will easily coarsen, and the stress will be difficult to control.

[0027] Preferably, in step 1.3), the flow rate of the inert gas is 36 sccm to 42 sccm, and the flow rate of the oxygen is 5 sccm to 6 sccm.

[0028] During magnetron sputtering, excessive oxygen flow (exceeding 6 sccm) can lead to the rapid formation of an insulating oxide layer on the PZT target surface. This oxide layer significantly reduces sputtering yield and causes target poisoning, manifested as drastic sputtering voltage drift and a sharp drop in deposition rate, severely impacting industrial production capacity and process repeatability. By strictly limiting the oxygen flow to 5-6 sccm, and simultaneously using an inert gas flow of 36-42 sccm, most of the target surface remains in a metallic / semi-metallic state. This maintains a high sputtering yield while preventing excessive lead volatilization due to excessively low deposition rates (lead volatilization is positively correlated with deposition time), ensuring process stability and precise control of PZT film thickness.

[0029] By using a low oxygen flow rate (5 sccm~6 sccm) and a high inert gas flow rate (36 sccm~42 sccm), the concentration of negative oxygen ions generated in the plasma was significantly reduced. This resulted in the particle flow reaching the substrate being dominated by low-energy deposited atoms and moderately energetic inert gas ions (assisting in densification). This effectively protected the perovskite lattice integrity and optimal crystal orientation of the PZT film, laying a structural foundation for subsequent improvements in piezoelectric performance.

[0030] An oxygen flow rate of 5 sccm to 6 sccm can replenish the oxygen atoms required for lattice growth in real time during the deposition process, controlling the oxygen vacancy concentration at an extremely low level through an in-situ oxygen replenishment mechanism. Low oxygen vacancies not only reduce domain wall pinning but also lower leakage current, enabling the PZT film to withstand higher polarization voltages and further activating domain wall mobility, providing a key guarantee for the synchronous improvement of the lateral piezoelectric coefficient.

[0031] If the oxygen flow rate is too low (<5 sccm), in addition to oxygen vacancies, the relative excess of lead volatilization will cause the precipitation of the pyrochlore phase, which, as an insulating inclusion, will block the continuity of ferroelectric domains. If the oxygen flow rate is too high (greater than 6 sccm), interstitial oxygen defects will be formed, leading to lattice distortion and also reducing the piezoelectric response.

[0032] An oxygen flow rate of 5 sccm to 6 sccm ensures complete oxidation of Pb, Zr, and Ti atoms while preventing over-oxidation; an inert gas flow rate of 36 sccm to 42 sccm dilutes the oxygen concentration, preventing localized oxygen excess. Ultimately, this ensures that the PZT film maintains a pure perovskite phase without the precipitation of impurity phases such as pyrochlore, providing a material basis for maximizing piezoelectric properties.

[0033] By setting the flow rates of inert gas and oxygen, the crystalline PZT film is ensured to have extremely low defect density and excellent crystal framework. This allows the subsequent rapid annealing process to focus on the activation and rearrangement of ferroelectric domains, rather than consuming thermal energy to repair inherent defects caused by improper deposition atmosphere.

[0034] Preferably, in step 1.1), the chamber of the magnetron sputtering equipment is evacuated to 1×10⁻⁶. -4 Pa-8×10 -4 Pa.

[0035] The aforementioned vacuum level effectively eliminates the erosion of the ferroelectric lattice by harmful impurities such as hydrogen, carbon, and nitrogen, eliminates the parasitic low dielectric layer at the substrate interface, and provides a clean template for the preferential orientation growth of the lattice. This enables the fabrication of dense, low-leakage, highly oriented PZT thin films with precise stoichiometry on the substrate, and is also a guarantee for achieving the desired effect of improving piezoelectric performance.

[0036] Preferably, the specific steps of step 2) are as follows: 2.1) Place the PZT film inside the furnace chamber of the rapid annealing furnace, close the furnace door, and evacuate the furnace chamber. 2.2) Oxygen is introduced into the furnace chamber of the rapid annealing furnace. While oxygen is continuously introduced into the furnace chamber, the furnace chamber is heated to a temperature greater than the Curie point of the PZT film at a set heating rate. After holding at the set temperature for a set time, the furnace chamber is allowed to cool to room temperature. Then, the PZT film is removed from the furnace chamber. During the introduction of oxygen, the mechanical pump of the rapid annealing furnace is turned on to evacuate the furnace chamber, thereby maintaining the vacuum level inside the furnace chamber.

[0037] PZT films prepared by magnetron sputtering typically exhibit significant residual stress in the deposited state (including ion bombardment stress during growth and thermal mismatch stress during cooling). These stresses forcibly stretch or compress the crystal lattice, restricting the degrees of freedom of the ferroelectric domains. When the annealing temperature exceeds the Curie point, PZT undergoes a first-order phase transition, transforming from a ferroelectric phase (tetragonal or rhombohedral, non-centrosymmetric) to a paraelectric phase (cubic, centrosymmetric). In the paraelectric state, spontaneous polarization within the unit cell disappears, and the lattice distortion previously caused by polarization is instantly released. At this point, the microscopic stress field within the PZT film undergoes complete thermal relaxation, dislocations glide, grain boundaries are adjusted, and the non-equilibrium stress accumulated during deposition is significantly eliminated. When the temperature is slowly cooled from above the Curie point back to room temperature, the PZT film undergoes a second phase transition from paraelectric to ferroelectric. At this point, ferroelectric domains re-nucleate and grow on a relatively perfect cubic lattice substrate where stress has been released. This regenerated domain structure no longer retains the stress memory from deposition but instead arranges itself optimally in three-dimensional space according to the principle of minimum energy. The reorganized domain structure exhibits higher activity and is more sensitive to external electric fields. This directly leads to a significant increase in the contribution of domain wall motion to the piezoelectric effect, thereby significantly improving the transverse piezoelectric coefficient.

[0038] Magnetron sputtered PZT thin films often generate a large number of oxygen vacancies due to oxygen deficiency. Oxygen vacancies are positively charged defects that tend to accumulate at domain walls, forming pinning centers, leading to ferroelectric fatigue and decreased piezoelectric properties. Continuously introduced oxygen provides the necessary oxidation potential to fill the oxygen vacancies in the crystal lattice, restoring the lattice's insulation and integrity. Compared to atmospheric pressure oxygen annealing, the low-pressure vacuum environment of this invention increases the mean free path of oxygen molecules, which is more conducive to the diffusion of oxygen atoms into the grain boundaries of the PZT thin film, achieving the repair of deep defects.

[0039] By rapidly annealing the PZT film obtained in step 1) which is crystallized but has high stress and many defects, step 2) results in a triple evolution of defect repair (oxygenation), stress release (phase transition), and structural remodeling (domain regeneration). This makes the final PZT film not only have a complete lattice, but also extremely active ferroelectric domains. Under the drive of an external electric field, it can generate greater lattice distortion and domain wall displacement, thereby ultimately achieving an improvement in the transverse piezoelectric coefficient.

[0040] Preferably, in step 1), the molecular formula of the lead zirconate titanate material of the PZT target is Pb. 1.1 Zr x Ti 1-x O3, and x takes values ​​from 0.48 to 0.55; In step 2.1), the furnace chamber of the rapid annealing furnace is evacuated to 10Pa-20Pa; In step 2.2), oxygen is introduced at a flow rate of 5 mL / min to 100 mL / min and maintained for 5 min to 10 min; In step 2.3), 1 o C-50 o The PZT film was heated to 500°C at a heating rate of C / s. o C-700 o C, and keep warm for 2 seconds to 2 minutes.

[0041] When Zr / Ti is around 52 / 48 (i.e.) x When the α value is approximately 0.52, the material is at a morphotropic phase boundary (MPB). x Limiting it to 0.48~0.55 is a material science prerequisite for achieving high voltage electrical performance.

[0042] Evacuating the furnace to 10-20 Pa removes impurities from the environment before introducing process gases (nitrogen / oxygen). This low-pressure environment ensures a longer mean free path for molecules. Carried by the oxygen flow, impurity atoms precipitated from the grain boundaries within the PZT film, as well as desorbed water vapor, can rapidly diffuse to the surface and be removed. This low-pressure purging mechanism ensures that the annealing process takes place in a continuously purified chemical environment.

[0043] The temperature range of 500°C to 700°C provides sufficient thermal activation energy, enabling vacancies to diffuse and recombine, and dislocations to glide and annihilate. Simultaneously, this temperature is sufficient to allow the amorphous phase at grain boundaries to fully crystallize, ensuring the density of the PZT film.

[0044] Prolonged annealing can lead to excessive grain growth. While larger grains exhibit better piezoelectricity, they also increase surface roughness, affecting the precision of subsequent photolithography processes. More seriously, prolonged high temperatures can cause significant lead volatilization. A short holding time of 2 seconds to 2 minutes precisely targets the time window between complete stress release and excessive grain coarsening / compositional decomposition. This ensures that the microstructure is frozen while phase transition and recombination are completed, preserving the mechanical integrity of the PZT film.

[0045] Combined with a low pressure of 10Pa-20Pa and an extremely low oxygen flow rate of 5mL / min-100mL / min, this ensures that oxygen flows across the wafer surface in a laminar flow manner. Laminar flow avoids the thermal inhomogeneity caused by turbulence, ensuring the annealing consistency between the center and the edges of the entire wafer.

[0046] Maintaining oxygen supply during rapid annealing ensures sufficient oxygen levels in the furnace, and the oxygen partial pressure is consistently maintained at a level sufficient to fill oxygen vacancies during heating. This in-situ dynamic oxygen replenishment mechanism allows oxygen atoms to rapidly diffuse along grain boundaries into the depths of the PZT film, repairing oxygen losses caused by sputtering, reducing leakage current density, and thus allowing for the application of higher polarization voltages to achieve greater piezoelectric deformation.

[0047] Preferably, in step 2.2), before introducing oxygen, nitrogen is introduced at a flow rate of 20 mL / min to 50 mL / min to purge the furnace for 5 min to 10 min to remove impurities in the furnace. At the same time as nitrogen is introduced, the mechanical pump of the rapid annealing furnace is turned on to evacuate the furnace, thereby maintaining the vacuum in the furnace.

[0048] During the transfer of PZT thin films from the sputtering chamber to the annealing furnace, the surface of the PZT film inevitably adsorbs water molecules, hydrocarbons, or dust from the atmosphere. During heating, these adsorbed impurities desorb thermally. If annealing is performed in a closed chamber, the desorbed water vapor and volatile organic compounds will remain inside the furnace and may react chemically with the PZT surface at high temperatures (such as carbonization or hydrogen reduction), forming a dead surface layer. The simultaneous introduction of nitrogen gas and evacuation creates a continuous, directional airflow within the furnace, rapidly entraining and expelling the desorbed impurity molecules. This ensures that the phase transformation recrystallization process takes place in a clean chemical environment, minimizing the interface defect state density and reducing the dielectric loss of the device.

[0049] Nitrogen purging, combined with continuous pumping from a mechanical pump, provides a nitrogen flow rate of 20-50 mL / min, acting as a carrier gas to rapidly entrain and expel desorbed impurities from the furnace. This process reduces the impurity concentration within the furnace, ensuring a pure oxygen + PZT system, rather than a complex oxygen + water + organic matter + PZT reaction system, when oxygen is subsequently introduced. This directly reduces the interfacial state density on the PZT film surface, minimizing leakage current channels. Under a nitrogen atmosphere, residual organic matter tends to volatilize rather than burn. After purging for 5-10 minutes to safely remove these volatiles, the atmosphere is switched to an oxidizing atmosphere (oxygen). This atmosphere-switching strategy of first using nitrogen for impurity removal and then for reactivation avoids surface oxidative shock and ensures the uniformity of the stoichiometry on the PZT film surface.

[0050] Preferably, in step 1), the substrate is ultrasonically cleaned sequentially with acetylacetone, anhydrous ethanol and deionized water. After ultrasonic cleaning, the substrate is dried with a nitrogen gas gun, and then a PZT thin film is deposited on the substrate by magnetron sputtering.

[0051] Preferably, in step 1), the substrate comprises a LaNiO3 layer, a Pt layer, a ZrO2 layer and a Si layer having a (100) crystal orientation arranged sequentially from top to bottom.

[0052] This specific multilayer composite substrate structure is not a simple stacking, but is carefully designed to maximize the piezoelectric properties of PZT thin films in conjunction with magnetron sputtering high-temperature deposition and over-Curie point vacuum annealing processes.

[0053] This invention forms a crystal structure during the deposition stage, with the LaNiO3 layer serving as the top layer in direct contact with PZT, playing a crucial seed layer role. LaNiO3 itself is a conductive perovskite oxide, and its lattice constant is extremely well-matched with PZT. Compared to growing PZT directly on a Pt layer, growing PZT on LaNiO3 significantly reduces the nucleation barrier, directly addressing the need to allow adsorbed atoms to migrate to the lattice sites with the lowest lattice potential.

[0054] Piezoelectric properties are extremely sensitive to crystal orientation. The LaNiO3 layer can induce PZT films to grow epitaxially or texturically along specific crystal orientations (such as (100)). This highly oriented crystal framework is the basis for subsequent phase and ferroelectric domain redistribution in the PZT film. If the crystal orientation is disordered, even after subsequent over-Curie annealing, the improvement of its piezoelectric coefficient will be limited.

[0055] As an oxide electrode, LaNiO3 can act as an oxygen reservoir or diffusion channel, effectively alleviating the oxygen depletion problem at the interface, thereby reducing the dead layer at the interface and improving the long-term reliability of PZT films.

[0056] This invention requires heating during deposition and annealing. The Pt layer has an extremely high melting point and oxidation resistance, enabling it to maintain excellent conductivity in these high-temperature, oxygen-rich environments without oxidation that would cause a sharp increase in resistance, thus ensuring the electrical connection performance of the device.

[0057] The dense Pt layer structure can, to a certain extent, prevent the diffusion of Pb and Ti elements from PZT into the underlying Si layer, thus preventing the formation of non-ferroelectric silicate impurities.

[0058] When the temperature exceeds 650°C, lead and titanium in PZT readily undergo severe interdiffusion with the silicon substrate, forming a dead interfacial layer with low dielectric constant, which significantly reduces the effective driving voltage. The ZrO2 layer acts as an extremely robust chemical barrier here, completely cutting off the elemental interdiffusion path between Pt / PZT and the Si substrate, ensuring the accuracy of the stoichiometry of the PZT thin film.

[0059] The coefficients of thermal expansion of PZT, Pt, and Si differ significantly. The ZrO2 layer, as an intermediate transition layer, helps to alleviate the thermal mismatch stress generated during deposition and annealing cooling, preventing cracking or peeling of the PZT film and thus ensuring the mechanical integrity of the film.

[0060] The selection of single-crystal silicon with (100) crystal orientation is not only for support, but also to influence the growth orientation of the upper PZT film through epitaxial relationship. The regular lattice of Si (100) is transferred through ZrO2 and Pt / LNO layers, which ultimately helps the PZT film to form a columnar crystal structure that is conducive to domain wall movement.

[0061] Furthermore, the use of Si(100) means that the PZT thin film preparation process is perfectly compatible with standard semiconductor CMOS processes or silicon micromachining processes (such as deep silicon etching), which facilitates large-scale mass production and device integration.

[0062] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: 1) This invention provides a method for rapidly annealing to enhance the piezoelectric properties of PZT thin films. Step 1) involves depositing a crystalline PZT thin film on a substrate heated to a set temperature, forming a crystalline structure. Step 2) involves annealing the PZT thin film above its Curie point temperature. This differs significantly from the traditional room-temperature deposition of amorphous thin films, where subsequent high-temperature annealing causes crystallization. In step 1), the high-temperature deposition on the substrate ensures sufficient surface migration energy for sputtered particles reaching the substrate surface, resulting in a dense crystalline structure through layered or island-like growth. In contrast, the traditional post-annealing process for amorphous thin films, during the amorphous-to-crystalline transformation, experiences significant volume shrinkage, easily leading to voids and microcracks at grain boundaries. The method of this invention ensures that the PZT film already has a dense and crack-free microstructure before entering the annealing process in step 2). The annealing in step 2) no longer undertakes the heavy task of nucleation and crystallization, but focuses on defect repair, phase and ferroelectric domain structure optimization, which greatly improves the transverse piezoelectric coefficient of the PZT film, reduces the risk of PZT film breakdown and leakage, and significantly improves the electrical reliability and withstand voltage performance of MEMS devices.

[0063] 2) The present invention provides a method for rapidly annealing to enhance the piezoelectric properties of PZT thin films. This method employs an annealing temperature higher than the Curie point of the PZT thin film. Above the Curie point, the PZT material undergoes a phase transition from a ferroelectric phase (tetragonal or rhombohedral phase) to a paraelectric phase (cubic phase). At this time, the crystal structure transforms into a highly symmetrical cubic structure, and the enormous growth stress and thermal mismatch stress accumulated within the PZT thin film during deposition are greatly released and relaxed. When the temperature decreases from above the Curie point, the PZT thin film undergoes a re-phase transition from the paraelectric to the ferroelectric phase. Because this process is carried out in a rapid annealing furnace and the stress has been released, the newly generated ferroelectric domains can be rearranged and distributed according to the principle of minimum energy. 2 This thermal reset mechanism effectively activates the domain wall mobility, so that the piezoelectric response of PZT films no longer depends solely on the intrinsic contribution of lattice distortion, but also significantly enhances the extrinsic contribution dominated by domain wall motion.

[0064] 3) The present invention provides a method for rapidly enhancing the piezoelectric properties of PZT thin films through annealing at temperatures above the Curie point. This method induces a redistribution of phases and ferroelectric domains, not just a single-directional orientation optimization, but a three-dimensional domain structure optimization. In MEMS applications, PZT typically operates near the quasi-isomorphic phase boundary (MPB), where tetragonal and rhombohedral phases coexist. The present invention promotes the uniform distribution and dynamic equilibrium of the two phases near the MPB through the high-temperature phase transition process during the annealing stage. This makes it easier for the polarization vector to rotate under the influence of an external electric field, thereby improving the lateral piezoelectric coefficient.

[0065] 4) The present invention provides a method for rapidly annealing to enhance the piezoelectric properties of PZT thin films. This method employs a rapid annealing furnace combined with a vacuum environment, effectively balancing the contradiction between providing sufficient heat energy to reorganize the domain structure and preventing excessive volatilization of lead. This precise heat treatment window ensures that the PZT thin film maintains an ideal perovskite stoichiometry, avoiding the precipitation of non-ferroelectric phases.

[0066] 5) The present invention provides a method for rapidly annealing to enhance the piezoelectric properties of PZT thin films. Annealing is performed at temperatures above the Curie point, providing sufficient thermal activation energy. This thermal energy not only facilitates phase transition but also promotes the diffusion and recombination of interstitial atoms and vacancies, effectively addressing microscopic damage generated during magnetron sputtering. After rapid annealing, the lattice quality of the PZT thin film is significantly improved, manifested as increased X-ray diffraction (XRD) peak intensity and decreased full width at half maximum (FWHM). Macroscopically, this directly translates to a reduction in leakage current density and an increase in breakdown field strength, enabling the PZT thin film to withstand higher driving voltages and thus output greater piezoelectric force.

[0067] 6) This invention provides a method for rapidly enhancing the piezoelectric properties of PZT thin films through annealing. This method is based on the deep integration of ferroelectric physics principles (phase transition, domain wall motion) and PZT thin film growth kinetics (nucleation, stress relaxation). It successfully overcomes the common industry challenges of limited optimization of the lateral piezoelectric coefficient of PZT thin films and severe substrate constraint through the synergistic effects of in-situ high-temperature deposition to lock in a dense crystal structure, over-Curie point vacuum annealing to reshape the phase and ferroelectric domains, and stress release. This method not only significantly improves the lateral piezoelectric properties of PZT thin films but also ensures process stability, reliability, and mass production feasibility, providing a solid technical foundation for the large-scale commercial application of high-performance piezoelectric MEMS devices. Attached Figure Description

[0068] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a schematic diagram of PZT thin film being tested on a cantilever beam structure using a laser Doppler vibration meter. Figure 3 A schematic diagram of electric field strength versus tip displacement obtained for testing the PZT thin film of Comparative Example 1. Figure 4 A schematic diagram of electric field strength versus tip displacement obtained from the PZT thin film of Example 1; Figure 5 A schematic diagram of electric field strength versus tip displacement obtained for testing the PZT thin film in Example 2. Detailed Implementation

[0069] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0070] Example 1 A method for rapidly annealing to enhance the piezoelectric properties of PZT thin films, characterized by comprising the following steps: 1) The substrate is ultrasonically cleaned sequentially with acetylacetone, anhydrous ethanol, and deionized water. After ultrasonic cleaning, the substrate is dried with a nitrogen gas gun. The substrate includes a LaNiO3 layer, a Pt layer, a ZrO2 layer, and a Si layer with a (100) crystal orientation arranged sequentially from top to bottom. The substrate is then placed in the sputtering chamber of a magnetron sputtering equipment. Under the vacuum environment of the sputtering chamber, a PZT target is deposited on the substrate heated to a set temperature using magnetron sputtering technology. The PZT film crystallizes directly during deposition to form a crystal structure. The specific steps are as follows: 1.1) Place the substrate in the sputtering chamber of the magnetron sputtering equipment, with the substrate positioned below the PZT target, and evacuate the sputtering chamber to 1×10⁻⁶. -4 Pa; the molecular formula of the lead zirconate titanate material of the PZT target is Pb. 1.1 Zr x Ti 1-x O3, and the value of x is 0.52; 1.2) The substrate is heated to a set temperature using the heating stage of a magnetron sputtering apparatus; wherein, the substrate is heated to 500°C. o C; 1.3) Open the inlet valve of the magnetron sputtering equipment to allow the process gas to flow into the sputtering chamber and ensure that the pressure in the sputtering chamber is 1 Pa; wherein, the process gas is a mixture of inert gas and oxygen; wherein, the flow rate of the inert gas is 40 sccm and the flow rate of the oxygen is 5 sccm. 1.4) A PZT thin film is deposited on a substrate that has been heated to a set temperature. After a set time for the PZT thin film to form a crystalline structure, the heating stage stops heating and the air inlet valve is closed. After the substrate cools down, the substrate and the PZT thin film on the substrate are removed. The magnetron sputtering power is 300W, the deposition time is 2h, and the thickness of the obtained PZT thin film is 2μm. 2) After removing the PZT thin film from the sputtering chamber of the magnetron sputtering equipment, place it into the furnace chamber of a rapid annealing furnace. Evacuate the furnace chamber to allow the PZT thin film to anneal in a vacuum environment and then cool with the furnace. The annealing temperature is higher than the Curie point of the PZT thin film to achieve phase structure reconstruction and ferroelectric domain reorientation, thereby improving the transverse piezoelectric coefficient of the PZT thin film. The specific steps are as follows: 2.1) Place the PZT film inside the furnace chamber of the rapid annealing furnace, close the furnace door, and evacuate the furnace chamber; wherein, the furnace chamber of the rapid annealing furnace is evacuated to 15 Pa; 2.2) First, purge the furnace with nitrogen at a flow rate of 20 mL / min for 10 min to remove impurities. Then, purge with oxygen at a flow rate of 5 mL / min for 10 min. While the oxygen is continuously introduced into the furnace, the furnace is heated at a set rate to a temperature higher than the Curie point of the PZT film. After holding at this temperature for a set time, the furnace is allowed to cool to room temperature. Then, the PZT film is removed from the furnace. During the introduction of nitrogen and oxygen, the mechanical pump of the rapid annealing furnace is activated to evacuate the furnace, thereby maintaining a vacuum within the furnace. o The PZT film was heated to 600°C at a heating rate of C / s. o C, and keep warm for 2 seconds.

[0071] Example 2 A method for rapidly annealing to enhance the piezoelectric properties of PZT thin films, characterized by comprising the following steps: 1) The substrate is ultrasonically cleaned sequentially with acetylacetone, anhydrous ethanol, and deionized water. After ultrasonic cleaning, the substrate is dried with a nitrogen gas gun. The substrate includes a LaNiO3 layer, a Pt layer, a ZrO2 layer, and a Si layer with a (100) crystal orientation arranged sequentially from top to bottom. The substrate is then placed in the sputtering chamber of a magnetron sputtering equipment. Under the vacuum environment of the sputtering chamber, a PZT target is deposited on the substrate heated to a set temperature using magnetron sputtering technology. The PZT film crystallizes directly during deposition to form a crystal structure. The specific steps are as follows: 1.1) Place the substrate in the sputtering chamber of the magnetron sputtering equipment, with the substrate positioned below the PZT target, and evacuate the sputtering chamber to 8 × 10⁻⁶. -4 Pa; the molecular formula of the lead zirconate titanate material of the PZT target is Pb. 1.1 Zr x Ti 1-x O3, and the value of x is 0.48; 1.2) The substrate is heated to a set temperature using the heating stage of a magnetron sputtering apparatus; wherein, the substrate is heated to 650°C. o C; 1.3) Open the inlet valve of the magnetron sputtering equipment to allow the process gas to flow into the sputtering chamber and ensure that the pressure in the sputtering chamber is 0.5 Pa; wherein the process gas is a mixture of inert gas and oxygen; wherein the flow rate of the inert gas is 42 sccm and the flow rate of the oxygen is 6 sccm. 1.4) A PZT thin film is deposited on a substrate heated to a set temperature. After a set time for the PZT thin film to form a crystalline structure, the heating stage is stopped and the inlet valve is closed. After the substrate cools down, the substrate and the PZT thin film on the substrate are removed. The magnetron sputtering power is 200W, the deposition time is 1.5h, and the thickness of the obtained PZT thin film is 1.5μm. 2) After removing the PZT thin film from the sputtering chamber of the magnetron sputtering equipment, place it into the furnace chamber of a rapid annealing furnace. Evacuate the furnace chamber to allow the PZT thin film to anneal in a vacuum environment and then cool with the furnace. The annealing temperature is higher than the Curie point of the PZT thin film to achieve phase structure reconstruction and ferroelectric domain reorientation, thereby improving the transverse piezoelectric coefficient of the PZT thin film. The specific steps are as follows: 2.1) Place the PZT film inside the furnace chamber of the rapid annealing furnace, close the furnace door, and evacuate the furnace chamber; wherein, the furnace chamber of the rapid annealing furnace is evacuated to 10 Pa; 2.2) First, purge the furnace with nitrogen at a flow rate of 50 mL / min for 5 minutes to remove impurities. Then, purge with oxygen at a flow rate of 100 mL / min for 5 minutes. While the oxygen is continuously introduced into the furnace, the furnace is heated at a set rate to a temperature higher than the Curie point of the PZT film. After holding at this temperature for a set time, the furnace is allowed to cool to room temperature. The PZT film is then removed from the furnace. During the introduction of nitrogen and oxygen, the mechanical pump of the rapid annealing furnace is activated to evacuate the furnace, thereby maintaining a vacuum within the furnace. The oxygen flow rate is 30 mL / min. o The PZT film was heated to 700°C at a heating rate of C / s. o C, and keep warm for 30 seconds.

[0072] Example 3 A method for rapidly annealing to enhance the piezoelectric properties of PZT thin films, characterized by comprising the following steps: 1) The substrate is ultrasonically cleaned sequentially with acetylacetone, anhydrous ethanol, and deionized water. After ultrasonic cleaning, the substrate is dried with a nitrogen gas gun. The substrate includes a LaNiO3 layer, a Pt layer, a ZrO2 layer, and a Si layer with a (100) crystal orientation arranged sequentially from top to bottom. The substrate is then placed in the sputtering chamber of a magnetron sputtering equipment. Under the vacuum environment of the sputtering chamber, a PZT target is deposited on the substrate heated to a set temperature using magnetron sputtering technology. The PZT film crystallizes directly during deposition to form a crystal structure. The specific steps are as follows: 1.1) Place the substrate in the sputtering chamber of the magnetron sputtering equipment, with the substrate positioned below the PZT target, and evacuate the sputtering chamber to a vacuum level of 4 × 10⁻⁶. -4 Pa; the molecular formula of the lead zirconate titanate material of the PZT target is Pb. 1.1 Zr x Ti 1-x O3, and the value of x is 0.55; 1.2) The substrate is heated to a set temperature using the heating stage of a magnetron sputtering apparatus; wherein, the substrate is heated to 550°C. o C; 1.3) Open the inlet valve of the magnetron sputtering equipment to allow the process gas to flow into the sputtering chamber and ensure that the pressure in the sputtering chamber is 0.8 Pa; wherein the process gas is a mixture of inert gas and oxygen; wherein the flow rate of the inert gas is 36 sccm and the flow rate of the oxygen is 5.2 sccm. 1.4) A PZT thin film was deposited on a substrate heated to a set temperature. After a set time for the PZT thin film to form a crystalline structure, the heating stage was stopped and the inlet valve was closed. After the substrate cooled down, the substrate and the PZT thin film on the substrate were removed. The magnetron sputtering power was 240W, the deposition time was 1.7h, and the thickness of the obtained PZT thin film was 1.8μm. 2) After removing the PZT thin film from the sputtering chamber of the magnetron sputtering equipment, place it into the furnace chamber of a rapid annealing furnace. Evacuate the furnace chamber to allow the PZT thin film to anneal in a vacuum environment and then cool with the furnace. The annealing temperature is higher than the Curie point of the PZT thin film to achieve phase structure reconstruction and ferroelectric domain reorientation, thereby improving the transverse piezoelectric coefficient of the PZT thin film. The specific steps are as follows: 2.1) Place the PZT film inside the furnace chamber of the rapid annealing furnace, close the furnace door, and evacuate the furnace chamber; wherein, the furnace chamber of the rapid annealing furnace is evacuated to 20 Pa; 2.2) First, purge the furnace with nitrogen at a flow rate of 30 mL / min for 8 minutes to remove impurities. Then, purge with oxygen at a flow rate of 60 mL / min for 8 minutes. While the oxygen is continuously introduced into the furnace, the furnace is heated at a set rate to a temperature higher than the Curie point of the PZT film. After holding at this temperature for a set time, the furnace is allowed to cool to room temperature. The PZT film is then removed from the furnace. During the introduction of nitrogen and oxygen, the mechanical pump of the rapid annealing furnace is activated to evacuate the furnace, thereby maintaining a vacuum within the furnace. The flow rate is 50 mL / min. o The PZT film was heated to 500°C at a heating rate of C / s. o C, and keep warm for 2 minutes.

[0073] Comparative Example A method for rapidly annealing to enhance the piezoelectric properties of PZT thin films, characterized by comprising the following steps: 1) The substrate is ultrasonically cleaned sequentially with acetylacetone, anhydrous ethanol, and deionized water. After ultrasonic cleaning, the substrate is dried with a nitrogen gas gun. The substrate includes a LaNiO3 layer, a Pt layer, a ZrO2 layer, and a Si layer with a (100) crystal orientation arranged sequentially from top to bottom. The substrate is then placed in the sputtering chamber of a magnetron sputtering equipment. Under the vacuum environment of the sputtering chamber, a PZT target is deposited on the substrate heated to a set temperature using magnetron sputtering technology. The PZT film crystallizes directly during deposition to form a crystal structure. The specific steps are as follows: 1.1) Place the substrate in the sputtering chamber of the magnetron sputtering equipment, with the substrate positioned below the PZT target, and evacuate the sputtering chamber to 1×10⁻⁶. -4 Pa; the molecular formula of the lead zirconate titanate material of the PZT target is Pb.1.1 Zr x Ti 1-x O3, and the value of x is 0.52; 1.2) The substrate is heated to a set temperature using the heating stage of a magnetron sputtering apparatus; wherein, the substrate is heated to 500°C. o C; 1.3) Open the inlet valve of the magnetron sputtering equipment to allow the process gas to flow into the sputtering chamber and ensure that the pressure in the sputtering chamber is 1 Pa; wherein, the process gas is a mixture of inert gas and oxygen; wherein, the flow rate of the inert gas is 40 sccm and the flow rate of the oxygen is 5 sccm. 1.4) A PZT thin film is deposited on a substrate that has been heated to the set temperature. After a set time for the PZT thin film to form a crystalline structure, the heating stage stops heating and the air inlet valve is closed. After the substrate cools down, the substrate and the PZT thin film on the substrate are removed. The magnetron sputtering power is 300W, the deposition time is 2h, and the thickness of the obtained PZT thin film is 2μm.

[0074] Therefore, compared to Example 1, the rapid annealing step in step 2) was omitted in the comparative example.

[0075] The transverse piezoelectric coefficients of the PZT thin films obtained in Examples 1, 2, and the comparative example were measured using a laser Doppler vibrometer. (See [reference needed]). Figure 2 This is a schematic diagram of the PZT thin film 2 being tested on a cantilever beam structure of a laser Doppler vibrometer. The cantilever beam structure includes a lower electrode 1, a PZT thin film 2, an upper electrode 3, and a laser reflection region 4. x 1 represents the length of the upper electrode. x 2 represents the distance between the end of the upper electrode furthest from the laser reflection area and the center of the laser reflection area. x 3 represents the total length of the cantilever end of the cantilever beam (which is also the distance between the end of the upper electrode away from the laser reflection zone and the end of the cantilever beam away from the lower electrode). w 1 represents the width of the upper electrode. w 2 represents the width of the cantilever beam.

[0076] Transverse piezoelectric coefficient e 31 The calculation formula is as follows: ; Note: E is the Young's modulus of the substrate (Si) (E=130GPa in actual testing), ν is the Poisson's ratio of the substrate (v=0.278 in actual testing), t is the thickness of the cantilever beam (t=525μm in actual testing), δ is the tip displacement, V is the voltage, and V = electric field strength × thickness of the PZT film.

[0077] according to Figures 3-5 The electric field intensity-tip displacement diagram, combined with the transverse piezoelectric coefficient e31 The calculation formula can be used to obtain the transverse piezoelectric coefficients of Examples 1, 2 and the comparative examples, as shown in Table 1.

[0078] Table 1 Transverse piezoelectric coefficients of each sample The superior performance of Examples 1 and 2 compared to the comparative example is due to the introduction of a vacuum annealing process above the Curie point (step 2) in Examples 1 and 2. The main reasons for the improvement are as follows: Complete release of residual stress: Magnetron sputtered deposited films (such as the comparative example) exhibit significant growth stress and thermal mismatch stress, which pin ferroelectric domains and restrict their movement under an external field. When the annealing temperature exceeds the Curie point, PZT transforms from a ferroelectric phase to a paraelectric cubic phase, spontaneous polarization disappears, and stress is thermally relaxed and released, breaking the constraint on the domain walls. During the furnace cooling process, the film undergoes a phase transition again due to the thermal reset and reorientation of the ferroelectric domains. Since the stress has been released, the newly generated ferroelectric domains are optimally distributed in three-dimensional space according to the principle of minimum energy. The resulting domain structure no longer has stress memory but is in an extremely active state. This mechanism activates domain wall movement, significantly increasing the "extrinsic contribution" dominated by domain wall movement in the piezoelectric response, in addition to the "intrinsic contribution" of lattice distortion. This is macroscopically manifested as a significant increase in the displacement peak of the butterfly curve. Defect repair combined with a vacuum environment that enhances insulation and allows for continuous oxygen supply effectively repairs oxygen vacancy defects generated during the sputtering process, reducing leakage current. This enables the thin film to withstand higher driving voltages without breakdown, further unlocking its piezoelectric potential.

[0079] The improved lateral piezoelectric coefficient performance of Examples 1 and 2 compared to the comparative example is a result of the synergistic effect of the high-quality in-situ crystalline framework in step 1) and the domain reshaping through over-Curie point annealing in step 2). This process successfully solves the industry challenge of severe substrate constraint and difficulty in optimizing the lateral piezoelectric coefficient of magnetron sputtered PZT films.

[0080] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for rapidly annealing to enhance the piezoelectric properties of PZT thin films, characterized in that, Includes the following steps: 1) In the vacuum environment of the sputtering chamber of the magnetron sputtering equipment, PZT target material is deposited on a substrate heated to a set temperature by magnetron sputtering technology, so that the PZT film crystallizes directly during deposition to form a crystal structure. 2) After removing the PZT thin film from the sputtering chamber of the magnetron sputtering equipment in step 1), place it into the furnace chamber of the rapid annealing furnace. Evacuate the furnace chamber of the rapid annealing furnace to allow the PZT thin film to anneal in a vacuum environment and then cool with the furnace. The annealing temperature is higher than the Curie point of the PZT thin film to achieve phase structure reconstruction and ferroelectric domain reorientation of the PZT thin film, thereby improving the transverse piezoelectric coefficient of the PZT thin film.

2. The method for rapidly annealing to enhance the piezoelectric properties of PZT thin films according to claim 1, characterized in that, The specific steps for step 1) are as follows: 1.1) Place the substrate in the sputtering chamber of the magnetron sputtering equipment and position the substrate below the PZT target, then evacuate the sputtering chamber; 1.2) The substrate is heated to the set temperature using the heating stage of a magnetron sputtering device; 1.3) Open the inlet valve of the magnetron sputtering equipment to allow the process gas to flow into the sputtering chamber, and ensure that the pressure in the sputtering chamber is 0.5 Pa - 1 Pa; wherein, the process gas is a mixture of inert gas and oxygen; 1.4) Deposit a PZT thin film on the substrate that has been heated to the set temperature. After a set time for the PZT thin film to become a crystal structure, stop heating on the heating stage and close the air inlet valve. After waiting for the substrate to cool down, remove the substrate and the PZT thin film on the substrate.

3. The method for rapidly annealing to enhance the piezoelectric properties of PZT thin films according to claim 2, characterized in that, In step 1.1), the molecular formula of the lead zirconate titanate material of the PZT target is Pb. 1.1 Zr x Ti 1-x O3, and x takes values ​​from 0.48 to 0.55; In step 1.2), the substrate is heated to 500°C. o C-650 o C; In step 1.4), the magnetron sputtering power is 200W-300W, the deposition time is 1.5h-2h, and the thickness of the obtained PZT film is 1.5μm-2μm.

4. The method for rapidly annealing to enhance the piezoelectric properties of PZT thin films according to claim 2, characterized in that, In step 1.3), the flow rate of the inert gas is 36 sccm to 42 sccm, and the flow rate of the oxygen is 5 sccm to 6 sccm.

5. The method for rapidly annealing to enhance the piezoelectric properties of PZT thin films according to claim 1, characterized in that, In step 1.1), the chamber of the magnetron sputtering equipment is evacuated to 1×10⁻⁶. -4 Pa-8×10 -4 Pa.

6. The method for rapidly annealing to enhance the piezoelectric properties of PZT thin films according to claim 1, characterized in that, The specific steps for step 2) are as follows: 2.1) Place the PZT film inside the furnace chamber of the rapid annealing furnace, close the furnace door, and evacuate the furnace chamber. 2.2) Oxygen is introduced into the furnace chamber of the rapid annealing furnace. While oxygen is continuously introduced into the furnace chamber, the furnace chamber is heated to a temperature greater than the Curie point of the PZT film at a set heating rate. After holding at the set temperature for a set time, the furnace chamber is allowed to cool to room temperature. Then, the PZT film is removed from the furnace chamber. During the introduction of oxygen, the mechanical pump of the rapid annealing furnace is turned on to evacuate the furnace chamber, thereby maintaining the vacuum level inside the furnace chamber.

7. The method for rapidly annealing to enhance the piezoelectric properties of PZT thin films according to claim 6, characterized in that, The molecular formula of the lead zirconate titanate material of the PZT target is Pb. 1.1 Zr x Ti 1-x O3, and x takes values ​​from 0.48 to 0.55; In step 2.1), the furnace chamber of the rapid annealing furnace is evacuated to 10Pa-20Pa; In step 2.2), oxygen is introduced at a flow rate of 5 mL / min-100 mL / min and maintained for 5 min-10 min, while at 1 o C-50 o The PZT film was heated to 500°C at a heating rate of C / s. o C-700 o C, and keep warm for 2 seconds to 2 minutes.

8. The method for rapidly annealing to enhance the piezoelectric properties of PZT thin films according to claim 7, characterized in that, In step 2.2), before introducing oxygen, nitrogen is introduced at a flow rate of 20 mL / min-50 mL / min to purge the furnace for 5 min-10 min to remove impurities in the furnace. At the same time as nitrogen is introduced, the mechanical pump of the rapid annealing furnace is turned on to evacuate the furnace, thereby maintaining the vacuum in the furnace.

9. The method for rapidly annealing to enhance the piezoelectric properties of PZT thin films according to claim 1, characterized in that, In step 1), the substrate is ultrasonically cleaned sequentially with acetylacetone, anhydrous ethanol and deionized water. After ultrasonic cleaning, the substrate is dried with a nitrogen gas gun, and then a PZT thin film is deposited on the substrate by magnetron sputtering.

10. The method for rapidly annealing to enhance the piezoelectric properties of PZT thin films according to claim 1, characterized in that, In step 1), the substrate includes a LaNiO3 layer, a Pt layer, a ZrO2 layer and a Si layer with a (100) crystal orientation arranged sequentially from top to bottom.

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