Study Of PZT Piezoelectricity Thick Film And PZT Piezoelectric Cantilever On Silicon Substrates For MEMS Application

The materials that the new and advantage performance MEMS devices constitute require high reliability with the structures and properties. That is reason why the piezoelectric PZT thin films have paid much more attentions in MEMS applications is those excellent properties for their dielectric, ferroelectric and piezoelectric. In this thesis, the piezoelectric PZT thick films with different thicknesses were prepared on Au/Cr/SiO₂/Si substrates by a sol-gel technique and the max thickness obtained is about 4μm. The silicon micro-cantilevers based on the PZT/Au/Cr/SiO₂/Si multilayer structures were fabricated through semiconductor min-machining process. The cantilevers fabricated processing and microstructures of the PZT thick films were investigated systematically, and their relationships between dielectric, ferroelectric and piezoelectric properties were confirmed. The fabrication processes of PZT films, the optimizing design for silicon-based PZT thick film and compatible processes of cantilevers with PZT thick films were investigated experimentally and theoretically.An improved method have been gained by ameliorate traditional Sol-Gel process, i.e., 0-3 mixing method, which is to prepare PZT ferroelectric membrane on Au/Ti/SiO₂/Si substrates. In this processes, zero-dimensional PZT nano-powder was firstly mixed with three-dimensional PZT precursory solution. Then the uniform and stable slurry was formed on Au/Cr/SiO₂/Si substrates by a spinning technique. If the films were fabricated by slurry directly, the surfaces will appeared roughly, and it is disadvantage to the MEMS device fabricating. So we presented a method that PZT Sol-Gel and the slurry mixed PZT powder were coated on the membrane alternately, and poly vinylpyrrolidine was simultaneously added. The thickness of the membrane was up to 4μm and no crackle was found in its surface. The thickness could be increased by the repetitious process, which overcomes the limit of membrane thickness and enhance the quality of the surface. The relationships of dielectric, ferroelectric and piezoelectric properties between the thicknesses of films were given by process studied systematically. The maximal piezoelectric constant d₃₃ of the films was 201pC/N that obtained by the cantilever beam load method, the maximal volume density was 4.31g/cm³ tested by buoyancy method, and the maximal dielectric constant was 808. The remanent polarization Pr and the coercive field Ec of PZT thick films were up to 60μC/cm² and 23kV/cm at 25V respectively. The above results demonstrate that the silicon-based PZT thick films have been provided with piezoelectric, ferroelectric and dielectric capacities property well.The expression of the resonance frequency and deflection displacement micro-cantilever were deduced systematically according piezoelectricity equation. The software Intellisuite was used to optimize the driving structure of the silicon-based PZT thick films. The factors influenced on the displacement and frequency characteristics of the cantilever, such as the thicknesses of PZT films and silicon films, length of cantilever, input voltage and so on, were also analyzed in order to determine the optimal structures of cantilever. The structure parameters of simulation provided important function on the micro-actuators fabricating.The new structure of PZT piezoelectric cantilever was fabricated by an improved Sol-Gel method and the MEMS technique including thermal oxidation, optical lithography and hydro-etching. Thus the problem of compatibility between piezoelectric thick films driving and MEMS processes was resolved.In addition, the characteristics of PZT piezoelectric cantilever were tested. The relationships between dynamic deflection displacement and resonance frequencies were measured by non-touch optical methods, and resonant frequency of PZT piezoelectric cantilever was also determined.