Dense PZT thick films derived from sol-gel based nanocomposite process

Dense, crack-free piezoelectric thick film integrated on silicon substrate has been the subject of considerable attention in recent years for potential application in microelectro mechanical systems (MEMS). We have proposed a new spin-coating route for this purpose in which films are made from homogenous slurry of sol-gel precursor and nano-sized powders. Commercially available ceramic PZT (53/47: Zr/Ti) powders are ball milled into different particle sizes by a higher energy planetary ball mill machine and uniformly dispersed into, with a selected dispersant, a PZT sol-gel solution identical with the powders in composition. The well-prepared resulting slurry looks like paint and was spin deposited onto a silicon wafer, fired, and annealed in the same manner as conventional sol-gel process. Films with several tens micron in thickness on platinum coated silicon can be fabricated with this route. The microstructure, crystallization process and the ferroelectric properties of the film have been investigated. It is revealed that the success of this route is due to the elimination of the agglomeration among the nano-sized particles. The smaller the particle, the more uniform the microstructure. The film derived from micron-sized particles has the porous structure with average pore size of sub-micron. For the films derived from nano-sized particles, the nanocrystalline structure is obtained at sintering temperature of 600-700 °C and fully developed submicron-sized grains have been demonstrated at sintering temperature of 700-800 °C. Such made thick film has comparative ferroelectric properties with respect to bulk PZT ceramic.