Piezoelectric PZT thick films: preparation and devices
Piezoelectric ceramic such as PZT thick films (10 to 100mm thick) can be widely used in microelectromechanical systems (MEMS), inkjet printers, and high frequency transducers. However, it is difficult to fabricate patterned PZT films in such thickness range. This is because, the traditional thin film processes, such as sol-gel processing and sputtering, can only fabricate films with thickness up to 10 mm. The traditional thick film processes, such as screen printing, can produce thick films only on the substrates which can withstand higher than 1100°C temperatures because the screen printed films, which usually use solid state powders, need to be sintered at above 1100°C for densification. In this talk we will present a new process, which is named as SPLAT – Screen Printing with Laser Assisted Transfer, to fabricate high quality, patterned PZT thick films on almost any substrates, including Si wafers with integrated circuits, metals, and plastics. PZT thick film elements will be first screen printed on a sapphire substrate and sintered at 1100 to 1350°C. Then the PZT elements will be bonded to the target substrate and will be released from the sapphire substrate by decomposing a thin surface layer of the PZT with an excimer laser from the backside of the sapphire substrate. The PZT elements are thereby transferred to the target substrate. We have also developed a new bonding method which uses a very thin and high strength bonding layer, thus the mechanical damping or absorption of the bonding layer can be neglected, and a dry tape polishing process which can homogenize the thickness of the PZT elements within about 1 mm range and without wearing the edges of the element. The SPLAT process is a clean and low-temperature process for the target substrate, and fully compatible with silicon microelectronics. We have demonstrated that bonding the PZT elements to a CMOS Si wafer and doing laser transfer will not affect the CMOS circuit. Bimorph, multilayer and other useful devices can also be developed using the SPLAT process. In particular, we will demonstrate a large area, flexible and smart piezoelectric tape, which consists of many PZT thick film elements sandwiched between two flexible tapes or foils. The PZT tape can be easily surface mounted to a curved structure or embedded in a structure which needs to be flexible, hence it can be widely used in many smart systems. The PZT elements in the tape can also work as sensors, actuators and transducers, thus itself is a smart panel or a smart skin.
Xu, B. ; Buhler, S. ; Weisberg, M. ; Wong, W. S. ; Fitch, J. ; Littau, K. Piezoelectric PZT thick films: preparation and devices. 2003 US Navy Workshop on Acoustic Transduction Materials and Devices; 2003 May 6-8; State College; PA.