Existing process technologies for integration of piezoelectric thin films into microsystems have been limited in various ways, including low piezoelectric coupling, limited maximum film thickness, low repeatability, and high-temperature processing. As an alternative, we introduced a new CMOS-compatible microfabrication technology, which allows wafer-level integration of bulk piezoelectric ceramics on silicon while preserving their original ferroelectric and piezoelectric properties. The developed processes include low-temperature gold-indium diffusion bonding of a bulk PZT or PMN-PT substrate on silicon, an enhanced lapping/polishing process to obtain a final film thickness of 5-100 μm with high precision and wafer-level uniformity (±0.5 μm), and various PZT thin/thick film patterning processes by wet-etching, dry-etching, and femto/nano-second laser ablation. This process is also extended to realize a stack of piezoelectric thin films, and suspended structures via surface micromachining. Currently, the introduced technology can provide the highest electromechanical coupling (kij2) and piezoelectric strain coefficient (dij) among other thin-film deposition methods.
E. E. Aktakka, R. L. Peterson, K. Najafi, “Wafer-level integration of high-quality bulk piezoelectric ceramics on silicon” IEEE Transactions on Electron Devices, vol. 60, pp. 2022-2030, 2013.
E. E. Aktakka, R. L. Peterson, K. Najafi, “Wet-etching and uniform wafer-level thinning of bulk piezoelectric ceramics on silicon”, Solid- State Sensors, Actuators, and Microsystems Workshop (Hilton Head 2012), Hilton Head Island, USA, pp. 256-257, June 2012.