A Fully MEMS-Compatible Process for Ultra-Thin Piezoelectric Actuators with Good Uniformity and High Coupling Efficiency

This paper presents a fully MEMS-compatible process for ultra-thin (≤500μm) multilayer piezoelectric actuators, which is attractive for high-integration applications such as micro-speakers, printing nozzles, and micro fluidic chips. The temporary bonding and parylene wafer bonding processes were used to enable easy assembly and individual optimization of piezoelectric vibrators and multilayered patterned substrates. This approach provides considerable design flexibility, allowing high-quality piezoelectric films, thinner actuators, and substrates with intricate patterns, such as acoustic holes or microchannels. PZT thin film was chosen due to its high piezoelectric constant e31. Using the Cr/Au top electrode and dense Al2O3 protective layer, PZT is protected from oxygen vacancies caused by top electrode oxidation and hydrogen-rich polymer. Experimental results show that the polarization of PZT preserved 94.27% of the initial value, and the demonstrated device has a higher uniformity (resonance frequency variation equals 0.576%) and a larger actuation amplitude (IOμm at ±4.5V AC) compared to unbonded or die-bonded devices.