Room Temperature Direct Writing of Ultrathin Zinc Oxide Piezoelectric Films Via Near-Field Electrohydrodynamic Jetting for High-Frequency Flexible Electronics

© 2019 IEEE.Using near-field electrohydrodynamic deposition (NFEHD) at atmospheric pressure and room temperature, we demonstrate, for the first time, ultrathin ceramic piezoelectric films that are capable of GHz level actuation. Through optimization of the zinc oxide (ZnO) nanoparticle printable feedstock and the deposition parameters, uniform, continuous traces as narrow as 198 ¿m and as thin as 128 nm were created on rigid and flexible substrates. The net orientation of the imprint's polar axis in the direction parallel to the substrate, i.e., the [100] direction, is augmented by increasing the charge density of the jet and the rastering speed of the nozzle, achieving ~10 GHz laterally excited resonators and ~5 GHz thickness-excited resonators; the estimated acoustic speed for the later resonator (i.e., ~2,000 m/s) is close to the velocity of transverse waves in ZnO. Our novel technology makes possible to additively manufacture high-frequency piezoelectric devices in low-temperature, e.g., flexible, substrates.