Structure, properties and application of HfO2-based piezoelectric films

Abstract

Recently metal element doped HfO2 ultrathin films, i.e. Hf1-xAxO2 (A= Zr, Si, La, Y, Sr, Al, Ta et al), have garnered significant attention in the pursuit of developing ferroelectric memory. The Hf1-xAxO2 ferroelectric films also exhibit strong piezoelectricity, with direct piezoelectric coefficients (d33) exceeding 37 pC/N. Moreover, epitaxial strain and polarization switching can modulate the converse piezoelectric coefficient (d33*) from positive to negative values. By utilizing Hf1-xAxO2 piezoelectric films, a wide variety of actuators, resonators, sensors, and other energy conversion devices can be manufactured. Importantly, high-quality, large-size Hf1-xAxO2 films can be grown using Atomic Layer Deposition (ALD) with an anneal temperature of ≤500 ℃, which aligns with MEMS fabrication technology at the level of the CMOS backend-of-line (BEOL). Integrating MEMS/NEMS devices with CMOS chips can significantly improve the speed of operation and data collection, opening new possibilities for advanced electronic systems in future.