Toward low-temperature processing of lead zirconate titanate thin films: Advances, strategies, and applications

Lead zirconate titanate (PZT) thin films stand for a prominent technological brick in the field of microsystems. The recent improvements of their manufacturability combined with excellent piezoelectric properties have enabled their introduction in industrial clean rooms all around the world. These films require annealing temperatures beyond 600 °C to crystallize in the desired perovskite phase, which exhibits outstanding piezoelectric coefficients. This temperature requirement forbids large application fields such as flexible electronics, smart glass but also system-on-chip approaches. Decreasing the annealing temperature of PZT films would therefore spread further their potential usage to other applications. The purpose of this paper is to provide the reader with a comprehensive review of the different techniques available in the literature to process piezoelectric PZT thin films at temperatures compatible with semiconductors (450 °C), smart glass (400 °C), or flexible electronics (350 °C). We first present the typical ferroelectric and piezoelectric properties of PZT films. The different deposition techniques and growth mechanisms of these films are then reviewed with a focus on thermodynamics. Then, all the low temperature processes are detailed, such as seeding effects, the modification of deposition parameters in vapor-phase deposition, special annealing technologies assisted with UV, lasers, flash lamps, microwave radiations or high-pressure, a focus on the hydrothermal method, and finally what is called solution chemistry design with notably combustion synthesis. Transfer processing is also detailed, as an alternative way to this low temperature approach. An outlook of future applications enabled by these innovative techniques is finally provided.