Preparation and characterization of unimorph actuators based on piezoelectric Pb(Zr0.52Ti0.48)O3 materials

This paper describes the preparation and characterization of unimorph actuators for deformable mirrors, based on Pb(Zr0.52Ti0.48)O3 (PZT52) thin film. As comparison, two different designs, where the PZT layer in the unimorph actuators was driven by either interdigitated electrodes (IDT-mode) or parallel plate electrodes (d31-mode), were investigated. The actuators utilize a unimorph membrane (diaphragm) structure consisting of an active PZT piezoelectric layer and a passive SiO2/Si composite layer. To fabricate the diaphragm structures, n-type (1 0 0) silicon-on-insulator (SOI) wafers with 1 μm thermal SiO2 were used as substrates (for d31-mode actuators, the upper Si part of SOI need to be heavily doped and used as bottom electrodes simultaneously). Sol–gel derived PZT piezoelectric layers with PbTiO3 (PT) bufferlayer in total of 0.86 μm were then fabricated on them, and 0.15 μm Al reflective layers were deposited and patterned into top electrode geometries, subsequently. The diaphragms were released using orientation-dependent wet etching (ODE) with 5–10 μm residual silicon layers. The complete unimorph actuators comprise 4 × 4 discrete units (4 mm2 in size) with patterned PZT films for parallel plate configuration or 3 × 3 individual pixels (2 mm in IDT diameter) with continuous PZT films in graphic region for IDT configuration. The measurement results indicated that both of the two configurations can generate considerable deflections at low voltage. The measured maximum central deflections at 15 V were approximately 2.5 μm and 2.8 μm, respectively. The intrinsic strain conditions shaping the deflection profiles for the diaphragm actuators were also analyzed. In this paper, the behaviors of clamped parallel plate configuration without a diaphragm were also evaluated.