Preparation and characterization of piezoelectric diaphragm actuator based on ring-shaped interdigitated electrodes

This paper describes the preparation and characterization of unimorph actuators for adaptive optics based on the Pb(Zr0.52Ti0.48)O3 (PZT52) thin film. The actuator utilizes a unimorph membrane (diaphragm) structure consisting of an active PZT piezoelectric layer and a passive ZrO2/Si composite layer. The PZT layer in the unimorph actuator is driven by ring-shaped interdigitated electrodes (IDT-mode). To fabricate the diaphragm structures, the Si (100) wafer is used as substrate, on which PZT52 and ZrO2 layer are deposited by a modified sol-gel process. The PZT layer can be crystallized with preferred (110) orientation by using PbTiO3 (PT) material as a seed layer. The Al reflective layer is deposited and patterned into top electrode geometries by lithographic process, subsequently. The electrode spacing is 50 μm and the diameter of the inactive circular regions is 2 mm. The diaphragms are released using orientation-dependent wet etching (ODE) with 5-10 μm residual silicon layers. The size of the diaphragms is 12 mm in diameter and the outer IDT diameter (10.5 mm) is fixed at 87.5% of the diaphragm diameter. The measured maximum central deflection at 100 kV/cm is approximately 6.5 μm. The deflection profiles are also modeled using finite element method (FEM) and their intrinsic strain behaviors are evaluated.