Piezoelectric micro-lens actuator

Abstract

This paper reports the design, simulation, fabrication and characterization of a piezoelectric actuation structure for out-of-plane micro-lens movement. The structure consists of eight unimorph piezoelectric actuators symmetrically attached to a lens holding frame at one end through eight connecting beams and to the silicon substrate at the other end. The unimorph piezoelectric actuator consists of a 1.5μm thick PZT (Lead Zirconate Titanate) film deposited on a 0.6μm thick ZrO2 seed layer that is coated on a 1μm thick SiO2 and 5μm thick monocrystalline silicon. The actuator is driven by a set of inter-digitated Pt/Ti top electrodes, of 10μm width and 5μm spacing, deposited on the 800μm long PZT film. The connecting beams and lens holding frame are single layers of 5μm thick silicon. Theoretical analysis of the actuator is confirmed by ANSYS simulation. The results show that the displacement range and response of the actuator can be controlled by the effective residual stress in the structure. The device has been successfully fabricated and characterized for its mechanical behavior. Both the simulation and theoretical results show good agreement with measurement. The actuator has been measured for its static out-of-plane displacement of 24μm at 60KV/cm with maximum displacement sensitivity to voltage of 0.52μm/V at 53KV/cm. The unloaded fundamental resonant frequency of the actuator is 2.42kHz. The resonant frequency is reduced to 752Hz after a 600μm diameter glass micro-lens weighing 320μg is loaded onto the lens holding frame. The static out-of-plane deflection characteristic is reduced slightly to 22μm deflection at 60KV/cm. The actuator demonstrates translation time of 10ms for 22μm displacement range with less than 5% ringing. In comparison to previously demonstrated lens actuation mechanism, the reported mechanism shows higher resonant frequency and hence suited for faster actuation.