Piezoelectric micro-lens actuator

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 1.5 μm thick PZT (Lead Zirconate Titanate) film deposited on a 0.6 μm thick ZrO2 seed layer that is coated on a 1 μm thick SiO2 and 5 μm thick monocrystalline silicon. The actuator is driven by a set of inter-digitated Pt/Ti top electrodes, of 10 μm width and 5 μm spacing, deposited on the 800 μm long PZT film. The connecting beams and lens holding frame are single layers of 5 μm 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 24 μm at 60 KV/cm with maximum displacement sensitivity to voltage of 0.52 μm/V at 53 KV/cm. The unloaded fundamental resonant frequency of the actuator is 2.42 kHz. The resonant frequency is reduced to 752 Hz after a 600 μm diameter glass micro-lens weighing 320 μg is loaded onto the lens holding frame. The static out-of-plane deflection characteristic is reduced slightly to 22 μm deflection at 60 KV/cm. The actuator demonstrates translation time of 10 ms for 22 μm 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.