PZT MEMS loudspeaker: hot poling optimization of actuators for improved linearity and acoustic distortions
* Presenting author
USound actuators work with PZT deposited on silicon wafer by a sol gel process; the design is based on a system of cantilevers and springs that traduces the piezoelectric effect in to a vertical movement. With ferroelectric materials one source of non linearity is the hysteresis of the polarization loop during loading and unloading cycles. This non linearity is hardly affected by design, one way for optimization is a polarisation process. Experiments include following parameters: Temperature 80°C to 120°C; DC Voltage 10V to 30V; Duration 1min to 10min. The mechanical measurements are done with a Polytec500 Laser Doppler Vibrometer for measuring elongation at given frequencies below fres both in static (step of DC voltages applied) and dynamic (time domain, DC+AC sinus signal) conditions. The acoustical measurements are done with an artificial ear (711 Coupler, a standard for in-ear headphones characterization), in this stage the MEMS parts are assembled in the final package and mounted in a earphone shell. The measurement system acquires acoustic SPL and THD form 20Hz to 20kHz.The results show a remarkable impact of both hot poling and driving induced poling improving the linearity of the displacement and reducing acoustic THD.