A Dual-Electrode MEMS Speaker Based on Ceramic PZT with Improved Sound Pressure Level by Phase Tuning

One of the challenges for piezoelectric MEMS speakers is their relatively low sound pressure level (SPL) due to the relatively small piezoelectric constants of sol-gel or sputtered lead zirconate titanate (PZT). In this paper, we present a piezoelectric MEMS speaker with improved SPL that is enabled by high-piezoelectric-coefficient ceramic PZT as well as a dual-electrode configuration with phase tuning. A dual-electrode piezoelectric MEMS speaker based on 4 μm thin ceramic PZT has been designed and fabricated with top electrodes consisting of an inner circular-shaped electrode and an outer ring-shaped electrode. The maximum SPL at 9.7 kHz reaches 121 dB with both electrodes activated simultaneously. Measurements have also revealed that 180° is not always the optimal phase delay between the two driving signals to yield the highest SPL. Instead, the output SPL of the MEMS speaker changes significantly with the phase delay and is frequency dependent, peaking at different phase delays for different frequencies. The optimal phase delays in the frequency band from 600 Hz to 10 kHz have been obtained by phase tuning experiments, which shows 2 to 10 dB SPL improvement compared with the single-electrode driving method.