Influence of top electrode design on pMUTs performance

Piezoelectric micromachined ultrasonic transducers (pMUTs) were designed, fabricated and tested to measure resonance and anti-resonance frequencies, and quality factor. Film quality was monitored via saturation polarization, remnant polarization and coercive electric field measurements in different films. Effective coupling coefficient and device efficiency are calculated based on those measured values. Single and split top electrode pMUTs designs, X and Y, respectively, are evaluated to understand the influence of top electrode design on device performance. It was found that resonance frequency decreases with an increase in membrane width. Top electrodes, smaller than the membrane width by 10 μm, show a positive effect on the effective coupling coefficient of the pMUTs. It was found that both quality factor and device efficiency are maximized when top electrode width is the same as that of membrane width. An increase in top electrode dimension beyond the membrane decreases device performance.