Bimorph pMUT with dual electrodes

The concept of “bimorph” piezoelectric micromachined ultrasonic transducers (pMUTs) has been demonstrated by utilizing a two active AlN layers structure constructed in a CMOS-compatible process. The prototype device has two 0.95μm-thick AlN layers sandwiched by three 0.15μm-thick Mo electrodes. In a prototype, both an inner circular and an outer annular electrode are designed on a 230 μm in radius, circular-shape diaphragm. When actuated with the inner electrode of 160μm in radius, the pMUT has a resonant frequency of 198.8 kHz and central displacement of 407.4 nm/V. Under the differential drive scheme using the dual-electrodes for large acoustic outputs at a low frequency, the measured central displacement is 13.0 nm/V, which is about 400% higher than that of a unimorph AlN-pMUT under similar actuation conditions. As such, the dual-electrode bimorph pMUT presents the improved operation as compared with the state-of-the-art flat pMUT design to achieve enhanced acoustic outputs.