High Frequency Piezoelectric MEMS Devices

High frequency ultrasound array transducers are being explored for high resolution imaging systems. This increase in resolution is made possible by enabling a simultaneous increase in operating frequency (50 MHz to about 1 GHz) and close-coupling of the electrical circuitry. Several different processing methods are being explored to fabricate array transducers. In one implementation, the piezoelectric transducer is prepared by mist deposition of PbZr_0.52Ti_0.48O₃ (PZT) films over Ni posts. In addition, a xylophone bar transducer has also been prototyped, again using thin film PZT as the active piezoelectric layer. Because the drive voltages of these transducers are low, close coupling of the electrical circuitry is possible. A CMOS transceiver for a 9 element-array has been fabricated in 0.35 mum process technology. The first generation CMOS transceiver chip contains beamforming electronics, receiver circuitry, and analog to digital converters with 27 Kbyte on-chip buffer memory.