Piezoelectric thin films for a high frequency ultrasound transducer with integrated electronics

Lead zirconate titanate (PZT) piezoelectric films were integrated into prototype one-dimensional array transducers. Linear arrays of diaphragm transducers were prepared using PZT films of 0.5–1.7 μm in thickness and surface micromachining techniques. For this purpose, the PZT and remaining films in the stack were patterned using ion-beam or reactive ion etching and partially released from the underlying silicon substrate by XeF2 etching. The PZT films were prepared by chemical solution deposition, and have e31,f piezoelectric coefficients of −6 to −12 C/m2, depending on the crystallographic orientation. Impedance measurements on the fabricated structures showed resonance frequencies between 3 and 70 MHz for fully and partially released structures depending on the transducer dimensions and vibration modes. In-water transmit and receive functionalities have been demonstrated. A bandwidth on receive of 66% has been determined. Because of the small thickness of the piezoelectric element, the elements can be driven at less than 5 V. This enables the ultrasound system to be CMOS compatible, and hence massive miniaturization. A custom designed CMOS chip which enables beamforming on transmit, transducer excitation, amplification, digitization, and data storage was designed and fabricated.