5I-4 Piezoelectric Micromachined Ultrasound Transducer (pMUT) Arrays for 3D Imaging Probes

Piezoelectric micromachined ultrasound transducers (pMUTs) have been fabricated and characterized in this work as a new approach for manufacture of 2D arrays for forward-looking 3D intravascular (IVUS) and intracardiac (ICE) imaging. Two-dimensional pMUT arrays containing 25 elements (5 times 5 arrays) were bulk micromachined in silicon substrates. The devices consisted of suspended PZT thin film membranes formed by deep reactive ion etching. Membrane widths ranged from 50 to 200 mum, with element pitch from 100 to 300 mum. Acoustic transmit properties were measured in de-ionized water with a calibrated hydrophone placed at a range of 20 mm. Measured transmit frequencies for the pMUT elements ranged from 4-11 MHz. Element capacitance for pMUTs ranged from 30 to over 400 pF depending on element size. Smaller element sizes generally produced higher acoustic transmit output than larger elements, and thicker PZT layers also produced higher output per unit electric field applied. Due to flexure mode operation above the PZT coercive voltage, transmit output also increased nonlinearly with increased drive voltage. The pMUT arrays were attached directly to the system amplifiers of the Duke University T5 Phased Array Scanner by a modified cable assembly in order to produce real-time pulse-echo B-mode images with the 2D pMUT arrays