Piezoelectric Micromachined Ultrasonic Transducers for Medical Imaging

Authors: Katherine Smyth and Sang-Gook Kim

Department of Mechanical Engineering

Diagnostic medical ultrasound imaging is becoming increasingly widespread because it is relatively inexpensive, portable, compact, and non-invasive compared to other diagnostic scanning techniques. However, commercial realization of advanced imaging trends will require cost effective, large scale arrays of miniaturized elements, which are messy, difficult and expensive to fabricate with the current bulk piezoelectrics.  At high volume, micro-fabricated transducers are an array compatible and low cost alternative.  Based on a high force output figure of merit, a vibrating plate-based piezoelectric micro-machined ultrasonic transducer (pMUT) design is developed for high acoustic pressure output. Based on developed analytical and finite element based models, a 31 mode, lead zirconate titanate (PZT) pMUTs are fabricated using common micro-fabrication techniques and a PZT sol-gel deposition process.  Fabricated device deflection, acoustic sensitivity and electrical impedance are extensively characterized to provide a list of useful transduction performance metrics, which are compared to the analytical model and simulations.  Current work is focused on quantifying electroacoustic performance through appropriate metrics and analytical models to construct a framework for future pMUT and more generally, ultrasonic transducer design.  In the future, the developed models will be applied to optimize transducer elements and arrays to be incorporated into realistic imaging systems.

Figure 1.  Fabricated pMUT array with overlay of measured fundamental vibration mode shape excited with voltage V.  Acoustic waves propagated into imaging medium via plate deflection in this fundamental mode.