Fabrication, characterization and modeling of K(31) piezoelectric Micromachined Ultrasonic Transducers (pMUTs).

摘要

Piezoelectric Micromachined Ultrasonic Transducers (pMUTs) offer a new approach for developing two dimensional array type ultrasonic transducers for real-time, three dimensional medical imaging. The studies reported in this dissertation represent part of the efforts towards this goal and consists four major tasks, namely, fabrication, characterization, analyzing and modeling of single element transducers, and development of a prototype of 2D array type transducer. The transducer belongs to K31 type in which a flexural vibration of the membrane is excited by a voltage applied in a direction that is normal to the surface of the membrane. The specific objectives of this study are to develop the fabrication technology for pMUTs and understand their behavior and performance through both experimental characterization and analytical and numerical modeling.;The pMUTs were fabricated using MEMS technology. There characteristics were measured by impedance measurement combined with equivalent circuit analysis. For the analytical prediction of pMUT performance, a one dimensional composite beam and a two dimensional composite plate model were developed. For the numerical prediction, a finite element code based on a combination of the equivalent single-layer theory and the classical laminated plate theory (CLPT) using a rectangular conforming plate element.;The majority of the pMUTs fabricated in this study has a large length to width aspect ratio. For this type of pMUTs, it was found that the resonant frequencies decreased from 2MHz to 600KHz as the widths of the membrane increased from 90mum to 180mum, but showed no appreciable length dependence. Effective coupling coefficients ( k2eff ) was found to increase with width up to 150mum and then decrease. The peak value of k2eff was found to be around 0.826%.;The measured resonance frequencies matched quite well with finite element calculations and analytical models. Based on the prediction of the 2D composite plate model, both the membrane size and electrode coverage have significant influence on k2eff . The maximum predicted k2eff was 2.908% which occurred when the electrode covered about 48.9% in both x and y directions for a square membrane, or about 23.9% of the membrane area covered from the center of the membrane.