Micromachined Ultrasonic Transducers and Acoustic Sensors Based on Piezoelectric Thin Films

Abstract

A review is given on the current state of the art in piezoelectric micromachined ultrasonic transducers (pMUT). It is attempted to quantify the limits of pMUT's with respect to the electromechanical coupling, and to relate current achievements. Best reported results so far is a coupling coefficient k 2 of 6 %. This was achieved with 2 µm thick PZT thin films on a 5 µm thick silicon layer obtained by micromachining from a SOI wafer. The material properties are the most important part for a good performance, however, design contributes as well. Electrode size, layer thickness relation, and border conditions must be dimensioned correctly. Main needs for future research are identified in design, micromachining and further improvements of PZT films. Applications are shortly reviewed. 38 Electroceramic-Based MEMS: Fabrication-Technology and Applications

Experiment and simulation validated analytical equivalent circuit model for piezoelectric micromachined ultrasonic transducers

“…Consistent with previous results [29], [42], bias voltage increases e 31,f and offset the dielectric loss responsible for static resistance. At high frequency, the application of the bias voltage can minimize the loss tangent and maximize responsiveness; however, a reduction in e 31,f compared to the static case is still present and likely caused by depoling effects.…”

“…Unlike in the bulk case, for thin film piezoelectric systems, it is common for a biasing DC electric field to be added to an AC field to maintain polarization when the operating AC field is close to the coercive field [35]. Biasing is also found to reduce the loss tangent in piezoelectric thin films [29], [42]. Despite the application of bias voltage, e 31,f extracted from the best fit circuit parameters and confirmed with simulations is smaller than in the static case as shown in Table IV.…”

Piezoelectric MEMS sensors: state-of-the-art and perspectives

“…Frequencies in the 3-5 MHz are typically used for deep organ investigations whereas frequencies in the 50 MHz region allow for investigations of thin tissues, artery walls, etc [215]. At present, commercial 2D ultrasonic transducer probes are limited to linear arrays with an element pitch of approximately 300 μm and operating frequencies of less than 5 MHz [213].…”

Design and Performance Analysis of Capacitive Micromachined Ultrasonic Transducer Linear Array

“…The transducer is square with 1 mm side length and its working frequency is 44 kHz. The Federal Institute of Technology in Sweden studied a piezoelectric ultrasonic transducer based on PZT thin film [5,6], of which the thickness of the PZT thin film is 1μm and the thickness of the vibration membrane is 10 μm. The transducer is circular with 150 μm radius and the resonance frequency is 1.2 MHz.…”