Low Temperature Adhesive Bonding-Based Fabrication of an Air-Borne Flexible Piezoelectric Micromachined Ultrasonic Transducer.

Wei Liu,Dawei Wu

doi:10.3390/s20113333

Abstract

This paper presents the development of a flexible piezoelectric micromachined ultrasonic transducer (PMUT) that can conform to flat, concave, and convex surfaces and work in air. The PMUT consists of an Ag-coated polyvinylidene fluoride (PVDF) film mounted onto a laser-manipulated polymer substrate. A low temperature (<100 °C) adhesive bonding technique is adopted in the fabrication process. Finite element analysis (FEA) is implemented to confirm the capability of predicting the resonant frequency of composite diaphragms and optimizing the device. The manufactured PMUT exhibits a center frequency of 198 kHz with a wide operational bandwidth. Its acoustic performance is demonstrated by transmitting and receiving ultrasound in air on curved surface. The conclusions from this study indicate the proposed PMUT has great potential in ultrasonic and wearable devices applications.

Highlights

Ultrasound has been widely used in non-destructive testing (NDT) [1,2], medical diagnostics and therapy [3,4,5], and sensing detection [6,7,8] because of its exceptional features such as noninvasiveness, convenience, high penetrability and sensitivity
We report the development of an air-borne flexible piezoelectric micromachined ultrasonic transducer (PMUT) based on a simple and robust low temperature adhesive bonding technique
There are some main parameters of PMUT design, such as the thickness of the polyvinylidene fluoride (PVDF) piezoelectric layer and the diameter of the cavity, whose changes will exert a great influence on the resonance frequency

Summary

Introduction

Ultrasound has been widely used in non-destructive testing (NDT) [1,2], medical diagnostics and therapy [3,4,5], and sensing detection [6,7,8] because of its exceptional features such as noninvasiveness, convenience, high penetrability and sensitivity. Piezoelectric nanofibers with excellent properties are one of the types of materials proposed for use in wearable electronics [16,17,18,19], and some sensors can be embedded as a part of human skin or clothing for health monitoring by the near field electrospinning (NFES) technique [20,21,22] Among these devices, flexible piezoelectric micro-ultrasonic transducers have advantages over traditional rigid ultrasonic transducers in terms of weight, volume, adaptability and portability. Available feasible strategies for fabricating flexible piezoelectric micro-ultrasonic transducers that can be mainly divided into two categories: island-bridge connection techniques and transfer printing techniques In the former case, the flexibility is achieved by connecting bulk piezoelectric ceramic islands to each other using polymer joints or embedding piezoelectric ceramics into patterned polymer holes [23,24,25,26,27].

Methods

Results

Conclusion