Abstract
Many applications of ultrasound for sensing, actuation and imaging require miniaturized and low power transducers and transducer arrays integrated with electronic systems. Piezoelectric micromachined ultrasound transducers (PMUTs), diaphragm-like thin film flexural transducers typically formed on silicon substrates, are a potential solution for integrated transducer arrays. This paper presents an overview of the current development status of PMUTs and a discussion of their suitability for miniaturized and integrated devices. The thin film piezoelectric materials required to functionalize these devices are discussed, followed by the microfabrication techniques used to create PMUT elements and the constraints the fabrication imposes on device design. Approaches for electrical interconnection and integration with on-chip electronics are discussed. Electrical and acoustic measurements from fabricated PMUT arrays with up to 320 diaphragm elements are presented. The PMUTs are shown to be broadband devices with an operating frequency which is tunable by tailoring the lateral dimensions of the flexural membrane or the thicknesses of the constituent layers. Finally, the outlook for future development of PMUT technology and the potential applications made feasible by integrated PMUT devices are discussed.
Highlights
In the last several decades, ultrasound has found ever-expanding industrial and biomedical applications, such as non-destructive evaluation (NDE) [1,2], ultrasonic actuation [3], medical imaging [4,5], therapeutic ultrasound [6], and particle and cell manipulation [7,8], at frequencies from tens of kilohertz to hundreds of megahertz
This paper presents an overview of recent advances towards the development of miniaturized and integrated arrays with Piezoelectric micromachined ultrasound transducers (PMUTs) technology, including a review of a specific new process
As is the case for conventional ultrasound transducers, the piezoelectric material most widely used in PMUTs is PZT, a ferroelectric material first formulated in the 1950s by Jaffe [56]
Summary
In the last several decades, ultrasound has found ever-expanding industrial and biomedical applications, such as non-destructive evaluation (NDE) [1,2], ultrasonic actuation [3], medical imaging [4,5], therapeutic ultrasound [6], and particle and cell manipulation [7,8], at frequencies from tens of kilohertz to hundreds of megahertz. The fabrication difficulty of conventional piezoelectric transducer structures increases dramatically for 1-D linear and 2-D matrix ultrasound arrays for beam steering and 3-D volumetric imaging [5,16], and in miniaturized devices with high element density to be fitted into small, constrained spaces, e.g., in intravascular ultrasound (IVUS) and intracardiac echocardiography (ICE) catheters [17,18,19]. Many of these problems can potentially be overcome by micromachined ultrasound transducers (MUTs). The requirements of the piezoelectric materials and variety of possible fabrication methods for PMUT elements and arrays are discussed
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