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Download as PDFPiezoelectric Transducers for Advanced Ultrasound Imagining Systems and Energy Harvesting
In this project, a piezoelectric 2-D array of ultrasound transducers will be developed for compact, portable 3-D ultrasound imaging systems. Piezoelectric materials have been used for macro-scale ultrasound systems due to their high polarization density. However, making tiny 2-D array of transducers with conventional piezoelectric materials (all ceramic or polymeric composite) has been extremely difficult. Dicing and bonding of crystallized piezoelectric ceramic bulk and subsequent delicate assembly operations require a lot of manual effort, which limits production yield, rate, and quality. In addition, piezo-ceramics inherently have high acoustic impedance, which is difficult to match in liquid or air medium. Capacitive Micromachined Ultrasonic Transducers (CMUTs) have been developed to leverage the MEMS fabrication techniques for small form factor transducer fabrication and to mitigate the acoustic impedance mismatch [1] . A CMUT consists of metallized silicon nitride membranes suspended above highly doped silicon bulk. These membranes vibrate when an electrostatic charge is generated under each membrane. Each membrane can also detect the reflected sound wave by measuring the capacitance change at the gap under each membrane. CMUTs offer greater bandwidth than piezoelectrics and are tunable [2] . Moreover, many of the available MEMS processing technologies could be used to make micro-scale arrays of CMUT elements effectively. However, CMUTs still have some technical issues such as high voltage requirement, which makes them not suitable for in vivo operations, result in insulator breakdown, and cause static charge accumulation at the membrane surface.
This research project will focus on developing PZT micromachined ultrasound transducers (PMUTs) and designing novel 2-D array PMUTs with a reliable PZT process technique of PZT. The initial goal of this project is to study the PZT structure appropriate for a 64×64 array and actuation voltage less than 10 volts. A prototype PZT structure will be fabricated and characterized to demonstrate the feasibility of the technology. In addition, the low voltage limits, potential efficiency, and sensitivity will be determined and optimized. Fabricating an array of PZT pillars with size less than 50 mm is one of the major challenges of this project. A new and flexible on-demand deposition process for high quality PZT thin films developed by Bathurst et al. will be used to solve this problem [3] .
In addition to the advanced medical applications, the core technology developed in this project will be applied to further improve the ultra-wide bandwidth of energy harvesters. This will lead energy harvesters to be deployable in real world applications including sensors for energy efficient buildings, structural monitoring devices of crude oil pipelines, and leak detectors in water supply networks.
- I. Landebaum et al., “Surface micromachined capacitive ultrasonic transducers,” IEEE Trans. Ultrasonics Ferroelectrics and Frequency Control, vol. 45, no. 3, pp. 678-690, 1998. [↩]
- B. Khuri-Yakub, “Next-generation ultrasound,” IEEE Spectrum, p. 45, May 2009. [↩]
- S. Bathurst, J. Jeon, H. W. Lee, and S. G. Kim, ”PZT MEMS by thermal ink jet printing,” presented at Solid-State Sensor and Actuator Workshop, Hilton Head, SC, 2008. [↩]