MEMS-based High-Frequency (100-300 MHz) Ultrasonic Linear Phased Arrays

High-frequency ultrasonic phased array transducer is a desired candidate in real-time and high resolution imaging. Many difficulties will arise in the development of array imaging systems with an operating frequency of above 100 MHz. These difficulties include high-frequency phase-delay system, electrical matching problem, mechanical matching problem, and especially the fabrication of high-frequency array transducers which play a critical role in ultrasonic phased array imaging systems. This dissertation focuses on the array transducers with a central frequency of above 100 MHz, which mainly investigates two aspects. The first one is the finite element numerical simulations in the optimized design. The second one is the fabrication using different experimental processes based on micro electromechanical system (MEMS) technologies.In the section of numerical studies, a commercial finite element tool, COMSOL3.5a, is employed which benefits from well-performed coupling capabilities in combining fluidic model, solid model and electrical model. In piezoelectric backing array transducers, the effects of pitch size, kerf filler and kerf depth on the acoustic field, electrical impedance and crosstalk are investigated. Systematic simulations are carried out for a designed buffered transducer array.In the section of experimental fabrication and characterization, MEMS based technologies are applied to obtain high-frequency array elements, such as radio frequency (RF) sputtering and etching thin film, etc. Single crystal LiNbO3 arrays are made using ICP RIE technique. Two kinds of ZnO arrays are kerfed using wet chemical etching technique and micromachining silicon substrate, respectively. All of these arrays are characterized by Network Analyzer. The measured electrical impedance and crosstalk are consistent with the theoretical predictions obtained from finite element calculations.