Atomic layer deposition for fabricating capacitive micromachined ultrasonic transducers: initial characterization

In this paper, we examine the utility of a new method for fabricating capacitive micromachined ultrasonic transducers (CMUTs). The method is based on atomic layer deposition (ALD) technology, which uses a self-limiting binary reaction process to produce ultra-thin membranes. Advantages of ALD include precise control of dimensions including gap-width between the capacitor plates, membrane thickness and radius, lower cost due to a reduction in the number of fabrication steps, the potential to use a large variety of materials, and increased reliability due to the enhanced surface quality of the membranes. These capabilities promise fabrication of transducers with superior operating characteristics. However, no study has yet documented sensitivity and power requirements for CMUTs created using ALD. We present here a first-order mechanical and equivalent circuit analysis along with a fabrication process to create and characterize CMUTs using ALD. Results show that these systems have the potential for excellent sensitivity and decreased power requirements. Work to test the fabricated elements is currently underway.