Design and verification of diamond based capacitive micromachined ultrasonic transducer


Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Electrical and Electronics Engineering, Turkey

Approval Date: 2011

Student: AHMET MURAT ÇETİN

Supervisor: BARIŞ BAYRAM

Abstract:

Potential applications such as high intensity focused ultrasound in medical therapeutics require larger output pressures. To offer unprecedented acoustic output pressure in transmit without the limitations, Capacitive Micromachined Ultrasonic Transducer operation modes of collapse and collapse-snapback are introduced in literature. Both operation modes require the membrane to contact the substrate surface, which poses a problem on the durability of the membrane in terms of structural integrity and tribological property. Based on the additional requirements of these modes, diamond is proposed as the ultimate solution to be used as the membrane material. Mechanical, thermal, and electrical properties of diamond are all in favor of its use in the microfabrication of CMUTs. This thesis introduces the design and test results of the first diamond-based CMUTs as an alternative to silicon and silicon nitride based CMUTs. Simulations are performed using Finite Element Methods (FEM) using a commercially available software package, ANSYS. The diamond-based CMUT is operated successfully both in air and immersion for the first time. Fully customizable in-house software is developed to command and control the test setup equipments for current dissertation and future work. Fresnel and Fraunhofer regions of the CMUT are characterized in sunflower oil using a combination of advanced hardware and software. The experimental results of radiation and diffraction for the diamond-based circular CMUT are verified by the theoretical calculations for a circular piston transducer. The results obtained from the first generation diamond-based CMUTs presented the diamond as a promising material for membranes in CMUTs.