Date of Award

5-28-2024

Publication Type

Thesis

Degree Name

M.A.Sc.

Department

Electrical and Computer Engineering

Supervisor

Arezoo Emadi

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

Abstract

Three sets of Multiple Moving Membrane Capacitive Micromachined Ultrasonic Transducers (M3-CMUTs), totaling eight devices have been designed to study the influence of the dimension of middle and top membranes of circular geometry on the transducer characteristics. The design is aimed towards ultrasonic imaging and Non-destructive testing (NDT) applications. CMUTs of same top membrane sizes as that of M3-CMUTs are also designed to compare their characteristics. Detailed finite element analysis-based simulation is carried out for each transducer device on COMSOL Multiphysics platform, and the results are analyzed to understand the effect of the size of membranes and bottom electrode on the critical characteristics such as effective cavity height, resonant frequency, and spring softening effect. By keeping the bias voltage of top membrane of each device fixed close to the respective collapse voltage and the bottom electrode grounded, the bias voltage of the middle membrane is varied in the positive and negative ranges to determine the range of effective cavity heights exhibited by each device. Following the simulation and analysis, the M3-CMUT devices are fabricated through the sacrificial layer procedure using PolyMUMPs process, a MEMS technology. Experimental measurements of electrical impedance as a function of frequency are carried out on the fabricated M3-CMUT and CMUT devices both to study the dimension induced behavior of transducer parameters such as collapse voltage, resonant frequency, and frequency shift to validate the simulation results. The experimental results are found to closely agree with that of simulation. The analysis on the whole reveals that the transducer with larger dimensions of middle membrane possesses larger range of effective heights or dynamic control realizable than with smaller middle membrane dimensions as the bias of the top membrane is varied. This large dynamic range of control possessed by M3-CMUTs has the potential for any single device to meet both ultrasonic transmission and reception requirements in NDT applications. Also, a transducer with smaller size middle membrane is found to have higher collapse voltage and larger resonant frequency making it suitable for relatively higher resolution ultrasonic NDT applications.

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