Date of Award

1-1-2022

Publication Type

Thesis

Degree Name

M.A.Sc.

Department

Electrical and Computer Engineering

Keywords

Capacitive micromachined ultrasonic Transducer, CMUT, MEMS. Microelectromechanical systems, Multiple moving membranes Capacitive Micromachined Ultrasonic Transducer, VOC sensor

Supervisor

D. Xiao

Supervisor

M. Azzouz

Rights

info:eu-repo/semantics/openAccess

Abstract

A challenge in greenhouses is the presence of various pests, virus, and bacteria. Although many pest management strategies are available, however, they all depend on visually identifying these invasive forces when they have eradicated the crop. To avoid the impacts on the agricultural sector due to such pests, early detection is required. Therefore, in this thesis MEMS-based capacitive mass resonators are proposed for early detection of such invasive forces through identifying their released volatile organic compounds (VOCs). In this work, multiple moving membrane capacitive micromachined ultrasonic transducer (M3-CMUT) as a mass sensor is proposed due to its advantages shared with and beyond capacitive micromachined ultrasonic transducer (CMUT) mass sensor such as reversibility, high sensitivity, low limit of detection and selectivity. Analytical modeling is done to identify critical design parameters of the proposed M3-CMUT sensor. This is followed by FEA simulations to analyze the effect of the critical design parameters on the operating resonant frequency of the sensor. Further FEA simulations are done to conduct a sensitivity analysis on the proposed sensor for PolyMUMPs parameters. Moreover, several M3-CMUT-based and CMUT-based mass sensors are fabricated using PolyMUMPs, after which measurements are done on the sensors and a comparative analysis done between the experimental and simulated results. The experimental results are in agreement with the simulated results, wherein, it has been found that larger anchor width devices have a higher collapse voltage than the small anchor width devices. Therefore, the larger anchor width mass sensors can be operated at a higher voltage to get a higher resonant frequency shift and hence a higher sensitivity. Furthermore, the larger anchor width mass sensors can also be run at lower voltages for low level mass detection, hence expanding the limit of detection. Therefore, in an unconventional manner, the detection range of capacitive micromachined resonator mass – based sensors has been increased by increasing the width of the anchors supporting the top flexible membrane.

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