Development and Characterization of Multi-Sensor Platforms for Real-Time Sensing Applications

Date of Award

2023

Degree Name

Ph.D. in Electrical Engineering

Department

Department of Electrical and Computer Engineering

Advisor/Chair

Guru Subramanyam

Abstract

Doping of metal oxide semiconductors with other metal oxides or metal ions is an effective way to improve the sensing performance of gas sensors. In this dissertation, In-doped SnO2 thin film is used in different gas sensing platforms, such as surface acoustic wave (SAW) transducers and impedance spectroscopy, for the detection of volatile organic vapors at room temperature. The properties of the piezoelectric materials play a critical role in determining the sensing response of the SAW based gas sensors. Recently, various ferroelectric materials have been used as piezoelectric materials in the manufacturing of SAW based gas sensors. Among them, Ba0.6Sr0.4TiO3 (BST) has emerged as a potential candidate due to its high acoustic velocity and electromechanical coupling coefficient. In the development of gas sensors, noble metals are extensively used as electrode or transducer materials. However, noble metals are expensive and scarce. On the basis of their favorable electrical conductivity, 2D metallic transition-metal dichalcogenides (VTe2, NbTe2, and TaTe2) are emerging as promising candidates for use in 2D electronic devices. In this dissertation, the design, fabrication, and validation of BST-based SAW and NbTe2- based impedance spectroscopy sensor platforms with the In-doped SnO2 sensing film were demonstrated. Different deposition and photolithography techniques were applied to fabricate the sensors. The morphology, structural, elemental compositions, and electrical properties of the as-deposited samples were characterized by HRSEM, XRD, EDS, and the four-point probe sheet resistance method. The samples exhibited excellent film adhesion. Furthermore, the sensing performances of the SAW and impedance spectroscopy-based gas sensors towards ethanol and humidity were evaluated at room temperature. The SAW sensors exhibited a significant negative frequency shift, which can be attributed to the mass and electric loading effects of the sensing film. Moreover, the sensor had a fast response time and a recovery time. Also, it exhibited good reproducibility. The impedance spectroscopy sensor exhibited a high sensitivity of 103.1 Ω/%RH (relative humidity), short response, and recovery times of 10.0 and 21 s, respectively, a low hysteresis value (2.58% RH), good linearity and good repeatability. In addition, the sensor had good long-term stability with a variation in impedance of less than 3% over five measurement cycles. The developed gas sensor platforms are suitable for practical room temperature sensing applications. Furthermore, this study demonstrated that NbTe2 has good potential as an electrode material for sensing and electronic devices.

Keywords

Surface Acoustic Wave Gas Sensor, Impedance Spectroscopy based humidity Sensor, Niobium Telluride and Barium strontium titanate, Ethanol and humidity sensor, Indium doped tin oxide sensing film

Rights Statement

Copyright © 2023, Author

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