Ultraviolet-activated Titanium Dioxide based Gas Sensor by Chemical Solution Process
Date Issued
2012
Date
2012
Author(s)
Chou, Chao-Hung
Abstract
In this study, the design of an end point detector for gas chromatography (GC) system was developed. The metal oxide (MOX) semiconductor type gas sensor was chose because of its long life time, high sensitivity and broad selectivity. Starting from Prof. Helwig’s dissociative gas sensing mechanism, adsorbed water layers on the metal oxide surface assisted the detection of acidic gases, basic gases and short chain alcohols at room temperature. This study focused on the development of a room-temperature-operated gas sensor with the titanium dioxide sensing film by the chemical solution process.
Sensors were fabricated by the combination of both conventional micro electro mechanical systems (MEMS) technology and the sol gel method. Gold metal layer deposited on thermally oxidized silicon wafer was patterned by lithography. With photoresisit were used as stop layer of wet etch process to gold, exposing interdigit electrodes on silicon subtract. To prepare materials used for the formation of the sol, the deionized water used as solvent, the acetic acid served as catalyst, the titanium isopropoxide, (TIP) utilized as precursor, were mixed. After the hydrolysis reaction and condensation reaction are done, the transparent TiO2 sol was formed. The sol was deposited on gaps between interdigit electrodes of the sensor. With the high temperature annealing, sol was transformed into TiO2 sensing film.
To characterize the sensor performances, the sensor was placed at the end point of the separation column of a GC system. Dry air was utilized as the carrier gas to push the sample mixture through the column, separated into bands and was detected by the TiO2 film of the sensor at the outlet of the column. It is found that the TiO2 film has the capability to detect more types of gas molecules than previously reported acidic gases, basic gases and short chain alcohols at room temperature. With or after the irradiation of ultraviolet light, signals of esters with a small molecular weight, molecule with ether-like structure and toluene are clear to distinguish.
Subjects
titanium dioxide
gas sensor
chromatography
sol-gel method
room temperature operation
Type
thesis
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