Graduation Year

2005

Document Type

Thesis

Degree

M.S.E.E.

Degree Granting Department

Electrical Engineering

Major Professor

Christos Ferekides, Ph.D.

Committee Member

Don Morel, Ph.D.

Committee Member

E.K. Stefanakos, Ph.D.

Keywords

Sputtered SnO2, MOCVD SnO2, Thin films, Oxygen Species, Fl doped SnO2

Abstract

Tin oxide (SnO2) has been investigated and used as a gas sensing material for numerous applications from the very start of the sensor industry. Most of these sensors use semiconductors (mostly SnO2) as the sensing material.

In this work, SnO2 was prepared using 2 techniques: firstly the MOCVD where we dope the sample with fluorine and secondly sputtering technique where samples are undoped in our case. These samples were tested at different conditions of temperature varying from room temperature to 150 degrees C, in ambient gas atmosphere of 200 CC Nitrogen (N2).

The typical thickness of the sputtered samples was 1500 Å with a sheet resistance of 300 Ω/ٱ and these sputtered samples were found to be more porous. These samples when tested in room temperature showed a change of -4 µA change for 10% and -9 µA for 90% of H2. While at higher temperatures (150⁰C) the current change for 10% increased from -4 µA to -2 mA showing that higher ambient temperatures increased the sensitivity of the samples. The repeatability of the samples after a period of 3 days were found to be well within 10%. The samples prepared by MOCVD were fluorine doped, the samples were conductive to 1 order of magnitude more than the sputtered ones. 3 different samples of approximate thicknesses 3000, 6000 and 9000 Å were prepared and tested in this work, with typical resistivity of 6 Ω/cm and the grains in this case are typically more compact. The conductive samples showed no response at room temperature, including the 6000 and 9000 Å samples. While at higher temperatures (150⁰C) the 3000 Å sample showed very sensitive response to H2. Also noticed was that the response was linear compared to the sputtered samples. The samples showed very good repeatability and sensitivity. A added feature noticed was that the sample did not need to be completely desorbed before detecting other (greater or lower) concentrations. Effect of temperature was studied by conducting similar tests under similar conditions on a sample, while varying ambient temperatures at 35, 75, 115 and 150 ºC. Results showed increase in sensitivity of sample as temperature increased (6µA, 40µA, 150µA and 300µA change in current respectively). But the response time was seen to increase too. Resistive Sputtered samples with 2% and 5% Zinc (Zn) deposits on it were tested but yielded no response.

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