Exjobbsförslag från företag

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Förslaget inkom 2007-09-21

Processing and characterization of materials sensitive to ambient oxygen concentration for application in field effect based oxygen sensor devices

The wide band gap of the semiconductor material silicon carbide (SiC) permits its use at elevated temperatures and the material is also chemically inert, what makes it suitable for use in aggressive environments. On application of a catalytic gate material, gas sensitive field effect transistor devices based on SiC can be realized and have also been shown to exhibit good properties for high temperature applications such as combustion control and monitoring of car exhaust after-treatment systems.

The sensor devices developed so far have proven robust but merely gives a measure of the total amount of emissions or the emissions level in relation to the oxygen level. Monitoring of concentrations of individual exhaust or flue gas species (like CO and NO/NO2) is possible only for certain species (like H2 and NH3) under very special conditions.

One substance of interest to monitor for combustion control applications both in the case of internal combustion engines for automotive applications as well as stationary, local or domestic heating systems is oxygen. By measuring the amount of oxygen in the exhaust or flue gases one can control the combustion by adjusting the air inlets so as to provide just the right amount of air to ensure complete combustion of the fuel. The kind of sensors used today to monitor exhaust or flue gas oxygen concentration is however quite expensive and also brittle, breaking when exposed to condensed water, making it impossible to use these devices in certain applications.

It might, however, be possible to construct SiC based field effect gas sensor devices sensitive to the ambient oxygen concentration, at the same time being both cheaper and more robust, by the application of a conducting oxide gate material that changes its work function with its state of oxidation (or the amount of oxygen vacancies), if the state of oxidation changes with the oxygen concentration of the surrounding atmosphere.

The main goal of the diploma work is the manufacturing of a sensor device with some sensitivity to variations in the ambient oxygen concentration with small cross-sensitivities to other exhaust or flue gas constituents. A diploma work in this field would thus be composed of a short theoretical investigation regarding suitable materials and methods for the manufacturing of such gates on SiC field effect gas sensor devices as well as processing, characterization and testing of some different materials. A more detailed plan for the diploma work will be set up when a proper introduction to the subject and some time to study background information has been given, and can to a large extent be influenced by the student herself/himself.

Supervisor: Mike Andersson [email protected] +46 13 281372
Examiner: Anita Lloyd Spetz [email protected] +46 13 281710
S-SENCE and Div of Applied Physics, Linköping University, Sweden


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