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The influence of the insulator surface properties on the hydrogen response of field-effect gas sensors
Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.ORCID iD: 0000-0002-0873-2877
Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
Institute of Microtechnology, University of Neuchâtel, Neuchâtel, Switzerland.
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2005 (English)In: Journal of Applied Physics, ISSN 0021-8979, Vol. 98, no 3, 34903-34908 p.Article in journal (Refereed) Published
Abstract [en]

The hydrogen response of gas-sensitive field-effect devices is mainly due to trapping of atomic hydrogen on the insulator side of the metal-insulator interface of the metal-insulator-semiconductor (MIS) structure. Therefore an influence of the choice of insulator on the hydrogen response properties is expected. We have investigated this influence by producing MIS capacitors with four different insulators; SiO2, Al2O3, Si3N4, and Ta2O5. The results show that the choice of insulator influences the detection limit, the saturation concentration, and the saturation response. Furthermore, there is a strong correlation between the observed saturation response and the oxygen concentration of the insulator surface, as measured by Auger electron spectroscopy, which indicates that the trapping of hydrogen at the interface occurs at the oxygen atoms of the insulator surface. Finally, if the metal film is porous a catalytic oxidation of the insulator surface appears to be facilitated, which can increase the hydrogen response.

Place, publisher, year, edition, pages
2005. Vol. 98, no 3, 34903-34908 p.
Keyword [en]
silicon compounds, alumina, tantalum compounds, hydrogen, dielectric materials, gas sensors, MIS capacitors, Auger electron spectra, catalysis, oxidation, interface states
National Category
Engineering and Technology
URN: urn:nbn:se:liu:diva-13384DOI: 10.1063/1.1994941OAI: diva2:20564
Available from: 2005-10-06 Created: 2005-10-06 Last updated: 2015-03-24
In thesis
1. New Materials for Gas Sensitive Field-Effect Device Studies
Open this publication in new window or tab >>New Materials for Gas Sensitive Field-Effect Device Studies
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Gas sensor control is potentially one of the most important techniques of tomorrow for the environment. All over the world cars are preferred for transportation, and accordingly the number of cars increases, unfortunately, together with pollutants. Boilers and powerplants are other sources of pollutants to the environment. Metal-Insulator-Silicon Carbide (MISiC) Field-effect sensors in car applications and boilers have the potential to reduce the amount of pollutants. These devices are sensitive to several gases in exhaust and flues gases, such as hydrogen, hydrocarbons, and ammonia (for the selective catalytic reduction (SCR) application). These applications require specific and long term stable sensors. The car industry for instance wants sensors that will stand at least 240 000 km.

This thesis presents studies of the active layers in MIS Fieldeffect gas sensors. Fundamental studies of the sensor mechanism has been performed in ultra high vacuum, UHV, to understand the gas response mechanism in more detail, and to find out how the sensing mechanism is affected by the catalytic active gate material. The influence of four different insulating layers was studied at atmospheric pressure. The catalytic layer has also been altered to metal oxide nanoparticles with or without impregnation of catalytic metals.

Nanoparticles are potential candidates to be used as the gate material for high temperature, long-term stable FET sensor devices. The combination of catalytic metals and metal oxides may prevent reconstruction of the metal. The use of nanoparticles will increase the number of triple points (catalytic material and insulator in contact with gas), which are crucial e.g. for the ammonia sensitivity. Another challenging aspect of nanoparticles is the possibility to get selectivity to different gases based on the particle size.

The goal is to find new sensitive, selective and more long term stable materials, which meet the requirements above.

From the UHV studies we learned that the two catalytic active metals Pt and Pd, do behave in a similar way, although there are some quantitative differences. Values for the heat of adsorption on both the Pd and Pt surfaces are estimated as well as the dipole moments for the adsorbates on the insulator surface.

The insulators play an important role in the sensing mechanism, since the adsorption of hydrogen atoms (or protons) that are detected by the sensor occur on the insulator surface. By changing the insulator material the saturation response of the sensors is affected. It was shown that Al2O3 gave a higher saturated response to hydrogen in Pt-MIS capacitors at 140°C as compared to Ta2O5, SiO2, and Si3N4.

We have tested wet synthesized ruthenium dioxide and ruthenium nanoparticles, which are electrically conducting and catalytically active sensing material. RuO2 is especially interesting as a high temperature material since it is already oxidized. Both materials show a sensitivity pattern comparable to porous platinum. The temperature dependence of the gas response indicates a higher catalytic activity of the RuO2 as compared to Ru nanoparticles.

Nanoparticles synthesized by aerosol technology provide several advantages like a good adhesion of the particles to the substrate, many possible material combinations and efficient methods for particle separation according to size. The methods to use this technology for sensing materials in MISiC sensors are now under development and some preliminary results are obtained.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2005. 64 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 957
ruthenium dioxide, nanoparticles, MISiCFET, sensors
National Category
Physical Sciences
urn:nbn:se:liu:diva-4243 (URN)91-8529-974-X (ISBN)
Public defence
2005-10-07, Hörsal Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
On the day of the public defence of the doctoral thesis, the status of articles I and II was: accepted for publication.Available from: 2005-10-06 Created: 2005-10-06 Last updated: 2015-03-24Bibliographically approved

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