Granular semiconductors can tell a good wine from its gas molecules
How much dangerous gas is there in the air? And is the wine good or bad? These are some instances of sensory detection where an electronic nose consisting of several different gas sensors can be utilised.
In his thesis in the field of semiconductor physics, ”Electrical properties of granular semiconductors – Modelling and experiments on metal-oxide gas sensors”, Licentiate of Science (Technology) Aapo Varpula from the Department of Micro and Nanosicences at the School of Electrical Engineering has studied the electrical properties of granular semiconductors, modelling the transients in these materials and their AC and DC characteristics.
Granular semiconductors useful in many applications
Granular semiconductor materials are in wide-spread use in various applications, for example solar cells, electronics and various sensors. The passage of electronic current through them depends on potential barriers at the grain boundaries. Consequently, the materials have exceptional electrical properties that can for instance be used in varistors and gas sensors.
- Gas sensors are used in anything from detecting toxic gases to air quality monitoring. The R&D efforts were carried out together with Environics Oy, a company specialising in such products as gas detectors for the authorities, Varpula explains.
A more every-day application of measuring gas molecules is breathalysers intended for consumers. Additionally, gas molecules have a link with diseases: an electronic nose can be used to detect and recognise such illnesses as diabetes, which causes the patient to exhale acetone fumes.
Experiment produced a micro gas sensor
In this study, a new physical chemistry related property of gas sensors was discovered and modelled: negative admittance. In addition, the study succeeded in explaining and modelling another new phenomenon, bias-dependent sensitivity. This can be used to improve the selectivity of gas sensors, or to improve their ability to sense and identify various gases.
The extensive cooperation project also designed and produced a micro gas sensor using a thin film created by means of atomic layer deposition (ALD).
- The ALD technique developed in Finland has not been used in this type of a gas sensor before, Varpula points out.
The ALD thin film improves the stability of the sensors, preventing variations while in use. The sensors can be used to measure e.g. ethanol and acetone fumes.
Text: Annika Artimo
Lic Sc (Tech) Aapo Varpula
tel. 050 374 8060
aapo.varpula [at] gmail [dot] com
To read the entire thesis, go to Thesis online (lib.tkk.fi)