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2 Electron Technology

2 2000

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Sensitivity of the atomic layer epitaxy (ALE) deposited SnOx thin films in function of their oxygen content

Varhegyi E. B., Perczel I. V., Pinter Z., Utriainen M., Reti F.

Electron Technology

2000

Vol. 33, No. 1/2

79-81

The SnOx layer deposited with a conventional atomic layer epitaxy (ALE) technique is highly oxygen deficient and the sensor has low resistance which increases with time. The CO sensitivity of the as deposited sensors is very low: as their resistance is low (great amount of charge carrier) the modification of the charge carrier concentration by the gas to be detected is negligible. A moderate temperature oxidative heat treatment leads to oxygen incorporation and to sensitivity increase. The oxygen incorporation into the vacancies was proved with AES and XPS analyses.

Characterization of oxide semiconductor gas sensors by the complex analysis of surface physico-chemical processes

Reti F.

Electron Technology

2000

Vol. 33, No. 1/2

255-260

This work discusses the importance of complex characterization of the surface (and bulk) physico-chemical processes taking place on the oxide semiconductor based chemical sensors during their high temperature operation. Several new result obtained at the Departament of Atomic Physics, Technical University of Budapest on β-Ga₂O₃ , CeO₂ and SrTiO₃ are presented. The applied modern and sophisticated research tools are: resistance measurements - impendence spectroscopy, ageing tests and surface analyses, self-heating and oven-heating, mass spectrometer coupled microreactor, kinetic studies. The DC method is the usualy way of reading the sensor signal. However, the AC measurement technique(impendence spectroscopy) made possible to distinguish the elementary steps of different time constants in the effect of oxugen on β-Ga₂O₃. This method seems also to be proper to increase the sensitivity and even selectivity. The long term ageing tests helped to estimate the stability of sensor materials in the presence of chemically reactive (corrosive) components. Combining this method with surface analyses (AES,SIMS and XPS) the compositional and structural changes were investigated. It was found that the sensor response depends on the heating mode applied. The question arises: in what extent the results of laboratory tests obtained by oven-heating can be transferred to the sensors applied in practice, operated by self-heating. The role of gas phase reactions is treated. Simultaneous resistance measurements and mass spectrometric analyses of the near surface gas environment allowed to detect the compositional chnages in the gas phase caused by the sensor and to understand the role of these chemical transformations in the sensing process. Conclusions were drawn on the catalytic activity of the sensor surface in the detection of certain reducing gases. The monitoring of DC resistance in function of time gave an insight into the kinetics and mechanism of the surface processes. The water/oxide-semiconductor surface interaction is discussed in detail.