AVS 46th International Symposium
    Thin Films Division Friday Sessions
       Session TF-FrM

Paper TF-FrM10
In-situ Structural, Chemical and Electrical Characterization of WO@sub 3@ Sensor Films

Friday, October 29, 1999, 11:20 am, Room 615

Session: In-situ Characterization and Material Process Imaging
Presenter: S.A. Ding, University of Maine
Authors: S.A. Ding, University of Maine
C.S. Kim, University of Maine
R.J. Lad, University of Maine
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Tungsten trioxide thin films are useful as active elements in semiconducting metal oxide conductance-type gas sensors. To explore the correlation between deposition parameters/post-deposition processing and sensing characteristics of the films, we have used a multi-chambered UHV system to deposit WO@sub 3@ films on r-cut sapphire. In-situ chemical and electrical characterizations of the films were then carried out before and after the exposure to target gases such as H@sub 2@S, Cl@sub 2@ and DMMP. The films were grown using rf magnetron sputtering of a W target in O@sub 2@/Ar mixtures ranging from 0 to 80% O@sub 2@. Additional deposition parameters included growth temperature, rf power and total pressure. Both in-situ RHEED and ex-situ XRD data indicate that a variety of film structures including amorphous, polycrystalline and highly textured films can be achieved by varying those parameters. In-situ conductivity measurements acquired using a four-point van der Pauw method show that the stoichiometry and microstructure have an influence on the electrical behavior of the sensor films. One other important parameter in dictating the electrical characteristics of the sensor films is found to be the deposition rate, which is altered by varying the rf power, O@sub 2@/Ar ratio and the total pressure. The conductivity measurements indicate that the higher rate yields higher baseline conductivity. In-situ XPS study of the films shows the formation of stable surface species upon exposure to the target gases. The observed chemical modification of the surface is discussed within the context of a dependence of sensor behavior on the post-deposition processing of the films.