IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Thin Films Monday Sessions
       Session TF+MM-MoM

Paper TF+MM-MoM5
On the Ammonia Response Mechanism of Field-effect Gas Sensors with Thin Pt Gates

Monday, October 29, 2001, 11:00 am, Room 123

Session: Thin Film Sensors
Presenter: M. Lofdahl, Linköping University, Sweden
Authors: M. Lofdahl, Linköping University, Sweden
M. Eriksson, Linköping University, Sweden
I. Lundstrom, Linköping University, Sweden
Correspondent: Click to Email
The ammonia sensitivity of Pt gate field-effect chemical sensors shows a strong dependence on the morphology of the thin metal gate. Several investigations have shown that thin Pt gates are necessary to achieve high ammonia sensitivity and that thick gates show a low or even no sensitivity to ammonia.@footnote 1,2,3@ Thin thickness means in this context that the Pt gate metal has to be made so thin that the underlying oxide is partly exposed. However, there exist an optimum, and if the thickness of the metal is made too thin the sensitivity decreases again. In this contribution the morphology of the thin Pt gate has been carefully investigated and characterised by SEM and complementary TEM studies and morphological parameters have been extracted for different processing conditions of the metal film deposition. By correlating the morphological parameters to measurements of the ammonia sensitivity in inert and oxygen-containing ambient the response mechanism is attributed to the existence of Pt-SiO2 boundaries in the metal. Further experimental investigations show that the Pt-SiO2 interfaces acts as catalytic sites for the dissociation of ammonia molecules and diffusion of detectable species from these sites determine the response. The diffusion length of the detectable species from the dissociation sites is strongly dependent on the existence of oxygen in the ambient. In an inert ambient the diffusion length can be several mm, whereas in 20 % of oxygen it is only in the order of mm. The most likely candidate for the detectable species is atomic hydrogen. @FootnoteText@ @footnote 1@ A. Spetz, M. Armgath, and I. Lundström, Journal of Applied Physics 63, 1274-1283 (1988). @footnote 2@ J. F. Ross, I. Robins, and B. C. Webb, Sensors and Actuators 11, 73 (1987). @footnote 3@ M. Löfdahl, C. Utaiwasin, A. Carlsson, I. Lundström, and M. Eriksson, Submitted to Sensors and Actuators B (2001).