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Property-Performance Studies of SnO2 Sensing Films Using Micromachined Arrays

Published

Author(s)

R M. Walton, Richard E. Cavicchi, Stephen Semancik

Abstract

The microstructure and composition of sensing materials profoundly affect the performance of solid state gas sensors. We report property/performance relationships of conductometric gas sensing films deposited on micromachined devices called microhotplates. Two novel lithographic processes are used for depositing catalytic metal/semiconducting oxide sensing films on microhotplates of four-element arrays. The methods rely on the localized heating and temperature control available with each microhotplate. In the first method, the microheater activates a CVD process for selected-area film deposition. In the second, an array is first coated with nitrocellulose and then selected elements are exposed by pulsing heaters to thermally degrade coatings. Following deposition of sensing films by evaporation or sputtering, lift-off of the nitrocellulose removes unwanted material from the rest of the device. Electrical contacts built-in to the microhotplates are used to measure the conductance of sensing films and for in situ monitoring of film growth. We demonstrate the power of this approach for studying film deposition, sintering, and sensor testing. SnO2 films are deposited by heating each 100 υm by 100 υm hotplate to 500 degrees C to 600 degrees C in a flow of tetramethyltin and O2 in Ar. We correlate the effects of catalyst thickness (0 nm to 20 nm), annealing (to 700 degrees C), and composition (evaporated Pd, Pt, Cu and Ni) with gas sensing response from 100 degrees C to 500 degrees C. SEM images show that annealing changes the morphology of metal catalysts on oxide grains to produce islands or porous structures that enhance sensitivity to reducing gases.
Citation
Property-Performance Studies of SnO<sub>2</sub> Sensing Films Using Micromachined Arrays

Keywords

gas sensors, microhotplates, micromachined arrays, sensing films, sensing materials, solid state gas sensors

Citation

Walton, R. , Cavicchi, R. and Semancik, S. (1999), Property-Performance Studies of SnO<sub>2</sub> Sensing Films Using Micromachined Arrays, Property-Performance Studies of SnO<sub>2</sub> Sensing Films Using Micromachined Arrays (Accessed March 1, 2024)
Created February 22, 1999, Updated February 17, 2017