Sensitivity, selectivity and stability of tin oxide nanostructures on large area arrays of microhotplates

In this paper, the sensitivity, stability and selectivity of nanoparticle engineered tin oxide (SnO2) are reported, for microhotplate chemical sensing applications. 16 angstrom of metals such as nickel, cobalt, iron, copper and silver were selectively evaporated onto each column of the microhotplate array. Following evaporation, the microhotplates were heated to 500 degrees C and SnO2 was deposited on top of the microhotplates using a self-aligned chemical vapour deposition process. Scanning electron microscopy characterization revealed control of SnO2 nanostructures in the range of 20-121 nm. Gas sensing in seven different hydrocarbons revealed that metal nanoparticles that helped in producing faster nucleation of SnO2 resulted in smaller grain size and higher sensitivity. Sensitivity as a function of concentration and grain size is addressed for tin oxide nanostructures. Smaller grain sizes resulted in higher sensitivity of tin oxide nanostructures. Temperature programmed sensing of the devices yielded shape differences in the response between air and methanol, illustrating selectivity. Spiderweb plots were used to monitor the materials programmed selectivity. The shape differences between different gases in spiderweb plots illustrate materials selectivity as a powerful mapping approach for monitoring selectivity in various gases. Continuous monitoring in 80 ppm methanol yielded stable sensor response for more than 200 h. This comprehensive study illustrates the use of a nanoparticle engineering approach for sensitive, selective and stable gas sensing applications.