Nanoscale manipulation and control of tin oxide nanostructures on large area arrays of microhotplates

This paper describes 36-element arrays of surface micromachined microhotplates as thermal platforms for manipulating and controlling the morphology of tin oxide (SnO/sub 2/) nanostructures for chemical sensing applications. A new technique of using metal nanoparticles as seed layers for the nucleation, growth and control of SnO/sub 2/ nanostructures on microhotplate arrays is described. 16 /spl Aring/ of metals such as nickel, cobalt, iron, copper and silver were selectively evaporated on each column of the microhotplate array. Following evaporation, the microhotplates were heated to 500/spl deg/C and SnO/sub 2/ was deposited on top of the microhotplates using a self-aligned CVD process. SEM characterization revealed control of SnO/sub 2/ nanostructures in the range of 20 nm to 121 nm. Gas sensing in seven different hydrocarbons revealed that metal nanoparticles that helped in faster nucleation of SnO/sub 2/ resulted in smaller grain size and higher sensitivity. Temperature programmed sensing (TPS) on the devices yielded shape differences in the response between air and methanol illustrating selectivity. Spider web plots were used to monitor materials programmed selectivity (MPS). The shape differences between different gases in spider web plots illustrate materials selectivity as a powerful approach for monitoring selectivity in various gases. Continuous monitoring in alcoholic gases yielded stable sensor response for more than 200 hours. This comprehensive study illustrates the use of nanoparticle seeding approach for sensitive, selective and stable gas sensing applications.