Platinum-doped nanogranular-tin dioxide layers prepared by spin-coating from colloidal dispersions as basis for gradient gas sensor micro arrays

Gradient micro arrays of the KAMINA type (Karlsruher Mikronase) were equipped for the first time with thin films of Pt-doped SnO₂ nano-particles. The nano-granular films were prepared from an aqueous colloidal dispersion by spin-coating subsequent to photolithographic structuring of a 3" silicon wafer, opening up 26 windows for the metal oxide deposition. The platinum was introduced by adding ammonium tetrachloroplatinate to the colloidal dispersion. Because of the poor wettability of the substrate, a non-ionic surfactant had to be used. After annealing at 400°C a mean particle size between 20 and 25 nm was determined with field emission scanning electron microcopy (FE-SEM). Depth resolved analysis with secondary neutral mass spectrometry (SNMS) proved the platinum content of ca. 1 at%. Investigations of the gas-analytical performance of the gradient micro arrays revealed a detection limit below 10 ppb for 2-propanol. The response times were found to be in the range of a few seconds.