Fabrication parameters and NO2 sensitivity of reactively RF-sputtered In2O3 thin films

The strong sensitivity of the electrical properties of In2O3 thin films toward O-3 and NO2 makes In2O3 a promising material fur gas sensors in the ail quality control and for the safety at work. The microstructure and the related gas-sensitive behavior of reactively sputtered In2O3 thin films can be altered by varying the fabrication parameters like the sputtering power and the composition of the process atmosphere, in particular, the sensitivity can be increased, The layers usually show a [111] texture. However, with specific process conditions (sputtering power: 100 W (power density: 0.32 W/cm(2)), process pressure: 9.0 x 10(-3) mbar, 80% Ar/20% O-2), a preferential [211] texture is obtained. The sensitivity (S = (Delta R/R)/c (gas), Delta R/R is the relative change of the electrical de-resistance, c (gas) is the gas concentration (ppm)) elf the films toward NO2 increases due to the [211] texture by one order of magnitude. At an operating temperature of 400 degrees C, the sensitivity toward 10 ppm NO2 is between 1.6 and 2.1 ppm(-1) and the response time tau(50) is 3.9 min. At 450 degrees C, tau(50) less than or equal to 1.0 min and a very good sensor linearity is found. The sensitivity at 450 degrees C is half as high than at 400 degrees C. These layers exhibit a. one order of magnitude smaller cross-sensitivity toward 10 ppm SO2 and a two orders of magnitude smaller cross-sensitivity toward 60 ppm CO, 100 ppm NH3 and 1000 ppm H-2 than toward 10 ppm NO2. (C) 2000 Elsevier Science S.A. All rights reserved.