Electrical humidity response of sol-gel processed undoped and alkali-dopedTiO2-Al2O3 thin films

Al2O3-TiO2 thin films were prepared by a sol-gel processing. Sols were prep ared having different TiO2/Al2O3 molar ratios, i.e., 9:1, 8:2, and 6:4, wit hout and with the addition of 10 at% of K ions. The films were prepared by dipping the substrates (silicon wafers, alkali-fi ee glass or alumina with comb-type Au electrodes) in the sols. The films were fired in air for 1 h a t 300, 500, 650 and 800 degrees C. The films were amorphous, at any composi tion, up to the firing temperature of 500 degrees C. Crystallization of the films was inhibited by larger contents of Al2O3 and K. The humidity-sensit ive electrical properties of the thin films were studied using d.c. and a.c . measurements. The addition of K dramatically improved the relative humidi ty response of the films. (C) 1999 Elsevier Science Limited. All rights res erved.