Fabrication of semiconductor oxide thick films by slide-off transfer printing and their NO2-sensing properties

Semiconductor gas sensors of thick film type were prepared by a slide-off transfer printing method. Slide-off transfer sheets were fabricated by screen printing the paste stuffs of SnO2, TiO2, In2O3 and noble metal-loaded In2O3 mixed with a suitable amount of a printing oil on a mount paper with gum, followed by screen printing a cover coat of lacquer. By firing the oxide sheets transferred on an alumina substrate at 800 degrees C in air, very uniform oxide films of 7-40 mu m thick were obtained for once to four times slide-off transferring in a pile in every case. The thick films could be easily fabricated also on a curved substrate. Furthermore, the method was useful for fabricating heterolayered thick films consisting of different oxide layers. The resultant oxide films of different thickness or heterolayered structure were subjected to sensitivity measurement to 111 ppm NO2 in air. Among the films examined, a 0.5 wt% Au-loaded In2O3 film of about 14 mu m thick exhibited the maximum sensitivity R-NO2/R-air = 120 at 250 degrees C, where R-NO2 and R-air were the resistance in the sample gas and in air, respectively. (C) 1998 Elsevier Science S.A. All rights reserved.