Surface Plasma Treatment and Sensibilization of Tin Dioxide Films for Enhancement of Gas Sensitivity and Selectivity

摘要

Results of investigation aimed at the improvement of gas sensitive characteristics of tin dioxide thin film's based gas sensors through their treatment in high frequent (HF) oxygen plasma and sensibilization by means of doping are presented. Tin dioxide thin films were deposited from alcohol solutions of SnCl_4 5H_2O by means of chemical spray pyrolysis method on alumina substrate at the temperatures in the range from 400 to 500°C. The thickness of films was varied in the range 20-100 nm. Surface treatment of obtained tin dioxide layers was carried out in pure oxygen plasma at room temperature and 3-4 times increase of the resistance and gas sensitivity was obtained at that. These parameters' changing is discussed from the point of view of thin film's stoichiometry alteration, for control of which there were used IR and SIMS measurements. Obtained results are compared with results of the film's high temperature (～600°C) thermal annealing on air. To increase thin film's gas sensitivity and selectivity the doping with Pd and Cu was applied. Doping was carried out also through chemical spray pyrolysis method from the solutions of corresponding compounds of Pd and Cu. Such modification of SnO_2 surface has allowed to increasing sensitivity to H_2 up to 5 10~3 rel. units (high selectivity) at the simultaneous shift of sensitivity maximum from 350 to 150°C. Doping with Cu has allowed to increasing 4-5 times sensitivity and selectivity toward CH_4 and C_3H_8 gases in air and reducing operating temperatures from 500-520°C to 350-370°C. It is concluded that combination of HF oxygen plasma tin dioxide film' treatment and its surface sensibilization is an effective way to considerably improvement of gas sensitive and selective characteristics of tin dioxide based thin film gas sensors (TFGS).