HUMIDITY SENSITIVITY OF SPUTTERED TIO2 THIN-FILMS

The humidity sensitivity of sputtered TiO2 thin films was studied by d.c. analysis techniques. Three different sets of specimens were prepared by sputtering in different conditions. The films prepared by reactive sputtering from a Ti target showed a current versus relative humidity (r.h.) sensitivity of 4 orders of magnitude in the r.h. range from 2 to 90%. For these films the current-voltage (I-V) characteristics were linear, while films prepared by sputtering from a TiO2 target and those prepared by the thermal oxidation of sputtered Ti layers showed a back-to-back diode behaviour. The formation of Schottky barriers at the metal/oxide interfaces indicates that these films are semiconductors. Using the charging and discharging processes it was determined that for films prepared by reactive sputtering intrinsic electronic conduction was negligible, while for the other films at low r.h. the conduction carriers were mainly electrons, and protons and electrons at high r.h., protons being the dominant carriers. The films prepared by reactive sputtering showed a slow response time during water adsorption, and a faster response time during water desorption.