Abstract
The surface-type and the sandwich-type humidity sensors were fabricated with nanometer barium titanate film. The resistance, capacitance and impedance properties of the sensors were measured and analyzed at different frequency when relative humidity (RH) changes from 11% RH to 98% RH. The two types of humidity sensors have the similar properties. The results indicate the high sensitivity and influence of frequency. The resistance and the impedance mainly decrease while the capacitance rises as the relative humidity increases. The former are affected greatly by the frequency in low RH but hardly in high RH. The frequency has a various effect on the latter at the whole RH range and the linearity of the Capacitance-frequency (C-f) curve is good. The curves of the impedance are quite consistent with that of the resistance. The humidity mechanisms are discussed based on this. We consider that the humidity sensitive properties are determined mainly by the abundant interfaces among grains, which are affected by the absorbed water.
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