Characterization of Al2O3 thin films prepared by spray pyrolysis method for humidity sensor

Abstract

Al2O3 thin films were deposited on silicon, steel and nickel substrates to fabricate MOS and MIM devices. The films were prepared by spray pyrolysis method using a spray solution of Aluminium acetyl acetonate dissolved in dimethyl formamide and this solution was sprayed on to the hot substrates at temperatures of 300 and 350°C. The films were amorphous in nature as detected by XRD. Capacitance versus voltage (C–V), current versus voltage (I–V) and capacitance versus frequency (C–f) measurements were taken for these films. MOS capacitor was used as a humidity sensor using the home made humidity sensor setup. ac capacitance and parallel resistance of the capacitor as a function of humidity were studied. It was found that the capacitance value increases from 0.537 to 2.073nf with the increase in relative humidity (RH) from 0 to 90% and the resistance decreases from 153 to 93kΩ with the increase in relative humidity from 20 to 87%. Relative dielectric constant versus temperature measurements were done for the MOS device to check its ferroelectric behavior and its critical temperature was found to be around 66°C. MIM device was also used as a humidity sensor by measuring capacitance as a function of time by keeping the sensor in a dessicator. The 555 timer circuits were used to check the sensor behavior of the MOS device. Volume resistivity and breakdown electric field of the film deposited on steel were measured and found to be 5×1011Ωcm and 5MV/cm, respectively.