Temperature Dependent Poly Crystalline Zinc Oxide Thin Film Transistor Characteristics

The temperature dependence of the electrical characteristics and parameters of a thin film transistor based on polycrystalline zinc oxide (pc-ZnO TFT) is numerically clarified. The drain current as a function the gate voltage (transfer characteristics), of the pc-ZnO TFT is simulated for temperatures ranging from 300 to 400 K. The transfer characteristics, the drain current versus gate voltage, were first computed. The threshold voltage and the electric field mobility were then extracted from these transfer characteristics. The drain current shows Arrhenius-type dependence with temperature. The activation energy varies almost linearly from 0.57 eV at VGS = 2 V to 0.019 eV at VGS = 26 V then goes up to 0.071 eV at VGS = 40 V. This means that this dependence is very strong in the sub-threshold regime while it is inactivated beyond threshold voltage. The threshold voltage and the electric field mobility were also found to be thermally activated. This temperature dependence may be attributed to the contribution of the density of states to the channel electrons in the sub-threshold region or to speed accumulation of electrons at the pc ZnO/SiO2 interface. However, the contribution of this density of states beyond threshold voltage is negligible. Furthermore, the threshold voltage was found to be proportional to the electric field mobility.