Contact Effects in Amorphous InGaZnO Thin Film Transistors

Control of the source-drain contact properties in amorphous InGaZnO semiconductor active layer is relevant since a high series resistance in the source-drain contacts causes degradation of electrical performance, particularly affecting short channel devices. We developed a method to extract the current-voltage characteristics of the injection contact, assuming that contact effects are negligible in long channel devices and by introducing a modified gradual channel approximation (quasi-two-dimensional model), to take into account for short channel effects. The present method allows to extract the parasitic resistance by using devices with only two different channel lengths. Assuming a transmission line scheme for the contact resistance and SCLC transport for the current density flowing along the vertical direction though the IGZO bulk, we have been able to evaluate the variation with Vds of contact resistance at source and drain electrodes.