Effect of the Oxygen Dependent Device Parameters on the Electrical Properties of A-Si-Zn-Sn-O Thin Film Transistors

The effect of partial pressure of oxygen on the amorphous Si-Zn-Sn-O thin film transistor is investigated. Sputtered amorphous films were deposited at various oxygen partial pressures (O 2 /(Ar+O 2 ) = 0, 0.07, and 0.11). The parameters, such as threshold voltage, field effect mobility, subthreshold slope, and on current for the channel deposited at P O2 = 0 is obtained as -6.47 V, 23.98 cm 2 V −1 s −1 , 663 mV/dec, and 3.11×10 −4 A, respectively. From the transfer curve (I D -V GS ) of transistors fabricated at various P O2 , it is observed that while the threshold voltage shifts from -6.47 to 0.21 V, the current decreases from 3.11×10 −4 to 2.46×10 −4 A with increasing P O2 . The increment in current at lower P O2 is due to the introduction of excess charge carriers as a result of elevated oxygen vacancies. It is further confirmed by the transmission line measurement that the channel resistance monotonously decreases as a function of oxygen flow rate. Moreover, the parasitic resistance increases from 0.96 to 1.95 kΩ, with respect to the increasing oxygen content. The increment in parasitic resistance is a result of the formation of an oxide layer (TiO x ) at the electrode and channel interface. The thickness of the oxide layer increases from 0.86 to 2.81 μm with increasing oxygen partial pressure, suggesting that the effective channel length reduces with increasing oxygen content in the channel layer