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 O 2 = 0 are obtained as −6.47 V, 23.98 cm2V−1s−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 O 2 , 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 O 2. The increment in current at lower P O 2 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 contact resistance increases from 0.96 to 1.95 kΩ, with respect to the increased oxygen content. The increment in contact 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. [Display omitted] • With increasing O 2 concentration in a-SZTO, I ON and μ FE decrease while the V TH increases. • Higher O 2 concentration increases the energy gap between the conduction band minima and the fermi level, reducing the shallow level defects and trap states. • The oxygen in the SZTO reacts with the electrode (Ti) to form TiOx at the interface. • The TiO x formation makes the contacts highly conducting, and the effective channel length reduces. [ABSTRACT FROM AUTHOR]