Effects of post-lift-off annealing conditions on contact oxidation of Ti–Au top-contacts in In-Sn–Zn–O TFT

Thin film transistors (TFT) with an indium based mixed oxide semiconductor are investigated for titanium–gold top-contacts. It is noticed that upon post annealing, in order to remove chemical residuals from top-contact lift-off steps, oxidation of titanium occurs depending on the annealing conditions. Mobility of the TFT is strongly affected by contact oxidation arising from this post lift-off annealing process. Oxidation of the top-contact is facilitated by adsorbed surface oxygen or out-diffusing oxygen from the semiconductor depending on the post lift-off annealing conditions. A passivation layer that binds effectively to surface vacancies and removes adsorbed oxygen species from the semiconductor surface is demonstrated. The combinations of this passivation layer with relatively low temperature and short post lift-off annealing in an oxygen deficient environment result in significantly reduced contact oxidation and subsequently better transistor performance. Contact resistance as low as 90 Ω cm and mobility as high as 5.3 cm²/V s are obtained for solution processed mixed metal oxide semiconductor in top-contact geometry.