Tuning the electrical properties of ZnO thin-film transistors by thermal annealing in different gases

• Different circuits require ZnO thin-film transistors with different thresholds.
• A way to tune (in both ways) the threshold by thermal annealing is demonstrated.
• Different annealing gas environments have shown different effects.
• Zero-bias conductivity changed by nearly six orders of magnitude.
• Annealed devices showed stability over 25 days.

A method has been developed to tune the electronic property of zinc-oxide thin-film transistors (TFTs) by annealing them in different gases. The experiments show that annealing in air increases the threshold voltage of the TFTs, while annealing in nitrogen gas reduces it. The zero-bias conductivity can be changed by nearly six orders of magnitude. With a combination of annealing in air and nitrogen it is hence possible to tune the threshold voltage over a wide range of pre-determined values to satisfy different circuit applications. The annealed devices also show good stability over a 25-day period in ambient air without encapsulation. The effects on other performance parameters of the TFTs and possible physical mechanisms are discussed.