Tantalum (Ta) is suggested to act as an electron donor and crystal phase stabilizer in titanium oxide (TiO x). A transition occurs from an amorphous state to a crystalline phase at an annealing temperature above 300 C in a vacuum ambient. As the annealing temperature increases from 300 C to 450 C, the mobility increases drastically from 0.07 cm 2 /Vs to 0.61 cm 2 /Vs. The remarkable enhancement of thin film transistor performance is suggested to be due to the splitting of Ti 3d band orbitals as well as the increase in Ta 5þ ions that can act as electron donors.

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