A Two-Mask Process for Fabrication of Bottom-Gate IGZO-Based TFTs

A simple process is presented with which a bottom-gate-type oxide thin-film transistor (TFT) can be fabricated by using two photomasks. The active channel, the source-drain electrode, and the pixel electrode layers were simultaneously formed via a single photolithography using a gray-tone mask (GTM). In particular, the gray-tone profiles of the photoresist were carefully observed to ensure process feasibility with the GTM. From the transparent-oxide TFTs fabricated in this letter, functional indices, such as threshold voltage V_T = 4.13 V (at V_DS = 10 V), subthreshold swing S = 0.59 V/dec, field-effect mobility μ_FE = 12.41 cm²/V·s, on-off current ratio lesser than 8 ×10⁶, and transmittance higher than 85%, were obtained.