Highly Stable, High Mobility Al:SnZnInO Back-Channel Etch Thin-Film Transistor Fabricated Using PAN-Based Wet Etchant for Source and Drain Patterning

We report the electrical characteristics of backchannel etch (BCE) metal-oxide-semiconductor thin-film transistor (TFT) comprised of aluminum-doped tin-zinc-indium oxide (ATZIO). It has high etch selectivity in wet chemical etchants, which consist of H₃PO₄, CH₃COOH, and HNO₃. This is contrary to the conventional metal-oxide-semiconductors of indium-gallium-zinc oxides, which are highly soluble in the acidic chemicals. As a result, no etch stop layer is needed to protect the backchannel from the wet etchant damage during the source and drain patterning in the bottom-gate-staggered TFT structure. This provides the possibility of oxide TFT fabrication process made as simple as that of the current amorphous silicon TFT using three or four photomasks with short channel length and less parasitic capacitance. The electrical characteristics of our ATZIO BCE-TFTs have the mobility of 21.4 cm²/V · s, subthreshold swing (S.S) of 0.11 V/decade, and threshold voltage of 0.8 V. In spite of the BCE structure, they have excellent stability against bias temperature stress, which shows the threshold voltage shifts of +0.75 V and -0.51 V under the prolonged positive (+20 V) and negative (-20 V) gate bias stresses for 10 000 s at 60 °C, respectively.