Plasma-enhanced atomic layer deposition of Sn-doped indium oxide semiconductor nano-films for thin-film transistors

Sn-doped indium oxide (ITO) semiconductor nano-films are fabricated by plasma-enhanced atomic layer deposition using trimethylindium (TMIn), tetrakis(dimethylamino)tin (TDMASn), and O2 plasma as the sources of In, Sn and O, respectively. A shared temperature window of 150 degrees C- 200 degrees C is observed for the deposition of ITO nano-films. The introduction of Sn into indium oxide is found to increase the concentration of oxygen into the ITO films and inhibit crystallization. Furthermore, two oxidation states are observed for In and Sn, respectively. With the increment of interfaces of In-O/Sn-O in the ITO films, the relative percentage of In3+ ions increases and that of Sn4+ decreases, which is generated by interfacial competing reactions. By optimizing the channel component, the In0.77Sn0.23O1.11 thin-film transistors (TFTs) demonstrate high performance, including mu FE of 52.7 cm2 V-1 s-1, and a high ION/IOFF of similar to 5 x 109. Moreover, the devices show excellent positive bias temperature stress stability at 3 MV cm-1 and 85 degrees C, i.e. a minimal Vth shift of 0.017 V after 4 ks stress. This work highlights the successful application of ITO semiconductor nano-films by ALD for TFTs.