Threshold Voltage Tuning in a-IGZO TFTs With Ultrathin SnOx Capping Layer and Application to Depletion-Load Inverter

Tunable threshold voltage of a thin-film transistor (TFT) is highly desirable for designing multifunctional electronic circuits. In this letter, an ultrathin SnOx capping layer was adopted to modify the threshold voltage of bottom-gate amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs. A threshold voltage shift from 15.2 to -9.0 V was observed as the SnOx thicknesses increased from 0 to 19 nm, accompanying by a sizable increase of the intrinsic electron concentration in the channel layer. It was believed that the SnOx capping layer can extract loosely bound oxygen from the a-IGZO, which was supported by the SnOx composition variation with its thickness. Combining an uncovered a-IGZO TFT with a SnOx capped a-IGZO TFT, an enhancement/depletion inverter with a voltage gain of up to 45.9 was successfully demonstrated.