Homojunction Solution-Processed Metal Oxide Thin-Film Transistors Using Passivation-Induced Channel Definition

A simple method of channel passivation and physical definition of solution-processed metal oxide thin-film transistors (TFTs) has been developed for aluminum oxide (AlOx) and indium oxide (InOx) thin films. A photoresist-free-based ultraviolet (UV) patterning process was used to define an InOx layer as the source/drain region and an AlOx layer as a passivation layer on the InOx layer. The Al diffused into the patterned InOx thin film during a thermal annealing step. As an electrode, the patterned InOx thin film had low resistivity, and as a channel, the Al-diffused InOx thin film had a low carrier concentration. Furthermore, the diffused Al behaved as a carrier suppressor by reducing oxygen vacancies within the InOx thin film. We succeeded in forming a coplanar homojunction-structured metal oxide TFT that used the passivation-induced channel-defining (PCD) method with an AlOx/InOx bilayer. The PCD TFT had a field-effect mobility of 0.02 cm(2)/V·s, a threshold voltage of -1.88 V, a subthreshold swing of 0.73 V/decade, and an on/off current ratio of 2.75 × 10(6) with a width/length (W/L) of 2000 μm/400 μm.