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 (AlO_x) and indium oxide (InO_x) thin films. A photoresist-free-based ultraviolet (UV) patterning process was used to define an InO_x layer as the source/drain region and an AlO _x layer as a passivation layer on the InO_x layer. The Al diffused into the patterned InO_x thin film during a thermal annealing step. As an electrode, the patterned InO_x thin film had low resistivity, and as a channel, the Al-diffused InO_x thin film had a low carrier concentration. Furthermore, the diffused Al behaved as a carrier suppressor by reducing oxygen vacancies within the InO_x thin film. We succeeded in forming a coplanar homojunction-structured metal oxide TFT that used the passivation-induced channel-defining (PCD) method with an AlO _x/InO_x bilayer. The PCD TFT had a field-effect mobility of 0.02 cm²/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.