Current Boosting of Self-Aligned Top-Gate Amorphous InGaZnO Thin-Film Transistors under Driving Conditions

Abstract

Oxide semiconductor transistors control the brightness and color of organic light-emitting diode (OLED) displays in large-screen televisions to portable telecommunications devices. Oxide semiconductor thin-film transistors under driving conditions are required to maintain a steady current through the OLED for constant illuminance. Interestingly, for driving conditions under strong saturation where both gate and drain bias are high, a boosting phenomenon of the drain current is discovered, even with compensation of the threshold voltage. In this paper, the current boosting effect of self-aligned InGaZnO transistors under driving conditions is comprehensively investigated. Based on experimental extraction methods, two distinct regions within the device are identified: an electron-capture-dominant region including electron trapping in the gate insulator and O-O dimer bond-breaking, and an electron-emission-dominant region caused by peroxide formation. A dual-transistor-in-series model is proposed, where each region is modeled as a local transistor. The current boosting phenomena as a function of time are well-reproduced for various channel length devices, which validate the accuracy of the model. Better understanding of the underlying mechanisms enables increased effectiveness of compensation schemes for transistors under long-term current-driving conditions.