TFT and Driving for Active‐Matrix Display

This chapter discusses thin-film transistor (TFT) technologies for active-matrix driving and the organic light-emitting diode (OLED) backplane, using a top-gate TFT structure. It shows transistor behavior in linear region operation. A transistor that switches on and off depending on the gate electrode potential is called a field effect transistor (FET). Especially, an FET whose channel conductance is modulated by the gate electrode placed across the dielectric layer is called a metal oxide semiconductor field effect transistor (MOSFET). An OLED device is driven by electric current, and to satisfy the luminance specification with respect to visibility in ambient environment conditions, a large current is necessary. The chapter explains the TFT characteristics necessary for this purpose. There are many difficulties with the low-temperature polysilicon (LTPS)-TFT formation process using excimer laser annealing (ELA), such as laser stability, TFT performance variation, poor laser process productivity, and lack of substrate size scalability. The chapter considers new approaches to these issues.