Bit Depth of Drivers for Micro-LED Displays Adopting Low-Temperature Polysilicon Oxide Thin-Film Transistors

Abstract

In this paper, the minimum bit depth of drivers for active-matrix light emitting diode (AMLED) displays has been specified to overcome luminance nonuniformity of LEDs for the first time. The pixel circuit comprises seven transistors and one capacitor (7T1C) based on low-temperature polysilicon oxide (LTPO) process. For the experiments, thirty green and blue LEDs were used. When the same data voltage was applied, there was luminance nonuniformity of up to 19 % and 41 % for green and blue LEDs compared to the reference LEDs. Data voltages were measured to get the same luminance as the target one. It was found that the maximum voltage intervals of 0.9 mV and 1.1 mV were necessary to overcome the luminance nonuniformity for green and blue LEDs, respectively. 1.62 V and 2.80 V were the data voltage ranges of green and blue LEDs, respectively. The bit depth of 11-bit (2,048) is the minimum one because 1.62 V / 0.9 mV for green LEDs is smaller than 2,047. In this way, at least 12-bit is necessary for the bit depth of drivers for blue LEDs.