Active-Matrix Micro-LED Display Driven by Metal Oxide TFTs Using Digital PWM Method

Abstract

This article presents a new micro-light-emitting diode (LED) pixel circuit driven by the digital pulsewidth modulation (PWM) method, in which the threshold voltage compensation of the driving thin-film transistor (TFT) is included. A scan driver integrated by metal oxide (MO) TFTs is also designed to provide the scan signals for pixel circuits array. A micro-LEDs array with <inline-formula> <tex-math notation="LaTeX">$76\,\, \times $ </tex-math></inline-formula> BBB <inline-formula> <tex-math notation="LaTeX">$\times \,\,78$ </tex-math></inline-formula> and a scan driver with 80 stages are simultaneously fabricated by MO TFTs backplane with back-channel etch (BCE) structure. A respective micro-LED display is consequently realized by a peripheral driving system based on a field-programmable gate array (FPGA), which is used as a core control unit to synchronize the scan signals with the data signals. It is shown that the micro-LED in the pixel circuit can operate at a constant current even at the 5-<inline-formula> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> pulsewidth of the emission (EM) signal. The micro-LED display can achieve 256 linear grayscales with an approximately 60 Hz flash rate under the minimum pulsewidth of 40 <inline-formula> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> of EM signal.