Pixel Circuit With P-Type Low-Temperature Polycrystalline Silicon Thin-Film Transistor for Micro Light-Emitting Diode Displays Using Pulse Width Modulation

Abstract

Herein, we present a novel low-temperature polycrystalline silicon (LTPS) thin-film transistor (TFT) pixel circuit for a micro light-emitting diode (<inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>LED) display based on pulse width modulation (PWM). By adopting PWM, we could achieve 10-bit gray levels of <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>LED without wavelength shift, which is a challenge in the realization of <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>LEDs. Furthermore, the proposed circuit compensated for the variation in threshold voltage (<inline-formula> <tex-math notation="LaTeX">${V}_{{\text {TH}}}$ </tex-math></inline-formula>) without an external sensing system. We simulated the error rate of the <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>LED emission time of the proposed pixel circuit depending on the V_TH change. We measured the wavelength shift of the <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>LED using the fabricated circuit. This shift in PWM was smaller than that in pulse amplitude modulation (PAM). Consequently, the proposed pixel circuit could overcome screen distortions caused by color shifts of <inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>LED displays using PWM techniques.