A New 13T4C LTPO MicroLED Pixel Circuit Producing Highly Stable Driving Current by Minimizing Effect of Parasitic Capacitors and Stabilizing Capacitor Nodes

Abstract

In this paper, we proposed a new low-temperature polycrystalline oxide (LTPO) thin-film transistor (TFT) pixel circuit for micro light-emitting diode (μ LED) displays that produces a highly stable and uniform driving current. The proposed pixel circuit suppresses the current level change along with the sweep signal due to the parasitic capacitances and compensates for the TFT's threshold voltage (VTH) variation-induced current error, including even falling shape. In addition, the proposed circuit produces a constant current regardless of the data voltage. As a result, a relative current error rate of less than 2% was achieved across all gray levels under the ±0.5 V VTH fluctuation. The proposed circuit was verified using HSPICE with a low-temperature polycrystalline silicon (LTPS) TFT and amorphous indium-galliumzinc- oxide (a-IGZO) TFT model based on the measured data. The simulation analysis confirmed that the optimal sweep signal input position and pulse width modulation (PWM) and constant current generation (CCG) parts connecting method were key design points for stable and uniform performance.

Keywords

• MicroLED (μ LED)
• pixel circuit
• a low-temperature polycrystalline oxide (LTPO) thinfilm transistor (TFT)
• threshold voltage (VTH)
• compensation
• falling time