p-GaN Gate HEMT-Based 2T1C for Active Matrix μLED Displays

This letter demonstrates an enhancement mode p-GaN gate HEMT-based 2T1C pixel circuit for active matrix (AM) mu LED displays. The 2T1C pixel circuit consists of two p-GaN gate HEMTs serving as the switching and driving transistors and a metal-insulator-metal (MIM) capacitor. The p-GaN gate HEMT shows a threshold voltage of 0.7 V and can provide a maximum driving current of 675 mu A. An on-off ratio of 10(8) is achieved, with an off-state current less than 10 pA. For the capacitor, a 20 nm Al2O3 layer is used as the dielectric, and the measured capacitance density is 4 fF/mu m(2). The proposed 2T1C can drive a 20 mu m mu LED under a scan rate of 120 Hz. The extracted rise time and fall time of the VOUT are 15.75 mu s and 8.42 mu s, respectively. In addition, the pulse amplitude modulation (PAM) of the 2T1C has been demonstrated, showing that the light intensity of the mu LED can be modulated by the amplitude of the data signal.