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 108 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 $ m2. 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.