p-GaN Gate HEMT-Based 2T1C for Active Matrix <i>μ</i>LED Displays

This letter demonstrates an enhancement mode p-GaN gate HEMT-based 2T1C pixel circuit for active matrix (AM) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$675~\mu $ </tex-math></inline-formula>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/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>m2. The proposed 2T1C can drive a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20~\mu $ </tex-math></inline-formula>m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>LED under a scan rate of 120 Hz. The extracted rise time and fall time of the VOUT are <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$15.75~\mu $ </tex-math></inline-formula>s and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8.42~\mu $ </tex-math></inline-formula>s, respectively. In addition, the pulse amplitude modulation (PAM) of the 2T1C has been demonstrated, showing that the light intensity of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>LED can be modulated by the amplitude of the data signal.