LTPO-TFT Compensating Pixel Structure Reduces Thermally Generated Leakage Current in Low-Frame-Rate AMOLED Displays

This work proposes a new pixel circuit that is based on low-temperature polycrystalline silicon and oxide (LTPO) thin-film transistors (TFTs) for use in low-frame-rate smartwatch active-matrix organic light-emitting diode (AMOLED) displays. The LTPO circuit features a leakage-balancing structure that includes amorphous indium-gallium-zinc oxide (a-IGZO) TFTs, which suppresses voltage distortion at the gate node of the driving TFT (D-TFT) and stabilizes the OLED current (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {OLED}}$ </tex-math></inline-formula>) at high temperatures. To achieve a pure black image, the anode of each OLED is actively discharged during the reset period to release the accumulated charge. The feasibility of the proposed circuit is evaluated using TFT models that were developed from experimental data on 1.28-in display panels. Analytical results reveal that the relative current error rates are below 5.87% and 5.45% at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$25~^{\circ }$ </tex-math></inline-formula>C and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$85~^{\circ }$ </tex-math></inline-formula>C, respectively, with a ±0.3 V change in the threshold voltage (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {TH}}$ </tex-math></inline-formula>) of p-type D-TFT. At <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$85~^{\circ }$ </tex-math></inline-formula>C, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {OLED}}$ </tex-math></inline-formula>s maintain low current deviation rates at different gray levels during a prolonged emission period of 1 s, demonstrating the high feasibility of using the proposed circuit for low-frame-rate operation of AMOLED displays.