Depletion-Mode Oxide TFT-Based MicroLED Pixel Circuit for High-Current Pulse Width Modulation With Low Driving Voltage

In this article, we propose a pixel circuit suitable for depletion-mode oxide thin-film transistors (TFTs) to drive micro-light-emitting diode (<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) with pulse width modulation (PWM). In the proposed pixel circuit, both the constant current generation (CCG) part and the PWM part compensate for the variation 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 the driving TFT (DRT) through a source-follower structure and store the data voltage entirely without capacitive division. By avoiding voltage division, the data range and the corresponding control signal range can be reduced, lowering the switching power. The operation of the proposed pixel circuit is verified and compared with the conventional pixel circuit through simulation using HSPICE from Synopsys, employing an oxide TFT model based on measured data from the fabricated device. In addition, the proposed circuit is experimentally validated through circuit fabrication. Both simulation and experimental results exhibit consistent PWM driving, indicating accurate compensation for variations in both parts, along with enhanced operation.