Micro-LED Pixel Circuit Using Low-Temperature Poly-Si Oxide TFTs With Fast Rise and Fall Times of Pulse Width Modulation for Low Gray Expression

• Published in: IEEE electron device letters 2023-09, Vol.44 (9), p.1-1
• Main Authors: Kim, Junyeong, Lee, Heonbang, Jeong, Myeonggi, Bae, Jinbaek, Park, Chanju, Jang, Jin
• Format: Article
• Language: English
• Subjects: Brightness; Circuits; Current measurement; Error analysis; Gray scale; Inverters; Light emitting diodes; Low temperature; low-temperature poly-Si oxide; Micro-LED; pixel circuit; Pixels; Polysilicon; Pulse duration modulation; Pulse width modulation; Semiconductor devices; Thin film transistors; thin-film transistor; Threshold voltage
• ISSN: 0741-3106; 1558-0563
• DOI: 10.1109/LED.2023.3299958

We report a micro light-emitting diode (μLED) pixel circuit using low-temperature poly-Si oxide (LTPO) thin film transistors (TFTs). The pixel circuit operates by pulse width modulation (PWM) to prevent the wavelength shift of μLED. The proposed PWM can support 10-bit gray scale at a refresh rate of 120 Hz by PWM, thanks to the fast rise and fall times. Note that the circuit also compensates for the variation of the threshold voltage (VTH) of the TFTs in the pixel. It is found that the current error rate is 3.7%, and the maximum pulse width error rate is 3.4% for low gray levels when the VTH shift is 0.5 V. The fabricated pixel circuit successfully demonstrates PWM of variable gray levels, with measured rise and fall times of 3 μs and 0.3 μs, respectively. Therefore, the proposed pixel circuit is suitable for μLED display capable of expressing 10-bit gray scale at a refresh rate of 120 Hz.