Depletion Mode Oxide TFT Shift Register for Variable Frame Rate AMOLED Displays

This letter demonstrates a shift register circuit at the backplane of depletion mode oxide thin-film transistors (TFTs), which can cover variable frame rates for low-power active matrix organic light emitting diode (AMOLED) displays. The proposed scheme focuses on the stable gate control of a pull-up TFT by securing the charging and discharging paths at the wide operating frequency range. In a prototype high-definition (HD: 1366 × 768) AMOLED panel, it is ensured that fabricated shift registers operate at the wide frame frequency range from 1 to 240 Hz. The measured current consumptions are 30, 4, 6, and 5.8 mA for four clock signals, VGH of 24 V, VGL1 of -6 V, and VGL2 of -14 V at a frame rate of 120 Hz.