A shift register for depletion-mode oxide TFTs with very low power consumption

Abstract

The shift register comprised of metal-oxide thin-film transistors (TFTs) is apt to exhibit anomalously high power consumption because the oxide TFT often has depletion-mode characteristic. We have developed a new shift register circuit in which one of the pull-down TFTs is controlled by capacitive coupling with the clock signal and the input carry signal. Employing this structure, the TFTs with non-zero V_DS are always turned off with negative V_GS. As a result, unnecessary current through the TFTs is eliminated and the power consumption of the new circuit decreases to the half of our previous one when the threshold voltage of the TFT is −5V.