A Flexible Low Dropout Regulator Based on InSnO Thin-Film Transistors With Superior Bending Robustness and Ultra-Low Quiescent Current

In this work, a flexible low dropout regulator (LDO) based on InSnO (ITO) thin film transistors (TFTs) on a 50- $\mu $ m polyimide (PI) substrate is demonstrated for the first time. The LDO is realized through integrated depleted- and enhanced-mode (D-mode and E-mode) ITO TFTs with 6-nm and 4-nm thick ITO channel layers respectively. Low-current design in 4-transistors (4T) voltage reference and restriction of tail current in error amplifier are adopted to achieve ultra-low quiescent current (I $_{\text {q}}\text {)}$ down to 10 nA for the LDO. The ITO TFTs show great electrical robustness in bending experiment under bent radii (r $_{\text {bent}}\text {)}$ of 5 mm with threshold voltage shift ( $\Delta $ V $_{\text {th}}\text {)}$ less than 0.01 V. Both the output voltage and line regulation of the LDO change little under rbent of 5 mm. Besides, after 10000 bending cycles, the electrical properties of ITO TFTs maintain unchanged. Therefore, the LDO exhibits great potential in flexible application of power management unit (PMU) with low power consumption.