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-<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>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<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text {q}}\text {)}$ </tex-math></inline-formula> down to 10 nA for the LDO. The ITO TFTs show great electrical robustness in bending experiment under bent radii (r<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text {bent}}\text {)}$ </tex-math></inline-formula> of 5 mm with threshold voltage shift (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta $ </tex-math></inline-formula>V<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text {th}}\text {)}$ </tex-math></inline-formula> 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.