Metal-Oxide thin-film transistors (TFTs) present unique opportunities to develop robust, low-cost and transparent electronics that can mechanically endure on flexible and stretchable substrates over large area in an industry compatible technology. Analog to digital converters (ADC) are an essential part of the Internet-of-Everything, where a multitude of sensing applications are envisaged, such as temperature and pressure sensor tags on human skin. In this work, dual-gate InGaZnO TFTs (IGZO) are demonstrated to achieve a 6-bit successive approximation (SAR) C-2C ADC operated at a clock of up to 400Hz and a power dissipation of 52.2µW at a power supply of V dd =15V. The ADC achieves a differential nonlinearity (DNL) of 0.7LSB and an integral nonlinearity (INL) of 0.58 LSB using only n-type TFTs. A figure of merit (FoM) of 66.7nJ/c.s. is achieved from an ADC on flexible substrate.