Analog-to-digital converter with oxide thin-film transistors

Abstract

A three-bit flash analog-to-digital converter (ADC) consisting of inverter-based comparators and logic gates using amorphous indium-gallium-zinc-oxide thin-film transistors (a-IGZO TFTs) was developed. The TFT has a bottom gate structure with a methyl-siloxane-based organic spin-on-glass passivation layer, which reduces the plasma damage on the active layer. A bootstrapped logic gate structure was used in the proposed ADC to overcome the reduced output swing in the inverters and the NAND gates caused by using only n-type a-IGZO TFTs. The output signals of the developed three-bit flash ADC with a-IGZO TFTs well matched the analog inputs. The output voltage swing was 0.2–3.6V, well matching the simulation result. The three-bit flash ADC was verified up to the 1 kHz operation frequency, and thus can be used in sensor applications such as the wearable sensor display and the integrated biosensing platform.