Self-Aligned InGaZnO Thin-Film Transistors and Circuits on Transparent Thin Glass and FEP Film

Abstract

Thin-film electronics realized on flexible substrates opens up a new realm of innovative applications, such as wearable technologies that are unviable with conventional electronic systems on rigid carriers. The challenge, however, is to establish the fabrication of miniaturized devices with dimensions at the micrometer scale and to take into account the possibility of misalignment on thin, flexible, and, potentially, soft substrates. One efficient way to structure short channels is to employ self-alignment where the channel length is defined by the gate contact. Such an approach relies on the transparency of the substrate and is extremely time consuming, and if traditional, only partially transparent substrates are used. Here, we implement self-aligned InGaZnO (IGZO) thin-film transistors (TFTs) and circuits on novel flexible and highly transparent substrates, namely, 100- $\mu $ m thin glass and 50- $\mu $ m fluorinated ethylene propylene (FEP) film, resulting in self-aligned IGZO TFTs with channel lengths as short as 2.2 and $4.5~\mu $ m, respectively. The IGZO TFTs on the respective substrates exhibit on-off current ratios and effective mobilities of ${\approx }10^{10}$ and 7.6 cm $^{2} \cdot $ V $^{-1} \cdot $ s−1, and ${\approx }10^{2}$ and 11.5 cm $^{2} \cdot $ V $^{-1} \cdot $ s−1. The ac performance of the TFTs reaches a maximum oscillation frequency up to 147 MHz. The IGZO TFT further demonstrates mechanical stability by showing full functionality on thin glass even when bent to a radius of 25 mm. At the same time, inverters and common-source amplifiers based on self-aligned IGZO TFTs demonstrate operation at frequencies in the kilohertz range. This work presents a facile approach for realizing high-speed and flexible transistors and circuits based on self-alignment, leveraging the merit of transparent substrates.