Monolithic Integration, Performance, and Comparison of Self-Aligned and Conventional IGZO Thin-Film Transistors on a Flexible Substrate

Flexible electronics, most prominently thin-film transistors (TFTs) on plastic substrates, are considered the prime building block for the realization of innovative wearable systems. Two of the currently most successful fabrication processes of transistors on free-standing polymer foils are large-area-compatible devices structured by conventional UV lithography and high-speed transistors realized by self-alignment. Here, both processes, based on InGaZnO (IGZO) technology, are combined for the first time. This not only demonstrates their compatibility, but also showcases the differences between the resulting devices. Concerning the geometry, TFTs with the same nominal designed channel length of 1.5μm exhibit a real channel length of 1.5μm (self-aligned) and 4.5μm (conventional). Furthermore, the integrated side-by-side fabrication enables the electrical comparison of both types of TFTs excluding external factors. While all TFTs exhibit similar threshold voltages around
$\mathrm {0 V}$
and excellent on/off ratios of
$\approx \mathrm {e10 }$
, conventional TFTs are easier to fabricate and have comparably higher mobilities up to 16cm2V−1s−1. At the same time, self-aligned TFTs demonstrate better ac performance, demonstrating a maximum oscillation frequency of 216 MHz. This integration shows new possibilities for the realization of complex systems made from building blocks optimized for reliability and speed.