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

Abstract

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 technology, are combined for the first time. This demonstrates their compatibility, but also showcases the differences between the resulting devices. Concerning the geometry, TFTs with the same nominal designed channel length of 1.5 μm, exhibit real channel length of 1.5 μm (self-aligned) and 4.5 μm (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 0 V and excellent on/off ratios of ≈10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> , conventional TFTs are easier to fabricate, and have comparably higher mobilities up to 16 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . 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.