Fabrication and AC Performance of Flexible Indium-Gallium-Zinc-Oxide Thin-Film Transistors

Abstract

The internet of things or foldable phones call for a variety of flexible sensor conditioning and transceiver circuits. However, the realization of high-performance, large-area, and deformable analog circuits is limited by the materials and the processes compatible with mechanically flexible substrates. Among the different semiconductors, InGaZnO is one of the most promising materials to realize high-frequency flexible thin-film transistors (TFTs) and circuits. In this work, the effect of different geometries, including self-aligned, vertical, and double-gate structures on the AC behaviour of flexible IGZO TFTs is presented. All TFTs are based on Al2O3 insulating layers, InGaZnO semiconductor, and polyimide substrates. The presented TFTs exhibit state-of-the-art performance including a field-effect mobility up to 15 cm 2 /Vs and a mechanical bendability down to radii of 3.5 mm. Due to different trade-offs required in the fabrication, flexible IGZO TFTs with the shortest channel length of 160 nm do not exhibit the highest measured frequency, whereas exceptional maximum oscillation and transit frequencies of 304 MHz and 135 MHz are demonstrated for 500 nm long self-aligned TFTs. Such optimized transistors can be used to realize entirely flexible analog circuits leading towards imperceptible electronic systems.

Ultrashort 15-nm flexible radio frequency ITO transistors enduring mechanical and temperature stress

“…As shown in Fig. 4C, f T remains at 9.4 GHz even after extreme bending cycles of 10,000, which is much higher than the previous IGZO RF transistors with the measurement at much milder bending conditions (25,40). This is much better than the previous flexible oxide RF transistor on thicker Kapton 500HN where f T degrades very fast for more than 50% just after 1000 bending cycles at the same radius of 1 mm (26).…”

“…On the other hand, an amorphous oxide semiconductor with wide bandgap and decent mobility has attracted great attention in thin-film transistor (TFT) applications since the first demonstration of IGZO in 2004 (24), with low thermal budget compatible with a conventional semiconductor process. Previous work on the flexible IGZO TFTs shows mobility values typically below 20 cm 2 /V⋅s, and the highest cutoff frequency achieved is 135 MHz (25). Indium tin oxide (ITO) has recently shown relatively higher mobility on flexible substrate with higher cutoff frequencies for a 160-nm-long channel device (26).…”

Analog and Mixed Signal Circuit Design Techniques in Flexible Unipolar a-IGZO TFT Technology: Challenges and Recent Trends

“…However, scaling of channel length below the micrometer regime and minimizing the overlap capacitances has made possible to reach f T in the range of GHz [63], [64]. Recent reports have documented further scaling of IGZO TFTs channel lengths down to 160 nm [65] and 32 nm [66].…”

Roadmap to Gigahertz Organic Transistors

“…TFTs, in contrast, can be fabricated directly on a wide range of inexpensive, transparent, flexible, stretchable, biodegradable, and/or biocompatible substrates, such as glass, plastics, paper, metal foils, and textiles, to name just a few. A wide range of semiconductors have been employed for the fabrication of TFTs, most notably metal chalcogenides, hydrogenated amorphous silicon (a‐Si:H), polycrystalline silicon, low‐temperature polycrystalline silicon (LTPS) produced by excimer laser annealing (ELA), metal nitrides, metal‐halide perovskites, metal oxides, carbon nanotubes, and single‐crystalline silicon …”