Mechanical and Electronic Properties of Thin‐Film Transistors on Plastic, and Their Integration in Flexible Electronic Applications

Abstract

The increasing interest in flexible electronics and flexible displays raises questions regarding the inherent mechanical properties of the electronic materials used. Here, the mechanical behavior of thin-film transistors used in active-matrix displays is considered. The change of electrical performance of thin-film semiconductor materials under mechanical stress is studied, including amorphous oxide semiconductors. This study comprises an experimental part, in which transistor structures are characterized under different mechanical loads, as well as a theoretical part, in which the changes in energy band structures in the presence of stress and strain are investigated. The performance of amorphous oxide semiconductors are compared to reported results on organic semiconductors and covalent semiconductors, i.e., amorphous silicon and polysilicon. In order to compare the semiconductor materials, it is required to include the influence of the other transistor layers on the strain profile. The bending limits are investigated, and shown to be due to failures in the gate dielectric and/or the contacts. Design rules are proposed to minimize strain in transistor stacks and in transistor arrays. Finally, an overview of the present and future applications of flexible thin-film transistors is given, and the suitability of the different material classes for those applications is assessed.

Metal oxide semiconductor thin-film transistors for flexible electronics

“…Flexible metal oxide semiconductor-based TFTs have not only made their entry in the market of optical displays 30 but also shown to be suitable for other novel electronic systems, e.g., for sensorics, power supplies, as well as data storage and transmission. This wide range of applicability of flexible metal oxide semiconductor technology is owed to its excellent electrical and mechanical properties, combined with unique features like transparency, light-weight, 3D conformability, stretchability, and/or solution-processability.…”

“…To date and to the best of our knowledge, no report has specifically targeted this topic. We are only aware of a book chapter dealing with flexible solution-processed metal oxide semiconductor TFTs, 119 as well as two review articles, respectively, on the mechanical and electronic properties of flexible TFTs (all technologies) 30 and on p-type metal oxide semiconductor materials and devices (rigid and flexible). 120 For this reason, this paper presents the recent progresses in the field of flexible TFTs and circuits, based on both n-and p-type metal oxide semiconductors grown by vacuum-and solutionprocessing techniques.…”

“…Among the state-of-the-art flexible TFT technologies, metal oxide semiconductors are especially suitable, owing to their high optical transparency, 29 good electrical performance [electron carrier mobility of !10 cm 2 V À1 s À1 even if processed at room temperature (RT)], 29 as well as excellent mechanical properties (large bendability down to 25 lm radii and good insensitivity to strain). 23,30 Table I provides a summary and a comparison of the most important device properties for the established flexible TFT technologies: amorphous silicon (a-Si), 31,32 organic semiconductors, 14,33 low temperature poly-crystalline silicon (LTPS), 34,35 and metal oxide semiconductors. As evident from Table I, metal oxide semiconducting technology presents several advantages typical of a-Si and organic materials, such as low cost, low process complexity and temperature, and large-area scalability, but at the same time yields a larger carrier mobility.…”

“…36 Furthermore, metal oxide semiconductor TFTs show a larger resistance to mechanical strain if compared with LTPS devices. 30 This is why metal oxide semiconductors are considered the most prominent candidate for next-generation flexible high-resolution active matrix organic light emitting diode (AMOLED) display backplanes, [38][39][40][41] as well as the most suitable technology to fuel the realization of tomorrow's ubiquitous electronics. Main aim of this review is to report the recent advances obtained in the field of flexible metal oxide semiconductor TFTs: from single devices (Sections II and III), large-area circuits (Section IV) up to entirely integrated systems (Section V).…”

The development of flexible integrated circuits based on thin-film transistors

“…A recent review of the effects of mechanical stress on the intrinsic electrical performance of different semiconductors concluded that amorphous metal-oxide semiconductors are the most resilient under mechanical strain 11 . In addition, semiconductors are patterned mostly into small islands and the critical layers of the TFT stack can be located near the neutral plane of the full stack by matching the substrate and the topstrate or encapsulation.…”