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

TLDR

Flexible electronics and displays raise questions about the mechanical properties of the electronic materials used. The study investigates the mechanical behavior of thin‑film transistors in active‑matrix displays, examines how mechanical stress alters their electrical performance—especially for amorphous oxide semiconductors—and reviews current and future flexible applications and material suitability. The authors experimentally characterize transistor structures under various mechanical loads and theoretically analyze stress‑induced band‑structure changes, comparing amorphous oxide semiconductors to organic, amorphous silicon, and polysilicon while accounting for strain contributions from other transistor layers. Bending limits are limited by gate dielectric or contact failures, and the authors propose design rules to reduce strain in transistor stacks and arrays, while outlining current and future flexible thin‑film transistor applications and material suitability.

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.