Abstract
ABSTRACTDemonstrated herein is the effect of mechanical stress on the device performance and stability of amorphous indium–gallium–zinc oxide thin-film transistors (TFTs) on a flexible polyimide substrate. Flexible TFTs were placed on jigs with various bending radii to apply different degrees of mechanical strain on them. When the tensile strain on the TFTs was increased from 0.19% to 0.93%, the threshold voltage shifted after a 10,000 s increase in bias–temperature–stress (BTS), under vacuum conditions. The BTS instability was further exacerbated when the device was exposed to the air ambient at a 0.93% strain. The device reliability deteriorated due to the increase in the subgap density of states as well as the enhanced ambient effects via the strain-induced gas permeation paths.
Highlights
Flexible displays have gained much attention due to their thinness, lightness, and durability, along with their adaptability to arbitrarily shaped surfaces compared to the conventional glass substrate-based displays
Among the many existing flexible substrates, such as plastic films, metal foil, and thin glass [1,2], polyimide (PI) plastic films are commonly used for fabricating flexible displays due to their high glass transition temperature ( ∼ 400°C) and low coefficient of thermal expansion (10 < ppm K−1) [3]
Several research groups have reported the electrical performance of flexible aIGZO thin-film transistors (TFTs) under mechanical stress, but no significant change has been observed [4,5,6,7,8,9]
Summary
Flexible displays have gained much attention due to their thinness, lightness, and durability, along with their adaptability to arbitrarily shaped surfaces compared to the conventional glass substrate-based displays. Amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors (TFTs) have desirable electrical properties, such as high mobility, high ION/IOFF ratio, and good stability, compared to the conventional amorphous silicon, as well as a low process temperature, good uniformity, and a low fabricating process cost, making it suitable for flexible applications. Several research groups have reported the electrical performance of flexible aIGZO TFTs under mechanical stress, but no significant change has been observed [4,5,6,7,8,9]. Reported in this paper are the electrical performance and stability of a-IGZO TFTs on a PI substrate for various degrees of mechanical stress created by changing the bending radius. Electrical, and thermal stress conditions were applied until differences in instability characteristics were observed, to investigate the effect of mechanical strain on the device characteristics. The subgap density of states (DOS) was extracted to understand the origin of strain-induced instability
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