Analysis of Mechanical and Electrical Origins of Degradations in Device Durability of Flexible InGaZnO Thin-Film Transistors

Abstract

Mechanically flexible In−Ga−Zn-O (IGZO) thin-film transistors (TFTs) were fabricated and characterized on poly(ethylene naphthalate) (PEN) with various film thicknesses. The physical origins of mechanical and electrical degradations in device characteristics were extensively and systematically investigated under various mechanical strain conditions to improve the device operational reliabilities. To investigate the mechanical durability of the IGZO TFTs, the effects of PEN thickness on the variations in critical radius of bending curvature were analyzed, which were estimated to be 3, 7, and 14 mm, when the PEN thickness was 25, 50, and 125 μm, respectively. During the cyclic bending tests for the TFTs fabricated on 25 μm thick PEN, the operation cycles were estimated to be markedly reduced from 10 000 to 150 when the applied strain increased from 0.3 to 0.45% (critical strain), respectively. It was clearly suggested that the main origin for the device degradation under bending deformation could be altered from electrical to mechanical ones in the vicinity of the critical strain determined by critical radius of curvature. In other words, the evolution of microcracks and the variations in the density of states within the IGZO channel were found to have critical impacts on the device characteristics of the flexible IGZO TFTs above and below the critical strain, respectively. Consequently, the systematic analysis and the obtained results provided design guidelines and insights for implementing more mechanically robust devices in flexible electronics.

Chemically Tunable Organic Dielectric Layer on an Oxide TFT: Poly(p-xylylene) Derivatives

“…In this study, the flexible TFT was fabricated without any buffer layer between the substrate and active layer and had a relatively large size (active layer 1 × 1.5 mm, width and length 800 and 200 μm, respectively). Despite the large size of the TFT and the absence of a buffer layer, the fabricated flexible TFT with a PPx dielectric layer exhibited excellent bending durability in comparison to previously reported TFTs. , Further research is currently underway to optimize the flexible or stretchable TFT fabrication process.…”

“…Despite the large size of the TFT and the absence of a buffer layer, the fabricated flexible TFT with a PPx dielectric layer exhibited excellent bending durability in comparison to previously reported TFTs. 70,71 Further research is currently underway to optimize the flexible or stretchable TFT fabrication process.…”

A natively flexible 32-bit Arm microprocessor

“…IGZO TFTs are known to be bent to a radius of curvature of 3 mm without damage 22 , which PragmatIC has also verified through repeated bending of its own circuitry to this radius of curvature. However, all PlasticARM measurements are performed while the flexible wafer remains on its glass carrier, using standard wafer test equipment located at Arm Ltd, at room temperature.…”

FlexiCores

“…FlexLogIC supports IGZO circuits made using n-type TFTs with resistive pull-up. The circuits are manufactured on a 30 µm flexible polyimide substrate which enables the TFTs to flex up to a radius of curvature of 3 mm without damage [41]. To fabricate IGZO integrated circuits, FlexLogIC uses a proprietary manufacturing process that deposits layers of IGZO TFTs and resistors and four routable aurum-free metal layers onto a 200 mm wafer of polyimide which has been spin-coated onto a glass backing.…”