Design of mechanically and thermally robust foldable electronics

Abstract

In current last decade, the foldable electronics have been drawn the great attention and rapidly developed due to its extraordinary advantages, such as light weight, portability, and free deformation during operating the devices. Finally, the first generation of foldable electronics is commercialized at 2019. However, the conventional mechanical reliability of foldable electronics, such as crack and delamination, is still issue in those commercial products. Thermal reliability has been further reported and as a result, the reliability of foldable electronics has been dealt as a key factor. Moreover, the current foldable electronics are limited to in-folding type, which imposes a compressive strain to the brittle films, unlike expected ideal free-forming type. The out-folding reliability, which imposes a tensile strain to the brittle films, and thermal reliability of devices should be enhanced to realize the free-form foldable electronics under practical operation temperature. In order to improve these reliability, the bending behavior of flexible substrate and thermal stability of pressure sensitive adhesive (PSA) are systematically studied in this thesis. The enlarged maximum tensile strain at edge of three-dimensional substrate bending due to the anticlastic curvature is proposed as a criterion of out-folding reliability. For reducing the maximum tensile strain of substrate under bending, the flexible substrate with a controlled neutral plane by asymmetric impregnation of glass fabric is fabricated. A transparent ITO heater is adopted in laminate to prevent the freezing of PSA at low temperature. Thermally stable PSA satisfied the industrial standard is synthesized by controlling the polymer network.