Best Paper Award

  Flexible liquid crystal displays (LCDs) using plastic substrates have advantages of thinness, light weight, softness and bendability. These features contribute to expansion of the degree of freedom in their portability, installation, and design, and creation of new viewing methods. Therefore, flexible LCDs have attracted significant interest as next-generation displays. For realization of flexible LCDs, the plastic substrate is required to have high dimensional stability against temperature during the fabrication process for the liquid crystal alignment layer and the thin film transistors.
   To address that issue, this study focused on fabrication of flexible LCDs using polyimide (PI) substrates which have high thermal stability. Previously, a coat-debond method was proposed for fabrication of ultra-thin PI substrate. However, application of PI substrates for high-performance flexible LCDs has been difficult because conventional PI substrates have low transmittance and large optical anisotropy along the thickness direction. These optical characteristics had negative influences on the viewing angles and contrast ratios of flexible LCDs.
   This paper proposed a coat-debond method using a novel PI material for high-performance flexible LCDs. The ultra-thin PI substrates with high heat resistance are formed on glass plates with dimensional stability. As a result, the authors have succeeded in formation of a 10 μm thickness transparent PI substrate in this study. Transmittance of fabricated PI substrates showed 90% in the visible light range and independence on wavelength. Also, the optical anisotropy along the thickness direction of the fabricated PI substrate was 1/10 of that of conventional PI substrate. In addition, improvement of the viewing angles of devices using PI substrate was observed by optical evaluation of fabricated flexible LC devices. This study clarified that fabricated PI substrates are useful for the substrates of flexible LCDs.
   As mentioned above, this research improved the transmittance and optical anisotropy of conventional PI substrates and demonstrated the possibility of realizing flexible LCDs by means of the coat-debond method. This accomplishment contributes to realization of flexible LCDs and progress on research into fields of application for mobile displays, wearable devices, and automotive displays. Therefore, this paper is deserving of the IEICE Best Paper Award.