We developed flexible liquid crystal devices using ultra-thin polyimide substrates and bonding polymer spacers, and discussed the effects of polymer spacer structure on the cell thickness uniformity of flexible LCDs. We clarified that the lattice-shaped polymer spacer is effective to stabilize the cell thickness by suppressing the flow of the liquid crystal during bending process.

We investigated the effects of a bending stress on the change in phase retardation of curved polycarbonate substrates and optical characteristics of flexible liquid crystal displays (LCDs). We clarified that the change in phase retardation was extremely small even for the substrates with a small radius of curvature, because bending stresses occurred in the inner and upper surfaces are canceled each other out. We compensated for the phase retardation of polycarbonate substrates by a positive C-plate and successfully suppressed light leakage in both non-curved and curved states. These results indicate the feasibility of high-quality flexible LCDs using polycarbonate substrates even in curved states.

We developed flexible LC devices using coat-debond polyimide substrates with a low birefringence and etched post spacers, and clarified that flexible LCDs using post spacers with small spacer distance have a high flexibility without degradation of the image quality. This result ensured the feasibility of flexible LCDs using coat-debond method.

To develop a flexible liquid crystal display (LCD) with a wide viewing angle range and high contrast ratio, we have proposed a flexible blue-phase LC device sustained by polymer walls inside the LC cell. We clarified that the polymer walls can maintain a constant cell gap and suppress the generation of alignment defects of the blue-phase LC in a bending state.

Optical compensation of flexible in-plane switching (IPS) mode liquid crystal display (LCD) using polycarbonate substrate with uniaxial optical anisotropy was achieved for wide viewing angle. We theoretically clarified that the slow axis of plastic substrate must be parallel to the absorption axis of polarizer and alignment direction of IPS mode LC. We successfully suppressed a light leakage in the dark state in a wide viewing angle range by fabricated device using uniaxial polycarbonate substrates. These results show that it is possible to realize a high quality flexible LCD using plastic substrates.

Electrical characteristics of the mechanically flexible driver LSI as thin as 35 µm mounted directly on a flexible display panel were precisely analyzed. The high-voltage transistors on this LSI show the current decrease by 10-30% in high voltage region, comparing with that of an ordinary thickness LSI. These phenomena can be associated with a self-heating effect. We considered the thermal diffusion on the thin chip by changing material of the measurement stage. Moreover, we analyzed the transistor characteristics on the thin chip under convex and concave bending conditions. The drain current change by piezoresistive effect was observed.