We developed a new liquid crystal display mode using banana shaped liquid crystals which shows a new type of smectic phase designated as SmX. [1] This phase is apparently the SmA phase; i.e., uniaxial smectic phase, but responds to an applied electric field like a ferroelectric phase. [2] Moreover, we can obtain well aligned cell both in homogeneous and homeotropic fashions. The presented new LCD mode is based on this phase.

The electrooptic response and second harmonic generation (SHG) were measured using a conventional simple setup. All the electrooptic measurements were performed at 135°C in the SmX phase. Homeotropically aligned cells were prepared using two pieces of aluminum foil of 12 µm thick for spacers as well as electrodes with a 100 µm gap. For SHG measurements, homogeneously aligned cells with ITO electrodes and rubbed polyimide alignment layer (AL-1254; JSR) were used.

The transmittance change as a function of the electric field exhibits an ideal performance, as shown in the Fig. 1. The transmittance shows a threshold voltage and starts to increase gradually. The contrast ratio achieved was 3000:1. The inset of Fig. 1 suggests that the response time is independent of the field strength. Except for a low field strength region, the response time upon field termination is almost constant, 40 µs. The response time upon field application is slightly field dependent, from 240 to 130 µs. The SHG intensity gradually increases with increasing the applied voltage, and the signal can be simulated with the two-dimensional Langevin process. The simulation suggested that about 150 molecules cooperatively respond to the applied field through a direct coupling between the quasi-long-range-ordered dipoles and the electric field. The bent molecular shape prohibits the free rotation of individual molecules and is responsible for the cooperative motion.

In conclusion, the high performance LCD mode using banana shaped LC is provided. This mode has all the requirements for an ideal display; (1) fast response (ca. 100 µs), (2) high contrast ratio (3000:1), (3) wide viewing angle (because optically identical to IPS), and (4) continuous gray levels even with a small threshold field. We keep addressing the improvement of this LCD mode. Effort is concentrated on the widening the temperature range of the presented novel phase and the stabilizing layer structure under a high electric field. The details of the improvements will be reported.

[1] Y. Shimbo et al., Jpn. J. Appl. Phys. 45, L282 (2006).

[2] D. Pociecha et al., Phys. Rev. Lett. 91, 185501 (2003).