We introduce drive schemes for fast switching of nematic liquid crystals (LCs) using three-terminal electrodes. Fast switching of LCs can be achieved by employing a vertical trigger pulse, by applying a vertical bias field, and by employing quasi-impulsive driving and overdrive. By applying high vertical and in-plane trigger pulse voltages between frames to an LC cell, the response time of the LC cell at -20°C was decreased by 12.5 times compared to that of a conventional fringe-field switching (FFS) cell. In addition to providing a fast response, the LC cell exhibited the same high transmittance as an FFS cell over a wide temperature range.
Recently, low-frequency driving of a display panel to reduce the power consumption has drawn much attention, especially in mobile devices. In case a liquid crystal display panel is driven by a fringe-field at a low frequency, the image flickering phenomenon can be observed when the sign of the applied electric field is reversed. Image flicker can be eliminated simply by applying a bias voltage to a liquid crystal cell so that the transmittance during the positive frame is the same as that during the negative frame. However, it may be difficult to employ this technique for practical applications because it requires a bias voltage that is dependent on the gray level. In this talk, we introduce methods to eliminate the image flicker by controlling the material parameters of liquid crystals, such as the flexoelectric anisotropy and the dielectric anisotropy. Methods to eliminate image flicker without controlling the material parameters, such as driving by a bipolar wave and optimization of the electrode spacing, are also introduced.
We demonstrate fast gray-to-gray (GTG) switching of a hybrid-aligned liquid crystal cell by applying both vertical and inplane electric fields to liquid crystals (LCs) using a four-terminal electrode structure. The LCs are switched to the bright state through downward tilting and twist deformation initiated by applying an in-plane electric field, whereas they are switched back to the initial dark state through optically hidden relaxation initiated by applying a vertical electric field for a short duration. The top electrode in the proposed device is grounded, which requires a much higher voltage to be applied for in-plane rotation of LCs. Thus, ultrafast turn-on switching of the device is achieved, whereas the turn-off switching of the proposed device is independent of the elastic constants and the viscosity of the LCs so that fast turn-off switching can be achieved. We experimentally obtained a total response time of 0.75 ms. Furthermore, fast GTG response within 3 ms could be achieved.
We propose a method for fast switching of nematic liquid crystals with neither alignment materials nor alignment process. A three-terminal electrode structure is used to apply in-plane and vertical electric fields to randomly-aligned liquid crystals. A vertical field is applied to align liquid crystals vertically for the dark state, whereas an in-plane field is applied to align liquid crystals homogeneously for the bright state. We obtained the turn-on time of 1.2 ms and turn-off time of 0.5 ms in the three-terminal electrode structure with neither alignment materials nor alignment process. However, three-terminal electrode structure with neither alignment material nor alignment process shows low transmittance. For higher transmittance, we mixed reactive mesogen and nano-particles with anisotropic molecular shape to liquid crystals. As a result, we obtained a transmittance similar to the conventional fringe field switching mode and achieved the total response time of less than 3 ms.
We studied two types of bistable liquid crystal devices that can be operated in the memory mode as well as in
the dynamic mode. One of them is a pixel-isolated twist-splay nematic LC cell that has two stable states of π-
twist and splay. Polymer walls are formed at pixel boundaries by anisotropic phase separation between
nematic liquid crystals and reactive mesogens. Operation in the memory mode can be achieved through
bistable switching between the splay and π-twisted states. The other one is a bistable twisted-nematic mode
that has two stable states of -π/2 and +π/2 twist. Three-terminal electrodes are used to apply both vertical and
in-plane electric field to both devices. The proposed bistable modes has an infinite memory time and the fast
transition time compared to other bistable liquid crystal modes.