Sun-Wook Choi

Vertical alignment of liquid crystals without alignment layers

We propose a method for vertical alignment (VA) of liquid crystals (LCs) without alignment layers by mixing only a very low concentration (0.05 wt%) of an organic compound with LCs. The electro-optic characteristics of a VA cell fabricated by the proposed method were almost the same as those of a conventional VA cell with VA layers. Moreover, we used the proposed method to realise a polymer-stabilised VA device with a rapid response time without alignment layers. The proposed method can simplify the fabrication process and reduce the manufacturing cost of LC display devices by removing the need for alignment layers and the alignment process such as coating of polyimide layers and the UV exposure for the photo-alignment. We believe that the proposed method can play an essential role in the fabrication of plastic flexible LC display devices requiring the low-temperature process.

Dual mode switching of cholesteric liquid crystal device with three-terminal electrode structure

We propose a cholesteric liquid crystal device with a three-terminal electrode structure that can be operated in both the dynamic and the bistable modes. Fast switching (less than 5 ms) between the planar and the in-plane-field-induced states can be realized by applying an in-plane electric field, and conventional bistable switching between the planar and focal conic states can be realized by applying a vertical electric field.

Formation of Polymer Networks for Fast In-Plane Switching of Liquid Crystals at Low Temperatures

We formed a polymer structure to enable fast in-plane switching of liquid crystals at low temperatures. The problem of the inevitable slow response at low temperatures was reduced by the formation of in-cell polymer networks in in-plane switching (IPS) cells. The electro-optic characteristics of polymer-networked IPS cells were measured at temperatures ranging from -10 to 20 °C. The turn-on and turn-off times of an IPS cell were reduced by 44.5 and 47.2% at -10 °C by the formation of polymer networks. We believe that the proposed technology can be applied to emerging display devices such as mobile phones and automotive displays that may be used at low temperatures.

High-transmittance Multi-domain Vertical Alignment Liquid Crystal Device with Protrusion Structure

We propose a high-transmittance multi-domain vertical alignment liquid crystal device with a protrusion structure. Disclination lines, which inevitably appear at the boundaries of domains in a multi-domain structure, can be reduced by adding a protrusion structure on the top substrate. The transmittance was improved by 11% using the proposed structure with no change of either the dark state or the operating voltage.

Formation of Dual Threshold in a Vertical Alignment Liquid Crystal Device

We present a method that enables dual threshold voltages in a vertical alignment liquid crystal device, through which the gamma shift can be reduced with no subsequent decrease in the contrast ratio. By forming polymer layers, the threshold voltage shift is accomplished through the utilization of the voltage drop effect. We expect that the proposed method can be applied to the conventional 4-domain mode in order to achieve an 8-domain mode without the need for complex driving schemes.

Fast Fringe-field-switching Liquid Crystal Cell with a Protrusion Structure

We propose a cell structure for the fast switching of liquid crystals by the fringe field. By forming protrusion between patterned electrodes, we can obtain enhancement of response time. The protrusion reduces the effective cell gap, with which a fast response time can be realized. There is little decrease in the transmittance because the protrusion is located between patterned electrodes. We confirmed that the total response time can be decreased by 33% with little loss of the transmittance by optimizing the shape of the protrusion structure.

Experimental evaluation of arrayed microcolumn with a monolithic structure

A 2 � 2 arrayed microcolumn structure based on a monolithic deflector was evaluated experimentally. The microcolumns of this structure consist of electron emission tungsten tips, silicon membrane microlenses, double silicon deflectors, and Cu grid samples. The assembly of the microlens and column component was performed on a custom-built alignment unit consisting of an optical microscope, an alignment jig, and a motor-driven micromanipulator. The alignment of the tungsten tip and microlens hole is performed under direct observation with two perpendicularly aligned microscopes. Microlenses and deflectors (silicon octupoles) are mounted on a low temperature co-fired ceramic (LTCC) substrate. The three-dimensional interconnection structure of the LTCC substrate provides common wiring for each double octupole for synchronous operation. Each deflector was operated with same voltage sources. The 2 � 2 arrayed microcolumns were tested in three modes; single column, independent, and parallel mode, and the properties of these modes were compared. [DOI: 10.1143/JJAP.44.5565]

Vertical Alignment Liquid Crystal Device With Reduced Off-Axis Gamma Shift

We propose a vertical alignment (VA) liquid crystal (LC) device with reduced off-axis gamma shift. We can form a multi-domain structure by simply designing the electrode structure . By applying a different bias voltage to each sub-pixel, we obtained a threshold voltage difference of 2.4 V, without any complex manufacturing process. We confirmed that the off-axis gamma shift can be significantly reduced by the proposed method. We believe that the proposed method can be easily applied to reduce the off-axis gamma shift in vertical alignment LC devices.

Dual mode operation of a chiral-nematic liquid crystal cell using three-terminal electrodes

We propose a chiral nematic liquid crystal cell using three-terminal electrodes that can be operated in both the dynamic and the memory modes. Fast switching between the planar and the in-plane-field-induced states can be realized by applying an in-plane electric field, whereas the memory mode can be achieved by conventional bistable switching between the planar and focal conic states.