About reflective LCD

Reflective LCD technology is an important element in our recent research plans.

Table: Fundamental characteristics of reflective LCDs.

Mode of LC		Principle
		Outline	Off state	On state
Trans- mission	TN	Most common mode used in the LCDs.
	ECB	By changing the orientation of the LC with an electric field, the birefringence changes and, with polarizers, controls the transmitted light intensity and color.
	F-STN	A TN-LCD consists of one polarize and one optical compensator.
Absorption	GH	A GH is an LC material containing a dye or pigment whose light absorption properties vary depending on its orientation. In the electric field, the orientation of the LC changes and light is absorbed by the dye; as a result, the displayed color changes.
	PCGH	A GH in which the phase of LC change.
Selective reflection	PSCT	In the planar state, a cell reflects incident rays due to the selective reflection from the texture, and appears bright. In the focal conic state, the incident rays are transmitted and typically absorbed by a non-reflective coating on the rear of the cell. In the strong electric field, a homeotropic texture that is transparent to the light appears (the "on state" in the figure).
Scattering	PDLC	PDLCs consist of LC droplets that are dispersed in a solid polymer backbone. In the field OFF, the random array of droplet provides large differences in refractive indices of the droplets and the polymer, and scatters the light so that the cell appears opaque. In the on-state field, the droplets align to reduce the difference of refractive index, and the cell appears transparent.

LC: liquid crystal TN: twisted nematic ECB: electrically controlled birefringence
F-STN: film-compensated super twisted nematic
GH: guest host PCGH: cholesteric-nematic phase change guest host
PSCT: polymer stabilized cholesteric textures
PDLC: polymer dispersed liquid crystal

The major problem with reflective LCDs is that they are "not bright enough," as a result of which:

• The contrast ratio is rather small
• Colors and white are not clear.

To realize a satisfactory level of brightness, a lot of improvements are needed in, for example, the structure of LC cell, the mode of the liquid crystal material, the reflectors and the optical filters. We will work hard to create better technologies and solutions.