KR20040043296A - Transflective Liquid Crystal Display using HAN Cell and Parallel rubbed VA Cell - Google Patents

Abstract

PURPOSE: A transflective liquid crystal display using a vertically aligned cell rubbed in parallel with a hybrid cell is provided to improve transmissivity and remove asymmetry of a viewing angle. CONSTITUTION: A single pixel of a liquid crystal cell is divided into a reflection mode region and a transmission mode region. The liquid crystal cell is formed using negative liquid crystal. A hybrid aligned nematic cell is applied to the reflection mode region as a liquid crystal mode, and a vertically aligned cell that has been parallel-rubbed is applied to the transmission mode region as a liquid crystal mode. The hybrid aligned cell of the reflection mode region is formed in a manner that a vertically aligned cell is made into a horizontally aligned cell using ion alignment.

Description

Transflective Liquid Crystal Display using HAN Cell and Parallel rubbed VA Cell}

Conventional transmissive LCD shows poor visibility in outdoor or ambient light. Reflective LCD does not need backlight and has low power consumption. However, brightness of display is low in indoor or ambient light. Has the disadvantage of falling a lot. Semi-transmissive LCD is a combination of reflective and transmissive LCD, and was developed to have good visibility regardless of whether it is bright or dark. In other words, if the ambient light is sufficient, the reflection mode is used, otherwise the transmission mode is used. The transflective mode, which consists of the reflection center design using the HAN mode, is shown in Figure 1. Existing technology shows excellent optical characteristics in reflection mode, but when switching to transmission mode, the asymmetry of HAN Cell asymmetrics the viewing angle characteristic, and the transmittance decreases because of the characteristic designed as the center of reflection.

There is a need for a design that improves the transmittance while eliminating the asymmetry of the viewing angle occurring in the transmission mode. For this purpose, we will introduce a multimode method that can obtain different liquid crystal states in reflection mode and transmission mode. When the multimode method is introduced, the design does not need to be designed around only one of the reflection or transmission modes, and there is an advantage in that desired optical and electrical characteristics can be obtained in each mode. The principle for obtaining the above characteristics is as follows. In order for the liquid crystal to become a dark state and a bright state, the total phase delay must be as follows.

* (2n-1) / 2 (n = integer)

* n / 2 (n = integer)

For example, if is a bright state, should be dark. In general, the reflection type requires a phase change of / 4 and the transmission type requires a phase change of / 2. Therefore, when the design criteria are matched with the reflection type, it is difficult to expect excellent optical characteristics in the transmission type. Therefore, the transflective structure designed using the HAN cell causes a significant loss of transmittance in the transmissive mode, and light leakage from the dark state, or the bright state is not bright enough and blurry phenomenon occurs. In addition, the asymmetrical viewing angle characteristic appears due to the asymmetry of the HAN cell when switching to the transmission mode. As shown in Fig. 5, low transmittance characteristics as well as asymmetrical viewing angle characteristics with respect to zero can be seen. In order to eliminate such low transmittance and viewing angle asymmetry, multimode is designed to make different liquid crystal array in reflection mode and transmission mode. As a result, by having different liquid crystal states in different regions, the overall phase change in the reflection mode and the transmission mode is designed for each mode, so that excellent optical characteristics can be expected. At this time, HAN Cell was applied as the liquid crystal mode of the reflector, and VA cells with parallel rubs were applied as the liquid crystal mode of the transmissive unit. As a method for obtaining a liquid crystal array state of different modes in one pixel, the energy state is about 250V, which may be implemented by using an ion alignment process.

1 is a transflective design using a conventional liquid crystal cell

Figure 2 is a view from above of a pixel using a reflection type and a transmission type

3 is a side view of one pixel using a reflection type and a transmission type.

4 is a transflective design of a multimode structure.

5 is the transmissivity of the transflective type using the existing structure

6 is a transflective transmittance using a multimode structure

Table 1 describes the states of the reflection mode and transmission mode.

Table 2 shows the optical axes of the compensation film required to secure a wide viewing angle.

11: Polarizer 12: Retarder film

13: Glass14: ITO Layer

15: Rubbing Layer 16: Reflector

17: Analyzer 18: Back Light

21: transmission region 22: reflection region

31: liquid crystal in transmission region 32: liquid crystal in reflection region

33: Glass41: Polarizer

42: Retarder Film43: Glass

44: ITO Layer 45: alignment layer

46: Reflector 47: Analyzer

48: Back Light

First, as shown in Figure 2, one pixel of the liquid crystal is divided into a reflection mode region and a transmission mode region. In the case of design based on transmission, the ratio between the reflection mode region and the transmission mode region was about 4: 1. In other words, if the area of the reflection area is 1/5 of the area of the transmission area, the desired area is obtained. When the reflection is centered, the width of the reflection area may be applied as desired. Negative liquid crystal was used as the liquid crystal. When the voltage is applied, the liquid crystal molecules line up in the direction of the electric field under the influence of the electric field, which is called positive liquid crystal. The dielectric constant has a negative value and is arranged perpendicular to the electric field direction. Negative liquid crystals have a larger phase delay value than positive liquid crystals when voltage is applied. The use of negative liquid crystals instead of positive liquid crystals results in a much more stable / 4 phase delay than positive liquid crystals before applying voltage in reflective mode, resulting in much better optical properties. The HAN (Hybrid Aligned Nematic) Cell was applied to the reflector in the liquid crystal mode. It is designed to have this / 4 phase delay before applying voltage and to have / 2 phase delay when applying voltage. In addition, VA (Vertically Aligned) Cell rubbed in liquid crystal mode was used for the transmission part. More specifically, due to the parallel rubbing treatment, a high bend structure is achieved. At this time, before the voltage is applied, there is no phase delay of the liquid crystal, and the voltage is appropriately applied so that the phase delay of / 2 is achieved. The values summarized in Table 1 are shown. The entire liquid crystal display is designed using Cell with multimode structure and other compensation films proposed in Figure 4. Table 2 shows the film values required for the design. A method for obtaining a liquid crystal array state of a multimode structure is described below. The liquid crystal cells were vertically oriented up and down to produce actual cells in reflective, transmissive mode. In order to show the reflection and transmission mode in one cell, the vertically oriented cell is used as it is in the transmission region of Figure 11, and the vertically oriented cell in the reflection region of 12 is horizontally oriented using ion orientation. You get

As shown in Fig. 4, the liquid crystal display was designed and its characteristics were observed. The result obtained by designing the transflective mode by the conventional method is shown in Figure 6. As mentioned earlier, it can be seen that low transmittance characteristics and asymmetry of the viewing angle are obtained. However, the design of the transflective mode with the improved method not only improved the low transmittance as shown in Fig. 6, but also eliminated the asymmetry of the viewing angle. In the transflective mode using only HAN Cell, the reflection type had excellent optical characteristics, but the asymmetry of the viewing angle occurred due to the characteristics of the hybrid structure in the transmissive design. The hybrid structure suitable for the reflection type was left as it is, and the parallel rubbed VA mode was used to show good characteristics for the transmission type. The parallel rubbed VA Cell has a better viewing angle than the Anti-Parallel rubbing VA Cell when the voltage is applied. As can be seen in Fig. 6, the problem of asymmetry of viewing angle caused by using only HAN Cell has been eliminated, and the optical characteristics are also excellent.

Before voltage application After voltage applied Phase delay value condition Phase delay value condition Reflective /4 Dark /2 Bright Transmissive 0 Dark /2 Bright

Plate Polarizer Compensation Film 1 LC Cell Compensation Film2 Polarizer / 2 film A-plate C-plate Optical axis angle 0 15 75 75 165 15 0

Claims (6)

In semi-transmissive design, hybrid structure is used for reflection area. In the transflective design, the parallel rubbing VA was used for the transmission area. Application of Ion Orientation Method to realize Horizontal Orientation Structure in Multimode Structure Design In the semi-transmissive design, the transmissive region is applied to the Splay structure by applying a voltage using the parallel rubbed VA mode. Negative liquid crystal was used in the semi-transmissive design. In the transflective design, wide viewing angle is realized by using biaxial film, A-plate and C-plate.