JPH0155312B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a structure in which active elements for liquid crystal display on a semiconductor substrate are provided in a matrix, and a display electrode is formed on each active element between the substrate and a glass substrate having a transparent electrode disposed opposite to the substrate. The present invention relates to an active matrix liquid crystal display device comprising a nematic liquid crystal composition having positive dielectric anisotropy sandwiched therebetween. More specifically, the present invention relates to a liquid crystal composition that has a wide temperature range necessary for active matrix display, and provides high contrast and high-speed response. Conventionally, liquid crystal displays using the active matrix method use a silicon substrate with aluminum electrodes formed as a semiconductor substrate, so twisted nematic (TN) mode, which uses two polarizing plates, cannot be used, and instead only one polarizing plate is used. Guest-host (G.H) mode was used. FIG. 1 shows an example of a cross section of a display device.
On the surface layer 2 of the semiconductor substrate 1, liquid crystal driving transistors and capacitors are formed in a matrix. Furthermore, an aluminum electrode 3 for driving a liquid crystal is provided thereon. On the aluminum electrode and the In ₂ O ₃ common electrode 5 on the opposing glass substrate side 4,
A SiO oblique vapor deposition film 6 for liquid crystal alignment is formed.
A nematic liquid crystal composition containing a dichroic dye has a homogeneous orientation 7 parallel to or slightly inclined to the substrate surface.
Take. The incident light 8 transmits a vibration light component in the orientation direction of the liquid crystal through a linear polarizing plate 9 on the outside of the glass substrate, and is strongly absorbed by the dye in the liquid crystal layer in the voltage-free section 10, so that the reflected light 11 is strongly colored. On the other hand, in the voltage application section 12, the liquid crystal molecules take a homeotropic orientation 13 perpendicular to the substrate, the incident light 14 is hardly absorbed by the dye, and the reflected light 15 is colorless. The characteristics of such a liquid crystal display device are summarized below. (1) Since the liquid crystal is statically driven in each pixel, high-density image display is possible. (2) Since it is a fine pattern, it is difficult to see the image if the display contrast is low. (3) When displaying videos, the LCD response is slow and the images flow. (4) It is dark because it uses a polarizing plate. The contrast of such a display device is determined by the degree of polarization of the polarizing plate and the dichroic ratio of the dye in the liquid crystal. Also, the response speed can be adjusted by voltage when turning on, but when erasing, it is mostly determined by the viscosity of the liquid crystal. Table 1 shows characteristic evaluations of various liquid crystals with positive dielectric anisotropy in terms of dichroism with respect to dyes, response speed, and driving voltage. As is clear from Table 1, both PCH and biphenyl liquid crystals have excellent alignment properties and complement each other in terms of voltage and response. The feature of the present invention is to focus on the above-mentioned characteristics, and to mainly use PCH and biphenyl, and to
By adding some additives, we have developed a liquid crystal composition with excellent alignment and responsiveness.

【table】

[Table] Particularly with a specified alkyl group, Comprised of compounds with similar skeletons to each other, reducing the number of other dissimilar compounds, and changing the terminals of compounds with similar skeletons, thereby impairing the unique properties of each compound. The object of the present invention is to provide a liquid crystal composition that has improved compatibility, a wide temperature range, and excellent response speed. Examples will be described below while comparing them with comparative examples.

【table】

【table】
(weight ratio)
Table 2 shows representative examples and comparative examples of liquid crystal compositions based on the present invention, and Table 3 shows their characteristics.

【table】

【table】 Furthermore, Table 4 shows the structures of typical dichroic dyes.

[Table] Examples contain compounds (1), (2), and (3), respectively, and contain 50% positive PCH, 20% negative PCH, and 15% positive biphenyl. Examples 1 and 2 are
They are composed of only positive PCH and positive PCH and positive biphenyl, respectively. Looking at these, this example shows that the temperature range Tc
, and the bicolorimetry is slightly lower. Further, although the voltage is slightly higher, the response speed is significantly lowered, especially at low temperature τ ⁰ °C _pff . This is because in active matrix liquid crystal display devices, the evaluation function is operated by transistor action, so it is suggested that the viscosity of the liquid crystal should be as low as possible and the liquid crystal molecules should be short. As you can see, being able to shorten τ ⁰ °C _pff is very effective. To summarize the effects of each additive on physical properties: (1) PCH and biphenyl of shotoalkyl contribute to lower voltage, but lower Tc. (2) PCH-negative addition contributes to faster response, but lowers Tc and dichroic ratio R. (3) High Tc additives: Among M and N, N has a much faster response. M has relatively uniform characteristics and low voltage. As described above, according to the present invention, short similar skeletons of liquid crystal molecules can be A compound having a predetermined alkyl group of a predetermined type and n-C ₅ By using a _mixture ^of
It is possible to provide a liquid crystal composition for an active matrix in which the time is reduced by nearly 20%, and thereby to provide an excellent liquid crystal display device for an active matrix that sufficiently satisfies display contrast and response speed. As a result, we believe that the present invention will play a major role in the information society where hand-held displays are required.

[Brief explanation of drawings]

FIG. 1 shows a sectional view of the structure of an active matrix display. 1: Semiconductor substrate, 2: Liquid crystal drive element section, 3: Display electrode (Al), 4: Glass substrate, 5: Transparent common electrode, 6: SiO alignment film, 7: Homogeneous alignment,
8: Incident light, 9: Polarizing plate, 10: No voltage applied part,
11: Reflected light, 12: Voltage application section, 13: Homeotropic alignment, 14: Incident light, 15: Reflected light.

Claims (1)

[Scope of Claims] 1. A glass substrate having a substrate in which active elements for driving a liquid crystal are provided in a matrix on a semiconductor substrate, display electrodes are formed on each active element, and transparent electrodes are arranged facing the substrate. In an active matrix liquid crystal display device in which a nematic liquid crystal composition with positive dielectric anisotropy is sandwiched between A liquid crystal display device for an active matrix, characterized in that it uses a mixture of compounds represented by: