JPH0194316A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal display element which is capable of making gradation control of the transmission quantity of light by holding a ferroelectric liquid crystal in place between a pair of electrodes forming a rugged spacing. CONSTITUTION:The transparent electrodes 4 having 90mum pitch are formed in a stripe shape on a lower substrate 1 having 0.5-0.6mum step and 90mum pitch (p) of ruggedness and the stripe-shaped transparent electrodes of 90mum pitch are also formed on an upper substrate 2 in the direction orthogonal with the striped transparent electrodes 4 on the lower substrate 1. Oriented films 5 are diagonally vapor deposited SiO films. The distance between the upper and lower substrates 1, 2 is maintained at about 2.0-2.6mum by line spacers 3. Uniform orientation is attained if a ferroelectric liquid crystal compd. 6 of an ester system is injected into this panel. Medium contrasts are thus uniformly displayed in many picture elements or elements by providing a gradient to the voltage to be impressed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a liquid crystal display element having a ferroelectric liquid crystal as a liquid crystal layer, which can control the gradation of the amount of transmitted light.

Prior Art In recent years, reports have been made on ferroelectric liquid crystals with fast response speed and memory properties (for example, Hideo Takezoe, Atsuo Fukuda, Sakae Kuze; "Industrial Materials", No. 31@, No. 10, 22 ).

Examples of conventional ferroelectric liquid crystal panels will be described below with reference to the drawings. FIG. 5 shows the structure of a conventional smectic liquid crystal panel. In FIG. 5, 21 is a glass substrate, 22 is a transparent electrode made of ITO (indium tin oxide), 24 is a ferroelectric liquid crystal layer, 25 is a C director of liquid crystal molecules, and 126 is a dipole moment.

Ferroelectric liquid crystals generally have a dipole moment in the direction perpendicular to the long axis of the molecules, and as they become thinner, they come to have spontaneous polarization. FIG. 6 shows how to describe ferroelectric liquid crystal using an example of a chiral smectic phase exhibiting ferroelectricity. 6th
Figure (a) shows a state in which the long axis of the molecules is tilted by ±θ degrees with respect to the normal 27 of the molecular layer. 28 is the long axis direction of the molecule n129 is the dipole moment Ps, 30 is n x
The C director -0131 when projected onto the y-plane is an inclination angle of ±θ degrees with respect to the normal to the long axis of the molecule. The operating principle of the ferroelectric liquid crystal panel having the above structure will be explained below with reference to the drawings.

FIG. 7 shows a principle diagram of a conventional ferroelectric liquid crystal panel display method. 32 is a liquid crystal molecule whose long axis of the molecule is tilted by -θ degrees with respect to the layer normal, 33 is a liquid crystal molecule whose molecular axis is tilted by 1 θ degree, 34 is a dipole moment in the direction of the paper, 35 is a dipole moment in the direction of the back of the paper, 36 is the direction of the two polarizing plates. Now, Figure 7 (a) shows the state where no voltage is applied, Figure 7 (bl) shows the case where a positive voltage is applied from the front to the back of the paper, and Figure 7 (C) shows the case where a positive voltage is applied from the back to the front of the paper. This is the principle of operation when voltage is applied.

In this way, the entire cell assumes two states tilted by ±θ degrees depending on the direction of applied voltage, and therefore, brightness and darkness can be expressed by utilizing birefringence or dichroism due to the electro-optic effect.

As mentioned above, ferroelectric liquid crystals can take only two states when viewed microscopically, so to produce halftones, it is necessary to select from Fig. 7(b) to Fig. 7(C1) or from Fig. 7(C) to Figure 7(b)
Methods are being considered, such as using a mixed state of the two states as shown in Figure 7(a) obtained during the transition period, or changing the ratio of the appearance times of the two states (for example, N.A. , Clark, Nis.

T., Ragabar, and J. Wall; Eurodisplay 84 Digest 1984, p. 73 (
N, A, C1ark, S, T, Lagerwal
l and J+ Wahl: Eurodispla
y '84 Digest (1984) p.
73)).

Problems to be Solved by the Invention However, it is extremely difficult to uniformly cause a mixture of the above two states to appear in many picture elements on a normal planar electrode. Furthermore, regarding the method of changing the appearance time ratio of two states, no detailed study has been made regarding matrix driving suitable for large-scale devices.

In view of the above-mentioned problems, the present invention provides a liquid crystal display element using ferroelectric liquid crystal that can control the gradation of light transmission.

Means for Solving the Problems In order to solve the above problems, the liquid crystal display element of the present invention includes:
Gradation control can be easily performed by sandwiching a ferroelectric liquid crystal between a pair of electrodes that form an uneven gap.

Operation On a conventional uniform electrode, when a voltage higher than the dark value voltage is applied to a ferroelectric liquid crystal element, the liquid crystal molecules on the electrode almost simultaneously reverse so that their spontaneous polarization points in the direction of the electric field. Therefore, by applying a pulse voltage that is slightly lower than the dark value voltage or has a short pulse width, it is possible to make a mottled state appear. The brightness distribution varies depending on the picture element or element because it is easily influenced by subtle factors that are difficult to control, such as orientation and orientation state. Therefore, in the liquid crystal element of the present invention, by providing unevenness in the gap between the picture element electrodes,
By changing the distance between the electrodes and creating an electric field distribution within one picture element, uniform and stable gradation control can be performed in every picture element.

EXAMPLE Hereinafter, an example of the liquid crystal display device of the present invention will be described with reference to the drawings.

FIG. 1 is an example of a configuration diagram of a liquid crystal display element of the present invention. 1 is a lower substrate, 2 is an upper substrate, 3 is a line spacer made of photosensitive resin, 4 is a transparent electrode, 5 is an alignment film, 6 is a ferroelectric liquid crystal, and 7 is a sealing material. Difference in unevenness on the lower board d
is 0.5 to 0.6 μm, and the pitch p is 90 μm. Transparent electrodes with a pitch of 90 μm are formed in stripes on the lower substrate 1. Also on the upper substrate 2, in the direction perpendicular to the striped transparent electrodes on the lower substrate 1,
Striped transparent electrodes with m pitches are formed.

The alignment film 5 is an SiO obliquely deposited film. Upper and lower boards 1.2
Due to the line spacer 3, the distance between the boards is approximately 2.0~
The thickness is maintained at 2.6 μm. When ester-based ferroelectric liquid crystal compound 6 was injected into this panel, uniform uniform alignment was obtained.

The electrode optical properties of the above panel were measured using a photomultiplier under crossed nicol conditions. FIG. 2 shows the voltage waveform applied to the scanning side electrode, and FIG. 3 shows the voltage waveform applied to the signal side electrode.

(Both scanning voltage and signal voltage Vo = 20V, τ/2-
．． It is 300 μs. ) In this embodiment, the stripe electrodes on the upper substrate 2 were used as scanning side electrodes, and the stripe electrodes on the lower substrate 1 were used as signal side electrodes. When the selection pulse shown in Figure 2 (al) is applied to the scanning side electrode and the voltage shown in Figure 3 (a) is applied to the signal side electrode, all pixels in the panel uniformly change from bright to dark state. Next, while a selection pulse was applied to the scanning side electrode, a voltage shown in Figure 3+1)l was applied to the signal side electrode. After the entire panel is reset to light,
Two-thirds of the liquid crystal layer from the convex side within the picture element exceeded the threshold voltage and entered a dark state. At this time, approximately 1/3 of the picture elements were bright and 2/3 were dark, and most of the picture elements in the panel were uniformly in the above state.

Similarly, when FIG. 3(C) was applied to the signal side electrode,
The area ratio of the bright state to the dark state within the picture element was 2:1, and when the waveform shown in FIG. 3 (fd) was further applied, the picture element became completely bright. The brightness change of the panel at this time is
As shown in the figure. Incidentally, when a non-selection voltage of FIG. 2 (bl) was applied to the scanning side electrode, the brightness hardly changed.

As a result of this experiment, it was found that the liquid crystal display element of the present invention uniformly displays four gradations for all picture elements. In conventional liquid crystal display elements that do not have an uneven structure in the gap between substrates,
Since only two gradations could be uniformly displayed using a similar driving method, the liquid crystal display element of the present invention has the effect of uniformly displaying two or more gradations. Regarding the driving method,
Pulse width modulation may also be used to change the panel width depending on the gradation. In addition, in this example, a difference of 0.6 μm was set in the distance between the substrates, but this difference in the distance between the substrates is determined in order to obtain the necessary gradation depending on the liquid crystal material, orientation, pixel size, driving method, etc. It is necessary to choose the optimal value of

Effects of the Invention The liquid crystal display element of the present invention makes it possible to uniformly display halftones in a large number of picture elements or elements by making the gap between the opposing picture element electrodes uneven, thereby giving a gradient to the applied voltage. can.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a liquid crystal display element in an embodiment of the present invention, Fig. 2 is a scanning voltage waveform diagram during matrix drive in the embodiment, and Fig. 3 is a signal diagram during matrix drive in the embodiment. Voltage waveform diagram, Figure 4 is a relative luminance change diagram during matrix driving, Figure 5 is a cross-sectional view of a conventional ferroelectric liquid crystal panel, Figure 6 is a schematic diagram showing the notation of chiral smectic C liquid crystal, Figure 7 The figure is a plan view showing the principle of display on a conventional ferroelectric liquid crystal panel. l...lower board, 2...upper board, 3...
... Line spacer, 4 ... Transparent electrode, 5
...Alignment film, 6...Ferroelectric liquid crystal, 7
...Seal material. Name of agent: Patent attorney Toshio Nakao Haka1 person! - Lower board - Upper board 3 - Line spanner 4 -. 4-size electrode 5-Alignment film 6-*High-density liquid crystal 7-Sealing material Fig. 1 Fig. 2 Fig. 3 Fig. 4 Call volume Fig. 5 Fig. 6 ((lJ (b J

Claims (7)

[Claims] (1) A liquid crystal display element in which a pair of electrodes are arranged in a matrix, in which uneven gaps are formed between the electrodes, and a gradient is created in the electric field applied to the sandwiched ferroelectric liquid crystal layer. A liquid crystal display element characterized by controlling the area ratio of an inverted domain and a non-inverted domain of a liquid crystal. (2) The liquid crystal display element according to claim (1), wherein the unevenness has a step difference of 0.3 to 2.0 μm. (3) The liquid crystal display element according to claim (1), wherein the pitch of the unevenness is 20 μm or more. (4) Claims (1), (2), or (2) characterized in that the unevenness is formed of a transparent conductive material.
3) The liquid crystal display element according to any one of the items. (5) Claim (1) characterized in that after the unevenness is formed of an insulator, an electrode is formed on the insulator.
2. The liquid crystal display device according to any one of Items 1, 2), and 3). (6) Claims (1), (2), or (3) characterized in that the unevenness is formed on a glass substrate.
) The liquid crystal display element according to any one of the items. (7) The liquid crystal display element according to any one of claims (1), (2), and (3), wherein the unevenness is formed on a transparent plastic substrate.