JPS62229230A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To relax the rise sharpness of liquid crystal molecules for an impressed voltage to facilitate control of the light transmissivity by specifying the thickness of an oriented film layer in a liquid crystal display device having a semiconductor substrate of thin film transistors (TFT). CONSTITUTION:A gate electrode 11a, an insulating layer 12a, a semiconductor layer 13a, a source electrode 14a, and a drain electrode 15a are provided on a transparent substrate 10b to form a TFT. This TFT is provided for each surface picture element to constitute an electrode and a counter transparent electrode 18 is provided. Oriented films 16a and 16b, a liquid crystal layer 17, etc., are provided between TFTs and electrodes 18 to constitute the liquid crystal display device. The thickness of oriented films 16a and 16b is set to 0.2-1mum. Oriented films 16a and 16b are made thicker to increase a ratio Vsat/ Vth of an applied voltage Vsat corresponding to 10% transmissivity to an impressed voltage Vth corresponding to 90% transmissivity. Since oriented films are made thicker, the light transmissivity is easily controlled to improve the gradation display.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a liquid crystal display device using a thin film transistor (T P T ).

(Summary of the Invention) The present invention provides a liquid crystal display device having a TFT array.
The thickness of the alignment film layer is set to 0.2 or more and 1 or less, and the steepness of the rise characteristics of liquid crystal molecules in response to the applied driving voltage is made gentler, making it easier to control light transmittance and display gradation. It is something.

(Prior Art) In recent years, liquid crystal display devices (active matrix panels) in which a liquid crystal is sandwiched between two substrates, a semiconductor substrate and a counter substrate having counter electrodes, have been developed due to their high contrast ratio, wide visual range, and response. It is attracting attention as a display device because of its speed. An electric field ffl is formed on the entire surface of one of the two substrates, and a plurality of small block pattern electric currents are formed on the surface of the other semiconductor substrate. Each pixel-electrode is provided with a thin film 1 to a transistor (T PT ) as a switching element.

FIG. 4 is a schematic cross-sectional view of a liquid crystal surface water device having such a TFT array, in which 40a and 40b are transparent substrates such as glass, 418 and 41b are gate electrodes, 42a and 4
2b is an insulating layer, 43a.

43b is a semiconductor layer, 448.44b is a source electrode, 45
a and 45b are drain electrodes, and 46a and 46b are drain electrodes with a thickness of 0.
There is an alignment layer (insulating layer) of about one size, 47 is a liquid crystal, and 48 is a transparent electrode.

The principle of gradation display using the liquid crystal display device explained in FIG. 4 will now be explained. Figure 5 shows the magnitude of the applied voltage and the transmission when the angle of the liquid crystal molecules is controlled by the magnitude of the voltage applied to the liquid crystal of the liquid crystal display device, and the intensity of light transmitted through the liquid crystal display device is changed. This shows the relationship between light intensity.

Reference numeral 51 in the figure indicates a direction indicating the intensity of transmitted light. Reference numeral 52 indicates a direction indicating the magnitude of the applied voltage. Reference numeral 57 is a curve showing the relationship between the magnitude of the applied voltage and the intensity of transmitted light.

In other words, as the voltage increases, the transmitted light intensity decreases,
When the voltage becomes sufficiently large, the transmitted light intensity reaches saturation.

The transmitted light intensities 5A, 5B, 5G, 5G, and 5E are voltage magnitudes 5a, 5b, 5c, and 5d, respectively.

Compatible with 5e. 5A is the transmitted light intensity corresponding to the case where the voltage magnitude is O, and 5E is the transmitted light intensity corresponding to the case where the voltage magnitude is sufficiently large.

When the relative intensity of transmittance is 100% for code 5A and 0% for code 5E, 5B, 5C, and 5D are 90%.

Corresponds to 50% and 10%.

In this way, by changing the magnitude of the voltage in the range of 5a to 50, the transmitted light intensity can be changed in the range of 5A to 5days.

(Problems to be Solved by the Invention) If the applied voltages corresponding to transmittances of 10% and 90% in FIG. , decrease Vth, increase ■, sat of ■/■th
The higher the sat ratio, the better.

However, in the conventional liquid crystal display device shown in FIG. 4, it is difficult to increase the v/th ratio to a large value in the nematic liquid crystal.

In addition, with so-called guest-host type liquid crystals in which dyes are added to nematic liquid crystals, it is possible to increase the ratio of Vsat/■th, but there are problems with reliability such as large current consumption and light resistance. was there.

Table 1 shows comparative values of V/Vth.

sat Table 1 (Means for solving the problems) In order to solve the above problems, the present invention is characterized in that the thickness of the alignment film layer is set to 0.2 to 11IIR.

(Function) When the alignment film layer is made thicker as described above, the light transmittance curve shifts from 61 to 62 as shown in FIG. That is, the steepness parameter of the liquid crystal shown in Table 1 increases. Therefore, the rate of change in the light transmittance value with respect to the change value in the driving voltage becomes small, which facilitates gradation display.

(Example) The details of the present invention will be explained below based on the illustrated example.

FIG. 1 is a schematic cross-sectional view of a liquid crystal display device according to the present invention, in which 1a and 1b are gate electrodes, and 12a.

12b is an insulating layer, 13a and 13b are semiconductor layers, 14a,
14b is a source electrode, 15a and 15b are drain electrodes,
16a and 16b are alignment layers (insulating layers), 17 is a liquid crystal, and 18
is a transparent electrode. 10a and iQb are transparent substrates such as glass.

If the thickness of the alignment film layer is less than 0.21 iIR, it will not be effective, and if it is more than 1 IR, the degree of adhesion between the substrate and the alignment film layer will deteriorate, so it is preferable to have a thickness of 0.2 or more and 1 or less.

The above-mentioned alignment film layer can be formed by vapor depositing Teflon or the like, coating with a polymer film such as polyimide, polyamide, polyamideimide, PVA, etc., and then subjecting it to alignment treatment by a rubbing method, or by oblique vapor deposition such as 310. .

With this alignment film, the same effect can be obtained even if the various alignment film layers described above are laminated.

In addition, the liquid crystal to be sealed has a twist angle of 360° from Oo.
Any field effect type twisted nematic liquid crystal may be used.

(Effect) As explained above, according to the present invention, the thickness distribution of the alignment film layer can be reduced to 0.
．． 2 tutr or more and hls+ or less, the rise characteristics of the liquid crystal molecules with respect to the applied driving voltage are made gentler, the light transmittance can be easily controlled, and gradation display can be easily performed.

In addition, when the alignment film layer becomes thick, the unevenness of TPT is absorbed into the alignment film, so when alignment treatment is performed by rubbing method,
Poor alignment and destruction of TPT can be prevented.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the liquid crystal display device of the present invention, and FIG. 2 is a TF
A cross-sectional view of a liquid crystal display device having a T array. Figure 3 shows the relationship between the magnitude of the applied voltage and the intensity of transmitted light. Figure 4 shows the rise characteristics of the liquid crystal when the alignment film layer is made thicker. This is a diagram. 10a, 10b...Transparent substrates 11a, 11 such as glass
b...Gate electrodes 12a, 12b..."Insulating layers 13a, 13b...Semiconductor layers 14a, 14b...Source electrodes 15a, 15b...Drain electrodes 16a, 16b...Orientation layer (insulating layer) 17...Liquid crystal 18...Transparent electrode Applicant Seiko Electronics Co., Ltd. Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] A semiconductor substrate on which a plurality of thin film transistors are formed for each display pixel, and an alignment film layer provided on an electrode of a counter substrate.
A nematic liquid crystal having a positive dielectric constant anisotropy and an optically active additive is sealed between the substrates, with the alignment film phase sides facing each other, and has a spiral structure twisted in the thickness direction. Katsu 2
In a liquid crystal display device in which a pair of polarizing plates is provided on the outside of a single substrate, the thickness of the alignment film layer is 0.2 μm or more and 1 μm.
A liquid crystal display device characterized by the following.