JPS63212918A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To reduce the influence of static electricity and to improve the stability and durability of an active matrix type cell by treating an external side surface of a glass substrate supporting a liquid crystal to have electroconductivity. CONSTITUTION:A liquid crystal 12 is sealed tightly between glass substrates 1, 2, and a polarizing plate 10 is provided to the external side surface of each substrate. Also, a picture element electrode 3 is formed on the substrate 2, and electric charge is transferred from a signal line 5 to the picture element electrode 3 through a semiconductor layer 6 and a drain electrode 4. The semiconductor layer 6 turns the charge transfer ON-OFF by a gate electrode 8 arranged through an insulating film 7. Further, a counter electrode 11 is provided to the substrate 1. If the polarizing plate 10 is not provided, transparent electroconductive films are formed on the external side surface of the substrate 1, 2. If the polarizing plate 10 is provided, transparent electroconductive films are formed on the external side surface of the polarizing plate 10. Since, such electroconductive films are formed, misoperation of an element due to static electricity from the outside of the element or deterioration of liquid crystal is prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field 1] The present invention relates to a thin film transistor type liquid crystal element, and particularly relates to a liquid crystal element that has taken anti-static measures to remove an electric field due to static electricity from outside the liquid crystal cell. be.

[Summary of the Disclosure] This specification and drawings describe the purpose of removing static electricity and preventing malfunction of a liquid crystal cell in a thin-film transistor type liquid crystal bare hand by applying conductive treatment to the surface of a glass substrate, etc. placed outside the liquid crystal cell. This article discloses a technology to prevent this.

[Prior Art] FIG. 1 is an explanatory diagram of a general liquid crystal element equipped with a thin film transistor (hereinafter referred to as TFT).

In the figure, pixel electrodes 3.2 are placed on two glass substrates 1.2, respectively. Charge is transferred from the @1 line 5 to the 0 pixel electrode 3 on which the counter electrode 11 is formed through the semiconductor layer 6 and the drain electrode 4. The semiconductor layer 6 is a gate electrode disposed through the gate insulating film 7. 8 controls on/off of the charge transfer.

[Problem to be Solved by the Invention j Here, when static electricity is applied to the surface of the polarizing plate 10 in FIG. 1 (the surface of the glass substrate 1.2 when a polarizing plate is not used), The surface of the is charged, and lines of electric force due to static charges penetrate the liquid crystal layer.Normally, liquid crystal elements use nematic liquid crystal with positive dielectric anisotropy aligned horizontally on the substrate, so the pixel electrode Even if no electric field is applied between the electrode 3 and the counter electrode 11, a problem arises in that the liquid crystal operates due to this static electricity.

A quantitative explanation will be given below with reference to FIG. FIG. 2 shows an equivalent circuit when the upper and lower electrodes of the pixel electrode 3 and the counter electrode 11 have an impedance of /\.

Now, if a static electricity of 10 KV is momentarily placed on the glass substrate, the glass thickness is 1.11 mm, the dielectric constant of the glass is 2.5, the alignment film thickness is 1000 A, the dielectric constant of the alignment film is 3, and the liquid crystal layer thickness is 10 mm. , the dielectric constant of the liquid crystal is 10, then the voltage VLC applied to the liquid crystal 12 is obtained by the following equation.

Here +"+ C'Peng 1. OPF/cm2 = 1.0 Vtc = t, o +885X 10 KV = 1
1.2 V However, C9: Glass capacitor capacitance C; Alignment film capacitor capacitance CEc: Liquid crystal capacitor RLC: Electrical resistance of the liquid crystal. In other words, a DC electric field of about 11 V will be applied to the liquid crystal part. This may not only cause malfunction of the element, but may also have an adverse effect on performance.

The electric field due to this static electricity is I? in Figure 2. tc, that is, positive and negative ions in the liquid crystal disappear through migration, and the liquid crystal returns to a state where there is no electric field. However, as the electrical resistance of the liquid crystal increases, the amount of ionic substances that are the source of this migration decreases. , the electric field remains maintained for a long time, and the liquid crystal continues to operate. In addition, in the case of TPT drive, the electric field applied to the liquid crystal layer is also applied to the drain electrode, and an electric field is also generated in the part facing the gate electrode. 6 In ordinary liquid crystal TVs, the voltage applied to the pixel electrode is at most ±3 to Since the voltage is approximately 6V, if a voltage of approximately 11V is generated in the pixel electrode portion, there is a possibility that dielectric breakdown of the opposing portion may occur.

Next, problems when using ferroelectric liquid crystal will be described.

Clark (C1ark) and Lagarwa (Lagarwa)
Ferroelectric liquid crystal device (υ5PNo) proposed by
, 4367924), the spontaneous polarization of the liquid crystal molecules is aligned in the direction of the DC electric field. Figure 3 is a diagram showing the principle of operation of a ferroelectric liquid crystal. In Figure 0, there are pixel electrodes 33 and opposing Electrodes 34 are formed, each connected to an external power source 36. Further, a ferroelectric liquid crystal (not shown) is sealed between both substrates, and numeral 37 indicates the direction of spontaneous polarization of the liquid crystal molecules.

Now, when 10KV of static electricity is placed on the glass substrate,
The voltage VLC applied to the liquid crystal is determined as follows.

However, the liquid crystal layer thickness is 1.5 pm, and the dielectric constant of liquid crystal is 4.0.
(at 100 KHz), and other conditions are the same as those described above.

8.85X 1G-+4 X 4.0 CLc = 1.5x 10-4 = 23
60pF/cm21.0 Vtc = 1. o+,,36oX 104V=
4.2 V In FIG. 3, when a DC electric field is applied from the external power supply 36, an electric field Eout applied from the external power supply and an electric field Es due to the static charge 35 are present in the liquid crystal cell 30. Since the spontaneous polarization of liquid crystal molecules simply coincides with the direction of the electric field, it is affected by both Eout and Es. Therefore, if an electric field as large as the 4.2 V calculated above is applied, it will naturally cause malfunction. Further, in the process of manufacturing a liquid crystal cell, ferroelectric liquid crystal is heated and injected into the cell in an isotropic liquid state, and then slowly cooled. At this time, it is undesirable to receive external stimulation such as an external electric field until the chiral smectic C (Sac) state is reached, which causes the inconvenience that the orientation becomes non-uniform.In this way, the electric field due to static charge is caused only by malfunction. This is not preferable from the viewpoint of uniformity of orientation.

The present invention aims to reduce the influence of static electricity and improve the stability and durability of cells.

[Means for Solving the Problems] and [Operations] The present invention is characterized in that the outer surfaces of the glass substrates that sandwich the liquid crystal are subjected to conductive treatment for dissipating static electricity. When a polarizing plate is placed outside the glass substrate, the same function can be obtained by subjecting the outside of the polarizing plate to conductive treatment. For conductive treatment, NE
SA membrane.

A transparent electrode film made of a metal oxide such as an ITO film can be used.

By performing such a conductive treatment, the electrostatic charge accumulated on the outermost surface of the cell can be released to the outside, F3, and the effect on the DC electric field can be eliminated.

[Example] Hereinafter, an example of the present invention will be described based on the drawings. Note that the liquid crystal cell used in this example has the same structure as that shown in FIG. 1, and will be explained using FIG. 1 for convenience.

Example 1 A nematic liquid crystal, ZLI 111i94 manufactured by Merck & Co., was sealed in the liquid crystal cell shown in FIG. 1 to prepare a cell. Also, without using the polarizing plate 10, use a glass substrate! A transparent electrode film (not shown) made of indium oxide (5OA) was formed in advance on the outer surface of 2 and 2, and when a liquid crystal cell treated with 0 or more was grounded via a conductive wire and was driven, abnormal lighting caused by static electricity was detected. It turns out that this does not occur.

The thickness of the transparent conductive film is preferably about 50 to 10A, but if the film thickness is made too thin, there will be areas with high resistance due to uneven film thickness, so it is desirable that the thickness is at least about 50A. The sheet resistance at the surface is 1O to Ω, making it possible to prevent the generation of static electricity.

Example 2 In the liquid crystal cell shown in FIG. 1, PVA was used as the liquid crystal alignment film 9.
(Polyvinyl alcohol) based resin alignment treatment and a ferroelectric liquid crystal inside made by Chisso.

09-1014 was sealed to form a cell layer with a cell thickness of 1.51L.

Furthermore, polarizing plates 10 are pasted on both sides of the glass substrate of this cell, and a transparent conductive film of 50A is coated on the outside of the polarizing plate 1G.
Formed.

When we drove a liquid crystal cell that had undergone the above treatment, the alignment of the liquid crystal molecules became clearer than before the electrostatic countermeasures were applied.
It was confirmed that the operating condition was stable.

[Effects of the Invention] As explained above, according to the present invention, malfunction of the device due to static electricity from outside the device can be prevented, and the application of a DC electric field having a high potential can be eliminated. It is possible to prevent deterioration of the liquid crystal. Especially 1
When applied to a ferroelectric liquid crystal element, the uniformity of initial alignment can be improved.

Furthermore, as a secondary effect, static electricity generated when attaching a polarizing plate can be eliminated, and electrostatic adhesion of dust and the like can be prevented.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a TFT liquid crystal element, FIG. 2 is an equivalent circuit diagram between upper and lower electrodes, and FIG. 3 is a diagram showing the operating principle of a ferroelectric liquid and crystal. 1.2...Substrate, 3...Pixel electrode, 4...Drain electrode, 5...Signal line. 6... Semiconductor layer, 7... Gate insulating film. 8... Gate electrode, 9... Liquid crystal alignment film, 10...
Polarizing plate, 11... counter electrode, 12... liquid crystal.

Claims (5)

[Claims] (1) A liquid crystal element of an active matrix type in which each pixel of a liquid crystal cell is equipped with a thin film transistor, characterized in that an electrically conductive treatment is applied to the outer surface of a glass substrate that sandwiches a liquid crystal. (2) The liquid crystal element according to claim 1, characterized in that a polarizing plate is disposed outside the glass substrate, and the outer surface of the polarizing plate is subjected to conductive treatment. (3) The liquid crystal element according to claim 1 or 2, wherein the conductive treatment is a transparent conductive film. (4) The liquid crystal element according to claim 1, 2 or 3, wherein the liquid crystal is a nematic liquid crystal. (5) The liquid crystal element according to claim 1, 2 or 3, wherein the liquid crystal is a ferroelectric liquid crystal.