JPS6112787A - Liquid crystal element - Google Patents

Abstract

PURPOSE:A liquid crystal element, having a thin film transistor (TFT) containing an adsorbent of an ionic substance in an implanted liquid crystal composition, and having stabilized operation performance in TFT driving. CONSTITUTION:A liquid crystal element, containing an adsorbent of an ionic substance, e.g. alumina, zeolite, ion exchange resin, carbon, metallic alumina, metallic nickel or iron-cobalt alloy, having 1-0.005mum particle diameter, in 0.5- 0.005wt% optimally 0.2-0.05wt% concentration in an implanted liquid crystal composition. The above-mentioned adsorbent is preferably uniformly dispersed in the liquid crystal composition with ultrasonic waves, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a liquid crystal element (hereinafter abbreviated as L(II)) that
ON/OFF control of display electrodes is performed using thin film transistors (
For details on what to do with TPT (hereinafter abbreviated as TPT), please see
The present invention relates to a liquid crystal element whose operating characteristics in TPT driving are stabilized by reducing ionic substances in the liquid crystal.

[Prior Art] FIG. 1 shows an example of cross-sectional factors for one pixel of a liquid crystal element equipped with a conventional thin film transistor (TPT) array.

A gate electrode 8 is attached on a substrate z such as glass, and a semiconductor layer 6 is attached with an insulating film 7 interposed therebetween. A source line (signal line) 5 and a drain line 4 are arranged on this, and the drain 4 is in contact with one of the pixel electrodes 3. On top of these, a liquid crystal alignment film 9
is applied to the entire surface to form a one-sided substrate. On the other substrate 1, a pixel electrode 3 and an alignment film 9 are arranged, and with these facing each other, the periphery of the LCD is sealed with an epoxy adhesive or the like, and a liquid crystal 11 is sealed.

FIG. 2 is an equivalent circuit of the above liquid crystal element. Here, R or R is the ON or OFF resistance of TPT, ON 0FF Cil"i2" LC is the capacitance of the alignment film and liquid crystal, respectively, and R1□'Ri2' RIJ is the resistance.

FIG. 3 shows an example of a voltage waveform when TPT is driven. V in FIG. 3 is applied to the gate electrode 8 in FIG. Assume that a gate pulse such as the following is applied and +V and volts are simultaneously applied to the source line 5. At this time, the voltage V generated between the upper and lower sides of the pixel electrode 3 rapidly reaches +V at CD speed. (Charging process) After this, V. By escaping with the electricity stored in the liquid crystal layer when the
The voltage will drop further. (Discharge process) The time constant of this discharge process. □ is expressed as τoFF=R−C (1) LCLC, and depends on the resistance RLC of the liquid crystal layer.

The effective voltage actually applied to the liquid crystal layer is the area shown by the shaded area in FIG. 3, where 1=1. So ■. It is indicated by (0). Further, vi is a voltage applied to the alignment film portion and does not contribute to the liquid crystal layer.

At this time, VLc(0) is expressed by the following equation.

(2) Furthermore, when the resistance RLG of the liquid crystal layer becomes smaller, the area of the shaded portion inevitably becomes smaller, and the effective voltage applied to the liquid crystal layer becomes smaller. Therefore, using a nematic liquid crystal with positive dielectric anisotropy,
In the case of horizontally aligned LCII, the VT curve when driven by TPT shifts to a higher voltage side than when driven by square wave. An example of the BDH liquid crystal E-7 is shown in the curve in Figure 4 (
Shown in a).

] D is polyimide 1000 for alignment film, cell gap J
pm, and the twist angle is 80°.

Also, in Fig. 5, V when V = 6V. In the case of 8QHz non-interlace mode, which shows the D waveform, LCD TVs usually display the screen by line sequential driving, but the information must be retained during the time when each scanning line is not selected. This time is about IB, 7m5ec, and if vLc(t) becomes less than vth of the liquid within this time, image display will no longer be possible.

In the case of untreated No. 7, a significant decrease in VLco was observed (No. 5
This is because the resistance RLC of the liquid crystal layer is small.

As mentioned above, in the case of TPT drive, when the resistance of the liquid crystal decreases, (a) the V-T curve shifts to the high voltage side and the drive voltage increases, and (b) in extreme cases, the picture does not appear. there were.

[Problems to be Solved by the Invention] The present invention has been made in order to eliminate the conventional problems as described above, which occur because the resistance of the liquid crystal layer decreases over time.

[Means and effects for solving the problems] The present invention provides that the reduction in the resistance of the liquid crystal layer is caused by ions eluted into the liquid crystal from a substance in contact with the liquid crystal, and
By adsorbing these ions with an adsorbent to prevent the ion concentration in the liquid crystal from increasing, it is possible to suppress the decrease in the resistance of the liquid crystal in a TPT-driven liquid crystal element, the resulting increase in the driving voltage, and the phenomenon in which images do not appear. This was done based on the discovery that it could be done.

According to the present invention, there is provided a liquid crystal element including a thin film transistor, a liquid crystal shutter element, etc., which is characterized in that an adsorbent for an ionic substance is contained in an injected liquid crystal composition. provided.

(1) If the liquid crystal layer resistance RLo in equation (1) is increased, τ. This increases the information retention time.

On the other hand, the specific resistance ρ of the liquid crystal layer is expressed by the following formula. be associated with.

-d RLC=5 (3) where S is the electrode area and d is the electrode spacing.

At the manufacturing stage of the liquid crystal composition, purification is repeated until ρ≧ix+
Although it is quite possible to obtain ouΩcm, after being injected into L(dl), the impurities in the cell are dissolved and ρ decreases.Experientially, the level of ρ is 5X109~5XIO1
0 Ωcm, and from another experiment, it can be estimated that the concentration of impurities dissolved at this time is several ppm or less. In other words, the number p
When impurities below pm dissolve in, p decreases by one order of magnitude, and RL
o similarly decreases. On the contrary, if several ppm of impurities are removed, there is no decrease in RLC.

Therefore, an attempt was made to increase the RLc by incorporating an adsorbent into the liquid crystal composition to be injected into the cell.

In addition to alumina, zeolite, ion exchange resins, and carbon, metals such as metal aluminum, metal nickel, and iron-cobalt alloys are used as adsorbents for ionic substances in the present invention.

The particle size of the adsorbent must be smaller than the spacer particle size (approximately 1 OILI11) in order to penetrate into the LCD.
The range is preferably from pm to 0.005 gm.

Note that the adsorbent itself can also be used as a spacer, in which case the particle size of the adsorbent should be approximately 1 mm, corresponding to the cell cap.
It is preferable to set it to 0 gm or less.

The concentration of the adsorbent is 0.5 to 0.005% by weight of the liquid crystal composition.
It is preferably 0.2 to 0.05% by weight, and more preferably 0.2 to 0.05% by weight.

The adsorbent is preferably uniformly dispersed in the liquid crystal composition using ultrasound or the like.

FIG. 4 shows a cross section of an embodiment of a liquid crystal element according to the present invention. lO are particles of adsorbent.

Materials for the liquid crystal alignment film 9 in the liquid crystal element of the present invention include synthetic resins such as polyimide resin, polyamide resin, polyvinyl alcohol, and phenol resin, silicone coupling agents, titanium cups, ring agents, and zirconium coupling agents. Coupling agents such as are used.

The liquid crystal alignment film is formed by applying the above-mentioned materials in solution or liquid form at a predetermined concentration onto the LCD substrate using a spinner, roll coater, or the like.

A gate pulse ■ is applied to the gate electrode 8 in FIG. When +V8 port is applied to the source line 5 at the same time, the pixel electrode 3
■LC[l rapidly reaches +V between the upper and lower sides of.

6(b) (in the case of V8=6V) shows the state in which V falls from the value Vs when ■G falls after this for the case of Example 1 of the implementation CD. In case of conventional example without adsorbent added [Figure 6 (a)
], compared to vLcD after 18.7 m5ec
It can be seen that the value of is large.

[Example] Next, the present invention will be explained with reference to Examples.

Example 1 Average particle size: 500 alumina (manufactured by Fujimi Abrasive Company) 0
．． 2% by weight was dispersed in Liquid Crystal Liquid Crystal 7 manufactured by BDH Co., Ltd. and injected into an LCD to create an LCD having the structure shown in FIG. 4. The VT curve obtained for this product is shown in FIG. 5(b), and the change in straddle is shown in FIG. 6(b).

FF: In the LCD of the present invention, the shift amount of the V-T curve is small, and at the same time, it is large.

As described above, the effects of the present invention are clearly manifested in TPT driving.

Examples 2 to 4 A liquid crystal composition containing an adsorbent was injected in the same manner as in Example 1, except that the alumina in Example 1 was changed to the adsorbent shown in Table 1 below, and a CD was prepared. When the waveforms of CD and V were examined, good results were obtained that were substantially the same as those of the example.

Table 1 [Effects of the Invention] In the present invention, as described above, since an adsorbent for an ionic substance is contained in the liquid crystal composition of a liquid crystal element equipped with TPT, the ionic substance eluted into the liquid crystal is The resistance of the liquid crystal layer decreases because it is adsorbed by the adsorbent. does not decrease, and V
The -T curve is prevented from shifting to the high voltage side, low voltage driving and constant voltage driving are possible, and the operating characteristics are stabilized. Furthermore, since RLC is kept high,
The time constant τ of the discharge process is large, the information retention time FF becomes long, and the quality of image display is improved.

In addition, an increase in τ also means that it becomes possible to increase the number of scanning lines per unit area of the image FF, which is connected to the development of high-quality displays (for example, improving the display quality of LCD TVs). Garu.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional diagram showing an example of a conventional liquid crystal element equipped with TPT, Fig. 2 is a circuit diagram showing an equivalent circuit of the element in Fig. 1,
FIG. 3 is a schematic explanatory diagram showing an example of a voltage waveform when the device shown in FIG. A graph showing the V-T curves of (a) when a liquid crystal composition without an adsorbent is used and (b) when a liquid crystal composition with an adsorbent according to the present invention is used. Case (a) using a liquid crystal composition with addition of adsorbent and case (a) using a liquid crystal composition with addition of adsorbent (
b) (7) It is a waveform diagram showing the ■ waveform of V s = 6 V (30H2 (7) case). CD 1.2... Glass substrate, 3... Transparent electrode, 4...
...Drain electrode, 5...Source electrode, 6.
... Semiconductor layer, 7... Insulating layer, 8... Gate electrode, 9... Liquid crystal alignment film, 10... Adsorbent particles, 11... Liquid crystal. 8. . □・・・
-TPT resistance R when ON or OFF ■G...gate voltage■,...source voltage■...voltage CD generated between the upper and lower electrodes

Claims (1)

[Claims] 1. A liquid crystal element comprising a thin film transistor, the liquid crystal element comprising an injected liquid crystal composition containing an adsorbent for an ionic substance.