JP3059491B2 - Nonlinear element and liquid crystal display device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention can be used as a display screen of a computer, a word processor, a television receiver or the like, and can be applied to a field requiring a gradation display.

[0002]

2. Description of the Related Art Conventionally, an STN (super twist nematic) type liquid crystal display device is often used for a display screen of a computer, a word processor or the like. The STN has a steep electro-optical characteristic of the liquid crystal material as compared with the previous TN (twisted nematic) type liquid crystal display device, so that it is possible to perform high time division driving with a large amount of information, which was difficult with the TN. It sparked notebook computers and notebook word processors. However, when time-division driving is performed, if the number of operation lines increases, it becomes difficult to obtain an applied voltage ratio between the selected and non-selected portions in the scanning line, and the display quality, particularly the contrast, is reduced.

In order to solve this problem, an active matrix for driving a TN liquid crystal using a TFT (thin film transistor) has been developed and has been developed up to the present. The active matrix type liquid crystal display device minimizes the influence on other operation lines because only the gate of the TFT connected to the operation line to be written is turned on, and crosstalk free display is possible. Became. Also, after writing once, the liquid crystal portion, which is substantially a capacitance component, is charged with electric charges, so that even while writing other operation lines, static driving that does not cause a decrease in contrast becomes possible, Significantly improved display quality. Further, by adjusting the voltage between the source and the drain, gray scale display can be easily performed. However, TF
In the manufacturing process of T, the use of 6 to 8 photomasks inevitably reduced the yield. In addition, many devices do not operate normally due to pin holes in the gate oxide film, etc.
Again, this was one of the factors that increased the overall manufacturing cost in terms of yield. Therefore, a liquid crystal display device having a simple structure and good display quality has been demanded.

[0004] Thus, what has been proposed by Clark Laguawall et al. Is a display using a ferroelectric liquid crystal. FIG. 1 shows a conceptual diagram thereof. Since the ferroelectric liquid crystal has spontaneous polarization, when the thickness of the liquid crystal layer is reduced until the helix is unwound, an interface stable state (SSFLC) is created, and once an electric field is applied, transmission occurs even when the electric field is removed. Alternatively, a memory effect in which a non-transmissive state continues can be obtained. By utilizing this memory state, the same static driving as the active matrix LCD of the TFT is enabled.

However, when this memory property is emphasized, a phenomenon called "burn" actually occurs, causing display failure. "Burning" becomes transparent and non-transparent once, and if the state is memorized and left for a long time, complete non-transparent or transparent state cannot be obtained even if the opposite state is displayed, and the contrast Was causing the decline. As a means for solving this problem, it has been found effective to perform display using a liquid crystal material having a minimum memory property. In a ferroelectric liquid crystal, there can be no composition having no memory property or having no spontaneous polarization, but when they are suppressed as much as possible to eliminate "burn", although there is memory property for several screens, However, the disadvantage that the display quality is deteriorated when the number of time divisions is increased has been highlighted. However, the high-speed responsiveness of ferroelectric liquid crystals is indispensable, and there has been a demand for a method that can solve the "burn" phenomenon while utilizing this characteristic.

Further, in the case of ferroelectric liquid crystal, since only two stable states, transmissive and non-transmissive, are taken, gradation display accompanying diversification of information is not good. As a method for solving this, a gray scale is displayed by dividing a unit pixel into a plurality of areas and forming a plurality of dots. For example, it has been devised that a unit pixel is divided into 1: 2: 4 in an area ratio and eight gradations are obtained by a combination of ON / OFF. FIGS. 2A and 2B show an electrode structure for two-gradation display and an electrode structure for eight-gradation display.

However, since the must be added three data signals for one unit pixel, it will have become very complicated external circuit, got decrease in yield during rising costs and the external circuit connection occurs Was. Further, since an insulating section is provided between the electrodes for division, the aperture ratio is reduced. For example, 250 μm
When a unit pixel having a pitch of 25 μm is considered, the aperture ratio is 81% when no division is made, whereas it is reduced to 63% when divided with the same gap. Furthermore, the width of the thinnest electrode (103) for division is 25 in the case of the pitch and gap.
μm. 1000 × 1 as a liquid crystal display
Even when a pixel having 000 pixels is manufactured using an ITO sheet resistance of 5Ω or less, the electrode in the data direction has a resistance of about 50 kΩ from end to end. In this case, the electric field intensity applied to the liquid crystal at both ends of the electrode is different, and uniform display cannot be performed.
Therefore, there has been a demand for a method capable of controlling the gradation in an analog manner.

[Problems to be solved by the invention]

[0008] The present invention is not to be spontaneous polarization and electrical interaction of the ferroelectric liquid crystal, it is an object to obtain a non-linear element does not affect the high-speed response of the ferroelectric liquid crystal.

[0009]

Means for Solving the Problems The present invention, Si _X C _Y O
Including a composition represented by _Z (X + Y + Z = 1, Y≪1)
Non-linear element having laminated film composed of thin film and DLC thin film
In the element, the above-mentioned Si _X C _Y O _Z (X + Y + Z = 1, Y≪
For a thin film or DLC thin film containing the composition shown in 1),
Use a non-linear element containing halogen or phosphorus
It is characterized by the following. Examples are shown below, and more detailed
Add a description.

[0010]

[Example 1 of manufacturing method of liquid crystal display device] An example of this manufacturing method is as follows.
As the structure of which is shown in FIG 7, on an insulating substrate which transmits visible light (1), having a first electrode (2) and the lead that transmits visible light, the electric superb Si _x C _Y O _Z (X + Y + Z =
A first substrate (10) having a second electrode (4) that transmits visible light and a first substrate (10) covered with a thin film (3) containing the composition shown in (1) above is disposed on the thin film. A second electrode having a third electrode (8) transmitting visible light and a lead on a conductive substrate (9).
And a liquid crystal composition (7) exhibiting ferroelectricity inside the first substrate (10) and the second substrate (11).
This is an example of a method for manufacturing a liquid crystal display device having means (5) for orienting the liquid crystal composition in a certain direction .

[0011] Hereinafter, first shows a method of producing a liquid crystal display device used in Examples of this manufacturing method. First, 100 nm of ITO was applied to 1.1 mm soda-lime glass (1) by DC sputtering.
and m deposition, then, by photolithography, and one side of the display pixel electrodes, a stripe having a width of substantially a same size, and the patterned, and a first electrode (2).

[0012] Thereafter, a glow discharge under the following _{conditions, Si x C Y O Z (} X + Y + Z = 1) layer (3) was 5 0 nm deposition. The film formation conditions were such that the gas mixture ratio C ₂ H ₄ was ₂ SCCM, N
F ₃ is 1 SCCM, H2 is 10 SCCM, a reaction pressure 50 Pa, RF power is 100W.

The reason why NF ₃ is added in the example of the present manufacturing method is to change the conductivity of the film (3) and to control the non-linear characteristics, and it is effective to add NF ₃ at a ratio of 30% by volume or less. . As a method of controlling the non-linearity, there is a method of adding thermal annealing. This is because the I (in
The hydrogen content in the film is controlled by measuring the dehydrogenation of the thin film (3) corresponding to the
It controls the non-linearity of the mold element. The processing conditions of this thermal annealing are as follows: temperature is 380 ° C., pressure is 100 Pa,
Processing atmosphere is Ar, the processing time is Ru Oh in one hour. Further, in the present invention the thickness of the _{Si x C Y O Z (X} + Y + Z = 1) thin film comprising a composition represented by (3) 20 0 nm or less, by preferably below 5 0 nm, the light transmittance Was able to enhance the character. Figure _{8 Si x C Y O Z (} X + Y +
5 shows the spectral transmittance at 50 nm of a thin film containing the composition represented by Z = 1).

[0014] conventionally insulator part of the MIM type element,
For example, when a TaO ₅ (tantalum pentoxide) film is to be used, its light transmittance is a problem, and there are restrictions in the process such as minimizing the area as much as possible. Then, ITO was again deposited on the film (3) to a thickness of 100 nm by DC sputtering.
The film was formed, and a second electrode (4) was obtained by using a photolithography method. In this case, a magnetron type RF sputtering method may be used.

The dimension of the second electrode is one of a pixel electrode, one side is a square 250 [mu] m, the gaps between pixels, and a 25 [mu] m. The second electrode (4) has a size to be a unit pixel at the time of display, and acts so that the electric field applied to the thin film (3) becomes uniform in each pixel. Thus, a first substrate (10) was obtained.

The other second substrate (11) is also coated on a 1.1 mm soda lime glass (9) by DC sputtering to obtain an IT.
O was deposited to a thickness of 100 nm . After that, using a photolithography method, the third electrode is patterned into a stripe shape having a width substantially equal to one side of the display pixel electrode.
(8).

On the first substrate (10), a polyimide thin film having a thickness of 20 nm was formed by a printing method, and then an alignment film (5) was provided by a rubbing method as a means for arranging liquid crystal molecules in a certain direction. .

Between the first substrate (10) and the second substrate (11),
A spacer (6) for maintaining the interval between the ferroelectric liquid crystal (7) and the substrate made of resin was inserted, and the periphery thereof was fixed with an epoxy adhesive.

[0019] Then, the first electrode (2), the lead connected to the third electrode (4), LSI for liquid crystal drive by a COG method
Was connected to obtain a liquid crystal display device.

The thin film formed in the example of the present manufacturing method (3)
Has optical transparency and has no optical problem if the thickness is 50 nm .

FIG . 14 and FIG. 15 show the current-voltage characteristics of the nonlinear element of this example of the manufacturing method .

[0022]

【Example】

[0023] The structure of the liquid crystal display device used in this embodiment is shown in FIG. 11. This embodiment is an insulating substrate that transmits visible light.
And (1), at least Si _x C covering the first electrode (2) and the lead that transmits visible light with a metal oxide provided on the insulating substrate, the electrodes and leads on _Y O _Z (X + _Y
+ Z = 1) a two-layer thin film containing the composition represented by the following formula:
(71), (72), a ferroelectric liquid crystal composition (7) provided on the thin film, and a second electrode that transmits visible light with a metal oxide provided on the liquid crystal layer (8) and the lead, and the liquid crystal display device comprising a second insulating substrate which transmits visible light (9), the _{Si x C Y O Z (X} + Y + Z = 1)
In the embodiment of the liquid crystal display device having a function of orienting a liquid crystal composition having ferroelectricity provided on the thin film on a surface of the thin film containing the composition shown in the liquid crystal layer side in a certain direction.
is there.

In this embodiment , Si _X C _Y O _Z (X + Y + Z
= Thin film containing a composition represented by 1), i.e. as the insulator of the non-linear element, Si _X C _Y O _Z as a first thin film
In (X + Y + Z = 1), a film (71) close to SiO ₂ containing carbon as Y≪1 is used as a second thin film of Si _X C _Y O _Z
(X + Y + Z = 1), X = 0, Z = 0 and DLC film
(72) was provided, and these two layers were used.

By the magnetron type RF sputtering method,
First, the first thin film (71) is formed to a thickness of 5 to 200 nm under the following conditions,
In this embodiment, the thickness is set to 30 nm . The film forming conditions are as follows: substrate temperature is 150 ° C., RF power is 400 W, film forming pressure is 0.5 Pa, film forming atmosphere is O ₂ volume 95%, NF ₃
The volume used was 5%, and the target used was an ingot obtained by adding a small amount of C to Si. Further, as a film forming method, a known photo CVD method may be used. Note that the non-linear characteristics of each pixel can be controlled by adding hydrogen to the atmosphere during the sputtering.

Next, the thin film (71) containing carbon as a main component on a surface on which is in contact with the liquid crystal layer (hereinafter referred to as DLC) thin film (7
2) was formed to a thickness of 2 to 200 nm under the following conditions, and 30 nm in this example. The film formation conditions are such that the gas mixture ratio is C ₂ H ₆ : NF.
₃ : H ₂ = 2: 1: 10 and the RF power is 100 W. An alignment treatment was performed on the surface (12) of the DLC thin film (72) in contact with the liquid crystal layer, and thereafter, the present example was completed in the same manner as in Example 1 of the method for manufacturing a liquid crystal display device .

The characteristics of this example method for manufacturing a liquid crystal display device
It was similar to example 1, but the electrical stability is high, the change in characteristics is small. In this embodiment, the thin film (71)
And a thin film 72 to form a portion corresponding to an insulator of the MIM type element. At this time, the thin film (71), which is a silicon oxide film in which fluorine and nitrogen elements are mixed, has a feature that it is extremely electrically stable without containing hydrogen. The thin film (72), which is a DLC film, is mainly composed of a group IV element, has no polarity, and has a low resistivity due to the action of hydrogen, nitrogen, and fluorine. When a layer is used, it does not interact with spontaneous polarization of the ferroelectric liquid crystal and does not affect the high-speed response of the ferroelectric liquid crystal.

[0028] a thin film (72) these thin films (71) since absolutely no need to pattern only process a manufacturing process to produce a thin film of two said liquid crystal display display device of a conventional simple matrix type increases It also has a feature in the manufacturing process. In addition, halogen element and phosphorus are mixed in 20% by atom or less in one of the films to be the insulator part.
Thus, the gettering (effect of taking in) hydrogen ions and the like separated from the bond which causes electric instability due to sodium ions diffused from the glass substrate to become fixed charges is obtained .

[0029] This embodiment includes a liquid crystal display as shown in FIG. 11
In Example 1 of a method for manufacturing a device _{Si x C Y O Z (X} + Y +
Z = 1) without the second electrode provided on the thin film containing the composition shown by 1).

The method for manufacturing a liquid crystal display device in [0030] this embodiment, the second electrode (4) corresponding to each pixel in the example 1 of a method for manufacturing a liquid crystal display device, an alignment film (5) that there is no, Si _x C _Y
A thin film containing a composition represented by O _Z (X + Y + Z = 1)
(3) film forming method and arrangement are different things, the alignment process on the surface in contact with the liquid crystal layer of the thin film (3) is made, other than the liquid crystal display instrumentation
Example 1 of the method of manufacturing the device and the method of manufacturing the same are the same.

[0031]

In the example of this manufacturing method [Example 2 of a method for manufacturing a liquid crystal display device]
As a second thin film of insulator embodiments, Si _x C _Y
A thin film containing the composition represented by O _Z (X + Y + Z = 1)
An SiC film may be provided with Z = 0.

[0032] Further, in the example of the present manufacturing method, the film (7
Orientation on this film using only one of 1) and film (72)
Processing may be performed.

[0033]

[Example of Driving Method of Liquid Crystal Display Device] The measure for lowering the memory property to avoid the “burn” phenomenon causes a fluctuation in transmittance at the time of non-selection in time-division driving shown in FIG. Has been reduced. FIG. 3 shows the driving waveform and the optical response of the liquid crystal display device.

[0034] To further perform gradation display, the case of changing the height of the signal pulse (voltage), for a given pixel is added a large voltage compared to the normal two-gradation display even if unselected, FIG 4 (202), which further reduced the contrast. FIG. 4 shows a driving waveform and an optical response of the liquid crystal display device when gradation display is performed on a normal ferroelectric liquid crystal.

As a method of solving the fluctuation of the transmittance at the time of non-selection at the time of the time-division driving, a method of connecting an element having a non-linear characteristic whose resistance component does not conform to Ohm's law to a liquid crystal display element electrode in series. is there.

Further, the strength of the two substrates sandwiching the ferroelectric liquid crystal, Si on the surface of at least several people or the other liquid crystal layer side of the
_{X C Y O Z (X +} Y + Z = 1) a liquid crystal display device having a thin film containing a composition substance represented by. Further, when driving the liquid crystal display device, a drive is performed in which a single-phase electric signal is applied to the scanning-side electrode within a unit time and an electric signal having a single-phase number or more is applied to the information-side electrode within a unit time. In the method, by changing the pulse height of the final phase,
We arbitrarily control the transmittance of the liquid crystal panel.

As shown in FIG. 5, the ferroelectric liquid crystal has a substantially constant product of the response speed and the voltage value of the applied pulse. That is, the product of the response speed and the voltage value at the time of the low voltage pulse is substantially equal to the product of the response speed and the voltage value at the time of the high voltage pulse. When this was applied to a liquid crystal composition having ferroelectricity with as little memory property as possible, it was found that the transmittance within a certain period could be controlled by changing the voltage while keeping the pulse width constant. FIG. 6 shows the driving pulse (waveform) and the optical response of the liquid crystal display device.

[0038] Therefore, in order to realize a gradation display, using the present effective as a driving method. (Driving Method Example 1) A liquid crystal display device an electrical signal consisting of 4 phases in unit time to the scan side electrode against the addition, in the driving method of applying electric signals composed of 4 phase information side electrode in a unit time, the second half 2 by varying the phase amount or the pulse height of the final phase, illustrating a method of driving you arbitrarily control the transmittance of the liquid crystal panel liquid crystal electro-optical device.

FIG. 9 shows a driving waveform applied to the liquid crystal device in the example of the present driving method . An electric signal (301) consisting of four phases is applied to the scanning electrode in a unit time, and an electric signal (302) consisting of four phases is applied to the information electrode in a unit time.
The transmittance of the liquid crystal panel is arbitrarily controlled by changing the pulse height of the phase or the final phase (303a, 303b). Signal when selected ON (304)
Is to control the transmittance by changing the last phase of the four phases between 3V and 4V.

FIG . 10 shows the driving signal and the optical response of the liquid crystal display device according to Example 1 of the present driving method . As is apparent from these figures, the liquid crystal cell is subjected to the electric field only when a signal electric field of a certain strength or more is applied to the liquid crystal device due to the effect of the nonlinear element. No fluctuation is observed. Also, it can be seen that the optical response can be controlled by changing the voltage of the final phase or the phase before the final phase.

[0041] (a driving method Example 2) 3 wherein against the liquid crystal display device, within a unit time to the scan side electrode
In a driving method in which an electric signal composed of three phases is applied and an electric signal composed of three or more phases is applied to the information side electrode within a unit time in a unit time, by changing a pulse height of two rear phases or a final phase, Arbitrarily controlling the transmittance of the LCD panel
Shows the driving method that the liquid crystal electro-optical device.

FIG. 12 shows a driving waveform applied to the liquid crystal device in Example 2 of the present driving method . A three-phase electric signal (305) is applied to the scanning-side electrode within a unit time, and a three-phase electric signal (306) is applied to the information-side electrode within a unit time. The transmittance of the liquid crystal panel is arbitrarily controlled by changing the height (307a, 307b). Signal when ON when selected (30
8) is to control the transmittance by changing the last phase of the three phases between 3V and 4V.

[0043] Examples of (a driving method Example 3) This driving method using the liquid crystal display device having the same structure as the embodiment, by adding the drive waveform shown in FIG. 13, thereby performing the gradation display. 2 times per unit time
In a driving method in which an electric signal composed of two phases or more and an electric signal composed of two or more phases are applied within a unit time to the information side electrode, by changing the pulse height of the rear two phases or the final phase, This shows a method for driving a liquid crystal electro-optical device, which is characterized by arbitrarily controlling the transmittance of a liquid crystal panel.

[0044]

According to the structure of the present invention, the non-linear
Depending on the use of the Si _X C _Y O _Z as an insulating film in the form element
And high electrical stability can be obtained.
When used, a film having a low resistivity can be obtained. Further
When a ferroelectric liquid crystal layer is used as the liquid crystal layer,
No strong interaction with spontaneous polarization of liquid crystal
It does not affect the high-speed response of dielectric liquid crystal.
can do.

In addition, since each pixel can have a non-linear characteristic, the liquid crystal display has a simple structure, does not cause fluctuation in transmittance when not selected during time-division driving, and has a high display contrast. A dielectric liquid crystal display was obtained.

In addition, any of the
20 atomic percent or less of halogen element and phosphorus mixed into the film
Sodium diffused from the glass substrate
The ions become fixed charges and cause electrical instability.
Gettering of hydrogen ions etc.
Effect).

[Brief description of the drawings]

Fig. 1 Conceptual diagram of ferroelectric liquid crystal

FIG. 2 is a gray scale display method based on a change in pixel electrode area.

FIG. 3 shows a driving waveform and an optical response when a normal ferroelectric liquid crystal is driven in a time division manner.

FIG. 4 shows a driving waveform and an optical response when a normal ferroelectric liquid crystal is operated by the driving method of the present invention.

FIG. 5: Relationship between voltage and response speed of ferroelectric liquid crystal

FIG. 6 shows the optical response of a ferroelectric liquid crystal with minimal memory when operated by changing the voltage.

FIG. 7 is a structural view of a liquid crystal display device used in this example.

FIG. 8 shows the transmittance of an insulating film for a non-linear element used in this example.

FIG. 9 shows a driving waveform according to the present invention.

FIG. 10 shows a driving waveform and an optical response according to the present invention.

FIG. 11 is a structural diagram of a liquid crystal display device used in this example.

FIG. 12 shows a driving waveform according to the present invention.

FIG. 13 shows a driving waveform according to the present invention.

FIG. 14 shows electro-optical characteristics of the nonlinear element used in this example.

FIG. 15 shows the electro-optical characteristics of the nonlinear element used in this example.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-50489 (JP, A) JP-A-64-53425 (JP, A) JP-A-64-47076 (JP, A) 289828 (JP, A) JP-A-57-197592 (JP, A) Patent 2945947 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1365 H01L 49/02

Claims (3)

(57) [Claims] 1. A _{Si X C Y O Z (X} + Y + Z = 1, Y <<
1 ) A non-linear element having a laminated film composed of a thin film containing the composition shown in ( 1 ) and a DLC thin film, wherein the thin film or DLC containing the composition shown in the above-mentioned Six _X C _Y O _Z (X + Y + Z = 1, Y << 1 ) A non-linear element, wherein the thin film contains halogen or phosphorus. 2. The method of claim 1, represented by _{Si X C Y O Z (X} + Y + Z = 1, Y << 1)
The thin film containing the composition to be formed has a thickness of 5 to 200 nm,
A DLC thin film having a thickness of 2 to 200 nm. 3. A liquid crystal display device using the nonlinear element according to claim 1.