JP3263053B2 - Liquid crystal display device and electric appliance - 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 scanning lines increases, it becomes difficult to obtain an applied voltage ratio between selected and non-selected portions of the scanning lines, resulting in a reduction in display quality, particularly in contrast.

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. Active matrix type liquid crystal display devices can minimize the influence on other scanning lines because only the gate of the TFT connected to the scanning 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 charge, so that even while writing other scanning 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 three data signals must be applied to one unit pixel, the external circuit becomes very complicated, resulting in an increase in cost and a decrease in the yield when the external circuit is connected. 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.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a display device having high electrical stability. For example, when a ferroelectric liquid crystal layer is used as a liquid crystal layer, it is necessary to obtain a liquid crystal display device that does not interact with the spontaneous polarization of the ferroelectric liquid crystal and does not affect the high-speed response of the ferroelectric liquid crystal. Make it an issue.

[0009]

Means for Solving the Problems The present invention, Si _X C _Y O
_{Z (X + Y + Z =} 1) display odor <br/> using a laminated film of a thin film and DLC film comprises a composition represented by Te, the Si _X C _Y O _Z composition represented by (X + Y + Z = 1 ) Or a DLC thin film containing halogen or phosphorus. Examples will be shown below, and further detailed description will be added.

[Example 1 of Manufacturing Method of Liquid Crystal Display Device] In an example of this manufacturing method, as shown in FIG. 7, the visible light is transmitted on an insulating substrate (1) that transmits visible light. having a first electrode (2) and leads, the electric superb Si _X C _Y
A thin film containing the composition represented by O _Z (X + Y + Z = 1) (3)
And a second electrode (4) that transmits visible light on the thin film.
Using a first substrate (10) having a transparent electrode and a second substrate (11) having a third electrode (8) transmitting visible light and a lead on an insulating substrate (9) transmitting visible light. Inside the first substrate (10) and the second substrate (11), a liquid crystal composition (7) exhibiting ferroelectricity and means (5) for orienting the liquid crystal composition in a certain direction are provided. 5 is an example of a method for manufacturing a liquid crystal display device having the following.

Hereinafter, a method of manufacturing a liquid crystal display device used in an example of the present manufacturing method will be described first. First, 100 n of ITO was applied to 1.1 mm soda-lime glass (1) by DC sputtering.
m, and then patterned by a photolithography method into a stripe having a width substantially equal to one side of the display pixel electrode to form a first electrode (2).

Thereafter, glow discharge was performed under the following conditions to form a 50 nm thick Si _X C _Y O _Z (X + Y + Z = 1) film (3). The film formation conditions were such that the gas mixture ratio C ₂ H ₄ was ₂ SCCM, N
F ₃ is 1 SCCM, and are H ₂ 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 (sulator) portion, thereby controlling the non-linearity of the MIM element. The conditions for the thermal annealing are as follows: temperature is 380 ° C., pressure is 100 Pa, processing atmosphere is Ar, and processing time is 1 hour. In the present invention, the light transmittance of the thin film (3) containing the composition represented by Si _x C _Y O _Z (X + Y + Z = 1) is set to 200 nm or less, preferably 50 nm or less. Could be enhanced. Figure _{8 Si X C Y O Z (} X + Y + Z
= 1) shows the spectral transmittance at 50 nm of a thin film containing the composition shown in 1).

Conventionally, in the insulator portion 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. After that, ITO is 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 size of the second electrode, which is one of the pixel electrodes, was a square having a side of 250 μm, and the gap between the pixels was 25 μm. The second electrode (4) has a size to be a unit pixel at the time of display, and acts so that an 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.

Thereafter, a liquid crystal driving LSI is formed on the leads connected to the first electrode (2) and the third electrode (4) by using the 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】

FIG. 11 shows the structure of the liquid crystal display device used in this embodiment. 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)
This is an embodiment of a liquid crystal display device having a function of orienting a ferroelectric liquid crystal composition provided on the thin film on a liquid crystal layer side of a thin film containing the composition shown in the above formula in a fixed direction. .

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 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, on the surface of the thin film (71) in contact with the liquid crystal layer, a thin film (hereinafter referred to as DLC) containing carbon as a main component (7) is formed.
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 the present example were the same as those of Example 1 of the method for manufacturing a liquid crystal display device, but the electrical stability was high and the change in the characteristics was 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.

Since the thin film (71) and the thin film (72) do not need to be patterned at all, only the steps of manufacturing the above two thin films are added to the manufacturing process of the conventional simple matrix type liquid crystal display device. It also has a feature in the manufacturing process. In addition, 20% by atom or less of halogen element and phosphorus are mixed into any of the films to be the insulator part, and sodium ions diffused from the glass substrate become fixed charges and hydrogen ions separated from the bond causing electrical instability etc. Gettering (effect of taking in).

[0029] This example, Si in the example 1 of a method for manufacturing a liquid crystal display device as shown in FIG. _{11 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)
The manufacturing method is the same as that of Example 1 of the liquid crystal display device except that the film forming method is different from the film forming method of (3), and the alignment treatment is performed on the surface of the thin film (3) in contact with the liquid crystal layer. is there.

[0031] In the example of this manufacturing method [Example 2 of a method for manufacturing a liquid crystal display device, a second thin film of insulator embodiments, including _{Si X C Y O Z (X} + Y + Z = 1) composition represented by The SiC film may be provided with Z = 0.

In the example of this manufacturing method, the film (7
Using only one of 1) and the film (72), an alignment treatment may be performed on this film.

[Example of Driving Method of Liquid Crystal Display Device] Measures to reduce the memory property to avoid the “burn” phenomenon are as follows.
Fluctuation of the transmittance at the time of non-selection at the time of the time-division driving shown in FIG. 3 (201) causes fluctuation of the contrast. FIG. 3 shows the driving waveform and the optical response of the liquid crystal display device.

Further, when the peak (voltage) of the signal pulse is changed to perform the gradation display, a larger voltage is applied as compared with the normal two-gradation display even when an arbitrary pixel is not selected. 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, at least one of the two substrates sandwiching the ferroelectric liquid crystal is provided with Si on the surface on the liquid crystal layer side.
_{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,
The transmittance of the liquid crystal panel is arbitrarily controlled.

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.

Therefore, in order to realize a gradation display, the present effect was used as a driving method. (Driving Method Example 1) In a driving method in which a four-phase electric signal is applied to a scanning-side electrode within a unit time and a four-phase electric signal is applied to an information-side electrode within a unit time to a liquid crystal display device, A method of driving a liquid crystal electro-optical device that arbitrarily controls the transmittance of a liquid crystal panel by changing the pulse height of the phase or the final phase will be described.

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.

(Driving Method Example 2) With respect to the liquid crystal display device, three electrodes are applied to the scanning
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, A method for driving a liquid crystal electro-optical device for arbitrarily controlling the transmittance of a liquid crystal panel will be described.

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.

(Driving Method Example 3) In this driving method example, a liquid crystal display device having the same structure as that of the embodiment is used, and gradation display is performed by adding a driving waveform shown in FIG. 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]

By taking the configuration of the present invention, it is possible to obtain a high electrical stability by the use of the Si _X C _Y O _Z as an insulating film of the display <br/> device, also, a DLC film And a film having a low resistivity can be obtained. Furthermore, when a ferroelectric liquid crystal layer is used as the liquid crystal layer, it does not interact with the spontaneous polarization of the ferroelectric liquid crystal and does not affect the high-speed response of the ferroelectric liquid crystal. it can.

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.

Further, by incorporating a halogen element or phosphorus in an amount of 20 atomic percent or less into any of the films serving as the insulator portion, sodium ions diffused from the glass substrate become fixed charges and cause a bond that causes electrical instability. This is effective in gettering (take-in action) of distant hydrogen ions and the like.

[Brief description of the drawings]

FIG. 1 shows a conceptual diagram of a ferroelectric liquid crystal.

FIG. 2 shows 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 time-divisionally driven.

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 shows the relationship between the voltage and the response speed of a ferroelectric liquid crystal.

FIG. 6 shows an optical response when a ferroelectric liquid crystal having a minimal memory property is operated by changing a voltage.

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

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

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

FIG. 14 shows the 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.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI C23C 16/42 C23C 16/42 G02F 1/141 G02F 1/137 510 (56) References JP-A-1-234566 (JP, A JP-A-2-250968 (JP, A) JP-A-2-15172 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1333 G02F 1/141 C23C 14 / 00-14/58 C23C 16/00-16/56

Claims (6)

(57) [Claims] 1. A liquid crystal display device using a laminated film composed of a thin film containing a composition represented by Si _X C _Y O _Z (X + Y + Z = 1) and a DLC thin film, wherein the _X C _Y O _Z (X + Y + Z) = liquid crystal display device is a thin film or DLC film, characterized in that it contains the halogen or phosphorus containing composition represented by 1). 2. A thin film containing carbon, oxygen and silicon and a DLC.
A liquid crystal display device using a laminated film of a thin film, liquid in thin film or DLC film containing the carbon, oxygen and silicon characterized in that it contains halogen or phosphorus
Crystal display device . 3. A liquid crystal display device according to claim 2, wherein said thin film containing carbon, oxygen and silicon is a silicon oxide thin film containing carbon. 4. A liquid crystal display device according to claim 1, wherein said laminated film has a thickness of 200 nm or less. 5. A any one of claims 1 to 4, a liquid crystal display device wherein the liquid crystal display device having a ferroelectric liquid crystal. 6. claimed in any one of claims 1 to 5
An electric device comprising the liquid crystal display device
Utensils.