JPH07110494A - Active matrix liquid crystal display - Google Patents

Abstract

PURPOSE:To provide the active matrix liquid crystal display capable of decreasing gradation inversion regions and improving visual field angle characteristics. CONSTITUTION:This active matrix liquid crystal display has a glass substrate 1 having pixel electrodes 5 formed to a matrix form on the surface, having thin-film transistors(TFTs) which are disposed near the respective pixel electrodes 5 and apply voltages to the pixel electrodes 5 and having further, protective layers 16 on the surfaces of the pixel electrodes 5 and TFTs, liquid crystals disposed on the protective layers 16 and a counter electrode superposed on the liquid crystals. The protective layers 16 on the respective surfaces of the pixel electrode 5 are partially removed, by which the parts varying in gaps with the liquid crystals are formed within the same pixel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix liquid crystal display using thin film transistors.

[0002]

2. Description of the Related Art Thin film transistor (hereinafter referred to as TFT)
A display using an active matrix type display substrate using is being actively researched because it can obtain higher image quality than a simple matrix type display device. FIG. 5 is a perspective view schematically showing a liquid crystal panel section of a conventional active matrix type liquid crystal display device. Reference numeral 1 is a glass substrate, which is an example of an insulating substrate, and 2 is a data line to be a TFT.
4 is connected to the source electrode 8 or the drain electrode 10. 3 is a scanning line which intersects with the data line 2 in an insulated manner
It is a gate bus connected to the gate 9 of the FT 4. Reference numeral 4 is a TFT, and 5 is a pixel electrode for driving a liquid crystal formed in a matrix on a glass substrate. In a normally transmissive liquid crystal display device, it is necessary to transmit light from the back light source, so the pixel electrode 5 must be a transparent conductive film. A glass substrate 1 in which the above elements serve as a TFT array substrate
Is formed by repeating selective etching and the like.

Reference numeral 6 is a black matrix, and 7 is a counter electrode made of a transparent conductive film. The counter electrode 7 is superposed on the array substrate with a liquid crystal interposed therebetween. The black matrix 6 cuts out light that escapes from portions other than the display electrode portion, enhances the contrast of the liquid crystal panel, and blocks light from the outside to prevent T
It has a function of preventing malfunction of the FT4 due to the photo controller. This counter substrate 7 is used when color display is to be performed on the liquid crystal panel.
It is possible to display by forming a color filter in each pixel.

In such a liquid crystal panel, the data line
The TFT4 is driven according to the image signal input through
Change the voltage applied to the liquid crystal layer.
To display an image by changing the transmittance of the liquid crystal panel.
You can Next, active matrix liquid crystal display panel
The driving method of will be described. Active matri
An equivalent circuit of the box-type liquid crystal display panel is shown. The image signal is
Inn A₁, A₂… A_nAdded to. Run to this line
Inspection line B₁, B₂... B_mTFT at the intersection with
Q₁₁, Q₁₂… Q_1m, Q_{twenty one}, Q_{twenty two}… Q_2m, Q_n1, Q_n2… Q
_nmSource (or drain) is connected. It
Scan line B₁As shown in the figure, the TFT Q₁₁
The gate electrodes of ... Are connected. TFT Q₁₁… De
Liquid crystal is passed through the rain (source) electrode and through the counter electrode T.
It is the same. Scan line B₁Driving pulse Φ₁ , Φ₂，
… Φ_mIs sequentially applied to the gate electrode, and TFT Q₁₁…But
Each pixel electrode is turned on through the source electrode
The image signal is written in. This state is the next field
Drive pulse Φ₁... is TFT Q₁₁Mark the gate electrode of
Hold until added. In this way the TV image
The display is done.

Next, a process for forming a TFT array of a liquid crystal panel will be described with reference to FIGS. 7 and 8. That is, first, (a) a glass substrate 1 is sputtered with Cr9A 10
00Å Accumulate. (B) Etching is performed so as to leave the gate 9 made of Cr and the scanning line 3 (FIG. 8).
(A)). (C) 1000 Å of transparent electrode ITO5A is deposited on the glass substrate 1 by DC sputtering. (D) Etching is performed so that the transparent electrode ITO remains in the shape of the pixel electrode 5 (FIG. 8B). (E) Next, 4000N of SiNx11 is deposited as a gate insulating layer by plasma CVD, 1000L of a-Si layer 12 is deposited as a semiconductor layer, and 500L of n ⁺ a-Si13 is deposited as an ohmic layer.
(F) The a-Si layer 12 and the n ⁺ a-Si 13 are denoted by reference numeral 1
Etching is performed by a photolithography process so as to leave it in the shape of the pattern indicated by 2a to form an a-Si island region 12a to be a channel region (FIG. 8C). (G) Pixel electrode 5
A hole 14 for making contact with is formed in the insulating layer 11 (FIG. 8D). (H) Al15 was deposited by DC sputtering
000Å Accumulate. (I) After the source (or drain) electrode 8 and the drain (or source) electrode 10 are formed by selective etching with Al, n ⁺ a on the channel is formed.
-Si is removed by etching (FIG. 8E). (J) SiNx 16 to be a protective layer for the TFT and the wiring is formed on the entire surface of 2000 Å by using the plasma CVD method, and then the protective layer 16 on the pixel electrode 5 and the take-out electrode is removed. The reason why the protective layer 16 is provided on the channel of the TFT 4 in this way is that it is necessary to suppress the change in the OFF characteristic of the TFT 4 with time and improve the reliability of the liquid crystal panel (IEICE Vol. 90No. .88 EID90-1).
On the other hand, by removing the protective layer 16 on the pixel electrode 5, the voltage drop due to the protective layer 16 is eliminated to lower the drive voltage of the liquid crystal and prevent fixed charges from being accumulated on the pixel electrode 5. .

Incidentally, the structure in which the protective layer 16 and the insulating layer 11 are left around the pixel electrode 5 is caused by the necessity in the process, and in this case, the display area black. The opening portion of the matrix 6 is entirely the region 17 where the protective layer 16 is removed. After the alignment film and the liquid crystal are formed and encapsulated on the TFT array substrate formed by the above process, the liquid crystal panel is completed by sticking the counter substrate 7 on which the black matrix 6 and the color filter are formed, and the active matrix. A liquid crystal display is formed.

[0007]

FIG. 9 shows the voltage-transmittance curve of the liquid crystal panel produced by the above process (normally white mode). The horizontal axis represents the applied voltage, and the vertical axis represents the transmittance. The parameter is the downward view angle θ with respect to the liquid crystal panel. Here, the angle of view θ is shown in FIG.
As shown in (b), the angle viewed from the lower side of the panel with respect to the normal to the panel surface, that is, the position of the angle φ = 180 ° in the rotation direction on the plane as shown in FIG. =
It may be 0 °, 15 °, 30 °, 45 °, 60 °.

As shown in FIG. 9, the slope of the voltage-transmittance curve becomes more gradual as the angle of view θ becomes larger. Above a certain slope, as shown by the dotted line in FIG. 18 occurs at a low transmittance. This area 18 is called a gradation reversal area, which causes deterioration of the viewing angle characteristics of the liquid crystal panel. The cause of this gradation inversion will be described. The display mode of the active matrix type liquid crystal panel is generally TN (twisted nematic) mode. In this display mode, the glass substrate 1 and the counter substrate 7 forming the array substrate are used.
The liquid crystal has a structure in which the alignment direction of the liquid crystal is twisted by 90 °. In the state where no voltage is applied, liquid crystal molecules are arranged in parallel with the array substrate and the counter substrate 7. As a voltage is applied from this state, the liquid crystal molecules 18 approach the counter substrate 7 from parallel to vertical as shown in FIG. Therefore, when such a display is made, when viewed with a certain inclination with respect to the normal direction of the panel surface, the liquid crystal molecules are inclined from the viewing angle direction as the liquid crystal is vertically aligned at a certain applied voltage or more. However, the leaked light becomes large.

FIG. 12 is a radar chart showing the gradation inversion angle of the TFT liquid crystal panel in the conventional example. The lines on the concentric circles show the same angle of view θ with respect to the normal direction,
It shows at which angle the gradation inversion occurs when the panel is rotated from the angle φ = 0 ° to 360 ° while maintaining the prospective angle θ. The shaded area in the figure is the area 19 in which gradation inversion occurs. According to this, when the liquid crystal panel is viewed from the lower side, gradation inversion occurs at an inclination of about 26 °.

Therefore, an object of the present invention is to provide an active matrix liquid crystal display capable of reducing the gradation inversion region and improving the viewing angle characteristics.

[0011]

According to another aspect of the present invention, there is provided an active matrix liquid crystal display having pixel electrodes for driving a liquid crystal formed in a matrix on a surface thereof and arranged in the vicinity of each of the pixel electrodes. An insulating substrate having a thin film transistor for applying a voltage and having an insulating protective layer on the surface of the pixel electrode and the thin film transistor, a liquid crystal disposed on the insulating protective layer, and a counter electrode overlaid on the liquid crystal, By partially removing the insulating protective layer on the surface of each pixel electrode, a portion having a different gap with respect to the liquid crystal is formed in the same pixel.

According to a second aspect of the present invention, in the active matrix liquid crystal display according to the first aspect, the counter electrode has a black matrix, and the region for removing the insulating protective layer on the pixel electrode and the remaining region are both inside the opening of the black matrix. It is the same as the one in.

[0013]

According to the active matrix liquid crystal display of claim 1, since the insulating protective layer on each surface of the pixel electrode is partially removed, a portion having a different gap with respect to the liquid crystal is formed in the same pixel. The voltage-transmittance characteristic is different for each region having a different gap, and the voltage having a voltage-transmittance characteristic of the portion having the insulating protective layer and the grayscale inversion of the transmittance characteristic and the voltage of the portion having the insulating protective layer removed-
Since the regions in which the grayscale inversion of the transmittance characteristics occurs are displaced and the different characteristics are superimposed as a whole, the grayscale inversion regions can be reduced, and therefore the viewing angle characteristics can be improved and improved. On the other hand, since the thin film transistor is covered with the insulating protection layer and a part of the pixel electrode is opened, the fixed charge is little accumulated and the reliability of the liquid crystal panel is less affected.

According to another aspect of the active matrix liquid crystal display of the present invention, in the first aspect, the counter electrode has a black matrix, and the area for removing the insulating protective layer on the pixel electrode and the remaining area are both openings of the black matrix. It has the same effect because it is inside.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. That is, in this active matrix liquid crystal display, the insulating protective layer on each surface of the pixel electrode is partially removed to form a portion having a different gap with respect to the liquid crystal in the same pixel.

FIG. 1 is a sectional view of the liquid crystal panel manufacturing process according to this embodiment, and FIG. 2 is a plan view thereof.
Further, the process is almost the same as the conventional process shown in FIG. 8, and common parts are denoted by the same reference numerals. The difference from the conventional example shown in FIGS. 7 and 8 is that the insulating layer 11 and the protective layer 16 on the pixel electrode 5 made of ITO are removed over almost the entire area (17) in the conventional example. This is to use both the region 20 for leaving the insulating layer 11 and the protective layer 16 on the pixel electrode 5 and the region 21 for removal as the display region. In this embodiment, the area ratio of the regions 20 and 21 on the pixel electrode is 1: 1.

The reason why the gradation inversion angle becomes small or disappears by such a configuration will be described. When the gap of the liquid crystal in the region (which is referred to as a pixel opening region) 21 where the protective layer 16 and the like are removed in one pixel is set to 5 μm, the portion where the insulating layer 11 and the protective layer 16 on the pixel electrode 5 are left ( In the pixel unopened area) 20, the remaining film thickness is set to 7000
If it is Å, the gap will be 4.3 μm. The voltage-transmittance characteristic of the pixel aperture region 21 has the gradation inversion region shown in FIG. 9 as shown by the dotted line 23 in FIG. Where θ
= 45 ° and φ = 180 °. On the other hand, the voltage-transmittance characteristic of the pixel unopened area 21 is shown by the broken line 24 in FIG. 4, but no gradation inversion area is formed at the same position as the characteristic of the dotted line 23. The reason why the optical characteristics of the two are different from each other is that the gap of the liquid crystal is different and that the voltage drop occurs in this portion because the protective layer is left.

The voltage-transmittance characteristic of an actual liquid crystal panel is determined by superposing the two, and the voltage-transmittance characteristic at this time is shown by a solid line 25 in FIG. As a result, it can be seen that the gradation inversion region, which has been generated when the prospective angle θ is large, is small. Further, it is possible to eliminate the gradation inversion region by changing and optimizing the area ratio of both.

Further, a TFT manufactured according to this embodiment
FIG. 3 is a radar chart showing the gradation inversion angle of the liquid crystal panel. From this, it can be seen that when observed from directly below the liquid crystal panel, there is a portion in which gradation inversion does not occur compared to the radar chart of the conventional example in FIG. 12, and the gradation inversion area is reduced. The effect of improving the gradation inversion angle is
The area ratio of the portion where the protective layer 16 and the like are left and the pixel electrode 5 is within a certain range.

Further, in this embodiment, the protective layer 1 is provided on the TFT.
Since the pixel electrode 5 is covered with 6 and a part of the pixel electrode 5 is opened, charge accumulation on the pixel electrode 5 does not occur, and the above-mentioned problem relating to panel reliability does not occur. In addition, in the present invention, since the gap with respect to the liquid crystal is made different, the protective layer 1
6 and the insulating layer 11 are removed, only the protective layer 16 may be removed, and the insulating protective layer of the present invention includes both.

[0021]

According to the active matrix liquid crystal display of the first aspect, since the insulating protective layer on each surface of the pixel electrode is partially removed, a portion having a different gap with respect to the liquid crystal is formed in the same pixel. The voltage-transmittance characteristics differ depending on the regions having different gaps in each part of the pixel electrode, and the voltage-transmittance of the area where the insulating protective layer is removed and the area where the gradation reversal of the voltage-transmittance characteristic of the portion having the insulating protective layer The region where the gradation inversion of the rate characteristic occurs is shifted, and the characteristics are superimposed as a whole, so that the gradation inversion region can be reduced, and therefore the viewing angle characteristic can be improved and improved. There is. On the other hand, since the thin film transistor is covered with the insulating protection layer and a part of the pixel electrode is opened, the fixed charge is little accumulated and the reliability of the liquid crystal panel is less affected.

According to a second aspect of the active matrix liquid crystal display of the first aspect, in the first aspect, the counter electrode has a black matrix, and the area for removing the insulating protective layer on the pixel electrode and the remaining area are both openings of the black matrix. It has the same effect because it is inside.

[Brief description of drawings]

FIG. 1 is a sectional view of a manufacturing process of a TFT array according to an embodiment of the present invention.

FIG. 2 is a plan view of each state of the manufacturing process.

FIG. 3 is a radar chart showing a gradation inversion angle of a liquid crystal panel.

4A and 4B are a voltage-transmittance characteristic diagram of a liquid crystal panel in a region where a protective layer is removed and a remaining region of this example, and a voltage-transmittance characteristic diagram in which both characteristics are superimposed.

FIG. 5 is a perspective view of a conventional liquid crystal panel.

FIG. 6 is an equivalent circuit diagram of an active matrix liquid crystal panel.

FIG. 7 is a cross-sectional view illustrating a manufacturing process of a conventional TFT array using an inverted stagger type TFT.

FIG. 8 is a plan view of each state of the manufacturing process.

FIG. 9 is a diagram showing the angle dependence of voltage-transmittance characteristics of a liquid crystal panel having a conventional structure.

FIG. 10 is an explanatory diagram illustrating an angle viewed from the bottom of the panel.

FIG. 11 is an explanatory diagram illustrating the reason why gradation inversion occurs.

FIG. 12 is a radar chart showing a gradation inversion angle of a liquid crystal panel having a conventional structure.

[Explanation of symbols]

 1 Glass Substrate as Insulating Substrate 5 Pixel Electrode 7 Counter Electrode 12 Protective Layer as Insulating Protective Layer 20 Area with Insulating Protective Layer 21 Area with Insulating Protective Layer Removed

Claims (2)

[Claims] 1. A pixel electrode for driving a liquid crystal formed in a matrix on the surface thereof, and a thin film transistor arranged in the vicinity of each of the pixel electrodes for applying a voltage to the pixel electrode. And an insulating substrate having an insulating protective layer on the surface of the thin film transistor, a liquid crystal disposed on the insulating protective layer, and a counter electrode laminated on the liquid crystal, and the insulating on each surface of the pixel electrode. An active matrix liquid crystal display, characterized in that a part having a different gap with respect to the liquid crystal is formed in the same pixel by partially removing the protective layer. 2. The counter electrode has a black matrix,
2. The active matrix liquid crystal display according to claim 1, wherein both the region where the insulating protective layer on the pixel electrode is removed and the region where it is left are inside the opening of the black matrix.