JP2004233959A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which reduces the reflection in a transmission region, improves the contrast of an image and suppresses display of a reversal image. <P>SOLUTION: The liquid crystal display device has a first base film 9 composed of silicon nitride and a second base film 10 composed of silicon oxide and a thin-film transistor (TFT), and a light transparent pixel part is formed on the second base film 20. The TFT comprises a polysilicon film 5, a gate electrode G, a drain electrode D and a source electrode S. A gate insulating film, interlayer insulating film, and organic film are formed in the pixel section. Also, the substrate has the function to reflect the external light and the inversion of the image of the transmission type liquid crystal panel is suppressed by forming the first base film thicker than the second base film. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device in which reflection of extraneous light is prevented to improve image contrast.
[0002]
[Prior art]
Liquid crystal display devices are used for displays of televisions, personal computers, portable terminals, and the like. 2. Description of the Related Art Liquid crystal display devices are used as display means for small electronic terminals such as mobile phones because of their light weight and low power consumption.
[0003]
Further, since the portable terminal is used indoors and outdoors, a partially transmissive liquid crystal display device is used. A partially transmissive liquid crystal display device displays an image using external light when the use environment is bright, and displays an image using light from a backlight when the use environment is dark. (For example, see Patent Document 1). In addition, there is a liquid crystal display device that can perform a transmissive display mainly using light of a backlight and a reflective display in which light incident from an image observation side is reflected by a reflector of the backlight even with a panel of a total transmission type. . (For example, see Patent Documents 2 and 3). In many liquid crystal display devices, a thin film transistor is used as a switching element.
[0004]
In recent years, a liquid crystal display device with higher definition has been demanded, and the number of pixels of the liquid crystal display device has been increasing. With the increase in the number of pixels, a thin film transistor with a high operation speed is required. In a high-definition liquid crystal display device, polysilicon (polycrystalline silicon) is used instead of amorphous silicon as a semiconductor layer of a thin film transistor. By using polysilicon as the semiconductor layer, the operation speed of the thin film transistor is increased, and as a result, a high-definition image can be displayed. Further, a technique is known in which an upper underlayer and a lower underlayer are deposited on a glass substrate, and the semiconductor thin film on the upper underlayer is irradiated with a laser to crystallize the semiconductor thin film. (For example, see Patent Document 4).
[0005]
[Patent Document 1]
JP 2001-350158 A
[Patent Document 2]
JP-A-2002-98960 (paragraphs 0034-0043, FIGS. 2-3)
[Patent Document 3]
JP-A-2002-98963 (paragraphs 0001-0007, 0016-0017, FIGS. 1, 3, and 5)
[Patent Document 4]
JP-A-6-132306 (paragraphs 0002-0007, FIGS. 1-4).
[0006]
[Problems to be solved by the invention]
Usually, a thin film transistor is formed on a glass substrate, and the glass substrate uses glass called non-alkali glass. This glass substrate contains impurities, and the impurities penetrate into the polysilicon film, and the transistor characteristics of the thin film transistor formed on the substrate deteriorate.
[0007]
In order to suppress the penetration of impurities from the glass substrate to the polysilicon film, a base film such as silicon nitride or silicon oxide is provided between the glass substrate and the polysilicon film. A base film is formed on the entire surface of the panel, and a light-transmissive pixel electrode is formed on the base film in addition to the thin film transistor. However, when a base film and a pixel electrode are stacked, reflection of extraneous light occurs due to a difference in the refractive index of each film.
[0008]
In a conventional liquid crystal display device using a backlight, a base film is also formed in a light transmitting region, so that when external light is reflected in a region where a light transmitting pixel electrode is formed, the image contrast is reduced. There was a problem.
[0009]
Further, in a partially transmissive liquid crystal display device, a light reflection region and a light transmission region are formed in one pixel. Therefore, when displaying an image using the light of the backlight, the transmitted light is blocked in the reflection area, and the luminance of the screen is low. A total transmission panel structure having no reflective electrode in the pixel electrode is used, and external light is reflected by the backlight, so that the luminance when the backlight is used can be improved. Since such a display device is formed by stacking a base film, an electrode, an interlayer insulating film, and the like, interface reflection due to a difference in refractive index occurs at the interface between the films. A total transmission type liquid crystal display device that reflects extraneous light with a backlight has a problem that, when an image is displayed with reflected light, an inverted image in which the density of the image is reversed is displayed.
[0010]
[Means for Solving the Problems]
In a typical liquid crystal display device of the present invention, the liquid crystal display device includes a thin film transistor and a pixel electrode formed over a substrate, and the thin film transistor includes a silicon film, a gate electrode, and a source electrode electrically connected to the pixel electrode. A silicon oxide film between the silicon film and the substrate and between the pixel electrode and the substrate, a silicon nitride film formed between the silicon oxide film and the substrate, and a thickness of the silicon nitride film. Is characterized by being thicker than the film thickness of silicon oxide.
[0011]
Here, when the silicon nitride film has a thickness of d (nm) and a refractive index of n when the wavelength is 555 nm (m is an arbitrary integer),
d−10 ≦ 555 × m / (2 × n) ≦ d + 10
Is satisfied.
[0012]
The silicon nitride film has a thickness d (nm) and a refractive index n when the wavelength is 555 nm (m is an arbitrary integer).
0.9d ≦ 555 × m / (2 × n) ≦ 1.1d
Is satisfied.
[0013]
Further, the thickness of the silicon nitride film is in a range from 130 nm to 160 nm.
[0014]
Alternatively, the thickness of the silicon nitride film is in a range from 126 nm to 165 nm.
[0015]
Further, another typical liquid crystal display device of the present invention includes a thin film transistor and a light-transmitting pixel electrode on a substrate, and the thin film transistor includes a polysilicon film, a gate electrode, a drain electrode, and a source electrode. The substrate has a base film, a polysilicon film and a light-transmissive pixel electrode are disposed on the base film, and the base film includes a silicon nitride film on the substrate side and a silicon oxide film on the liquid crystal layer side. And the silicon nitride film is thicker than the silicon oxide film.
[0016]
Here, when the thickness of the silicon nitride film is d (nm) and the refractive index at a wavelength of 555 nm is n (m is an arbitrary integer),
d−10 ≦ 555 × m / (2 × n) ≦ d + 10
Meet.
[0017]
Further, a silicon oxide film and a second silicon nitride film are sequentially laminated between the silicon nitride film on the substrate side and the light transmitting pixel electrode. When the thickness of the silicon oxide film and the interlayer insulating film of the second silicon nitride is d (nm) and the refractive index at a wavelength of 555 nm is n (m is an arbitrary integer),
d−10 ≦ 555 × m / (2 × n) ≦ d + 10
Satisfy each.
[0018]
Further, the silicon oxide film disposed between the silicon nitride film on the substrate side and the light-transmitting pixel electrode serves as a base film, a gate insulating film and an interlayer insulating film on the liquid crystal side, and the second silicon nitride film is an interlayer insulating film. is there.
[0019]
In another structure of the present invention, one of two substrates opposed to each other with a liquid crystal layer interposed therebetween has a thin film transistor, and the thin film transistor has a semiconductor layer, a gate electrode connected to a gate line, A drain electrode connected to the drain line and a source electrode connected to the pixel electrode are included. A reflection region having a reflection electrode connected to the source electrode and reflecting external light passing through the liquid crystal layer in a region surrounded by two adjacent gate lines and two adjacent drain lines; A transparent region having a light-transmitting pixel electrode connected to the source electrode and transmitting light from the backlight; and the thickness of the liquid crystal layer is different between the reflective region and the transmissive region. Further, a first film and a second film are provided between the light-transmitting pixel electrode in the transmission region and the substrate, and the first film and the second film have different refractive indices. The film No. 2 has a thickness d (nm) and a refractive index n when the wavelength is 555 nm (n is an arbitrary integer),
d−10 ≦ 555 × m / (2 × n) ≦ d + 10
Satisfy each.
[0020]
Here, the first film is made of silicon nitride, and the second film is made of silicon oxide.
[0021]
In addition, a third film of silicon nitride is provided over the second film, and the third film has a thickness d (nm) and a refractive index n at a wavelength of 555 nm (m is Any integer),
d−10 ≦ 555 × m / (2 × n) ≦ d + 10
Are respectively satisfied.
[0022]
Further, another liquid crystal display device of the present invention includes a liquid crystal panel having two substrates opposed to each other with a liquid crystal layer interposed therebetween, and a total transmission liquid crystal display device having a backlight on one surface side of the liquid crystal panel. One substrate has a base film, and a thin film transistor and a light transmissive pixel electrode are provided on the base film. The thin film transistor has a polysilicon film, a gate electrode, a drain electrode, and a source electrode. Here, the base film includes a silicon nitride film on the substrate side and a silicon oxide film on the liquid crystal layer side, and the silicon nitride film is formed thicker than the silicon oxide film. The silicon nitride film has a thickness d (nm) and a refractive index n when the wavelength is 555 nm (m is an arbitrary integer).
0.9d ≦ 555 · m / (2 · n) ≦ 1.1d
Meet.
[0023]
Further, a silicon oxide film and a second silicon nitride film are sequentially stacked between the base film and the pixel electrode, and the silicon oxide film and the second silicon nitride film have a thickness of d (nm), When the refractive index when the wavelength is 555 nm is n (m is an arbitrary integer),
0.9d ≦ 555 · m / (2 · n) ≦ 1.1d
Meet.
[0024]
In addition to the above structure, a common electrode is formed over the same substrate as the pixel electrode, or a common electrode is formed over the other substrate.
[0025]
According to the present invention, it is possible to provide a display device with improved contrast and improved image visibility.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0027]
FIG. 1 is a plan view of a pixel portion of a liquid crystal display device according to a first embodiment of the present invention.
[0028]
One of the two substrates facing each other with a liquid crystal layer interposed therebetween has a thin film transistor. In addition, a switching element that is turned on by a scanning signal from the gate line and a video signal from the drain line are supplied to each region surrounded by the gate line group and the drain line group that intersect each other via the switching element. Are formed to form a so-called pixel. A region surrounded by the gate line group and the drain line group is a pixel region. As the switching element, there is a thin film transistor.
[0029]
One pixel is formed in a region surrounded by two adjacent gate lines 1 and two adjacent drain lines 2. A color image can be displayed on the front surface of the panel using three types of these pixels (red pixels, green pixels, and blue pixels).
[0030]
One pixel includes a light reflection region in which the reflection electrode 3 is formed and a light transmission region 4 in which the reflection electrode is not formed. The light transmitting region is formed by providing an opening in the reflective electrode 3. A transparent electrode 7 is formed in the light transmitting region 4, and the reflective electrode 3 and the transparent electrode 4 constitute a pixel electrode.
[0031]
A gate line (gate electrode) 1, a drain line (drain electrode) 2, a polysilicon film 5, a storage line (storage electrode) 6, and a transparent electrode 7 are formed below the reflective electrode.
[0032]
FIG. 2 is a sectional view taken along the line II of FIG.
[0033]
A first base film 9 is formed on a substrate 8 on which a thin film transistor is formed, and a second base film 10 is formed on the first base film 9. Then, a polysilicon film 5 is formed on the second base film.
[0034]
The polysilicon film can be formed by a solid phase growth method or a laser annealing method. In the solid phase growth method, since the entire substrate is heated at a high temperature, a heat-resistant material such as quartz glass must be used. On the other hand, the laser annealing method is formed by annealing an amorphous silicon layer formed on a glass substrate with a laser. Therefore, it is not necessary to heat the entire substrate at a high temperature. A polysilicon film that can be formed at a lower temperature than the solid phase growth method is formed on a glass substrate called non-alkali glass. This glass substrate contains impurities. A base film is formed on a glass substrate so that impurities do not penetrate the polysilicon film.
[0035]
In order to form a polysilicon film, a layer with few grain boundaries can be formed by crystallization on a silicon oxide film. However, in order to suppress the penetration of impurities from the glass substrate with the silicon oxide film, the thickness of the silicon oxide film must be increased.
[0036]
Therefore, a silicon nitride film was formed as the first base film 9. Although the silicon nitride film is not suitable for forming the polysilicon film 5, it can suppress the penetration of impurities from the glass substrate 8 into the polysilicon film 5. Therefore, deterioration of transistor characteristics due to diffusion of sodium or the like from the glass substrate can be suppressed.
[0037]
A silicon oxide film was formed as the second base film 10. By forming the polysilicon film 5 on the silicon oxide film, crystallized silicon having a large grain size can be formed. Further, the formation of the oxide film can prevent the threshold voltage of the transistor from fluctuating.
[0038]
By forming a silicon nitride film as the first base film 9 and forming silicon oxide as the second base film 10, a thin base film as a whole can be formed. By reducing the thickness of the base film, a base film with less undulation can be formed, and a change in film thickness can be reduced.
[0039]
Gate insulating film 12 is formed to cover polysilicon film 5. Gate electrode 1 is formed on gate insulating film 12. Gate insulating film 12 is arranged to insulate polysilicon film 5 from gate electrode 1. In this embodiment, the gate insulating film 12 is a silicon oxide film, and the gate electrode 1 is molybdenum tungsten.
[0040]
A first interlayer insulating film 13 is formed on the gate insulating film 12 so as to cover the gate line 1. The first interlayer insulating film 13 is formed of a silicon oxide film, and is mainly intended to insulate the gate electrode 1 from the drain electrode 2 or the source electrode 14.
[0041]
A contact hole 15 is formed in the gate insulating film 12 and the first interlayer insulating film. The contact hole 15 connects the drain electrode 1 to the semiconductor layer 5 and the source electrode 14 to the semiconductor layer 5. In this embodiment, the drain electrode and the source electrode have a three-layer structure (titanium / aluminum / titanium) of titanium in the upper layer, aluminum in the middle layer, and titanium in the lower layer. By arranging titanium in the upper layer and the lower layer, electrical connection between the polysilicon film 5 and the transparent electrode (ITO) 7 is ensured.
[0042]
On the first interlayer insulating film 13, a second interlayer insulating film 16 is formed to cover the drain electrode 2 and the source electrode. The second interlayer insulating film 16 is a silicon nitride film. The use of silicon nitride for the second interlayer insulating film 16 prevents contaminants from penetrating from the organic insulating film 18 to the thin film transistor, and improves the adhesion between the organic insulating film 18 and the second interlayer insulating film. I do.
[0043]
The transparent electrode 7 is formed on the second interlayer insulating film 16. A contact hole 15 is formed in the second interlayer insulating film 16, and the source electrode 14 and the transparent electrode 7 are electrically connected at the contact hole 15. The transparent electrode uses ITO (Indium Tin Oxide).
[0044]
A third interlayer insulating film 18 is formed on the second interlayer insulating film 16 so as to partially cover the transparent electrode 7. The third interlayer insulating film is formed of an organic material (organic insulating film). By disposing the organic insulating film 18, the coupling capacitance between wirings such as gate lines or drain lines can be reduced. By reducing the coupling capacitance, power consumption of the liquid crystal display device can be reduced.
[0045]
The reflective electrode 3 is formed on the third interlayer insulating film 18. The reflective electrode 3 has a two-layer structure (titanium tungsten / aluminum) of titanium tungsten in the upper layer and aluminum in the lower layer. Titanium tungsten ensures electrical connection with the transparent electrode 7.
[0046]
FIG. 3 is a sectional view taken along line II-II of FIG.
The area where the reflection electrode 3 is formed is the reflection area RA, and the area where the reflection electrode 3 is not formed is the transmission area TA.
[0047]
A first base film 9 and a second base film 10 are formed on a glass substrate 8. These base films are formed over the entire pixel region. If the underlying film is removed in the course of the low-temperature polysilicon manufacturing process, a developing solution, an etching solution, a resist removing solution, and the like come into direct contact with the glass substrate in a subsequent photolithography process. Therefore, ions such as sodium on the glass substrate are eluted.
[0048]
Due to the base film, the developing solution, etching solution, resist removing solution, etc. do not come into contact with the glass in the photolithography process, so that these solutions can be reused after passing through the filter, thereby preventing the entire line from being contaminated. . Further, the manufacturing cost can be reduced.
[0049]
A polysilicon film 5 is formed on the second base film, and a first interlayer insulating film 13 is formed on the second base film so as to cover the polysilicon film. The storage electrode 6 is formed on the first interlayer insulating film. The storage electrode 6 faces the source electrode 14 and the transparent electrode 7 via an insulating film, and forms a storage capacitor.
[0050]
Further, since the storage electrode 6 is formed in the reflection area RA, there is no need to transmit light. Therefore, it can be formed with a molybdenum tungsten film.
[0051]
The third interlayer insulating film 18 has an opening in a part. As shown in FIG. 1, the reflective electrode 3 forms an opening 4 by tracing the opening of the third interlayer insulating film. The reflection electrode has a connection portion 11 at an opening of the third interlayer insulating film. The connection portion 11 is electrically connected to the transparent electrode 7.
[0052]
The third interlayer insulating film 18 has an inclined portion 17 having an angle θ between itself and the transparent electrode 7. Is less than 90 degrees, about 45 degrees. By forming the inclined portion 17, rubbing unevenness of the alignment film is reduced.
[0053]
The transparent electrode 7 is formed in a region wider than the opening 4 of the reflection electrode. A backlight (not shown) is disposed below the glass substrate, and the transparent electrode 7 is a light-transmitting pixel electrode that transmits light from the backlight.
[0054]
The pixel portion faces a counter substrate 21 having a counter electrode 20 with a liquid crystal layer 19 interposed therebetween. The thickness (gap) of the liquid crystal layer is different between the gap L1 in the reflection region and the gap L2 in the transmission region. That is, the thickness of the liquid crystal layer differs between the reflection region and the transmission region.
[0055]
In this embodiment, the above-described configuration is applied to a normally black liquid crystal display device.
[0056]
A liquid crystal display device of a normally black display has a higher light transmittance than a liquid crystal display device of a normally white display, so that a dark color filter can be used and the color reproducibility is excellent.
[0057]
Further, the luminance can be improved by making the gap L2 of the transmission area larger than the gap L1 of the reflection area.
[0058]
In the transmission region, light-transmitting films are stacked, and these stacked films have different refractive indexes. The thickness of the light-transmitting film is controlled in order to prevent reflection of extraneous light from the counter substrate side.
[0059]
In the transmission region, between the transparent electrode 7 and the glass substrate 8, there are a first base film 9, a second base film 10, a gate insulating film 12, and a first interlayer insulating film 13.
[0060]
Assuming that each of these films has a thickness d (nm) and a refractive index n when the wavelength is 555 nm (m is any non-negative integer),
d−10 ≦ 555 × m / (2 × n) ≦ d + 10
Are satisfied.
[0061]
With this configuration, reflection of extraneous light in the transmission region can be suppressed, and a liquid crystal display device with improved contrast can be provided.
[0062]
FIG. 4 shows more specific examples of the material, thickness (film thickness), and refractive index when the wavelength is 555 nm of each film or layer. In this embodiment, the gap L2 in the transmissive area is 5.2 μm, and the gap L1 in the reflective area is 3.7 μm.
[0063]
The first base film and the second base film have different refractive indexes. In order to protect the polysilicon film from impurities on the glass substrate, the first underlayer may be at least 45 nm. In the present embodiment, the material of the first base film 9 is silicon nitride, the refractive index is 2.0, and the film thickness is 130 nm to 150 nm. The material of the second base film 10 is silicon oxide, the refractive index is 1.5, and the film thickness is 100 nm. The first underlayer was formed thicker than the second underlayer.
[0064]
The material of the gate insulating film 12 is silicon oxide, like the second base film, and has a refractive index of 2.0 and a thickness of 100 nm. The material of the first interlayer insulating film 13 is silicon oxide, like the second base film, and has a refractive index of 2.0 and a thickness of 540 nm. The material of the second interlayer insulating film 16 is silicon nitride, the refractive index is 2.0, and the film thickness is 200 nm. The material of the transparent electrode is ITO, the refractive index is 2.0, and the film thickness is 77 nm. The refractive indexes of the alignment film 22 and the liquid crystal are 1.5.
[0065]
Among these films, the second base film, which is the base film on the liquid crystal layer side, can be regarded as the same film because it has the same refractive index as the gate insulating film and the first interlayer insulating film. Since the second interlayer insulating film and the transparent electrode also have substantially the same refractive index, they can be regarded as the same film. Therefore, the first film is a silicon nitride film serving as a first base film, and has a refractive index of 2.0 and a thickness of 130 nm to 150 nm. The second film is a silicon oxide film composed of a second base film, a gate insulating film, and a first interlayer insulating film, and has a refractive index of 1.5 and a thickness of 740 nm. Further, the third film has a refractive index of 2.0 and a thickness of 277 nm.
[0066]
The above-mentioned film has a thickness d (nm) and a refractive index n at a wavelength of 555 nm, where n is:
d−10 ≦ 555 × m / (2 × n) ≦ d + 10
Satisfy each. (M is any non-negative integer)
With this configuration, reflection of extraneous light in the transmission region can be suppressed, and a liquid crystal display device with improved contrast can be provided.
[0067]
More preferably, the thickness of the first base film is 140 nm.
[0068]
FIG. 5 shows a case where the values of the second base film, the gate insulating film, the first interlayer insulating film, and the second interlayer insulating film are set to those in FIG. 4 and the first base film is changed to 50 nm to 180 nm. It is a figure which shows the reflectance which carried out the visibility correction. FIG. 6 is a diagram showing the relationship between the wavelength of light and the luminosity correction reflectance when the first underlayer of FIG. 5 is 50 nm, and FIG. 7 is a diagram showing the light when the first underlayer of FIG. 5 is 140 nm. FIG. 6 is a diagram showing a relationship between the wavelength of the luminosity and the luminosity correction reflectance.
[0069]
As is clear from FIGS. 5, 6, and 7, the visibility correction reflectance is lowest when the base film is set to 140 nm.
[0070]
This value is represented by d (nm) for the film thickness and n for the refractive index when the wavelength is 555 nm.
d = 555 · m / 2 · n
Matches. Light having a wavelength of 555 nm is the most sensitive for humans, and the contrast can be improved by suppressing reflection at a wavelength near 555 nm.
[0071]
It is necessary to adjust the thickness of about 10% of the film thickness in consideration of the manufacturing error in addition to the calculated value. Preferably, the film thickness is controlled to an error of 10 nm.
[0072]
FIG. 8 is a diagram showing a film configuration of a partially transmissive liquid crystal display device of normally black display.
[0073]
The thickness of the liquid crystal layer in the transmission region is set in consideration of the polarizing plate and the phase difference plate so that transmission optical characteristics such as contrast and transmittance are best with respect to transmitted light that passes through the liquid crystal layer once. . In addition, the thickness of the liquid crystal layer in the reflection area is set in consideration of the polarizing plate and the phase difference plate so that the transmission optical characteristics such as contrast and transmittance are best with respect to the reflected light that passes through the liquid crystal layer twice. It is. For this reason, when light passing through the liquid crystal layer, the reflective electrode, and the liquid crystal layer in this order is blocked by the phase difference plate and the deflecting plate to perform black display, the reflected light from the transmission region has a thickness of the transmitted liquid crystal layer. Because of the difference, the retardation of the liquid crystal layer is different, and the liquid crystal layer is in a deflected state that cannot be blocked by the retardation plate and the deflector.
[0074]
That is, when there is no difference between the gap L2 of the transmissive area and the gap L1 of the reflective area, the retardation of the liquid crystal is the same in the transmissive area and the reflective area. . However, when there is a difference between the gap L2 of the transmission region and the gap L1 of the reflection region, the retardation of the liquid crystal is different between the transmission region and the reflection region, and the reflected light from the transmission region cannot be blocked.
[0075]
FIG. 9 is a perspective view including a partial cross section of a liquid crystal display device 24 to which the present invention is applied. The liquid crystal display device 24 includes an opposing substrate 21 having an image display surface in a frame 25, a glass substrate 8 disposed on the opposing substrate 21 via a liquid crystal layer, and a backlight assembly 23 disposed on the back surface of the glass substrate 8. It is composed of
[0076]
The present invention can suppress the reflection of extraneous light in the transmission region, and therefore can improve the contrast, particularly in a liquid crystal display device having a difference between the transmission region gap L2 and the reflection region gap L1.
[0077]
Reflected light from the multilayer film is caused by interfacial reflection between the respective layers due to the difference in the refractive index of the individual layers constituting the multilayer film, and the interfacial reflection is caused by interference.
[0078]
The low-temperature polysilicon thin film transistor includes a silicon oxide film, a silicon nitride film, an organic interlayer insulating film, and ITO. Among these, a film having a large refractive index has a photochemical thickness of n · d (n: refractive index, d: film). When the thickness is set to 555/2 (nm), the phase of the reflected light is reversed at both interfaces of the film having a large refractive index to cancel the green light having the highest visibility, so that the reflectance is small. Become.
[0079]
Further, while the thicknesses of the gate insulating film, the interlayer insulating film, and the transparent electrode are set to the optimum thickness for the electrical characteristics of the low-temperature polysilicon transistor and the storage capacitor, the thickness of the silicon nitride used for the base film is set in the above-described embodiment. By doing so, interface reflection can be reduced.
[0080]
FIG. 10 is a diagram for explaining the second embodiment of the present invention, and is a plan view of a pixel portion of a liquid crystal display device. FIG. 10 is applied to a total transmission type display device which does not have a reflective electrode for displaying an image by reflecting external light to a pixel portion.
[0081]
A thin film transistor is formed on one of the two substrates facing each other with a liquid crystal layer interposed therebetween (first substrate). A color filter is formed on another substrate (second substrate) described later.
[0082]
In each region surrounded by a group of gate lines 1 and a group of drain lines 2 which intersect each other, a switching element which is turned on by a scanning signal from the gate line 1 and a video signal from the drain line 2 are transmitted through the switching element. The supplied pixel electrode 3 is formed. A region surrounded by the gate line group and the drain line group is a pixel region. As a switching element, there is a thin film transistor (TFT). The thin film transistor comprises a gate electrode G connected to a gate line, a polycrystalline silicon film 5, a drain electrode D connected to a drain line, and a source electrode S connected to a pixel electrode.
[0083]
One pixel is formed in a region surrounded by two adjacent gate lines 1 and two adjacent drain lines 2. A color image can be displayed on the front surface of the panel using three types of these pixels (red pixels, green pixels, and blue pixels).
[0084]
The common electrode C and the pixel electrode 3 are formed in one pixel. The common electrode C and the pixel electrode 3 are formed on the same substrate, and constitute a so-called in-plane switching (In-Plane Switching) type liquid crystal display device. The pixel is enlarged by arranging the common line 6 connected to the common electrode C in parallel with the upper layer of the gate line.
[0085]
FIG. 11 is a sectional view taken along the line II of FIG.
[0086]
The thin film transistor is formed on a glass substrate 8, and the glass substrate 8 uses glass called non-alkali glass. The glass substrate 8 contains impurities, and there is a possibility that the impurities permeate the polysilicon film 5 and deteriorate the transistor characteristics of the thin film transistor formed on the substrate. In order to suppress the penetration of impurities from the glass substrate 8 to the polysilicon film 5, a base film such as silicon nitride or silicon oxide is formed between the glass substrate 8 and the polysilicon film 5. A base film is formed on the entire surface of the panel. On the base film, a light-transmissive pixel electrode 3 and a common electrode C are formed in addition to the thin film transistor.
[0087]
A first base film 9 is formed on a substrate 8 on which a thin film transistor is formed, and a second base film 10 is formed on the first base film 9. Then, a polysilicon film 5 is formed on the second base film. The method for forming them, the configuration of the first interlayer insulating film and the second interlayer insulating film, and the forming method are the same as those in the first embodiment.
[0088]
The organic insulating film 18 formed on the second interlayer insulating film is also called a flattening film, and the surface on which the common electrode C and the pixel electrode 3 are formed is formed by forming the organic insulating film 18. A flat surface which is not affected by the 16 irregularities can be formed. By disposing the organic insulating film 18, the coupling capacitance between the gate line and the drain line and the common line can be reduced. By reducing the coupling capacitance, power consumption of the liquid crystal display device can be reduced.
[0089]
The common electrode C and the pixel electrode 3 are formed on the organic insulating film 18. The common electrode C and the pixel electrode 3 are formed in the pixel, and are light transmitting films. For example, ITO (Indium Tin Oxide) is used as the transparent electrode.
[0090]
A contact hole 15 for electrically connecting the source electrode S and the pixel electrode 3 is formed in the second interlayer insulating film 16 and the organic insulating film 18.
[0091]
In this embodiment, the above-described configuration is applied to a normally black liquid crystal display device.
[0092]
In the pixel portion, light-transmitting films are stacked, and these stacked films have different refractive indexes. The thickness of the light-transmitting film is controlled in order to prevent reflection of extraneous light from the counter substrate side.
[0093]
FIG. 12 is a sectional view taken along line II-II in FIG.
[0094]
By having the base film, the developing solution, the etching solution, the resist removing solution and the like do not come into contact with the glass in the photolithography process, so that the elution of ions such as sodium from the glass substrate can be suppressed. If the ions are not eluted, these liquids can be reused after passing through the filter, and contamination of the entire line can be prevented. Further, the manufacturing cost can be reduced.
[0095]
A gate insulating film 12, a first interlayer insulating film 13, a second interlayer insulating film 16, and an organic insulating film 18 are stacked on the second base film. The pixel electrode 3 and the common electrode C are formed on the same substrate on the organic insulating film 18. The alignment film 22 is formed to cover the organic insulating film 18, the pixel electrode 3, and the common electrode C. A liquid crystal layer is formed in contact with the alignment film 22.
[0096]
These films are arranged in the pixel and have light transmission characteristics. In particular, the pixel electrode and the common electrode are formed of ITO (Indium Tin Oxide) which is a transparent conductive film because a predetermined voltage is applied. The liquid crystal molecules are controlled by the electric field between the pixel electrode and the common electrode to control the amount of transmitted light.
[0097]
Ideally, when the thickness of each film is d (nm) and the refractive index at a wavelength of 555 nm is n (m is any non-negative integer),
d = 555 · m / (2 · n)
Are respectively satisfied. However, in practice, there is a manufacturing error or the like, so it is necessary to add or subtract about 10% of the film thickness in addition to the calculated value. Preferably, the film thickness is controlled to an error of 10 nm.
[0098]
In the pixel region, a second base film 10 having a relatively low refractive index, a gate insulating film 12, a first interlayer insulating film 13, and a planarizing film 18 having a relatively low refractive index are provided on a glass substrate 8. Underlayer 9 and a second interlayer insulating film 16.
[0099]
When each film having a relatively high refractive index has a thickness d (nm) and a refractive index n when the wavelength is 555 nm (m is any non-negative integer),
0.9d ≦ 555 · m / (2 · n) ≦ 1.1d
Are respectively satisfied. In the above range, ± 10% of the film thickness is allowed as the error range, but when the film thickness d exceeds 200 nm, it can be up to ± 15% of the predetermined film thickness. With such a configuration, when light passes from a film having a high refractive index to a film having a low refractive index, reflection of extraneous light caused by a difference in the refractive index can be suppressed, and display of an inverted image can be suppressed.
[0100]
Further, when the film having a relatively low refractive index has a thickness d (nm) and a refractive index n when the wavelength is 555 nm (m is any non-negative integer),
0.9d ≦ 555 · m / (2 · n) ≦ 1.1d
Are respectively satisfied. In the above range, ± 10% of the film thickness is allowed as the error range, but when the film thickness d exceeds 200 nm, it can be up to ± 15% of the predetermined film thickness. With this configuration, it is possible to further suppress the reflection of extraneous light in the transmission region, and to suppress the display of the inverted image.
[0101]
FIG. 13 shows a specific example of the material and thickness (film thickness) of each film or layer and the refractive index when the wavelength is 555 nm. In this embodiment, the gap L2 of the transmission region is set to 5.2 μm.
[0102]
The first base film and the second base film have different refractive indexes. In order to protect the polysilicon film from impurities in the glass substrate, the first underlayer may be at least 45 nm. In the present embodiment, the material of the first base film 9 is silicon nitride, the refractive index is 1.85, and the film thickness is 150 nm. The material of the second base film 10 is silicon oxide, the refractive index is 1.5, and the film thickness is 100 nm. The first underlayer was formed thicker than the second underlayer.
[0103]
The material of the gate insulating film 12 is silicon oxide, like the second base film, and has a refractive index of 1.5 and a thickness of 100 nm. The material of the first interlayer insulating film 13 is silicon oxide, like the second base film, and has a refractive index of 1.5 and a thickness of 540 nm. The material of the second interlayer insulating film 16 is silicon nitride, the refractive index is 1.85, and the film thickness is 300 nm. The flattening film 18 uses an organic film having a refractive index of 1.6 and a thickness of 1750 nm. The pixel electrode 3 and the common electrode 6 are made of ITO, have a refractive index of 2.0, and a thickness of 140 nm. The refractive indexes of the alignment film 22 and the liquid crystal are 1.5.
[0104]
Among these films, the second base film, which is the base film on the liquid crystal layer side, can be regarded as the same film because it has the same refractive index as the gate insulating film and the first interlayer insulating film. Therefore, the first film is a silicon nitride film serving as a first base film, and has a refractive index of 1.85 and a thickness of 150 nm. The second film is a silicon oxide film composed of a second base film, a gate insulating film, and a first interlayer insulating film, and has a refractive index of 1.5 and a thickness of 740 nm. Further, the third film is a second interlayer insulating film, the fourth film is a flattening film, and the fifth film is ITO.
[0105]
When the first film and the fifth film have a thickness of d (nm) and a refractive index of n at a wavelength of 555 nm (m is any non-negative integer),
d (1-0.1) ≦ 555 · m / (2 · n) ≦ d (1 + 0.1)
The filling,
When the second film, the third film, and the fourth film have a thickness of d (nm) and a refractive index of n at a wavelength of 555 nm (n is an arbitrary non-negative integer),
d (1−0.15) ≦ 555 · m / (2 · n) ≦ d (1 + 0.15)
Satisfy each.
[0106]
With this configuration, it is possible to suppress the reflection of extraneous light on the various films formed on the glass substrate 8 in the transmission region, and to view the image when displaying the image by reflecting the external light on the backlight side of the panel. Performance can be improved. In particular, since the first base film is formed thick, it is possible to suppress the penetration of impurities from the substrate to the polysilicon film.
[0107]
FIG. 14 and FIG. 15 are diagrams illustrating the luminosity correction reflectance of a region where the pixel electrode and the common electrode are not formed in the pixel.
[0108]
FIG. 14 shows the values of FIG. 13 for the first underlayer, the second underlayer, the gate insulating film, the first interlayer insulating film, the flattening film, and ITO, and the second interlayer insulating film is changed between 100 nm and 500 nm. FIG. 7 is a diagram showing reflectance after luminosity correction when the illuminance is corrected. The vertical axis represents the visibility correction reflectance, and the horizontal axis represents the thickness of the second interlayer insulating film. The luminous reflectance when the second interlayer insulating film is approximately 150 nm is approximately 0.45%, which is the lowest luminous reflectance. Next, the luminous reflectance at about 300 nm is low, and the luminous reflectance is about 0.88%.
[0109]
FIG. 15 shows a case where the second base film, the gate insulating film, the first interlayer insulating film, the second interlayer insulating film, the flattening film, and the ITO have the values shown in FIG. 13 and the first base film is changed between 25 nm and 350 nm. FIG. 7 is a diagram showing reflectance after luminosity correction when the illuminance is corrected. The vertical axis represents the visibility correction reflectance, and the horizontal axis represents the thickness of the first underlayer. The luminous reflectance when the first underlayer is approximately 150 nm is approximately 0.88%, which is the lowest luminous reflectance. Next, the luminous reflectance at about 300 nm is low, and the luminous reflectance is about 1.33%.
[0110]
FIGS. 16, 17 and 18 are diagrams showing the luminosity correction reflectance of the region where the pixel electrode and the common electrode are formed among the pixels.
[0111]
FIG. 16 shows a case where the first underlayer, the second underlayer, the gate insulating film, the first interlayer insulating film, the second interlayer insulating film, and the flattening film have the values shown in FIG. 13 and the ITO is changed between 50 nm and 300 nm. FIG. 7 is a diagram showing reflectance after luminosity correction when the illuminance is corrected. The vertical axis represents the visibility correction reflectance, and the horizontal axis represents the ITO film thickness. As shown in FIG. 16, when the ITO film thickness is about 140 nm, the luminous reflectance is about 1.3%, which is the lowest. Next, the luminous reflectance at about 280 nm is low, and the luminous reflectance is about 2.1%.
[0112]
FIG. 17 shows the case where the first underlayer, the second underlayer, the gate insulating film, the first interlayer insulating film, the flattening film, and ITO are set to the values shown in FIG. 13 and the second interlayer insulating film is changed between 100 nm and 400 nm. FIG. 7 is a diagram showing reflectance after luminosity correction when the illuminance is corrected. The vertical axis represents the visibility correction reflectance, and the horizontal axis represents the thickness of the second interlayer insulating film. The luminous reflectance when the second interlayer insulating film is approximately 150 nm is approximately 1.02%, which is the lowest luminous reflectance. Next, the luminous reflectance at about 300 nm is low, and the luminous reflectance is about 1.3%.
[0113]
FIG. 18 shows the values of FIG. 13 for the second base film, the gate insulating film, the first interlayer insulating film, the second interlayer insulating film, the flattening film, and ITO, and the first base film is changed between 50 nm and 325 nm. FIG. 7 is a diagram showing reflectance after luminosity correction when the illuminance is corrected. The vertical axis represents the visibility correction reflectance, and the horizontal axis represents the thickness of the first underlayer. The luminous reflectance when the first underlayer is approximately 150 nm is approximately 1.3%, which is the lowest luminous reflectance. Next, the luminous reflectance at about 300 nm is low, and the luminous reflectance is about 1.56%.
[0114]
In the present embodiment, in addition to the results of FIGS. 14 and 17, the thickness of the second interlayer insulating film is set to 300 nm from the viewpoint of reducing the capacity, reducing contamination from the organic film, and the like. Was 150 nm in thickness. With such a configuration, it is possible to suppress interface reflection that occurs when light travels from a film having a relatively high refractive index to a relatively low refractive index.
[0115]
FIG. 19 is a diagram showing the relationship between the wavelength of light and the luminosity correction reflectance when the first underlayer of FIG. 12 is 75 nm, and FIG. 20 is the wavelength of light when the first underlayer of FIG. 12 is 150 nm. FIG. 7 is a diagram showing a relationship between the luminosity correction reflectance and the luminosity correction reflectance. 19 and 20, the vertical axis represents the reflectance (%), the luminosity correction reflectance (%), and the luminosity, and the horizontal axis represents the light wavelength (nm). The visibility was set to 1 at 555 nm, which is the strongest for humans. In FIG. 19, the visibility when the wavelength is 555 nm is about 0.028.
[0116]
On the other hand, in FIG. 20, the visibility at the wavelength of 555 nm was about 0.0009, and the reflected light of the wavelength of 555 nm could be suppressed to such an extent that it could hardly be recognized. Light having a wavelength of 555 nm is the most sensitive for humans, and the contrast can be improved by suppressing reflection at a wavelength near 555 nm.
[0117]
Reflected light from the multilayer film is caused by interfacial reflection between the respective layers due to the difference in the refractive index of the individual layers constituting the multilayer film, and the interfacial reflection is caused by interference.
[0118]
FIG. 21 is a plan view when the second substrate 7 on which a color filter is formed is superimposed on the first substrate 4. FIG. 3 is a diagram for explaining a positional relationship between a position of a drain line and a gate line formed on a first substrate and a position of a black matrix BM formed on a second substrate. A color filter and a black matrix BM are formed on the second substrate 7.
[0119]
In a transmissive liquid crystal display device, external light is reflected by a drain line or a gate line formed of a metal thin film, and image contrast is deteriorated. Therefore, the black matrix BM is arranged so as to overlap with the drain line and the gate line. By arranging the black matrix BM, deterioration of the image contrast can be suppressed.
[0120]
FIG. 22 is a diagram for explaining the third embodiment, and is a plan view of a liquid crystal display device in which a substrate on which a pixel electrode is formed and a substrate on which a common electrode is formed are opposed to each other via a liquid crystal layer. Parts having the same functions as in the first embodiment are denoted by the same reference numerals. FIG. 22 is applied to a total transmission type display device having no reflective electrode for displaying an image by reflecting external light to a pixel portion.
[0121]
Hereinafter, points different from the second embodiment will be described in detail.
[0122]
A thin film transistor and a pixel electrode 3 are formed on one of the two substrates facing each other with a liquid crystal layer interposed therebetween. As in the first embodiment, the pixel portion includes a gate electrode G, a drain electrode D, a source electrode S, a gate line 1, a drain line 2, a pixel electrode 3, a polysilicon film 5, and a contact hole 14 for forming a TFT. , A contact hole 15 is formed. The major difference from the first embodiment is that the common electrode is not formed in the same layer as the pixel electrode 3 and that the storage line (storage electrode) 6 is formed in the same layer as the gate line. The storage capacity of the pixel electrode is increased by forming the storage line.
[0123]
FIG. 23 is a plan view of the black matrix BM formed on the second substrate 7 (color filter substrate). The black matrix BM is arranged so as to hide the gate electrode G, the drain electrode D, the source electrode S, the gate line 1, the drain line 2, and the storage line 6, which are the metal portions in FIG. With such an arrangement, reflection of external light by the metal portion can be prevented, and the contrast can be improved. A counter electrode (common electrode) C is formed on the surface of the second substrate 7 facing the liquid crystal layer, and an alignment film is formed to cover the counter electrode C.
[0124]
FIG. 24 is a sectional view taken along the line III-III in FIG.
[0125]
A first base film 9 and a second base film 10 are formed on a glass substrate 8, and a polysilicon film 5 is formed on the second base film 10. A gate insulating film 12 is formed to cover the polysilicon film 5, and a gate electrode G is formed on the gate insulating film. The storage electrode 6 is formed on the gate insulating film 12 in the same layer as the gate electrode G. A first interlayer insulating film 13 is formed to cover the gate electrode G, the storage electrode 6, and the gate insulating film. A contact hole 14 is formed in a part of the first interlayer insulating film and a part of the gate insulating film so that the polysilicon film 5 and the gate electrode G can be connected, and the polysilicon film 5 and the source electrode S can be connected. The drain electrode D and the source electrode S formed on the first interlayer insulating film have a three-layer structure of titanium tungsten in the lower layer, aluminum in the middle layer, and titanium tungsten in the upper layer. In FIG. 24, the lower layer and the middle layer are shown as one film. The upper layer of titanium tungsten ensures electrical connection with the pixel electrode 3. A second interlayer insulating film 16 is formed to cover the drain electrode, the source electrode, and the first interlayer insulating film, and an organic insulating film 18 is formed to cover the second interlayer insulating film. A contact hole 15 is formed in a part of the organic insulating film to enable connection between the source electrode and the pixel electrode. The pixel electrode uses ITO (Indium Tin Oxide). An alignment 22 film is formed on the surface of the first substrate on which these layers are formed, facing the liquid crystal layer 19.
[0126]
In the pixel region, light transmissive films are laminated, and these laminated films have different refractive indexes. The thickness of the light-transmitting film is controlled in order to prevent reflection of extraneous light from the counter substrate side.
[0127]
Also in the third embodiment, ideally, when the thickness of each film is d (nm) and the refractive index when the wavelength is 555 nm is n (m is any non-negative integer),
d = 555 · m / (2 · n)
Are respectively satisfied. In addition, in consideration of manufacturing errors, visibility, and the like, it is necessary to add or subtract about 10% of the film thickness in addition to the calculated value. Preferably, the film thickness is controlled to an error of 10 nm.
[0128]
That is, when the film thickness is d (nm) and the refractive index when the wavelength is 555 nm is n (m is any non-negative integer),
0.9d ≦ 555 · m / (2 · n) ≦ 1.1d
Are respectively satisfied.
[0129]
Further, from the permissible range of the visibility, when the film thickness d exceeds 200 nm, it can be permitted up to ± 15% of the predetermined film thickness.
[0130]
That is, when the film thickness is d (nm) and the refractive index when the wavelength is 555 nm is n (m is any non-negative integer),
0.85d ≦ 555 · m / (2 · n) ≦ 1.15d
The specific thickness is as shown in FIG.
[0131]
With such a configuration, when light passes from a film having a high refractive index to a film having a low refractive index, reflection of extraneous light caused by a difference in the refractive index can be suppressed, and display of an inverted image can be suppressed.
[0132]
FIG. 25 is a cross-sectional view of a liquid crystal display device for explaining the arrangement of a backlight structure commonly used in the embodiments of the present invention.
[0133]
The first substrate 4 and the second substrate 7 are opposed to each other with the liquid crystal layer 19 interposed therebetween. The first substrate and the second substrate are bonded with a sealant 11.
[0134]
A polarizing plate 20 is provided on the image display surface side (image observation surface side) of the second substrate, and a polarizing plate 21 is also provided on the backlight side (opposite to the image observation surface) of the first substrate. ing. There is a light diffusion layer 17 between the first substrate 7 and the polarizing plate 21. Further, a reflective polarizing plate 23 is disposed on the backlight side of the polarizing plate 21.
[0135]
The backlight assembly includes at least a light guide plate 25, a light source 26, and a reflection plate 27. If necessary, the light diffusion sheet 24 may be arranged on the front surface of the light guide plate 25.
[0136]
The light diffusion layer 17 used a diffusion adhesive. The diffusion adhesive has both a light diffusion function and a function of bonding the polarizing plate and the first substrate. Further, a light diffusion sheet 24 is arranged in front of the light guide plate (on the observation window side) to diffuse light.
[0137]
Light 28 incident on the panel from the observation window is diffused by the light diffusion layer 17 and the light diffusion sheet 24 and reaches the reflection plate 27. The reflected light 29 also passes through the diffusion sheet and the light diffusion layer 17 and is emitted from the panel. Therefore, light is sufficiently diffused, so that uneven brightness can be suppressed. In addition, it is possible to prevent the shadow of the image generated when the image is viewed from an oblique direction, and the image recognizability is improved. In particular, a horizontal electric field type liquid crystal display device has a wide viewing angle and is preferably applied to such a display device. Further, by arranging the reflective polarizing plate 23, external light can be effectively used.
[0138]
On the other hand, light 30 emitted from the light source 26 of the backlight passes through the light guide plate 25 and is bent toward the image surface ground. Since the light 30 is also diffused by the light diffusion sheet and the light diffusion layer, it is possible to suppress uneven brightness on the image display surface. With such a configuration, an image can be displayed using light from a backlight when the use environment is dark, and an image can be displayed by reflecting external light when the use environment is bright. In particular, it is possible to suppress the reverse display of an image when displaying an image by reflecting external light.
[0139]
In addition, both external light and a backlight can be used, and an image with good contrast can be displayed even in a bright environment.
[0140]
In each of the embodiments described above, the first substrate 4 is described as a glass substrate, but similar problems occur if the substrate requires a base film. An object other than a glass substrate may be used as the first substrate. In addition, even if it is other than the base film, the image recognizability can be improved by applying the above-described configuration to the structure in which the multilayer film is formed in the light transmitting portion.
[0141]
In the application on which the priority claim of the present application is based, the thickness of silicon nitride is
d ± 10 = 555 · m / 2 · n
It was prescribed. However, in the earlier application, as is apparent from FIGS. 5, 6, and 7, it is shown that the visibility correction reflectance becomes lowest when the thickness of the base ground film is 140 nm. That is, assuming that the thickness of the underlayer is d (nm) and the refractive index at a wavelength of 555 nm is n,
d = 555 · m / 2 · n
Is satisfied. Furthermore, it is described that it is necessary to adjust the thickness of the base film to about 10% in consideration of a manufacturing error, and it is preferable that the thickness be controlled to an error of 10 nm. That is, according to the concept of the present invention, when the thickness of the base film is d (nm) and the refractive index when the wavelength is 555 nm is n,
d−10 ≦ 555 × m / (2 × n) ≦ d + 10
However, in the specification of the previous application, there was a defect in the description of the formula.
[0142]
In the display device of the present invention, it is preferable that the thickness of the silicon nitride of the base film be in the range of 140 nm to ± 10 nm (130 nm to 150 nm), which is the thickness at which the luminosity correction refractive index is minimized. However, this range is a value when the refractive index of silicon nitride is 2.0, and the refractive index of silicon nitride varies from 2.0 to 1.85. When the refractive index is 1.85, it is preferable that the refractive index is in a range of 150 nm to ± 10 nm (a range of 140 nm to 160 nm). Therefore, in consideration of the change in the refractive index of silicon nitride, it can be said that the thickness of the silicon nitride as the base film is preferably formed in the range of 130 nm to 160 nm.
[0143]
Further, in the specification of the previous application, it is described that it is necessary to adjust the thickness of the silicon nitride of the base film to 10% in consideration of a manufacturing error. Under this condition, when the refractive index of the silicon nitride of the base film is 2.0, it is necessary to adjust the film thickness in a range from 140 nm to ± 14 nm, that is, in a range from 126 nm to 154 nm. Further, when the refractive index of silicon nitride is 1.85, it is necessary to adjust the film thickness in a range from 150 nm to ± 15 nm, that is, in a range from 135 nm to 165 nm. Therefore, in consideration of the change in the refractive index of silicon nitride, it can be said that the thickness of the silicon nitride as the base film needs to be adjusted in the range from 126 nm to 165 nm. Note that the thickness of the silicon nitride may vary by about 15% depending on the manufacturing apparatus and the manufacturing process. In that case, it is necessary to form the silicon nitride underlayer in a range of about 120 nm to 170 nm. Even in this range, it is possible to reduce the reflection of silicon nitride as compared with the conventional case. Further, as described above, in order to protect the polysilicon film from impurities in the substrate, the thickness of the silicon nitride as the first base film may be 45 nm or more. The range of 50 nm to 180 nm of the thickness of the silicon nitride base film shown in FIG. 4 focuses on the effect of reducing the entry of impurities from the substrate, and further obtains the effect of reducing the reflection of the silicon nitride film. It is preferable to suppress the film thickness to a narrower range.
[0144]
Note that the relationship between the thickness of the underlying silicon nitride film and the luminosity correction reflectance shown in FIG. 5 is obtained by setting the refractive index of the silicon nitride film to about 2 (approximately 1.98). Is also 1.85. However, the refractive index of the silicon nitride film varies between 1.8 and 2.1 depending on the characteristics of the manufacturing apparatus and the manufacturing process. Therefore, when the refractive index of silicon nitride is 2.1, the film thickness is 132 nm, and when the refractive index is 1.8, the luminosity correction reflectance is the lowest when the film thickness is 154 nm. Become. That is, in consideration of the change in the refractive index of the silicon nitride film as the base film, it is possible to suppress the visibility correction reflectance by forming the silicon nitride film in the range of 132 nm to 154 nm.
[0145]
Here, in consideration of the fact that the refractive index of the base film varies from 1.8 to 2.1, when the film thickness is adjusted in the range of 10 nm as described above, the film thickness is set in the range of 122 nm to 164 nm. Is preferred. Further, when the thickness of the silicon nitride of the base film is adjusted to 10%, it is necessary to adjust the thickness of the silicon nitride of the base film from 118 nm to 169 nm.
[0146]
The definition of the film thickness of the silicon nitride underlayer shown here relates to the transmission portion in the pixel region.
[0147]
As described above, the numerical values of the film thickness have been shown. These numerical values indicate that the film thickness is ± 10 nm when the film thickness of the silicon nitride base film is d (nm) and the refractive index at a wavelength of 555 nm is n. If you want to keep in the range of
d−10 ≦ 555 × m / (2 × n) ≦ d + 10
Satisfy the formula of
To keep the film thickness within the range of ± a%,
d × (1−0.01 × a) ≦ 555 × m / (2 × n) ≦ d (1 + 0.01a)
It is preferable to form the film thickness so as to satisfy the following expression.
[0148]
In the above description, the gate insulating film of the thin film transistor is formed using silicon oxide, but may be formed using a silicon nitride film. In this case, only the gate insulating film (silicon nitride film) sandwiched between the silicon oxide films may be determined by the above-described formula in consideration of the reflectance.
[0149]
Note that in this specification, the silicon nitride film and the silicon oxide film formed over the substrate are referred to as a base film, but the base film is an insulating film formed between the thin film transistor and the substrate. That is. Therefore, those films may be formed on the substrate from the beginning or may be formed before the thin film transistor is formed.
[0150]
【The invention's effect】
According to the present invention, by reducing the reflection from the transmission region, the contrast of the reflection image formed by the reflection pixel electrode, the liquid crystal layer thereon, the phase difference plate, and the deflection plate can be improved. . Further, according to the present invention, it is possible to provide a display device in which the visibility of an image when displaying an image by reflecting external light on the back side of the first substrate is improved. Also, when the reflected light and the light of the backlight are used at the same time, the visibility of the image can be improved.
[Brief description of the drawings]
FIG. 1 is a plan view of a pixel portion of a liquid crystal display device of the present invention.
FIG. 2 is a sectional view taken along the line II of FIG.
FIG. 3 is a cross-sectional view taken along the line II-II of FIG.
FIG. 4 is a diagram showing the material and thickness of a film or layer and the refractive index when the wavelength is 555 nm.
FIG. 5 is a diagram showing reflectance after visibility correction when the first underlayer is changed to 50 nm to 180 nm.
6 is a diagram showing the relationship between the wavelength of light and the luminosity correction reflectance when the first base film in FIG. 5 is 50 nm.
FIG. 7 is a diagram showing the relationship between the wavelength of light and the luminosity correction reflectance when the first base film in FIG. 5 is 140 nm.
FIG. 8 is a view showing a film configuration of a partially transmissive liquid crystal display device of normally black display.
FIG. 9 is a perspective view including a partial cross section of a liquid crystal display device to which the present invention is applied.
FIG. 10 is a plan view of a pixel portion of a liquid crystal display device according to a second embodiment of the present invention.
11 is a sectional view taken along the line II of FIG. 10;
FIG. 12 is a sectional view taken along the line II-II in FIG.
FIG. 13 is a diagram showing a material or thickness (film thickness) of a film or a layer and a refractive index when a wavelength is 555 nm.
FIG. 14 is a diagram showing the reflectance corrected for visibility when the second interlayer insulating film is changed between 100 nm and 500 nm.
FIG. 15 is a diagram showing reflectance after visibility correction when the first underlayer is changed to 25 nm to 350 nm.
FIG. 16 is a diagram showing reflectance with luminosity corrected when ITO is changed between 50 nm and 300 nm.
FIG. 17 is a diagram showing the reflectance with the visibility corrected when the second interlayer insulating film is changed between 100 nm and 400 nm.
FIG. 18 is a diagram showing reflectance after luminosity correction when the first underlayer is changed between 50 nm and 325 nm.
FIG. 19 is a diagram showing the relationship between the wavelength of light and the luminosity correction reflectance when the first underlayer is 75 nm.
FIG. 20 is a diagram showing the relationship between the wavelength of light and the luminosity correction reflectance when the first base film is 150 nm.
FIG. 21 is a plan view when a second substrate on which a color filter is formed is superimposed on a first substrate.
FIG. 22 is a plan view of a pixel region of a liquid crystal display device according to a third embodiment of the present invention.
FIG. 23 is a plan view of a black matrix BM formed on a second substrate.
24 is a sectional view taken along the line III-III in FIG.
FIG. 25 is a cross-sectional view of the liquid crystal display device for explaining the arrangement of the backlight assembly.
[Explanation of symbols]
1, G ... gate electrode, 2, D ... drain electrode, 3 ... reflection electrode, 4 ... reflection electrode opening, 5 ... polysilicon film, 6 ... storage electrode (storage) Line), 7: transparent electrode, 8: glass substrate, 9: first base film, 10: second base film, 11: connection part, 12: gate insulation Film, 13: first interlayer insulating film, S: source electrode, 15: contact hole, 16: second interlayer insulating film, 17: inclined portion, 18: organic Insulating film, 19: liquid crystal layer, 20: counter electrode, 21: counter substrate, 22: alignment film, C: common electrode, 1: gate line, 2: drain Line, 3 ... pixel electrode, 4 ... first substrate, 7 ... second substrate, 11 ... sealing material, 14, 15 ... contact hole , 16 ... second interlayer insulating film, 17 ... light diffusion layer, 20, 21 ... polarizer, 23 ... reflective polarizer, 24 ... light diffusion sheet, 25 ... Light guide plate, 26 light source, 27 reflector plate.

Claims (21)

A liquid crystal display device having a thin film transistor and a pixel electrode formed on a substrate,
The thin film transistor has a silicon film, a gate electrode, and a source electrode electrically connected to the pixel electrode,
A silicon oxide film and a silicon nitride film formed between the silicon oxide film and the substrate, between the silicon film and the substrate, and between the pixel electrode and the substrate,
A liquid crystal display device, wherein the thickness of the silicon nitride film is greater than the thickness of the silicon oxide. When the silicon nitride film has a thickness of d (nm) and a refractive index of n when the wavelength is 555 nm (m is an arbitrary integer),
d−10 ≦ 555 × m / (2 × n) ≦ d + 10
The liquid crystal display device according to claim 1, wherein the following condition is satisfied. When the silicon nitride film has a thickness of d (nm) and a refractive index of n when the wavelength is 555 nm (m is an arbitrary integer),
0.9d ≦ 555 × m / (2 × n) ≦ 1.1d
The liquid crystal display device according to claim 1, wherein the following condition is satisfied. 4. The liquid crystal display device according to claim 2, wherein the refractive index is 2.0. The liquid crystal display device according to claim 2, wherein the refractive index is 1.85. 2. The liquid crystal display device according to claim 1, wherein the thickness of the silicon nitride film ranges from 130 nm to 160 nm. 2. The liquid crystal display device according to claim 1, wherein the thickness of the silicon nitride film ranges from 126 nm to 165 nm. A gate insulating film is formed between the silicon layer and the gate electrode,
8. The liquid crystal display device according to claim 1, wherein an interlayer film adjacent to the gate insulating film is formed between the gate insulating film and the pixel electrode. 2. The semiconductor device according to claim 1, wherein the interlayer film includes a first interlayer insulating film, and a second interlayer insulating film formed between the first interlayer insulating film and the pixel electrode. 9. The liquid crystal display device according to any one of 8. 10. The liquid crystal display device according to claim 9, wherein the gate insulating film and the first interlayer insulating film are formed of the same material. The gate insulating film and the first interlayer insulating film are formed of silicon oxide, and the total thickness of the silicon oxide film, the gate insulating film, and the first interlayer insulating film is d (nm); When m is an arbitrary integer,
0.9d ≦ 555 × m / (2 × 1.5) ≦ 1.1d
The liquid crystal display device according to claim 10, wherein the following condition is satisfied. When the total thickness of the second interlayer insulating film and the pixel electrode is d (nm) and m is an arbitrary integer,
0.9d ≦ 555 × m / (2 × 2) ≦ 1.1d
The liquid crystal display device according to claim 8, wherein the following condition is satisfied. The pixel electrode has a reflective electrode and a light-transmissive electrode,
13. The liquid crystal display device according to claim 1, wherein a distance from the substrate to the reflective electrode is different from a distance from the substrate to the light transmissive electrode. 14. The liquid crystal display device according to claim 13, wherein an organic film is formed between the reflective electrode and the substrate. The pixel electrode is a light transmissive electrode,
The liquid crystal display device according to claim 1, wherein an organic film is formed between the light transmissive electrode and the substrate. When the thickness of the organic film is d (nm) and m is an arbitrary integer,
0.9d ≦ 555 × m / (2 × 1.6) ≦ 1.1d
The liquid crystal display device according to claim 14, wherein the following condition is satisfied. 17. The liquid crystal display device according to claim 1, wherein a light transmissive counter electrode is formed on the substrate facing the substrate. The liquid crystal display device according to claim 15, wherein a backlight is provided outside the substrate, and the backlight is provided with a reflector. The pixel electrode is formed on an organic film formed on a substrate,
The liquid crystal display device according to claim 1, wherein a common electrode is also formed on the organic film. When the thickness of the organic film is d (nm) and m is an arbitrary integer,
0.9d ≦ 555 × m / (2 × 1.6) ≦ 1.1d
20. The liquid crystal display device according to claim 19, wherein: 20. The liquid crystal display device according to claim 19, wherein a backlight is provided outside the substrate, and the backlight is provided with a reflection plate.

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