JP2013190580A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device excellent in reliability and efficiency for light utilization.SOLUTION: According to the embodiment, a liquid crystal display device includes a Fabry-Perot type interference filter having a first reflective layer, a second reflective layer, and a spacer layer disposed between the first reflective layer and the second reflective layer. The spacer layer has a first area in which at least a first layer, a second layer and a third layer are laminated, a second area in which the second layer and the third layer are laminated, and a third area in which the third layer is provided. The spacer layer further has a protective film provided at at least either one of a position between the first layer and the second layer and a position between the second layer and the third layer.

Description

  Embodiments described herein relate generally to a liquid crystal display device.

  Liquid crystal displays using thin film transistors (TFT-LCDs) are increasingly in demand due to the start of digital terrestrial broadcasting and the spread of the Internet and mobile phones. In order to meet these demands, TFT-LCDs are mounted on mobile devices as small displays, while demand for large-screen TVs is increasing.

  The color display of the TFT-LCD is generally controlled by arranging a color filter on a counter substrate and emitting red, green, and blue light from corresponding pixels. As this color filter, an absorption type using a pigment or a dye is used. For this reason, when white light incident on the liquid crystal panel from a backlight installed on the back surface of the liquid crystal panel passes through, for example, a blue filter, green and red light are absorbed by the blue filter and light loss occurs. Similar light loss occurs in the green and red filters, and the light use efficiency in the color filters is reduced to about one third as a whole.

  Therefore, a method using not only an absorption type color filter but also an interference type color filter has been proposed. This is because red, green, and blue interference filters are provided corresponding to the color of each pixel, and light that has not passed through the interference filter is returned to the backlight side, so that light of other colors is reused. The light utilization efficiency is improved.

  In order to form such red, green, and blue interference filters, a substrate is generally formed by combining a film forming process by a CVD method or a sputtering method, a photolithography process for patterning, an etching process, a resist stripping process, and the like. An interference filter layer having a different structure for each display color is formed thereon. At this time, in the photolithography process, the etching process, and the resist stripping process, the surface of the interference filter layer is treated with various chemicals, reactive gases, and the like, so that there is a high possibility that mobile ions such as alkali metals adhere.

  On the other hand, in the TFT-LCD, the luminance of each pixel is adjusted using a change in resistance between the source and drain of the TFT. In the TFT, a semiconductor layer and a gate electrode are formed via a gate insulating film, and a resistance between the source and the drain is adjusted by changing a voltage between the semiconductor layer and the gate electrode. For this reason, if there are mobile ions such as alkali metals in the semiconductor layer, the TFT characteristics may change during use of the TFT-LCD, and the display characteristics may be deteriorated.

JP-A-9-258207

  In the display device using the interference filter as described above, in the process of forming the interference filter that transmits red, green, and blue colors for each pixel, impurities such as alkali metal are adsorbed on the surface, and the reliability of the TFT is increased. Increased risk of decline.

  The problem to be solved by the embodiments of the present invention is to provide a liquid crystal display device excellent in reliability and light utilization efficiency.

  According to the embodiment, the liquid crystal display device includes a first reflective layer, a second reflective layer, and a spacer layer disposed between the first reflective layer and the second reflective layer. A Fabry-Perot interference filter is provided. The spacer layer includes at least a first region in which the first layer, the second layer, and the third layer are stacked, and the second layer and the third layer. A second region; and a third region provided with the third layer. The spacer layer further includes a protective film provided on at least one of the first layer and the second layer and the second layer and the third layer. .

1 is a cross-sectional view illustrating an example of a configuration of a liquid crystal display device according to a first embodiment. FIG. 3 is a diagram illustrating an example of a configuration of an interference filter according to the first embodiment and an example of an optical characteristic of a material constituting the interference filter. FIG. 5 is a diagram illustrating an example of optical characteristics of the interference filter according to the first embodiment. The figure which shows an example of the optical characteristic of the absorption type filter which concerns on 1st Embodiment. The figure for demonstrating the color gamut of the liquid crystal display device which concerns on 1st Embodiment. The figure for demonstrating an example of the manufacturing process of the interference filter which concerns on 1st Embodiment.

[First Embodiment]
A first embodiment will be described with reference to the drawings. FIG. 1 shows an outline of a cross section of a liquid crystal display device using an interference filter according to this embodiment. On a transparent glass substrate 1, a Fabry-Perot interference color filter layer 2 (interference filter 2) is provided. A thin film transistor (TFT) array 9 is provided on the interference filter 2. A substrate in which the interference filter 2 and the TFT array 9 are formed on the transparent glass substrate 1 is referred to as an array substrate 20. The liquid crystal display device has a plurality of pixels, and each pixel includes a plurality of sub-pixels. Each sub-pixel transmits light of a color such as red, green, or blue with a higher transmittance than light of other colors.

  In general, in the liquid crystal display device, a single layer of silicon oxide film or the like is formed under the TFT array 9 as an undercoat layer. This undercoat layer is intended to prevent the diffusion of impurities from the glass substrate and improve the flatness of the glass substrate. On the other hand, in this embodiment, a Fabry-Perot interference filter is formed instead of the undercoat layer.

  The interference filter 2 includes, in order from the glass substrate 1 side, a first reflective layer 3 that is semi-transmissive / reflective with respect to the visible light region, a spacer layer 5, and a second member that is semi-transmissive / reflective with respect to the visible light region. It has a reflective layer 4 and is a Fabry-Perot interference filter. That is, the interference filter 2 transmits light in a predetermined wavelength range determined mainly by the optical thickness of the spacer layer 5 and the phase shift between the first reflective layer 3 and the second reflective layer 4, and in other wavelength ranges. It has the property of reflecting light.

  As shown in FIG. 1, the optical paths 24a, 24b, and 24c pass through the spacer layers 5 having different thicknesses. In other words, the transmission wavelength region and the reflection wavelength region of the optical paths 24a, 24b, and 24c are different. In the present embodiment, the interference filter 2 is formed so as to have a different thickness corresponding to each sub-pixel, and any one of red, green, and blue light is selectively transmitted to each sub-pixel. The spacer layer 5 designed in the above is provided.

  Each of the first reflective layer 3 and the second reflective layer 4 is formed by laminating, for example, a total of four layers of, for example, a silicon nitride film (silicon nitride) having a thickness of 58 nm and a silicon oxide film (silicon oxide) having a thickness of 92 nm alternately. Is formed. The spacer layer 5 includes a silicon nitride film, and the thickness thereof is different for each subpixel. The spacer layer 5 is mainly made of a silicon nitride film, for example. That is, for example, the film thickness of the silicon nitride film is 30 nm at the position of the sub-pixel corresponding to red, and the film thickness of the silicon nitride film is 115 nm at the position of the sub-pixel corresponding to green. In position, the thickness of the silicon nitride film is 78 nm. Thus, the interference filter 2 includes portions that function as the red filter 6, the green filter 7, and the blue filter 8. The spacer layer 5 includes a silicon oxide film layer that is required in a process described later.

  The TFT array 9 includes a thin film transistor 18 including a gate line 15, a gate insulating film 16, and a signal line 19. The TFT array 9 includes a pixel electrode 17 that is a transparent conductive film connected to the thin film transistor 18. The pixel electrode 17 is formed on the gate insulating film 16. The positions of the pixel electrodes 17 correspond to the positions of the red filter 6, the green filter 7, and the blue filter 8, respectively. A first polarizing plate 30 and various optical films (not shown) are provided on the surface of the glass substrate 1 opposite to the surface on which the interference filter 2 is formed.

  On the TFT array 9 side of the array substrate 20, a counter substrate 21 is disposed facing the liquid crystal layer 22. The array substrate 20 and the counter substrate 21 are fixed with a suitable distance by a spacer or the like, and a liquid crystal layer 22 is provided between the array substrate 20 and the counter substrate 21. The liquid crystal layer 22 includes liquid crystal molecules.

  The counter substrate 21 is formed using a glass substrate 25. An absorption filter 32 is provided on the surface of the glass substrate 25 facing the array substrate 20. The absorption filter 32 includes a red filter 26, a green filter 27, and a blue filter 28, which are absorption color filters. The red filter 26 is disposed to face the red filter 6 of the interference filter 2, the green filter 27 is disposed to face the green filter 7 of the interference filter 2, and the blue filter 28 is opposed to the blue filter 8 of the interference filter 2. Are arranged. A common electrode 29 that is a transparent conductive film is formed on the entire surface of the absorption filter 32. A second polarizing plate 31 and various optical films (not shown) are provided on the surface of the glass substrate 25 opposite to the surface on which the absorption filter 32 is formed.

  On the side of the array substrate 20 where the first polarizing plate 30 is provided, a backlight unit 40 is disposed. The backlight unit 40 includes a light guide plate 41, a reflection plate 42, and a light emitting diode 43 that generates light incident on the light guide plate 41. A reflection plate 42 is provided on the surface of the light guide plate 41 opposite to the array substrate 20. A groove 44 is formed on the surface of the light guide plate 41 on which the reflection plate 42 is provided. A light emitting diode 43 is provided on, for example, a side surface of the light guide plate 41. Light generated from the light emitting diode 43 enters the light guide plate 41 and travels while being totally reflected in the light guide plate 41. When the light hits the groove 44, the reflection angle changes, and the light exits from the light guide plate 41 and enters the array substrate 20. The backlight unit 40 is not limited to the above configuration, and may have any configuration as long as it functions as a surface light source.

  The interference filter 2 will be further described. A schematic diagram of an example of the configuration of the interference filter 2 is shown in FIG. As described above, the interference filter 2 includes, in order from the glass substrate 1, the first reflective layer 3 made of a silicon nitride film, a silicon oxide film, a silicon nitride film, and a silicon oxide film, a spacer layer 5 made of a silicon nitride film, A silicon oxide film, a silicon nitride film, a silicon oxide film, and a second reflective layer 4 made of a silicon nitride film are stacked. Here, the thickness of the silicon nitride film other than the spacer layer is, for example, 58 nm, and the thickness of the silicon oxide film is, for example, 92 nm. The spacer layer has a different thickness depending on the corresponding color of the sub-pixel. That is, the thickness of the silicon nitride film of the spacer layer is, for example, 30 nm for the red filter 6, 115 nm for the green filter 7, and 78 nm for the blue filter 8.

  FIG. 2B shows values of the refractive index n, which is an optical constant of the silicon oxide film and the silicon nitride film according to the present embodiment, with respect to the wavelength. Here, a solid line indicates a silicon nitride film, and a broken line indicates a silicon oxide film. The refractive index of the silicon nitride film is adjusted to be 2.3 near the wavelength of 550 nm. FIG. 2C shows values of the extinction coefficient k, which is an optical constant of the silicon oxide film and the silicon nitride film according to this embodiment, with respect to the wavelength. Here, a solid line indicates a silicon nitride film, and a broken line indicates a silicon oxide film. As shown in this figure, the silicon nitride film absorbs on the short wavelength side.

  An example of optical characteristics of the color filter of the interference filter 2 according to the present embodiment is shown in FIG. 3A shows the transmission spectrum (vertical axis) with respect to the wavelength (horizontal axis), and FIG. 3B shows the reflection spectrum (vertical axis) with respect to the wavelength (horizontal axis). 3A, the solid line 70R indicates the transmission spectrum of the red filter 6, the broken line 70G indicates the transmission spectrum of the green filter 7, and the alternate long and short dash line 70B indicates the transmission spectrum of the blue filter 8. 3B, the solid line 80R indicates the reflection spectrum of the red filter 6, the broken line 80G indicates the reflection spectrum of the green filter 7, and the alternate long and short dash line 80B indicates the reflection spectrum of the blue filter 8. In general, almost no absorption occurs in the interference filter, so the sum of the reflection spectrum and the transmission spectrum is approximately 1. In contrast, in this embodiment, as shown in FIG. 2C, a silicon nitride film having absorption on the short wavelength side (blue side) is used as the material of the dielectric multilayer film. Light loss occurs on the side. As a result, the sum of the reflection spectrum and the transmission spectrum of the interference filter according to the present embodiment is not 1.

  An example of the optical characteristics of the absorption filter 32 is shown in FIG. In this figure, the vertical axis represents transmittance and the horizontal axis represents wavelength. Solid line 90R indicates the transmittance of red filter 26, broken line 90G indicates the transmittance of green filter 27, and alternate long and short dash line 90B indicates the transmittance of blue filter 28. The absorptive filter shown in this figure is used as a color filter of a general liquid crystal display device. Light that does not pass through the absorption color filter of each color is absorbed and lost. Note that the spectral characteristics of the color filter shown in FIG. 4 overlap in the low transmittance region, which is not preferable for color reproducibility.

  The operation of the liquid crystal display device according to this embodiment will be described with reference to FIG. The light emitted from the light emitting diode 43 in the backlight unit 40 is totally reflected on the bottom surface (the surface facing the reflection plate 42) and the top surface (the surface facing the counter substrate 21) of the light guide plate 41. Propagate and spread. When the light hits the groove 44, the total reflection condition is broken and enters the array substrate 20. That is, light is incident on the array substrate 20 from the backlight unit 40 in a planar shape.

  This light first passes through the first polarizing plate 30 to become polarized light, passes through the glass substrate 1 and reaches the interference filter 2. The interference filter 2 transmits light of a predetermined wavelength as shown in FIG. 3A and reflects light of other wavelengths as shown in FIG. For example, red light incident on the red filter 6 portion of the interference filter 2 passes through the interference filter 2, but red light incident on the green filter 7 or blue filter 8 portion is reflected by the interference filter 2.

  The light reflected by the interference filter 2 travels toward the backlight unit 40 and is reflected by the reflecting plate 42 with almost no loss. The light reflected by the reflecting plate 42 enters the array substrate 20 again. For example, when green light reflected by the red filter 6 part enters the green filter 7 part, the light passes through the interference filter 2.

  In other words, as shown in FIG. 1, the red light 50 incident on the red filter 6 part passes through the interference filter 2. On the other hand, the green light 51 incident on the red filter 6 is reflected by the interference filter 2. The green light 51 is repeatedly reflected between the reflection plate 42 and the interference filter 2, and passes through the interference filter 2 when reaching the green filter 7 portion of the interference filter 2. For example, 90% or more of the light returned to the backlight unit 40 can be used again. If the conditions are set appropriately, more than 95% of the light can be utilized again.

  The light transmitted through the interference filter 2 enters the liquid crystal layer 22 and passes through the liquid crystal layer 22. Here, the voltage applied between each pixel electrode 17 and the common electrode 29 for each sub-pixel is selectively controlled by the thin film transistor 18. The alignment of the liquid crystal molecules in the liquid crystal layer 22 is changed by the electric field between the pixel electrode 17 and the common electrode 29. As a result, the polarization plane of light transmitted through the liquid crystal layer 22 rotates for each pixel.

  The light transmitted through the liquid crystal layer 22 enters the absorption filter 32. The color of the absorption filter 32 for each sub-pixel corresponds to the color of the interference filter 2. Therefore, the wavelength of light incident on the absorption filter 32 is selected by the interference filter 2. Here, as shown in FIG. 3, the transmission spectrum of the interference filter 2 has a narrower spectral width than the transmission spectrum of the absorption filter 32 shown in FIG. For this reason, most of the light incident on the absorption filter 32 is transmitted. As shown in FIG. 3, the transmission spectrum of the interference filter 2 has a wavelength band in which the transmittance is high in the tail portion in addition to the peak of each color. The absorption filter 32 absorbs light in the wavelength band of the bottom portion.

  The light that has passed through the absorption filter 32 passes through the glass substrate 25 and enters the second polarizing plate 31. Light having a polarization plane that coincides with the transmission axis of the second polarizing plate 31 passes through the second polarizing plate 31 and is emitted from the liquid crystal display device. On the other hand, light whose polarization plane does not coincide with the transmission axis of the second polarizing plate 31 is absorbed by the second polarizing plate 31. Since the plane of polarization of transmitted light is controlled by controlling the orientation of the liquid crystal molecules in the liquid crystal layer 22, the amount of light transmitted through the second polarizing plate 31 and emitted from the liquid crystal display device is controlled for each subpixel. Can be done. In this way, the liquid crystal display device can display an image.

  If the interference filter 2 is not disposed, light of all colors is directly incident on the absorption filter 32. Therefore, light having a wavelength other than the wavelength band transmitted by each color filter is absorbed by the absorption filter 32. The As a result, approximately two thirds of the light is absorbed by the absorption filter 32. On the other hand, in this embodiment, since the light absorbed by the absorption filter 32 is small, the light use efficiency is good, and the liquid crystal display device is energy efficient.

  A color gamut obtained by combining the interference filter 2 and the absorption filter 32 will be described. The color gamut when the Fabry-Perot interference filter (interference filter 2) whose wavelength characteristics are shown in FIG. 3 is used alone has an NTSC ratio of about 30%. The color gamut when the absorption color filter (absorption filter 32) whose wavelength characteristic is shown in FIG. 4 is used alone has an NTSC ratio of about 55%. When the interference filter 2 and the absorption filter 32 are used in combination as in the present embodiment, light that deteriorates the color purity recognized at the bottom of the transmission spectrum of the interference filter 2 is absorbed by the absorption filter 32. So the color gamut is improved.

  FIG. 5 shows the relationship of the total color gamut (NTSC ratio (vertical axis)) by the combined use of the interference filter 2 and the absorption filter 32 with respect to the color gamut (NTSC ratio (horizontal axis)) of the absorption filter 32. When the NTSC ratio of the absorption filter 32 is about 55%, the total NTSC ratio is 90% or more. In order to achieve an NTSC ratio of 70% or more, which is generally said to be beautiful, the NTSC ratio of the absorption filter 32 may be about 17%. A small NTSC ratio in the absorption filter means that the filter is light in color. For example, the color material thickness of a color filter having an NTSC ratio of 17% is about 20% of the color material thickness of a color filter having an NTSC ratio of 55%. By using a thin filter, light loss when passing through the absorption filter 32 is suppressed, and light utilization efficiency is improved. Therefore, if a filter having a lower color purity than the conventional color filter shown in FIG. 4 is used for the absorption filter 32, sufficient color purity can be obtained by the combined use of the interference filter 2 and the absorption filter 32. In addition, the light utilization efficiency of the entire liquid crystal display device is improved.

  In the Fabry-Perot interference color filter, light interference based on the configuration of the optical thin film group is used. Therefore, in principle, the light incident obliquely shifts the transmission wavelength region to a short wavelength, that is, the blue side. This corresponds to the fact that the color appears to change greatly when the liquid crystal display device is observed from an oblique direction. In the present embodiment, the color change is also eliminated by providing the absorption filter 32. That is, even if the light emitted obliquely from the array substrate 20 is shifted to the blue side, the above-described color change is sufficiently suppressed by allowing the absorption filter 32 to transmit only the desired wavelength region.

  As described above, the liquid crystal display device of the present embodiment increases the light use efficiency by light recycling using the interference filter 2, and improves the color gamut that is insufficient with the interference filter 2 by the absorption filter 32.

  Note that the color change caused by the interference filter 2 of the obliquely incident light described above can also be eliminated by increasing the directivity of the light emitted from the backlight unit 40 and suppressing the obliquely incident light component to the interference filter 2. . In this case, the viewing angle of the liquid crystal display device becomes narrow. However, for example, a light scattering agent such as a diffusion plate may be provided on the second polarizing plate 31.

  An example of a method for forming the interference filter 2 according to the present embodiment will be described. First, the first reflective layer 3 is formed on the glass substrate 1. Therefore, a silicon nitride film is formed on the glass substrate 1 by, for example, chemical vapor deposition (CVD). Subsequently, a silicon oxide film is formed on the silicon nitride film by CVD. Further, a silicon nitride film and a silicon oxide film are formed in this order by CVD. These films can be continuously formed by controlling the gas pressure of each composition in CVD. In this way, the first reflective layer 3 composed of four layers is formed.

  Next, a silicon nitride film constituting the spacer layer 5 is formed by CVD. The thickness of the spacer layer 5 varies depending on the color corresponding to the sub-pixel as described above. The spacer layer 5 having a different thickness depending on the location is formed by, for example, film formation and etching using photolithography. A method for forming the spacer layer 5 will be described with reference to FIG.

  First, as shown in FIG. 6A, a silicon nitride film 10 (first layer) having a thickness of about 37 nm is formed on the entire surface of the first reflective layer 3 by CVD following the formation of the first reflective layer 3. Is formed. Subsequently, a silicon oxide film 101 having a thickness of about 5 nm is formed as a first protective film on the silicon nitride film 10 by CVD. Next, as shown in FIG. 6B, the resist 11 is patterned by, for example, a photolithography process.

  Thereafter, as shown in FIG. 6C, the silicon oxide film 101 and the silicon nitride film 10 are etched by, for example, chemical dry etching to form a pattern, and then the resist is removed. The portion where the silicon nitride film 10 is left by this etching is the portion that becomes the green filter 7. In this way, a part of the spacer layer 5 is selectively formed on the silicon oxide film of the first reflective layer 3.

  Here, first, the silicon oxide film 101 is chemically dry etched. The chemical dry etching conditions at this time are set so that the selection ratio of the silicon oxide film and the silicon nitride film is sufficiently high, that is, the etching rate of the silicon nitride film is sufficiently slow compared to the silicon oxide film. In this dry etching, only the silicon oxide film is selectively etched, and the underlying silicon nitride film is hardly etched.

  Next, in order to chemically dry etch the silicon nitride film 10, the chemical dry etching conditions are sufficiently high in the selection ratio between the silicon nitride film and the silicon oxide film, that is, the etching rate of the silicon oxide film is higher than that of the silicon nitride film. By changing so as to be sufficiently slow, only the silicon nitride film is selectively etched in this dry etching, and etching damage to the underlying silicon oxide film can be suppressed. When the silicon nitride film 10 is subjected to chemical dry etching, an etching selection ratio of about 20 is obtained. In this case, etching damage of the silicon oxide film can be ignored.

  Next, as shown in FIG. 6D, a silicon nitride film 12 (second layer) having a thickness of about 48 nm is formed on the entire surface by CVD. Subsequently, a silicon oxide film 102 having a thickness of about 5 nm is formed as a second protective film on the silicon nitride film 12 by CVD. Next, as shown in FIG. 6E, the resist 13 is patterned by a photolithography process. Thereafter, as shown in FIG. 6F, the silicon oxide film 102 and the silicon nitride film 12 are etched and patterned by chemical dry etching, and then the resist is removed. Finally, as shown in FIG. 3G, a silicon nitride film 14 (third layer) having a thickness of about 30 nm is formed on the entire surface by CVD.

  In this way, the spacer layer 5 is formed. Here, the portion where the three silicon nitride films are overlapped is the portion that becomes the green filter 7, and the thickness of the silicon nitride film is 37 + 48 + 30 = 115 nm. The portion where the two silicon nitride films overlap is the portion that becomes the blue filter 8, and the thickness of the silicon nitride film is 48 + 30 = 78 nm. A portion of the silicon nitride film is a portion where the red filter 6 is formed, and the thickness of the silicon nitride film is 30 nm.

  A second reflective layer 4 made of a silicon oxide film and a silicon nitride film is formed continuously with the formation of the silicon nitride film 14. That is, by CVD, a silicon oxide film, a silicon nitride film, a silicon oxide film, and a silicon nitride film are sequentially formed on the silicon nitride film 14 to form a second reflective layer 4 having four layers. As described above, the interference filter 2 that is a Fabry-Perot interference color filter including the first reflective layer 3, the spacer layer 5, and the second reflective layer 4 is formed on the glass substrate 1.

  Thus, for example, the first reflective layer 3 functions as a first reflective layer. For example, the second reflective layer 4 functions as a second reflective layer. For example, the spacer layer 5 functions as a spacer layer disposed between the first reflective layer and the second reflective layer. For example, the silicon nitride film 10 functions as a first layer, the silicon nitride film 12 functions as a second layer, and the silicon nitride film 14 functions as a third layer. For example, the green filter 7 functions as a first region in which a first layer, a second layer, and a third layer are stacked. For example, the blue filter 8 functions as a second region in which the second layer and the third layer are stacked. For example, the red filter 6 functions as a third region in which the third layer is provided. For example, the silicon oxide film 101 and the silicon oxide film 102 are protective films provided in at least one of the first layer and the second layer and the second layer and the third layer. Function.

  According to the present embodiment, the three types of filters, the red filter 6, the green filter 7, and the blue filter 8, of the interference filter 2 are formed by two patterning steps. For this reason, the manufacturing cost of the interference filter 2 can be kept very low. Further, since the silicon nitride film is used for the spacer layer 5 and the etching rate is selected to be faster than that of other silicon oxide films, the etching is easily stopped by the silicon oxide film and the manufacture is easy. In addition, when a dielectric multilayer film is commonly formed on the entire surface as a Fabry-Perot reflective layer as in this embodiment, it is advantageous in terms of film thickness control and process reduction compared to the conventional multilayer thin film system. is there.

  In this embodiment, in the formation of the spacer layer 5, a silicon oxide film as a protective film is formed on the silicon nitride film. This silicon oxide film prevents surface contamination of the silicon nitride film. After the thin film is formed by CVD, the surface of the silicon nitride film is easily contaminated with impurities when moving to a photolithography process or a chemical dry etching process. One reason that this contamination is likely to occur is that the composition of the silicon nitride film is stoichiometrically stable, and the silicon-to-nitrogen atomic ratio is set to be silicon richer than 3: 4. This is considered to be high. Contaminants can include oxygen and carbon as well as sodium and potassium. In this embodiment, a stoichiometrically stable silicon oxide film is formed as a protective film on the silicon nitride film. Since the silicon oxide film is chemically stable, the surface of the silicon oxide film is not easily contaminated. Therefore, according to this embodiment, after forming a thin film by CVD, contamination by impurities on the surface, which is likely to occur when moving to a photolithography process or a chemical dry etching process, is prevented. If impurities are mixed under the TFT array 9, the performance of the thin film transistor 18 and the like may be adversely affected. On the other hand, in this embodiment, high performance of the thin film transistor 18 and the like can be maintained by preventing contamination during the manufacturing process by the silicon oxide film.

  In the present embodiment, the thickness of the silicon oxide film as the protective film is about 5 nm, but it may be about 1 to 20 nm. It has been confirmed that even if a silicon oxide film having such a thickness is inserted into the spacer layer 5, the optical characteristics of the interference filter 2 are not greatly affected. In particular, in the green filter 7, it has been confirmed that the presence of a 10 to 15 nm silicon oxide film does not affect the optical characteristics of the green filter 7. It has been confirmed that the influence of the silicon oxide film on the optical characteristics is greater for the blue filter 8 than for the green filter 7. In this embodiment, both a silicon oxide film 101 as a protective film for the silicon nitride film 10 and a silicon oxide film 102 as a protective film for the silicon nitride film 12 are provided. May be provided.

  The Fabry-Perot interference color filter is realized by stacking dielectric multilayer films having different refractive indexes. In the present embodiment, a silicon oxide film is used as a thin film having a high refractive index, a silicon nitride film is used as a thin film having a low refractive index, and the interference filter 2 is formed by laminating these silicon oxide film and silicon nitride film. Is formed. If a material having a different refractive index is used, an interference filter is formed. Therefore, if a titanium oxide film or a silicon oxynitride film is used instead of the silicon oxide film or the silicon nitride film, the interference filter 2 is similarly formed. obtain.

[Second Embodiment]
A second embodiment will be described. Here, differences from the first embodiment will be described, and the same portions will be denoted by the same reference numerals and description thereof will be omitted. In the first embodiment, a silicon oxide film is used as the first protective film and the second protective film in the spacer layer 5. In contrast, in the present embodiment, the first protective film and the second protective film include a silicon nitride film in which the atomic ratio of silicon to nitrogen is close to 3: 4 instead of the silicon oxide film. For example, instead of the silicon oxide film, a silicon nitride film having an atomic ratio of silicon and nitrogen close to 3: 4 is provided as the first protective film and the second protective film. Here, when the atomic ratio is close to 3: 4, the silicon nitride film other than the protective film of the spacer layer 5 has a silicon-rich composition as described above. The silicon nitride film as the protective film and the second protective film means that the atomic ratio of silicon and nitrogen is close to 3: 4. Other configurations and the manufacturing method of the array substrate 20 are the same as those in the first embodiment.

  According to the present embodiment, since the silicon nitride film having a silicon to nitrogen atomic ratio close to 3: 4 is chemically more stable than the silicon-rich silicon nitride film, the surface of the silicon nitride film that is likely to occur during the process is used. Contamination is prevented. That is, the same effect as the first embodiment can be obtained.

  Further, as the first protective film and the second protective film, a silicon oxynitride film can be used instead of a silicon oxide film or a silicon nitride film. Silicon oxynitride films are also stoichiometrically stable compared to silicon-rich silicon nitride films. Accordingly, the silicon oxynitride film also functions as a protective film in the same manner as in the first and second embodiments, and as a result, the same effect can be obtained.

[Third Embodiment]
A third embodiment will be described. Here, differences from the first embodiment will be described, and the same portions will be denoted by the same reference numerals and description thereof will be omitted. In the first embodiment, silicon oxide films are used as the first protective film and the second protective film in the spacer layer 5. On the other hand, in this embodiment, a silicon oxide film is used as the first protective film, and the atomic ratio of silicon and nitrogen is set to 3: 4 as the second protective film as in the second embodiment. A close silicon nitride film is used. Other configurations and the manufacturing method of the array substrate 20 are the same as those in the first embodiment.

  As described above, when the influence on the optical characteristics of the blue filter 8 due to the presence of the protective film is compared with the influence on the optical characteristics of the green filter 7, the influence on the blue filter 8 is larger. Therefore, in the present embodiment, a silicon nitride film that has a relatively small influence on the optical characteristics is used for the second protective film to be included in the blue filter 8. On the other hand, a silicon oxide film that is more effective as a protective film is used for the first protective film that is included only in the green filter 7.

  According to the present embodiment, the effect of preventing contamination by the protective film can be obtained as in the case of the first embodiment and the second embodiment, and the influence on the optical characteristics can be reduced. In the present embodiment, a silicon oxide film is used for the first protective film and a silicon nitride film is used for the second protective film. However, the first protective film is used depending on the influence on the design and optical characteristics. A combination of a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or the like used for the film and the second protective film may be changed. For example, depending on the thickness relationship between the red filter 6, the green filter 7, and the blue filter 8, a silicon nitride film may be used as the first protective film and a silicon oxide film may be used as the second protective film. At this time, a silicon nitride film in which the atomic ratio of silicon to nitrogen is close to 3: 4 may be used as the first protective film as in the second embodiment.

  According to these embodiments and modifications thereof, it is possible to provide a liquid crystal display device that is excellent in reliability and light utilization efficiency.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Fabry-Perot type interference color filter layer (interference filter), 3 ... 1st reflection layer, 4 ... 2nd reflection layer, 5 ... Spacer layer, 6 ... Red filter, 7 ... Green filter , 8 ... Blue filter, 9 ... Thin film transistor array (TFT array), 10 ... Silicon nitride film, 11 ... Resist, 12 ... Silicon nitride film, 13 ... Resist, 14 ... Silicon nitride film, 15 ... Gate line, 16 ... Gate insulation Membrane, 17 ... pixel electrode, 18 ... thin film transistor, 19 ... signal line, 20 ... array substrate, 21 ... counter substrate, 22 ... liquid crystal layer, 25 ... glass substrate, 26 ... red filter, 27 ... green filter, 28 ... blue filter , 29 ... Common electrode, 30 ... First polarizing plate, 31 ... Second polarizing plate, 32 ... Absorption filter, 40 ... Backlight unit, 41 ... Light guide plate, 42 ... Reflecting plate, 43 Light emitting diode, 44 ... groove, 50 ... red light, 51 ... green light, 101 ... silicon oxide film, 102 ... silicon oxide film.

Claims (8)

A first reflective layer;
A second reflective layer;
A spacer layer disposed between the first reflective layer and the second reflective layer;
A liquid crystal display device comprising a Fabry-Perot interference filter having
The spacer layer is at least
A first region in which the first layer, the second layer, and the third layer are stacked;
A second region in which the second layer and the third layer are laminated;
A third region in which the third layer is provided;
Have
A protective film is further provided between at least one of the first layer and the second layer and between the second layer and the third layer. Liquid crystal display device.   The liquid crystal display device according to claim 1, wherein the protective film is a silicon oxide film. The first layer, the second layer, and the third layer include silicon nitride,
The protective film is made of silicon nitride in which the atomic ratio of silicon to nitrogen is closer to 3: 4 than silicon nitride contained in the first layer, the second layer, and the third layer. A silicon nitride film containing,
The liquid crystal display device according to claim 1. The first layer, the second layer, and the third layer include silicon nitride,
The protective film includes a first protective film provided between the first layer and the second layer, and a second provided between the second layer and the third layer. Including a protective film,
The first protective film is a silicon oxide film;
In the second protective film, the atomic ratio of silicon and nitrogen is closer to 3: 4 than silicon nitride contained in the first layer, the second layer, and the third layer. A silicon nitride film containing silicon nitride,
The liquid crystal display device according to claim 1. The first layer, the second layer, and the third layer include silicon nitride,
The protective film includes a first protective film provided between the first layer and the second layer, and a second provided between the second layer and the third layer. Including a protective film,
In the first protective film, the atomic ratio of silicon and nitrogen is closer to 3: 4 than silicon nitride contained in the first layer, the second layer, and the third layer. A silicon nitride film containing silicon nitride,
The second protective film is a silicon oxide film;
The liquid crystal display device according to claim 1.   2. The liquid crystal display device according to claim 1, wherein the protective film is a silicon oxynitride film.   The liquid crystal display device according to claim 1, wherein the protective film has a thickness of 1 nm to 20 nm.   The first layer, the second layer, and the third layer include silicon nitride having a composition in which an atomic ratio of silicon to nitrogen is greater than 3: 4. Item 8. The liquid crystal display device according to any one of Items 1 to 7.

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