Patent Publication Number: US-9412334-B2

Title: Liquid crystal display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/357,196 filed Jan. 24, 2012, and is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2011-158425, filed Jul. 19, 2011, the entire contents of each of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a liquid crystal display device. 
     BACKGROUND 
     In recent years, flat-panel display devices have been vigorously developed. By virtue of such advantageous features as light weight, small thickness and low power consumption, special attention has been paid to liquid crystal display devices among others. In particular, in active matrix liquid crystal devices in which thin-film transistors (TFTs) are incorporated in respective pixels as switching elements, there is known such a configuration that a transmissive liquid crystal display panel and a backlight are combined. 
     In a structure wherein a top-gate-type polysilicon TFT including a polysilicon semiconductor layer is applied as a switching element, a problem arises with an increase of OFF current due to an increase in luminance of a backlight. Specifically, a drain current of a TFT increases by the absorption of backlight in the polysilicon semiconductor layer. The increase in drain current conspicuously occurs in the state in which the TFT is in the OFF state, and such a drain current is called “photo-leakage current”. In recent years, to meet a demand for a higher luminance of the screen, there is a tendency to increase the luminance of backlight. Consequently, there is concern that the display quality is adversely affected by, e.g. crosstalk or flicker due to the increase in photo-leakage current. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view which schematically illustrates a structure of a liquid crystal display device according to an embodiment. 
         FIG. 2  is a view which schematically illustrates a structure and an equivalent circuit of a liquid crystal display panel shown in  FIG. 1 . 
         FIG. 3  is a view which schematically shows a cross-sectional structure of the liquid crystal display panel shown in  FIG. 2 . 
         FIG. 4  is a cross-sectional view which schematically shows a dielectric film multilayer with a 5-layer structure, which constitutes a first color filter, a second color filter and a third color filter. 
         FIG. 5  is a cross-sectional view which schematically shows a dielectric film multilayer with a 7-layer structure, which constitutes the first color filter, second color filter and third color filter. 
         FIG. 6  is a cross-sectional view which schematically shows a dielectric film multilayer with a 9-layer structure, which constitutes the first color filter, second color filter and third color filter. 
         FIG. 7  is a graph showing an example of a relationship between a light emission spectrum of a backlight and reflection spectra of color filters of the embodiment. 
         FIG. 8  is a graph showing a relationship between a photo-leakage amount in a switching element of each of pixels and the number of layers of the dielectric film multilayer. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, a liquid crystal display device includes an array substrate including a first color filter configured to transmit light in a first wavelength range; a second color filter configured to transmit light in a second wavelength range of greater wavelengths than the first wavelength range; a first switching element disposed above the second color filter; a second switching element disposed above the second color filter; a first pixel electrode which is electrically connected to the first switching element and is located above the first color filter; and a second pixel electrode which is electrically connected to the second switching element and is located above the second color filter. 
     According to another embodiment, a liquid crystal display device includes an array substrate including an insulative substrate; a first semi-transmissive layer disposed on the insulative substrate; a first transmissive layer with a first film thickness, a second transmissive layer with a second film thickness which is different from the first film thickness, and a third transmissive layer with a third film thickness which is different from the first film thickness and the second film thickness, the first transmissive layer, the second transmissive layer and the third transmissive layer being disposed on the first semi-transmissive layer; a second semi-transmissive layer disposed on the first transmissive layer to constitute a first color filter configured to transmit light in a first wavelength range, disposed on the second transmissive layer to constitute a second color filter configured to transmit light in a second wavelength range of greater wavelengths than the first wavelength range, and disposed on the third transmissive layer to constitute a third color filter configured to transmit light in a third wavelength range of greater wavelengths than the second wavelength range; a first switching element, a second switching element and a third switching element, which are disposed on the second semi-transmissive layer which constitutes the second color filter or the third color filter; a first pixel electrode which is electrically connected to the first switching element and is located above the first color filter; a second pixel electrode which is electrically connected to the second switching element and is located above the second color filter; and a third pixel electrode which is electrically connected to the third switching element and is located above the third color filter. 
     According to another embodiment, a liquid crystal display device includes an array substrate including an insulative substrate, a dielectric film multilayer formed on the insulative substrate and configured to reflect light of a blue wavelength to the insulative substrate side, a top-gate-type thin-film transistor including a silicon semiconductor layer disposed on the dielectric film multilayer, and a pixel electrode electrically connected to the thin-film transistor; a counter-substrate disposed to be opposed to the array substrate; and a liquid crystal layer held between the array substrate and the counter-substrate. 
     Embodiments will now be described in detail with reference to the accompanying drawings. In the drawings, structural elements having the same or similar functions are denoted by like reference numerals, and an overlapping description is omitted. 
       FIG. 1  is a view which schematically illustrates a structure of a liquid crystal display device according to an embodiment. 
     Specifically, the liquid crystal display device  1  includes an active-matrix-type transmissive liquid crystal display panel LPN, a driving IC chip  2  and a flexible wiring board  3  which are connected to the liquid crystal display panel LPN, and a backlight  4  which illuminates the liquid crystal display panel LPN. 
     The liquid crystal display panel LPN includes an array substrate AR, a counter-substrate CT which is disposed to be opposed to the array substrate AR, and a liquid crystal layer which is held between the array substrate AR and the counter-substrate CT. The liquid crystal display panel LPN includes an active area ACT which displays an image. The active area ACT is composed of a plurality of pixels PX which are arrayed in a matrix of m×n (m and n are positive integers). 
     The backlight  4  is disposed on the back side of the array substrate AR. As the backlight  4 , use may be made of either a backlight including a light-emitting diode (LED) as a light source, or a backlight including a cold cathode fluorescent lamp (CCFL) as a light source. A description of the detailed structure of the backlight  4  is omitted. 
       FIG. 2  is a view which schematically shows a structure and an equivalent circuit of the liquid crystal display panel LPN shown in  FIG. 1 . 
     The array substrate AR includes, in the active area ACT, a plurality of gate lines G (G 1  to Gn), a plurality of storage capacitance lines C (C 1  to Cn), and a plurality of source lines S (S 1  to Sm). Each of the gate lines G is led out of the active area ACT and is connected to a gate driver GD. Each of the source lines S is led out of the active area ACT and is connected to a source driver SD. 
     Each of the pixels PX includes a switching element SW, a pixel electrode PE and a counter-electrode CE. The switching element SW is electrically connected to the gate line G and source line S. The pixel electrode PE is electrically connected to the switching element SW. The counter-electrode CE is formed common to plural pixel electrodes PE via a liquid crystal layer LQ. The counter-electrode CE is electrically connected to a power supply module VS. 
     In the present embodiment, the switching element SW and pixel electrodes PE are provided on the array substrate AR. On the other hand, the counter-electrode CE may be provided on the array substrate AR, or on the counter-substrate CT. In the liquid crystal display panel LPN that is configured such that the counter-electrode CE, as well as the pixel electrodes PE, is disposed on the array substrate AR, liquid crystal molecules, which constitute the liquid crystal layer LQ, are switched by mainly using a lateral electric field which is produced between the pixel electrodes PE and the counter-electrode CE. In the liquid crystal display panel LPN that is configured such that the counter-electrode CE is disposed on the counter-substrate CT, the liquid crystal molecules, which constitute the liquid crystal layer LQ, are switched by mainly using a vertical electric field or an oblique electric field, which is produced between the pixel electrodes PE and the counter-electrode CE. 
       FIG. 3  is a view which schematically shows a cross-sectional structure of the liquid crystal display panel LPN shown in  FIG. 2 .  FIG. 3  shows cross-sectional structures of a first pixel PX 1  which displays blue, a second pixel PX 2  which displays green, and a third pixel PX 3  which displays red. 
     Specifically, the first pixel PX 1  includes a first color filter CF 1 , a first switching element SW 1  and a first pixel electrode PE 1 . The second pixel PX 2  includes a second color filter CF 2 , a second switching element SW 2  and a second pixel electrode PE 2 . The third pixel PX 3  includes a third color filter CF 3 , a third switching element SW 3  and a third pixel electrode PE 3 . 
     The array substrate AR is formed by using a first insulative substrate  10  with light transmissivity, such as a glass substrate. The first color filter CF 1 , second color filter CF 2  and third color filter CF 3  are disposed on the first insulative substrate  10 . The first color filter CF 1  transmits light of a first wavelength range (e.g. wavelength range of 400 nm to 500 nm) which is a blue wavelength range. The second color filter CF 2  transmits light of a second wavelength range (e.g. wavelength range of 500 nm to 580 nm) which is a green wavelength range and is a range of greater wavelengths than the first wavelength range. The third color filter CF 3  transmits light of a third wavelength range (e.g. wavelength range of 580 nm to 700 nm) which is a red wavelength range and is a range of greater wavelengths than the second wavelength range. 
     The first color filter CF 1 , second color filter CF 2  and third color filter CF 3  mainly reflect light of wavelengths, which are other than the light of wavelengths that is transmitted. The first color filter CF 1  has a higher reflectance in the second wavelength range and the third wavelength range than in the first wavelength range. The second color filter CF 2  has a higher reflectance in the first wavelength range and the third wavelength range than in the second wavelength range. The third color filter CF 3  has a higher reflectance in the first wavelength range and the second wavelength range than in the third wavelength range. 
     As will be described later in detail, the backlight  4 , which is applied to the embodiment, has a light emission spectrum having a light emission peak (about 450 nm) in the first wavelength range. The second color filter CF 2  and third color filter CF 3  have such reflectance characteristics that the reflectance in the neighborhood of 450 nm, which is the light emission peak of the backlight  4 , is higher than the reflectance in the second wavelength range and third wavelength range. 
     In the example illustrated, the first color filter CF 1  is disposed in accordance with the first pixel PX 1 , except under the first switching element SW 1 . The second color filter CF 2  is disposed in accordance with the second pixel PX 2 , except under the second switching element SW 2 . The third color filter CF 3  is disposed in accordance with the third pixel PX 3 . In addition, the third color filter CF 3  is also disposed under the first switching element SW 1 , second switching element SW 2  and third switching element SW 3 . In the example illustrated, the third color filter CF 3  is applied as the underlayer of the first switching element SW 1 , second switching element SW 2  and third switching element SW 3 . Alternatively, the second color filter CF 2 , which reflects light of the first wavelength range, may be applied. 
     As the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 , light-absorption-type filters (e.g. filters formed of colored resins) may be used. In the example illustrated, however, Fabry-Ferot-type filters, which make use of the principle of optical interference, are adopted. Specifically, the first color filter CF 1 , second color filter CF 2  and third color filter CF 3  are formed by stacking a plurality of thin films with different refractive indices, and include a first semi-transmissive layer  31  which is disposed on an inner surface  10 A of the first insulative substrate  10 , a second semi-transmissive layer  32  which is opposed to the first semi-transmissive layer  31 , and a transmissive layer (or a spacer layer)  33  which is disposed between the first semi-transmissive layer  31  and the second semi-transmissive layer  32 . 
     To be more specific, the first semi-transmissive layer  31  and the second semi-transmissive layer  32  are provided common to the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 . Each of the first semi-transmissive layer  31  and the second semi-transmissive layer  32  may be a metal thin film formed of, silver (Ag) with a thickness on the several-ten nm order, or may be a multilayer structure in which a plurality of dielectric films with different refractive indices are stacked. For example, each of the first semi-transmissive layer  31  and the second semi-transmissive layer  32  can be formed by a multilayer in which a silicon nitride (SiN) layer and a silicon oxide (SiO 2 ) layer are alternately stacked. The number of stacked dielectric films of the multiplayer is two or more. However, as the number of layers increases, the number of fabrication steps increases and the manufacturing cost increases. It is thus desirable that the number of layers be set at four or less. 
     The transmissive layer  33  is a single dielectric film, and can be formed of a silicon nitride layer or a silicon oxide layer. The transmissive layer  33  includes a first transmissive layer  331 , a second transmissive layer  332  and a third transmissive layer  333 , which have different film thicknesses. 
     The first color filter CF 1  includes the first transmissive layer  331  with a first film thickness T 1 , as the transmissive layer  33  disposed between the first semi-transmissive layer  31  and second semi-transmissive layer  32 . The second color filter CF 2  includes the second transmissive layer  332  with a second film thickness T 2 , which is different from the first film thickness T 1 , as the transmissive layer  33  disposed between the first semi-transmissive layer  31  and second semi-transmissive layer  32 . The third color filter CF 3  includes the third transmissive layer  333  with a third film thickness T 3 , which is different from the first film thickness T 1  and second film thickness T 2 , as the transmissive layer  33  disposed between the first semi-transmissive layer  31  and second semi-transmissive layer  32 . The first transmissive layer  331 , second transmissive layer  332  and third transmissive layer  333 , although having different film thicknesses, are mutually continuous. In the example illustrated, the second film thickness T 2  is greater than the first film thickness T 2 , and the third film thickness T 3  is less than the first film thickness T 1 . 
     The first switching element SW 1 , second switching element SW 2  and third switching element SW 3  are all composed of top-gate-type thin-film transistors (TFTs), and have substantially the same structure. In the description below, the first switching element SW 1  is described more concretely, and a description of the structure of each of the second switching element SW 2  and third switching element SW 3  is omitted. 
     Specifically, the first switching element SW 1  includes a semiconductor layer SC which is disposed on the third color filter CF 3  (strictly speaking, on the second semi-transmissive layer  32 ). The silicon semiconductor layer is formed of polysilicon, but there may be a case in which the silicon semiconductor layer is formed of amorphous silicon. The silicon semiconductor layer SC is covered with a first insulation film  11 . The first insulation film  11  covers the first color filter CF 1 , second color filter CF 2 , and third color filter CF 3 . 
     A gate electrode WG of the first switching element SW 1  is formed on the first insulation film  11  and is located immediately above the silicon semiconductor layer SC. The gate electrode WG is electrically connected to the gate line and is covered with a second insulation film  12 . The second insulation film  12  is also disposed on the first insulation film  11 . 
     A source electrode WS and a drain electrode WD of the first switching element SW 1  are formed on the second insulation film  12 . The source electrode WS is electrically connected to the source line. The source electrode WS and drain electrode WD are put in contact with the silicon semiconductor layer SC via contact holes which penetrate the first insulation film  11  and second insulation film  12 . 
     The first switching element SW 1  having the above-described structure is covered with a third insulation film  13 . Similarly, the second switching element SW 2  and third switching element SW 3  are covered with the third insulation film  13 . The third insulation film  13  is also disposed on the second insulation film  12 . 
     The first pixel electrode PE 1  is formed on the third insulation film  13  and is located above the first color filter CF 1 . The first pixel electrode PE 1  is electrically connected to the drain electrode WD of the first switching element SW 1  via a contact hole which penetrates the third insulation film  13 . 
     Similarly, the second pixel electrode PE 2  is formed on the third insulation film  13  and is located above the second color filter CF 2 . The second pixel electrode PE 2  is electrically connected to the drain electrode WD of the second switching element SW 2 . In addition, similarly, the third pixel electrode PE 3  is formed on the third insulation film  13  and is located above the third color filter CF 3 , and is electrically connected to the drain electrode WD of the third switching element SW 3 . 
     The first pixel electrode PE 1 , second pixel electrode PE 2  and third pixel electrode PE 3  are formed of a light-transmissive, electrically conductive material, such as indium tin oxide (ITO) or indium zinc oxide (IZO). These first pixel electrode PE 1 , second pixel electrode PE 2  and third pixel electrode PE 3  are covered with a first alignment film AL 1 . 
     The counter-substrate CT is formed by using a second insulative substrate  20  having light transmissivity, such as a glass substrate. The counter-substrate CT includes a black matrix BM on an inner surface  20 A of the second insulative substrate  20 , which is opposed to the array substrate AR. The black matrix BM is formed so as to be opposed to the first switching element SW 1 , second switching element SW 2  and third switching element SW 3 , and wiring parts such as source lines, gate lines, and storage capacitance lines. 
     In the example illustrated, the counter-substrate CT includes a first color layer CF 11 , a second color layer CF 12  and a third color layer CF 13  on the inner surface  20 A of the second insulative substrate  20 , but the first color layer CF 11 , second color layer CF 12  and third color layer CF 13  may be dispensed with. The first color layer CF 11  is formed of a color resin (e.g. blue resin) which transmits light of the first wavelength range. The second color layer CF 12  is formed of a color resin (e.g. green resin) which transmits light of the second wavelength range. The third color layer CF 13  is formed of a color resin (e.g. red resin) which transmits light of the third wavelength range. 
     In addition, in the example illustrated, the counter-electrode CT includes the counter-electrode CE on those surfaces of the first color layer CF 11 , second color layer CF 12  and third color layer CF 13 , which are opposed to the array substrate AR. The counter-electrode CE, as described above, may be provided on the array substrate AR. The counter-electrode CE is formed of a light-transmissive, electrically conductive material, such as ITO or IZO. That surface of the counter-electrode CT, which is opposed to the array substrate AR, is covered with a second alignment film AL 2 . 
     The above-described array substrate AR and counter-substrate CT are disposed such that their first alignment film AL 1  and second alignment film AL 2  are opposed to each other. In this case, a predetermined cell gap, for example, a cell gap of 2 to 7 μm, is created between the array substrate AR and the counter-substrate CT by columnar spacers which are formed of, e.g. a resin material so as to be integral to one of the array substrate AR and counter-substrate CT. The liquid crystal layer LQ is held in the cell gap which is created between the array substrate AR and the counter-substrate CT, and is disposed between the first alignment film AL 1  and second alignment film AL 2 . 
     A first optical element OD 1 , which includes, e.g. a first polarizer PL 1 , is disposed on an outer surface  10 B of the first insulative substrate  10  which constitutes the array substrate AR. The first optical element OD 1  is located on that side of the liquid crystal display panel LPN, which is opposed to the backlight  4 , and controls the polarization state of incident light which enters the liquid crystal display panel LPN from the backlight  4 . A second optical element OD 2 , which includes, e.g. a second polarizer PL 2 , is disposed on an outer surface  20 B of the second insulative substrate  20  which constitutes the counter-substrate CT. The second optical element OD 2  is located on the display surface side of the liquid crystal display panel LPN, and controls the polarization state of emission light emerging from the liquid crystal display panel LPN. 
     According to the above-described structure, when light emitted from the backlight  4  has passed through the liquid crystal display panel LPN, transmissive light traveling through the first pixel electrode PE 1  via the first color filter CF 1  is colored in blue (B), transmissive light traveling through the second pixel electrode PE 2  via the second color filter CF 2  is colored in green (G), and transmissive light traveling through the third pixel electrode PE 3  via the third color filter CF 3  is colored in red (R). That part of the light, which has not passed through the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 , is almost entirely reflected, sent back to the backlight  4 , and re-used. Specifically, the backlight  4  has a high-reflectance surface which covers the light source, etc, and the reflective light reflected toward the backlight  4  is then reflected once again toward the liquid crystal display panel LPN, with little light loss at the high-reflectance surface. Thus, the reflective light from the first color filter CF 1 , second color filter CF 2  and third color filter CF 3  is re-used, and the efficiency of use of light is improved. 
     Next, more concrete structure examples of the first color filter CF 1 , second color filter CF 2  and third color filter CF 3  are described. 
       FIG. 4  is a cross-sectional view which schematically shows a dielectric film multilayer  41  with a 5-layer structure, which constitutes the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 . 
     Specifically, the dielectric film multilayer  41  is composed of a first silicon nitride layer  311  which is disposed on the inner surface  10 A of the first insulative substrate  10 ; a first silicon oxide layer  312  stacked on the first silicon nitride layer  311 ; a second silicon nitride layer  33  stacked on the first silicon oxide layer  312 ; a second silicon oxide layer  321  stacked on the second silicon nitride layer  33 ; and a third silicon nitride layer  322  stacked on the second silicon oxide layer  321 . 
     The first silicon nitride layer  311  and first silicon oxide layer  312  function as the first semi-transmissive layer  31 . The second silicon nitride layer  33  functions as the transmissive layer  33 . The second silicon oxide layer  321  and third silicon nitride layer  322  function as the second semi-transmissive layer  32 . Specifically, each of the first semi-transmissive layer  31  and second semi-transmissive layer  32  is a dielectric multilayer of two layers. 
     The first insulative substrate  10  is a glass substrate, and the refractive index thereof in the visible light wavelength range is about 1.5. The first silicon nitride layer  311 , second silicon nitride layer  33  and third silicon nitride layer  322  are formed of, e.g. SiN, and the refractive index thereof in the visible light wavelength range is about 2.0 to 2.7. Specifically, the first silicon nitride layer  311 , second silicon nitride layer  33  and third silicon nitride layer  322  function as high-refractive-index layers having a higher refractive index than the first insulative substrate  10 . The first silicon oxide layer  312  and second silicon oxide layer  321  are formed of, e.g. SiO 2 , and the refractive index thereof in the visible light wavelength range is about 1.5. Specifically, the first silicon oxide layer  312  and second silicon oxide layer  321  function as low-refractive-index layers having a lower refractive index than the high-refractive-index layers. 
     The first silicon nitride layer  311  and third silicon nitride layer  322  have the same thickness, for example, 60 nm, in each of the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 . The first silicon oxide layer  312  and second silicon oxide layer  321  have the same thickness, for example, 90 nm, in each of the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 . Specifically, the low-refractive-index layers, which constitute the first semi-transmissive layer  31  and second semi-transmissive layer  32 , are thicker than the high-refractive-index layers. 
     The second silicon nitride layer  33  has different film thicknesses in the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 , respectively. For example, the thickness of the second silicon nitride layer  33  in the first color filter CF 1  is about 85 nm, the thickness of the second silicon nitride layer  33  in the second color filter CF 2  is about 115 nm, and the thickness of the second silicon nitride layer  33  in the third color filter CF 3  is about 150 nm. 
     The first color filter CF 1 , which is composed of the dielectric film multilayer  41  having the above-described structure, has a transmittance peak in the neighborhood of 470 nm, and has a reflectance bottom in the neighborhood of the same wavelength. Similarly, the second color filter CF 2  has a transmittance peak in the neighborhood of 540 nm, and has a reflectance bottom in the neighborhood of the same wavelength. Likewise, the third color filter CF 3  has a transmittance peak in the neighborhood of 610 nm, and has a reflectance bottom in the neighborhood of the same wavelength, while having a high reflectance in the wavelength range other than this wavelength. 
     The third silicon nitride layer  322  of the second color filter CF 2  or third color filter CF 3  serves as an underlayer of the silicon semiconductor layer. The silicon semiconductor layer has a high light absorption coefficient at short wavelengths. On the other hand, the backlight, which is combined with the liquid crystal display panel, has such a light emission spectrum that the light intensity at relatively short wavelengths is high. As described above, since the second color filter CF 2  or third color filter CF 3 , which is disposed under the silicon semiconductor layer, has a relatively high reflectance in the wavelength range of short wavelengths, this second color filter CF 2  or third color filter CF 3  can suppress light absorption in the silicon semiconductor layer. Accordingly, in the switching element including this silicon semiconductor layer, photo-leakage current can be reduced. Thereby, the occurrence of crosstalk or flicker can be suppressed, and a liquid crystal display device with a good display quality can be provided. 
       FIG. 5  is a cross-sectional view which schematically shows a dielectric film multilayer  42  with a 7-layer structure, which constitutes the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 . 
     Specifically, the dielectric film multilayer  42  is composed of a first silicon nitride layer  311  which is disposed on the inner surface  10 A of the first insulative substrate  10 ; a first silicon oxide layer  312  stacked on the first silicon nitride layer  311 ; a second silicon nitride layer  313  stacked on the first silicon oxide layer  312 ; a second silicon oxide layer  33  stacked on the second silicon nitride layer  313 ; a third silicon nitride layer  321  stacked on the second silicon oxide layer  33 ; a third silicon oxide layer  322  stacked on the third silicon nitride layer  321 ; and a fourth silicon nitride layer  323  stacked on the third silicon oxide layer  322 . 
     The first silicon nitride layer  311 , first silicon oxide layer  312  and second silicon nitride layer  313  function as the first semi-transmissive layer  31 . The second silicon oxide layer  33  functions as the transmissive layer  33 . The third silicon nitride layer  321 , third silicon oxide layer  322  and fourth silicon nitride layer  323  function as the second semi-transmissive layer  32 . Specifically, each of the first semi-transmissive layer  31  and second semi-transmissive layer  32  is a dielectric multilayer of three layers. 
     The first silicon nitride layer  311 , second silicon nitride layer  313 , third silicon nitride layer  321  and fourth silicon nitride layer  323  are formed of, e.g. SiN, and function as high-refractive-index layers (the refractive index in the visible light wavelength range is about 2.0 to 2.7). The first silicon oxide layer  312 , second silicon oxide layer  33  and third silicon oxide layer  322  are formed of, e.g. SiO 2 , and function as low-refractive-index layers (the refractive index in the visible light wavelength range is about 1.5). 
     The first silicon nitride layer  311 , second silicon nitride layer  313 , third silicon nitride layer  321  and fourth silicon nitride layer  323  have the same thickness, for example, 60 nm, in each of the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 . The first silicon oxide layer  312  and third silicon oxide layer  322  have the same thickness, for example, 90 nm, in each of the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 . 
     The second silicon oxide layer  33  has different film thicknesses in the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 , respectively. For example, the thickness of the second silicon oxide layer  33  in the first color filter CF 1  is about 130 nm, the thickness of the second silicon oxide layer  33  in the second color filter CF 2  is about 180 nm, and the thickness of the second silicon oxide layer  33  in the third color filter CF 3  is about 30 nm. 
     The fourth silicon nitride layer  323  of the second color filter CF 2  or third color filter CF 3  serves as an underlayer of the silicon semiconductor layer. 
     The first color filter CF 1 , which is formed of the dielectric film multilayer  42  having the above-described structure, has a transmittance peak and a reflectance bottom in the neighborhood of 470 nm. In addition, in this first color filter CF 1 , compared to the first color filer CF 1  that is formed of the dielectric film multilayer  41 , the wavelength range in the neighborhood of the transmittance peak and reflectance bottom becomes narrower, and the wavelength range of a high reflectance becomes wider. Similarly, the second color filter CF 2 , which is formed of the dielectric film multilayer  42 , has a transmittance peak and a reflectance bottom in the neighborhood of 540 nm. In addition, in this second color filter CF 2 , compared to the second color filer CF 2  that is formed of the dielectric film multilayer  41 , the wavelength range in the neighborhood of the transmittance peak and reflectance bottom becomes narrower, and the wavelength range of a high reflectance becomes wider. Likewise, the third color filter CF 3 , which is formed of the dielectric film multilayer  42 , has a transmittance peak and a reflectance bottom in the neighborhood of 610 nm. In addition, in this third color filter CF 3 , compared to the third color filer CF 3  that is formed of the dielectric film multilayer  41 , the wavelength range in the neighborhood of the transmittance peak and reflectance bottom becomes narrower, and the wavelength range of a high reflectance becomes wider. 
     As has been described above, by increasing the number of layers of the dielectric film multilayer, the wavelength range in the neighborhood of the transmittance peak becomes narrower. Therefore, the color purity of each of the first color filter CF 1 , second color filter CF 2  and third color filter CF 3  can be improved. In addition, since the wavelength range of the high reflectance of the second color filter CF 2  or third color filter CF 3 , which is disposed under the silicon semiconductor layer, becomes wider, this second color filter CF 2  or third color filter CF 3  can further suppress light absorption in the silicon semiconductor layer. Thus, a liquid crystal display device with a good display quality can be provided. 
       FIG. 6  is a cross-sectional view which schematically shows a dielectric film multilayer  43  with a 9-layer structure, which constitutes the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 . 
     Specifically, the dielectric film multilayer  43  is composed of a first silicon nitride layer  311  which is disposed on the inner surface  10 A of the first insulative substrate  10 ; a first silicon oxide layer  312  stacked on the first silicon nitride layer  311 ; a second silicon nitride layer  313  stacked on the first silicon oxide layer  312 ; a second silicon oxide layer  314  stacked on the second silicon nitride layer  313 ; a third silicon nitride layer  33  stacked on the second silicon oxide layer  314 ; a third silicon oxide layer  321  stacked on the third silicon nitride layer  33 ; a fourth silicon nitride layer  322  stacked on the third silicon oxide layer  321 ; a fourth silicon oxide layer  323  stacked on the fourth silicon nitride layer  322 ; and a fifth silicon nitride layer  324  stacked on the fourth silicon oxide layer  323 . 
     The first silicon nitride layer  311 , first silicon oxide layer  312 , second silicon nitride layer  313  and second silicon oxide layer  314  function as the first semi-transmissive layer  31 . The third silicon nitride layer  33  functions as the transmissive layer  33 . The third silicon oxide layer  321 , fourth silicon nitride layer  322 , fourth silicon oxide layer  323  and fifth silicon nitride layer  324  function as the second semi-transmissive layer  32 . Specifically, each of the first semi-transmissive layer  31  and second semi-transmissive layer  32  is a dielectric multilayer of four layers. 
     The first silicon nitride layer  311 , second silicon nitride layer  313 , third silicon nitride layer  33 , fourth silicon nitride layer  322  and fifth silicon nitride layer  324  are formed of, e.g. SiN, and function as high-refractive-index layers (the refractive index in the visible light wavelength range is about 2.0 to 2.7). The first silicon oxide layer  312 , second silicon oxide layer  314 , third silicon oxide layer  321  and fourth silicon oxide layer  323  are formed of, e.g. SiO 2 , and function as low-refractive-index layers (the refractive index in the visible light wavelength range is about 1.5). 
     The first silicon nitride layer  311 , second silicon nitride layer  313 , fourth silicon nitride layer  322  and fifth silicon nitride layer  324  have the same thickness, for example, 60 nm, in each of the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 . The first silicon oxide layer  312 , second silicon oxide layer  314 , third silicon oxide layer  321  and fourth silicon oxide layer  323  have the same thickness, for example, 90 nm, in each of the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 . 
     The third silicon nitride layer  33  has different film thicknesses in the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 , respectively. For example, the thickness of the third silicon nitride layer  33  in the first color filter CF 1  is about 80 nm, the thickness of the third silicon nitride layer  33  in the second color filter CF 2  is about 115 nm, and the thickness of the third silicon nitride layer  33  in the third color filter CF 3  is about 30 nm. 
     The fifth silicon nitride layer  324  of the second color filter CF 2  or third color filter CF 3  serves as an underlayer of the silicon semiconductor layer. 
     The first color filter CF 1 , which is formed of the dielectric film multilayer  43  having the above-described structure, has a transmittance peak and a reflectance bottom in the neighborhood of 470 nm. In addition, in this first color filter CF 1 , compared to the first color filer CF 1  that is formed of the dielectric film multilayer  42 , the wavelength range in the neighborhood of the transmittance peak and reflectance bottom becomes narrower, and the wavelength range of a high reflectance becomes wider. Similarly, the second color filter CF 2 , which is formed of the dielectric film multilayer  43 , has a transmittance peak and a reflectance bottom in the neighborhood of 540 nm. In addition, in this second color filter CF 2 , compared to the second color filer CF 2  that is formed of the dielectric film multilayer  42 , the wavelength range in the neighborhood of the transmittance peak and reflectance bottom becomes narrower, and the wavelength range of a high reflectance becomes wider. Likewise, the third color filter CF 3 , which is formed of the dielectric film multilayer  43 , has a transmittance peak and a reflectance bottom in the neighborhood of 610 nm. In addition, in this third color filter CF 3 , compared to the third color filer CF 3  that is formed of the dielectric film multilayer  42 , the wavelength range in the neighborhood of the transmittance peak and reflectance bottom becomes narrower, and the wavelength range of a high reflectance becomes wider. 
     Thus, the color purity of each of the first color filter CF 1 , second color filter CF 2  and third color filter CF 3  can further be improved. In addition, the light absorption in the silicon semiconductor layer can further be suppressed. Therefore, a liquid crystal display device with a good display quality can be provided. 
     In the meantime, the position of the reflectance bottom of the reflection spectrum or the position of the transmittance peak of the transmission spectrum, in each of the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 , can be adjusted by varying the film thickness of the transmissive layer  33 . The number of layers and the thickness of the transmissive layer can be determined, while taking into account the capabilities which are required in the first color filter CF 1 , second color filter CF 2  and third color filter CF 3 , and the photo-leakage resistance. 
       FIG. 7  is a graph showing an example of the relationship between the light emission spectrum of the backlight  4  and the reflection spectra of the color filters of the embodiment. In  FIG. 7 , the abscissa indicates wavelength (nm) and the ordinate indicates the light intensity of the backlight  4  and the reflectance of the color filter. The light intensity and the reflectance are relative values in the case where the maximum value is set at 1. 
     The reflection spectra of the color filters, which are shown in  FIG. 7 , were obtained by calculating the reflectance on the first insulative substrate  10  side of the incident light from the first insulative substrate  10 , with respect to a model which is fabricated in the following manner. A third color filter CF 3  is disposed on the first insulative substrate. A polysilicon semiconductor layer with a thickness of 50 nm of a switching element is disposed on the third color filter CF 3 . This polysilicon semiconductor layer is covered with a first insulation film (gate insulation film)  11  with a thickness of 80 nm, which is formed of silicon oxide (SiO). A gate electrode with a thickness of 300 nm, which is formed of molybdenum (Mo), is disposed on the first insulation film. 
     In  FIG. 7 , “BL intensity” is a light emission spectrum of the backlight  4 .  FIG. 7  shows reflection spectra in a case (corresponding to “TFT on 5-layer CF 3 ” in  FIG. 7 ) where the dielectric film multilayer  41  of the 5-layer structure shown in  FIG. 4  was applied to the structure of the third color filter CF 3 , a case where (“TFT on 7-layer CF 3 ”) where the dielectric film multilayer  42  of the 7-layer structure shown in  FIG. 5  was applied to the structure of the third color filter CF 3 , and a case where (“TFT on 9-layer CF 3 ”) where the dielectric film multilayer  43  of the 9-layer structure shown in  FIG. 6  was applied to the structure of the third color filter CF 3 .  FIG. 7  shows, as a comparative example, a reflection spectrum in a case (corresponding to “TFT/UC” in  FIG. 7 ) where only an undercoat layer (SiN/SiO), in place of the third color filter, was disposed under the switching element. 
     As shown in  FIG. 7 , the light emission spectrum of the backlight  4  has a light emission peak in the neighborhood of 450 nm. By contrast, in the reflection spectrum of “TFT/UC” of the comparative example, it is understood that the reflectance at the wavelength of 450 nm is very low. On the other hand, the reflectance spectrum of “TFT on 5-layer CF 3 ” of the embodiment has a reflectance of about 50% in the neighborhood of 450 nm. In addition, the reflectance spectrum of “TFT on 7-layer CF 3 ” has a reflectance of about 70% in the neighborhood of 450 nm. Besides, the reflectance spectrum of “TFT on 9-layer CF 3 ” has a reflectance of about 80% in the neighborhood of 450 nm. It was thus confirmed that the reflectance of light in the neighborhood of a specific wavelength (450 nm in this example) increases as the number of layers of the dielectric film multilayer becomes larger. 
     Although not illustrated, the inventor conducted similar calculations in the case where the second color filter CF 2  was disposed under the switching element, and confirmed that the reflectance of 50% or more was obtained in the neighborhood of 450 nm, and that the reflectance of light in the neighborhood of a specific wavelength increases as the number of layers of the dielectric film multilayer, which constitutes the second color filter CF 2 , becomes larger. 
       FIG. 8  is a graph showing the relationship between the photo-leakage amount in the switching element of each of pixels and the number of layers of the dielectric film multilayer. In  FIG. 8 , the abscissa indicates the number of layers of the dielectric film multilayer (third color filter CF 3 ) which is disposed under the switching element, and the ordinate indicates a ratio of a photo-leakage amount in the case where the photo-leakage amount at a time when only the undercoat layer (SiN/SiO), in place of the third color filter, was disposed under the switching element, is set at 1. 
     It was confirmed that the photo-leakage amount is about 65% when the switching element is disposed on the third color filter CF 3  which is composed of the dielectric film multilayer  41  of the 5-layer structure. It was confirmed that the photo-leakage amount is about 45% when the switching element is disposed on the third color filter CF 3  which is composed of the dielectric film multilayer  42  of the 7-layer structure. It was confirmed that the photo-leakage amount is about 40% when the switching element is disposed on the third color filter CF 3  which is composed of the dielectric film multilayer  43  of the 9-layer structure. 
     The SiN layers, which are used as high-refractive-index layers in the 5-layer structure, 7-layer structure and 9-layer structure, are formed by plasma CVD using SiH 4  and NH 3  as a principal material gas, under the condition that the in-film hydrogen amount may become 2×10 21  cm −3  or more. In order to obtain a film of a high refractive index, it can be thought that a silicon nitride (SiN) film is formed by, e.g. sputtering. In general, the in-film hydrogen amount in a SiN film that is formed by sputtering is very low. By using an SiN film containing hydrogen, the characteristics of a top-gate-type thin-film transistor, which serves a switching element, can be improved. For example, when polysilicon was used for the silicon semiconductor SC of the switching element, the threshold voltage of the thin-film transistor, in the case where the color filter layer was formed of a multiplayer of silicon nitride films and silicon oxide films formed by sputtering, was 5.0 V on average. On the other hand, the threshold voltage of the thin-film transistor, in the case where the color filter layer was formed of a multiplayer of silicon nitride films and silicon oxide films formed by plasma CVD with an in-film hydrogen amount of 2×10 21  cm −3  or more, decreased to 2.1 V. Thereby, the active matrix circuit can be driven with a low voltage, contributing to reduction in power consumption. 
     As has been described above, according to the present embodiment, a liquid crystal display device which has a good display quality can be provided. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.