Liquid crystal display device

Abstract

To provide a liquid crystal display device that can increase a transmissive display region without spoiling brightness of a reflective display and suppresses an increase in light leakage.SOLUTION: A liquid crystal display device 1 includes a backlight 3 and a liquid crystal panel 2. The liquid crystal panel 2 includes: a first substrate 21 provided above the backlight; a bottom-gate thin-film transistor 23 including a gate electrode 24 and provided on a surface of the first substrate; a first reflective film 30 provided above the thin-film transistor; a second reflective film 31 provided above the first reflective film; an insulating film 32 provided on the second reflective film; and a pixel electrode 33 provided on the insulating film. The first reflective film 30 has a lower light reflectance than the second reflective film 31.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a liquid crystal display device. [Background technology]

[0002] Semi-transmissive LCD technology has been gaining attention because it has both transmissive and reflective display areas, making the screen easier to see even in direct sunlight and improving outdoor visibility. For example, a semi-transmissive LCD device has a configuration that combines a transmissive LCD and a reflective LCD.

[0003] The simplest way to create a reflective LCD is to replace the transparent pixel electrodes of a conventional transmissive LCD with a material that has a high light reflectivity. However, this configuration means that the two electrodes facing each other across the liquid crystal layer are made of different materials, which results in different contact potentials with the liquid crystal layer, which can easily lead to problems such as burn-in of the liquid crystal, increased flicker, and corrosion of the electrodes.

[0004] Patent Document 1 exemplifies a reflective liquid crystal display device in which a light-reflecting film that reflects external light and a pixel electrode that applies voltage to a liquid crystal layer are separate layers separated by an insulating film, and the materials for the pixel electrode and the counter electrode can be made of ITO (Indium Tin Oxide) as in the past. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-79207 Summary of the Invention [Problem to be solved by the invention]

[0006] As a candidate material for the light-reflecting film, metals with a relatively high light reflectance, such as aluminum and silver, are preferable, and in reality, alloys containing aluminum as the main component are preferably used because of their hillock resistance and migration resistance.

[0007] Figure 10 is a cross-sectional view showing a part of the configuration of the reflective liquid crystal display device described in Patent Document 1. For the sake of explanation, different reference numerals are used in Figure 10 than in Patent Document 1. As shown in Figure 10, in the reflective liquid crystal display device described in Patent Document 1, a light-reflecting film 122 is arranged across an interlayer insulating film 121 so as to cover the top of a bottom-gate TFT (Thin Film Transistor) element 111, and a pixel electrode 124 is further arranged above the light-reflecting film 122 with an insulating film 123 in between. By adopting this configuration, the top of the TFT can be used as a light-reflecting section, which increases the area available for reflective display, thereby offering the advantage of enabling a brighter reflective display.

[0008] However, TFTs have the drawback that when light enters the channel, current leakage (hereinafter referred to as "light leakage") occurs, which causes the voltage applied to the liquid crystal layer to be insufficiently maintained, resulting in a decrease in display quality.

[0009] Consider, for example, a case where the configuration of FIG. 10 is applied to a transflective liquid crystal display device. An example of the configuration in this case is shown in FIG. 11. In the configuration of FIG. 11, external light incident from above the pixel electrode 124 is strongly reflected by the light-reflecting film 122, resulting in a relatively bright display. For example, if the light-reflecting film 122 is made of aluminum or an aluminum alloy, which is a metal film with a relatively high light reflectance, light is more strongly reflected in the viewing direction, resulting in a relatively bright display. On the other hand, because a metal film with a relatively high light reflectance is disposed above the channel, light from a backlight irradiated from below the TFT is more strongly reflected by the light-reflecting film 122 and enters the channel portion of the TFT, which may lead to increased light leakage.

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a liquid crystal display device that can expand the transmissive display area without spoiling the brightness of the reflective display, and that can suppress an increase in light leakage. [Means for solving the problem]

[0011] According to one aspect of the present invention, there is provided a liquid crystal display device comprising: a backlight; a first substrate provided above the backlight; a bottom-gate thin film transistor including a gate electrode and provided on a surface of the first substrate; a first reflective film provided above the thin film transistor; a second reflective film provided above the first reflective film; an insulating film provided on the second reflective film; and a pixel electrode provided on the insulating film, wherein the first reflective film has a lower light reflectance than the second reflective film.

[0012] According to another aspect of the present invention, there is provided a liquid crystal display device according to the above aspect, wherein the first reflective film faces the gate electrode in a first direction perpendicular to the surface of the first substrate.

[0013] According to yet another aspect of the present invention, there is provided a liquid crystal display device according to the above aspect, wherein the liquid crystal panel includes a plurality of pixels, each of the plurality of pixels includes a plurality of sub-pixels, and in each of the plurality of sub-pixels, the first reflective film has approximately the same area as the gate electrode in the first direction.

[0014] According to yet another aspect of the present invention, there is provided a liquid crystal display device according to the above aspect, wherein in each of the plurality of sub-pixels, the first reflective film has substantially the same shape as the gate electrode in the first direction.

[0015] According to yet another aspect of the present invention, there is provided a liquid crystal display device according to the above aspect, wherein, in each of the plurality of sub-pixels, the second reflective film has approximately the same area as the first reflective film in the first direction.

[0016] According to yet another aspect of the present invention, there is provided a liquid crystal display device according to the above aspect, wherein, in each of the plurality of sub-pixels, the second reflective film has substantially the same shape as the first reflective film in the first direction.

[0017] According to yet another aspect of the present invention, there is provided a liquid crystal display device according to any one of the above aspects, wherein the second reflective film contains aluminum or an alloy containing aluminum.

[0018] According to yet another aspect of the present invention, there is provided a liquid crystal display device according to the above aspect, wherein the first reflective film contains molybdenum or an alloy containing molybdenum.

[0019] According to yet another aspect of the present invention, there is provided a liquid crystal display device according to the above aspect, wherein the first reflective film contains chromium or an alloy containing chromium.

[0020] According to yet another aspect of the present invention, there is provided a liquid crystal display device according to the above aspect, wherein the first reflective film contains a resin.

[0021] According to yet another aspect of the present invention, there is provided a liquid crystal display device according to the above aspect, wherein the first reflective film has a thickness of 10 nm or more and 50 nm or less.

[0022] According to yet another aspect of the present invention, there is provided a liquid crystal display device according to the above aspect, wherein the first reflective film has a thickness of 30 nm or more.

[0023] According to yet another aspect of the present invention, there is provided a liquid crystal display device according to the above aspect, wherein the liquid crystal panel further includes a liquid crystal layer provided on the pixel electrodes and a second substrate provided above the liquid crystal layer. [Effects of the Invention]

[0024] According to the present invention, a technique is provided that can expand the transmissive display area without spoiling the brightness of the reflective display, and can also suppress an increase in light leakage. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a block diagram showing an example of the configuration of a liquid crystal display device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing an example of the cross-sectional structure of the liquid crystal display device shown in FIG. [Figure 3] FIG. 3 is a plan view showing an example of the planar structure of the liquid crystal display device shown in FIG. [Figure 4] FIG. 4 is a plan view showing an example of the planar structure of the liquid crystal display device shown in FIG. [Figure 5] FIG. 5 is a plan view showing an example of the planar structure of the liquid crystal display device shown in FIG. [Figure 6] FIG. 6 is a diagram illustrating reflection of light from a backlight in the liquid crystal display device shown in FIG. [Figure 7] FIG. 7 is a diagram illustrating a state in which the effect of suppressing reflection of light from the backlight is insufficient. [Figure 8] FIG. 8 is a diagram showing the configuration of a sample for measuring reflectance. [Figure 9] FIG. 9 is a graph showing the results of measurements using a sample for reflectance measurement. [Figure 10] FIG. 10 is a cross-sectional view showing a part of the configuration of a conventional reflective liquid crystal display device. [Figure 11] FIG. 11 is a diagram illustrating the problem to be solved by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments described below are more specific embodiments of any of the above aspects. The following items can be incorporated into each of the above aspects, either singly or in combination.

[0027] Furthermore, the embodiments shown below are merely examples of configurations for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention is not limited by the materials, shapes, structures, etc. of the components described below. Various modifications can be made to the technical idea of ​​the present invention within the technical scope defined by the claims.

[0028] In the drawings, elements having the same or similar functions are denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, the drawings are schematic, and the relationship between dimensions in one direction and dimensions in another direction, and the relationship between the dimensions of one member and the dimensions of another member, etc. may differ from the actual relationship.

[0029] <1> Embodiment A liquid crystal display device according to an embodiment will be described. The liquid crystal display device according to this embodiment is a semi-transmissive liquid crystal display device that can perform, for example, reflective display using external light and transmissive display using a backlight.

[0030] <1.1>Liquid crystal display device <1.1.1> Configuration of liquid crystal display device FIG. 1 is a block diagram showing an example of the configuration of a liquid crystal display device according to an embodiment.

[0031] As shown in FIG. 1, the liquid crystal display device 1 includes a liquid crystal panel 2, a backlight unit 3, a control circuit 11, a voltage generating circuit 12, a scanning line driver 13, a signal line driver 14, and a common electrode driver 15.

[0032] The liquid crystal panel 2 is a display that displays images. The liquid crystal panel 2 includes a plurality of pixels PX. The pixels PX are arranged in a matrix. Hereinafter, the area in which the pixels PX are arranged will be referred to as a "display area DA." Each of the pixels PX includes, for example, three subpixels SPX. The three subpixels SPX in the pixel PX are, for example, a subpixel SPX corresponding to red (R), a subpixel SPX corresponding to green (G), and a subpixel SPX corresponding to blue (B).

[0033] The liquid crystal panel 2 is also provided with a plurality of scanning lines GL and a plurality of signal lines SL. The plurality of scanning lines GL extend in the row direction, and the plurality of signal lines SL extend in the column direction. Sub-pixels SPX are arranged in the intersections of the scanning lines GL and the signal lines SL. One scanning line GL is connected to a plurality of sub-pixels SPX arranged in the row direction. One signal line SL is connected to a plurality of sub-pixels SPX arranged in the column direction.

[0034] In the following description, the direction in which the scanning lines GL extend is referred to as the X direction, the direction in which the signal lines SL extend is referred to as the Y direction, and the direction perpendicular to the X and Y directions is referred to as the Z direction.

[0035] The backlight unit 3 is, for example, a surface light source that irradiates light onto the back surface of the liquid crystal panel 2. As the backlight unit 3, for example, a direct type or side light type (edge ​​light type) LED backlight is used. Hereinafter, the backlight unit 3 is also referred to as a "backlight 3."

[0036] The control circuit 11 is a circuit that comprehensively controls the operation of the liquid crystal display device 1. The control circuit 11 receives a control signal CNT and image data DT from the outside. The control circuit 11 controls the operations of the voltage generation circuit 12, the scanning line driver 13, the signal line driver 14, and the common electrode driver 15 based on the control signal CNT and the image data DT.

[0037] For example, the control circuit 11 generates a control signal S1 based on the control signal CNT and transmits the control signal S1 to the voltage generating circuit 12. The control circuit 11 generates a control signal S2 based on the control signal CNT and transmits the control signal S2 to the scanning line driver 13. The control circuit 11 generates a control signal S3 based on the control signal CNT and transmits the control signal S3 to the signal line driver 14. The control circuit 11 generates a control signal S4 based on the control signal CNT and transmits the control signal S4 to the common electrode driver 15. The control circuit 11 also transmits image data DT to the signal line driver 14.

[0038] The voltage generation circuit 12 is a circuit that generates various voltages necessary for the operation of the liquid crystal display device 1. The voltage generation circuit 12 receives a control signal S1 from the control circuit 11. Based on the control signal S1, the voltage generation circuit 12 generates voltages to be supplied to the scanning line driver 13, the signal line driver 14, and the common electrode driver 15.

[0039] For example, the voltage generation circuit 12 generates a voltage V1 based on the control signal S1 and supplies the voltage V1 to the scanning line driver 13. The voltage generation circuit 12 generates a voltage V2 based on the control signal S1 and supplies the voltage V2 to the signal line driver 14. The voltage generation circuit 12 generates a voltage V3 based on the control signal S1 and supplies the voltage V3 to the common electrode driver 15.

[0040] The scanning line driver 13 is a circuit that drives the scanning lines GL. The scanning line driver 13 is connected to the multiple scanning lines GL. The scanning line driver 13 receives a control signal S2 from the control circuit 11. Based on the control signal S2, the scanning line driver 13 transmits a scanning signal for turning on or off a switching element 23 (described later) in the corresponding sub-pixel SPX to the liquid crystal panel 2 via the corresponding scanning line GL.

[0041] The signal line driver 14 is a circuit that drives the signal lines SL. The signal line driver 14 is connected to a plurality of signal lines SL. The signal line driver 14 receives a control signal S3 and image data DT from the control circuit 11. Based on the control signal S3, the signal line driver 14 transmits a gradation signal (driving voltage) corresponding to the image data DT to the liquid crystal panel 2 via the corresponding signal line SL.

[0042] The common electrode driver 15 is a circuit that generates a voltage to be applied to a common electrode 53 (described later) in the liquid crystal panel 2. The common electrode driver 15 receives a control signal S4 from the control circuit 11. The common electrode driver 15 generates a common voltage Vcom based on the control signal S4 and supplies the common voltage Vcom to the common electrode 53.

[0043] Fig. 2 is a cross-sectional view taken along line SS in Fig. 1, showing an example of the cross-sectional structure of the liquid crystal display device 1. Hereinafter, the direction perpendicular to the X and Y directions and extending from the backlight 3 toward the liquid crystal panel 2 is referred to as the Z1 direction. The direction perpendicular to the X and Y directions and extending from the liquid crystal panel 2 toward the backlight 3 is referred to as the Z2 direction. When either the Z1 direction or the Z2 direction is not specified, it is referred to as the Z direction.

[0044] 2, in the Z1 direction, a liquid crystal panel 2 is provided above the backlight 3. The liquid crystal panel 2 includes a TFT substrate 21, a polarizing plate 22, a switching element 23, an interlayer insulating film 29, a first reflective film 30, a second reflective film 31, an interlayer insulating film 32, a pixel electrode 33, a liquid crystal layer 41, a CF (Color Filter) substrate 51, a polarizing plate 52, and a common electrode 53.

[0045] 2 shows three subpixels SPX adjacent to each other in the Y direction. These subpixels SPX have the same structure. The cross-sectional structure of the liquid crystal panel 2 will be described below, focusing on one subpixel SPX.

[0046] In the Z1 direction, a TFT substrate 21 is provided above the backlight 3. The TFT substrate 21 faces the backlight 3 in the Z direction. The TFT substrate 21 is made of a transparent material, and may be, for example, glass, ultra-thin (bendable) glass, quartz, sapphire, or resin. In addition, these materials may be coated with a coating for the purpose of imparting gas barrier properties, etc.

[0047] In the Z1 direction, a polarizing plate 22 is provided above the backlight 3 and below the TFT substrate 21. The polarizing plate 22 is appropriately selected depending on the display mode (normally white or normally black) and the liquid crystal orientation.

[0048] A switching element 23 is provided on the surface of the TFT substrate 21 opposite to the backlight 3 in the Z1 direction. The switching element 23 is, for example, configured by a TFT. Hereinafter, the switching element 23 will also be referred to as a "TFT 23." The TFT 23 is a bottom-gate thin-film transistor in which a gate electrode is provided below (on the TFT substrate 21 side) the source electrode and the drain electrode. The TFT 23 includes a gate electrode 24, a gate insulating film 25, a semiconductor layer 26, an ohmic contact layer (not shown), a source electrode 27, and a drain electrode 28.

[0049] In the Z1 direction, a gate electrode 24 is provided on the TFT substrate 21. The gate electrode 24 extends in the X direction. The gate electrode 24 functions as a scanning line GL. The gate electrode 24 is made of, for example, any one of aluminum (Al), molybdenum (Mo), tantalum (Ta), tungsten (W), chromium (Cr), and titanium (Ti), or an alloy containing one or more of these. These may be stacked for the sake of improving processability.

[0050] In the Z1 direction, a gate insulating film 25 is provided on the gate electrode 24 and on the TFT substrate 21. The gate insulating film 25 covers the gate electrode 24. The gate insulating film 25 is made of a transparent insulating material, and may be, for example, silicon nitride (SiN), silicon oxide (SiO), silicon oxynitride (SiON), an insulating film formed by a method such as anodizing the gate electrode, or a resin, or these may be stacked together.

[0051] In the Z1 direction, a semiconductor layer 26 is provided on the gate insulating film 25. The semiconductor layer 26 faces the gate electrode 24 in the Z direction. The semiconductor layer 26 is made of, for example, hydrogenated amorphous silicon (a-Si:H).

[0052] In the Z1 direction, two ohmic contact layers (not shown) are provided on the semiconductor layer 26 and on the gate insulating film 25, spaced apart in the Y direction. One ohmic contact layer covers an edge of the upper surface of the semiconductor layer 26, the side surfaces of the semiconductor layer 26, and part of the upper surface of the gate insulating film 25. Similarly, the other ohmic contact layer covers an edge of the upper surface of the semiconductor layer 26, the side surfaces of the semiconductor layer 26, and part of the upper surface of the gate insulating film 25. The ohmic contact layer is made of, for example, amorphous silicon doped with n-type impurities. Note that the ohmic contact layer does not necessarily have to be provided.

[0053] In the Z1 direction, a source electrode 27 is provided on one of the ohmic contact layers. A drain electrode 28 is provided on the other ohmic contact layer. That is, the source electrode 27 and the drain electrode 28 are provided spaced apart from each other in the Y direction. The source electrode 27 and the drain electrode 28 also cover the edge of the upper surface of the semiconductor layer 26, the side surface of the semiconductor layer 26, and part of the upper surface of the gate insulating film 25. In other words, part of the semiconductor layer 26 is not covered by the source electrode 27 and the drain electrode 28. The part of the semiconductor layer 26 that is not covered by the source electrode 27 and the drain electrode 28 functions as a channel portion of the TFT 23.

[0054] The source electrode 27 includes a base portion BP1 and an extension portion EP1 (described later). The source electrode 27 functions as a signal line SL. The drain electrode 28 includes a base portion BP2 and an extension portion EP2. The source electrode 27 and the drain electrode 28 are made of, for example, aluminum (Al), molybdenum (Mo), tantalum (Ta), tungsten (W), chromium (Cr), or titanium (Ti), or an alloy containing one or more of these. These may be stacked for ease of processing. However, when using an alloy primarily composed of aluminum, it is preferable not to use the aluminum alloy as the top layer of the stack. This is because aluminum is easily oxidized when the aluminum alloy is in the top layer of the stack, which can result in poor electrical contact between the drain electrode 28 and the pixel electrode 33. Furthermore, if aluminum is in the top layer of the stack, the aluminum will dissolve in the developer used in photolithography.

[0055] In addition, when an ohmic contact layer is not provided, the source electrode 27 and the drain electrode 28 are spaced apart from each other in the Y direction and are provided so as to cover the end of the upper surface of the semiconductor layer 26, the side surface of the semiconductor layer 26, and part of the upper surface of the gate insulating film 25.

[0056] 2 shows an example of a connection state of the TFT 23. Therefore, the electrode 27 may be a drain electrode, and the electrode 28 may be a source electrode.

[0057] In the Z1 direction, an interlayer insulating film 29 is provided on the source electrode 27, the drain electrode 28, the semiconductor layer 26, and the gate insulating film 25. The interlayer insulating film 29 is made of a transparent insulating material, and may be, for example, silicon nitride (SiN), silicon oxide (SiO), silicon oxynitride (SiON), an insulating film formed by a method such as anodizing the gate electrode, or a resin, or may be a laminate of these.

[0058] In the Z1 direction, a first reflective film 30 is provided on the interlayer insulating film 29. In other words, the first reflective film 30 is provided above the TFT 23. The first reflective film 30 extends in the X direction. The first reflective film 30 faces the gate electrode 24 in the Z direction (a direction perpendicular to the surface of the TFT substrate 21). The first reflective film 30 has an area that covers the gate electrode 24. The first reflective film 30 is made of a material having a lower light reflectance than the second reflective film 31, and includes, for example, molybdenum (Mo) or an alloy containing molybdenum.

[0059] A second reflective film 31 is provided above the first reflective film 30 in the Z1 direction. The second reflective film 31 extends in the X direction. The second reflective film 31 has an area covering the gate electrode 24 and the first reflective film 30. The second reflective film 31 is made of a material with a relatively high light reflectance, such as aluminum (Al) or an alloy containing aluminum. A material with a relatively high light reflectance is used for the second reflective film 31 for the following reasons. The reason is that a smaller area of ​​the second reflective film 31 more strongly reflects external light to obtain a brighter reflective display, and a smaller area of ​​the second reflective film 31 increases the area irradiated with light from the backlight 3, i.e., the area of ​​the transmissive display region.

[0060] In the subpixel SPX, the region where the second reflective film 31 is provided is the reflective display region RA, and the region where the second reflective film 31 is not provided (the region where the gate electrode 24, the source electrode 27, and the drain electrode 28 are not provided) is the transmissive display region TA. The reflective display region RA is a region where reflective display is performed using external light including sunlight. External light is incident on the liquid crystal panel 2 from the CF substrate 51 side. Since the second reflective film 31 is located above the gate electrode 24 and the first reflective film 30, the external light incident on the liquid crystal panel 2 is reflected by the second reflective film 31. The transmissive display area TA is an area where transmissive display is performed using light from the backlight 3. The light from the backlight 3 enters the liquid crystal panel 2 from the backlight 3.

[0061] In the Z1 direction, an interlayer insulating film 32 is provided on the second reflective film 31 and on the interlayer insulating film 29. The interlayer insulating film 32 also functions as an insulating film that constitutes a storage capacitor. The storage capacitor is composed of two electrodes (the second reflective film 31 and the pixel electrode 33) and the interlayer insulating film 32 sandwiched between them. The interlayer insulating film 32 is made of a transparent insulating material, and may be, for example, silicon nitride (SiN), silicon oxide (SiO2), or silicon oxynitride (SiON). However, if it is desired to increase the storage capacitance, a high-dielectric-constant material such as hafnium oxide may be used, or these may be stacked.

[0062] A contact hole 34 is provided on the extending portion EP2 of the drain electrode 28. The contact hole 34 penetrates the interlayer insulating film 32 and reaches the extending portion EP2 of the drain electrode 28 from the upper surface of the interlayer insulating film 29. The contact hole 34 has, for example, a rectangular shape in top view (when viewed from the CF substrate 51 side). The contact hole 34 may also have a circular shape in top view.

[0063] In the Z1 direction, a pixel electrode 33 is provided on the interlayer insulating film 32. The pixel electrode 33 is provided in the subpixel SPX. The pixel electrode 33 is also provided on the side surface and bottom surface of the contact hole 34 (the upper surface of the extension portion EP2 of the drain electrode 28). As a result, the pixel electrode 33 is connected to the extension portion EP2 of the drain electrode 28. The pixel electrode 33 is made of a transparent electrode, and is made of, for example, ITO, IZO (zinc oxide (ZnO) doped with indium (In)), AZO (zinc oxide (ZnO) doped with aluminum (Al)), or GZO (zinc oxide (ZnO) doped with gallium (Ga)).

[0064] The CF substrate 51 is provided above the TFT substrate 21 in the Z1 direction. The CF substrate 51 is provided above the liquid crystal layer 41 in the Z1 direction. The CF substrate 51 faces the TFT substrate 21 in the Z direction. The CF substrate 51 is made of a transparent material, and may be made of, for example, glass, ultra-thin glass, quartz, sapphire, or resin. In addition, these materials may be coated with a coating for the purpose of imparting gas barrier properties, etc.

[0065] In the Z2 direction, a polarizing plate 52 is provided below the CF substrate 51. The polarizing plate 52 is appropriately selected depending on the display mode and liquid crystal orientation.

[0066] In the Z2 direction, a black matrix (not shown) is provided on the CF substrate 51. The black matrix is ​​made of a material that can block light.

[0067] In the Z2 direction, color filters (not shown) are provided on the black matrix and on the CF substrate 51. The color filters include red, green, and blue filters. The color filters have, for example, a stripe arrangement. The color filter arrangement can be designed arbitrarily.

[0068] A common electrode 53 is provided on the color filters in the Z2 direction. The common electrode 53 is provided over the entire display area DA. The common electrode 53 has, for example, a rectangular shape when viewed from above. The common electrode 53 is made of a transparent electrode, for example, ITO, IZO, AZO, or GZO.

[0069] In the Z direction, the liquid crystal layer 41 is sandwiched and filled between the TFT substrate 21 and the CF substrate 51. In the Z1 direction, the liquid crystal layer 41 is provided on the pixel electrodes 33. For example, the liquid crystal layer 41 is sealed in a display area DA surrounded by the TFT substrate 21, the CF substrate 51, and a sealant (not shown). The sealant is made of, for example, an ultraviolet curable resin, a thermosetting resin, or a combined ultraviolet and heat curable resin, and is applied to the TFT substrate 21 or the CF substrate 51 in the manufacturing process and then cured by ultraviolet irradiation, heating, or the like.

[0070] The liquid crystal material constituting the liquid crystal layer 41 changes its optical properties as the orientation of the liquid crystal molecules is controlled in response to an applied electric field. The liquid crystal display device 1 of this embodiment is, for example, a VA mode device using vertical alignment (VA) type liquid crystal. For example, negative type (N type) nematic liquid crystal having negative dielectric anisotropy is used as the liquid crystal layer 41.

[0071] In the Z direction, an alignment film (not shown) is provided between the pixel electrode 33 and the liquid crystal layer 41. Similarly, an alignment film (not shown) is provided between the common electrode 53 and the liquid crystal layer 41.

[0072] Fig. 3 is a plan view of region A1 in Fig. 1, showing an example of the planar structure of the liquid crystal display device 1. In Fig. 3, the backlight 3, the TFT substrate 21, the polarizing plate 22, the gate insulating film 25, the interlayer insulating film 29, the first reflective film 30, the second reflective film 31, the interlayer insulating film 32, the liquid crystal layer 41, the CF substrate 51, the polarizing plate 52, and the common electrode 53 are not shown.

[0073] 3, the gate electrode 24 extends in the X direction. The gate electrode 24 is connected to the scanning line driver 13. The gate electrode 24 is an electrode common to the sub-pixels SPX arranged in the X direction.

[0074] The semiconductor layer 26 has, for example, a rectangular shape when viewed from above.

[0075] A base portion BP1 of the source electrode 27 extends in the X direction. An extension portion EP1 of the source electrode 27 contacts one end of the base portion BP1 in the X direction and extends in the Y direction. The extension portion EP1 of the source electrode 27 is connected to the signal line driver 14. The source electrode 27 is an electrode common to the sub-pixels SPX arranged in the Y direction.

[0076] The base portion BP2 of the drain electrode 28 extends in the X direction. The extension portion EP2 of the drain electrode 28 contacts a part of one Y-direction end of the base portion BP2 and extends in the Y direction. The one Y-direction end of the extension portion EP2 of the drain electrode 28 that is not in contact with the base portion BP2 has, for example, a substantially octagonal shape in top view and surrounds the contact hole 34.

[0077] The pixel electrode 33 has, for example, a rectangular shape in top view, and has an area covering part of the gate electrode 24, the semiconductor layer 26, part of the source electrode 27, and the drain electrode .

[0078] Fig. 4 is a plan view of an area A1 in Fig. 1, showing an example of the planar structure of the liquid crystal display device 1. Fig. 4 is the same as Fig. 3 except that the first reflective film 30 is shown.

[0079] The first reflective film 30 extends in the X direction. In each subpixel SPX, the first reflective film 30 has approximately the same area as the gate electrode 24 in the Z direction, and has approximately the same shape as the gate electrode 24 in a top view. In other words, in each subpixel SPX, the first reflective film 30 overlaps with the gate electrode 24 in the Z direction. One end of the first reflective film 30 on the scanning line driver 13 side in the X direction does not reach the scanning line driver 13. In other words, the first reflective film 30 has a portion that does not overlap with the gate electrode 24 in the Z direction.

[0080] In this specification, when two members "have approximately the same area," this also means that there may be a slight difference in their areas. When two members "have approximately the same shape," this also means that there may be a slight difference in their shapes.

[0081] Fig. 5 is a plan view of the region A1 in Fig. 1, showing an example of the planar structure of the liquid crystal display device 1. Fig. 5 is the same as Fig. 4 except that the second reflective film 31 is shown.

[0082] The second reflective film 31 extends in the X direction. In each subpixel SPX, the second reflective film 31 has approximately the same area as the first reflective film 30 in the Z direction and has approximately the same shape as the first reflective film 30 in a top view. In other words, in each subpixel SPX, the second reflective film 31 overlaps with the first reflective film 30 in the Z direction. The first reflective film 30 is located below the second reflective film 31 in the Z1 direction and is therefore not shown in FIG. 5 . Like the first reflective film 30, one end of the second reflective film 31 on the scanning line driver 13 side in the X direction does not reach the scanning line driver 13. In other words, like the first reflective film 30, the second reflective film 31 has a portion that does not overlap with the gate electrode 24 in the Z direction. Note that, in each subpixel SPX, the second reflective film 31 may have a smaller area in the Z direction than the first reflective film 30.

[0083] <1.1.2> Reflection of light from the backlight The reflection of light from the backlight 3 will now be described.

[0084] Fig. 6 is a diagram illustrating reflection of light from the backlight 3 in the liquid crystal display device 1. Fig. 6 shows an enlarged view of the subpixel SPX in the liquid crystal panel 2 of Fig. 2, and does not illustrate the TFT substrate 21.

[0085] As shown in FIG. 6 , light incident on the subpixel SPX from the backlight 3 (hereinafter also referred to as "light from the backlight 3") passes through the gate insulating film 25 and the interlayer insulating film 29 and is reflected by the first reflective film 30. The light reflected by the first reflective film 30 is incident on the channel portion of the TFT 23 (semiconductor layer 26). In this embodiment, the first reflective film 30 and the second reflective film 31 are stacked in this order above the TFT 23 in the Z1 direction. As a result, reflection of light from the backlight 3 is dominated by reflection by the first reflective film 30 located on the backlight 3 side. Furthermore, in this embodiment, the first reflective film 30 has a lower light reflectivity than the second reflective film 31. As a result, reflection of light from the backlight 3 can be suppressed.

[0086] <1.1.3> Thickness of the first reflective film The film thickness of the first reflective film 30 will be described.

[0087] Generally, in the manufacture of products having metal thin film wiring, a thinner film is preferable in terms of manufacturing conditions, as it shortens the manufacturing time, saves materials and energy, reduces steps and improves coverage, etc. Therefore, in this embodiment as well, it is preferable that the film thickness of the first reflective film 30 is as thin as possible, within a range that does not spoil the optical performance.

[0088] However, as shown in FIG. 7 , if the first reflective film 30 is too thin, light from the backlight 3 passes through the gate insulating film 25 and the interlayer insulating film 29 and is reflected by the first reflective film 30, as in FIG. 6 . Furthermore, light from the backlight 3 passes not only through the gate insulating film 25 and the interlayer insulating film 29 but also through the first reflective film 30 and is reflected by the second reflective film 31. Therefore, light reflected by the first reflective film 30 and light reflected by the second reflective film 31 enter the channel portion of the TFT 23. In this case, because the second reflective film 31 has a relatively high optical reflectivity, more light enters the channel portion of the TFT 23 than when the first reflective film 30 is sufficiently thick. This results in an insufficient effect of suppressing reflection of light from the backlight 3, and may result in an inability to suppress an increase in light leakage. Therefore, it is preferable that the thickness of the first reflective film 30 be thick enough to prevent light from the backlight 3 from passing through.

[0089] Therefore, in order to determine the optimum film thickness of the first reflective film 30, a sample for measuring reflectance shown in FIG. 8 was prepared, and data on the reflectance of light was measured using the sample.

[0090] As shown in FIG. 8 , the reflectance measurement sample had a configuration in which a second reflective film 31 and a first reflective film 30 were laminated in this order on a substrate 81. A glass substrate was used as the substrate 81. An alloy containing aluminum was used as the second reflective film 31. An alloy containing molybdenum was used as the first reflective film 30. Seven reflectance measurement samples were fabricated in which the film thickness of the first reflective film 30 was varied to 0 nm, 10 nm, 20 nm, 30 nm, 50 nm, 80 nm, and 180 nm. The reflectance measurement sample in which the film thickness of the first reflective film 30 was 0 nm did not have the first reflective film 30. Light was irradiated onto each of the seven reflectance measurement samples from the first reflective film 30 side, and the reflectance of the light on the first reflective film 30 side was measured.

[0091] As a result of the above measurement, wavelength dependency was observed in the reflectance of the reflectance measurement sample, with the most significant change in reflectance occurring at a red wavelength (700 nm). The results of the above measurement are shown in Figure 9. The vertical axis of Figure 9 represents the light reflectance [%]. The horizontal axis of Figure 9 represents the film thickness [nm] of the first reflective film 30. Figure 9 shows the reflectance at a red wavelength (700 nm).

[0092] 9, when the film thickness of the first reflective film 30 is 0 nm, the reflectance is approximately 87%, which is the reflectance due to the aluminum-containing alloy of the second reflective film 31. In this case, the light from the backlight 3 is incident on the channel portion with a reflectance of nearly 90%, which is relatively likely to cause an increase in light leakage.

[0093] When the thickness of the first reflective film 30 is greater than 0 nm and less than 180 nm, the reflectance decreases as the thickness increases, and at a thickness of 10 nm the reflectance is approximately 70%, and at a thickness of 30 nm or more the reflectance remains almost constant. Therefore, it can be said that a thickness of 10 nm or more of the first reflective film 30 can provide a reflectance suppression effect, and a thickness of 30 nm or more can provide a sufficient reflectance suppression effect.

[0094] When the thickness of the first reflective film 30 is 180 nm, the reflectivity is approximately 56%, assuming that the film is sufficiently thick (to prevent light from passing through). However, from the above results, it can be said that even if the thickness of the first reflective film 30 is not increased to 180 nm, a film thickness of 30 nm can sufficiently achieve the same effect as when the film thickness is 180 nm.

[0095] On the other hand, in terms of manufacturing conditions, controllability deteriorates in the thin film region, and in particular, mass production equipment uses high film formation speed conditions to achieve high throughput. For this reason, since forming a thin film on the order of several tens of nanometers increases the difficulty of the process, taking into account variations, it is preferable that the film thickness of the first reflective film 30 be approximately 50 nm.

[0096] <1.2>Method of manufacturing a liquid crystal display device The above-described liquid crystal display device 1 can be manufactured, for example, by the following method. A method for manufacturing the liquid crystal panel 2 in the liquid crystal display device 1 will be described below.

[0097] First, prepare the TFT substrate 21. The TFT substrate 21 is made of the above-mentioned material.

[0098] 2, the TFT 23 is formed in the Z1 direction on the TFT substrate 21. The TFT 23 can be manufactured by a known manufacturing method.

[0099] 2, an interlayer insulating film 29 is formed in the Z1 direction on the TFT 23 and on the gate insulating film 25. The interlayer insulating film 29 is made of the material described above.

[0100] Next, as shown in FIG. 2, a first reflective film 30 is formed on the interlayer insulating film 29 in the Z1 direction. The film thickness of the first reflective film 30 is set to be thinner, for example, in the range of 10 nm to 50 nm. The film thickness of the first reflective film 30 is preferably, for example, 30 nm or more. The first reflective film 30 is made of a material having a lower light reflectance than the second reflective film 31, for example, molybdenum or an alloy containing molybdenum. In other words, the first reflective film 30 is made of a material that does not contain aluminum.

[0101] 2, a second reflective film 31 is formed in the Z1 direction on the first reflective film 30. The second reflective film 31 is made of a material having a relatively high light reflectance, such as aluminum or an alloy containing aluminum.

[0102] Next, for example, by using photolithography, a mask (hereinafter referred to as a "first mask") is formed on the second reflective film 31 in the Z1 direction. The first mask covers the portions where the first reflective film 30 and the second reflective film 31 are to be provided. For example, a photoresist is used as the first mask.

[0103] Next, using the first mask, the second reflective film 31 and the first reflective film 30 are simultaneously etched by, for example, wet etching. As a result, the outer shapes of the first reflective film 30 and the second reflective film 31 become approximately the same. Thereafter, the first mask is removed.

[0104] Note that the first reflective film 30 and the second reflective film 31 are made of different materials, and therefore have different etching rates. Therefore, due to the difference in etching rate, the outer shapes of the first reflective film 30 and the second reflective film 31 do not necessarily become completely the same. The above-mentioned "having substantially the same outer shape" also means that when the two layers are simultaneously wet-etched using the same mask, there may be some difference in the outer shapes due to the difference in etching rate between the two layers.

[0105] 2, the interlayer insulating film 32 is formed in the Z1 direction on the second reflective film 31. The interlayer insulating film 32 is made of the material described above.

[0106] Next, for example, by photolithography, a mask (hereinafter referred to as a "second mask") is formed on the interlayer insulating film 32 in the Z1 direction. The second mask covers areas other than the areas where the contact holes 34 are to be formed. For example, a photoresist is used as the second mask.

[0107] Next, the interlayer insulating film 32 and the interlayer insulating film 29 are etched by, for example, dry etching using the second mask. As a result, a contact hole 34 is formed that extends from the upper surface of the interlayer insulating film 32 to the upper surface of the drain electrode 28. Thereafter, the second mask is removed.

[0108] 2, a transparent conductive material (ITO, IZO, AZO, GZO, or the like) is formed in the Z1 direction on the interlayer insulating film 32, on the side surfaces of the contact holes 34, and on the bottom surfaces of the contact holes 34. Thereafter, the transparent conductive material is patterned to form pixel electrodes 33.

[0109] Through the above steps, the layered structure of the TFT substrate 21 is manufactured. Thereafter, the layered structure of the CF substrate 51 is manufactured using a known manufacturing method. Then, the TFT substrate 21 and the CF substrate 51 are bonded together with the liquid crystal layer 41 and the sealant interposed therebetween. In this manner, the liquid crystal panel 2 shown in FIG. 2 is manufactured.

[0110] <1.3> Effects The above-described technology provides the following advantages, for example.

[0111] In the liquid crystal display device 1 according to this embodiment, a bottom-gate TFT 23 is provided above the backlight 3, a first reflective film 30 is provided above the TFT 23, and a second reflective film 31 is provided above the first reflective film 30. The first reflective film 30 has a lower optical reflectivity than the second reflective film 31. This reduces reflection of light from the backlight 3. This reduces the risk of light leakage, which would otherwise occur if light emitted from the backlight 3 and reflected by the first reflective film 30 were to enter the channel of the TFT 23. The second reflective film 31 also has a relatively high optical reflectivity (higher than the first reflective film 30). This allows the smaller area of ​​the second reflective film 31 to more strongly reflect external light, resulting in a brighter reflective display. Furthermore, reducing the area of ​​the second reflective film 31 increases the area of ​​the transmissive display region. As described above, this embodiment allows the transmissive display region to be expanded without compromising the brightness of the reflective display, and also reduces the increase in optical leakage.

[0112] In the liquid crystal display device 1 according to this embodiment, the first reflective film 30 faces the gate electrode 24 in the Z direction. This increases the area of ​​the transmissive display region compared to when the first reflective film 30 does not face the gate electrode 24 in the Z direction.

[0113] In the liquid crystal display device 1 according to this embodiment, in each subpixel SPX, the first reflective film 30 has approximately the same area in the Z direction as the gate electrode 24. As a result, compared to when the first reflective film 30 has an area larger than that of the gate electrode 24 in the Z direction, the area over which light from the backlight 3 is reflected by the first reflective film 30 is smaller, and therefore the amount of light reflected by the first reflective film 30 is reduced. As a result, the amount of light incident on the channel portion of the TFT 23 is reduced. Furthermore, compared to when the gate electrode 24 has an area larger than that of the first reflective film 30 in the Z direction, the area of ​​the transmissive display region is larger.

[0114] In the liquid crystal display device 1 according to this embodiment, in each subpixel SPX, the second reflective film 31 has approximately the same area in the Z direction as the first reflective film 30. This increases the area of ​​the transmissive display region compared to when the second reflective film 31 has an area larger than that of the first reflective film 30 in the Z direction.

[0115] In the liquid crystal display device 1 according to this embodiment, the second reflective film 31 contains aluminum or an alloy containing aluminum, which allows the second reflective film 31 to more strongly reflect external light, thereby achieving a brighter reflective display.

[0116] In the liquid crystal display device 1 according to this embodiment, the second reflective film 31 contains aluminum or an alloy containing aluminum, and the first reflective film 30 contains molybdenum or an alloy containing molybdenum, which allows the second reflective film 31 and the first reflective film 30 to be etched simultaneously.

[0117] <2> Variations Various modifications are possible to the above-described liquid crystal panel 2. For example, one or more other reflective films may be provided between the first reflective film 30 and the second reflective film 31. That is, the liquid crystal panel 2 may have a laminated structure of three or more reflective films, with the first reflective film 30 as the bottom layer and the second reflective film 31 as the top layer.

[0118] Furthermore, various modifications are possible for the material used for the first reflective film 30 that has a lower light reflectance than the second reflective film 31. For example, the first reflective film 30 may be a material that can suppress light reflection, a material that can prevent light reflection, a material that can absorb light, or a material that can block light. For example, the first reflective film 30 may contain chromium or an alloy containing chromium, or may contain resin. [Explanation of symbols]

[0119] 1...liquid crystal display device, 2...liquid crystal panel, 3...backlight unit (backlight), 11...control circuit, 12...voltage generation circuit, 13...scanning line driver, 14...signal line driver, 15...common electrode driver, 21...TFT substrate, 22...polarizer, 23...switching element (TFT), 24...gate electrode, 25...gate insulating film, 26...semiconductor layer, 27...source electrode, 28...drain electrode, 29...interlayer insulating film, 30...first reflective film, 31...second reflective film, 32...interlayer insulating film, 33...pixel electrode, 41...liquid crystal layer, 51...CF substrate, 52...polarizer, 53...common electrode

Claims

1. Backlight and a first substrate provided above the backlight; a bottom-gate thin film transistor including a gate electrode and provided on a surface of the first substrate; a first reflective film provided above the thin film transistor; a second reflective film provided above the first reflective film; an insulating film provided on the second reflective film; a pixel electrode provided on the insulating film; Including a liquid crystal panel and Equipped with the first reflective film has a lower light reflectance than the second reflective film; LCD display device.

2. the first reflective film faces the gate electrode in a first direction perpendicular to the surface of the first substrate; 2. The liquid crystal display device according to claim 1.

3. the liquid crystal panel includes a plurality of pixels; each of the plurality of pixels includes a plurality of sub-pixels; In each of the plurality of sub-pixels, the first reflective film has approximately the same area as the gate electrode in the first direction.

3. The liquid crystal display device according to claim 2.

4. In each of the plurality of sub-pixels, the first reflective film has substantially the same shape as the gate electrode in the first direction.

4. The liquid crystal display device according to claim 3.

5. In each of the plurality of sub-pixels, the second reflective film has approximately the same area as the first reflective film in the first direction.

4. The liquid crystal display device according to claim 3.

6. In each of the plurality of sub-pixels, the second reflective film has substantially the same shape as the first reflective film in the first direction.

6. The liquid crystal display device according to claim 5.

7. the second reflective film contains aluminum or an alloy containing aluminum; 7. The liquid crystal display device according to claim 1.

8. the first reflective film contains molybdenum or an alloy containing molybdenum; 8. The liquid crystal display device according to claim 7.

9. the first reflective film contains chromium or an alloy containing chromium; 8. The liquid crystal display device according to claim 7.

10. the first reflective film contains a resin; 8. The liquid crystal display device according to claim 7.

11. The thickness of the first reflective film is 10 nm or more and 50 nm or less.

9. The liquid crystal display device according to claim 8.

12. The thickness of the first reflective film is 30 nm or more. The liquid crystal display device according to claim 11.

13. The liquid crystal panel is a liquid crystal layer provided on the pixel electrodes; a second substrate provided above the liquid crystal layer; Further comprising:

2. The liquid crystal display device according to claim 1.

Images