JP2016110062A - Reflective liquid crystal display device - Google Patents

Abstract

Provided is a reflective liquid crystal display device which can be manufactured at low cost and can improve response speed and aperture ratio. A liquid crystal layer 15 is a positive liquid crystal layer 15 having liquid crystal molecules 15a vertically aligned between an array substrate 13 and a counter substrate 14. The array substrate 13 includes a plurality of pixel electrodes 27, a plurality of common electrodes 28, a color filter 26, and a reflective layer 25. The common electrode 28 forms a lateral electric field that orients the liquid crystal molecules 15a between the pixel electrodes 27. The color filter 26 is disposed below the pixel electrode 27 and the common electrode 28. The reflective layer 25 is electrically connected to either the common electrode 28 or the pixel electrode 27, is disposed at least below the color filter 26, and reflects light that has passed through the color filter 26. [Selection] Figure 1

Description

  Embodiments described herein relate generally to a reflective liquid crystal display device having a liquid crystal layer including liquid crystal molecules vertically aligned between a first substrate and a second substrate.

  Conventionally, for example, there is a TN (twisted nematic) type reflective liquid crystal display device. In recent years, high definition of liquid crystal display devices has been advanced, and in the case of TN type liquid crystal display devices, the response speed is slow, and the display quality is deteriorated due to electrostatic breakdown such as thin film transistors accompanying the rubbing treatment process of the alignment film. Alternatively, there is a problem that a so-called edge reverse (disclination) in which liquid crystal molecules are inverted occurs between pixel electrodes of different polarities in the case of a driving method using column inversion driving or the like.

  Therefore, by applying a liquid crystal layer in which liquid crystal molecules are vertically aligned using an alignment film, and configured to collapse the liquid crystal molecules in a transverse electric field mode such as IPS mode, the response speed is improved and the alignment film is rubbed. It can be considered that the processing is omitted to prevent electrostatic breakdown and improve the display quality. In such a liquid crystal display device, a configuration with a higher aperture ratio is desired.

JP 2002-55357 A

  The problem to be solved by the present invention is to provide a reflective liquid crystal display device that can be manufactured at low cost and can improve response speed and aperture ratio.

  The reflective liquid crystal display device according to the embodiment includes a first substrate, a second substrate, and a liquid crystal layer. The second substrate is disposed to face the first substrate. The liquid crystal layer is a positive liquid crystal layer including liquid crystal molecules vertically aligned between the first substrate and the second substrate. The first substrate includes a plurality of pixel electrodes, a plurality of common electrodes, a color filter, and a reflective layer. The common electrode forms a lateral electric field that aligns liquid crystal molecules with each pixel electrode. The color filter is disposed below the pixel electrode and the common electrode. The reflective layer is electrically connected to either the common electrode or the pixel electrode, is disposed below the color filter, and reflects light that has passed through the color filter.

FIG. 2 is a cross-sectional view schematically showing an enlarged part of the reflective liquid crystal display device of the first embodiment, where (a) shows the OFF state of the switching element and (b) shows the ON state of the switching element. . It is sectional drawing which shows a reflection type liquid crystal display device same as the above. FIG. 5 is a cross-sectional view schematically showing an enlarged part of the reflective liquid crystal display device of the second embodiment, where (a) shows an off state of the switching element and (b) shows an on state of the switching element. . It is a top view which shows typically a part of reflection type liquid crystal display device of 2nd Embodiment. It is a top view which shows typically a part of reflective type liquid crystal display device of 3rd Embodiment.

  Hereinafter, the configuration of the first embodiment will be described with reference to FIGS. 1 and 2.

  In FIGS. 1 and 2, reference numeral 11 denotes an active matrix reflective liquid crystal display device which is a reflective display device. The reflective liquid crystal display device 11 is roughly a first substrate as a non-display side substrate. An array substrate 13, a counter substrate 14 as a second substrate as a display side substrate, and a liquid crystal layer 15 as a light modulation layer interposed between the substrates 13 and 14 are provided. Further, the reflective liquid crystal display device 11 includes a gap holding member (spacer) (not shown) that holds a gap between the substrates 13 and 14, and the periphery of the liquid crystal layer 15 is, for example, an ultraviolet curable resin or a heat It is enclosed and sealed by a seal member 17 provided with a curable resin or the like. Hereinafter, the reflective liquid crystal display device 11 may be simply referred to as a display device 11. Further, FIGS. 1 and 2 are schematically shown by changing the aspect ratio in order to make the description clearer.

  The array substrate 13 includes a glass substrate 21 as a non-display side substrate main body (first substrate main body) having translucency and insulating properties. On the glass substrate 21, a plurality of scanning lines (gate lines) 22, A plurality of signal lines (source lines) 23, a plurality of thin film transistors 24 as switching elements, a reflective layer 25, a color filter (CF) 26, a plurality of pixel electrodes 27, a plurality of common electrodes 28, and a (first) orientation Each of the membranes 29 is provided. That is, the display device 11 has a COA (Color filter On Array) structure.

  More specifically, for example, a flattening undercoat layer (not shown) is provided on the array substrate 13, and a semiconductor layer (not shown) such as for the thin film transistor 24 is provided on the undercoat layer. An insulating layer 31 is provided so as to cover, a scanning line 22 (gate electrode of the thin film transistor 24) is provided on the insulating layer 31, a gate insulating film 32 is provided on the scanning line 22, and the gate insulating film 32 is provided on the gate insulating film 32. A reflective layer 25 electrically connected to the common electrode 28 (having the same potential as the common electrode 28) is provided, an interlayer insulating film 33 is provided on the reflective layer 25, and a signal line 23 is provided on the interlayer insulating film 33. (Source electrode and drain electrode of the thin film transistor 24) are provided. In addition, a color filter 26 is provided on the interlayer insulating film 33 including the signal lines 23, a pixel electrode 27 and a common electrode 28 are provided on the color filter 26, and a color filter including the pixel electrode 27 and the common electrode 28 is provided. An alignment film 29 is provided on 26. As the array substrate 13, any substrate having translucency and insulating properties such as a synthetic resin substrate can be used instead of the glass substrate 21.

  The scanning line 22 is disposed along the horizontal (H) direction, and is electrically connected to a driver (not shown) provided on the glass substrate 21, for example.

  The signal line 23 is disposed along the vertical (V) direction intersecting (orthogonal) with the scanning line 22 while being insulated from the scanning line 22, and is provided on the glass substrate 21, for example, not shown. Electrically connected to the driver. This signal line 23 is electrically connected to an external circuit (not shown). In the present embodiment, the signal line 23 is set to a thickness of about 0.35 μm, for example.

  The thin film transistors 24 are respectively arranged at positions where the scanning lines 22 and the signal lines 23 intersect. Therefore, the thin film transistors 24 are arranged in a matrix. In these thin film transistors 24, the gate electrode is disposed opposite to the channel region of the semiconductor layer via the gate insulating film 32, and the source electrode and the drain electrode are electrically connected to the source region and the drain region of the semiconductor layer, respectively. . In each thin film transistor 24, the gate electrode is electrically connected to the scanning line 22, the source electrode is electrically connected to the signal line, and the drain electrode is electrically connected to the pixel electrode 27.

  The reflective layer 25 is a reflective pixel that reflects external light, and is provided in a predetermined thickness with, for example, aluminum, silver, or a compound or alloy containing these as one component. The reflective layer 25 is located above the scanning line 22 (gate electrode) and below the color filter 26, and is disposed to face the entire surface of the scanning line 22 and the color filter 26. Alternatively, it is electrically connected to the common electrode 28 and shields an undesired leakage electric field from the scanning line 22 toward the liquid crystal layer 15. In the present embodiment, the reflective layer 25 is set to a thickness of about 0.13 μm, for example.

  The color filter 26 is located below the pixel electrode 27 and the common electrode 28. For example, the filter units 26r, 26g, and 26b corresponding to red (R), green (G), and blue (B), and these Each filter unit 26r, 26g, 26b is provided corresponding to each pixel electrode 27. The filter unit 26r, 26g, 26b has a light blocking unit (black matrix) (not shown) that partitions between the filter units 26r, 26g, 26b and blocks unnecessary light. Yes. In the present embodiment, the filter units 26r, 26g, and 26b are located in the pixel regions A that are surrounded by the scanning lines 22 and the signal lines 23 and arranged in a matrix. Further, the periphery of the color filter 26 is surrounded by a black light shielding portion 35. In the present embodiment, the color filter 26 (filter portions 26r, 26g, 26b) is set to a thickness of about 2.0 μm, for example.

  The pixel electrode 27 is formed in an elongated shape along the direction of the signal line 23 by a transparent conductive member such as ITO or IZO, and is disposed in each pixel region A.

  The common electrode 28 is formed in an elongated shape in the direction of the signal line 23 between adjacent pixel regions A and A by a transparent conductive member such as ITO or IZO. Each common electrode 28 is disposed at a position immediately above the signal line 23. That is, the common electrodes 28 are spaced apart from the pixel electrodes 27 and are disposed corresponding to the pixel electrodes 27, and the pixel electrodes 27 and the common electrodes 28 are alternately disposed along the scanning line 22 direction. Yes. Further, these common electrodes 28 are formed to have a width dimension substantially equal to that of the pixel electrode 27, and the interval between the pixel electrode 27 and the common electrode 28 is set to be twice or more the width of the pixel electrode 27 and the common electrode 28. Has been. In this embodiment, for example, the width dimensions of the pixel electrode 27 and the common electrode 28 are each set to about 2.5 μm, the thicknesses are respectively set to about 0.07 μm, and the pixel electrode 27 and the common electrode 28 Is set to 15.0 μm or more.

  Then, liquid crystal molecules in the liquid crystal layer 15 are formed by a horizontal electric field formed between the common electrodes 28 and 28 sandwiching each pixel region A and the pixel electrode 27 located between the common electrodes 28 and 28 in the pixel region A. (Director) 15a is switched (FIGS. 1A and 1B).

  The alignment film 29 is provided by a synthetic resin such as polyimide, for example. In the present embodiment, the alignment film 29 is set to a thickness of, for example, about 0.07 μm.

  The insulating layer 31 is, for example, a silicon oxide film or a silicon nitride film.

  The gate insulating film 32 is, for example, a silicon nitride film.

  The interlayer insulating film 33 is, for example, a silicon oxide film. In the present embodiment, the interlayer insulating film 33 is set to a thickness of about 0.18 μm, for example.

  Further, the counter substrate 14 includes a glass substrate 41 as a display-side substrate body (second substrate body) having translucency and insulation, and liquid crystal molecules 15a when a voltage is applied on the glass substrate 41. A not-shown saddle-shaped structure as a control unit for controlling the tilting direction of the film, a (second) alignment film 43 that covers the structure and is in contact with the liquid crystal layer 15 are provided. That is, no electrode is formed on the counter substrate 14, and the liquid crystal layer 15 is divided into a plurality of domains in a portion corresponding to each pixel region A by the structure. Further, a polarizing plate 45 is attached to the side of the glass substrate 41 opposite to the liquid crystal layer 15, that is, the display side. The counter substrate 14 may be any substrate having translucency and insulating properties, such as a synthetic resin substrate, for example, instead of the glass substrate.

  The alignment film 43 is made of, for example, a synthetic resin such as polyimide, and the liquid crystal molecules 15a of the liquid crystal layer 15 are aligned substantially vertically with the alignment film 29 on the array substrate 13 side by a bowl-shaped structure. I am letting. In the present embodiment, the alignment film 43 is set to a thickness substantially equal to the alignment film 29, for example, about 0.07 μm.

  The liquid crystal layer 15 has a liquid crystal molecule 15a vertically aligned between the alignment films 29 and 43, and has a positive dielectric constant in order to lay the liquid crystal molecule 15a against a lateral electric field between the pixel electrode 27 and the common electrode 28. A positive type liquid crystal layer having anisotropy is used. In the present embodiment, the liquid crystal layer 15 is set to a thickness of, for example, about 2.8 μm.

  In the display device 11 described above, each thin film transistor 24 independently drives the pixel electrode 27 according to the signal from the scanning line 22, and the pixel electrode 27 and the pixel electrode according to the signal from the signal line 23. The liquid crystal molecules 15 a of the liquid crystal layer 15 are collapsed by a lateral electric field set between the common electrodes 28 and 28 sandwiching 27. The polarity of the pixel electrode 27 can be selected by the signal line 23 located below the common electrodes 28, 28. For example, the polarity is inverted every predetermined number of signal lines 23 and inverted every scanning line 22, column inversion driving, etc. The appropriate driving method is used. In this state, external light incident from the counter substrate 14 side passes through the filter portions 26r, 26g, and 26b of the color filter 26 via the liquid crystal layer 15, and then is reflected by the reflective layer 25 positioned below the color filter 26. Thus, the transmittance of the reflected light by each pixel electrode 27 is set according to the angle of the liquid crystal molecules 15a of the liquid crystal layer 15, and the reflected light that passes through the color filter 26 again and exits to the counter substrate 14 side is used as an image. Is displayed.

  According to the first embodiment described above, it can be manufactured at low cost by using the positive liquid crystal layer 15 including the vertically aligned liquid crystal molecules 15a, and, for example, as in the case of using a TN liquid crystal layer. Edge reversal that tends to occur between pixel electrodes of different polarities during column inversion driving can be improved, and a circularly polarizing plate can be used for the polarizing plate 45, which is a reflective liquid crystal with normally black display and high transmittance The display device 11 can be realized. The liquid crystal layer used in the normal vertical alignment (VA) mode uses a negative type liquid crystal layer to lay liquid crystal molecules against a vertical electric field. In the present embodiment, a plurality of liquid crystal layers are provided on the array substrate 13. A horizontal electric field method for forming a horizontal electric field for aligning liquid crystal molecules 15a between the pixel electrode 27 and the common electrode 28. By using the positive type liquid crystal layer 15 having a faster response speed than the negative type liquid crystal layer, the response speed can be improved. Furthermore, by providing the color filter 26 on the array substrate 13, for example, it is easier to adjust the position of the array substrate 13 and the counter substrate 14 than when the color filter is provided on the counter substrate side. The aperture ratio can be prevented from decreasing due to the positional deviation between the counter substrate 14 and the counter substrate 14, and a high aperture ratio can be realized. The reflective layer 25 is scanned by disposing the reflective layer 25 below the entire color filter 26 and above the scanning line 22, that is, between the color filter 26 (liquid crystal layer 15) and the scanning line 22. It can be used as a shield against an undesired leakage electric field from the line 22 toward the liquid crystal layer 15, and a reduction in display quality due to this leakage electric field can be suppressed.

  Further, since the counter electrode is not required for the counter substrate 14, the position adjustment between the array substrate 13 and the counter substrate 14 becomes easier.

  Further, since the liquid crystal molecules 15a are vertically aligned, alignment processing by the rubbing is not required for the alignment films 29 and 43, electrostatic breakdown caused by rubbing can be prevented and the yield can be improved, and the display device 11 can be manufactured at a lower cost. .

  Furthermore, the width dimensions of the pixel electrode 27 and the common electrode 28 are made substantially equal to each other, and the distance between the pixel electrode 27 and the common electrode 28 is set to be twice or more the width dimension, so that the pixel electrode 27 and the common electrode 28 While suppressing the light (incident light and reflected light) blocked by 28 and suppressing the liquid crystal molecules 15a that are located immediately above the pixel electrode 27 and the common electrode 28 and do not fall down due to the lateral electric field, while realizing high transmittance, for example A low driving voltage such as less than 5V can be obtained.

  Next, a second embodiment will be described with reference to FIGS. In addition, about the structure and effect | action similar to the said 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  In the second embodiment, ribs 48 are respectively provided at positions facing the pixel electrodes 27 of the counter substrate 14 of the first embodiment.

  Each rib 48 is formed of a member having a high transmittance and a low dielectric constant. That is, each rib 48 has translucency. The ribs 48 are formed along the pixel electrodes 27 along the center position of the pixel region A. Therefore, in the present embodiment, each rib 48 is formed in a straight line. The dielectric constants of the ribs 48 are smaller than the dielectric constant of the liquid crystal layer 15 and are set to about 1/7, for example, and are desirably 0.1 times or more and 0.2 times or less. The cross-sectional shape of each rib 48 is a quadrangular shape, and the thickness (height) and width are set to be larger than those of the pixel electrode 27. Each rib 48 is set to have a thickness of, for example, 0.7 ± 0.1 μm and a width of, for example, 6.0 ± 0.25 μm. Each rib 48 preferably has a width not less than 0.3 times and not more than 0.4 times that of the color filter 26, and has a thickness (height) of not less than 0.3 times the thickness of the liquid crystal layer 15 and 0.00. It is desirable that it is 4 times or less.

  Since the rib 48 having a high transmittance and a low dielectric constant is provided on the counter substrate 14 at a position facing the pixel electrode 27 as described above, when the voltage is applied to the pixel electrode 27, the pixel electrode 27 is formed by the rib 48. And the common electrode 28 can be disturbed, and the liquid crystal molecules 15a located above (directly above) the pixel electrode 27 can also be brought down. Therefore, the reflectance can be improved.

  Further, since the rib 48 is set to have a larger thickness and width than the pixel electrode 27, the liquid crystal molecules 15a can be more reliably tilted when a voltage is applied to the pixel electrode 27.

  In the second embodiment, for example, when each pixel region A is multi-domained for the purpose of improving the viewing angle, the shape of the pixel region A is not necessarily rectangular but may be bent. At this time, for example, as in the third embodiment shown in FIG. 5, by forming the rib 48 in a bent shape along the center position of the pixel region A, the same operational effects as in the second embodiment can be obtained. be able to.

  Further, in each of the above embodiments, the arrangement and color of the filter units 26r, 26g, and 26b of the color filter 26 can be set to any values that can realize color display on the display device 11.

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

11 reflective LCD
13 Array substrate as the first substrate
14 Counter substrate as the second substrate
15 Liquid crystal layer
15a Liquid crystal molecules
25 Reflective layer
26 Color filter
27 Pixel electrode
28 Common electrode
48 Ribs

Claims (6)

A first substrate;
A second substrate disposed opposite the first substrate;
A positive-type liquid crystal layer having liquid crystal molecules vertically aligned between the first substrate and the second substrate;
The first substrate is
A plurality of pixel electrodes;
A plurality of common electrodes for forming a transverse electric field for aligning the liquid crystal molecules between the pixel electrodes;
A color filter disposed below the pixel electrode and the common electrode;
A reflection layer that is electrically connected to any one of the common electrode and the pixel electrode, disposed below the color filter, and that reflects light that has passed through the color filter; Type liquid crystal display device. The pixel electrode and the common electrode each have a predetermined width, and an interval between the pixel electrode and the common electrode is set to be twice or more the width. Reflective liquid crystal display device. The said 2nd board | substrate is equipped with the rib which has a translucency and a dielectric constant lower than the dielectric constant of the said liquid crystal layer in the position facing the said pixel electrode. The reflective liquid crystal display device described. The reflective liquid crystal display device according to claim 3, wherein the rib is set to have a thickness and a width larger than those of the pixel electrode. The rib has a width of 0.3 to 0.4 times that of the color fill, and a thickness of 0.3 to 0.4 times the thickness of the liquid crystal layer. The reflective liquid crystal display device according to claim 4. 6. The reflective liquid crystal display device according to claim 4, wherein a dielectric constant of the rib is 0.1 to 0.2 times a dielectric constant of the liquid crystal layer.

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