JP2005128082A - Liquid crystal display device and electronic appliance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device in which a viewing angle in the horizontal direction is limited while the viewing angle in the vertical direction is widened by adopting an alignment division structure. <P>SOLUTION: In the liquid crystal display device 100 equipped with a liquid crystal layer 50 composed of a liquid crystal with vertical alignment as an initial alignment state and having negative dielectric anisotropy between a pair of circularly polarizing plates placed opposite to each other, the liquid crystal layer 50 is constructed so as to satisfy following conditions, that is, inside a dot region, liquid crystal molecules are alignment divided at least in one direction, the ratio of the number of the liquid crystal molecules aligned in the direction to the number of the liquid crystal molecules aligned in other directions is 2:1 or more, and retardation Δnd of the liquid crystal layer 50 satisfies an inequality 0.4<Δnd<1.0. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device and an electronic device, and more particularly to a liquid crystal display device capable of contributing to privacy protection and an electronic device including the liquid crystal display device as a display unit.

In general, a liquid crystal display device provided in a word processor or a computer is required to have a display brightness, a contrast ratio, a wide viewing angle, etc., and the higher these characteristics, the easier the work and the fatigue due to the work. Can be reduced. For this reason, in such a liquid crystal display device, in order to widen the viewing angle, alignment division is performed by forming protrusions, electrode slits, and the like within one dot (see Patent Documents 1 to 3).
Japanese Patent Laid-Open No. 2002-40428 Japanese Patent Laid-Open No. 2001-235751 Japanese Patent No. 3398025

However, there is a demand for the user of the liquid crystal display device to protect the privacy by limiting the viewing angle, particularly in the case of a cellular phone. For example, in a mobile phone or the like, the user rarely sees the display unit from the lateral direction, and often sees the display unit tilted forward or downward. For this reason, there is a demand for a liquid crystal display device that can provide a high-luminance display when viewed from the top and bottom, but is difficult to view from the side.
The present invention has been made to solve the above-described problems, and is a liquid crystal display device that can limit the viewing angle in the left-right direction while adopting an alignment division structure to widen the viewing angle in the up-down direction. And it aims at providing the electronic device provided with this in the display part.

  In order to achieve the above object, a liquid crystal display device of the present invention comprises a liquid crystal layer comprising a liquid crystal layer made of a liquid crystal having a negative dielectric anisotropy and an initial alignment state of vertical alignment between a pair of opposing circularly polarizing plates. In the display device, the liquid crystal layer has the following conditions, that is, the liquid crystal molecules are aligned and divided in at least one direction within one dot region, and the ratio of the liquid crystal molecules aligned in the above direction and the other directions The ratio of the liquid crystal molecules to be aligned is 2: 1 or more, and the retardation Δnd of the liquid crystal layer satisfies the condition of 0.4 <Δnd <1.0.

  In the alignment-divided liquid crystal display device, the main alignment direction (the above-described one direction) of the liquid crystal when a voltage is applied can be defined by liquid crystal alignment control means such as protrusions and electrode slits arranged in one dot region. For example, when a slit extending in the vertical direction is formed in the pixel electrode, the liquid crystal molecules in one dot are aligned and divided to the left and right across the slit when a voltage is applied. When this alignment division is mainly performed in only one direction, the viewing angle characteristics of the display are different between the direction and the direction perpendicular thereto. For example, in the above-described example, the orientation division is mainly performed in the left-right direction, and thus the viewing angle characteristic in the left-right direction is different from the viewing angle characteristic in the up-down direction. The present inventor investigated the relationship between the viewing angle characteristics and the retardation Δnd of the liquid crystal layer, and found the following facts (this point will be described in detail later in [Best Mode for Carrying Out the Invention]).

(1) When the retardation Δnd is changed, only the viewing angle characteristic in the direction parallel to the main alignment direction (first direction; left-right direction in the above example) is greatly changed, and the direction perpendicular to the direction (second direction; In this example, the viewing angle characteristic in the vertical direction is hardly changed. For example, when Δnd increases, the display brightness viewed from the first direction decreases, and conversely, when Δnd decreases, the display brightness in the first direction increases.
(2) The display luminance in the first direction changes greatly when Δnd is between 0.4 and 0.5, and when Δnd is 0.4 or less, there is almost no difference in viewing angle characteristics between the first direction and the second direction. No longer occurs.
(3) When Δnd is 0.7 or more, a direction in which the display luminance starts to increase is started between the first direction and the second direction, and when Δnd is 1 or more, most directions other than the second direction are started. As a result, the display brightness increases and the effect of limiting the viewing angle cannot be obtained.

  Therefore, according to the configuration of the present invention in which the range of Δnd is 0.4 <Δnd <1.0, the visibility in the second direction (for example, the vertical direction) is enhanced by the effect of the orientation division, and other than this The viewing angle in the direction (for example, the first direction; the left-right direction) can be limited to make it difficult to look from the side. In particular, by configuring Δnd to satisfy 0.45 <Δnd <0.7, a favorable viewing angle limiting effect can be obtained.

  The present invention is not limited to a transmissive liquid crystal display device, but a transflective liquid crystal display device in which a transmissive display region for performing transmissive display and a reflective display region for performing reflective display are provided in one dot region. It can also be applied to. In this case, if at least the liquid crystal layer in the transmissive display region satisfies the above conditions, a good viewing angle limiting effect can be obtained during transmissive display.

  In addition, an electronic apparatus according to the present invention includes the above-described liquid crystal display device. Thereby, the electronic device provided with the display part with high confidentiality of the information with respect to a 3rd party can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The liquid crystal display device of this embodiment is an example of an active matrix liquid crystal display device using a thin film transistor (hereinafter abbreviated as TFT) as a switching element.

  FIG. 1 is an equivalent circuit diagram of a plurality of dots arranged in a matrix constituting the image display area of the liquid crystal display device of the present embodiment, FIG. 2 is a plan view showing the structure in the dot of the TFT array substrate, and FIG. FIG. 2 is a diagram showing a cross-sectional structure of the liquid crystal device. In each of the following drawings, the scale of each layer and each member is different in order to make each layer and each member recognizable on the drawing.

  As shown in FIG. 1, in the liquid crystal display device 100 of the present embodiment, a plurality of dots arranged in a matrix constituting an image display area are provided with a pixel electrode 9 and a switching element for controlling the pixel electrode 9. Each TFT 30 is formed, and a data line 6 a to which an image signal is supplied is electrically connected to the source of the TFT 30. Image signals S1, S2,..., Sn to be written to the data line 6a are supplied line-sequentially in this order, or are supplied for each group to a plurality of adjacent data lines 6a. Further, the scanning line 3a is electrically connected to the gate of the TFT 30, and the scanning signals G1, G2,..., Gm are applied to the plurality of scanning lines 3a in a pulse-sequential manner at a predetermined timing. Further, the pixel electrode 9 is electrically connected to the drain of the TFT 30, and by turning on the TFT 30 as a switching element for a certain period, the image signals S1, S2,. Write at the timing.

  A predetermined level of image signals S1, S2,..., Sn written to the liquid crystal via the pixel electrode 9 is held for a certain period with the common electrode described later. The liquid crystal modulates light by changing the orientation and order of the molecular assembly according to the applied voltage level, thereby enabling gradation display. Here, in order to prevent the held image signal from leaking, a storage capacitor 70 is added in parallel with the liquid crystal capacitor formed between the pixel electrode 9 and the common electrode. Reference numeral 3b denotes a capacity line.

Next, a planar structure of the TFT array substrate that constitutes the liquid crystal device 100 of the present embodiment will be described with reference to FIG.
As shown in FIG. 2, a plurality of rectangular pixel electrodes 9 (contours are indicated by dotted line portions 9 </ b> A) are provided in a matrix on the TFT array substrate 10, and extend along the vertical and horizontal boundaries of the pixel electrodes 9. A data line 6a, a scanning line 3a, and a capacitor line 3b are provided. In the present embodiment, the inside of each pixel electrode 9 and the region where the data line 6a, the scanning line 3a, the capacitor line 3b, etc. disposed so as to surround each pixel electrode 9 are one dot region, The structure is such that display is possible for each dot area arranged in a shape.

  The data line 6a is electrically connected to a source region to be described later through a contact hole 5 in the semiconductor layer 1a made of, for example, a polysilicon film constituting the TFT 30, and the pixel electrode 9 is connected to the semiconductor layer 1a in the semiconductor layer 1a. These are electrically connected to a drain region described later via a contact hole 8. Further, in the semiconductor layer 1a, the scanning line 3a is disposed so as to face the channel region (the region with the oblique line rising to the left in the drawing), and the scanning line 3a functions as a gate electrode in a portion facing the channel region. .

  The capacitance line 3b is formed from a main line portion (that is, a first region formed along the scanning line 3a in plan view) extending substantially linearly along the scanning line 3a and a location intersecting the data line 6a. And a protruding portion (that is, a second region extending along the data line 6 a when viewed in a plan view) protruding toward the previous stage (upward in the drawing) along the data line 6 a. In FIG. 2, a plurality of first light shielding films 11 a are provided in a region indicated by a diagonal line rising to the right.

  More specifically, each of the first light shielding films 11a is provided at a position that covers the TFT 30 including the channel region of the semiconductor layer 1a when viewed from the TFT array substrate side, and is opposed to the main line portion of the capacitor line 3b. The main line portion extending linearly along the scanning line 3a and the protruding portion protruding from the portion intersecting with the data line 6a to the rear side (that is, downward in the figure) adjacent to the data line 6a. The tip of the downward protruding portion in each stage (pixel row) of the first light shielding film 11a overlaps the tip of the upward protruding portion of the capacitor line 3b in the next stage under the data line 6a. A contact hole 13 for electrically connecting the first light-shielding film 11a and the capacitor line 3b to each other is provided at the overlapping portion. In other words, in the present embodiment, the first light-shielding film 11a is electrically connected to the upstream or downstream capacitor line 3b through the contact hole 13.

  Further, liquid crystal alignment control means 21 for controlling the alignment direction of the liquid crystal is provided in one dot region. Specific examples of the liquid crystal alignment control means 21 include a slit formed in the pixel electrode 9 and a protrusion provided on the pixel electrode. The liquid crystal alignment control means 21 has a long axis in the direction parallel to the data line 6a (Y-axis direction), and the liquid crystal alignment direction at the time of voltage application is mainly defined in the direction parallel to the scanning line 3a (X-axis direction). doing. That is, the alignment of the liquid crystal is mainly performed in the X-axis direction when a voltage is applied.

On the other hand, looking at the cross-sectional structure, the liquid crystal display device 100 of the present embodiment has an initial alignment state of vertical alignment between the TFT array substrate 10 and the counter substrate 25 disposed opposite thereto, as shown in FIG. A liquid crystal layer 50 made of a liquid crystal material having a negative dielectric anisotropy is sandwiched.
The TFT array substrate 10 includes a pixel electrode 9 as a means for applying a voltage to the liquid crystal layer 50 and a liquid crystal layer 50 on the inner surface side (the liquid crystal layer 50 side) of the substrate body 10A made of a translucent material such as quartz or glass. An alignment film 23 that defines the initial alignment state in the direction perpendicular to the substrate 10 is formed in order. The counter substrate 25 has an initial alignment state of the common electrode 31 as a voltage applying means and the liquid crystal layer 50 in a direction perpendicular to the substrate 25 on the inner surface side of a substrate body 25A made of a translucent material such as quartz or glass. The defining alignment film 32 is formed in order. On the other hand, a quarter retardation plate 43 and a polarizing plate 44 are laminated on the outer surface side of the substrate body 10A, and a quarter retardation plate 41 and a polarizing plate 42 are laminated on the outer surface side of the substrate body 25A in this order. . And the circularly-polarizing plate of this invention is each comprised by the 1/4 phase difference plate and polarizing plate provided in each board | substrate. In FIG. 3, reference numeral 64 denotes a backlight.

  By the way, in this embodiment, in order to prevent the side view, the main alignment direction of the liquid crystal (direction of alignment division; X-axis direction in this embodiment) is optimally set with respect to the direction in which the viewing angle is desired to be limited. Yes. Specifically, the direction in which the viewing angle is desired to be matched with the main alignment direction (X-axis direction) of the liquid crystal. Further, in order to further enhance the effect of limiting the viewing angle, the ratio of the liquid crystal molecules aligned in that direction in one dot region is set to 2/3 or more of the whole, and the retardation Δnd of the liquid crystal layer 50 is set to 0.4 <Δnd. The range is set to <1.0.

Hereinafter, the relationship between these parameters and the viewing angle limiting effect will be described using simulation results.
4 and 5 are diagrams showing the viewing angle characteristics of the liquid crystal layer 50. Light is emitted from the backlight 64 during voltage application (white display), and the viewing angle is 0 ° with respect to the normal direction of the counter substrate 25. FIG. The relationship between the light reception angle (measurement angle) and the brightness (transmitted light amount) when it is swung from a position (vertical direction) to a position of 90 ° is shown. FIG. 4 shows viewing angle characteristics when the liquid crystal molecules are oriented and divided only in the X-axis direction and not oriented in the Y-axis direction (that is, when the orientation is divided into two domains), and FIG. 5 shows the viewing angle characteristics shown in FIG. Fig. 6 shows viewing angle characteristics when the orientation is uniformly controlled in each direction. 4A to 4G show viewing angle characteristics when the retardation Δnd of the liquid crystal layer is changed from 0.4 to 1.0, respectively. In the figure, the area indicated by the symbol A is the area having the largest transmitted light amount, and the areas indicated by the symbols B, C, D,...

  As shown in FIGS. 4 and 5, when the liquid crystal layer is uniformly oriented, the viewing angle is uniformly narrowed in all directions as the retardation Δnd of the liquid crystal layer increases. However, when the retardation Δnd is large in the two-domain state, The brightness in the direction (Y-axis direction) hardly changes, and only the left-right direction (X-axis direction) becomes darker. When Δnd exceeds 0.8, a bright portion begins to be formed on the wide-angle side, and when Δnd is 1.0, the amount of transmitted light increases in most directions other than the left-right direction, and the viewing angle limiting effect cannot be obtained. Specifically, in FIG. 4, a bright area is formed up to about 40% of the front.

  FIG. 6 is a diagram showing how the brightness in the left-right direction changes according to Δnd in a two-domain structure. From this figure, when Δnd is 0.7 or more, inversion on the wide-angle side starts to occur. I understand. In addition, when Δnd is 0.4 to 0.5, the viewing angle limit in the left-right direction is greatly changed. Therefore, the preferable range of Δnd is 0.4 <Δnd <1.0, more preferably 0.45. It can be seen that <Δnd <0.7.

FIG. 7 shows the viewing angle characteristics of white display when there is an orientation control portion in a direction other than the left-right direction (for example, the Y-axis direction) (FIG. 2 is an example thereof). For comparison, FIGS. 8 and 9 show cases where liquid crystal molecules are aligned only in the left-right direction (when a two-domain structure is adopted) and liquid crystal molecules are isotropically aligned in all directions, respectively.
FIG. 7 shows a case where the ratio of the liquid crystal molecules aligned in the left-right direction to the liquid crystal molecules aligned in the other direction in one dot region is 10: 6. In this case, although a certain viewing angle limiting effect is recognized as compared with the case where the orientation is controlled isotropically in all directions shown in FIG. 9, the restriction is limited as compared with the case of FIG. 8 where the orientation is controlled only in the left-right direction. It has been greatly relaxed. For this reason, in the alignment control, two-thirds or more of the whole is set in the horizontal direction (that is, the ratio of the liquid crystal molecules aligned in the horizontal direction and the ratio of the liquid crystal molecules aligned in other directions is 2: 1 or more) is a desirable condition.

  As described above, according to the liquid crystal display device of the present embodiment, when the display is viewed in a state tilted in the front direction or the vertical direction (Y-axis direction), a display with high contrast and less inversion display is possible. When the display is viewed from the horizontal direction (X-axis direction), the display can be made difficult to view with low contrast. For this reason, it is possible to eliminate the peep from the side while sufficiently ensuring the visibility to the user by the effect of the orientation division.

[Electronics]
Next, specific examples of the electronic apparatus including the liquid crystal display device according to the above embodiment of the present invention will be described.
FIG. 11 is a perspective view showing an example of a mobile phone. In FIG. 11, reference numeral 1000 denotes a mobile phone body, and reference numeral 1001 denotes a display unit using the liquid crystal display device. Since the mobile phone of this example is provided with the above-described liquid crystal display device in the display portion, it provides a display with excellent visibility for the user, and realizes an electronic device with an emphasis on privacy that is difficult for others to see. be able to.

The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in the above embodiment, the liquid crystal display device has a transmissive structure, but the present invention is not limited to this. For example, the transmissive display area for performing transmissive display within one dot area and the reflective display for performing reflective display. The present invention can also be applied to a transflective liquid crystal display device provided with a region. In this case, at least the liquid crystal layer in the transmissive display region is in the above-described condition, that is, the liquid crystal molecules are aligned and divided in at least one direction (for example, the left-right direction) in one dot region, and the ratio of the liquid crystal molecules aligned in the above direction The ratio of liquid crystal molecules aligned in other directions (for example, the vertical direction) is 2: 1 or more, and the retardation Δnd of the liquid crystal layer is 0.4 <Δnd <1.0 (particularly 0.45 <Δnd <0). If the condition of (7) is satisfied, a good viewing angle limiting effect can be obtained during transmissive display.

  In the above embodiment, an example in which the present invention is applied to an active matrix liquid crystal display device using TFT as a switching element has been described. However, in addition to an active matrix liquid crystal display device using TFD as a switching element, a passive matrix liquid crystal display device is also used. The present invention can also be applied to a display device or the like.

1 is an equivalent circuit diagram of a liquid crystal display device according to an embodiment of the present invention. The top view which shows the structure of the dot of a liquid crystal display device equally. The figure which shows the cross-section of a liquid crystal display device. The figure which shows the transmittance | permeability distribution when changing retardation (DELTA) nd of a liquid-crystal layer in a liquid crystal display device similarly. The figure which shows the transmittance | permeability distribution when changing retardation (DELTA) nd of a liquid-crystal layer in a liquid crystal display device similarly. The figure which shows the viewing angle characteristic in the left-right direction of a liquid crystal display device. The figure which shows the transmittance | permeability distribution when changing retardation (DELTA) nd of a liquid-crystal layer in a liquid crystal display device similarly. The figure which shows the transmittance | permeability distribution when changing retardation (DELTA) nd of a liquid-crystal layer in a liquid crystal display device similarly. The figure which shows the transmittance | permeability distribution when changing retardation (DELTA) nd of a liquid-crystal layer in a liquid crystal display device similarly. The figure which shows the plane structure of 1 dot at the time of carrying out the orientation control of a liquid crystal isotropic. FIG. 14 is a perspective view illustrating an example of an electronic device of the invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... TFT array substrate, 25 ... Opposite substrate, 50 ... Liquid crystal layer, 100 ... Liquid crystal display device, 1000 ... Electronic device

Claims (4)

A liquid crystal display device comprising a liquid crystal layer made of a liquid crystal having negative dielectric anisotropy and having an initial alignment state of vertical alignment between a pair of opposing circularly polarizing plates,
In the liquid crystal layer, the liquid crystal molecules are aligned and divided in at least one direction within one dot region, and the ratio of the liquid crystal molecules aligned in the above direction and the liquid crystal molecules aligned in other directions And a retardation Δnd of the liquid crystal layer satisfies a condition of 0.4 <Δnd <1.0.   A transmissive display region for performing transmissive display and a reflective display region for performing reflective display are provided in one dot region, and at least a liquid crystal layer in the transmissive display region is configured to satisfy the above-described conditions. Item 2. A liquid crystal display device according to item 1.   The liquid crystal display device according to claim 1, wherein the retardation Δnd satisfies 0.45 <Δnd <0.7. An electronic apparatus comprising the liquid crystal display device according to claim 1.

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