JP2015132732A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device that can display a half tone within a wide temperature range.SOLUTION: A liquid crystal display device 10 includes substrates 11 and 12 that are arranged opposite to each other, a polymer dispersion type liquid crystal layer 13 that is held between the substrates 11 and 12, a first display electrode 15 that is provided on the substrate 11, an insulating layer 18 that is provided on the first display electrode 15, a second display electrode 19 that is provided on the insulating layer 18 for displaying a common character together with the first display electrode 15, and a common electrode 21 that is provided on the substrate 12. The first display electrode 15 is formed not to be overlapped with the second display electrode 19 in plane projection.

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device using polymer dispersed liquid crystal.

  A polymer-dispersed liquid crystal has a structure in which liquid crystals are phase-separated in a polymer (polymer network) formed in a three-dimensional network, and liquid crystal molecules are randomly arranged along the side wall of the polymer network. A light scattering state and a light transmission state are respectively created in a state where the liquid crystal molecules are arranged in the electric field direction by applying an electric field (for example, Patent Document 1). The degree of scattering is determined by the voltage applied to the liquid crystal, and the voltage applied to the liquid crystal is determined by the partial pressure between the polymer material and the liquid crystal.

  FIG. 15 is a cross-sectional view showing an example of a conventional liquid crystal display device. A transparent display electrode 102 is formed on one glass substrate 101, and a transparent common electrode 104 is formed on the other glass substrate 103. A region where the display electrode 102 is formed is a region where pattern display is possible. The polymer dispersed liquid crystal layer 105 is sandwiched between the two glass substrates 101 and 103 described above, and the two glass substrates 101 and 103 are bonded together with a sealant 106 so as to enclose the polymer dispersed liquid crystal layer 105. The liquid crystal display device in FIG. 15 performs pattern display by applying a voltage between the display electrode 102 and the common electrode 104. For example, when 5 V is applied between the display electrode 102 and the common electrode 104, a transparent state is obtained, and when 0 V is applied between the display electrode 102 and the common electrode 104, a scattering state is obtained.

  FIG. 16 is a graph illustrating the relationship between voltage and transmittance at a plurality of types of temperatures (as an example, −10 ° C., 25 ° C., and 50 ° C.) by replacing the degree of scattering with transmittance. The maximum transmittance (near 90%) in the graph of FIG. 16 corresponds to the threshold value of the liquid crystal layer.

  As can be understood from FIG. 16, the transmittance at the same voltage varies greatly with temperature. The cause of this is that the dielectric constant of the liquid crystal is small when the temperature is high, and conversely, the dielectric constant is large when the temperature is low. For this reason, since the effective voltage substantially applied to the liquid crystal is divided by the polymer material, the effective voltage is high at a high temperature, and the effective voltage is low at a low temperature. Therefore, the characteristics of the liquid crystal display device using the polymer dispersion type liquid crystal greatly change with temperature as shown in FIG.

  When binary display of scattering (0 V) and transmission (5 V) is performed, even if the temperature changes, the display is not affected. However, when a halftone is expressed by the voltage, the transmittance greatly changes depending on the temperature. For example, at a voltage of 2.2 V, the transmittance is 50% at 25 ° C., but the transmittance is 86% at 50 ° C., the transmittance is 5% at −10 ° C., and the halftone is at 50 ° C. and −10 ° C. There is a problem that it cannot be expressed and is in the same level as a binary display.

  Patent Document 2 discloses a technique for displaying a halftone by dithering.

JP 2000-195853 A Japanese translation of PCT publication No. 2003-533751 International Publication No. 2012/111626

  An object of the present invention is to provide a liquid crystal display device capable of halftone display in a wide temperature range.

  A liquid crystal display device according to an aspect of the present invention includes a first and a second substrates disposed opposite to each other, a polymer-dispersed liquid crystal layer sandwiched between the first and second substrates, and a first substrate on the first substrate. A first display electrode provided; an insulating layer provided on the first display electrode; a second display electrode provided on the insulating layer for displaying a common character together with the first display electrode; And a common electrode provided on the second substrate. The first display electrode is formed so as not to overlap the second display electrode in planar projection.

  A liquid crystal display device according to an aspect of the present invention includes a first and a second substrates disposed opposite to each other, a polymer-dispersed liquid crystal layer sandwiched between the first and second substrates, and a first substrate on the first substrate. An insulating layer provided; a first display electrode provided on the insulating layer; and a character that is provided on the insulating layer and is electrically separated from the first display electrode and is shared with the first display electrode. And a common electrode provided on the second substrate.

  According to the present invention, it is possible to provide a liquid crystal display device capable of halftone display in a wide temperature range.

1 is a cross-sectional view of a liquid crystal display device according to a first embodiment of the present invention. Schematic which shows an example of the character which a liquid crystal display device can display. The top view of the lower display electrode and upper display electrode in a 1st pattern example. The top view of the lower display electrode and upper display electrode in the 2nd pattern example. Schematic explaining the state of the liquid crystal layer at the time of voltage control. The voltage waveform in the transparent state of a polymer-dispersed liquid crystal layer. Voltage waveform in the scattering state of the polymer dispersed liquid crystal layer. The voltage waveform in the weak scattering state 1 of a polymer dispersion type liquid crystal layer. The voltage waveform in the weak scattering state 2 of a polymer dispersion type liquid crystal layer. The top view which extracted and showed one character pattern. Sectional drawing of the liquid crystal display device which concerns on 2nd Embodiment of this invention. The top view of the 1st display electrode and 2nd display electrode in a 1st pattern example. The top view of the 1st display electrode and 2nd display electrode in a 2nd pattern example. FIG. 14 is a cross-sectional view of the first display electrode and the second display electrode along the line AA ′ shown in FIG. 13. Sectional drawing which shows an example of the conventional liquid crystal display device. The graph explaining the temperature dependence of the conventional liquid crystal display device.

  Hereinafter, embodiments will be described with reference to the drawings. However, it should be noted that the drawings are schematic or conceptual, and the dimensions and ratios of the drawings are not necessarily the same as the actual ones. Further, even when the same portion is represented between the drawings, the dimensional relationship and ratio may be represented differently. In particular, the following embodiments exemplify an apparatus and a method for embodying the technical idea of the present invention, and the technical idea of the present invention depends on the shape, structure, arrangement, etc. of components. Is not specified. In the following description, elements having the same function and configuration are denoted by the same reference numerals, and redundant description will be given only when necessary.

[First Embodiment]
[1. Configuration of liquid crystal display device]
FIG. 1 is a cross-sectional view of a liquid crystal display device 10 according to the first embodiment of the present invention. The liquid crystal display device 10 according to the present embodiment is a pattern display type liquid crystal display device that displays a plurality of characters such as characters and figures.

  The liquid crystal display device 10 is sandwiched between a first substrate 11 on which display electrodes are provided, a second substrate 12 on which common electrodes are provided and opposed to the first substrate 11, and the first substrate 11 and the second substrate 12. The liquid crystal layer 13 is provided.

  The liquid crystal layer 13 is sealed between the first substrate 11 and the second substrate 12 by a frame-shaped sealing material 14 surrounding the display region (screen region). The sealing material 14 bonds the first substrate 11 and the second substrate 12. The thickness (gap) of the liquid crystal layer 13 is, for example, about 7 μm. The liquid crystal layer 13 is composed of polymer dispersed liquid crystal (PDLC) or polymer network liquid crystal (PNLC). PDLC has a structure in which liquid crystals are dispersed in a polymer layer (polymer network), that is, a structure in which liquid crystals are phase-separated in the polymer. Alternatively, the liquid crystal in the polymer network may have a continuous phase.

  A photo-curing resin can be used as the polymer layer. For example, PDLC irradiates a solution in which liquid crystal is mixed with a photopolymerizable polymer precursor (monomer) by irradiating ultraviolet rays, polymerizes the monomer to form a polymer, and the liquid crystal is dispersed in the polymer network. . As the liquid crystal, for example, nematic liquid crystal having positive (positive) dielectric anisotropy is used. That is, when no voltage is applied to the liquid crystal layer, the liquid crystal molecules are randomly arranged in the polymer network, and when a voltage is applied to the liquid crystal layer, the liquid crystal molecules are in the electric field direction (liquid crystal The long axis of the molecule is oriented in the direction of the electric field).

  On the substrate 11 on the liquid crystal layer 13 side, a lower display electrode 15, a lower wiring electrode 16 electrically connected to the lower display electrode 15, and an upper wiring electrode 17 are provided. An insulating layer 18 is provided on the substrate 11 so as to cover the lower display electrode 15, the lower wiring electrode 16, and the upper wiring electrode 17. An upper display electrode 19 is provided on the insulating layer 18. One end of the upper display electrode 19 and the upper wiring electrode 17 are electrically connected by a contact plug 20 that penetrates the insulating layer 18. The lower wiring electrode 16 and the upper wiring electrode 17 are lead wirings for supplying a voltage to the lower display electrode 15 and the upper display electrode 19, respectively. In FIG. 1, a plurality of lower display electrodes 15 are shown, but these are electrically connected by an electrode portion (or wiring) (not shown) to form one lower display electrode 15. Similarly, in FIG. 1, a plurality of upper display electrodes 19 are shown, but these are electrically connected by an electrode portion (or wiring) (not shown) to form one upper display electrode 19.

  Here, the lower display electrode 15 and the upper display electrode 19 are formed so as not to overlap in a planar projection (plan view). Each of the lower display electrode 15 and the upper display electrode 19 is formed in a uniform pattern within the area of the character. A pattern example of the lower display electrode 15 and the upper display electrode 19 will be described later. The lower display electrode 15 and the upper display electrode 19 have substantially the same outer shape, and the character display is enabled by processing the lower display electrode 15 and the upper display electrode 19 into a character pattern.

  A common electrode 21 is provided on the substrate 12 on the liquid crystal layer 13 side. The surface opposite to the liquid crystal layer 13 of the substrate 12 is an image display surface of the liquid crystal display device 10.

  In FIG. 1, a lower display electrode 15 and an upper display electrode 19 for displaying one character are extracted and shown. The lower wiring electrode 16 and the upper wiring electrode 17 are provided for each character. On the other hand, one common electrode 21 is provided in common for all characters. Therefore, the common electrode 21 has substantially the same size as the screen size of the liquid crystal display device 10.

  Each of the first substrate 11 and the second substrate 12 is a transparent substrate made of glass, quartz, plastic, or the like. The lower display electrode 15, the lower wiring electrode 16, the upper wiring electrode 17, the upper display electrode 19, the contact plug 20, and the common electrode 21 are each composed of a transparent electrode, and for example, ITO (indium tin oxide) is used. The film thicknesses of the lower display electrode 15, the upper display electrode 19, and the common electrode 21 are each about 25 nm, for example. The insulating layer 18 is made of a transparent insulating material, and for example, silicon nitride is used. The film thickness of the insulating layer 18 is, for example, about 500 nm.

  FIG. 2 is a schematic diagram illustrating an example of characters that can be displayed by the liquid crystal display device 10. FIG. 2A is a plan view, and FIG. 2B is a side view. The area surrounded by the sealing material 14 is the display area DA of the liquid crystal display device 10, and the liquid crystal layer 13 is provided in the display area DA. The common electrode 21 has the same size as or larger than the display area DA.

  The plurality of square-shaped patterns shown in the display area DA are an example of a plurality of characters that can be displayed on the liquid crystal display device 10. A plurality of characters shown in FIG. 2 represent focus points to be displayed on a camera finder or the like. Each of the lower display electrode 15 and the upper display electrode 19 is processed into the same shape as the character pattern. The lower wiring electrode 16, the upper wiring electrode 17, and the common electrode 21 are each drawn out to the terminal 23. The plurality of terminals 23 are electrically connected to the drive circuits 21 and 22. As the character pattern, various figures and characters other than the square shape can be used.

[2. Example of lower display electrode and upper display electrode pattern]
Next, a pattern example of the lower display electrode 15 and the upper display electrode 19 will be described. FIG. 3 is a plan view of the lower display electrode 15 and the upper display electrode 19 in the first pattern example.

  The upper display electrode 19 is a mesh pattern having a plurality of openings 19A. The shape of the opening 19A may be a circle as shown in FIG. 3, or may be an ellipse, a rectangle, or another polygon. The diameter D of the opening 19A is, for example, about 50 μm, and the distance S between two adjacent openings 19A is, for example, about 18 μm. The upper display electrode 19 is electrically connected to the upper wiring electrode 17.

  The lower display electrode 15 includes a plurality of electrode portions 15A having the same planar shape as the plurality of openings 19A of the upper display electrode 19, and a plurality of connection portions 15B that electrically connect the plurality of electrode portions 15A. . That is, the plurality of electrode portions 15A of the lower display electrode 15 are arranged so as not to overlap the upper display electrode 19 in the planar projection. The lower display electrode 15 is electrically connected to the lower wiring electrode 16.

  In the present embodiment, the first area A1 in which the upper display electrode 19 and the common electrode 21 face each other directly, and the second area A2 in which the lower display electrode 15 and the common electrode 21 face each other directly (that is, the opening of the upper display electrode 19). The halftone is displayed by dithering with the area 19A. Therefore, in order to make the halftone display uniform, it is desirable that the plurality of openings 19A formed in the upper display electrode 19 are arranged uniformly. In the present embodiment, the plurality of openings 19A formed in the upper display electrode 19 have a staggered arrangement. A staggered arrangement is a plurality of openings arranged in the next row at a position half the distance between two adjacent openings or the distance between the centers of two adjacent openings (referred to as pitch). This is a pattern in which the openings are arranged. When a staggered arrangement is used as the pattern of the openings 19A formed in the upper display electrode 19, it is possible to prevent unevenness from occurring in a halftone display due to dithering.

  FIG. 4 is a plan view of the lower display electrode 15 and the upper display electrode 19 in the second pattern example. The upper display electrode 19 includes a plurality of electrode portions 19B and a plurality of connection portions 19C that electrically connect the plurality of electrode portions 19B. The planar shape of each electrode portion 19B is a polygon, for example, an octagon as shown in FIG. That is, the upper display electrode 19 has a pattern in which a plurality of polygons are uniformly arranged. The plurality of electrode portions 19B are electrically connected to the upper wiring electrode 17 (not shown).

  The lower display electrode 15 includes a plurality of electrode portions 15A and a plurality of connection portions 15B that electrically connect the plurality of electrode portions 15A. The planar shape of each electrode portion 15A is a polygon, for example, an octagon as shown in FIG. The area (size) of the electrode portion 15A of the lower display electrode 15 may be the same as or different from the area of the electrode portion 19B of the upper display electrode 19. Similar to the upper display electrode 19, the lower display electrode 15 has a pattern in which a plurality of polygons are uniformly arranged. The plurality of electrode portions 15A are electrically connected to a lower wiring electrode 16 (not shown).

  The lower display electrode 15 is disposed so as not to overlap the upper display electrode 19 in the planar projection. The plurality of electrode portions 15A of the lower display electrode 15 are arranged so as to have a minimum gap with the plurality of electrode portions 19B of the upper display electrode 19 in planar projection. For example, the pattern composed of the plurality of electrode portions 15A and the plurality of electrode portions 19B has a staggered arrangement, that is, the electrode portions 15A are arranged with a half-pitch shift from the electrode portions 19B.

  Also in the second pattern example shown in FIG. 4, the first area A1 in which the upper display electrode 19 and the common electrode 21 face each other and the second area A2 in which the lower display electrode 15 and the common electrode 21 face each other directly. Halftones can be displayed by dithering.

[3. Operation]
Next, the operation of the liquid crystal display device 10 will be described. The image display operation of the liquid crystal display device 10 is controlled by the drive circuits 21 and 22. The drive circuit 21 is electrically connected to the lower wiring electrode 16 and the common electrode 21, and applies a binary voltage (two kinds of voltages) between the lower wiring electrode 16 and the common electrode 21. The drive circuit 22 is electrically connected to the upper wiring electrode 17 and the common electrode 21, and applies a binary voltage (two types of voltages) between the upper wiring electrode 17 and the common electrode 21. Thereby, the lower display electrode 15 connected to the lower wiring electrode 16 and the upper display electrode 19 connected to the upper wiring electrode 17 can be independently voltage controlled.

FIG. 5 is a schematic diagram for explaining the state of the liquid crystal layer 13 during voltage control. FIG. 5A is a diagram illustrating a scattering state of the liquid crystal layer 13, and FIG. 5B is a diagram illustrating a transmission state of the liquid crystal layer 13. In FIG. 5, a part of the liquid crystal layer 13 sandwiched between the common electrode 21 and the upper display electrode 19 is extracted and shown. Liquid crystal molecules are represented by the spheroidal optically (rotation in the ellipse long axis), the refractive index n _o of the size in the short-axis direction of the normal _light, the refractive index n _e of the diameter in the major axis direction is abnormal light It becomes.

  When no electric field is applied to the liquid crystal layer 13, liquid crystal molecules are randomly arranged. In this case, when white light is incident on the liquid crystal layer 13, the incident light is scattered and is observed as a white turbid state from the outside (white display).

On the other hand, when an electric field is applied to the liquid crystal layer 13, the liquid crystal molecules are aligned in the electric field direction (that is, the vertical direction). In this case, when the incident white light to the liquid crystal layer 13, (the direction perpendicular to the traveling direction) vibration direction of the light incident light so aligned to the refractive index n _o goes straight through the liquid crystal layer 13. For this reason, incident light is transmitted and observed as a transparent state from the outside (black display).

  In the present embodiment, since the upper display electrode 19 and the lower display electrode 15 are arranged so as not to overlap, the state of the liquid crystal layer 13 in the first region A1 where the upper display electrode 19 and the common electrode 21 face each other directly, It becomes possible to independently control the state of the liquid crystal layer 13 in the second region A2 in which the lower display electrode 15 and the common electrode 21 face each other directly. Therefore, when one character is displayed, four types of display, transparent, halftone (weak scattering 1 and 2), and scattering, can be performed by dithering the first area A1 and the second area A2.

  FIG. 6 is a voltage waveform in the transparent state. In the transparent state, the drive circuit 22 applies a high voltage (for example, 5 V) between the upper display electrode 19 and the common electrode 21, and the drive circuit 21 applies 5 V between the lower display electrode 15 and the common electrode 21. Thereby, since 5V is applied to the whole character pattern, the whole character pattern can be made into a transparent state. In addition, since the liquid crystal deteriorates when a DC voltage is continuously applied to the liquid crystal layer, inversion driving is used in which the polarity of the voltage is inverted every certain time. The period for performing the inversion driving can be appropriately designed according to the liquid crystal material, the magnitude of the voltage, and the like, and is, for example, “1/30” seconds in this embodiment.

  FIG. 7 is a voltage waveform in the scattering state. In the scattering state, the drive circuit 22 applies 0 V between the upper display electrode 19 and the common electrode 21, that is, the upper display electrode 19 and the common electrode 21 are set to the same potential, and the drive circuit 21 has the lower display electrode 15 and the common electrode 21. 0 V is applied between them, that is, the upper display electrode 19 and the common electrode 21 are set to the same potential. Thereby, since the electric field is not applied to the whole character pattern, the whole character pattern can be made into a scattering state.

  FIG. 8 is a voltage waveform in the weak scattering state 1. In the weak scattering state 1, the drive circuit 22 applies 5 V between the upper display electrode 19 and the common electrode 21, and the drive circuit 21 applies 0 V between the lower display electrode 15 and the common electrode 21. As a result, an electric field is applied to the first area A1 of the character pattern and no electric field is applied to the second area A2 of the character pattern, so that the first area A1 is in a transparent state and the second area A2 is in a scattering state. Can do. Therefore, the first halftone by dithering is displayed by the voltage control of FIG.

  FIG. 9 is a voltage waveform in the weak scattering state 2. In the weak scattering state 2, the drive circuit 22 applies 0 V between the upper display electrode 19 and the common electrode 21, and the drive circuit 21 applies 5 V between the lower display electrode 15 and the common electrode 21. As a result, no electric field is applied to the first area A1 of the character pattern, and an electric field is applied to the second area A2 of the character pattern, so that the first area A1 is in a scattering state and the second area A2 is in a transparent state. can do. Therefore, the second halftone different from the first halftone can be displayed by the voltage control of FIG.

  Note that the first halftone, the second halftone, and the transmittance can be arbitrarily designed by changing the area ratio between the lower display electrode 15 and the upper display electrode 19. In this way, by appropriately setting the area ratio between the lower display electrode 15 and the upper display electrode 19, it is possible to display the character with four-level gradation.

  Further, in the first pattern example of FIG. 3, when the diameter of the opening 19A of the upper display electrode 19 is as small as 25 μm or less, the light is split by light diffraction and a rainbow can be seen. Is preferably 25 μm or more. In addition, when the diameter of the opening 19A is as large as 100 μm or more, the character display does not look uniform, and display unevenness such as, for example, a dot appears. Therefore, the diameter of the opening 19A is preferably 100 μm or less. Similarly, in the second pattern example of FIG. 4, the diameter of the electrode portion 15A of the lower display electrode 15 and the diameter of the electrode portion 19B of the upper display electrode 19 are preferably 25 μm or more and 100 μm or less, respectively.

[4. Specific example of character pattern]
Next, a specific example of one character pattern will be described. FIG. 10 is a plan view showing one character pattern extracted. The character pattern is, for example, a square shape shown in FIG.

  The character pattern having a square shape is represented by a lower display electrode 15 and an upper display electrode 19 having the same outer shape as the character pattern. The line width of the letter B is, for example, 120 μm. The upper display electrode 19 has a mesh pattern having an opening with a diameter of 50 μm, for example. The upper display electrode 19 is electrically connected to the drive circuit 22 via the contact plug 20 and the upper wiring electrode 17.

  The lower display electrode 15 includes a plurality of electrode portions 15 </ b> A having a circular shape and a plurality of connection portions 15 </ b> B that electrically connect the plurality of electrode portions 15. In addition, in order to avoid a figure becoming complicated, illustration of the connection part 15B of the lower display electrode 15 is abbreviate | omitted. The lower display electrode 15 is electrically connected to the drive circuit 21 through the lower wiring electrode 16.

  An upper display electrode 30 formed in a planar shape is provided in a region inside the letter-shaped character pattern. An upper display electrode 31 formed in a planar shape is provided in a region outside the letter-shaped character pattern. The upper display electrode 30 and the upper display electrode 31 are formed of a wiring layer at the same level as the upper display electrode 19. The upper display electrode 19, the upper display electrode 30, and the upper display electrode 31 are electrically separated from each other by a gap. The upper display electrode 30 and the upper display electrode 31 are electrically connected by a jumper 32, and are electrically connected to the drive circuit 22 via the jumper 32. The jumper 32 is formed of a wiring layer at the same level as the lower display electrode 15.

  The square character pattern can display four gradations of transparency, first halftone, second halftone, and scattering. Since the upper display electrode 30 and the upper display electrode 31 are formed in a planar shape, the two regions of transparency and scattering can be displayed in the inner and outer regions of the letter B.

  Here, since the line width of the square is as small as about 120 μm, the opening of the upper display electrode 19 may be interrupted at the pattern edge of the square. Since the upper display electrode 19 does not exist in the region where the opening is interrupted, the alignment of the liquid crystal layer 13 cannot be controlled by the upper display electrode 19 and the display of the pattern edge is easily blurred. In order to suppress the display blur of the pattern edge, it is desirable to trim the upper display electrode 19 along the pattern edge of the square shape. In other words, the edge 19-1 of the upper display electrode 19 is always provided at the pattern edge of the square shape. Thereby, since the gradation of the pattern edge can be accurately displayed, display blur of the pattern edge can be suppressed.

[5. effect]
As described above in detail, the liquid crystal display device 10 according to the first embodiment includes the substrate 11 on which the lower display electrode 15 and the upper display electrode 19 are formed, the substrate 12 on which the common electrode 21 is formed, the substrate 11 and the substrate. 12 and a liquid crystal layer 13 made of PDLC (or PNLC). The lower display electrode 15 and the upper display electrode 19 are separated from each other by the insulating layer 18 and processed into the same outer shape as the character pattern. The lower display electrode 15 and the upper display electrode 19 are patterned so as not to overlap each other. Then, using a binary voltage, display is performed in four gradations of transparency, halftone (weak scattering 1 and 2), and scattering.

The current value consumed in the liquid crystal display device is estimated below. The current value I per unit area is expressed by Expression (1). f is the frequency of the ON waveform, C is the capacitance value per unit area, and V ₀ is the peak value of the ON waveform.

I = 2fCV ₀ (1)

I ₁ , I ₂ , and I ₃ are respectively between the common electrode 21 and the upper display electrode 19, between the common electrode 21 and the lower display electrode 15, and between the lower display electrode 15 and the upper display electrode 19. This is the current value (current density) per unit area. ε ₁ is the dielectric constant of the liquid crystal layer 13, ε ₂ is the dielectric constant of the insulating layer 18, d ₁ is the thickness of the liquid crystal layer 13, and d ₂ is the thickness of the insulating layer 18. I ₁ , I ₂ , and I ₃ are represented by Formula (2), Formula (3), and Formula (4), respectively.

I ₁ = 2fε ₁ V ₀ / d ₁ (2)
I ₂ = 2fε ₁ ε ₂ V ₀ / (ε ₁ d ₂ + ε ₂ d ₁ ) (3)
I ₃ = 2fε ₂ V ₀ / d ₂ (4)

Here, when ε ₁ and ε ₂ are equal in the vicinity of 4ε ₀ (ε ₀ : dielectric constant of vacuum), and d ₁ = 10 μm and d ₂ = 0.4 μm, I ₁ , I ₂ , and I ₃ are expressed by the formula ( 5).

_{I 1: I 2: I 3} = d 1 -1: (d 1 + d 2) -1: d 2 -1 ≒ 1: 1: 25 ··· (5)

From the equation (5), the current value I ₃ between the lower display electrode 15 and the upper display electrode 19 becomes the largest. However, in the present embodiment, since the lower display electrode 15 and the upper display electrode 19 are arranged so as not to overlap, the current value I ₃ between the lower display electrode 15 and the upper display electrode 19 can be reduced. Thereby, the consumption current of the liquid crystal display device 10 can be reduced.

  Further, in the conventional nematic liquid crystal, an intermediate voltage is displayed by applying an intermediate voltage (for example, 2.1 V) to tilt the liquid crystal molecules. In such a conventional example, the response speed for displaying a halftone is increased. On the other hand, in the present embodiment, no intermediate voltage is used to display halftones. Thereby, halftone display over a wide temperature range is possible. In addition, the response speed for displaying halftones can be increased.

  Further, since the liquid crystal layer 13 made of PDLC or PNLC is used, a plurality of gradations can be expressed without using a polarizing plate or an alignment film. Thereby, the liquid crystal display device 10 capable of reducing the manufacturing cost and miniaturizing can be realized.

  Further, since the openings 19A of the upper display electrode 19 are arranged in a staggered arrangement, the upper display electrode 19 has a uniform net pattern. Thereby, the display unevenness of a halftone can be suppressed.

[Second Embodiment]
In the second embodiment, two types of display electrodes for performing dithering are configured by wiring layers of the same level. FIG. 11 is a cross-sectional view of the liquid crystal display device 10 according to the second embodiment of the present invention.

  The first display electrode 15 and the second display electrode 19 are provided on the insulating layer 18. The first display electrode 15 and the second display electrode 19 are formed so as not to overlap each other in a planar projection (plan view) and are electrically separated from each other. The first display electrode 15 is electrically connected to the first wiring electrode 16 formed on the substrate 11 via the contact plug 40. The second display electrode 19 is electrically connected to the second wiring electrode 17 formed on the substrate 11 through the contact plug 20. Other configurations are the same as those of the first embodiment.

  Next, a pattern example of the first display electrode 15 and the second display electrode 19 will be described. FIG. 12 is a plan view of the first display electrode 15 and the second display electrode 19 in the first pattern example.

  The first display electrode 15 includes a plurality of electrode portions 15A and a plurality of connection portions 15B that electrically connect the plurality of electrode portions 15A. The planar shape of each electrode portion 15A is a polygon, for example, an octagon as shown in FIG. That is, the first display electrode 15 has a pattern in which a plurality of polygons are uniformly arranged. The plurality of electrode portions 15A are electrically connected to a first wiring electrode 16 (not shown).

  The second display electrode 19 includes a plurality of electrode portions 19B and a plurality of connection portions 19C that electrically connect the plurality of electrode portions 19B. The planar shape of each electrode portion 19B is a polygon, for example, an octagon as shown in FIG. The area (size) of the electrode portion 19B of the second display electrode 19 may be the same as or different from the area of the electrode portion 15A of the first display electrode 15. Similar to the first display electrode 15, the second display electrode 19 has a pattern in which a plurality of polygons are uniformly arranged. The plurality of electrode portions 19B are electrically connected to a second wiring electrode 17 (not shown).

  The second display electrode 19 is disposed so as not to overlap the first display electrode 15 in the planar projection, and is electrically separated by opening a predetermined gap. For example, the pattern composed of the plurality of electrode portions 15A of the first display electrode 15 and the plurality of electrode portions 19B of the second display electrode 19 has a staggered arrangement.

  Similar to the first embodiment, also in the first pattern example shown in FIG. 12, the first region A1 in which the first display electrode 15 and the common electrode 21 face each other directly, the second display electrode 19 and the common electrode 21 Can be displayed by dithering with the second area A2 facing each other directly.

  FIG. 13 is a plan view of the first display electrode 15 and the second display electrode 19 in the second pattern example. FIG. 14 is a cross-sectional view of the first display electrode 15 and the second display electrode 19 along the line AA ′ shown in FIG.

  The second display electrode 19 is a mesh pattern having a plurality of openings 19A. For example, the plurality of openings 19A formed in the second display electrode 19 have a staggered arrangement. The shape of the opening 19A may be a circle as shown in FIG. 13, or may be an ellipse, a rectangle, or another polygon. The diameter D of the opening 19A is, for example, about 50 μm, and the distance S between two adjacent openings 19A is, for example, about 18 μm. The second display electrode 19 is electrically connected to the second wiring electrode 17.

  The first display electrode 15 includes a plurality of electrode portions having the same planar shape as the plurality of openings 19 </ b> A of the second display electrode 19. The plurality of electrode portions 15 are electrically connected to the first wiring electrode 16 through the plurality of contact plugs 40. The first display electrode 15 composed of a plurality of circular electrode portions is arranged so as not to overlap the second display electrode 19 in planar projection.

  Also in the second pattern example shown in FIG. 13, the first region A1 in which the first display electrode 15 and the common electrode 21 face each other, and the second region A2 in which the second display electrode 19 and the common electrode 21 face each other directly. A halftone can be displayed by dithering. In order to make the halftone display uniform, it is desirable that the openings 19A formed in the second display electrode 19 be uniformly arranged. Also in the second embodiment, the opening 19A formed in the second display electrode 19 has a staggered arrangement. When a staggered arrangement is used as the pattern of the openings 19A formed in the second display electrode 19, it is possible to prevent unevenness from occurring in a halftone display due to dithering.

  As described above in detail, according to the second embodiment, since the first display electrode 15 and the second display electrode 19 are arranged so as not to overlap with each other, the current consumption of the liquid crystal display device 10 can be reduced. In addition, since the first display electrode 15 and the second display electrode 19 are composed of the same level of wiring layers, the first display electrode 15 and the second display electrode 19 are processed once (photolithography and etching). Can be formed. Thereby, the manufacturing cost can be reduced and there is no need to consider misalignment between the first display electrode 15 and the second display electrode 19. Other effects are the same as those of the first embodiment.

  The liquid crystal display device 10 of the first and second embodiments can be applied to a pattern display type liquid crystal display device that displays characters and figures superimposed on a finder such as a camera. In addition, the liquid crystal display device 10 of the first and second embodiments can be applied to a digital clock, a light control glass, a liquid crystal display device capable of segment display, a liquid crystal display device capable of matrix display, and the like. .

  The present invention is not limited to the above embodiment, and can be embodied by modifying the constituent elements without departing from the scope of the invention. Further, the above embodiments include inventions at various stages, and are obtained by appropriately combining a plurality of constituent elements disclosed in one embodiment or by appropriately combining constituent elements disclosed in different embodiments. Various inventions can be configured. For example, even if some constituent elements are deleted from all the constituent elements disclosed in the embodiments, the problems to be solved by the invention can be solved and the effects of the invention can be obtained. Embodiments made can be extracted as inventions.

  DESCRIPTION OF SYMBOLS 10 ... Liquid crystal display device 11,12 ... Board | substrate, 13 ... Liquid crystal layer, 14 ... Seal material, 15, 19 ... Display electrode, 16, 17 ... Wiring electrode, 18 ... Insulating layer, 20, 40 ... Contact plug, 21 ... Common electrode, 21, 22 ... Drive circuit, 23 ... Terminal, 30,31 ... Upper display electrode, 32 ... Jumper, 101,103 ... Substrate, 102 ... Display electrode, 104 ... Common electrode, 105 ... Polymer dispersed liquid crystal layer 106: Sealing material.

Claims (8)

First and second substrates disposed opposite to each other;
A polymer dispersed liquid crystal layer sandwiched between the first and second substrates;
A first display electrode provided on the first substrate;
An insulating layer provided on the first display electrode;
A second display electrode provided on the insulating layer for displaying a common character together with the first display electrode;
A common electrode provided on the second substrate;
Comprising
The liquid crystal display device, wherein the first display electrode is formed so as not to overlap the second display electrode in planar projection. First and second substrates disposed opposite to each other;
A polymer dispersed liquid crystal layer sandwiched between the first and second substrates;
An insulating layer provided on the first substrate;
A first display electrode provided on the insulating layer;
A second display electrode provided on the insulating layer, electrically separated from the first display electrode, for displaying a common character together with the first display electrode;
A common electrode provided on the second substrate;
A liquid crystal display device comprising:   The liquid crystal display device according to claim 1, wherein each of the first and second display electrodes has a uniform pattern. The second display electrode is composed of a mesh pattern having a plurality of openings,
4. The liquid crystal display device according to claim 1, wherein the first display electrode includes a plurality of electrode portions having the same planar shape as the plurality of openings. 5.   4. The liquid crystal display device according to claim 1, wherein each of the first and second display electrodes includes a plurality of polygonal electrode portions. 5. A first wiring provided on the first substrate and electrically connected to the first display electrode;
The liquid crystal display device according to claim 1, further comprising: a second wiring provided on the first substrate and electrically connected to the second display electrode. A first drive circuit for applying a first voltage between the common electrode and the first display electrode;
The liquid crystal display device according to claim 1, further comprising: a second drive circuit that applies a second voltage between the common electrode and the second display electrode.   8. The liquid crystal display device according to claim 7, wherein each of the first and second voltages is two kinds of voltages.

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