JP5446668B2 - Liquid crystal display element - Google Patents

Description

  The present invention relates to an active matrix liquid crystal display element.

  In recent years, with the development of mobile devices such as portable information terminals, there is an increasing demand for display elements with low power consumption and high image quality. As a flat panel display satisfying such a demand, there is a reflective liquid crystal display element which does not require a backlight and has low power consumption. However, since all of the liquid crystal display elements in the twisted nematic (TN) mode or the super-twisted nematic (STN) mode that are generally used at present must use polarizing plates, There is a problem that utilization efficiency is low and the display is very dark when used as a reflective display.

  As a liquid crystal display method that does not use a polarizing plate, there is a light scattering display mode in which an action with respect to incident light is switched between a scattering state (bright display) and a transmission state (dark display) by an electric field. Among light-scattering display modes, active matrix driving type polymer dispersed liquid crystal (PDLC) as shown in Patent Document 1 is attracting attention in terms of application to electronic paper. .

Japanese Patent Laid-Open No. 5-165019

  In a reflection type / active matrix driving type polymer dispersed liquid crystal display element, since a light shielding film is not usually disposed on a signal line or scanning line in order to brighten the display, the orientation of liquid crystal molecules on the signal line or scanning line is adjusted. There is a problem that image quality unevenness such as tailing caused by a domain that cannot be controlled occurs and display quality deteriorates.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a reflection type active matrix drive type polymer dispersed liquid crystal display element that can stably obtain a high-quality and bright display without causing uneven image quality such as tailing.

According to a first aspect of the present invention, there is provided a liquid crystal display element comprising: a first substrate disposed on a display viewing side; a second substrate disposed opposite to the first substrate; and a polymer material. A liquid crystal is held in a dispersed state, and is formed on the inner surface of the second substrate and a polymer dispersed liquid crystal sandwiched between the inner surfaces of the first substrate and the second substrate. The auxiliary capacitance electrode formed on the reflection surface that reflects light, the first insulating layer formed on the inner surface of the second substrate and covering the auxiliary capacitance electrode, and the first 1 of a plurality of pixel electrodes made of the storage capacitor electrode in the opposing transparent conductive film formed in a matrix arranged at a position on the insulating film, is disposed between the rows of the pixel electrodes adjacent a plurality of the pixels a plurality of signal lines for supplying a signal voltage to the electrode, supplying all the signal voltage and the signal line A plurality of switching elements interposed respectively between a plurality of pixel electrodes, are Hi設on the inner surface of the first substrate, a common electrode formed of a transparent conductive film which common voltage is applied, the second substrate side It is disposed over a plurality of the signal lines second insulating layer respectively on, and a plurality of shield electrode to which the common voltage is applied, possess, the storage capacitor electrode and the extending direction of the signal line The pixel electrodes are extended in a direction perpendicular to each other, the entire pixel electrodes overlap the auxiliary capacitance electrodes, and the width of the auxiliary capacitance electrodes in the direction of extension of the signal lines is the direction of extension of the signal lines of the pixel electrodes. It is characterized by being larger than the width of .

  According to a second aspect of the present invention, in the liquid crystal display element of the first aspect, the shield electrode is made of a transparent conductive film made of the same material as the pixel electrode, and is disposed on the insulating film surface on which the pixel electrode is provided. It is characterized by being.

  According to a third aspect of the present invention, in the liquid crystal display element of the first or second aspect, the polymer dispersed liquid crystal is a polymer network type liquid crystal.

  According to the present invention, it is possible to obtain a reflective active matrix driving type polymer dispersion type liquid crystal display element which can stably obtain a high-quality and bright display without causing unevenness in image quality such as tailing.

It is a partial enlarged plan view which shows PNLCD as one Embodiment of this invention. (A) is the II-II sectional view taken on the line of FIG. 1 which shows a permeation | transmission state, (b) is typical II-II sectional view taken on the line of FIG. 1 which shows a scattering state. (A) is a top view which shows the display by PNLCD as one Embodiment of this invention, (b) is the top view which showed the display by PNLCD as a comparative example. FIG. 6 is a schematic cross-sectional view showing the operation of the PNLCD as the comparative example, where (a) is an on (transmission) display state, (b) is an off (scattering) display state in a pixel row without an on display, and (c) is on. The off display state in the same pixel column as the display is shown.

  In FIG. 2A, of the pair of glass substrates 1 and 2 arranged opposite to each other, the inner surface (opposite side surface) of the rear glass substrate 2 on the opposite side to the front glass substrate 1 positioned on the display viewing side is provided. The auxiliary capacitance electrode 3 is disposed. The auxiliary capacitance electrode 3 also serves as a reflective electrode, and therefore the surface thereof is formed as a mirror surface.

  Thereafter, a gate electrode 4 (see FIG. 1) is formed on the inner surface of the glass substrate 2 so as to correspond to the arrangement position of a TFT (Thin Film Transistor) as a switching element arranged for each pixel arranged in a matrix. A plurality of gate lines 5 that are disposed and electrically connect the gate electrodes 4 for each simultaneous scanning row are provided extending in parallel with each other. The auxiliary capacitance electrode 3, the gate electrode 4, and the gate line 5 are collectively formed in the same process on a thin film having a thickness of 100 to 300 nm using the same metal material such as an aluminum alloy.

  A gate insulating film 6 is deposited so as to cover the auxiliary capacitance electrode 3, the gate electrode 4, and the gate line 5. The gate insulating film 6 is formed as a transparent thin film having a thickness of 300 to 600 nm using silicon nitride as a material.

Amorphous silicon a-Si film 7 (see FIG. 1) having a thickness of 250 to 500 nm made of a dielectric material such as SiN or SiO ₂ is patterned in an island shape above gate electrode 4 on the surface of gate insulating film 6. The source electrode 8 and the drain electrode 9 are disposed so as to face each other with a part of the a-Si film 7 formed thereon. The source electrode 8 and the drain electrode 9 are patterned to a thickness of 100 to 300 nm using a metal material such as Mo alloy.

  On the surface of the gate insulating film 6, a plurality of source lines 11 are extended in parallel to each other between pixel columns in a direction orthogonal to the gate lines 5 in a display region in which pixels are arranged in a matrix. The source line 11 supplies an image signal to each pixel through a TFT as a switching element, and is formed in a single process by using a Mo alloy of the same material as the source electrode.

  An interlayer insulating film 12 is provided so as to cover the source electrode 8, the drain electrode 9 and the source line 11. Similar to the gate insulating film 6, the interlayer insulating film 12 is also formed as a transparent thin film having a thickness of 100 to 200 nm using silicon nitride as a material.

  On the surface of the interlayer insulating film 12, a plurality of pixel electrodes 13 are formed in a matrix arrangement. The pixel electrode 13 is patterned in a transparent conductive film having a film thickness of 50 to 100 nm using a transparent conductive material such as ITO (indium tin oxide), and the installation range of the one pixel electrode 13 is one. It becomes a pixel.

  Umbrella electrodes 14 are disposed above the source lines 11 on the surface of the interlayer insulating film 12. The umbrella electrode 14 is collectively formed in the same process on a transparent conductive film having the same film thickness using ITO of the same material as the pixel electrode 13. Thereby, the increase in raw material cost and man-hour by providing the umbrella electrode 14 is avoided.

  The umbrella electrode 14 is provided to shield the electric field caused by the image signal voltage supplied to the source line 11 so as to cover the lower source line 11 so as not to affect the alignment of the liquid crystal. w1 is set to a dimension sufficiently larger than the width w2 of the source line 11, so that each source line 11 can be reliably covered. The same voltage as the common voltage applied to the common electrode described below is applied to these umbrella electrodes 14.

  A common electrode 15 is uniformly formed on the inner surface of the front glass substrate 1 with the same film thickness. Similar to the pixel electrode 13, the common electrode 15 is formed on a single thin film using ITO, which is a transparent conductive material. A predetermined common voltage is applied to the common electrode 15.

  The common voltage applied to the common electrode 15 is applied to form an electric field for driving the liquid crystal between the pixel electrode 13 on the rear glass substrate 2 side and is usually set to a stable voltage such as a ground potential. Is set. Accordingly, in a region facing the pixel electrode 13, that is, the pixel region D 1, when an on voltage having a predetermined potential is applied to the pixel electrode 13 through the source line 11, an electric field corresponding to the on voltage is formed in the pixel region. Here, an umbrella electrode 14 is formed so as to cover the source line 11 between the adjacent pixel columns where the source line 11 extends (between the pixel columns) and the common electrode 15, that is, the inter-pixel column region D 2. Since a voltage having the same potential as the common voltage applied to the common electrode 15 is applied to the umbrella electrode 14, the opposite region between the umbrella electrode 14 and the common electrode 15, that is, the inter-pixel column region D 2 is provided. An electric field is not formed stably at all times. An image signal voltage corresponding to the input image signal is supplied to the source line 11, but the source line 11 is reliably covered with the umbrella electrode 14 having a sufficiently wide width w 1, and therefore, between the source line 11 and the umbrella electrode 14. An electric field is not formed between the common electrode 15 and only an electric field is formed.

  Between the pair of glass substrates 1 and 2, a polymer dispersed liquid crystal 16 in which liquid crystal is dispersed and held in a polymer material is sandwiched. In this embodiment, a polymer network type liquid crystal (hereinafter referred to as PNLC) in which a large number of voids formed in a net shape like a sponge is filled is used as the polymer dispersion type liquid crystal. This PNLC is obtained by sandwiching a mixture of a liquid crystal material and a photopolymerizable compound (monomer) between a pair of glass substrates 1 and 2 and irradiating with ultraviolet rays under certain conditions. Phase separation occurs upon irradiation with ultraviolet rays, and the photopolymerizable compound is converted into a polymer by photopolymerization, and a polymer network having an infinite number of fine domains 161 (polymer voids filled with liquid crystal) by cross-linking. (PN: Polymer Network) is formed in the liquid crystal. Such a display element using PNLC (PNLCD) does not require an alignment film or an alignment treatment required for a general liquid crystal display element (LCD), and a polarizing plate or a retardation film is also unnecessary. Since a simple structure can be obtained and light loss due to the polarizing plate does not occur, it is superior to a TN liquid crystal display element in terms of brightness.

  Next, a display operation by the PNLCD of the present embodiment configured as described above will be described.

  First, as shown in FIG. 2A, in the on display state in which the scanning signal voltage is supplied to the gate electrode to turn on the TFT and the on signal voltage is supplied to the pixel electrode 13 through the source line 11, An electric field based on the ON signal voltage is formed in the region D1, the liquid crystal molecules in the domain 161 in the pixel region D1 are aligned in the direction of the electric field, and the refractive indexes of the liquid crystal layer in the domain 161 and the polymer net layer 162 are substantially the same. The pixel area D1 becomes transparent. Therefore, the light incident on the pixel region D1 from the front glass substrate 1 side is transmitted as it is, is reflected by the auxiliary capacitance electrode 3 which also serves as a reflection electrode, passes through the pixel region D1 again, and is emitted from the front glass substrate 1 to the outside. . This emitted light is mirror-reflected light from the mirror-reflected reflecting surface of the auxiliary capacitance electrode 3.

  Next, as shown in FIG. 2B, an electric field is applied to the pixel region D1 in the off-display state in which an off-voltage having substantially the same voltage level as the common voltage applied to the common electrode 15 is applied to the pixel electrode 13. Is not formed, the liquid crystal molecules in the domain 161 are aligned in any direction for each domain 161, and the refractive index of the liquid crystal layer in the domain 161 and the polymer net layer 162 do not match, so that the pixel region D1 is in a light scattering state. Become. Therefore, most of the light incident on the pixel region D1 from the front glass substrate 1 side is scattered and emitted from the front glass substrate 1. As a result, the pixel region D1 is displayed in white.

  Here, the inter-pixel column region D2 is shielded by the umbrella electrode 14 regardless of the image signal voltage supplied to the source line 11 in any of the above-described ON display state and OFF display state. Therefore, the liquid crystal molecules in the domain 161 in the inter-pixel electrode region D2 are aligned in an arbitrary direction for each domain 161 and are incident in the same manner as the pixel region D1 in the off-display state. The light is scattered to display white.

  FIG. 3A is a plan view showing a display screen in the PNLCD of this embodiment, which is a two-tone display composed of a mirror display area A1 and a white display area A2. The white display area A2 is the same as the mirror display area A1 in the same row area A21 or in a different row area A22, and the white display state shown in FIG. There are no image irregularities such as streaks.

  Here, as a comparative example, a display operation by the PNLCD in which the umbrella electrode 14 is omitted from the PNLCD of this embodiment will be described. In this case, since the umbrella electrode is not provided, an electric field is formed in the inter-pixel column region D2 according to the image signal voltage supplied to the source line 11.

  First, the ON display state will be described. As shown in FIG. 4A, an ON electric field based on an ON signal voltage applied to the pixel electrode 13 is formed in the pixel region D1 of the ON display pixel area, and the pixel region D1. Is an ON display state in which the liquid crystal molecules of the domain 161 are aligned in the ON electric field direction, that is, a mirror display by the reflected light of the auxiliary capacitance electrode 3.

  In the inter-pixel column region D2 in the on-display pixel area, an electric field is formed by the signal voltage supplied to the source line 11 and the common voltage. The source line 11 is appropriately supplied with an ON signal voltage supplied to the ON display pixels of the connected pixel column and an OFF signal voltage supplied to the OFF display pixels in accordance with the display image information. Therefore, the liquid crystal molecules are aligned. Although the effective voltage varies depending on the display image, it is a voltage between the on-voltage and the off-voltage. As a result, the liquid crystal molecules in the domain 161 of the inter-pixel column region D2 are in an intermediate alignment state that is aligned to some extent along the formed electric field, and the reflected light from the source line 11 is different from the display white. In addition, intermediate gradation display (gray display) in which mirror reflected light from the auxiliary capacitance electrode 3 is mixed is obtained.

  Next, in the off display state, a pixel area (hereinafter referred to as the same column pixel area) in the same column as the above-described on display pixel area (a pixel column connected to the same source line 11) and a column different from the on display pixel area. This pixel (hereinafter referred to as a different row area pixel) has a different display state.

  In both the different pixel area shown in FIG. 4B and the same pixel area shown in FIG. 4C, the voltage applied to the pixel electrode 13 is an off voltage. Therefore, each pixel region D1 is white in a light scattering state. It is displayed.

  However, in the inter-pixel region D2 in the different pixel area shown in FIG. 4B, the off-voltage is always supplied to the source line 11, whereas the pixel column in the same pixel area shown in FIG. In the inter-region D2, an on voltage and an off voltage are appropriately supplied to the source line 11 according to display image information.

  Therefore, as shown in FIG. 4C, an effective voltage between the on-voltage and the off-voltage is applied to the inter-pixel region D2 in the same-column pixel area, so that an intermediate gradation display is achieved by the intermediate alignment state. On the other hand, as shown in FIG. 4B, the off-voltage is always applied in the inter-pixel region D2 in the different-column pixel area, so that the white display is caused by the scattering orientation state.

  That is, as shown in FIG. 4B, even in the white display area A2 in which the off-voltage is applied to the pixel electrodes, the white display area A22 in the same row as the on-display mirror display area A1 is arranged. In the white display area A21, the alignment state of the liquid crystal molecules in each inter-pixel column region D2 is different, so that the entire area is displayed differently.

  As a result, in the white display area A21 in the same row as the on-display mirror display area A1 as shown in the drawing, the gray display of the intermediate gradation by the intermediate orientation of the inter-pixel region D2 is displayed in the white display by the scattering orientation of the pixel region D1. In addition, the gray display is almost the same as the white display as a whole, and the display becomes uneven with respect to the white display area A22 (background display area) having no mixed colors of different rows. This display unevenness occurs in the form of vertical stripes in the same row as the mirror display pixel row.

  In contrast to such a PNLCD as a comparative example, in the PNLCD as an embodiment of the present invention, a width sufficiently wider than the width of the source line 11 is provided above each source line 11 and commonly connected to the common electrode 15. Since the umbrella electrode 14 is disposed, the inter-pixel column region D2 is always maintained in an electric field-free state regardless of the voltage applied to the pixel electrode 13. Accordingly, it is possible to stably obtain image quality of advanced mirror display in which the off display pixel area (background display area) other than the on display pixel area is a uniform white display without vertical stripes.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, the pixel electrode 13 is used as a transparent conductive film to transmit light, and is reflected by the mirrored surface of the auxiliary capacitance electrode 3 disposed on the back surface thereof. The present invention is not limited to this, and the pixel electrode may be formed of a metal material such as aluminum so that the surface thereof is mirrored and the light transmitted through the polymer dispersed liquid crystal layer is reflected by the mirror surface. Thereby, since a reflective surface becomes closer with respect to a display surface (outer surface of the front glass substrate 1), parallax is reduced.

  In addition, a reflective display other than the mirror reflective display can be obtained by separately providing a reflective plate having a reflective surface of a specific color separately from the auxiliary capacitance electrode.

  In addition, the polymer-dispersed liquid crystal layer sandwiched between glass substrates is not limited to PNLC, but liquid crystal is filled in voids (droplets) dispersed and formed in bubbles in the polymer layer, so that the liquid crystal is more liquid than PNLC. Of course, a so-called droplet type polymer dispersed liquid crystal layer having a small mixing ratio may be used.

DESCRIPTION OF SYMBOLS 1 Front glass substrate 2 Rear glass substrate 3 Auxiliary capacity electrode 4 Gate electrode 5 Gate line 6 Gate insulating film 7 Amorphous silicon film 8 Source electrode 9 Drain electrode 11 Source line 12 Interlayer insulating film 13 Pixel electrode 14 Umbrella electrode 15 Common electrode 16 High Molecular dispersion type liquid crystal layer 161 Domain 162 Polymer net layer

Claims (3)

A first substrate disposed on the viewing side of the display;
A second substrate disposed opposite to the first substrate;
A polymer-dispersed liquid crystal layer that is held in a state in which liquid crystal is dispersed in a polymer material, and is sandwiched between the opposing inner surfaces of the first substrate and the second substrate;
An auxiliary capacitance electrode formed on the inner surface of the second substrate, and the observation side surface is formed on a reflection surface that reflects light;
A first insulating layer formed on the inner surface of the second substrate so as to cover the storage capacitor electrode ;
A plurality of pixel electrodes made of a transparent conductive film formed in a matrix arrangement at a position facing the storage capacitor electrode on the first insulating film;
A plurality of signal lines that are arranged between adjacent pixel electrode columns and supply a signal voltage for driving liquid crystal to the plurality of pixel electrodes;
A plurality of switching elements respectively interposed between the signal line and a plurality of pixel electrodes to which the signal voltage is to be supplied;
A common electrode made of a transparent conductive film provided on the inner surface of the first substrate and applied with a common voltage;
Is disposed over the second insulating layer respectively on the plurality of the signal lines of the second substrate side, and a plurality of shield electrode to which the common voltage is applied, possess,
The auxiliary capacitance electrode is provided extending in a direction orthogonal to the extending direction of the signal line,
The whole of each pixel electrode overlaps the auxiliary capacitance electrode,
The liquid crystal display element, wherein a width of the auxiliary capacitor electrode in the extending direction of the signal line is larger than a width of the pixel electrode in the extending direction of the signal line .   2. The liquid crystal display element according to claim 1, wherein the shield electrode is made of a transparent conductive film made of the same material as the pixel electrode, and is disposed on the surface of the insulating film on which the pixel electrode is provided.   The liquid crystal display element according to claim 1, wherein the polymer dispersed liquid crystal is a polymer network type liquid crystal.

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