JP2007017720A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device which includes an illumination layer on the front face and has an improved contrast. <P>SOLUTION: The illumination layer 14 is disposed on a display part 10. Light emitting elements 22 are disposed, for example, in a striped shape on the illumination layer 14. Each light emitting element 22 has an anode 26 on a level difference forming layer 24 and, over them, an organic EL layer 28 is formed. Further, over the organic EL layer 28, a cathode 30 is formed on a ridge. Accordingly, light generated by light emission of the organic EL layer 28 is applied toward a display part 10 by the cathode 30. Thus, the directivity is imparted to the illumination light to the display part 10 and, thereby, reflection light from adjoining pixels is hardly incorporated and, therefore, the contrast is improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a display device having an illumination layer that illuminates a display unit on an observation side.

  Conventionally, a liquid crystal display (LCD) has been widely used as a typical flat panel display. This liquid crystal display device includes a passive type and an active matrix type, and an active matrix type in which each pixel has an individual pixel electrode and voltage supply to the pixel electrode is controlled by an individual pixel circuit is mainly used. It has become.

  Liquid crystal display devices include a transmissive type, a transflective type, and a reflective type. The transmissive type usually has a backlight and performs display by modulating light from the backlight with liquid crystal. In the reflection type, light incident from the observation side is reflected by the reflection layer below the liquid crystal layer and returned to the observation side. For this reason, the reflected and emitted light is modulated by the liquid crystal layer. The transflective type is a combination of both a transmissive type and a reflective type.

  The transmissive type can display a sufficient contrast in a dark place by the light of the backlight, but there is a problem that the display is difficult to see in a bright environment such as outdoors. On the other hand, the reflection type has a problem that it can display sufficiently under the condition of strong external light, but the display cannot be seen in a dark place. The transflective type can be adapted to both environments, but usually has both a transmissive region and a reflective region for each pixel, and thus has a problem that display efficiency is not so good in either environment.

  There has also been proposed a display device in which a reflection type liquid crystal display device is provided with a front light (light on the observation side) to make the display easy to see even in a dark environment (see Patent Documents 1 and 2). According to this, it is possible to perform sufficient display using the front light in a dark environment and the outside light in a bright environment, and always using almost all of the pixels.

JP-A-5-325586 JP 2003-255375 A

  However, in the above prior art, a transparent acrylic plate having a triangular groove formed on the surface is used as the front light, and light is introduced into the acrylic plate from the side so that the light is inclined to the inclined surface of the triangular groove. Reflected towards the liquid crystal display. However, since a part of the light introduced into the acrylic plate leaks not only to the liquid crystal display unit side but also to the observation side, there is a problem that the contrast in the liquid crystal display is lowered.

  The present invention controls the voltage applied to the display element to modulate the light incident from the observation side based on the optical characteristics of the display layer and reflect and emit the light to the observation side of the display unit. An illumination layer provided to irradiate light toward the display unit, transmit light incident from the observation side toward the display unit, and transmit light emitted from the liquid crystal display unit to the observation side; The illumination layer includes a transparent substrate, a light emitting element partially provided on the transparent substrate, covers the light emitting element, collects light from the light emitting element, and faces the display unit. And a reflective film for reflecting.

  The light emitting element is preferably an organic EL element.

  Further, the organic EL element includes a step forming film partially formed on the transparent substrate, a first electrode layer formed on the insulating film, and an organic EL formed on the first electrode layer. The layer and the second electrode layer formed on the organic EL layer are preferable.

  The reflective film is a second electrode layer of an organic EL element, and it is preferable that the second electrode layer has a concave mirror shape toward the display unit.

  The step forming film is preferably an insulating film.

  The display unit is preferably a liquid crystal display unit using a liquid crystal layer as a display layer.

  According to the present invention, the illumination layer has the light emitting element and the reflective film, and the light from the light emitting element is condensed by the reflective layer and directed to the display unit. Thus, by providing directivity to the light incident on the display portion from the light emitting element, the viewing angle dependency can be relaxed and the contrast in display can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a conceptual configuration of a liquid crystal display device according to an embodiment.

  First, the display unit 10 is, for example, an active matrix reflective liquid crystal display device. Accordingly, a plurality of pixel electrodes are arranged in a matrix on the pixel substrate, and pixel circuits for controlling voltage supply to the pixel electrodes are individually provided for each pixel. A counter substrate provided with a common electrode is provided opposite to the pixel substrate, and liquid crystal is sealed between the two. Therefore, by controlling the potential of the pixel electrode, a different potential can be applied to the liquid crystal for each pixel to change its optical characteristics and display can be performed.

  In particular, the display unit 10 reflects light incident from the sealing substrate side by providing a reflective film below the pixel electrode or by using the pixel electrode as a reflective film. Therefore, the reflected light modulated by the liquid crystal of each pixel is obtained on the counter substrate side. An electrophoretic display or the like can also be used as the display unit 10.

  An illumination layer 14 is disposed above the display unit 10 via a transparent adhesive layer 12. The illumination layer 14 includes a glass substrate 20 and a light emitting element 22 partially formed on the upper surface thereof. The light emitting elements 22 are formed in a stripe shape, a lattice shape, or an island shape on the glass substrate 20. In the case of an island shape, wiring for supplying power to each light emitting element is separately provided. This can be easily formed by a metal wiring pattern on the glass substrate 20 or the like.

  The transparent adhesive layer 12 is made of UV resin, visible light curable UV resin, or the like, and bonds the counter substrate made of glass in the display unit 10 and the glass substrate 20 of the illumination layer 14.

  In this example, the light emitting element 22 is an organic EL element, and the step forming layer 24 is formed on the glass substrate 20. For the step forming layer 24, for example, a photosensitive acrylic resin is used. An anode 26 made of a transparent conductive material such as ITO or IZO is formed on the step forming layer 24. Here, the step forming layer 24 and the anode 26 are patterned in the same shape, and a normal patterning technique such as photolithography is used for this patterning.

  Then, an organic EL layer 28 is formed on the anode 26 and covering the upper surface and side surfaces of the step forming layer 24 and the anode 26. The organic EL layer 28 includes a hole transport layer, an organic light emitting layer, and an electron transport layer. In particular, the mountain-shaped organic EL layer 28 can be formed so as to cover the entire step forming layer 24 and the anode 26 by forming the hole transport layer positioned on the anode 26 side relatively thick. The organic EL layer 28 is formed by sequentially depositing a hole transport layer, an organic light emitting layer, and an electron transport layer using one mask.

  In addition, an organic light emitting layer is comprised from the 1st light emitting layer and the 2nd light emitting layer, and white light is obtained by light-emitting in orange or blue, respectively. It is also preferable to form islands and emit light separately for each color of RGB.

  Next, a cathode 30 made of a metal such as aluminum or chromium is formed so as to cover the organic EL layer 28. The cathode 30 is formed by patterning only a desired portion after being deposited on the entire surface by vapor deposition or the like.

  In this manner, when the light emitting element 22 is formed, the counter substrate 32 made of glass is disposed to face the other, and the periphery of both is sealed to isolate the peripheral space of the light emitting element 22 from the outside. It is preferable to enclose dry nitrogen gas in this space, and it is also preferable to accommodate a desiccant in the space. Thereby, it is possible to suppress the organic EL layer 28 from being deteriorated by moisture. It is also possible to fill the space with resin. The reflection at the interface can be suppressed by making the refractive index of the resin close to the refractive index of the glass. Note that the peripheral space of the light-emitting element 22 can be filled with an acrylic resin containing a desiccant or the like.

  In FIG. 2, a peripheral seal portion is shown. A counter substrate 32 made of glass is provided corresponding to the glass substrate, and the periphery of both is hermetically connected by a sealing material 34 such as UV resin. A desiccant 36 is disposed on the inner surface side of the sealing material 34. It is also preferable to mix desiccant particles in the sealing material 34.

  In FIG. 3, the schematic perspective view at the time of producing the light emitting element 22 in bowl shape is shown. In this case, both sides of the cathode 30 are slightly widened, and a portion where the cathode 30 is directly formed on the glass substrate 20 is formed. Thus, the organic EL layer 28 can be reliably covered with the cathode 30 and moisture and the like can be reliably prevented from entering. For this reason, it is preferable to cover all the end portions of the organic EL layer 28 with the cathode 30. On the other hand, the dead space from the observation side increases accordingly. Therefore, it is also preferable to superimpose the portion where the light emitting element 22 is formed on the black matrix between the pixels.

  The light emitting elements 22 do not have to be provided corresponding to each pixel, but moire is generated when the pitch is deviated from the pixel pitch. Therefore, both pitches are the same or the integer multiple of the other pitch. Is preferred.

  In such an embodiment, the display unit 10 performs display as a normal liquid crystal display device. On the other hand, the illumination layer 14 is turned on when the illuminance of outside light is small, and a predetermined voltage is applied between the anode 26 and the cathode 30. As a result, a current corresponding to the organic EL layer 28 flows, and light emission occurs in the organic EL layer 28. That is, as shown in FIG. 4, a current easily flows in a portion corresponding to the anode 26 and the cathode 30, and the organic EL layer 28 in this portion emits light.

  The anode 26 and the step forming layer 24 are transparent, and the downward light in the figure goes directly to the display unit 10. On the other hand, light directed from the organic EL layer 28 in the other direction is reflected by the cathode 30, condensed downward, and irradiated on the display unit 10.

  Thus, in this embodiment, the directivity of the light from the light emitting element 22 is controlled so as to go to the display unit 10. As a result, the light emitted from the display unit 10 is reduced in the oblique direction, and the contrast in the display is improved and a clear display can be performed.

"Configuration of total reflection LCD"
FIG. 5 shows a part of a planar configuration on the pixel substrate side of the active matrix type total reflection LCD according to the present embodiment, and FIG. 6 shows a schematic sectional configuration at a position along the line AA in FIG. . In an active matrix LCD, a plurality of pixels are provided in a matrix in a display area, and here, a TFT 110 is provided as a switch element for each pixel.

  The TFT 110 has an active layer 220, and a drain region 220d, a channel region 220c, and a source region 220s are formed by the active layer 220. A gate insulating film 130 is formed so as to cover the active layer 220, and a gate electrode 132 is formed on the gate insulating film 130 at a position that is above the channel region 220 c. Then, an interlayer insulating film 134 is formed so as to cover the gate insulating film 130 and the gate electrode 132. A data line 136 is disposed on the interlayer insulating film 134, and the gate line 136 is connected to the drain region 220 d through a contact penetrating the interlayer insulating film 134. In addition, a contact hole is formed in the interlayer insulating film 134 and the planarization insulating film 38 on the drain region 220d, and a part of the pixel electrode (first electrode) 150 extends and is electrically connected thereto.

  The TFT 110 is formed for each pixel, for example, on the pixel substrate 100 side, and pixel electrodes (first electrodes) 150 formed in individual patterns are connected to the TFT 110, respectively. Further, the counter substrate 200 is disposed to face the pixel substrate 100 with the liquid crystal interposed therebetween.

  A transparent substrate such as glass is used for the pixel substrate 100 and the counter substrate 200, and in the case of a color type, a color filter 210 is formed on the pixel substrate 100 and the counter substrate 200 side. A second electrode 250 made of a conductive material is formed. As the transparent conductive material of the second electrode 250, IZO (Indium Zinc Oxide), ITO, or the like is employed. In the active matrix type, the second electrode 250 is formed as a common electrode for each pixel. An alignment film 260 made of polyimide or the like is formed on the second electrode 250.

  In the present embodiment, an electrode structure is adopted in which the electrical characteristics of the liquid crystal layer 300 on the pixel substrate 100 side are aligned with the counter substrate 200 side configured as described above. Specifically, as shown in FIG. 6, a material having a work function similar to that of the second electrode 250, not a reflective metal electrode as in the related art, is directly below the alignment film on the first transparent substrate 100. That is, the first electrode 150 made of the same transparent conductive material as the second electrode 250 such as IZO or ITO is formed. In order to obtain a reflective LCD, a reflective layer 44 that reflects incident light from the counter substrate 200 side is formed below the first electrode 150.

  The material used as the first electrode 150 is the same as the material of the second electrode 250, so that an electrode having the same work function is disposed on the liquid crystal layer 300 with the alignment films 60 and 260 interposed therebetween. Therefore, the first electrode 150 and the second electrode 250 can drive the liquid crystal layer 300 with very good symmetry. However, even if the work functions of the first electrode 150 and the second electrode 250 are not completely the same, they may be approximated as long as the liquid crystal layer 300 can be driven with good symmetry. For example, if the difference between the work functions of both electrodes is about 0.5 eV or less, even if the liquid crystal drive frequency is CFF (critical flicker frequency) or less, high quality display without flickering or liquid crystal burn-in is possible. Is possible.

  As the first electrode 150 and the second electrode 250 that satisfy such conditions, for example, the first electrode 150 has an IZO (work function of 4.7 eV to 5.2 eV), and the second electrode 250 has an ITO (workpiece). Function 4.7 eV to 5.0 eV), or vice versa, and in selecting the material, the material used for each electrode in consideration of process characteristics such as transmittance and patterning accuracy, manufacturing cost, etc. Each may be selected.

  As the reflection layer 44, a material having excellent reflection characteristics such as Al, Ag, and an alloy thereof (Al—Nd alloy in this embodiment) is used at least on the surface side (liquid crystal layer side). The reflective layer 44 may be a single layer of a metal material such as Al, but a refractory metal layer such as Mo may be provided as a base layer in contact with the planarization insulating film 38. By forming such a base layer, the adhesion between the reflective layer 44 and the planarization insulating film 38 is improved, so that the reliability of the element can be improved. In the configuration of FIG. 6, an inclined surface having a desired angle is formed in each pixel region of the planarization insulating film 38, and a reflective layer 44 is laminated so as to cover the planarization insulating film 38. A similar slope is formed on the surface of the layer 44. If such an inclined surface is formed at an optimum angle and position, it is possible to collect and emit external light for each pixel. For example, it is possible to improve the display brightness at the front position of the display. is there. Of course, such an inclined surface does not necessarily exist.

In the present embodiment, a protective film 46 is formed between the reflective layer 44 and the first electrode 150 so as to cover the reflective layer 44. For example, acrylic resin or SiO ₂ is used for the protective film 46. The protective film 46 is a film for protecting the reflective layer 44, and in particular, in the light etching that exposes the active layer 220 on the bottom surface of the contact hole for connecting the active layer 220 of the TFT 110 and the first electrode 150. It has a function of protecting the reflective surface of the reflective layer 44 from the etching solution used.

The protective film 46 only needs to have a function of protecting the reflective layer 44 from the etching process and maintaining good reflective characteristics, and the material thereof is not limited to resin, SiO _2, or the like. The thickness is sufficient if it can exhibit this protective function. Further, from the viewpoint of flattening the formation surface of the first electrode 150 formed on the upper layer of the protective film 46, it is preferable to employ a material having a flattening function on the upper surface such as an acrylic resin. Further, the film thickness and material of the protective film 46 are selected so as to have an optimum thickness and refractive index, so that the protective film 46 can be used as an optical buffer layer having, for example, colored compensation and a function of improving reflectance. Is possible.

  Note that it is preferable to scatter the reflected light to some extent by forming irregularities on the reflective layer 44. By forming appropriate irregularities on the surface of the planarization insulating film 38 below the reflective layer 44 and forming the reflective layer 44 thereon, the irregularities can be easily formed in the reflective layer 44.

It is a figure which shows the conceptual structure of this embodiment. It is a figure which shows the structural example of an illumination layer. It is a perspective view which shows the structure of an illumination layer. It is a figure which shows the light emission state of a light emitting element. It is a top view which shows the structure of total reflection LCD. It is AA sectional drawing in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Display part, 12 Transparent adhesive layer, 14 Illumination layer, 20 Glass substrate, 22 Light emitting element, 24 Level difference formation layer, 26 Anode, 28 Organic EL layer, 30 Cathode, 32 Opposite substrate, 34 Sealing material, 36 Desiccant, 38 Flattening insulating film, 44 reflective layer, 46 protective film, 60, 260 alignment film, 100 pixel substrate, 150 first electrode, 200 counter substrate, 210 color filter, 220 active layer, 250 second electrode, 300 liquid crystal layer.

Claims (6)

By controlling the voltage applied to the display element, the display unit that modulates the light incident from the observation side based on the optical characteristics of the display layer and reflects and emits the light,
Provided on the observation side of this display unit, irradiates light toward the display unit, transmits light incident from the observation side toward the display unit, and transmits light emitted from the liquid crystal display unit to the observation side An illumination layer that is transparent to
Including
The illumination layer is
A transparent substrate;
A light emitting device partially provided on the transparent substrate;
A reflective film that covers the light emitting element, collects light from the light emitting element, and reflects the light toward the display unit;
A display device comprising: The display device according to claim 1,
The display device, wherein the light emitting element is an organic EL element. The display device according to claim 2,
The organic EL element is
A step forming film partially formed on the transparent substrate;
A first electrode layer formed on the insulating film;
An organic EL layer formed on the first electrode layer;
A second electrode layer formed on the organic EL layer;
A display device comprising: The display device according to claim 3,
The reflective film is a second electrode layer of an organic EL element, and the second electrode layer has a concave mirror shape toward the display unit. The display device according to claim 3 or 4,
The display device, wherein the step forming film is an insulating film. The display device according to claim 1,
The display device is a liquid crystal display unit using a liquid crystal layer as a display layer.

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