JP2013134813A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress crosstalk well in a display device using an organic EL element, even when a charge transport layer is deposited by dry deposition method.SOLUTION: An organic EL element comprises an organic compound layer including a first electrode 4 divided for each element, a charge transport layer 5, and a luminous layer 6 where the resistance of the charge transport layer 5 is lower than that of the luminous layer 6, and a second electrode 7 provided commonly to a plurality of organic EL elements. There is provided between the plurality of organic EL elements, a groove 3 having a cross section of reverse tapered shape in the width direction, and having a depth larger than the thickness of the charge transport layer 5 but smaller than the thickness of the second electrode 7, or a barrier rib having a height larger than the thickness of the charge transport layer 5 but smaller than the thickness of the second electrode 7, thus segmenting the charge transport layer 5 between adjoining organic EL elements.

Description

  The present invention relates to a display device using an organic electroluminescence (EL) element.

  In recent years, self-luminous devices compatible with flat panels have attracted attention. Examples of the self-luminous device include a plasma light-emitting display element, a field emission element, and an electroluminescence (EL) element. In particular, organic EL elements are being researched and developed vigorously, and an array of area color types that add a single color such as green, blue, red, etc. has been commercialized and is now full color. Development is becoming more active. When a full-color light emitting array is manufactured, there are a method in which a light emitting layer is applied for each pixel (element) and a method in which the light emitting layer is white and a color filter is applied for each pixel.

  In recent years, high-definition light emitting arrays are also being studied. When the pixel size is reduced due to higher definition, the distance between adjacent electrodes becomes closer, so crosstalk in which peripheral pixels of the intended pixel emit light due to leakage current through the low-resistance charge transport layer is a problem. May be. In order to solve such a problem, Patent Document 1 discloses an organic EL device having a relief pattern that separates a charge transport layer between an electroluminescent layer and a first electrode layer along a first electrode. It is disclosed. Patent Document 2 discloses an organic electroluminescence display panel in which a second electrode is divided by a partition wall having an overhang portion.

Special table 2003-530660 gazette JP-A-8-315981

  In the invention described in Patent Document 1, when the charge transport layer is formed by a wet film formation method such as a spin coating method, a relief having a forward taper angle is provided, so that the charge transport layer is provided between the plurality of first electrodes. Divide by. Since the charge transport layer is formed by a wet film formation method, the relief should have a sufficient height even if it has a forward taper angle, or the surface of the relief should be surface treated so as to repel the solution of the charge transport layer forming material. Thus, it is assumed that the charge transport layer can be divided spontaneously. Moreover, since it is a forward taper angle, the 2nd electrode formed by the dry-type film-forming method like vacuum evaporation is not interrupted.

  However, in dry deposition methods such as vacuum deposition, which is another common means of charge transport layer deposition, the film also adheres to the side and top surfaces of the relief, so the charge transport layer is divided by reliefs with a forward taper angle. It is difficult to do. This is the same as that in the invention described in Patent Document 1, the second electrode formed by the dry film forming method is not interrupted.

  On the other hand, as disclosed in Patent Document 2, in the example in which the partition wall having the overhang portion is provided, the second electrode is also divided for simple matrix driving. In active matrix driving in which a switching element such as a transistor is provided on the substrate side, it is desirable that the second electrode be common. When the second electrode is divided, it is necessary to individually provide a contact portion or to remove the organic layer of the contact portion, which may increase the cost.

  An object of the present invention is to satisfactorily suppress crosstalk even when a charge transport layer is formed by a dry film formation method in a display device using an organic EL element.

The present invention includes a plurality of organic EL elements, and the organic EL element includes a first electrode divided for each element, an organic compound layer including a charge transport layer, and a light emitting layer, and a plurality of organic EL elements. In the display device having the second electrode provided in common,
The charge transport layer has a smaller resistance than the light emitting layer,
Between the plurality of organic EL elements, a cross section in the width direction has a groove or partition wall having a reverse taper shape,
The depth of the groove or the height of the partition wall is larger than the thickness of the charge transport layer and smaller than the thickness of the second electrode.

  ADVANTAGE OF THE INVENTION According to this invention, even when forming a charge transport layer with a dry-type film-forming method, the crosstalk produced via a charge transport layer is suppressed, and the display apparatus which can perform favorable display is provided.

It is sectional drawing which shows typically the structure of one Embodiment of the display apparatus of this invention. It is a cross-sectional schematic diagram for demonstrating the effect | action of the groove | channel or the partition in the display apparatus of this invention. It is sectional drawing which shows typically the cross-sectional shape of the groove | channel and the partition in the display apparatus of this invention. It is sectional drawing which shows typically the structure of other embodiment of the display apparatus of this invention. It is a top view which shows typically the position of the groove | channel or the partition in the display apparatus of this invention. It is a figure which shows typically the vapor deposition source and the position at the time of charge transport layer film-forming of the display apparatus of this invention.

  Hereinafter, the present invention will be described in more detail with reference to the drawings.

  FIG. 1 is a cross-sectional view schematically showing a configuration of an embodiment of a display device of the present invention. In the present embodiment, a plurality of first electrodes 4 connected to wirings and switching elements (not shown) are provided on a base layer 2 on a substrate 1. The first electrode 4 is divided for each organic EL element, and includes a charge transport layer 5, a light emitting layer 6, and a plurality of first electrodes 4 on the first electrode, and a second electrode 7. . Between the plurality of first electrodes 4, a groove or partition wall having a reverse taper shape in cross section in the width direction is provided, and the depth of the groove or the height of the partition wall is larger than the thickness of the charge transport layer. It is a feature of the present invention that it is smaller than the thickness of the two electrodes. FIG. 1 shows an embodiment in which the groove 3 is provided, and FIG. 4 shows a schematic cross-sectional view of the embodiment in which the partition wall 14 is provided. In the present invention, the cross section in the width direction of the groove or partition is an inversely tapered shape. In the case of a groove, the width in the cross section in the width direction is narrower on the bottom side than the opening. The upper part is wider than the upper part.

  The charge transport layer 5 is a layer closer to the first electrode 4 than the light emitting layer 6. In general, a material having a lower resistance than the light emitting layer 6 is often used for the charge transport layer 5 in order to lower the drive voltage. In particular, an electron donating or electron accepting material may be included at the interface with the first electrode 4 or between the first electrode 4 and the light emitting layer 6. In this case, the surrounding organic compound film and Electrons are exchanged between the two and carriers are generated, so that the electric resistance value is greatly reduced. The present invention is particularly effective when it has a layer containing such an electron donating or electron accepting material. Of course, even if such a material is not included, it is effective when the electrical resistance is small or the distance between the adjacent first electrodes 4 is short and the light emission of the unintended pixel occurs due to the leakage current between the adjacent pixels. Have.

  As shown in FIG. 2, when the film is formed by an anisotropic film formation method such as vacuum deposition, the reverse-tapered groove 3 or the partition wall is provided, so that charge transport is performed on the groove 3 or the side wall 8 of the partition wall. Layer 5 is substantially unattached. For this reason, since the charge transport layer 5 is divided between the adjacent first electrodes 4, crosstalk caused by current flowing through the charge transport layer 5 can be suppressed. On the other hand, since the depth of the groove 3 or the height of the partition wall is made smaller than the thickness of the second electrode 7, the display quality deteriorates due to the disconnection of the second electrode 7 and the uneven emission due to the increased resistance. Can be avoided.

  The partition used in the display device using the organic EL element is formed so as to cover the end of the first electrode 4, and is formed between the first electrode 4 and the second electrode 7 due to the disconnection of the organic compound layers (5, 6). In order to prevent the short circuit and the disconnection of the second electrode 7, it is common to have a forward taper angle. On the other hand, the partition used in the display device of the simple matrix drive is usually intended to divide the second electrode 7, and therefore has a sufficiently larger height than the second electrode 7 even in the case of reverse taper. . The present invention is characterized in that the cross-sectional shape of the groove 3 or the partition wall 14 is an inversely tapered shape, and has a height larger than the thickness of the charge transport layer 5 and smaller than the thickness of the second electrode 7.

  In the present invention, it is desirable that the second electrode 7 has a sufficient film thickness in order to prevent luminance unevenness and increase in power consumption due to disconnection or increase in resistance. The second electrode 7 may be made of a transparent conductive film and may have a top emission configuration, or the second electrode 7 may be a reflective electrode such as a metal and may have a bottom emission configuration. On the other hand, if the film thickness of the second electrode 7 is too thick, the cost increases. When a transparent conductive film is used as the second electrode 7, if the second electrode 7 is too thick, the light emission efficiency is reduced due to absorption of the film. The film thickness of the second electrode 7 is preferably 30 nm to 2 μm. More preferably, the film thickness is 200 nm to 1 μm.

  On the other hand, the thickness of the charge transport layer 5 should not be too thin in order to ensure injection from the electrodes and to suppress leakage of excitons and carriers from the light emitting layer 6. Moreover, since it will cause the drive voltage to rise if it is too thick, it is better not to be too thick. The thickness of the charge transport layer 5 is preferably 5 nm to 300 nm, more preferably about 10 nm to 200 nm.

  The depth of the groove 3 having a reverse-tapered cross section or the height of the partition wall 14 is such that the charge transport layer 5 is sufficiently disconnected, and the thickness of the charge transport layer 5 is lowered in order to reduce the resistance of the second electrode 7. It is desirable that it is larger than the thickness of the second electrode 7. More preferably, it is not less than twice the film thickness of the charge transport layer 5 and not more than half the film thickness of the second electrode 7. In such a case, crosstalk can be prevented and disconnection of the second electrode 7 can be suppressed. Further, in order to satisfy such a film thickness relationship, the film thickness of the charge transport layer 5 needs to be smaller than the film thickness of the second electrode 7.

  The taper angle of the inversely tapered groove 3 or the partition wall 14 is preferably as large as possible because the charge transport layer 5 is easily disconnected. As shown in FIG. 2, the taper angle in the present invention is a line connecting the most retracted point of the groove 3 or the partition 14 and the most protruding point among the points above the retracted point. And the substrate normal line (an angle indicated by 11 in FIG. 2). If the charge transport layer 5 can be disconnected, the angles of the side surfaces of the groove 3 and the partition wall 14 are not limited to be inclined. In FIG. 2, for the sake of convenience, the shape of the groove 3 is shown. However, if the side surface 8 of the groove 3 is regarded as the side surface of the partition wall 14, the operation in the present invention is exactly the same.

  FIG. 3 shows examples of cross-sectional shapes of the groove 3 and the partition wall 14. In the case of a groove, a reverse taper shape as shown in FIG. 3A is exemplified, and a plurality of layers may be laminated as shown in FIG. Further, as shown in FIG. 3C, a part may be a forward tapered shape in the height direction. In this case, it is sufficient that the reverse tapered portion of the side surface is higher than the charge transport layer 5 and the overall height is smaller than the film thickness of the second electrode 7. Further, as shown in FIG. 3D, a shape having an overhang is also included in the reverse tapered shape referred to in the present invention. Further, examples of the partition wall 14 include a reverse taper shape as shown in FIG. 3E and a T-shape, that is, a shape having an overhanged side surface as shown in FIG.

  When the reverse tapered groove 3 is provided, as shown in FIG. 1, the width 12 of the opening of the groove 3 is preferably smaller than the interval 13 between the adjacent first electrodes 7. In such a case, since the first electrode 4 can be prevented from being exposed at the portion where the disconnection of the charge transport layer 5 occurs, a short circuit between the first electrode 4 and the second electrode 7 can be avoided. Further, in order to prevent the charge transport layers 5 attached on both sides of the opening from contacting each other and to reliably disconnect the charge transport layer 5, the width 12 of the opening of the groove 3 is at least the film of the charge transport layer 5. It is preferably at least twice the thickness. Further, if the width of the groove 3 is too wide, the aperture ratio of the pixel is lowered, so it is preferable that the groove 3 is not too wide. The width of the groove 3 is preferably 50 nm or more and 2 μm or less. More preferably, it is 100 nm or more and 1 μm or less.

  On the other hand, as shown in FIG. 4, when the partition 14 is provided, the width 15 of the widest portion of the partition 14 is preferably smaller than the interval 13 between the adjacent first electrodes 4. In this case, a short circuit between the first electrode 4 and the second electrode 7 can be avoided at the portion where the disconnection of the charge transport layer 5 occurs. More preferably, the distance 16 in the substrate in-plane direction between the most protruding portion on the partition wall 14 and the end portion of the first electrode 4 is larger than the portion that becomes a shadow of the partition wall 14 when the charge transport layer 5 is formed. Is also preferably long. In the region that is shaded by the partition wall 14, the deposited film thickness is reduced. It is preferable to separate the partition wall 14 from the first electrode 4 because a short circuit between the first electrode 4 and the second electrode 7 can be avoided. Further, if the width of the partition wall 14 is too wide, the aperture ratio of the pixel is lowered, and therefore it is preferable that the partition wall 14 is not too wide. The width of the partition wall 14 is preferably 50 nm or more and 2 μm or less. More preferably, it is 100 nm or more and 1 μm or less.

  Further, the place where the partition wall 14 and the groove 3 are provided may be closer to the substrate 1 than the first electrode 4, may be located farther from the substrate 1 than the first electrode 4, and may be the same height as the first electrode 4. Good. For example, it may be provided on the base of the first electrode 4, or an element isolation film may be provided so as to cover the end of the first electrode 4, and a groove or a partition may be provided on the element isolation film.

  The end of the first electrode 4 may be exposed or covered with an element isolation film (not shown). When the end portion of the first electrode 4 is exposed, it is preferable that the angle of the end portion is gentler than the angle of the groove 3 or the partition wall 14. In this case, the loose definition is assumed to be gentle in the order of reverse taper, vertical, and forward taper. In comparison between the same reverse taper, the smaller the angle (11 in FIG. 2) between the side surface and the substrate surface normal, the smaller the angle. In comparison between the forward taper, the side surface and substrate surface normal line It is assumed that the larger the angle between the two, the gentler the angle. In such a case, disconnection of the charge transport layer 5 at the end of the first electrode 4 is prevented, leakage between the first electrode 4 and the second electrode 7 is prevented, and charge transport on the side surface of the groove 3 or the partition wall 14 is prevented. The layer 5 can be divided. When providing the element isolation film, it is preferable that the angle of the surface where the element isolation film and the first electrode 4 are in contact is gentler than the angle of the partition wall 14 or the groove 3. Even in such a case, the first electrode 4 and the second electrode 7 are prevented from being short-circuited due to the disconnection of the charge transport layer 5 at the edge of the element isolation film, and the charge transport layer 5 is divided on the side surface of the groove 3 or the partition wall 14. Can be achieved.

  For film formation of the charge transport layer 5, it is preferable to use a vacuum deposition method (see FIG. 2). In this case, since the straightness of the film forming molecules is high, if the film is formed using an evaporation source using a shielding plate or the like so that the incident angle 10 of the molecules is smaller than the angle 11 of the reverse taper, Since the upper part of the groove 3 serves as an umbrella and the charge transport layer 5 can be suitably divided, it is preferable.

  The place where the partition wall 14 and the groove 3 are provided may be provided between all the pixels, or may be provided in a part. An example is shown in FIG. As shown in FIG. 5A, a groove 3 or a partition wall 14 may be provided so as to surround the periphery of the first electrode 4, and as shown in FIG. 5B, the long side of the first electrode 4 may be provided. You may provide the groove | channel 3 or the partition 14 only between. In the latter case, the long side with a long leak path between pixels is divided by the groove 3 or the partition wall 14, and the aperture ratio can be improved by not placing the groove 3 or the partition wall on the short side.

  Furthermore, when an organic material is vapor-deposited on a large-sized substrate, a film-formation method may be employed using a linear vapor deposition source while moving the substrate or the vapor deposition source (see FIG. 6). In this case, in the direction perpendicular to the long side of the vapor deposition source 17 (FIG. 6A), it is easy to restrict the molecular incident angle 19 by providing the limiting plate 18 or the like, but the direction parallel to the long side of the vapor deposition source (FIG. 6). 6 (b)), the molecular incident angle 19 tends to be wide. In such a case, it is more preferable to install the long side direction of the pixel and the long side of the vapor deposition source 17 in parallel (FIG. 6C). With such a configuration, the charge transport layer in the long side direction having a long leak path between pixels can be divided.

  On the other hand, the film may be formed using a point evaporation source provided with a limiting plate that limits the incident angle in both the vertical and horizontal directions. In this case, the charge transport layer can be divided in both the vertical and horizontal directions.

Next, a method for manufacturing the partition wall 14 and the groove 3 will be described. For example, in the example of the groove 3, a SiN / SiO / SiN laminated film is first formed by using the CVD method, and the first electrode 4 is formed thereon by forming an electrode material and patterning. Thereafter, using a photolithography technique, a resist pattern that covers the portion other than the portion where the groove 3 is to be formed is produced. The uppermost SiN is patterned by reactive ion etching using CF ₄ as an etching gas. Furthermore, when wet etching is performed using a buffered hydrofluoric acid solution, the side etching of the SiO layer proceeds more than the uppermost SiN due to the difference in etching rate, and an overhang structure can be formed.

  Further, a material having a small etching rate may be provided as an etching stop layer under the groove 3 formation portion so that the depth of the groove 3 does not become too deep. In such a case, it is preferable because unevenness in appearance due to unevenness of the depth of the groove 3 can be avoided.

  Further, as an example of the partition wall 14, a negative resist is used, and the exposure time is made longer than usual so that a reverse taper shape in which the line width increases toward the upper part can be formed.

  The colors displayed in each pixel may be the same or different for each pixel. As a method of changing the display color for each pixel, the light emitting layer 6 may be applied for each pixel using a shadow mask, or the white light emitting layer 6 is provided in common for all pixels, and a color filter is applied for each pixel. Thus, multi-color display may be performed.

  Hereinafter, other components will be described.

  As the substrate 1, any material such as quartz, glass, silicon wafer, resin, metal and the like may be used. On the substrate 1, switching elements such as thin film transistors (not shown) and wirings are provided.

  As the underlayer 2, any material may be used as long as a contact hole can be formed and insulation from an unconnected wiring can be ensured in order to ensure conduction between the first electrode 4 and a wiring (not shown). For example, a resin such as polyimide or an oxide film such as silicon oxide or silicon nitride can be used.

  As the 1st electrode 4, when using as a reflective electrode, chromium, aluminum, silver, titanium, or these alloys, what laminated | stacked, etc. can be used, for example. Moreover, when using as a transparent electrode, metal oxides, such as ITO and IZO, etc. can be used, However, It is not limited to these. A known photolithography technique can be used for forming the electrode. For example, a plurality of electrodes having a shape of 4 μm × 16 μm may be provided at intervals of 2 μm. Multicolor display is possible by driving these electrodes independently by a switching element via a contact hole (not shown).

  As the charge transport layer 5, a known material can be suitably used. When the first electrode 4 is an anode, a hole transport layer is used. A known material can be suitably used for the hole transport layer. For example, a triphenyldiamine derivative, an oxodiazole derivative, a polyphylyl derivative, a stilbene derivative, and the like can be used, but are not limited thereto. Further, the stacked body of the hole injection layer and the hole transport layer, that is, a plurality of layers may serve as the hole transport layer. As the hole injection layer, oxides such as molybdenum oxide and tungsten oxide, organic compounds such as 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), and A mixed layer of these materials and a hole transport layer may be used. In particular, when a material such as F4TCNQ is mixed with the hole transport layer, a low-resistance hole injection / transport layer is formed, and the drive voltage can be reduced. The thickness of the hole transport layer may be common to each pixel, or the thickness may be changed according to the color in order to match interference.

  On the other hand, when the first electrode 4 is used as a cathode, an electron transport layer is used as the charge transport layer 5. A known material can be suitably used for the electron transport layer. Examples include, but are not limited to, aluminum quinolinol derivatives, oxadiazole derivatives, triazole derivatives, phenylquinoxaline derivatives, silole derivatives, phenanthroline derivatives, and the like. Further, a stacked body of an electron injection layer and an electron transport layer, that is, a plurality of layers may serve as the electron transport layer.

As the electron injection layer, a mixture of an electron donating dopant and an electron transporting material may be used. As the electron-donating dopant, an alkali metal, an alkaline earth metal, a rare earth metal, or a compound thereof can be used. The electron injection layer is formed by containing 0.1 to several tens of percent of an alkali metal compound in the electron transporting material. More preferably, the alkali metal compound is a cesium compound. More preferably, the cesium compound is cesium carbonate and a substance derived from cesium carbonate. A preferred method for forming the electron injection layer is to co-evaporate cesium carbonate and an electron transporting material. In order to ensure good electron injection properties, the thickness of the electron injection layer is preferably 10 to 100 nm. In addition, cesium carbonate decomposes during co-evaporation, and suboxides such as (Cs ₁₁ O ₃ ) Cs ₁₀ , (Cs ₁₁ O ₃ ) Cs, and Cs ₁₁ O ₃ are formed in the electron injection layer. May be. In addition, a coordination compound may be formed between cesium and an organic compound.

  As the light emitting layer 6, any known light emitting material can be suitably used. As the light emitting material, a material that functions as an organic light emitting layer by itself may be used, or a material that functions as a mixed system of a host material and a light emitting dopant, a charge transport dopant, a light emission assisting dopant, or the like may be used. The light emitting layer 6 may use a different material or a common material depending on the color displayed in each pixel.

  In addition, the light emitting layer 6 in the present invention may be a single layer, or another layer may be laminated on the light emitting layer 6 on the second electrode 7 side. For example, when the second electrode 7 is a cathode, a hole blocking layer / electron transport layer / electron injection layer may be further provided. Further, when the second electrode 7 is an anode, an electron blocking layer / hole transport layer / hole injection layer or the like may be provided. As these materials, those described as materials for the charge transport layer 5 can be used. In the present invention, the organic compound layer refers to a laminate composed of an organic compound film including at least the charge transport layer 5 and the light emitting layer 6 disposed between the first electrode 4 and the second electrode 7.

  The second electrode 7 may be a top emission element using a transparent electrode such as ITO, or may be a bottom emission element using a reflection electrode such as aluminum (Al), and is not particularly limited. An oxide conductive film is preferable. Any method may be used for forming the second electrode 7. However, it is more preferable to use a direct current or alternating current sputtering method because the film coverage is good and the resistance is easily lowered.

  A sealing member (not shown) may be provided after the formation of the second electrode 7. For example, by adhering a glass provided with a hygroscopic agent on the second electrode 7, it is possible to suppress the intrusion of water or the like into the organic compound layer and suppress the occurrence of display defects. Further, as another embodiment, a passivation film such as SiN may be provided on the second electrode 4 to suppress intrusion of water or the like into the organic compound layer. For example, after forming the second electrode 4, it may be transferred to another chamber without breaking the vacuum, and a 5 μm SiN film may be formed by a CVD method to form a sealing film.

  A color filter may be provided for each pixel. For example, a color filter matching the size of the pixel may be provided on another substrate, which may be bonded to the substrate provided with the light emitting layer, or the color filter may be patterned on a sealing film such as SiN. .

  The display device of the present invention can be suitably used for various displays. A display is an image display device such as a display unit of a television or a personal computer or a display unit mounted on an electronic device. The display unit mounted on the electronic device is preferably a display unit in a vehicle, an image display unit of a digital camera, or an operation panel of office equipment such as a copying machine or a laser beam printer.

  3: groove, 4: first electrode, 5: charge transport layer, 6: light emitting layer, 7: second electrode, 14: partition

Claims (4)

A plurality of organic EL elements are provided, and the organic EL element is provided in common for the plurality of organic EL elements, an organic compound layer including a first electrode divided for each element, a charge transport layer, and a light emitting layer In the display device having the second electrode formed,
The charge transport layer has a smaller resistance than the light emitting layer,
Between the plurality of organic EL elements, a cross section in the width direction has a groove or partition wall having a reverse taper shape,
The display device, wherein a depth of the groove or a height of the partition wall is larger than a thickness of the charge transport layer and smaller than a thickness of the second electrode.   2. The display device according to claim 1, wherein the width of the opening of the groove or the width of the widest portion of the partition is narrower than the interval between the plurality of first electrodes.   The display device according to claim 1, wherein the second electrode is made of an oxide conductive film.   The display device according to claim 1, wherein the charge transport layer is formed by vapor deposition.

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