JP2009009708A - Organic el array - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL array superior in drive voltage and luminance, and low in cost. <P>SOLUTION: The organic EL array is provided with a substrate, a lower electrode and an upper electrode which are on the substrate and at least one of which is divided at each pixel, an organic layer which is interposed between the upper electrode and the lower electrode and includes at least an organic luminous layer, an element separation film which is arranged around the pixel, and a charge injection layer which is located between the lower electrode and the organic layer and composed of a conductor or a semiconductor, and is formed of a plurality of pixels. The charge injection layer is formed throughout a display region including the lower electrode and the element separation film, and a high resistance region of the charge injection layer is formed at a tapered portion of the element separation film. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an organic EL element that emits light by energizing an organic layer including an organic light emitting layer formed between electrodes, and in particular, a plurality of pixels of the organic EL element are formed on a substrate. The present invention relates to an organic EL array.

  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 area color type array with a single color such as green, blue, red, etc. has been commercialized and is now full color. Development is active.

  The structure of a typical organic EL device is that a transparent anode such as ITO, an organic layer composed of a hole transport layer, an organic light emitting layer, an electron transport layer, and the like, and a low work function upper reflective electrode are sequentially formed on a glass substrate. It becomes. This element structure is generally referred to as a bottom emission type, and light emitted from the element is emitted from the back side of the substrate through a transparent anode and substrate.

  When an organic EL array in which such bottom emission type organic EL elements are arranged in a two-dimensional array is driven by an active matrix method, the bottom emission type has a narrow aperture ratio due to TFTs and wiring on the substrate. There is a problem of becoming. As an attempt to improve this, a so-called top emission type organic EL element that emits emitted light in the stacking direction of the organic layer has been proposed.

  In the top emission type organic EL element, a substrate having a high visible light reflectance is used as the lower electrode on the substrate side, and a material having a high visible light transmittance is used as the upper electrode. Also, when the organic layer is stacked in the same manner as the bottom emission type and the lower electrode is an anode and the upper electrode is a cathode, if the lower electrode is made of aluminum or aluminum alloy having a high visible light reflectivity, Work function is relatively small. Therefore, the hole (hole) injection barrier becomes high. On the other hand, a method is known in which a transparent electrode having a large work function such as indium tin oxide (ITO) is laminated on aluminum.

  Patent Document 1 discloses a technique in which a metal having low transmittance or a metal that is difficult to be patterned by lithography is used as a charge injection layer, and these metals are mask-deposited on an electrode.

JP 2002-198182 A

  However, in Patent Document 1, since it is necessary to divide the charge injection layer for each pixel by mask vapor deposition, the cost increases due to the mask cost. Further, when the charge injection layer is formed in all the pixels, the ratio of the opening portion becomes large, and it becomes more difficult to maintain the mask strength. Further, when the mask strength is reduced, the mask is likely to deteriorate due to repeated use, which may lead to further cost increase.

  The present invention has been made in view of the above problems, and provides a low-cost organic EL array having excellent driving voltage and luminance.

As means for solving the above problems, the present invention provides:
A substrate, a lower electrode and an upper electrode at least one of which is divided for each pixel, the organic layer sandwiched between the upper electrode and the lower electrode, and including at least an organic light emitting layer; In an organic EL array comprising a plurality of pixels, comprising an element isolation film disposed around a pixel, and a charge injection layer made of a conductor or a semiconductor between the lower electrode and the organic layer,
The charge injection layer is formed over the entire display region including the lower electrode and the element isolation film, and a high resistance region of the charge injection layer is formed in a tapered portion of the element isolation film. To do.

  According to the present invention, it is possible to provide an organic EL array in which a drive voltage is suppressed by the charge injection layer and a decrease in luminance is suppressed, thereby suppressing an increase in cost.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2, but the present invention is not limited to this embodiment.

  FIG. 1 is a schematic sectional view showing an embodiment of the present invention. Although two pixels are shown in the figure, of course, the present invention is not limited to this. In addition, the size of each part in the drawing is partly emphasized for explanation, and does not necessarily reflect the actual shape.

  In the present embodiment, description will be made using a top emission type element in which the lower electrode is a reflective electrode and the upper electrode is a transparent electrode. However, the present invention is not limited to this. For example, the present invention can be applied to a bottom emission type element or a double-sided light emitting element in which the lower electrode is a transparent electrode and the upper electrode is a reflective electrode.

  As shown in FIG. 1, in the present embodiment, a substrate 1, a lower electrode 2 divided for each pixel on the substrate 1, a periphery of the pixel, and an end portion of the lower electrode 2 are covered. And an element isolation film 3 disposed on the substrate. Further, a charge injection layer 4 is provided so as to cover both the lower electrode 2 and the element isolation film 3. On top of this, an organic layer 5 including at least an organic light emitting layer and an upper electrode 6 are provided. The lower electrode 2 and the upper electrode 6 are respectively connected to a power source and a switch (not shown), and a current is passed between the two electrodes to cause the organic light emitting layer to emit light. However, the upper electrode 6 may also be divided for each pixel. In short, it is only necessary that the lower electrode 2 as one electrode is divided for each pixel.

  The present invention is characterized in that the charge injection layer 4b on the tapered portion of the element isolation film 3 in the charge injection layer 4 is a high resistance region.

  The lower electrode 2 in the present embodiment is made of a metal having high reflectance, such as aluminum, silver, or an alloy thereof. However, since the work function is small as the anode, the hole injection barrier is large. By providing the charge injection layer 4 with a small hole injection barrier to the organic layer 5 thereon, the driving voltage is lowered. The drive voltage can be reduced by using the charge injection layer 4 when the charge injection barrier from the lower electrode 2 is large.

  A conductor or a semiconductor is used as the charge injection layer 4. Here, the conductor or semiconductor refers to a material having a resistance that causes display disturbance due to leakage between pixels when a film is formed over the entire display region without using a special dividing means.

  More specifically, any material may be used as the charge injection layer 4 as long as it is conductive and has a lower injection voltage to the organic layer 5 than the lower electrode 2. For example, a metal oxide such as indium tin oxide (ITO) or indium zinc oxide (IZO), or a metal such as gold can be used. When these materials are used, an increase in driving voltage based on the resistance in the film thickness direction is small as compared with the case where a high-resistance insulating film is used.

  A method for forming the charge injection layer 4 is not particularly limited. In addition to sputtering methods such as magnetron sputtering and ion beam sputtering, a highly anisotropic film forming method such as vacuum deposition may be used, and the charge injection layer 4 is displayed by appropriately selecting these film forming methods. It is formed over the entire area.

  However, when a low-resistance material is connected between pixels, a desired display cannot be performed due to current leakage. Therefore, it is necessary to divide (divide) the charge injection layer 4 between pixels.

  Therefore, in the present invention, the thickness of the charge injection layer 4 is made extremely thin, and the taper angle of the element isolation film 3 is made steep. As a result, the charge injection layer 4a on the lower electrode 2 has a film thickness sufficient for charge injection, but the charge injection layer 4b on the taper portion of the element isolation film 3 becomes thinner due to the inclination, It becomes an island-like discontinuous film. That is, since the inclined surface is increased in area by the amount inclined with respect to the plane, for example, when the charge injection layer 4 is formed by using a highly anisotropic film forming method, the taper portion of the element isolation film 3 is at the lower part. Compared with the flat part of the electrode 2, the film formation density per unit area is thin, and the film formation state becomes insufficient. Therefore, the charge injection layer 4b on the taper portion of the element isolation film 3 is a discontinuous film having an island structure. In the case of such an island structure, the electric resistance is remarkably increased as compared with the continuous film.

The conceptual diagram is shown in FIG. When the thickness of the conductor or semiconductor is reduced, the electrical resistance gradually increases compared to the bulk electrical resistance, but the film has a discontinuous island structure in some places, so it has several digits of resistance. (See t _{1 in} FIG. 2). At this time, for example, in the case of a conductor, in the case of a continuous film (thicker than t ₁ ), the resistivity has a positive temperature coefficient, but in the case of an island-like structure (thickness is equal to or less than t ₁ ), it is negative between islands. It has the characteristic of having a temperature coefficient of. Note that in this specification, the island-shaped structure refers to a thin film made of discontinuous islands and having an average diameter smaller than the average distance between the islands. In the charge injection layer 4b on the taper portion of the element isolation film 3, the current leakage between the pixels is prevented by setting the film thickness to be equal to or less than the film thickness at which this resistance increase occurs. As a result, a device isolation film 3 having a taper portion is formed in advance, and then a charge injection layer 4 is formed on the entire display region composed of the pixel portion and the device isolation film 3, and charge injection is performed between adjacent pixels. Layer 4 can be substantially divided. Therefore, patterning of the charge injection layer 4 becomes unnecessary, and the cost can be reduced. In particular, when a material having a volume resistivity of 10 ⁸ Ωcm or less is used as the material of the charge injection layer 4, the use of the present invention can suppress leakage between pixels, which is more preferable.

  Incidentally, the surface of the element isolation film 3 can be rubbed to produce an uneven shape, and the charge injection layer can be substantially divided between adjacent pixels.

  The film thickness of the charge injection layer 4 needs to be set so that the charge injection characteristics are improved and an island structure is formed in the taper portion of the element isolation film 3 so that it is substantially divided between pixels. is there. Specifically, the film thickness is preferably 0.1 nm to 10 nm, and more preferably 2 nm to 8 nm.

  The angle of the taper portion of the element isolation film 3 may be any angle as long as the charge injection layer 4 has an island-like structure on the taper portion to increase the resistance. Specifically, when the thickness of the charge injection layer 4 is 0.1 nm or more and 10 nm or less, 45 degrees or more and 90 degrees or less are preferable. More preferably, when the thickness of the charge injection layer 4 is 2 nm or more and 8 nm or less, the angle of the tapered portion of the element isolation film 3 is preferably 60 degrees or more and 90 degrees or less. For example, although it depends on the film thickness of the charge injection layer, it may be about 50 degrees if the film thickness is about 3 nm.

  The manufacturing method of the element isolation film 3 is not particularly limited. When manufacturing using a known photolithography technique, it can be controlled by changing exposure and development conditions. Alternatively, it can be formed by dry etching such as RIE using a mask.

  As the material of the element isolation film 3, any material such as a polymer material containing a resin such as a resist, an inorganic material such as SiN, SiO2, or the like may be used.

  The upper electrode 6 needs to have a sufficient thickness so as not to be divided at the tapered portion of the element isolation film 3, and preferably has a thickness of 20 nm or more. Thereby, even in the same tapered portion, the very thin charge injection layer 4 is substantially divided, but the thicker upper electrode 6 is not divided because it forms a continuous film.

  Next, each member used in the present embodiment will be described.

  Examples of the material suitably used as the substrate 1 include various types of glass, glass substrates on which driving circuits such as TFTs are formed using poly-Si, a-Si, and the like, and those in which driving circuits are provided on a silicon wafer. It is done.

  Any material may be used as the lower electrode 2 as long as it has appropriate conductivity. If the reflective electrode is used, a material having a high visible light reflectance is preferable. For example, Cr, Pt, Ag, Au, Al, etc., and alloys containing these metal materials are preferably used. If a transparent electrode is used, a transparent conductive material such as ITO or IZO (indium zinc oxide) is used. Alternatively, a metal material may be formed as a thin film with a thickness of about 1 nm to 10 nm and used in a light-transmitting state.

  When a material having a high ionization tendency such as aluminum is used as the reflective electrode, if a transparent electrode (for example, ITO) on the reflective electrode is patterned using a well-known photolithography technique without using the present invention, the reflectance decreases. There is. This is a phenomenon in which, when coming into contact with a processing solution used in the development, peeling process, etc., the dissolution of aluminum is promoted by the electrolytic corrosion reaction due to the difference in ionization tendency between the transparent electrode and aluminum, and the reflectance is lowered. In particular, in a blue element having a short wavelength, it is necessary to reduce the film thickness of the transparent electrode in order to realize wider color reproducibility. In this case, since it becomes easy to make a pinhole in a transparent electrode, the influence of a reflectance fall becomes larger. In the present invention, since a wet process such as etching is not performed after the charge injection layer is formed, aluminum is more preferably not damaged by an electrolytic corrosion reaction due to a difference in work function between the charge injection layer and aluminum.

  The organic layer 5 involved in light emission is not particularly limited. It may be a single layer film or a laminated film. Moreover, you may include inorganic substances other than organic substance in the one part. An example of each material is given below.

  Examples of the hole injection layer include, but are not limited to, organic materials such as steel phthalocyanine, starburst amine compounds, polyaniline, and polythiophene, metal oxide films, and a mixture of a plurality of these materials. In addition, the hole injection layer is not necessarily required when sufficient hole injection property can be obtained without the hole injection layer.

  Examples of the hole transport material forming the hole transport layer include, but are not limited to, low molecular compounds such as triphenyldiamine derivatives, polyphyllyl derivatives, and stilbene derivatives.

  As the organic light emitting layer, a material that obtains desired light emission with a single material or a host material doped with a guest material is used. An organic light-emitting layer having an arbitrary dope concentration can be obtained by simultaneously vacuum-depositing a host material and a guest material and adjusting the respective deposition rates. At this time, it is possible to obtain arbitrary light emission by each organic EL element by changing the material of the organic light emitting layer or the host / guest combination constituting the organic light emitting layer corresponding to the emission color.

  Examples of the electron transport material for forming the electron transport layer include, but are not limited to, an aluminum quinolinol derivative, an oxadiazole derivative, a triazole derivative, a phenylquinoxaline derivative, and a silole derivative.

  Examples of the electron injection layer include an aluminum quinolinol derivative, an oxadiazole derivative, a triazole derivative, a phenylquinoxaline derivative, a silole derivative, and the like, and those doped with a guest material. However, it is not limited to these.

  Each organic layer including these organic light emitting layers is preferably formed by vapor deposition or the like. In particular, the organic light emitting layer is formed at an arbitrary position by using a mask at the time of formation.

  Any material may be used as the upper electrode 6 as long as it has appropriate conductivity. A material similar to that of the lower electrode 2 can be used.

  A cap may be provided on the element which is such a laminated body for the purpose of shielding from moisture, oxygen, etc. in the air. When light emission is taken out from the side opposite to the substrate, the cap is preferably translucent and glass or the like is used. Further, a gap may be provided between the cap and the element, and a desiccant or the like may be disposed.

  As another method for protecting the element from moisture, oxygen, etc. in the air, a protective film may be formed on the element surface. Specific examples of the material include inorganic films such as SiN, SiO, and SiON, polymer films, and laminated films thereof. A transparent material that can block moisture and oxygen is preferable.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

<Example 1>
An active element and a lower electrode of 100 × 100 pixels are formed on a glass with a thickness of 1 mm using a known lithography technique (not shown). At this time, an Al electrode having a thickness of 100 nm is used as the lower electrode. Further, an element isolation film having a height of 1 μm is formed on the Al electrode so as to surround the pixel. A photosensitive acrylic resin is used for the element isolation film, and the element isolation film is formed into a desired shape using a known lithography technique. The taper angle of the element isolation film is 60 degrees.

  A charge injection layer made of ITO is formed with a film thickness of 5 nm on the lower electrode and the element isolation film by sputtering. At this time, no film is formed using a mask outside the display area.

  The organic layer is formed using a vacuum evaporation method under a vacuum degree of 1E-4 Pa. The chemical structure of each material used in this example is shown in the following chemical formula 1.

A hole transport layer (HT-1) is formed to a thickness of 20 nm at a deposition rate of 0.3 nm / sec. Thereafter, the organic light emitting layer (EM-1 + EM-2) was co-deposited by adjusting the rate so that the deposition rate of EM-1 was 0.087 nm / sec and the deposition rate of EM-2 was 0.013 nm / sec. The film is formed with a film thickness. Subsequently, an electron transport layer (ET-1) is formed to a thickness of 10 nm at a deposition rate of 0.3 nm / sec. Further, the electron injection layer (ET-1 + Cs ₂ CO ₃ ) is adjusted so that the doping concentration of Cs ₂ CO ₃ is 0.65 vol% with respect to the deposition rate of 0.3 nm / sec of ET-1. Co-deposited with a film thickness of 40 nm.

  ITO is formed into a film with a film thickness of 60 nm as an upper electrode by a sputtering method, and sealed with a glass cap provided with a hygroscopic agent. Further, it is connected to a power source (not shown) to obtain an organic EL array. In addition, the organic light emitting layer formed by co-evaporation of EM-1 and EM-2 used here exhibits blue light emission.

The luminance of the organic EL array of this example at a current density of 10 mA / cm ² is 155 cd / m ² , the driving voltage at the current density is 4.5 V, the CIE chromaticity coordinates are x = 0.14, and y = 0.08. is there. Compared to a comparative example described later, the luminance and blue color purity are high, and low voltage driving is possible. Further, there is no signal crosstalk due to inter-pixel leakage.

<Comparative Example 1>
An organic EL array is obtained in the same manner as in Example 1 except that the charge injection layer made of ITO is not provided on the lower electrode.

  When the device of this comparative example is driven, the drive voltage is 10 V, which is significantly higher than that of the device of Example 1.

<Comparative Example 2>
Example 1 except that an ITO thin film having a thickness of 20 nm is formed on the lower electrode, patterned in the same manner as the lower electrode, and thereafter an element isolation film is formed, and the thickness of the hole transport layer is 5 nm. In the same manner as above, an organic EL array is obtained.

When the organic EL array of this comparative example is driven, the luminance at a current density of 10 mA / cm ² is 100 cd / m ² , the driving voltage at the current density is 4.5 V, the CIE chromaticity coordinates are x = 0.14, y = 0.09. Compared to the organic EL array of Example 1, the blue color purity is slightly lower and the luminance is also lower.

  The organic EL array of the present invention can be applied as a display. For example, the present invention can be applied to a screen of a digital camera, a finder screen, a screen of a mobile phone, an operation screen of a printer such as a copying machine, a television, a display for a personal computer, or a vehicle-mounted panel.

It is sectional drawing explaining the outline of the organic electroluminescent array of one Embodiment of this invention. It is a conceptual diagram for demonstrating this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Lower electrode 3 Element isolation film 4 Charge injection layer 4a Charge injection layer 4b on lower electrode Charge injection layer 5 on taper part of element isolation film Organic layer 6 Upper electrode

Claims (6)

A substrate, a lower electrode and an upper electrode at least one of which is divided for each pixel, the organic layer sandwiched between the upper electrode and the lower electrode, and including at least an organic light emitting layer; In an organic EL array comprising a plurality of pixels, comprising an element isolation film disposed around a pixel, and a charge injection layer made of a conductor or a semiconductor between the lower electrode and the organic layer,
The charge injection layer is formed over the entire display region including the lower electrode and the element isolation film, and a high resistance region of the charge injection layer is formed in a tapered portion of the element isolation film. An organic EL array.   2. The organic EL array according to claim 1, wherein the high resistance region is formed of a discontinuous film in which the charge injection layer formed in the tapered portion of the element isolation film has an island-like structure.   The film thickness of the charge injection layer is 0.1 nm or more and 10 nm or less, and the angle of the tapered portion of the charge injection layer is 45 degrees or more and 90 degrees or less. Organic EL array.   3. The organic EL according to claim 1, wherein a thickness of the charge injection layer is 2 nm or more and 8 nm or less, and an angle of a taper portion of the charge injection layer is 60 degrees or more and 90 degrees or less. array.   The organic EL array according to claim 1, wherein the upper electrode has a thickness of 20 nm or more.   The organic EL array according to any one of claims 1 to 5, wherein the charge injection layer is indium tin oxide.

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