JP2009076544A - Organic el element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element which prevents external light reflection caused in a contact hole of a lower electrode without increasing manufacturing processes to obtain excellent emission characteristics of high contrast. <P>SOLUTION: The top emission type organic EL element is so configured that the aspect ratio (α) of the contact hole formed in a flattening film is α<2. A transparent conductive oxide film consisting principally of indium oxide is used as the lower electrode, and comes into contact with a thin film transistor in the contact hole. A bottom surface of the contact hole is parallel to a substrate surface, and the angle (θ) of a surface of the transparent conductive oxide film at the bottom portion of the contact hole to a surface of the transparent conductive oxide film at a side surface portion of the contact hole is θ≈90°. A circular polarizing plate is disposed closer to a light extraction side than to an upper electrode. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an organic electroluminescent element (organic EL element).

  The structure of the organic EL element currently being developed is based on the lamination of anode / light emitting layer / cathode, and a transparent anode is formed on a substrate using a glass plate or the like, and light emission is extracted from the substrate side. This is the so-called bottom emission type. Recently, a panel of an active matrix system in which a driving transistor is provided for each light emitting pixel has been studied. However, when light is extracted from the substrate side, these drive circuits and wiring portions block light, so that there is a problem that the aperture ratio of the pixel (the area ratio of the portion that actually emits light in the element) becomes small.

  Therefore, as disclosed in Patent Document 1 and Patent Document 2, a cathode on the organic layer is formed of a transparent electron injection metal layer and an amorphous transparent conductive oxide layer, and light is extracted from the cathode side. A so-called top emission type element configuration has been attempted. In this top emission type element configuration, a pixel electrode (anode) is formed on a TFT drive circuit substrate, and an organic EL layer and a transparent cathode are further provided. Since light is extracted from the cathode, the problem of lowering the aperture ratio is solved.

  By the way, since light from the outside (hereinafter referred to as external light) enters the organic EL element, the external light is reflected by the contact holes of the metal electrode and the lower electrode, the pixel surface becomes bright, and the display contrast is lowered. There is a problem.

  There have been proposals for preventing external light reflection and improving display contrast. In Patent Document 3, the reflected light (external light reflection) reflected by the reflective electrode of the incident external light is cut by disposing a conductive thin film made of a low reflective material on the outside (observer side) of the electrode on the light extraction side. Proposals have been made. In the above proposal, the anode (anode) contact hole is filled with a transparent conductive film material made of ITO or the like, so that reflection of external light generated in the anode (anode) contact hole can be prevented. Yes.

Japanese Patent Laid-Open No. 10-162959 JP 2001-43980 A JP 2003-28892 A

  The configuration of Patent Document 3 has the following problems.

  In order to form a transparent conductive film of good quality (low stress & low resistance & high transmittance), it is formed by sputtering or ion plating. However, when filling a contact hole with a transparent conductive film, it is necessary to form a film with a thickness equal to or close to the depth of the contact hole. Will increase.

  An object of the present invention is to provide an organic EL device that prevents external light reflection that occurs in a contact hole of a lower electrode without increasing the number of manufacturing processes, and that provides good light emission characteristics with high contrast.

As means for solving the above problems, the present invention provides:
A planarization film that covers the thin film transistor on the substrate to planarize the surface, a pair of electrodes composed of a lower electrode and an upper electrode, an organic compound layer formed between the pair of electrodes, and a pixel periphery A contact hole that opens the planarization film at a lower portion of the partition wall separating the pixels formed to make electrical contact between the lower electrode and the thin film transistor, and transmits light from the film surface side of the upper electrode. In the top emission type organic EL element to be taken out,
The aspect ratio (α) of the contact hole is α <2,
A transparent conductive oxide film mainly composed of indium oxide is used as the lower electrode, and the transparent conductive oxide film is in contact with the thin film transistor through the contact hole,
The bottom surface of the contact hole is parallel to the substrate surface, and the surface of the transparent conductive oxide film on the bottom surface portion of the contact hole and the surface of the transparent conductive oxide film on the side surface portion of the contact hole The angle (θ) to be made is θ≈90 °,
A circularly polarizing plate is disposed closer to the light extraction side than the upper electrode.

  According to the present invention, it is possible to prevent reflection of external light generated in the contact hole of the lower electrode without increasing the number of manufacturing processes, and to obtain good light emission characteristics with high contrast.

(First embodiment)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a sectional view showing a basic configuration of a top emission type organic EL element according to the present invention of the first embodiment.

  The organic EL element shown in the figure includes a thin film transistor (hereinafter simply referred to as TFT) 2 on a glass substrate 1, a planarizing film 3 that covers the TFT 2 and planarizes the surface, a lower electrode 6 that is an anode, and an upper part that is a cathode. The electrode 9 includes an organic compound layer 8 formed between the pair of electrodes. Furthermore, it includes a partition wall 7 that separates each pixel formed along the periphery of the pixel, a sealing glass 10 that blocks the element from the outside air, and a circularly polarizing plate 13 that cuts regular reflection of external light. The light is extracted from the film surface side.

  The partition wall 7 of the organic EL element is made of an insulating organic material such as acrylic or polyimide. Immediately below the partition wall 7, the planarization film 3 made of an organic material such as acrylic is opened to electrically connect the lower electrode 6 made of a transparent conductive oxide film mainly composed of indium oxide and the drain electrode 21 of the TFT. Contact hole 14 is formed.

  The generation mechanism of external light reflection due to the shape of the surface of the lower electrode 6 formed on the side surface of the lower electrode 6, the contact hole 14, and the contact hole 14, which is a feature of the present invention, will be described.

  In this embodiment, an indium oxide-based transparent conductive oxide film such as ITO, IZO, or IWZO is used as the lower electrode 6. The transparent conductive oxide film is usually formed by sputtering. The sputtering method is a film forming method with good coverage, and a film can be formed on a shadowed portion such as a side surface of the contact hole 14. Also in this embodiment, the lower electrode 6 is formed by sputtering, and the current flows in contact with the drain electrode 21 on the bottom surface of the contact hole 14. The function required for the contact hole 14 is that the lower electrode 6 and the drain electrode 21 are in electrical contact with each other and supply current to the lower electrode 6 from the power supply line side.

  The contact hole 14 generally used has a structure in which the bottom surface is small, the top surface is large, and the side surface is inclined (so-called tapered shape). The size of the bottom surface of the contact hole 14 where the lower electrode 6 and the drain electrode 21 are in contact is defined by the contact resistance between the lower electrode 6 and the drain electrode 21, but the length of one side is 3 to 10 μm. Degree. The upper surface has a side length of 5 to 15 μm. In this case, since the side surface of the contact hole 14 is forward tapered and inclined, a film is sufficiently formed on the side surface, and there is no problem of an increase in resistance value due to a decrease in the film thickness of the lower electrode 6 on the side surface portion. However, external light reflection caused by the surface of the lower electrode 6 on the side surface portion of the contact hole 14 occurs, and the display contrast of the element deteriorates. This is because light incident on the side surface portion is reflected at a larger angle (reflection angle) with respect to the normal direction of the circularly polarizing plate, thereby generating light that cannot be cut by the circularly polarizing plate. Further, if the light incident on the side surface portion is reflected a plurality of times (especially even times) in the contact hole, the phase changes at the time of reflection, so that it cannot be cut by the circularly polarizing plate. A circularly polarizing plate generally has a high antireflection effect for light in the positive direction, but has a property that the antireflection effect decreases as the angle of incidence on the circularly polarizing plate increases.

  Therefore, in order to prevent external light reflection due to the shape of the lower electrode 6 on the side surface portion of the contact hole 14, that is, to reduce external light incident on the side surface portion, the bottom surface of the contact hole 14 is parallel to the substrate surface. Is formed. An angle θ between the surface of the lower electrode 6 on the side surface portion of the contact hole 14 and the surface of the lower electrode 6 on the bottom surface portion of the contact hole 14 is θ≈90 °. Note that θ≈90 ° means that the angle does not have to be strictly 90 °. Even if the contact hole 14 is formed so that the angle formed between the side surface and the bottom surface is 90 °, an error of several degrees (specifically, about 3 ° to 5 °) occurs. The present invention does not exclude the case where there is an error of several degrees. Even when there is an error of several degrees, almost the same effect as in the case of 90 ° can be obtained.

  In addition, the aspect ratio α (A (depth) / B (bottom length)) of the contact hole 14 is set to α <2. In this embodiment, when the aspect ratio of the contact hole 14 is increased, the amount of deposition of the lower electrode 6 on the side surface of the contact hole 14 is reduced and the resistance value of the contact hole 14 is increased even if the sputtering method is good. The resistance value increases. In the case of an organic EL element, if the resistance value of the contact hole 14 is greater than 10 kΩ, a light emission abnormality such as a decrease in light emission intensity occurs.

  FIG. 3 shows the relationship between the aspect ratio of the contact hole 14 and the resistance value of the contact hole 14. It can be seen that when the aspect ratio of the contact hole 14 is smaller than 2, the resistance value of the contact hole 14 can be made sufficiently low. In this configuration, the opening area of the upper surface of the contact hole 14 is substantially equal to the opening area of the bottom surface. That is, the area of the entire contact hole can be reduced as compared with a conventional tapered contact hole. Therefore, it is possible to increase the display pixel area relative to the conventional organic EL element and increase the display area (aperture ratio) over the entire panel surface. In addition, the number of pixels can be increased and higher definition can be achieved.

  Next, the mechanism of external light reflection due to the shape of the surface of the lower electrode 6 on the side surface portion of the contact hole 14 will be described.

  A circularly polarizing plate 13 is disposed on the light extraction side (display surface side) with respect to the upper electrode 9. Without impairing conduction between the lower electrode 6 and the drain electrode 21 of the TFT, external light reflection generated on the surface of the lower electrode 6 on the side surface portion of the contact hole 14 and on the surface of the lower electrode 6 on the bottom surface portion of the contact hole 14. The generated external light reflection can be prevented. Therefore, the contrast of the element can be improved.

  That is, the external light incident on the side surface portion of the contact hole 14 can be reduced, and the amount of reflected light that cannot be cut by the polarizing plate among the external light incident on the contact hole 14 can be relatively reduced. Further, the light incident on the contact hole 14 is emitted at the same angle as the incident angle because it is reflected by the surface of the transparent conductive oxide film that is the lower electrode 6 in the contact hole 14 and is emitted to the display surface side. Most of the light can be cut by the circularly polarizing plate 13.

  More specifically, a partition wall 7 and an upper electrode 9 are formed above the contact hole 14, and light incident from the outside is reflected by the surface of the upper electrode 9. However, when the partition wall 7 is made of an insulating organic material, the surface is flattened, and the upper electrode 9 is also formed following the surface of the partition wall 7, so that the surface of the upper electrode 9 is also flattened. Therefore, since the light incident on the surface of the upper electrode 9 is regularly reflected, it can be cut by the circularly polarizing plate 13 disposed on the upper portion of the sealing glass 10.

  The light transmitted through the upper electrode 9 is reflected by the surface of the partition wall 7, but the material of the partition wall 7 is an organic material such as acrylic and the refractive index is as low as about 1.4, so most of the light is refracted and the angle is changed. It progresses in the contact hole 14 in a state.

  Subsequently, the light incident into the contact hole 14 is reflected by the surface of the lower electrode 6 formed in the upper layer of the contact hole 14. When the incident light is incident on the surface of the lower electrode 6 on the side surface portion of the contact hole 14, the side surface (the surface of the lower electrode 6) ⇒the bottom surface (the surface of the lower electrode 6) ⇒the side surface on the opposite side (the surface of the lower electrode 6) is repeated. The light is reflected and emitted to the display surface side (observer side), and becomes external light reflection.

  FIG. 4 shows how light incident on the surface of the lower electrode 6 on the conventional contact hole 14 is reflected. In the case of the conventional tapered contact hole 14, the surface shape of the lower electrode 6 is also tapered following the contact hole 14. When the surface of the lower electrode 6 is tapered, light is repeatedly reflected on the surface of the lower electrode 6 and emitted to the display surface side in a state where the directions of light emitted to the display surface side are uneven. That is, light that is reflected at an angle larger than the angle (incident angle) incident on the contact hole 14 is generated. Therefore, only a part of the light emitted to the display surface side can be cut by the circularly polarizing plate 13 disposed on the display surface side with respect to the upper electrode 9, so that the reflection of external light is increased and the display of the element is increased. Contrast deteriorates.

  FIG. 5 shows how light incident on the surface of the lower electrode 6 on the contact hole 14 of the present embodiment is reflected. In the case of the contact hole 14 of the present embodiment, external light having an incident angle with respect to the contact hole is reduced, and most of the light incident on the contact hole is in the regular reflection direction or near the regular reflection direction. Directional light. The light incident on the contact hole is emitted from the contact hole at the same angle as the incident angle. Therefore, most of the light emitted to the display surface side can be cut by the circularly polarizing plate 13 disposed on the display surface side with respect to the upper electrode 9, and therefore, compared with the conventional tapered contact hole 14. The display contrast of the element can be greatly improved.

  When the lower electrode 6 is a metal, the light incident on the surface of the lower electrode 6 does not enter the lower part of the lower electrode 6 and is emitted to the display surface side in the above mode. Since the lower electrode 6 of this embodiment is a transparent conductive oxide film, the lower electrode 6 also reflects at the interface between the lower electrode 6 and the planarizing film 3 (the planarized film surface). However, since the planarizing film 3 is an organic material such as acrylic and the refractive index is as low as about 1.4, most of the light is refracted and proceeds to the lower part of the pixel in the planarizing film 3 with the angle changed. . Therefore, the light reflective metal layer 5 is formed below the lower electrode of the light emitting region (pixel), and the adhesive layer 4 for ensuring the adhesion between the planarizing film 3 and the light reflective metal layer 5 is formed below the light reflective metal layer 5. It is preferable that Most of the light that has traveled to the bottom of the pixel is attenuated by repeatedly reflecting between the adhesion layer 4 or the light-reflecting metal layer 5 and the TFT 2 and absorbed, so that it is not emitted to the display surface side.

  As the adhesion layer 4, Mo, W, Ti, MoW, or the like that enhances the adhesion between the organic material and the inorganic material can be used. As the light reflective metal layer 5, Al, Au, Ag, Cr, an Ag alloy, an Al alloy, or the like can be used.

  A structure in which the light reflecting metal layer 5 is extended to the contact hole 14 and is in contact with the drain electrode 21 is also conceivable. In this case, the electrical connection between the light reflective metal layer 5 and the lower electrode 6 is deteriorated due to the oxidation of the light reflective metal layer 5, and the supply of current to the organic compound layer 8 is reduced. ) Will worsen. In particular, in the Al-based light reflective metal layer 5, the oxidation may be greatly insulated. In addition, a structure in which the lower electrode 6 is not provided and only the light reflective metal layer 5 is used as the lower electrode 6 is also conceivable, but in this case, the efficiency of hole injection from the light reflective metal layer 5 to the organic compound layer 8 is lowered. Good device characteristics cannot be obtained.

  As described above, most of the light emitted to the display surface side by the light incident on the contact hole 14 is reflected by the surface of the lower electrode 6, and the light can be cut by the circularly polarizing plate 13. Is possible. Therefore, the display contrast of the element can be improved without increasing the manufacturing process as compared with the conventional organic EL element.

  As a method of forming the lower electrode 6 and the contact hole 14, a negative acrylic photosensitive material mixed with a UV absorber is applied onto the TFT 2 by a spin coating method and prebaked. Thereafter, UV exposure is performed using a photomask having a predetermined pattern so that the drain electrode 21 of the TFT 2 is exposed, and development is performed. Thereafter, the side surface of the opening (contact hole 14) of the planarizing film 3 is about 90 ° with respect to the plane of the glass substrate 1 by heat curing. Subsequently, film formation and patterning are performed so that the adhesion layer 4 and the light reflective metal layer 5 are formed in the pixel portion. Subsequently, a transparent conductive oxide film such as ITO, IZO or IWZO is DC sputtered to obtain the lower electrode 6. In the case of sputtering, a film is formed in a form that follows the state of the underlying layer. However, particularly when sputtering a transparent conductive oxide film having low resistance, high transmittance, and low stress, the film is formed under conditions where the film forming pressure is high. In order to form a film, the film is deposited in a shape very close to the state of the base. As a result, the angle formed by the surface of the lower electrode 6 on the side surface portion of the contact hole 14 and the surface of the lower electrode 6 on the bottom surface portion of the contact hole 14 is about 90 °. Subsequently, resist is applied, exposed, developed and patterned so that the lower electrode 6 is formed in the pixel and contact hole 14.

  Other members constituting the organic EL element of this embodiment will be described.

  The organic compound layer 8 includes a light emitting layer 82 that emits light by recombination of holes supplied from the lower electrode 6 and electrons supplied from the upper electrode 9. Furthermore, a hole transport layer 81, an electron transport layer 83, and an electron injection layer 84 are included. A hygroscopic material 11 is disposed inside the sealing glass 10.

  The organic compound that can be used as the material of the hole transport layer 81 is not particularly limited, and for example, a triphenyldiamine derivative, an oxadiazole derivative, a polyphylyl derivative, a stilbene derivative, and the like can be used, but are not limited thereto. is not.

Examples of organic compounds that can be used as the material of the light-emitting layer 82 include triarylamine derivatives, stilbene derivatives, and polyarylenes;
Aromatic condensed polycyclic compounds, aromatic heterocyclic compounds, aromatic heterocyclic condensed ring compounds, metal complex compounds, etc., and single or composite oligos thereof can be used. In addition, one or more of these light emitting materials can be doped into the hole injection layer, the hole transport layer, or the electron transport layer. These materials and configurations are not limited to these.

  As an organic compound that can be used as a material for the electron transport layer 83, a phenanthroline compound, a quinoline derivative, a phenylanthracene derivative, or the like can be used, and a phenanthroline compound is particularly preferable.

  The organic compound that can be used as the material of the electron injection layer 84 is an organic compound doped with a carbonate such as cesium carbonate or lithium carbonate, and an organic compound obtained by doping a phenanthroline compound with a carbonate is particularly preferable.

  In forming the hole transport layer 81, the light emitting layer 82, the electron transport layer 83, and the electron injection layer 84, it is preferable to use a vapor deposition apparatus using resistance heating, Knudsen cell or bulb cell. In the light emitting layer 82 and the electron injection layer 84, it is preferable to use a co-evaporation method in which a doping material and an organic compound are simultaneously deposited by heating.

The upper electrode 9 is preferably an indium oxide-based transparent conductive oxide film such as ITO or IZO, which has high transparency and low resistance. In forming the upper electrode 9, it is preferable to use a magnetron sputtering apparatus capable of forming a high-quality film. Specifically, transparent conductive material is formed on the electron injection layer 84 by a DC magnetron reactive sputtering method in which O ₂ gas is introduced as a dopant using a target of a transparent conductive oxide film material such as ITO or IZO and reacted. A conductive oxide film is formed. In addition to the magnetron sputtering method, an ion plating method in which O ₂ gas is introduced as a dopant and allowed to react can also be adopted as a film forming method for the upper electrode 9. An RF magnetron reactive sputtering method can also be employed, but a DC magnetron sputtering method is preferable because a high-quality film can be obtained with little increase in substrate temperature.

  The sealing glass 10 is bonded to the glass substrate 1 at the outer periphery using an acrylic adhesive 12. On the surface of the sealing glass 10 on the substrate side, a sheet-like hygroscopic material 11 is affixed at a position away from the light emitting portion, so that the airtightness of the element portion is maintained. Instead of the hygroscopic material 11, a structure in which a hygroscopic film such as SrO or CaO is formed on the substrate side of the sealing glass 10 can also be adopted.

  The circularly polarizing plate 13 is disposed on the display surface side on the sealing glass 10 and has a function of cutting regular reflection of external light reflection generated from the substrate side.

(Second embodiment)
FIG. 2 is a cross-sectional view showing a basic configuration of a top emission type organic EL element according to the second embodiment of the present invention.

In 2nd embodiment, it is the structure which formed the partition 7 with the insulating inorganic material. Other configurations are the same as those in the first embodiment. When the partition 7 is formed of an insulating inorganic material, it is formed of a SiN _x film using a CVD method or a sputtering method. In the CVD method as well as the sputtering method, a film is formed in a state following the shape of the base, so that a shape almost the same as the surface of the lower electrode 6 in the contact hole 14 is obtained. That is, the film surfaces of the partition wall 7 and the upper electrode 9 in the contact hole 14 are substantially the same as the shape of the film surface of the lower electrode 6.

In this embodiment, reflection when light is incident from the outside can be handled in the same manner as when light is incident on the lower electrode 6 in the first embodiment. Specifically, the upper electrode 9 is an indium oxide-based transparent conductive oxide film like the lower electrode 6 and has the same refractive index, so that the incident light is incident on the lower electrode 6. Through the same reflection process, the light is emitted to the display surface side in a state where the directions are aligned. The light transmitted through the upper electrode 9 passes through the partition 7 and the lower electrode 6 as it is without being reflected or refracted at the interface between the upper electrode 9 and the partition 7 and the interface between the partition 7 and the lower electrode 6. Then, the light is refracted at the interface between the lower electrode 6 and the planarizing film 3 and proceeds to the lower part of the pixel in the planarizing film 3 in a state where the angle is changed. This is because the refractive index of SiN _x of the partition wall 7 is 2.0 to 2.1, which is equivalent to the indium oxide-based transparent conductive oxide film used in the lower electrode 6 and the upper electrode 9. This is because reflection and refraction generated at the interface are extremely reduced.

  After that, most of the light traveling to the lower part of the pixel is attenuated by repeatedly reflecting between the adhesion layer 4 or the light-reflecting metal layer 5 and the TFT 2 and is not emitted to the display surface side because it is absorbed. .

  Most of the light incident on the contact hole 14 and emitted to the display surface side is light reflected on the surface of the upper electrode 9, and the light can be cut by the circularly polarizing plate 13. Therefore, the display contrast of the element can be improved without increasing the manufacturing process as compared with the conventional organic EL element.

  Examples of the present invention will be described below.

Example 1
[Formation of planarization layer 3]
A negative acrylic photosensitive material in which a UV absorber is mixed is applied to a plurality of glass substrates 1 on which TFTs 2 are formed for each pixel, and is pre-baked by applying the spin coating method so that the thickness varies depending on the substrate. did. UV exposure, development, and heat-curing were performed using a photomask having a predetermined pattern so that the drain electrode 21 of the TFT 2 was exposed. In this way, the side surface of the opening (contact hole 14) of the planarizing film 3 was approximately 90 ° with respect to the plane (substrate surface) of the glass substrate 1, and the surface of the glass substrate 1 was planarized. The thickness of the planarized film 3 after heat curing thus prepared is 1.5 to 10 μm, the size and shape of the bottom surface of the contact hole 14 are 3.0 μm, the size of the top surface of the contact hole, The shape was 3.0 □ μm.

[Adhesion layer 4 and light reflective metal layer 5 formation]
On a plurality of glass substrates 1 on which the planarizing film 3 was formed, a MoW film was formed to a thickness of 100 nm by DC sputtering using a MoW target. Subsequently, the Al target was DC sputtered to form an Al film with a thickness of 100 nm. Next, a photosensitive resist was applied by a spin coat method, dried, and exposed using a photomask having a predetermined pattern. After exposure, it was developed and cured by heating to form a predetermined resist pattern. Subsequently, the Al film and the MoW film were collectively etched using an etching solution to form the adhesion layer 4 and the light reflective metal layer 5 having a predetermined pattern. Thereafter, the resist was removed with a stripping solution.

[Formation of lower electrode 6]
On a plurality of glass substrates 1 on which the adhesion layer 4 and the light reflective metal layer 5 were formed, an ITO target was DC sputtered to form an ITO film having a thickness of 100 nm. Subsequently, a photosensitive resist was applied by a spin coating method, dried, and exposed using a photomask having a predetermined pattern. After exposure, it was developed and cured by heating to form a predetermined resist pattern. Subsequently, the ITO film is etched using an etching solution so as to cover the adhesion layer 4 and the light-reflecting metal layer 5 (the ITO film pattern is increased by about 2.0 μm at the outer peripheral portion) and the contact hole 14 is covered. A lower electrode 6 having a shape pattern was formed. Thereafter, the resist was removed with a stripping solution. The shape of the lower electrode 6 formed in this way is such that the angle formed by the surface of the lower electrode 6 on the side surface of the contact hole 14 and the surface of the lower electrode 6 on the bottom surface of the contact hole 14 is about 90 in the contact hole 14. °.

[Partition 7 formation]
A positive photosensitive polyimide resin was applied to a plurality of glass substrates 1 on which the lower electrode 6 was formed by a spin coat method so as to have a thickness of 1.0 μm. After pre-baking, exposure was performed using a photomask having a predetermined pattern (a shape in which the center of each pixel is exposed to cover the outer periphery and cover the contact hole 14). Thereafter, exposure, development, and heat curing were performed in an oven. The film thickness of the partition wall 7 formed in this way was 0.7 μm, and the surface of the partition wall 7 on the contact hole 14 was flattened.

[Washing]
A plurality of glass substrates 1 on which the partition walls 7 are formed are transferred to an in-line type substrate cleaning machine to perform megasonic cleaning, two-fluid nozzle cleaning, and then the glass substrate 1 is transferred to a vacuum oven at 200 ° C. for 3 hours. Vacuum drying was performed.

[Preprocessing]
The glass substrate 1 on which the partition walls 7 were formed and cleaned was transferred to an organic EL vapor deposition apparatus and evacuated, and 50 W RF power was applied to a ring electrode provided near the substrate in the pretreatment chamber to perform an oxygen plasma cleaning process. The oxygen pressure was 0.6 Pa and the treatment time was 40 seconds.

[Hole transport layer formation]
The plurality of pretreated glass substrates 1 were moved from the pretreatment chamber to the film formation chamber, and the film formation chamber was evacuated to 1 × 10 ⁻⁴ Pa. Thereafter, α-NPD having a hole transporting property represented by the following general formula [I] is vapor-deposited by a resistance heating vapor deposition method at a film forming rate of 0.2 to 0.3 nm / sec. A transport layer 81 was formed. Note that the hole transport layer 81, the light emitting layer 82, the electron transport layer 83, and the electron injection layer 84 were deposited on predetermined portions by using the same deposition mask.

[Light emitting layer deposition]
The light emitting layer 82 is formed by depositing Alq3, which is an alkylate complex, on the hole transport layer 81 with a film thickness of 35 nm under the same film formation conditions as the hole transport layer 81 by a resistance heating vapor deposition method using a vapor deposition mask having a predetermined pattern. did. The film formation rate was ~ 0.5 nm / s.

[Electron transport layer formation]
A phenanthroline compound represented by the following general formula [II] was deposited on the light emitting layer 82 by a resistance heating vapor deposition method under the same film formation conditions as the hole transport layer 81 to form an electron transport layer 83. The film formation rate was ~ 0.5 nm / s.

[Electron injection layer formation]
The deposition rate is adjusted so that the phenanthroline compound and cesium carbonate (Cs ₂ CO ₃ ) are uniformly mixed in the film at a ratio of 9: 1 on the electron transport layer 83 by resistance heating co-evaporation. Then, an electron injection layer 84 having a thickness of 40 nm was formed. Specifically, the material set in each vapor deposition boat was evaporated by a resistance heating method, and each boat current value was adjusted to form a film at a vapor deposition rate of ˜0.5 nm / s.

[Formation of upper electrode 9 (transparent conductive oxide film)]
The glass substrate 1 on which the organic compound layer was formed was transferred to another film forming chamber (sputtering chamber), and an upper electrode 9 having a thickness of 130 nm was formed on the electron injection layer 84 by DC sputtering using an ITO target.

The film formation conditions were as follows: room temperature film formation without substrate heating, film formation pressure of 1.0 Pa, Ar, and O ₂ gas, flow rates of 100 and 1.0 sccm, and input power applied to the target of 500 w. Film formation was performed. As characteristics of the single film of the upper electrode 9, the transmittance was 86% (at 450 nm), and the specific resistance value was 6.5 × 10 ⁻⁴ Ωcm. The refractive index was 2.0.

[Glass sealing]
The glass substrate 1 on which the upper electrode 9 was formed was transferred to a glove box, leaked with N ₂ , and the sealing glass 10 was adhered and sealed to the glass substrate 1 using a UV curable acrylic adhesive 12. A circularly polarizing plate 13 is attached to the display surface side of the sealing glass 10, and the hygroscopic material 11 is attached to the substrate side.

[Element evaluation]
Thus, on the glass substrate 1 on which the TFT 2 is formed, the planarization film 3, the lower electrode 6, the partition wall 7, the hole transport layer 81, the light emitting layer 82, the electron transport layer 83, the electron injection layer 84, the upper part The electrode 9, the sealing glass 10, and the circularly polarizing plate 13 were provided to obtain a plurality of single color light emitting elements. Subsequently, in this light emitting device, the light emission characteristics of the device were examined by applying a DC voltage with the lower electrode 6 as an anode and the upper electrode 9 as a cathode. Table 1 shows the results of measuring the light emission state and the contrast ratio.

  As can be seen from Table 1, the light emitting element having the contact hole 14 with an aspect ratio smaller than 2 has a good light emitting state and a good contrast ratio.

(Example 2)
To form the planarizing film 3, a plurality of positive photosensitive polyimide resins applied by spin coating and negative photosensitive polyimide resin mixed with UV absorber applied by spin coating are produced. did. The taper angle of the slope of the contact hole 14 was changed by changing the exposure conditions. Other than that, a plurality of light-emitting elements manufactured under the same conditions as in Example 1 were manufactured. The taper angle of the slope of the contact hole 14 is 45 ° to 110 °. The angle formed between the surface of the lower electrode 6 at the bottom surface portion of the contact hole 14 and the surface of the lower electrode 6 at the side surface portion of the contact hole 14 formed on the contact hole 14 by sputtering is similarly 45 ° to 110 °. there were.

  Similarly to Example 1, the light emission characteristics of the device were examined by applying a DC voltage with the lower electrode 6 as an anode and the upper electrode 9 as a cathode. Table 2 shows the results of measuring the light emission state and the contrast ratio.

  As can be seen from Table 2, a good contrast ratio is obtained in a light emitting device in which the angle between the surface of the lower electrode 6 at the side surface portion of the contact hole 14 and the surface of the lower electrode 6 at the bottom surface portion of the contact hole 14 is about 90 °. It was.

(Example 3)
A device was fabricated under the conditions of Example 1 except that the thickness of the planarizing film 3 was 1.5 μm and a SiN _x film was formed as the partition wall 7 using the CVD method. Specifically, the SiN _x film was formed using the CVD method in forming the partition walls 7 so that the composition of the material gas was varied during film formation so that the film composition varied continuously in the depth direction of the film. Subsequently, a photosensitive resist is applied onto the SiN _x film by a spin coating method and dried, and a photomask having a predetermined pattern (in which the center of each pixel is exposed to cover the outer periphery and the contact hole 14) is formed. And exposed. After exposure, it was developed and cured by heating to form a predetermined resist pattern. Subsequently, the SiN _x film was etched by a dry etching method to form partition walls 7 having a predetermined pattern.

As for the shape of the device thus fabricated in the contact hole 14 of the partition wall 7 and the upper electrode 9, the angle between the bottom surface and the side surface was about 90 ° in the same manner as the shape of the lower electrode 6. In addition, since the film composition of the SiN _x film continuously changes in the film thickness direction and the etching rate by dry etching is different, a forward tapered shape can be obtained at the edge portion of the pixel.

  Similarly to Example 1, the light emission characteristics of the device were examined by applying a DC voltage with the lower electrode 6 as an anode and the upper electrode 9 as a cathode.

  The light emission state was good, and a good contrast ratio of 650: 1 was obtained.

It is a schematic diagram which shows the laminated structure example in the organic EL element as 1st embodiment of this invention. It is a schematic diagram which shows the laminated structure example in the organic EL element as 2nd embodiment of this invention. It is a figure which shows the relationship between the aspect-ratio of a contact hole, and the resistance value of the said contact hole. It is sectional drawing which shows a mode that the light which injected into the surface of the lower electrode on a conventional contact hole reflects. It is sectional drawing which shows a mode that the light which injected into the surface of the lower electrode on the contact hole of this invention reflects.

Explanation of symbols

1 Glass substrate 2 TFT
21 Drain electrode 3 Flattening film 4 Adhesion layer 5 Light reflective metal film 6 Lower electrode 7 Partition 8 Organic compound layer 81 Hole transport layer 82 Light emitting layer 83 Electron transport layer 84 Electron injection layer 9 Upper electrode 10 Sealing glass 11 Adsorption Agent 12 Adhesive 13 Circular Polarizing Plate

Claims (4)

A planarization film that covers the thin film transistor on the substrate to planarize the surface, a pair of electrodes composed of a lower electrode and an upper electrode, an organic compound layer formed between the pair of electrodes, and a pixel periphery A contact hole that opens the planarization film at a lower portion of the partition wall separating the pixels formed to make electrical contact between the lower electrode and the thin film transistor, and transmits light from the film surface side of the upper electrode. In the top emission type organic EL element to be taken out,
The aspect ratio (α) of the contact hole is α <2,
A transparent conductive oxide film mainly composed of indium oxide is used as the lower electrode, and the transparent conductive oxide film is in contact with the thin film transistor through the contact hole,
The bottom surface of the contact hole is parallel to the substrate surface, and the surface of the transparent conductive oxide film on the bottom surface portion of the contact hole and the surface of the transparent conductive oxide film on the side surface portion of the contact hole The angle (θ) to be made is θ≈90 °,
An organic EL element, wherein a circularly polarizing plate is disposed on the light extraction side with respect to the upper electrode.   The organic EL element according to claim 1, wherein the partition wall is formed of an insulating organic material or an insulating inorganic material.   2. The organic EL element according to claim 1, wherein a light-reflective metal layer and an adhesion layer are formed below the lower electrode in the pixel portion.   The organic EL element according to claim 1, wherein an ITO film is used as the lower electrode.

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