JPH10289787A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain abnormal growth of cathode crystals and reduce physical damages to the organic layer of a cathode having a film, formed on an organic electroluminescent body structure on a substrate by use of the sputtering method by applying surface roughness equal to or less than a prescribed level to a boundary adjacent to the organic layer. SOLUTION: A boundary adjacent to a cathode organic layer has a maximum surface roughness equal to or less than 100 nm, and the mean surface roughness thereof is preferably taken at a value equal to or less than 30 nm. Aluminum or an aluminum alloy is used for a cathode, and the film thereof is preferably made free from compressive stresses inside. Also, the film is formed by the DC sputtering method using a film-forming gas of one or more types of Ar, Kr and Xe, and in this case, a product of film-forming gas pressure and a distance between a substrate and a target is preferably taken at a value between 20 Pa.cm and 65 Pa.cm. As a result, an optimally crystallized state results, and a film having smooth surface and high adhesion is formed. Also, the initial luminous brightness of the luminous element using the cathode is high and the half-life of brightness is also long. Furthermore, no current leakage takes place across electrodes, and the number of dark spots at an initial stage and after drive is few.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic EL device using an organic compound (hereinafter referred to as an organic EL device), and more particularly to a negative electrode for supplying electrons to a light emitting layer.

[0002]

2. Description of the Related Art In recent years, organic EL devices have been actively studied. This is because a tetraphenyldiamine (T) is formed on a transparent electrode (positive electrode) such as tin-doped indium oxide (ITO).
Basic structure in which a hole transporting material such as PD) is formed into a thin film by vapor deposition, a fluorescent substance such as an aluminum quinolinol complex (Alq3) is laminated as a light emitting layer, and a metal electrode (negative electrode) such as Mg having a small work function is formed. With several 100 to 1000 cd / c at a voltage around 10 V
very high luminance and m ² are noted by obtained.

As a material used as a negative electrode of such an organic EL device, a material that injects a large amount of electrons into a light emitting layer is considered to be effective. In other words, it can be said that a material having a smaller work function is more suitable for the negative electrode. There are various materials having a small work function. Examples of materials used as a cathode of an EL light emitting element include MgAg described in JP-A-4-233194,
AlLi is common. The reason for this is that the manufacturing process of the organic EL light-emitting element mainly involves evaporation using resistance heating, so that the evaporation source is naturally limited to those having a low temperature and a high vapor pressure. In addition, since an evaporation process using such resistance heating is used, adhesion at a film interface is poor. As a result, a non-image portion called a dark spot on a pixel is generated immediately after manufacturing, and the non-image portion is enlarged according to driving, and this is a factor that determines the element life.

As one of the vacuum film forming methods, it is conceivable to use a sputtering method. However, in the case of the conventional sputtering method, an inert gas such as Ar is used, and the gas pressure is 0.5 to 1.0.
It is performed under the condition of 0 Pa. However, for example, as described in JP-A-8-250284,
The atoms and atomic groups sputtered have a higher kinetic energy of about several tens to several hundreds times as compared with the case of vapor deposition.
For this reason, if a sputter film is formed directly on a light emitting layer or the like formed of an organic substance, sputtered atoms having high kinetic energy will damage the organic layer. More specifically, a large number of sputtered atoms having a high energy collide with the organic EL device structure, and the light emitting layer or the like made of an organic substance is physically destroyed or leaked due to abnormal grain growth of the negative electrode crystal. This causes a problem that the initial light emission characteristics of the organic EL element are significantly reduced due to the induction.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for forming a negative electrode of an organic EL device by using a sputtering method.
An object of the present invention is to realize an organic EL device having a negative electrode in which the negative electrode crystal formed by sputtered atoms or the like has little abnormal grain growth and has little physical damage to an organic layer.

[0006]

The above objects are achieved by the following constitutions (1) to (7). (1) The negative electrode formed by sputtering on the organic EL structure formed on the substrate has an organic electrode having a maximum surface roughness (Rmax) of 100 nm or less at the interface in contact with the organic layer.
L element. (2) The organic EL device according to the above (1), wherein the negative electrode has an average surface roughness (Ra) of 30 nm or less at an interface in contact with an organic layer. (3) The organic EL device according to (1) or (2), wherein the cathode is aluminum or an alloy of aluminum and another metal. (4) The organic EL device according to any one of (1) to (3), wherein the negative electrode has no compressive stress in its film. (5) The organic sputtering method according to any one of (1) to (4), wherein the negative electrode is formed under film forming conditions in which a product of a film forming gas pressure and a distance between substrate targets satisfies 20 to 65 Pa · cm. EL element. (6) The organic EL device according to any one of (1) to (5), wherein one or more of Ar, Kr, and Xe are used as the film forming gas. (7) The organic EL device according to any one of (1) to (6), wherein the sputtering method is a DC sputtering method.

[0007]

By using the cathode obtained by the present invention, an organic EL
The light emitting element has a high initial light emission luminance and a long half life of the luminance.
Also, no current leakage occurs between the electrodes, the number of initial dark spots is extremely small, and the number of occurrences after driving is also small.
As described above, the generation of a dark spot was the biggest problem of the vapor deposition method. However, according to the present invention, this is solved and the light emission characteristics are significantly improved. As will be understood from the examples described later, such an effect does not occur outside the scope of the present invention. This is presumably because a smooth and good-adhesion film was formed according to the present invention.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a specific configuration of the present invention will be described in detail.

The organic EL device of the present invention is manufactured by forming a negative electrode on the organic EL device structure formed on a substrate by using a sputtering method. The negative electrode is formed under appropriate film-forming conditions so that the maximum surface roughness (Rmax) of the interface in contact with the organic layer is 100 nm or less, preferably 60 nm or less, and particularly 50 nm or less. The lower limit is not particularly limited, but is usually about 5 to 6 nm. here,
The organic EL element structure is a structure in which an organic material layer such as a light emitting layer is formed on a substrate having a positive electrode such as ITO, and is completed as an organic EL element by forming a negative electrode.

In the formation of the negative electrode of the organic EL element, if the electrode is crystallized, the particles forming the negative electrode grow abnormally depending on the conditions, and the flatness of the film is poor at the surface of the negative electrode or at the interface with the organic layer. Become. In this case, if projections (generally called hillocks) or the like which are abnormally grown on the surface of the negative electrode are formed, they are partially connected to the underlying anode, causing current leakage between the electrodes. Therefore, sputtering conditions are appropriately selected, abnormal grain growth on the electrode surface is suppressed, and a negative electrode having a maximum surface roughness (Rmax) at the interface in contact with the organic layer is within the above range.

The formed negative electrode has an average surface roughness (Ra) of an interface in contact with the organic layer of 30 nm or less, preferably 10 n.
m or less is good. If there is no protrusion having a height of 100 nm or more, current leakage between the electrodes can be suppressed. However, if the average surface roughness (Ra) of the electrode surface is 30 nm or more, the occurrence of dark spots tends to increase with the device driving time. Become. Preferably, the average surface roughness of the interface in contact with the organic layer is as small as possible, and the lower limit is not particularly limited, but is equal to the above-mentioned maximum surface roughness (Rmax). These surface roughnesses can be measured using, for example, a stylus type surface roughness meter. If it is difficult to directly measure the surface roughness of the organic layer interface, measure the surface roughness on the surface side opposite to the organic layer interface and substitute the surface roughness of the organic layer interface. You may. This is because the surface roughness of the negative electrode tends to form a similar surface state on both the front side and the back side.

The cause of abnormal grain growth of the negative electrode material is considered to be high kinetic energy and heat energy of the electrode material particles themselves. In addition, the strain energy introduced into the thin film during the cathode formation process is considered. Etc. are also possible. The strain energy includes a tensile stress and a compressive stress, and it is known that a problem such as a dark spot does not easily occur in the negative electrode having the tensile stress, and that abnormal grain growth is mainly related to the compressive stress. In this case, when the surface of the negative electrode is evaluated by the X-ray diffraction method, the diffraction peak slightly shifts to a high angle or a low angle with respect to the diffraction angle observed in the bulk. (Tensile stress, compressive stress). Therefore, if the type of the internal stress can be determined and the film can be formed in a state where no compressive stress is present, damage to the organic layer and leakage can be prevented.

For example, in the case of aluminum or an aluminum alloy system, it is preferable that the distance is shifted in a direction equal to or larger than about 0.0002 nm with respect to the plane distance d of the bulk (111) plane. Therefore, in the case of aluminum, it is preferable that the surface distance d of the bulk surface is shifted to a direction equal to or larger than d = 0.23380 nm, up to about 0.0002 nm.

By the way, from the viewpoint of preventing the current leakage of the device, it is desirable that the negative electrode is in a completely amorphous state in which no crystal grains grow. However, when the negative electrode is made too amorphous, the electrical resistivity, the work function, and the like change, and the light emitting characteristics of the organic EL element may be reduced.
Therefore, it is necessary to select an optimal crystallization state depending on the negative electrode material.

In the present invention, as long as the negative electrode can be formed under the above conditions, the sputtering apparatus and the film forming conditions are not particularly limited. The product Ts · P of the distance Ts and the film forming gas pressure P is preferably in the range of 20 to 65 Pa · cm. By forming the film under such conditions, the film can be formed in a stable state of the crystal, abnormal grain growth of the crystal is suppressed, and the interface of the negative electrode is kept within the above surface roughness. The sputtered atoms lose their kinetic energy on their way to the substrate, the rate of which depends on both the deposition gas pressure and the distance between the substrate targets. Therefore, the above-described film forming conditions are good in which the kinetic energy of the sputtered atoms is lost due to the scattering by the sputter gas, and the kinetic energy becomes almost zero. The product of the deposition gas pressure and the distance between the substrate targets is 20 Pa · cm
If it is less than 3, the kinetic energy of the sputtered molecules is large, compressive stress is likely to be generated in the film, and abnormal growth of crystal grains is likely to occur, and the organic layer is likely to be physically damaged. When the product of the deposition gas and the distance between the substrate targets exceeds 65 Pa · cm, the deposition gas itself is scattered,
Reverse sputtering on the substrate started, film formation conditions were not stable,
It tends to cause abnormal grain growth of the crystal, and tends to reduce the initial light emission characteristics of the organic EL light emitting device.

More preferably, when a negative electrode is formed by a sputtering method, any one of Ar, Kr, and Xe or a mixed gas containing at least one of these gases is used as a sputter gas. An electrode is formed by sputtering, and the product of the film forming gas pressure and the distance between the substrate targets is 20.
It is preferable that the film formation conditions satisfy the condition of ６５65 Pa · cm.

The sputtering gas may be an inert gas used in a usual sputtering apparatus, or a reactive gas such as N ₂ , H ₂ , O ₂ , C ₂ H ₄ , NH _{3 in the case} of reactive sputtering. Although it can be used, it is preferable to use any of Ar, Kr, and Xe, or a mixed gas containing at least one or more of these gases. These are preferred because they are inert gases and have a relatively large atomic weight. Particularly, Ar, Kr, and Xe alone are preferred. Ar, Kr, Xe
By using a gas, the sputtered atoms repeatedly collide with the gas while reaching the substrate while arriving at the substrate, and reach the substrate with reduced kinetic energy. For this reason, physical damage caused by the kinetic energy of the sputtered atoms to the organic EL structure is reduced. Ar, K
A mixed gas containing at least one gas of r and Xe may be used. When such a mixed gas is used, Ar,
The total partial pressure of Kr and Xe is set to 50% or more and used as a main sputtering gas. By using a mixed gas obtained by combining at least one of Ar, Kr, and Xe with an arbitrary gas, reactive sputtering can be performed while maintaining the effects of the present invention.

When any of Ar, Kr, and Xe is used as the main sputtering gas as the sputtering gas, the product of the distance between the substrate targets is preferably 25 to 55 Pa · cm, particularly 30 to 55 Pa · cm, respectively. 5
When 0 Pa · cm and Kr are used: 20 to 50 Pa · cm, especially 25 to 4
When using 5 Pa · cm and Xe: 20 to 50 Pa · cm, especially 20 to 4
A range of 0 Pa · cm 2 is preferable. Under these conditions, a preferable result can be obtained by using any sputtering gas, but it is particularly preferable to use Ar.

As a sputtering method, a high-frequency sputtering method using an RF power source or the like is also possible, but it is preferable to use a DC sputtering method in order to reduce damage to the organic EL element structure. As the power of the DC sputtering device,
Preferably 0.1 to 4 W / cm ² , especially 0.5 to 1 W / cm ²
Range. The film formation rate is 5 to 100 nm / min.
Particularly, a range of 10 to 50 nm / min is preferable.

As a constituent material of an electrode formed by such a sputtering method, in the case of a negative electrode, as a material having a low work function for effectively injecting electrons, for example, K, Li, N
a, Mg, La, Ce, Ca, Sr, Ba, Al, A
g, In, Sn, Zn, Zr, Cs, Er, Eu, G
a, Hf, Nd, Rb, Sc, Sm, Ta, Y, Yb or other metal element alone, or BaO, BaS, CaO,
HfC, LaB ₆ , MgO, MoC, NbC, PbS,
SrO, TaC, ThC, ThO ₂ , ThS, TiC,
TiN, UC, UN, UO ₂ , W ₂ C, Y ₂ O ₃ , ZrC,
It is preferable to use a compound such as ZrN or ZrO ₂ . Alternatively, in order to improve the stability, two components containing a metal element,
It is preferable to use an alloy system of the components. As an alloy system, for example, Al.Ca (Ca: 5 to 20 at%), Al.Ca
In (In: 1 to 10 at%), Al.Li (Li: 50
at%), Al.R (R represents a rare earth element containing Y and Sc), and In.Mg (Mg:
50 to 80 at%) and the like. Among these, in particular, Al alone, Al.Li (Li: 3 to 6 at%), Al.R
(R: 0.1 to 25, especially 0.5 to 20 at%) is preferable because it does not easily generate a compressive stress. Therefore, such a negative electrode constituting metal or alloy is usually used as a sputter target.

The thickness of the negative electrode thin film may be a certain thickness or more for sufficiently injecting electrons, and may be 50 nm or more, preferably 100 nm or more. Although the upper limit is not particularly limited, the film thickness may be usually about 100 to 500 nm.

In the organic EL device of the present invention, one or more oxides, nitrides or carbides of the constituent material of the negative electrode may be provided as a protective film by utilizing the above-mentioned reactive sputtering. In this case, the raw material of the protective film usually has the same composition as the negative electrode material, but may have a different composition ratio from the negative electrode material, or may lack one or more of the material components. In this manner, by using the same material or the like as the negative electrode, continuous film formation with the negative electrode becomes possible.

The amount of O in the oxide, the amount of N in the nitride or the amount of C in the carbide may deviate from this stoichiometric composition, and may be in the range of 0.5 to 2 times the composition. I just need.

The target is preferably the same as the negative electrode.
Uses one material and forms oxide as reactive gas
If O_Two, CO etc. to form nitrides
If N_Two, NH_Three, NO, NO_Two, N_TwoO etc.
To form carbides, CH _Four, C_TwoH_Two, C_TwoH
_FourAnd the like. These reactive gases are used alone
Or two or more of them may be used in combination.

The thickness of the protective film may be a certain thickness or more, preferably 50 nm or more, more preferably 100 nm or more, particularly preferably in the range of 100 to 1000 nm, in order to prevent entry of moisture, oxygen or an organic solvent.

The total thickness of the negative electrode and the protective film is not particularly limited, but may be generally about 100 to 1000 nm.

By providing such a protective film, oxidation of the negative electrode and the like are further prevented, and the organic EL element can be driven stably for a long period of time.

The organic EL device manufactured according to the present invention comprises:
The substrate has at least one charge transport layer and at least one light emitting layer sandwiched between a positive electrode and a negative electrode on the substrate, and further has a protective layer as the uppermost layer. Note that the charge transport layer can be omitted. As described above, the negative electrode is formed of a metal, compound or alloy having a small work function formed by a sputtering method, and the positive electrode is formed of tin-doped indium oxide (ITO), zinc-doped indium oxide (IZO), ZnO, SnO ₂ , In ₂ O ₃
Etc. are formed by sputtering.

FIG. 1 shows an example of the structure of an organic EL device manufactured according to the present invention. The EL device shown in FIG. 1 has a positive electrode 22, a hole injection / transport layer 23, a light emission and electron injection / transport layer 24, a negative electrode 25, and a protective layer 26 in this order on a substrate 21.

The organic EL device of the present invention is not limited to the illustrated example, but can be of various configurations. For example, a light emitting layer is provided alone, and an electron injection / transport layer is interposed between the light emitting layer and the negative electrode. It is also possible to adopt a structure in which they have been made. Further, if necessary, the hole injection / transport layer 23 and the light emitting layer may be mixed.

The negative electrode can be formed as described above, the organic layer such as the light-emitting layer can be formed by vacuum deposition, and the positive electrode can be formed by vapor deposition or sputtering. Depending on the conditions, patterning can be performed by a method such as etching after mask evaporation or film formation, whereby a desired light emitting pattern can be obtained. Further, the substrate is a thin film transistor (TFT), and by forming each film according to the pattern, a display and drive pattern can be used as it is.

[0032] After the electrode film formation, the protective film or / and Al, a metal material, an inorganic material such as SiO _X, may be formed of other protective layer using an organic material such as Teflon.
This protective film may be transparent or opaque in a configuration in which light emitted from the substrate 1 is extracted. In the case of the reverse lamination, etc., it is necessary to be transparent.
Select and use a transparent material (for example, SiO ₂ etc.)
Alternatively, the thickness may be controlled to be transparent (preferably, the transmittance of emitted light is 80% or more). Generally, the thickness of the protective film is about 50 to 1200 nm. In addition to the reactive sputtering method described above, a general sputtering method,
It may be formed by an evaporation method or the like.

Further, it is preferable to form a sealing layer on the element in order to prevent oxidation of the organic layer and the electrode of the element. The sealing layer is made of an adhesive resin layer such as a commercially available low-moisture-absorbing light-curing adhesive, an epoxy-based adhesive, a silicone-based adhesive, and a cross-linked ethylene-vinyl acetate copolymer adhesive sheet to prevent moisture from entering. Is used to adhere and seal a sealing plate such as a glass plate. Besides a glass plate, a metal plate, a plastic plate or the like can be used.

Next, the organic material layer provided in the EL device of the present invention will be described.

The light emitting layer has a function of injecting holes (holes) and electrons, a function of transporting them, and a function of generating excitons by recombination of holes and electrons. It is preferable to use a relatively electronically neutral compound for the light emitting layer.

The charge transport layer has a function of facilitating injection of holes from the positive electrode, a function of transporting holes, and a function of blocking electrons, and is also called a hole injection transport layer.

In addition, if necessary, for example, when the electron injecting / transporting function of the compound used in the light emitting layer is not so high, injection of electrons from the negative electrode between the light emitting layer and the negative electrode as described above. May be provided with an electron injecting and transporting layer having a function of facilitating electron transport, a function of transporting electrons, and a function of blocking holes.

The hole injection transport layer and the electron injection transport layer are
Increases and confines holes and electrons injected into the light emitting layer,
Optimize the recombination region and improve luminous efficiency.

The hole injecting and transporting layer and the electron injecting and transporting layer may be provided separately for the layer having an injection function and the layer having a transport function.

The thickness of the light emitting layer, the thickness of the hole injecting and transporting layer, and the thickness of the electron injecting and transporting layer are not particularly limited, and vary depending on the forming method.
It is preferable to set it to 300 nm.

The thickness of the hole injecting / transporting layer and the thickness of the electron injecting / transporting layer depend on the setting of the recombination / light emitting region, but may be about the same as the light emitting layer or about 1/10 to 10 times. I just need. When the injection layer and the transport layer for electrons or holes are separated from each other, it is preferable that the injection layer has a thickness of 1 nm or more and the transport layer has a thickness of 20 nm or more. At this time, the upper limit of the thickness of the injection layer and the transport layer is usually about 500 nm for the injection layer and 50 nm for the transport layer.
It is about 0 nm. Such a film thickness is the same when two injection / transport layers are provided.

In addition, by controlling the film thickness in consideration of the carrier mobility and carrier density (determined by ionization potential and electron affinity) of the light emitting layer, the electron injection / transport layer, and the hole injection / transport layer to be combined, the film thickness can be re-established. It is possible to freely design the coupling region and the light emitting region, and it is possible to design the light emission color, control the light emission luminance and light emission spectrum by the interference effect of both electrodes, and control the spatial distribution of light emission.

The light emitting layer of the EL device of the present invention contains a fluorescent substance which is a compound having a light emitting function. Examples of the fluorescent substance include metal complex dyes such as tris (8-quinolinolato) aluminum [Alq3] disclosed in JP-A-63-264692. In addition, in addition or alone, quinacridone, coumarin, rubrene, styryl dyes, other tetraphenylbutadiene, anthracene, berylene,
Coronene, a 12-phthaloberinone derivative, or the like can also be used. The light emitting layer may also serve as the electron injection / transport layer. In such a case, it is preferable to use tris (8-quinolinolato) aluminum or the like. These fluorescent substances may be deposited.

The electron injecting and transporting layer, which is provided as necessary, includes an organic metal complex such as tris (8-quinolinolato) aluminum, an oxadiazole derivative, a berylen derivative, a pyridine derivative, a pyrimidine derivative, a quinoline derivative, and a quinoxaline derivative. , A diphenylquinone derivative,
Nitro-substituted fluorene derivatives and the like can be used.
As described above, the electron injection / transport layer may also have a light emitting layer. In such a case, it is preferable to use tris (8-quinolinolato) aluminum or the like.
The formation of the electron injecting and transporting layer may be performed by vapor deposition or the like, similarly to the light emitting layer.

When the electron injecting and transporting layer is divided into an electron injecting layer and an electron transporting layer, a preferable combination can be selected from the compounds for the electron injecting and transporting layer. At this time, it is preferable to stack the layers of the compound having the higher electron affinity from the cathode side. This stacking order is the same when two or more electron injection / transport layers are provided.

The hole injecting and transporting layer is described in, for example, JP-A-63-295695 and JP-A-2-191694.
JP, JP-A-3-792, JP-A-5-2346
No. 81, JP-A-5-239455, JP-A-5
JP-A-299174, JP-A-7-126225, JP-A-7-126226, JP-A-8-100
Various organic compounds described in JP-A-172, EP0650955A1, and the like can be used. For example, a tetraarylbendicine compound (tetraaryldiamine or tetraphenyldiamine: TPD), an aromatic tertiary amine, a hydrazone derivative, a carbazole derivative, a triazole derivative, an imidazole derivative, an oxadiazil derivative having an amino group, polythiophene, or the like. . Two or more of these compounds may be used in combination, and when they are used in combination, they may be stacked as separate layers or mixed.

When the hole injecting and transporting layer is divided into a hole injecting layer and a hole transporting layer, a preferred combination can be selected from the compounds for the hole injecting and transporting layer. At this time, it is preferable to stack the layers of the compound having the smaller ionization potential in order from the positive electrode (ITO or the like) side. It is preferable to use a compound having a good thin film property on the surface of the positive electrode. Such a stacking order is the same when two or more hole injection / transport layers are provided. With such a stacking order, the driving voltage is reduced, and the occurrence of current leakage and the occurrence and growth of dark spots can be prevented. In the case of forming an element, a thin film of about 1 to 10 nm can be made uniform and pinhole-free because of the use of vapor deposition, so that the hole injection layer has a small ionization potential and has absorption in the visible part. Even when such a compound is used, it is possible to prevent a change in the color tone of the emission color or a decrease in efficiency due to reabsorption.

The above compound may be deposited on the hole injecting / transporting layer in the same manner as in the light emitting layer.

In the present invention, the material and thickness of the transparent electrode used as the positive electrode are preferably determined so that the transmittance of emitted light is preferably 80% or more. Specifically, for example, tin-doped indium oxide (ITO), zinc-doped indium oxide (IZ)
O), ZnO, SnO ₂ , In ₂ O _{3 and the} like are preferably used for the positive electrode. The thickness of the positive electrode is 10 to 500.
It is preferable to set it to about nm. It is necessary that the driving voltage be low in order to improve the reliability of the device, but it is preferable that the driving voltage be 10 to 30 Ω / □ (film thickness: 50 to 300 nm).
ITO. If you actually use it,
The electrode thickness and optical constants may be set so that the interference effect of O or the like at the positive electrode interface sufficiently satisfies the light extraction efficiency and color purity.

In a large device such as a display, since the resistance of the positive electrode such as ITO is large and a voltage drop occurs, metal wiring such as Al may be provided.

As a substrate material, in the case of a configuration in which light emitted from the substrate side is extracted, a transparent or translucent material such as glass, quartz, or resin is used. Further, the emission color may be controlled by using a color filter film, a color conversion film containing a fluorescent substance, or a dielectric reflection film on the substrate. In the case of the reverse lamination, the substrate may be transparent or opaque, and when opaque, ceramics or the like may be used.

As the color filter film, a color filter used in a liquid crystal display or the like may be used, but the characteristics of the color filter are adjusted according to the light emitted from the organic EL to optimize the extraction efficiency and the color purity. do it.

When a color filter capable of cutting off short-wavelength external light that is absorbed by the EL element material or the fluorescence conversion layer is used, the light resistance of the element and the display contrast are improved.

Further, an optical thin film such as a dielectric multilayer film may be used instead of the color filter.

The fluorescence conversion filter film absorbs EL light and emits light from the phosphor in the fluorescence conversion film to convert the color of the emitted light. It is formed from a fluorescent material and a light absorbing material.

As the fluorescent material, basically, a material having a high fluorescence quantum yield may be used, and it is desirable that the fluorescent material has strong absorption in the EL emission wavelength region. Actually, laser dyes are suitable, and rhodamine compounds, perylene compounds, cyanine compounds, phthalocyanine compounds (including subphthalo, etc.) naphthaloimide compounds, condensed ring hydrocarbon compounds, condensed heterocyclic compounds, A styryl compound, a coumarin compound, or the like may be used.

Basically, a material which does not extinguish the fluorescence may be selected as the binder, and a material which can be finely patterned by photolithography, printing or the like is preferable.
Further, a material that does not suffer damage during the deposition of ITO is preferable.

The light absorbing material is used when the light absorption of the fluorescent material is insufficient, but may be omitted when unnecessary. As the light absorbing material, a material that does not quench the fluorescence of the fluorescent material may be selected.

For forming the hole injecting and transporting layer, the light emitting layer and the electron injecting and transporting layer, it is preferable to use a vacuum deposition method since a uniform thin film can be formed. When a vacuum deposition method is used, a homogeneous thin film having an amorphous state or a crystal grain size of 0.1 μm or less can be obtained. If the crystal grain size exceeds 0.1 μm, the light emission becomes non-uniform, the driving voltage of the device must be increased, and the charge injection efficiency is significantly reduced.

The conditions for vacuum deposition are not particularly limited.
The degree of vacuum is 0 ^-4 Pa or less, and the deposition rate is 0.01 to 1 nm /
It is preferable to set it to about sec. Further, it is preferable to form each layer continuously in a vacuum. If they are formed continuously in a vacuum, impurities can be prevented from adsorbing at the interface between the layers, so that high characteristics can be obtained. Further, the driving voltage of the element can be reduced, and the growth and generation of dark spots can be suppressed.

In the case where a plurality of compounds are contained in one layer when a vacuum evaporation method is used for forming each of these layers, it is preferable to co-deposit each boat containing the compounds by individually controlling the temperature.

The organic EL device of the present invention is usually used as a DC drive type EL device, but it can be AC drive or pulse drive. The applied voltage is usually 2 to 2
It is about 0V.

[0063]

EXAMPLES Hereinafter, the present invention will be described in more detail by showing specific examples of the present invention together with comparative examples.

Example 1 A 200-nm-thick ITO was formed as a transparent electrode on a glass substrate by sputtering, followed by patterning, ultrasonic cleaning using a neutral detergent, acetone and ethanol, and then boiling in ethanol. And dried. After cleaning the transparent electrode surface with UV / O ₃ ,
Fix it with the substrate holder of the vacuum evaporation equipment, and
The pressure was reduced to 10 ⁻⁴ Pa or less.

Then, N, N'-
Diphenyl-m-tolyl-4,4'-diamine-1,
1′-biphenyl (TPD) was deposited at a deposition rate of 0.2 nm / sec to a thickness of 55 nm to form a hole injection transport layer.

Further, while maintaining the reduced pressure, Alq3: tris (8-quinolinolato) aluminum was evaporated at a vapor deposition rate of 0.1.
Evaporation was performed at a thickness of 50 nm at 2 nm / sec to form an electron injection / transport / light-emitting layer.

Next, the film was transferred from the vacuum evaporation apparatus to a sputtering apparatus, and a negative electrode was formed to a thickness of 200 nm by DC sputtering using Al (purity: 99.9%) as a target. At this time, Ar was used as a sputtering gas and a gas pressure of 4.5 P
a, the distance between the target and the substrate (Ts) was 9.0 cm.
The input power was 100W.

Finally, SiO ₂ was sputtered to a thickness of 200 nm to obtain an organic EL device as a protective layer. This organic E
In the L light emitting element, two parallel striped negative electrodes and eight parallel striped positive electrodes are orthogonal to each other, and element elements (pixels) of 2 × 2 mm vertically and horizontally are arranged at an interval of 2 mm from each other. It is an element of × 2 16 pixels.

A direct current voltage was applied to this organic thin film light emitting device in an N ₂ atmosphere, and the device was continuously driven at a constant current density of 10 mA / cm ² . Initially, green light emission (maximum emission wavelength λmax = 520 nm) of 9 V and 200 cd / cm ² was confirmed. The half-life of luminance is 600 hours, during which the drive voltage rises by 2V
Met. The luminescence characteristics were almost the same as those of the negative electrode deposited by resistance heating, and no deterioration of the luminescence characteristics due to the use of the sputtering method was observed.

During the manufacturing process of the organic EL device, after forming the negative electrode, a part of the electrode was peeled off with a tape, and the interface with the organic light emitting layer was examined. When the surface shape on the electrode side was examined with a surface roughness meter, it was a relatively flat surface without protrusions, etc.
Maximum surface roughness (Rmax) is 50 nm, average surface roughness is 10n
m or less. FIG. 3 shows the results of measuring the surface shape of the negative electrode using a surface roughness meter.

When the separated negative electrode was subjected to X-ray diffraction, a crystallization peak of Al was observed. Al
When the plane spacing is calculated from the (111) diffraction peak, d = 0.23
392 nm was obtained, which was found to be larger than that of the bulk (d = 0.23380 nm). This indicates that the formed negative electrode has a tensile stress in the film.

With respect to the obtained organic EL element, the initial light emission luminance of 160 pixels (10 elements) was examined, the average luminance, the presence or absence of dark spots (after 200 hours from the start of light emission), and the number of current leaks between the electrodes. Table 1 shows the maximum surface roughness (Rmax) and the average surface roughness (Ra). The occurrence of dark spots was evaluated according to the following criteria. ◎: No dark spots ○: Two or less spots can be confirmed in a 10 mm square area of the light emitting surface. X: Three or more can be confirmed in a 10 mm square area of the light emitting surface. Table 1 shows the results. The results for the types of internal stress and the shift direction of X-ray diffraction are also shown.

Example 2 In forming the organic EL device of Example 1, the sputtering gas was changed to Kr, the gas pressure was 3.5 Pa, and the distance between the target and the substrate (Ts) was 9.0 cm.
And Otherwise, an organic EL element was formed in the same manner. The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 3 In forming the organic EL device of Example 1, the sputtering gas was changed to Xe, the gas pressure was 2.5 Pa, and the distance between the target and the substrate (Ts) was 9.0 cm.
And Otherwise, an organic EL element was formed in the same manner. The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 4 In forming the organic EL device of Example 1, the film forming gas pressure was 2.5 Pa and Ts = 9.
An organic EL element was formed in the same manner except that the thickness was changed to 0 cm.
The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 5 In the formation of the organic EL device of Example 1, the film forming gas pressure was 6.0 Pa and Ts = 9.
An organic EL element was formed in the same manner except that the thickness was changed to 0 cm.
The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 6 In the formation of the organic EL device of Example 1, the film forming gas pressure was 8.0 Pa and Ts = 5.
An organic EL element was formed in the same manner except that the thickness was changed to 0 cm.
The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 7 In the formation of the organic EL device of Example 1, the film forming gas pressure was 12 Pa and Ts = 5.0 c.
An organic EL element was formed in the same manner except that m was changed. The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 8 In forming the organic EL device of Example 1, the film forming gas pressure was 8.0 Pa and Ts = 7.
An organic EL element was formed in the same manner except that the size was changed to 5 cm.
The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Embodiment 9 In forming the organic EL device of Embodiment 1, the film forming gas pressure was set to 2.5 Pa and Ts = 15 c.
An organic EL element was formed in the same manner except that m was changed. The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

<Embodiment 10> In Embodiment 1, Al · Ca (Ca: 10 at) was used instead of Al as the target.
%), Al.In (In: 5 at%), Al.Li (L
i: 5 at%), Al.Sc (Sc: 10 at%), Al.
Y (Y: 10 at%) and In.Mg (Mg: 65 at%) were used, respectively, and the others were the same as in Example 1.
A light-emitting element was manufactured.

Example 1 of the obtained organic EL device
As a result, the same results as in Example 1 were obtained for each organic EL element.

Comparative Example 1 An organic EL device was formed in the same manner as in Example 1, except that the gas pressure was changed to 0.3 Pa. The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

As a result, both the average value of the initial light emission luminance and the light emission half-life decreased. The occurrence of dark spots was remarkable, and the number of current leaks between the electrodes was very large.
During the manufacturing process of the organic EL device, after forming the negative electrode, a part of the electrode was peeled off with a tape, and the interface with the organic light emitting layer was also examined. When the surface shape on the electrode side was examined with a surface roughness meter, the maximum surface roughness (R
max) was 300 nm or more, the average surface roughness was 100 nm or more, and the negative electrode surface was found to be very rough. FIG. 4 shows the results of measuring the negative electrode surface shape using a surface roughness meter.
Shown in

X-ray diffraction of the peeled negative electrode showed a crystallization peak of Al. Al (11
1) When the plane spacing is calculated from the diffraction peak, d = 0.23334 nm
Was obtained, which was smaller than the bulk value (d = 0.23380 nm). This indicates that the formed negative electrode has a compressive stress in the film. Table 1 shows the results.

Comparative Example 2 An organic EL device was formed in the same manner as in Example 1, except that the gas pressure was changed to 1.5 Pa. The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 3 An organic EL device was formed in the same manner as in Example 1, except that the gas pressure was changed to 8.0 Pa. The obtained organic EL device was evaluated in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 4 An organic EL device was formed in the same manner as in Example 1 except that the gas pressure was changed to 1.0 Pa and Ts = 5.0 cm. The obtained organic EL device was evaluated in the same manner as in Example 1.
Table 1 shows the results.

[0089]

[Table 1]

FIG. 2 shows the relationship between the distance Ts between the target sputters and the sputter gas pressure P in each of the examples and comparative examples.

As is apparent from Table 1 and FIGS. 2 to 4, the organic EL device of the present invention has extremely low occurrence of dark spots and current leakage, and has a long half-life of luminance. The conditions for obtaining such characteristics are as follows: the maximum surface roughness at the organic layer interface of the negative electrode is 100 nm or less;
It turns out that it is below nm. On the surface of such a cathode, the product Ts · P of the target-substrate Ts and the sputtering gas pressure P is preferably in the range of 20 to 65 Pa · cm.

[0092]

According to the present invention, when a negative electrode of an organic EL element is formed by a sputtering method, abnormal grain growth of a negative electrode crystal formed by sputtered atoms and the like is small, and an organic layer is formed. It is possible to form a negative electrode with little physical damage to the element, prevent a decrease in initial light emission luminance, and extend the life of the element.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a configuration example of an organic EL element.

FIG. 2 is a graph showing a relationship between a distance Ts between target sputtering and a sputtering gas pressure P.

FIG. 3 shows the results of measuring the surface of the negative electrode produced in Example 1 with a surface roughness meter.

FIG. 4 shows the result of measuring the surface of the negative electrode produced in Comparative Example 1 with a surface roughness meter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Substrate 22 Positive electrode 23 Hole injection / transport layer 24 Light emitting layer 25 Negative electrode 26 Protective layer

Claims (7)

[Claims] 1. An organic EL device in which a negative electrode formed by sputtering on an organic EL structure formed on a substrate has a maximum surface roughness (Rmax) at an interface in contact with an organic layer of 100 nm or less. element. 2. The organic EL device according to claim 1, wherein an average surface roughness (Ra) of an interface of the cathode in contact with the organic layer is 30 nm or less. 3. The organic EL device according to claim 1, wherein the cathode is made of aluminum or an alloy of aluminum and another metal. 4. The organic EL device according to claim 1, wherein said negative electrode has no compressive stress in its film. 5. The organic EL device according to claim 1, wherein in the sputtering method, the negative electrode is formed under film forming conditions in which a product of a film forming gas pressure and a distance between substrate targets satisfies 20 to 65 Pa · cm. element. 6. The organic EL device according to claim 1, wherein one or two or more of Ar, Kr, and Xe are used as the film forming gas. 7. The organic EL device according to claim 1, wherein said sputtering method is a DC sputtering method.