Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2002-01-02
2004-05-11
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S505000, C313S506000, C313S503000, C313S498000, C428S690000
Reexamination Certificate
active
06734622
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is directed to an organic electroluminescent component, particularly an organic light-emitting diode.
The visualization of data is constantly increasing in significance due to the great increase in the amount of information. The technology of flat picture screens (“flat panel displays”) was developed therefor for employment in mobile and portable electronic devices. The market of flat panel displays is currently largely dominated by the technology of liquid crystal displays (LC displays). In addition to cost-beneficial manufacture, low electrical power consumption, low weight and slight space requirement, however, the technology of LC displays also exhibits serious disadvantages.
LC displays are not self-emitting and can therefore only be easily read or recognized given especially beneficial ambient light conditions. This makes a back-illumination device necessary in most instances, but this multiplies the thickness of the flat panel display. Moreover, the majority part of the electrical power consumption of the display is then needed for the illumination, and a higher voltage is required for the operation of the lamps or fluorescent tubes, which higher voltage is usually generated from batteries or accumulators with the assistance of “voltage-up converters”. Other disadvantages are the highly limited observation angles of LC displays and the long switching times of individual pixels, which switching times typically lie at a few milliseconds and also are highly temperature-dependent. The delayed image build-up is considered extremely disturbing, for example, given utilization in means of conveyance or given video applications.
There are other flat panel display technologies in addition to LC displays, for example the technology of flat display panel cathode ray tubes, of vacuum-fluorescence displays and of inorganic thin-film electroluminescent displays. However, either these technologies have not yet achieved the required degree of technological maturity or—due to high operating voltages or, respectively, high manufacturing costs—they are only conditionally suited for utilization in portable electronic devices.
Displays on the basis of organic light-emitting diodes, which are called OLEDs, do not exhibit these disadvantages. The necessity of a back-illumination is eliminated due to the self-emissivity, as a result whereof the space requirement and the electrical power consumption are considerably reduced. The switching times lie at about one microsecond and are only slightly temperature-dependent, which enables employment for video applications. The reading angle amounts to nearly 180°, and polarization films that are required given LC displays are eliminated, so that a greater brightness of the display elements can be achieved. Further advantages are the employability of flexible and non-planar substrates as well as a simple and cost-beneficial manufacture.
The construction of organic light-emitting diodes typically ensues in the following way.
A transparent substrate, for example glass, is coated with a transparent electrode (bottom electrode, anode), composed, for example, of indium tin oxide (ITO). Dependent on the application, the transparent electrode is then structured with the assistance of a photolithographic process.
One or more organic layers composed of polymers, oligomers, low-molecular compounds or mixtures thereof are applied on the substrate with the structured electrode. Examples of polymers are polyaniline, poly(p-phenylene-vinylene) and poly(2-methoxy-5-(2′-ethyl)-hexyloxy-p-phenylene-vinylene). Examples of low-molecular compounds that preferably transport positive charge carriers are N,N′-bis-(3-methylphenyl)-N,N′-bis-(phenyl)-benzidine (m-TPD), 4,4′,4″-tris-N-3-methylphenyl-N-phenyl-amino)-triphenylamine (m-MTDATA) and 4,4′,4″-tris-(carbazole-9-yl)-triphenylamine (TCTA). Hydroxy-chinoline aluminum-III salt (Alp
3
) that can be doped with suitable chromophores (chinacridone derivatives, aromatic hydrocarbons, etc.), for example, is employed as an emitter. As warranted, additional substances, that influence the electro-optical and the long-term properties, such as copper phthalocyanine, can be present. The application of polymers usually ensues from the liquid phase with doctor blades or spin-coating; low-molecular and oligomeric compounds are usually deposited from the vapor phase by vapor deposition or “physical vapor deposition” (PVD). The overall layer thickness can amount to between 10 nm and 10 &mgr;m and it typically lies in the range between 50 and 200 nm.
A cooperating electrode (top electrode, cathode), which is usually composed of a metal, of a metal alloy or of a thin insulator layer and a thick metal layer, is applied onto the organic layer or layers. The manufacture of the cathode layer usually ensues with vapor phase deposition by means of thermal evaporation, electron beam evaporation or sputtering.
When metals are employed as cathode material, then these must have a low work function (typically <3.7 eV) so that electrons can be efficiently injected into the organic semiconductor. Alkaline metals, alkaline earth metals or rare earth metals are usually employed for this purpose and the layer thickness lies between 0.2 nm and a few hundred nanometers but generally at a few 10 nanometers. Since, however, these non-precious metals tend toward corrosion under atmospheric conditions, it is necessary to additionally apply a layer of a more precious, inert metal such as aluminum (Al), copper (Cu), silver (Ag) or gold (Au) onto the cathode layer that protects the non-precious metal layer against moisture and atmospheric oxygen.
For increasing the stability of the cathodes against a corrosion-caused hole formation, an alloy composed of an efficiently electron-injecting but corrosion-susceptible non-precious metal (work function <3.7 eV) and a corrosion-resistant or precious metal, such as Al, Cu, Ag and Au, is often employed instead of an unalloyed non-precious metal. The proportion of the non-precious metal in the alloy can amount to between a few tenths of a percent and approximately 90%. The alloys are usually generated by simultaneous deposition of the metals from the vapor phase, for example by co-vapor deposition, simultaneous sputtering with a plurality of sources and sputtering upon employment of alloy targets. However, a layer of a precious metal or corrosion-resistant metal, such as Al, Cu, Ag or Au, is usually also additionally applied onto such cathodes as protection against corrosion.
Cathodes composed of precious metals, i.e. metals having a work function >3.7 eV, are very inefficient electron injectors when they are utilized in direct contact with the organic semiconductor. When, however, a thin insulating intermediate layer (layer thickness generally between 0.2 and 5 nm) is arranged between the uppermost, electron-conducting organic layer and the metal electrode, then the efficiency of the light-emitting diodes rises substantially. Oxides such as aluminum oxide, alkaline and alkaline earth oxides and other oxides as well as alkaline and alkaline earth fluorides come into consideration as the insulating material for such an intermediate layer (in this respect, see Appl. Phys. Lett., Vol. 71 (1997), pages 2560 through 2562; U.S. Pat. No. 5,677,572; European Published Application 0 822 603). A metal electrode that is composed of a pure metal or of a metal alloy is then applied onto the thin, insulating intermediate layer. The insulating material can thereby also be applied together with the electrode material by means of co-vapor deposition (Appl. Phys. Lett., Vol. 73 (1998), pages 1185 through 1187).
SUMMARY OF THE INVENTION
An object of the invention is to fashion an organic electroluminescent component, particularly an organic light-emitting diode, such that, on the one hand, a hermetic seal of the top electrode can be foregone and, on the other hand, the selection of materials employable at the cathode side is greater.
This is inventively ac
Kanitz Andreas
Stoessel Matthias
Osram Opto Semiconductors GmbH & Co. oHG
Patel Nimeshkumar D.
Roy Sikha
Schiff & Hardin LLP
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