Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2000-05-10
2003-07-22
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S503000, C313S504000
Reexamination Certificate
active
06597110
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the use of conductive nitrides, particularly TiN, as electrode material in organic light emitting devices.
BACKGROUND OF THE INVENTION
Organic light emitting devices (OLEDs), which make use of thin film materials that emit light when excited by electric current, are becoming an increasingly popular form of flat panel display technology for applications such as television sets, computer terminals, telecommunications equipment and a host of other applications. There are presently three predominant types of OLED construction: the “double heterostructure” (DH) OLED, the “single heterostructure” (SH) OLED, and the single layer polymer OLED.
In the DH OLED, as shown in
FIG. 1A
, a substrate layer of glass
10
is coated by a thin layer of indium-tin-oxide (ITO)
11
. Next, a thin (100-500 Å) organic hole transporting layer (HTL)
12
is deposited on ITO layer
11
. Deposited on the surface of HTL
12
is a thin (typically, 50Å-500Å) emission layer (EL)
13
. The EL
13
provides the site for electrons injected from a 100-500Å thick electron transporting layer
14
(ETL) to recombine with holes from the HTL
12
. Examples of prior art ETL, EL and HTL materials are disclosed in U.S. Pat. No. 5,294,870, the disclosure of which is incorporated herein by reference.
Often, the EL
13
is doped with a highly fluorescent dye to tune color and increase the electroluminescent efficiency of the OLED. The device as shown in
FIG. 1A
is completed by depositing metal contacts
15
,
16
and top electrode
17
. Contacts
15
and
16
are typically fabricated from indium or Ti/Pt/Au. Electrode
17
is often a dual layer structure consisting of an alloy such as Mg/Ag
17
′ directly contacting the organic ETL
14
, and a thick, high work function metal layer
17
″ such as gold (Au) or silver (Ag) on the Mg/Ag. The thick metal
17
″ is opaque. When proper bias voltage is applied between top electrode
17
and contacts
15
and
16
, light emission occurs from emissive layer
13
through the glass substrate
10
. An LED device of
FIG. 1A
typically has luminescent external quantum efficiencies of from 0.05% to 2% depending on the color of emission and the device structure.
The (SH) OLED, as shown in
FIG. 1B
, makes use of multi-functional layer
13
′ to serve as both EL and ETL. One limitation of the device of
FIG. 1B
is that the multi-functional layer
13
′ must have good electron transport capability.
A single layer polymer OLED is shown in FIG.
1
C. As shown, this device includes a glass substrate
1
coated by a thin ITO layer
3
. A thin organic layer
5
of spin-coated polymer, for example, is formed over ITO layer
3
, and provides all of the functions of the HTL, ETL, and EL layers of the previously described devices. A metal electrode layer
6
is formed over organic layer
5
. The metal is typically Mg or other conventionally used low work function metal.
The choice of materials to be used in OLEDs is based on several criteria. For example, the anode in a conventional OLED must have good optical transparency, good electrical conductivity and chemical stability. Indium tin oxide (ITO) meets these criteria and is the most widely used anode material in OLEDs. ITO films combine high transparency (≈90%) with low resistivity (1×10
−3
-7×10
−5
&OHgr;·cm) and can be prepared by a variety of methods including sputtering, chemical vapor deposition (CVD) and sol-gel techniques.
However, OLEDs using ITO films do have a few areas which could be improved upon. First, the work function of ITO (4.4-4.7 eV, based on ultraviolet photoemission spectroscopy measurements) lies near the HOMO levels of typical OLED hole transporting or injecting materials, thus leading to a barrier for hole injection into organic material. Second, an OLED's stability and efficiency strongly depend on the nature of the anode/organic film interface. Therefore, any changes in this interface over time will destabilize the OLED. For example, one cause of long term OLED degradation involves the diffusion of metal ions or oxygen from the ITO film into the organic film. Finally, another issue arising from the use of an ITO anode is the tendency of SnO
x
and InO
x
islands to form through reorganization of the ITO film over time.
Therefore, although ITO electrodes have been used with many different organic materials, additional OLED anode materials are needed.
SUMMARY OF THE INVENTION
The present invention provides organic light emitting devices, including polymer, (e.g. single and multi-layer), single heterostructure, and double heterostructure, which use conductive nitride films as anode material. These anode layers can be transparent or opaque and can be used in OLEDs with transparent cathodes. In addition, the formed OLEDs with TiN or TiN/ITO anode layers can be used to form stacked OLEDs.
The OLEDs of the present invention can be incorporated in electronic devices, including computers, monitors, televisions, large area wall screens, theater screens, stadium screens, billboards, signs, vehicles, printers, telecommunication devices, and telephones.
One embodiment of the present invention comprises forming a thin TiN film on a glass substrate and then forming an OLED using the TiN film as an anode layer. Another embodiment of the present invention uses a multi-layered anode of TiN on top of ITO in forming an OLED.
REFERENCES:
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patent: 5707745 (1998-01-01), Forrest et al.
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J. N. Musher et al., “Atmospheric Pressure Chemical Vapor Deposition of Titanium Nitride from Tetrakis (diethylamido) Titanium and Ammonia,”Journal of Electrochemical Society, vol. 143, No. 2, Feb. 1996, pp. 736-744.
J.N. Musher et al., “Atmospheric pressure chemical vapor deposition of TiN from tetrakis (dimethylamido) titanium and ammonia,”1996 Materials Research Society, vol. 11, No. 4, Apr. 1996, pp. 989-1001.
P. J. Martin et al., “Optical properties of TiNxproduced by reactive evaporation and reactive ion-beam sputtering,”Vacuum, vol. 32, No. 6, pp. 359-362 (1982).
Adamovich Vadim
Shoustikov Andrei
Thompson Mark E.
Kenyon & Kenyon
Patel Ashok
The University of Southern California
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