Data processing: structural design – modeling – simulation – and em – Electrical analog simulator – Of physical phenomenon
Reexamination Certificate
1998-12-15
2001-12-04
Teska, Kevin J. (Department: 2123)
Data processing: structural design, modeling, simulation, and em
Electrical analog simulator
Of physical phenomenon
C703S002000, C703S004000, C703S012000, C359S584000, C359S244000
Reexamination Certificate
active
06327554
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an organic EL (electroluminescent) device using an organic compound. More specifically, this invention is concerned with a simulation method and system for providing an organic EL device that enable the light emitted therefrom to be effectively available with a reduced emission luminance variation, and an organic EL device as well.
2. Discussion of the Background
In recent years, organic EL devices have been under intensive investigation. One such device is basically built up of a thin film form of hole transporting material such as triphenyldiamine (TPD) deposited by evaporation on a hole injecting electrode, a light emitting layer of fluorescent material such as an aluminum quinolinol complex (Alq
3
) laminated thereon, and a metal (electron injecting) electrode of a metal having a low work function such as Mg and formed on the light emitting layer. This organic EL device now attracts attention because a very high luminance ranging from several hundred to tens of thousand cd/m
2
can be achieved with a voltage of approximately 10 V.
The organic EL device has a basic arrangement including on a substrate a film form of organic EL structure comprising an electron injecting electrode, an organic layer, a hole injecting electrode, etc., as mentioned just above. Usually, the light emitted from the device is taken out of the substrate side via the hole injecting electrode.
Regarding an organic EL device in general, it is known that emission spectra of light emitting species are modulated by optical interference in the device, upon which they leave the device. For this reason, even when an organic EL device comprising the same light emitting material is applied to a different optical system, there are changes in the spectra emitted out of the device, and their intensity.
The greatest optical modulation is known to occur by interference between forwardly emitted light and light emitted backwardly and reflected at a metal surface (electron infecting electrode), as set forth in JP-A 4-328295. This effect is expressed in terms of a function determined by a distance between a light emitting point and the metal surface, and so an optical arrangement for obtaining the desired modulated spectra can be known therefrom. However, this is still less than satisfactory for making much more precise estimations, for the reason of large errors. In other words, another parameter for consideration is required.
In this regard, JP-A 7-240277 reveals another problem, i.e., the modulation of light emitted out of an organic EL device due to interference of light reflected at an interface between glass and a transparent electrode. However, the publication merely states that to increase the intensity of emitted light of a specific wavelength in a narrow range by making use of optical modulation, it is only required to regulate an optical thickness between the glass/transparent conductive film interface and a metal surface with an organic multilayer structure interleaved between them to a specific value.
Here assume a certain optical system. Then, it would be difficult to make any detailed study of spectral modulation without expectation of to what degree the spectra are modulated by interference caused by a parameter other than the aforesaid one. This would in turn make the optical design of an optimized device difficult. In the prior art, the influence of a more sophisticated arrangement, for instance, an arrangement comprising many reflective interfaces in addition to the interface between the organic multilayer structure and the transparent conductive film is not taken into account. Nor is the utilization of such an arrangement investigated.
SUMMARY OF THE INVENTION
As mentioned above, the changes in the thickness of films forming an organic EL device give rise to changes in the spectra and luminance of light emitted out of the device. In order to use this device with a display device, it is desired that characteristic variations ascribable to them be reduced as much as possible. Never until now, however, is any argument adduced about to what degree the optical thickness is controlled. It is thus still difficult to reduce such variations and, hence, provide consistent products.
An object of the invention is to provide a simulation method and system for simulating an organic EL device, which, by making approximations to reflected light components other than reflected light with consideration given so far thereto, can make an accurate estimation of spectra emitted out of an organic EL device having a general and arbitrary structure, thereby enabling a device design for obtaining the desired spectra.
Another object of the invention is to provide a simulation method and system for simulating an organic EL device, which enables light to be effectively taken out of even a structure comprising many reflective surfaces.
Yet another object of the invention is to provide a simulation method and system for simulating an organic EL device, by which a device arrangement capable of reducing optical variations is achievable.
Still yet another object of the invention is to provide an organic EL device which, on the basis of the results of simulations, is such designed as to reduce optical variations.
In order to construct an accurate simulation model, the inventors have made study after study on the following premises:
(1) reflected light other than light reflected at a metal surface is quantitatively taken into consideration;
(2) since the device to which the present invention is applied is a multilayer structure with a refractive index difference of at most 2 times, only one reflection at an interface other than the metal surface is taken into account; that is, two or more reflections can be neglected; and
(3) the concept of localized light emitting surfaces is extended to a non-localized model.
These objects are achieved by the inventions defined below as (1) to (8):
(1) A simulation method for simulating an organic EL device having a metal surface on one side and comprising a light emitting source and a plurality of optical thicknesses, in which a simulation model represented by I, given below, is formulated, and a structural design for taking out light is prepared from emission spectra obtained from the simulation model I:
Simulation Model I
an organic EL device comprising a q-species layer located on a metal surface side of a light emitting source, and a p-species layer located on a side that faces away from said metal surface side and having a refractive index different from that of said q-species layer, wherein:
a total composite wave &PHgr;[&lgr;] composed of waves &PHgr;nm reflected at interfaces is given by
Φ
[
λ
]
=
Φ
1
+
∑
t
=
1
p
-
1
Φ
t
,
t
+
1
+
∑
t
=
1
q
-
1
Φ
t
_
,
t
+
1
_
+
∑
t
=
1
q
Φ
t
_
,
t
-
1
_
where &lgr; is a wavelength, &PHgr;nm is a reflected wave upon incidence from an n-layer on an m-layer, p>1, and q 1, with the proviso that the p-layer is made up of a glass or atmosphere having a thickness sufficient to make no contribution to interference, and when q=1, a third term on a right-hand side is zero, and provided that − written above each suffix, i.e., an invert symbol is a quantity regarding a layer located on the metal surface side with respect to a light emitting point, and the same shall apply hereinafter,
a composite wave &PHgr;l, which is encompassed in the total composite wave &PHgr;[&lgr;] and is composed of a light component emitted forwardly from the light emitting source and then emitted out without reflection at an interface, and a light component emitted backwardly from the light emitting source, reflected forwardly at the metal surface and then emitted out without reflection at another interface, is given by
Φ
1
=
Φ
0
+
Φ
0
_
Φ
0
_
=
r
q
_
,
m
Φ
0
exp
[
2
π
ⅈ
(
2
L
1
q
_
λ
)
]
L
1
Jones Hugh
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
Teska Kevin J.
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