Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With reflector – opaque mask – or optical element integral...
Reexamination Certificate
2001-06-18
2003-10-28
Lebentritt, Michael S. (Department: 2824)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With reflector, opaque mask, or optical element integral...
C257S089000, C438S029000, C438S035000, C438S099000
Reexamination Certificate
active
06639250
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to light emitting devices capable of emitting light of a plurality of colors and suitable for use as organic electro-luminescence (EL) devices, and particularly to the improvement of reflecting layers therein.
DESCRIPTION OF THE RELATED ART
Art is known for combining reflecting layers with multi-layer dielectric films laminated in alternating layers having different refractive indexes and thereby reflecting light of specific wavelengths. In the Shingaku Giho OME 94-79 (March, 1995), pp 7-12, there is a discussion on how to emit multiple colors of light using a micro resonance structure based on such a multi-layer dielectric film. According to this literature, by adjusting the positions of the light emitting layers and the reflecting layers where reflection occurs in the micro resonance structure, it is possible to output resonant light of any wavelength contained in the light emitting layers.
In Japanese Patent Application Laid-Open No. H6-275381/1994 (gazette), for example, a light emitting device having the laminar structure diagrammed in
FIG. 9
is set forth. This light emitting device comprises a transparent substrate
100
, a micro resonance structure
102
, a positive electrode
103
, a hole transport layer
104
, an organic electro-luminescence (EL) layer
105
, and a negative electrode
106
. Of these, the thickness of the positive electrode
103
is varied respectively to select the wavelength of the light that resonates. Aluminum or alkali metals are used as the material for the negative electrode.
In a conventional electro-luminescence device, the negative electrode is ideally designed so that it completely reflects light. In actual practice, the negative electrode has been designed at times so that it is made as thin as possible to make the relative drive resistance of the EL-layer smaller.
When the negative electrode is formed thinly, however, the reflectance thereof is not always sufficient, whereupon some of the light leaks out to the back side of the electro-luminescence device without being reflected. Light utilization has thus been rather low compared to the ideal reflecting layer where complete reflection is assumed. When a mirror formed by a micro resonance structure such as cited in Japanese Patent Application No. H6-275381/1994 is positioned on the front surface (light output side) of the EL layer and wavelength selectivity thereby raised, the amount of light returning to the light emitting layer side from this mirror is increased. In a conventional device having such a structure as this, the reflectance of the negative electrode at the back surface of the EL layer is low, wherefore the light utilization factor declines significantly, which is a problem.
If only light reflecting efficiency is to be considered, there are materials known which exhibit high reflectance. However, there are restrictions on the materials which can be used for the negative electrode in an electro-luminescence device, such as energy level, and it has not been possible to use negative electrodes of high reflectance in conventional devices.
Returning the light that leaks out with a reflecting mirror is conceivable, but no suitable reflecting mirror has been devised that is suitable for a thin-film device.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide a multiple-wavelength light emitting device that can emit light in a plurality of wavelengths with higher efficiency than conventionally.
A second object of the present invention is to provide a multiple-wavelength light emitting device that has higher efficiency than conventionally for multiple wavelengths and that has a simpler structure.
A third object of the present invention is to provide an electronic apparatus that can emit light in a plurality of wavelengths with higher efficiency than conventionally.
The present invention is a multiple-wavelength light emitting device for emitting light in a plurality of different wavelengths, comprising:
(1) light emission means for emitting light containing wavelength components to be output,
(2) a semi-transparent layer that transmits at least a portion of the light, placed at the back surface of the light emission means,
(3) a reflecting layer group provided on a first surface side of the light emission means, with the semi-transparent layer intervening, wherein reflecting layers that reflect light having specific wavelengths of the light ejected to (or transmitted towards) the first surface side from the light emission means via the semi-transparent layer are laminated in order in the direction of the light axis, which is in the direction of light advance, in correspondence with wavelengths of light to be output, and
(4) a semi-reflecting layer group provided on a second surface side in opposition to the first surface of the light emission means, wherein semi-reflecting layers that reflect a portion of light having specific wavelengths of the light ejected to the second surface side from the light emission means and transmit the remainder thereof are laminated in order in the direction of the light axis, which is in the direction of light advance, in correspondence with the wavelengths of light to be output.
In two or more light emission regions wherein the output light wavelength differs, the distance between the reflecting surface for light from the light emission means in a reflecting layer in the reflecting layer group that reflects light of the wavelength output in that light emission region and the reflecting surface for light from the light emission means in a semi-reflecting reflecting layer in the semi-reflecting layer group that reflects a portion of light of the wavelength output in that light emission region is adjusted so that it becomes a resonating optical path length for light ejected from that light emission region.
As based on the configuration described in the foregoing, the light that is ejected to the second surface (back surface) from the light emission means and passes through the semi-transparent layer to leak out is reflected by the action of the reflecting layer group, again passes through the semi-transparent layer, and is ejected to the first surface (front surface) side of the light emitting device. By adjusting the distance between the semi-reflecting layer and the reflecting layer, the wavelength of the light output from that light emission region is determined. In that light emission region, other reflecting layers that are optimized for light having wavelengths other than the wavelength of the light output do no more than act equally in every light emission region as semi-transparent layers simply having a constant attenuation factor, wherefore it is possible to maintain light volume balance between light of multiple wavelengths.
The terms employed in this patent application are now defined. The term “light emission means” is not limiting, but it is at least necessary that wavelength components for the light that is to be output be contained. It is desirable that the “reflecting layers” form a flat plane, but it does not necessarily have to be a uniform plane. By “light emission region” is meant a region for outputting light having some wavelength dispersion, meaning that light is output in wavelengths that differ for each light emission region. The “wavelengths” include not only wavelengths in the so-called visible light region but all wavelengths of a wider range including ultraviolet and infrared radiation. “Reflecting layers” include such structures as simple completely reflecting mirrors, half mirrors, and polarizing panels in addition to interference-causing laminar structures wherein multiple layers of film having different refractive indexes are laminated. “Semi-reflecting layers” include structures such as half mirrors and polarizing panels in addition to interference-causing laminar structures wherein multiple layers of film having different refractive indexes are laminated. By “optical path length” is meant a distance corresponding to the product of the refractive i
Burroughes Jeremy Henry
Kaneko Takeo
Koyama Tomoko
Shimoda Tatsuya
Lebentritt Michael S.
Seiko Epson Corporation
Wilson Christian D.
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