Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – Plural light emitting devices
Reexamination Certificate
2002-05-08
2003-11-04
Fahmy, Wael (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
Plural light emitting devices
C257S088000
Reexamination Certificate
active
06642545
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor light emitting device used for display lights and the like of various kinds of electric apparatus, and particularly to a semiconductor light emitting device by which a plurality of emission colors can be obtained.
2. Description of Related Art
In a semiconductor light emitting device such as a light emitted diode, when a forward voltage is applied to a p-n junction, an electric energy is converted to a light energy to cause light emission. In such a semiconductor light emitting device, a variety of color lights can be realized depending upon the composition of the material of the semiconductor or the kind of impurities.
By incorporating a plurality of semiconductor light emitting chips having different emission colors respectively in a semiconductor light emitting device, a semiconductor light emitting device having a plurality of emission colors can be obtained. When the emission colors of two semiconductor light emitting chips have the complimentary color relationship with each other, visibly white light emission can be realized by making the two semiconductor light emitting chips emit light at the same time with a suitable brightness ratio.
For example, by incorporating a semiconductor chip having blue emission color and a semiconductor chip having yellow green emission color, a semiconductor light emitting device having emission colors including blue, yellow green and an intermediate color thereof can be obtained. By suitably determining the brightness ratio between blue light and yellow green light, white color emission can be obtained.
In a conventional semiconductor light emitting device having the above-mentioned structure, a plurality of semiconductor light emitting chips having different emission colors are laterally disposed on a support body.
However, in a semiconductor light emitting device having such a structure, when semiconductor light emitting chips having different emission colors respectively are made to emit light at the same time, sometimes respective emission colors of the semiconductor light emitting chips are not sufficiently mixed. This is because, since the semiconductor light emitting chips are shifted, though only slightly, with respect to each other in the lateral direction, not only an intermediate color but also the respective emission colors of the semiconductor light emitting chips are observed. Further, depending upon the angle of observation, the emission colors are not well mixed, so that white emission light cannot be obtained.
Further, there are semiconductor light emitting devices in which a fluorescent substance having a suitable fluorescent color is applied on the outside of each semiconductor chip in order to obtain a specified emission color such as white. However, with such a structure, though the above-mentioned problem does not occur, only one emission color can be obtained.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor light emitting device by which a plurality of emission colors can be obtained.
Another object of the present invention is to provide a semiconductor light emitting device in which a plurality of emission colors of a plurality of semiconductor light emitting chips can be sufficiently mixed.
A semiconductor light emitting device according to the present invention includes a first semiconductor light emitting chip in which a first light emitting layer is formed on a first substrate, and a second semiconductor light emitting chip in which a second light emitting layer is formed on a second substrate, the second semiconductor light emitting chip being stacked on and bonded to the first semiconductor light emitting chip.
The first and second semiconductor light emitting chips may be bonded to each other by a bonding material such as an adhesive.
The first and second semiconductor light emitting chips may have emission colors respectively within the range of visible light wavelengths. These emission colors preferably have the complementary color relationship with each other. In this case, by making the semiconductor light emitting chips emit light at the same time, visibly white emission color can be realized.
It is preferable that the first and second light emitting layers at least partly (preferably substantially wholly) overlap each other when seen in the direction of the stacking of the first and second semiconductor light emitting chips. In such a case, since a part or substantially the whole of the light emitting regions of the first and second semiconductor light emitting chips overlap each other, the emission colors thereof are sufficiently mixed and seen in this sufficiently mixed state.
Further, the main direction of the light emission of the first semiconductor light emitting chip may be a direction of going from the first semiconductor light emitting chip toward the second semiconductor light emitting chip. In this case, it is preferable that the above-mentioned second substrate is made of a material having permeability with respect to the light emitted from the first light emitting layer. Further, when an adhesive is used as a bonding material, the adhesive preferably has permeability with respect to the light emitted from the first light emitting layer.
Thereby, when the layered first and second semiconductor light emitting chips are seen from the second semiconductor light emitting chip side, the light emitted from the first light emitting layer is seen through the adhesive and the second substrate of the second semiconductor light emitting chip.
Further, it is preferable that, on the first substrate, the first light emitting layer is formed on the surface on the opposite side of the second semiconductor light emitting chip, and the first substrate is formed of a material having permeability with respect to the light emitted from the first light emitting layer. Thereby, when the layered first and second semiconductor light emitting chips are seen from the second semiconductor light emitting chip side, the light emitted from the first light emitting layer is seen through the first substrate and the second substrate of the second semiconductor light emitting chip.
The above-mentioned stacked and bonded first and second semiconductor light emitting chips may be mounted on an insulating substrate, on one surface of which external connection electrodes are formed. The first semiconductor light emitting chip may have electrodes on the surface thereof on the opposite side of the second semiconductor light emitting chip, and these electrode may be bump-bonded to the external connection electrodes. The second semiconductor light emitting chip may have electrodes on the surface thereof, and these electrodes may be wire-bonded to the external connection electrodes. The external connection electrodes may be extended to the other surface of the insulating substrate, and may be connected to mounting electrodes for mounting this semiconductor light emitting device on a wiring substrate.
A semiconductor light emitting device having such a structure can be suitably surface-mounted on a wiring substrate. Since the main direction of seeing the semiconductor light emitting device mounted on the wiring substrate is substantially perpendicular to the wiring substrate, the direction of seeing substantially coincides with the direction of the stacking of the first and second semiconductor light emitting chips. Therefore, the emission color of the first semiconductor light emitting chip and the emission color of the second semiconductor light emitting chip are sufficiently mixed and seen in this sufficiently mixed state.
The above-mentioned external connection electrodes may include a first and a second control electrodes insulated from each other for independently driving the first and second semiconductor light emitting chips. The electrodes of the first semiconductor light emitting chip may be bump-bonded to the first control electrodes and the electrodes of the second semiconductor
Fahmy Wael
Rabin & Berdo P.C.
Rohm & Co., Ltd.
Wille Douglas A.
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