Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure
Reexamination Certificate
2003-04-28
2004-09-14
Prenty, Mark V. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
C257S098000, C257S100000
Reexamination Certificate
active
06791116
ABSTRACT:
The present application is based on Japanese Patent Applications No.2002-128790 and No.2002-276184, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a light emitting diode which is usable, for example, in light sources for photosensors, printers, and backlights of various displays and the like. More particularly, the invention is concerned with a light emitting diode including a light emitting element and a phosphor material, in which light of a desired uniform color can be radiated from the light emitting diode as viewed from an emission observing surface of the light emitting diode.
In this specification, an LED chip per se is referred to as “light emitting element,” and the whole system including an LED chip-mounted package resin or lens system or other optical system is referred to as “light emitting diode.”
2. Related Art
A conventional light emitting diode, which uses a light emitting element and a phosphor to emit light of a desired color, is schematically shown in FIG.
1
. This light emitting diode includes a pair of lead frames
102
,
103
. The lead frame
102
has a concave part in its leading end. A light emitting element
101
is mounted on the bottom of the concave part. The light emitting element
101
is covered with a phosphor-mixed resin
104
. Further, the space within of the concave part is filled with the phosphor-mixed resin
104
. The phosphor-mixed resin
104
is a resin, such as a transparent epoxy resin, into which a phosphor has been mixed. This phosphor absorbs light emitted from the light emitting element
101
, performs wavelength conversion of the absorbed light, and gives off light with a wavelength different from the absorbed light. The whole assembly has been sealed with a sealing resin
105
.
In the light emitting diode having the above construction, assuming that, for example, the light emitting element
101
is a blue light emitting element and the phosphor is one which absorbs blue light emitted from the blue light emitting element, performs wavelength conversion of the blue light and gives off yellow light, the blue light emitted from the blue light emitting element is mixed with the yellow light given off from the phosphor. Therefore, theoretically, white light can be radiated to the outside of the light emitting diode as viewed from an emission observing surface of the light emitting diode.
This light emitting diode, however, suffers from a problem that, as viewed from the emission observing surface of the light emitting diode, color of light radiated from the light emitting diode varies from position to position of the emission observing surface of the light emitting diode. The above unfavorable phenomenon will be hereinafter referred to as “lack of uniformity of color of radiated light.” This problem is attributable to the following fact. A part of light is radiated from the light emitting element
101
in a direction just above the light emitting element
101
. Another part of light is radiated obliquely from the top surface or side surface of the light emitting element
101
. Further, after emission from the light emitting element
101
, a part of light is reflected from the inner wall of the concave part. Therefore, the amount of the phosphor, in the phosphor-mixed resin
104
, through which the light is passed in a period between the emission of the light from the light emitting element and the emergence of the light from the light emitting diode varies depending upon optical paths through which the light is passed and radiated to the outside of the light emitting diode. This variation in the amount of phosphor will be hereinafter often referred to as “a difference in the amount of light-permeated phosphor among the optical paths.” In this case, as viewed from the emission observing surface side of the light emitting diode, the emission observing surface in its portion just above the light emitting element
101
is perceived as emitting white light, and a portion around that portion just above the light emitting element
101
is perceived as emitting yellow light. Thus, the light radiated from the light emitting diode lacks in uniformity of color.
In particular, in recent years, there is an ever-increasing demand for a reduction in size and a reduction in thickness of the light emitting diode. To meet this demand, for example, shell-shaped or SMD (surface mounted device) type light emitting diodes have been desired in the art. In this case, in order to realize the small and thin light emitting diode, the concentration of the phosphor in the phosphor-mixed resin, which covers the light emitting element and fills up the space within the concave part, should be enhanced. The enhancement in the concentration of the phosphor in the phosphor-mixed resin can certainly meet the demand for a reduction in size and a reduction in thickness of the light emitting diode. In this case, however, the difference in the amount of light-permeated phosphor among the optical paths is further increased. Therefore, the lack of uniformity of color of radiated light becomes more significant.
Japanese Patent No. 3065263 proposes a light emitting diode which reduces the lack of uniformity of color of radiated light. This light emitting diode is shown in FIG.
2
. As shown in
FIG. 2
, the light emitting diode includes a reflecting member
127
having a concave part. A light emitting element
123
is mounted on the bottom of the concave part. The light emitting element
123
is provided with a pair of electrodes (not shown). These electrodes are bonded respectively to external electrodes
124
through electrically connecting members
126
. The light emitting element
123
and the electrically connecting members
126
are covered with and are embedded in a first resin
121
. The first resin
121
is in a concave spherical surface as viewed from an emission observing surface of the light emitting diode. The remaining space, on the first resin
121
, of the concave part is filled with a second resin
122
which is a phosphor-mixed resin. The claimed advantage of this construction is to substantially reduce the difference in the amount of light-permeated phosphor among the optical paths, and thus to reduce the lack of uniformity of color of light radiated from the light emitting diode.
In the above light emitting diode, however, the thickness of the phosphor-containing second resin
122
is the largest in a portion just above the light emitting element
123
and gradually decreases toward the side wall of the concave part. A part of light emitted from the light emitting element
123
is radiated in a direction just above the light emitting element
123
to the outside of the light emitting diode through the second resin
122
in its large thickness portion. On the other hand, another part of light emitted from the light emitting element
123
advances toward the inner wall of the reflecting member
127
, is reflected from the side wall of the concave part, and advances toward the outside of the light emitting diode through the second resin
122
in its small thickness portion. Therefore, regarding the emitted light passed through an optical path including the small-thickness portion of the second resin
122
, the amount of light-permeated phosphor is smaller than that in the emitted light passed through the other optical paths. That is, a difference in the amount of light-permeated phosphor among optical paths exists, and, thus, the light radiated from the light emitting diode lacks in uniformity of color. In other words, also in the above light emitting diode, light radiated from the light emitting diode disadvantageously lacks in uniformity of color as viewed from the emission observing surface of the light emitting diode.
Further, in the above light emitting diode, light emitted from the light emitting element
123
is directly incident in a high-optical density state to the phosphor mixed second resin
122
. According to experiments conducted by the present inve
Arakane Katsunori
Fukumoto Shigeru
Hadame Kunihiro
Hirano Atsuo
Kitahara Hiromi
Prenty Mark V.
Toyoda Gosei Co,., Ltd.
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