Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2000-06-03
2004-06-29
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S498000, C313S501000, C257S010000, C257S088000, C257S098000, C257S099000, C257S100000
Reexamination Certificate
active
06756731
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor light emitting device, such as a light emitting diode device, particularly having a semiconductor light emitting element which generates a wavelength-converted light to emit the light having its wavelengths of 550 nm or less to the outside.
2. Description of the Prior Art
Use of a semiconductor light emitting element having a large energy gap allows realization of a semiconductor light emitting device which generates fight at relatively short wavelengths from visible light of short wavelengths to ultraviolet light. A semiconductor light emitting element for generating light having such wavelengths, includes nitrogen gallium compound semiconductors, such as GaN, GaAlN, InGaN and InGaAlN which can be utilized to provide a new solid-state ultraviolet light source to offer a variety of advantages including small size, low power consumption, and long life.
FIG. 4
shows a sectional view of a prior art light emitting diode device
1
which utilizes a fluorescent substance
7
a
for converting the wavelength of the light projected from a light emitting diode chip
2
. As shown in
FIG. 4
, the light emitting diode chip
2
is secured to a bottom surface
3
b
of a concavity
3
a
formed in a first external terminal
3
as a cathode lead. A cathode electrode
2
g
formed on the light emitting diode chip
2
is connected to a first wire connection
9
a
of the first external terminal
3
by means of a first lead wire
5
. Also, an anode electrode
2
f
formed on the light emitting diode chip
2
is connected to a second wire connection
9
b
of a second external terminal
4
as an anode lead by means of a second lead wire
6
. The light emitting diode chip
2
secured on the concavity
3
a
is covered with a light permeable protective plastic material
7
filled in the concavity
3
a
with fluorescent substance
7
a
blended in the plastic material
7
. Moreover, a light permeable plastic encapsulant
8
encapsulates the light emitting diode chip
2
, concavity
3
a
and first and second wire connections
9
a
,
9
b
of the first and second external terminals
3
and
4
, and lead wires
5
,
6
.
When a voltage is applied across the first and second external terminals
3
and
4
of the light emitting diode device
1
, the light emitting diode chip
2
is activated to generate a light which passes through the protective plastic material
7
, and then is reflected on a side wall
3
c
of the concavity
3
a
formed in the first external terminal
3
. Subsequently, the light passes through the transparent plastic encapsulant
8
and is then released out of the light emitting diode device
1
. Some of the light is projected from a top of the light emitting diode chip
2
, and is directly passed through the protective material
7
and plastic encapsulant
8
without the reflection on the side wall
3
c
of the concavity
3
a
before the release to the outside of the light emitting diode device
1
. The plastic encapsulant
8
is formed with a lens portion
8
a
at the top so that the lens portion
8
a
converges the light passed through the plastic encapsulant
8
for increased directivity. Upon passing through the protective plastic material
7
, the light projected from the light emitting diode chip
2
is converted into the light of different wavelength by the fluorescent substance
7
a
mixed into the protective plastic
7
before the release. Accordingly, the light emitting diode device
1
releases light different in wavelength from the light projected out of the light emitting diode chip
2
.
Generally, a semiconductor light emitting element is covered with a plastic sealer or plastic encapsulant
8
which comprises an organic polymeric compound in which elements such as carbon, hydrogen, oxygen and nitrogen are linked together in the mesh form. In this case, it is known that the bonds of the organic polymer are cut, when the plastic sealer or epoxy resin encapsulant
8
of the diode device is irradiated with ultraviolet light or the like, resulting in deterioration of various optical or chemical characteristics of the plastic sealer. For example, a GaN (gallium nitride) light emitting diode chip generates ultraviolet light having wavelengths up to approximately 365 nm, and therefore, when irradiated with ultraviolet light, the plastic sealer
8
is gradually yellowed or discolored, starting from the periphery with the highest light intensity of the light emitting diode chip
2
. Accordingly, the visible light generated by the light emitting diode chip
2
is absorbed by the colored area, causing the light to be decayed. Also, the discoloration results in the deterioration, reduced moisture resistance and increased ion permeability of the plastic sealer
8
so that contamination or undesirable ions can enter from outside through the plastic sealer
8
into the light emitting diode chip
2
, which results in the deterioration of the diode chip
2
itself and synergistically decreased intensity of emission light for the light emitting diode device
1
.
In addition, when a light emitting diode chip of GaN (gallium nitride) has a high forward voltage, it generates the high power loss even with a relatively low forward current, and the considerably elevated temperature in the diode chip
2
in operation. It is generally known that a plastic material is gradually deteriorated to be yellowed or discolored when subjected to heat or a high temperature. Therefore, if a GaN light emitting diode chip is assembled to prepare a prior art light emitting diode device, the plastic material is gradually yellowed or discolored, starting from the area contacting with the high-temperature light emitting diode chip, as light of short wavelength is projected from the light emitting diode chip, thereby causing the degradation in quality of the appearance and gradually lowered emission light intensity of the light emitting diode device. Thus, the prior art light emitting diode device causes a limited and reduced number of selectable types of material, a decrease in reliability, imperfection of light conversion function and a rise in product price.
In view of the above-mentioned fact that the ultraviolet light causes the debasement of the plastic sealer for a short period of time with the reduced light emission efficiency, a hermetically sealed structure has been proposed for some of the light emitting devices which include an outer container for hermetically sealing the semiconductor light emitting element in the container to completely insulate it from the external atmosphere, and an inactive or stable sealing gas such as nitrogen filled in the container.
Although the hermetically sealed structure does not cause the deterioration of the plastic sealer, it raises a problem of the final expensive products because it requires costly materials and a relatively complicated process for manufacture. In addition, because the container is filled with an inactive gas of its refractive index greatly different from that of the gallium nitride compound semiconductor, disadvantageously a reflection plane is formed at the boundary between the gallium nitride compound semiconductor and the inactive gas. Consequently, a defect is presented in that the light projected from the semiconductor light emitting element is repetitively reflected at the boundary between the gallium nitride compound semiconductor and the inactive gas, resulting in the decayed or attenuated light and the lowered light emission efficiency.
Further, various problems in practical use have been presented with the conventional light emitting diode device
1
which comprises the light emitting diode chip
2
surrounded by the protective plastic material
7
with the fluorescent substance
7
a
contained therein, and the plastic encapsulant
8
for surrounding the whole of the diode chip
2
and plastic material
7
. Firstly, when the protective plastic
7
and the plastic encapsulant
8
do not always have a sufficient environmental resistance, only a spe
Bachman & LaPointe P.C.
Hodges Matt
Patel Nimeshkumar D.
Sanken Electric Co. Ltd.
LandOfFree
Semiconductor light emitting device resistible to... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor light emitting device resistible to..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor light emitting device resistible to... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3358836