Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
1994-10-04
2004-08-31
Clark, Sheila V. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S432000, C257S431000
Reexamination Certificate
active
06784511
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a laser diode device which is formed by sealing a laser diode chip with resin, and more particularly to an improvement of the laser diode device so that its sealing resin is prevented from being damaged by the laser beam from the laser diode chip, and the far field pattern thereof is satisfactory at all times.
A conventional laser diode device is, in general, of a can type as shown in FIG.
9
. That is, a laser diode chip
10
is soldered to a radiator
62
mounted on a stem
61
, and a cap
63
with a glass window is welded to the stem to seal the laser diode chip
10
.
On the other hand, resih type light emitting elements have been employed in the light emitting elements low in optical density per unitary area such as light emitting diodes (LED), and resin-sealed laser diodes also have been known in order to make the laser diodes low in manufacturing cost and shaped with greater freedom. However, in sealing a light emitting element such as a laser diode high in optical density with resin, a problem is still involved which has not sufficiently solved yet. The problem is that the sealing resin is damaged by the laser beam, and the resultant light emitting element is therefore low in reliability or short in life time.
For instance, when a life test was given to a resin-sealed laser diode, which was sealed with a transparent epoxy resin high in optical transmission, under automatic power control (APC) for an ambient temperature of 60° C. and an optical output of 3 mW, the sealing resin in contact with the laser beam emergence section (about 5 &mgr;m×1 &mgr;m) of the laser diode was optically damaged within 100 hours; that is, holes were formed in the portions of the sealing resin which corresponded in position to the laser beam emergence section, thus lowering the characteristics of the laser diode.
On the other hand, it has been found that the above-described deterioration in characteristic of the laser diode can be effectively prevented by formation of an end-face breakage preventing layer between the laser diode chip and the sealing resin by using a material which is low in absorption coefficient with the band of wavelengths of the laser beam and high in heat resistance. The method has been filed with the Patent Office (U.S. Ser. No. 07/788,601 assigned to the same assignee as this application). The material of the end-face breakage preventing layer may be non-organic materials such as alumina, silica and low melting point glass, or organic materials such as silicone resin. For more information, see Japanese Patent Unexamined Publication No. Hei. 5-3377.
One example of the above-described resin-sealed laser diode device is as shown in
FIG. 1
, a perspective view.
FIG. 2
is also a perspective view, with parts cut away, of a laser diode chip
10
shown in FIG.
1
.
FIG. 3
is a sectional view of the laser diode chip, taken along the longitudinal axis of an electrode
7
.
The laser diode chip
10
is formed as follows: An n-type clad layer
3
of AlGaAs, an active layer
4
, a p-type cladding layer
5
, and p-type cap layer
6
of GaAs are formed on an n-type substrate
2
of GaAs in the state order. An electrode
7
is formed on the p-type cap layer
6
, and another electrode
8
is formed on the substrate
2
. In order to allow current to concentrate at the center of the active layer
4
, the p-type cladding layer
5
has a current narrowing portion (not shown). The surfaces of light emitting end-faces
9
are coated with an insulating dielectric thin film, namely, an end-face protecting film
20
b
to a thickness of 0.5 &mgr;m or less. In the chip
10
, the light-emitting end faces have a laser beam emergence section about 5 &mgr;m×1 &mgr;m. In addition, end-face breakage preventing layers
20
, which are low in absorption coefficient to the band of wavelengths of the laser beam and high in heat resistance, are formed on the end-face protecting film
20
b
which is formed on the light emitting end faces
9
including the laser beam emergence sections. As shown in
FIG. 4
, a sectional view of a resin-sealed laser diode different in external configuration from the one shown in
FIG. 1
, the laser diode chip
10
with the end-face breakage preventing layers
20
is mounted on a heat radiating board
71
supported by a lead frame
72
, and then sealed with a sealing resin
30
such as transparent epoxy resin so that the resin-sealed laser diode is formed.
The heat radiating board
71
is made of a Si substrate. A photo-diode
73
(see
FIG. 1
) is formed on a part of the upper surface of the heat radiating board
71
. Its light receiving surface is in parallel with the above-described layers
2
through
6
and electrodes
7
and
8
of the chip
10
, thus being able to monitor an emergent laser beam
101
b
(see
FIG. 4
) from the back side of the chip
10
. The laser beam
101
emergent from the emergence section about 5 &mgr;m×1 &mgr;m forms a divergent angle; i.e., a horizontal angle of about 10° and a vertical angle of about 40° in the half width of the laser beam intensity distribution. Accordingly, the beam area
102
(see
FIG. 2
) increases substantially in proportion to the square of the distance m which the laser beam
101
travels, whereas the optical density decreases substantially in proportion to the square of the distance m.
On the other hand, in the case where the light emitting end face of a laser diode chip high in optical density is covered with the end-face breakage preventing layer, as shown in
FIG. 5
(which is an enlarged sectional view of the laser beam emergence section of the laser diode chip), the optical density of the laser beam
101
advancing towards the surface
20
a
of the end-face breakage preventing layer from the light emitting end face
9
is decreased at the surface
20
a
in proportion to the square of the thickness of the end-face breakage preventing layer
20
.
Intensive research has been conducted with the above-described facts taken into consideration. During the research, it has been found that the thickness of the end-face breakage preventing layer
20
necessary for sufficiently reducing the optical intensity of the laser beam, and the life time of the resin-sealed laser diode are closely related to each other. This end-face breakage preventing layer, being greatly related to the present invention, will be described in more detail.
The material most suitable for formation of the end-face breakage preventing layer is silicone resin.
FIGS.
6
(
a
) to
6
(
e
) show a process of manufacturing a laser diode whose end-face breakage preventing layer is formed by using the silicone resin. First, a laser diode chip
10
having end-face protecting films
20
b
of Al
2
O
3
on the light-emitting end faces is soldered, as indicated at
74
, to a heat radiating board
71
of Si by a junction down method in such a manner that the chip
10
is adjacent to the light receiving surface
73
a
of a photo-diode
73
formed on the heat radiating board
71
, and the light emitting end face of the chip
10
is flush with the side end face of the heat radiating board
71
(FIG.
6
(
a
)). Next, the heat radiating board
71
, on which the chip
10
has been fixedly mounted, is fixedly mounted in place on a lead frame
72
with an Ag epoxy adhesive
75
(FIG.
6
(
b
)). Under this condition, the chip
10
, the photo-diode
73
, and external lead electrode terminals
721
and
722
of the lead frame
71
are connected by wire bonding (FIG.
6
(
c
)). Thereafter, a dispenser (not shown) is used to apply a suitable amount of silicone resin to the chip
10
from obliquely above. The silicone resin thus applied is heated and hardened to form an end-face breakage preventing layer
20
(FIG.
6
(
d
)). The resultant product is sealed with an epoxy resin
30
, which transmits laser beam, to a predetermined configuration (FIG.
6
(
e
)). Thus, the aimed laser diode has been manufactured. The laser diode is high in the flexibility of configuration. It may have the same configuration
Kunihara Kenji
Mojikawa Hiromi
Nagano Satoru
Shindo Yoichi
Umegaki Tadashi
Clark Sheila V.
Fuji Electric & Co., Ltd.
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