Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2000-10-05
2003-07-01
Scott, Jr., Leon (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S065000, C372S036000
Reexamination Certificate
active
06587491
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a small-sized and inexpensive semiconductor laser suitable for use as a pickup light source in, for example, DVDs (digital video disks) and DVD-ROMs. More particularly, it relates to a stem type semiconductor laser which can be formed in a small outside dimension even if a laser chip for DVDs is large-sized.
BACKGROUND OF THE INVENTION
The stem type semiconductor laser used as conventional pickups for CDs has such a structure as shown in FIG.
7
. Specifically, a stem
20
is used which is produced by forming a metallic material such as iron by cold forging, raising a part of the center portion of a base
21
to form a heat sink section
22
and fixing leads
23
and
25
by using a glass
26
or the like. A laser chip
31
is mounted on the heat sink section
22
through a submount
34
made of a silicon substrate or the like. One electrode (backface electrode of the chip
31
) is electrically connected to the lead
23
through a relay portion
38
of the submount
34
by a wire
33
and another electrode is connected to the submount
34
through a wire
33
and is also electrically connected to a common lead
24
by way of the heat sink section
22
and the base
21
via the backface of the submount
34
.
32
represents a light receiving element for monitor. One electrode of the light receiving element
32
is electrically connected to a lead
25
through a wire
33
and another electrode is electrically connected to the common lead
24
through the submount
34
, the heat sink section
22
and the base
21
. The periphery of these portions is covered by a cap
35
to form the semiconductor laser. A through-hole
35
a
is formed in the center of the top of the cap
35
to transmit light emitted from the laser chip
31
and a glass plate
36
is sealed by an adhesive
37
.
In this structure, although the heat sink section
22
must be formed between the leads
23
and
25
, the leads
23
and
25
must be sealed by the glass
26
or the like. It is therefore impossible to decrease the diameter of the stem
20
. Hence, only semiconductor lasers having an outside dimension of about 5.6 mm &phgr; have been manufactured.
On the other hand, as shown in
FIG. 8
, there is a type obtained by processing a plate-like body by drawing to form a ring
27
and a pedestal portion
28
to be a heat sink into one united body, directly sealing leads
23
and
25
within the ring
27
by using a glass
29
or the like to form a stem
20
and a cap
35
is allowed to cover the periphery of the stem
20
by press fitting. By making the semiconductor laser having such a structure, it is unnecessary to form the heat sink section directly on the base of the stem and also a space used to weld the cap. Hence a semiconductor laser with a diameter of about 3.3 mm &phgr; is produced. In
FIG. 8
, the same parts as in
FIG. 7
are represented by the same symbols and the explanations of these parts are omitted.
As to a light source used for the conventional pickups for CDs, the size of a laser chip used in the light source is about a 0.25 mm by 0.25 mm square and operating current is small. Even if a semiconductor laser having the structure shown in the aforementioned
FIG. 8
is used as the light source, no problem arises because the operating current is small to reduce the calorific value. On the contrary, a laser chip for DVDs is as large as about a 0.25 mm by 0.5 mm square and operating current is about two times that of the chips for CDs. There is the problem that insufficient heat dissipation results in no emission of the laser chip. Because of this reason, it is necessary to make the heat sink section as large as possible to thereby promote heat dissipation. Moreover, in the structure shown in
FIG. 8
, it is necessary to form a thick solder plating on the surface of the stem since the cap is fitted by press fitting, giving rise to the problem that a thick solder plating is formed on a lead, leading to difficult wire bonding.
While, for pickups used to detect signals of, for example, CDs or DVDs, very thin types are required along with the development of light-weight, thin and small-sized electronic equipment as typified by recent note-type personal computers. As a semiconductor laser used side-wise in a pickup, one having a small diameter is needed. For even types which are made to have a large chip size and must have good heat dissipation characteristics, it is desired to decrease the outside diameter to about 3.3 mm &phgr; or less.
SUMMARY OF THE INVENTION
The present invention has been conducted in view of the aforementioned situation and has an object of providing a semiconductor laser having a small outside diameter, the semiconductor laser being improved in heat dissipation characteristics by making a heat sink section large even if a laser chip having a large chip size and a large calorific value is used.
Another object of the present invention is to make such an optical pickup as used in a note type personal computer thinner and to provide an optical pickup device which allows electronic equipment to be thinner.
A semiconductor laser according to the present invention comprises: a stem which is secured such that at least two leads are projected from both sides; a support section disposed on one side bottom (lead-fixed section) of the stem; a heat sink section formed on the upper portion of the support in a wide width extending to the side of the two leads; and a laser chip secured to the heat sink section.
Here, the meaning that the heat sink section is formed in a wide width extending to the side of the two leads implies either one or both of the case where the support section disposed between the two leads extends in the direction of the width of the leads and the case where the support section disposed behind the lead extends to the side of the front lead (in a direction perpendicular to the direction of the width of the leads). It is to be noted that the portion formed in a wide width may be wide in width either such that it covers the upper portion of the top of the lead or to the extent that it covers the glass portion securing the leads though it uncovers the top of the leads.
This structure ensures that even if the support section is limited in width by the interval between the leads and the like on a plan view (viewing the stem from the above), the volume of the heat sink section can be secured even if the interval between the leads is narrow because in the structure, the heat sink section is overlapped on the leads (including the glass portion securing the leads). As a result, a heat sink section enough to dissipate heat can be provided even if the interval between the leads is made narrow to obtain a semiconductor laser with an outside diameter of 3.3 mm &phgr;. Also, even laser chips, such as those for DVDs, having a large chip size and a large calorific value can be made into small packages. That is, conventional semiconductor lasers of this type are manufactured based on the idea that a heat sink section and a support section have the same widths and the heat sink portion and leads are arranged such as in line on a plan view; therefore, a restriction is imposed on the interval of the leads in the stem and such a restriction that the heat sink section cannot be made large is imposed. However, by adopting such an idea that the heat sink section is extended and made large so as to overlap on the leads on a plan view, even semiconductor lasers for DVDs having a large chip size and a large calorific value could be formed into a small-sized one with an outside diameter of about 3.3 mm &phgr;.
Preferably the stem is formed by securing the at least two leads to the through-hole of the metal base with an insulated material, the support section is integrated with the base and the heat sink section is stuck to the support section. This structure makes it possible to use a copper material or the like having high heat conductivity for the heat sink section.
Preferably the aforementioned at least two leads are secured to the through
Arent Fox Kintner Plotkin & Kahn
Jr. Leon Scott
Rohm & Co., Ltd.
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