Coherent light generators – Particular temperature control – Heat sink
Reexamination Certificate
1999-07-19
2003-07-22
Leung, Quyen (Department: 2828)
Coherent light generators
Particular temperature control
Heat sink
C372S050121
Reexamination Certificate
active
06597713
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus with an optical functional device having a special wiring electrode, such as a surface emitting semiconductor device or a light receiving device, whose fabrication is easy, whose yield is high, and which can be suitably constructed as a two-dimensional array or the like. This invention also relates to a fabrication method of the above apparatus and apparatuses using the above apparatus, such as an optical transceiver apparatus, an optical interconnection apparatus and an optical recording apparatus.
2. Related Background Art
Recently, development of a solid-state light emitting device of a two-dimensional array type has been desired for purposes of its applications to a large-capacity parallel optical information processing, a high-speed optical connection, a high-speed optical recording and a panel-type display apparatus. Low cost, low consumption of an electric power, high productivity, and high reliability are required to achieve those applications. A variety of materials for such a solid-state surface emitting device have been studied and developed. It has been found that single-crystal semiconductors are notably suitable for reliability. In particular, development of a surface emitting device using compound semiconductors has been energetically advanced.
Among light emitting devices, a laser diode (LD) including reflection mirrors at its opposite ends is quite excellent in a light emitting efficiency, compared to devices using spontaneous emission. Therefore, the electric power consumption can be greatly lowered when those LDs are arranged in a two-dimensional form. In light of these facts, development of a VCSEL (vertical cavity surface emitting laser) has been actively advanced in recent years.
With the VCSEL, devices have been developed over a range from a blue color at a wavelength of about 400 nm to a communication wavelength band of 1.55 &mgr;m. Studies have been made in material series, such as AlGaN/InGaN series on a sapphire substrate, InGaAlP/InAlP and InGaAs/AlGaAs series on a GaAs substrate, and InGaAs/InGaAsP series on an InP substrate.
A fundamental structure of the two-dimensional arrayed VCSELs is illustrated in FIG.
1
. Laser light is emitted perpendicularly to a substrate
1001
. Each device is provided with highly-reflective coatings
1002
and
1004
of over 99% reflectivity at opposite ends of epitaxially-grown layers with a thickness of about several microns. A multiplicity of alternately-layered layers with different refractive indices and a common &lgr;/4 thickness are used as the reflective mirror. The materials are generally dielectric or epitaxially-grown semiconductors (see, for example, an AlAs/GaAs mirror as disclosed in ELECTRONICS LETTERS, 31, p.560 (1995).
Regarding other elements shown in
FIG. 1
, reference numeral
1003
designates an active layer, reference numeral
1005
designates an insulating layer, reference numeral
1006
designates an electrode on the epitaxial layers, reference numeral
1007
designates a laser functional portion, reference numeral
1008
designates an electrode on the laser substrate side, reference numeral
1009
designates a burying layer, reference numeral
1010
designates a window region formed in the electrode
1006
, and reference numeral
1011
designates a laser cavity.
Several mounting or packaging methods of the VCSEL have also been proposed so far. Japanese Patent Laid-Open No. 8-186326 (1996), for example, discloses a mounting method in which the laser is thermally and electrically connected to a package and heat-sink substrate that is transparent to laser light, as illustrated in FIG.
2
. In this case, a wiring electrode is formed on a portion of the heat sink corresponding to a portion of the VCSEL, and the electric connection is achieved by a solder heating or an ultrasonic-wave bonding between Au portions at the VCSEL portion.
In
FIG. 2
, reference numeral
1110
designates a resin mold body, reference numeral
1111
designates a laser electrode, reference numeral
1112
designates a laser substrate, reference numerals
1113
and
1117
designate reflective layers, reference numerals
1114
and
1116
designate cladding layers, reference numeral
1115
designates an active layer, reference numeral
1118
designates a current blocking layer, reference numeral
1119
designates a contact layer, reference numeral
1120
designates a package window (also referred to, herein, as a heat sink window), and reference numeral
1121
designates an electrode on the package window side.
Further, Japanese Patent Laid-Open No. 6-237016 (1994) discloses another mounting method in which a wiring electrode is formed on a substrate
1201
with an electronic circuit, the wiring electrode is electrically connected to a VCSEL
1203
and an optical fiber
1210
is inserted into a hole formed in a VCSEL substrate
1202
. Herein, a transistor
1204
is arranged under the VCSEL
1203
, and a cathode of the VCSEL
1203
is connected to a collector of the transistor
1204
as illustrated in FIG.
3
.
Regarding other elements shown in
FIG. 3
, reference numeral
1205
designates an emitter electrode, reference numeral
1206
designates a base electrode, reference numeral
1207
designates an anode electrode, reference numeral
1208
designates an insulating layer, reference numeral
1209
designates a guide hole, and reference numeral
1211
designates an adhesive.
Further, Japanese Patent Laid-Open No. 9-15459 (1997) discloses a mounting method of arrayed VCSELs in which a wiring
1304
is formed on a support substrate
1305
and the wiring
1304
is connected to each VCSEL
1302
as illustrated in FIG.
4
.
In
FIG. 4
, reference numeral
1301
designates a semiconductor substrate, reference numeral
1303
designates a guide for an optical fiber, reference numeral
1306
designates an optical fiber tape, reference numeral
1307
designates a core of the fiber, reference numeral
1308
designates a clad of the fiber, reference numeral
1309
designates a core wire of the optical fiber, reference numeral
1310
designates a coating material, reference numeral
1311
designates a light beam, and reference numeral
1312
designates a length of an exposed portion of the core wire
1309
of the optical fiber.
In those prior art mounting methods, VCSELs with an electrode pad formed on an upper surface (i.e., a surface of epitaxial layers) of each VCSEL are bonded to a wiring substrate with an electrode pad corresponding to each VCSEL while electrical connections between pairs of these pads are maintained. In such mounting methods, however, an alignment precision is required when the pads on the VCSEL and the wiring substrate are bonded, especially where the density of a two-dimensional array of VCSELs is great or where the electrode pad is made small to secure a preferable rapid response. The reason therefor is that the pads must be precisely positioned and in addition thereto the alignment and bonding must be performed such that the pad would not be brought into contact with other wirings on the wiring substrate. As the density increases, such undesired contact is more likely to occur since a number of wirings are formed between the pads. Accordingly, in such methods wherein mutually-bonding faces cannot be directly monitored, the alignment is difficult to achieve and yield and productivity decrease.
Further, the uses of solder to perform bonding cause several problems. For example, the melted solder flows into a window through which laser light emerges and blocks the laser light. Also, a resistance of an ohmic contact with the VCSEL rises since the solder melts an Au electrode. Additionally, when the Au electrodes are directly bonded by ultrasonic waves, the VCSEL is likely to be damaged and less effective if the bonding point is close to the VCSEL.
Further, in the prior art structure of
FIG. 2
, when light emerging from the VCSEL through the heat sink window
1120
is spatially transmitted or coupled to an optical fiber
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Leung Quyen
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