Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2001-08-14
2002-11-19
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S100000, C257S431000, C257S436000
Reexamination Certificate
active
06483161
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a passive optical part for optical communications system which transmits bidirectionally optical signals of two wavelengths between ports simultaneously. Light source devices, for example, light emitting diodes (LEDs) or semiconductor laser diodes (LDs) and photodetectors, for example, photodiodes(PDs) or avalanche photodiodes (APDs) are active optoelectronic parts which are indispensable for building optical communications networks.
2. Description of Related Art
This invention does not propose such an active optoelectronic device but proposes a new passive optical device, that is, a “submount” with a filtering function. The submount is a chip base used for mounting a device chip which requires insulation from a package. The submount is an intermediate passive part between a chip and a package. A main purpose of the submount is to insulating the device from the package. Some devices need no submount (chip base). For example, an independent transistor stored in a metal package has a collector which is directly in contact with the package without a chip base. An independent diode kept in a metallic case is also directly mounted upon the metallic case without submount, since the metallic case is either an anode or a cathode.
Optoelectronic device chips of laser diodes (LDs), photodiodes (PDs) and light emitting diodes (LEDs) are diodes having an anode and a cathode. Unlike the independent metal-case stored diodes or transistors, some reasons forbid the optoelectronic device chips from adhering directly to the package. A package may include a monitoring photodiode (PD), an amplifier IC besides the laser diode (LD) or the photodiode (PD). The coexistence of various device chips prohibit the bottom electrodes (cathode in many cases) of PD chips, LED chips or LD chips from being in direct contact to the metallic package (the ground level). The bottom electrodes of the device chips should be electrically insulated from the package ground level. The “submount” is an insulating board which should be inserted between the chip bottom and the package ground level. Besides the insulation, the submount has other roles of facilitating thermal diffusion, harmonizing the thermal expansion coefficients between the chip and the package or adjusting the height of the chip. In the case of enhancing thermal diffusion, regulating the thermal expansion coefficients or controlling the chip height, the submount need not be an insulator. In the case of the devices stored in metallic packages, the submount is a passive, intermediate chip base which plays the role of keeping a device chip upon a package. The submount has metallized layers formed on both surfaces for the sake of bonding.
Recently planar lightguide circuit (PLC) type transmitting/receiving modules (LD/PD modules) attract attentions instead of the prior discrete type modules which have independent PD, LD, AMP or ICs assembled on print circuit boards. The planar lightguide circuit (PLC) type device contains a silicon bench (Si-platform), device chips, a leadframe and a resin package. The PLC module is made by fixing the device chips upon the silicon bench, fitting the silicon bench on a central part of the leadframe and enclosing the silicon bench and the leadframe with a resin. The leadframe is a thin metal plate having a central part and a number of lead pins.
The PLC type modules never fit device (PD, LD) chips directly upon the leadframe but upon the silicon bench. Sometimes the device chips are directly fitted upon the silicon bench. Other times, rectangle thin plates are inserted between the chips and the silicon bench for adjusting the height of the chips. The rectangle plates for adjusting the height are also called “submount”. The submount (chip base) has a wider concept than the insulating base. The submount is a passive optical part which is held between the silicon bench and the chip. Then, the object of the invention is called a “submount” or “optical part” which intervenes between a case and a chip.
The submount or chip base is usually a rectangular intervening plate which is directly fitted upon a case (package, silicon-bench or so) for mounting a chip thereupon. The submount (chip base) is a rectangular opaque insulator having a metallized top surface and a metallized bottom surface. The metallized layers are made by plating, evaporating or printing a metal. Bonding the submount upon a case and die-bonding a chip upon the submount require the metallization on both surfaces.
The submount basic material is opaque and the metallized layers are also opaque. The chip base is triply opaque. There has been no transparent submount. No device chip on the submount has required light entrance via the bottom from the case. High heat conductivity is also one of desired properties of the chip base (submount) for removing heat from the chip rapidly. Ceramics or other dielectric materials are chosen as a material for making submounts. Prevailing submounts are made from alumina (Al
2
O
3
). Alumina excels in rigidity, chemical stability, electrical insulation and inexpensiveness. Alumina is also opaque. There has been no requirement for transparent submounts. There is actually no transparent submount. Prevalent submounts are simple rectangular insulating plates with an m/i/m layered structure, where “m” means a metal and “i” means an insulator.
However, chip bases with an opening are seldom used for mounting a bottom incidence type photodiode upon a silicon bench of a PLC type module.
FIG. 1
shows a proposed PLC type PD portion in an LD/PD module which receives 1.55 &mgr;m wavelength light and transmits 1.3 &mgr;m wavelength light. The PD portion is fabricated upon a flat silicon bench
1
. A V-groove
2
is dug from a front end to an intermediate point upon the silicon bench
1
in a longitudinal direction. A PD chip
3
is fitted upon the silicon bench
1
above a rear end of the V-groove
2
. The PD chip
3
is a bottom incidence type PD which has a dielectric multilayered filter
5
on the bottom surface and an annular n-electrode
6
enclosing the filter on the bottom. The PD chip has a light receiving part
4
with a p-type region at the top. A frame-shaped rectangular submount
7
is soldered on a metallized pattern on the silicon bench
1
. The bottom annular n-electrode
6
of the PD
3
is soldered on the frame-shaped submount
7
having an opening. An optical fiber
8
is fitted in the V-groove
2
with an adhesive. A mirror
9
is formed at the rear end of the V-groove
2
. The signal light going out of the optical fiber
8
is reflected by the mirror
9
, is turned upward and is introduced into the PD via the dielectric multilayered filter
5
. The signal light arrives at the light receiving part
4
and produces photocurrent.
FIG. 1
shows only the PD portion. The LD/PD module contains an LD module (not shown in the figure) besides the device of FIG.
1
. The LD module and the PD module are separated by a WDM (wavelength division multiplexer) filter with wavelength selectivity. In addition to the WDM, the PD has the dielectric multilayered filter
5
on the bottom. The transmitting wavelength is 1.3 &mgr;m and the receiving wavelength is 1.55 &mgr;m. The WDM separates the 1.3 &mgr;m sending light and the 1.55 &mgr;m receiving light. However, the extinction ratio of the WDM filter is still too poor to forbid a part of the 1.3 &mgr;m light from leaking into the PD as stray light. The stray light would induce optical crosstalk in the PD module. The multilayered filter
5
is added to the PD for supplementing the WDM filter. Conventional InP PD has sensitivity to both the 1.55 &mgr;m and the 1.3 &mgr;m wavelengths. The reason why the conventional InP PD has sensitivity for both 1.55 &mgr;m and 1.3 &mgr;m.
FIG. 2
shows a section of a conventional InP PD equipped in PD modules.
FIG. 2
shows a top incidence type PD having the same layer structure as the bottom incidence type PD. The top incidence type PD differs only on the shape of the electrodes from t
Iguchi Yasuhiro
Kuhara Yoshiki
Lewis Monica
Meier Stephen D.
Smith , Gambrell & Russell, LLP
Sumitomo Electric Industries Ltd.
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