Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package
Reexamination Certificate
1999-12-27
2002-06-11
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
C257S930000, C257S706000, C257S707000, C257S712000
Reexamination Certificate
active
06404042
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to subcarrier structures and semiconductor devices. More particularly but not exclusively, this invention relates to subcarrier structures for use in immovably mounting a variety of types of semiconductor elements including but not limited to semiconductor lasers, which are preferably adapted to be built in Peltier cooler-associated optical semiconductor modules. The invention also relates to semiconductor devices employing such subcarriers.
Electronic component support structures or packages called “subcarriers” are typically employed to immovably mount a wide variety of types of semiconductor elements including semiconductor lasers and transistors or else. The subcarriers are required to make use of a certain material with preselected thermal expansion coefficient for suppression or “moderation” of possible thermal distortion in view of longevity of a semiconductor element used. It is also required that the material be excellent in thermal conductivity to facilitate or “accelerate” outward escape of heat radiated from semiconductor elements toward an outer housing or package enclosure with increased efficiency. The subcarriers include those using optical semiconductor elements, such as for example semiconductor lasers or light-emitting diodes (LEDs) or else, some examples of which will be described below.
Most optical semiconductor elements are variable in characteristics with a change in temperature. Accordingly, in those optical conductor modules as required to offer constant characteristics, a subcarrier that mounts one or more semiconductor elements as used therein is likewise required to let these elements remain constant in temperature during operations. To do this, the subcarrier is designed to employ cooling means. In case the optical semiconductor elements are in high-speed modulation modes, it will also be required that electrical lead wiring be done by use of a specific strip line pattern which has a prespecified impedance value and is formed to extend up to “nearby” portions of such optical semiconductor elements.
During such modulation operations the subcarrier can experience creation of electrical capacitance between the Earth or ground plane of a optical semiconductor element on the subcarrier and the underlying Peltier cooler, which would affect modulation signals. The higher the signal transmission frequency, the greater the influence. Thus, at higher transfer frequencies, the subcarrier should be arranged so that the capacitance stays less in value. One prior known approach to reducing the ground-to-cooler capacitance is to increase the thickness of the subcarrier as rigidly mounted on the Peltier cooler.
Another problem faced with the related art subcarrier structure lies in its limited cooling/heating abilities. This would result in limitation of temperature differences between the optical semiconductor element and its outside atmosphere. To achieve increased temperature differences therebetween, it is required to minimize heat radiation and absorption or thermal exchange relative to the subcarrier held on the Peltier cooler. This also leads to improvements in efficiency.
See Fig
7
. This figure of drawing illustrates, in cross-section, one related art modulator-associated optical semiconductor laser diode module, also known as electroabsorption modulator laser (EML) module among those skilled in the art to which the invention pertains. The module contains a subcarrier as mounted therein. At part (a) of this drawing, there is depicted a planar sectional view of the EML module whereas part (b) shows its side view in cross-section. In FIGS.
7
(
a
)-(
b
), reference numeral “
71
” designates an EML chip; numeral
72
denotes a subcarrier for rigid attachment of the EML chip;
73
indicates a thermistor for detection of the temperature of the EML chip;
74
shows a photodiode (PD) chip for detection of the amount of light intensity as emitted from the EML chip;
75
is a sub-mount member for fixation of the PD;
76
, a glass window as immovably attached to a PKG
81
for permitting outward radiation of light from the EML chip;
78
, a metal plate for tightly jointing said lens holder and subcarrier together;
79
, a lens for collection of light from the EML chip;
80
, a lens holder made of a metallic material for fixation of said lens
79
;
81
, a package (PKG) of the EML module;
82
, a Peltier cooler for temperature control of the EML chip;
83
, electrical leads of the PKG
81
;
84
, bonding wires of gold (Au) for electrical interconnection with the leads
83
;
85
, a terminate end resistor at which more than one terminate-end resistor of the modulator in the EML chip is formed;
87
, an isolator for use in preventing production of return light from the outside;
88
, a coupling lens for introducing light emitted from the EML into an optical fiber;
89
, optical fiber;
90
, ferrule holder for securing the optical fiber
89
to isolator
87
; and,
91
, link plate (bridge) as formed in the PKG for fixation of the PD sub-mount.
The EML chip
71
is mounted with its junction facing up side. The EML
71
includes a laser unit consisting essentially of a semiconductor laser diode (LD) and also an optical modulator unit for modulation of the intensity of light emitted from the former. The subcarrier
72
for rigidly supporting this EML chip
71
is made of an electrically insulative material with good thermal conductivity, such as for example aluminum nitride (AlN) ceramics. The subcarrier
72
has its top surface on which several electrodes are provided, which include an electrode for fixation of the EML chip
71
, 50-Ohm microstrip line pattern for use in inputting electrical signals to the modulator unit of the EML chip
71
, more than one electrode for electrical connection to the thermistor, and electrode(s) for electrical connection to the laser unit of EML chip
71
.
In the EML module thus arranged, light emitted from the EML element
71
is collected by the condensing lens
79
and is then optically guided to pass through the glass window
76
attached to the PKG
81
and next penetrate inside of the isolator
87
to finally reach the optical fiber
89
via the coupling lens
88
.
Note that the characteristics of the EML element
71
can vary with changes in temperature. In view of this, the EML module is designed so that the thermistor
73
is operable to detect the temperature of EML chip
71
for rendering the Peltier cooler
82
operative by using temperature adjuster circuitry, not shown, to thereby control the temperature of EML element
71
.
Also note that transmission signals are sent to the EML element
71
by the 50-Ohm strip line pattern on a microstrip substrate. Unfortunately, certain electrical capacitance can take place between the electrodes formed on the surface of the subcarrier
72
and its associated Peltier cooler. Thus, in order to suppress influence of such capacitance with respect to transmission signals, it is required that the subcarrier
72
be designed to have an increased thickness at a specified value or greater. In practical implementation, transmitting signals at 10 Gbits per second (Gbps) requires the subcarrier
72
to measure in thickness approximately 2 millimeters (mm) or more.
EML modules are such that the outside air temperature is often variable due to the fact that these modules are to be installed for usage under a variety of kinds of environments. In addition, current is injected into the laser unit of the EML element resulting in generation of heat due to its inherent internal resistivity, which in turn causes the element to increase in temperature. The EML element's characteristics will change as the temperature changes. It is thus required that the EML be used with its temperature made constant during operation thereof. To this end, the EML module is designed so that the thermistor
73
detects the temperature of such EML element to generate a detection signal, which is used to appropriately adjust the cooling/heating performance
Furuyama Hideo
Morinaga Motoyasu
Sone Minoru
Tanioka Akira
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Lee Eddie
Nguyen Joseph
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