Active solid-state devices (e.g. – transistors – solid-state diode – Physical configuration of semiconductor – Mesa structure
Reexamination Certificate
2002-08-01
2004-12-14
Ho, Hoai (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Physical configuration of semiconductor
Mesa structure
C257S675000, C257S706000, C257S707000, C257S796000, C438S122000, C438S123000, C438S125000
Reexamination Certificate
active
06831351
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device comprising first and second semiconductor chips which are contained in a single package and at least one of which is formed by using a wide gap semiconductor (such as silicon carbide or gallium nitride) as the base material. The following description of the present invention centers mainly on semiconductor devices for use in high voltage applications; however, the present invention is not limited to such power semiconductor devices but could be used with any kind of semiconductor devices.
2. Description of the Background Art
In applications to voltage-source inverters, in general, a switching chip having switching capability and a circulating diode chip are connected in inverse-parallel with each other.
FIG. 9
is a longitudinal cross-sectional view illustrating the configuration of a conventional module element
400
for use in voltage-source inverters. Active elements of the module element
400
each are formed by using silicon as the base material. That is, a switching chip
401
and a diode chip
402
contained in a closed container
417
are both made of silicon. The switching chip
401
has a cathode electrode
403
and a control electrode
404
formed on the front surface and an anode electrode
405
formed on the rear surface. The diode chip
402
has an anode electrode
406
formed on the front surface and a cathode electrode
407
formed on the rear surface. The anode electrode
405
of the switching chip
401
and the cathode electrode
407
of the diode chip
402
are electrically connected to each other by being soldered to a conductive plate
408
by a solder layer
409
. The cathode electrode
403
and the control electrode
404
of the switching chip
401
are connected respectively to a cathode conducting bar
410
and a control conducting bar
411
by a bonding wire
413
, and the anode electrode
406
of the diode
402
is connected by the bonding wire
413
to the cathode conducting bar
410
. The conductive plate
408
is connected through an insulating substrate
414
to a heat sink
415
having cooling capability. Also, the conductive plate
408
is electrically connected through a metal body
416
to an anode conducting bar
412
.
In this configuration, heat generated by the energy losses of the chips
401
and
402
can be dissipated from their respective rear electrodes
405
and
407
to the outside through the path formed of the solder layer
409
, the conductive plate
408
, the insulating substrate
414
and the heat sink
415
.
However, in the configuration of the conventional module element
400
illustrated in
FIG. 9
, since the switching chip
401
and the diode chip
402
are both electrically and mechanically connected to the conductive plate
408
, even the use of the low-loss wide gap semiconductor for production of the switching chip
401
and/or the diode chip
402
can achieve neither simplification of an element cooling mechanism nor significant reductions in the size and weight of the closed container
417
or the module element
400
itself. Accordingly, even if the chips in the module element with the configuration of
FIG. 9
are replaced by wide gap semiconductor chips, reductions in the cost of the semiconductor device cannot be achieved.
SUMMARY OF THE INVENTION
The present invention has been made to solve the aforementioned conventional problems and an object thereof is to achieve significant simplification of an element cooling mechanism by providing a way to locate a semiconductor chip in a position where in the conventional module element having active elements formed of only semiconductor chips using silicon as the base material, the chips cannot be placed for reasons of the design of heat dissipation. Another object of the present invention is to achieve reductions in the size, weight and cost of a module element having a wide gap semiconductor chip.
According to an aspect of the present invention, the semiconductor device includes a heat sink, an insulating substrate, a conductive plate, a first semiconductor chip, a second semiconductor chip and a container. The heat sink has a bottom surface exposed to the outside and an upper surface opposed to the bottom surface. The insulating substrate is jointed to the upper surface of the heat sink, and the conductive plate is jointed to an upper surface of the insulating substrate. The first semiconductor chip has a first main electrode electrically connected through a first conductive layer to an upper surface of the conductive plate, and a second main electrode opposed to and having a smaller area than the first main electrode. The second semiconductor chip has a first main electrode electrically connected through a second conductive layer to and having a smaller area than the second main electrode of the first semiconductor chip, and a second main electrode opposed to the first main electrode. The container encloses the heat sink except an exposed portion of the bottom surface, the insulating substrate, the conductive plate, the first semiconductor chip and the second semiconductor chip in its interior space. A portion above the second main electrode of the second semiconductor chip is the interior space of the container, and a base material of the second semiconductor chip is a wide gap semiconductor having a greater interband energy gap than silicon.
The second semiconductor chip can, without decline of its capabilities, be placed in a position farther from an element cooling mechanism formed of the heat sink, the insulating substrate and the conductive plate (i.e., in a position where a silicon semiconductor chip cannot be placed for reasons of the design of heat dissipation), as compared with the first semiconductor chip. Further, the second semiconductor chip can be cooled indirectly through the first semiconductor chip. This achieves simplification of the element cooling mechanism. With the simplified element cooling mechanism, the aspect of the present invention can achieve reductions in the size, weight and cost of the semiconductor device. Besides, the aspect of the present invention can reduce the size of the second semiconductor chip by using a wide gap semiconductor chip as the second semiconductor chip, thereby further reducing the size of the semiconductor device.
According to another aspect of the present invention, the semiconductor device includes a heat sink, an insulating substrate, a conductive plate, a first semiconductor chip, a metal base, a second semiconductor chip and a container. The heat sink has a bottom surface exposed to the outside and an upper surface opposed to the bottom surface. The insulating substrate is jointed to the upper surface of the heat sink, and the conductive plate is jointed to an upper surface of the insulating substrate. The first semiconductor chip has a first main electrode electrically connected through a first conductive layer to a first surface portion of an upper surface of the conductive plate, and a second main electrode opposed to the first main electrode with respect to a first direction which is equivalent to a direction of a normal to the upper surface of the conductive plate. The metal base includes a first portion and a second portion. The first portion has a first end which is electrically connected through a second conductive layer to a second surface portion of the upper surface of the conductive plate adjacent to the first surface portion, and extending from the first end to a second end in the first direction, and the second portion is coupled to the second end of the first portion and extends in a second direction orthogonal to the first direction so as to form an L-shape with the first portion. The second semiconductor chip has a first main electrode electrically connected through a third conductive layer to an upper surface of the second portion of the metal base, and a second main electrode opposed to the first main electrode with respect to the first direction. The container encloses the heat
Hirao Masayoshi
Matsuo Kazushige
Satou Katsumi
Tooi Shigeo
Ho Hoai
Tran Long
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