Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – With large area flexible electrodes in press contact with...
Reexamination Certificate
2000-09-18
2002-10-15
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
With large area flexible electrodes in press contact with...
C257S785000, C257S659000, C257S687000
Reexamination Certificate
active
06465881
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to a compression bonded type semiconductor device, such as GCT (Gate Commutated Turn-off) thyristor.
2. Description of the Background
Although a GTO (Gate Turn-OFF) thyristor has been widely used as a device for large capacity power electronics, the GTO requires a snubber circuit. Further, it is difficult to suppress an increase of snubber loss due to an increase in an operating voltage of the GTO. However, a GCT (Gate Commutated Turn-off) thyristor does not require such a snubber circuit and realizes a performance of 6000 A for a maximum breaking current and less than or equal to 3 &mgr;s for a turn-off storage time. The GCT also has an increased capacity and speed.
FIG. 3
is a cross-sectional view illustrating a background compression bonded type semiconductor device (e.g., a GCT) described in Japanese Patent Laid-Open No. Hei. 8-330572 (1996). In the figure, reference numeral
1
denotes a semiconductor substrate. An aluminum gate electrode
2
a
is formed at an outer peripheral portion on a surface of the semiconductor substrate
2
, a cathode electrode
2
b
is formed at an inside of the gate electrode
2
a
, and an anode electrode
2
c
is formed on a back surface of the substrate
2
. Also shown are a cathode distortion buffer disk
3
and an external cathode electrode
4
mounted one after another on a side of the cathode electrode
2
b
, and an anode distortion buffer disk
5
and an external anode electrode
6
mounted one after another on a side of the anode electrode
2
c
. A ring gate electrode
7
made of iron or nickel alloy contacts the gate electrode
2
a
, and a ring-shaped external gate terminal
8
made of iron or nickel alloy is electrically connected with the ring gate electrode
7
, though it is not fixed thereto. In addition, an elastic body
9
(such as a disk spring) presses the ring gate electrode
7
to the gate electrode
2
a
together with the external gate terminal
8
via an annular insulator
10
.
Further shown is an insulator
11
for insulating the ring gate electrode
7
from the cathode distortion buffer disk
3
and the external cathode electrode
4
, a first flange
12
secured to the external cathode electrode
4
, a second flange
13
secured to the external anode electrode
6
, and an insulating cylinder
14
made of ceramics or the like and which is divided into upper and lower parts. An outer periphery of the external gate terminal
8
protrudes out of a side of the insulating cylinder
14
and is hermetically secured to a divisional portion
14
a by soldering. In addition, an end portion
15
secured to the insulating cylinder
14
by soldering is hermetically secured to the first and second flanges
12
and
13
by arc welding. Thus, the GCT
1
has a closed structure and the inside is filled with an inert gas.
Next, the operation of the GCT
1
will be explained. Current flows toward the external cathode electrode
4
from the external gate terminal
8
when the GCT
1
is turned on. A gradient of rise of the gate current at this time is generally set at 1000 A/&mgr;s or more in operating the GCT
1
without a current limiting reactor and the turn-on spreading speed of the GCT
1
must be increased. While current flows toward the external gate terminal
8
from the external cathode electrode
4
when the GCT
1
is turned off, the current must be fed with the gradient of several thousands A/&mgr;s to commutate a current equivalent to the main current of the GCT
1
to the gate in about 1 &mgr;s to operate it without a snubber circuit. A contact resistance of a current feeding path from the external gate terminal
8
to the external cathode electrode
4
must be minimized to feed such a large current instantly.
While the cathode electrode
2
b
,the cathode distortion buffer disk
3
and the external cathode electrode
4
are pressed by a large force of several hundreds kg/cm
2
from outside of the GCT
1
, the gate electrode
2
a
, the ring gate electrode
7
, and the external gate terminal
8
are pressed only by the elastic body
9
. This is because the elastic body
9
is disposed at a peripheral part of the external cathode electrode
4
. Thus, the pressure at a portion A, where the external gate terminal
8
contacts the ring gate electrode
7
, is several kg/cm
2
and a contact resistance sufficient to feed the above-discussed instantaneous large power cannot be obtained.
The above-constructed background GCT
1
also has the following problems.
First, there is a case in which the external gate terminal
8
causes a waviness in a circumferential direction at the contact portion A between an inner peripheral portion of the external gate terminal
8
and the ring gate electrode
7
due to a strain caused by a thermal residual stress from soldering the external gate terminal
8
and the divisional portion
14
a
of the insulating cylinder
14
. In addition, because the external gate terminal
8
is only pressed by the elastic body
9
, the pressure at the contact portion A is several kg/cm
2
and the waviness can not be corrected. Therefore, the contact resistance of the contact portion A is greater than a desired contact resistance. That is, the contact resistance of the feeding path from the external gate terminal
8
to the external cathode electrode
4
is too large. Thus, the power feeding capability of the gate is inhibited, because the gradient of the inverse direction gate current is insufficient when the GCT
1
is turned off, for example.
Secondly, the abnormality of the contact caused by the waviness also results in a contact resistance which fluctuates within the plane of the ring-shaped external gate terminal
8
. Thus, the power feeding capability of the gate partially drops, which causes an extreme drop in the turn-off capability of the GTC
1
.
Thirdly, the GTC
1
abnormally generates heat by locally receiving electromagnetic induction from the magnetic field of an external circuit when operating at high frequencies, because iron or nickel alloy is used for the external gate terminal
8
to thereby solder with ceramics (which is the material of the insulating cylinder
14
). This problem influences the characteristics of the semiconductor substrate
2
.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to solve the above-noted and other problems.
Another object of the present invention is to provide a novel compression bonded type semiconductor device which decreases a contact resistance of a current feeding path from an external gate terminal to an external cathode electrode.
Yet another object of the present invention is to provide a novel compression bonded type semiconductor device which can suppress a fluctuation of contact resistance within the plane of the external gate terminal caused by waviness produced in the circumferential direction of the external gate terminal from occurring at a portion where the inner peripheral part of the external gate terminal contacts a ring gate electrode.
Still another object of the present invention is to provide a novel compression bonded type semiconductor device which prevents the external gate terminal from abnormally generating heat by locally receiving electromagnetic induction by the magnetic field of the external circuit when operating at a high frequency.
To achieve these and other objects, the present invention provides a novel gate electrode and a cathode electrode formed on a top surface of a semiconductor substrate, and an anode electrode formed on a back surface of the substrate. An external cathode electrode is disposed to be compression bondable to the cathode electrode and an external anode electrode is disposed to be compression bondable to the anode electrode. Also included is an insulating cylinder containing the semiconductor substrate, and an external gate terminal whose outer peripheral portion protrudes out of the side of the insulating cylinder and which is fixed to the insulating cylinder. The external gate terminal also has a protrusi
Flynn Nathan J.
Mandala Jr. Victor A.
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