Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device
Reexamination Certificate
2000-08-08
2002-04-30
Bowers, Charles (Department: 2813)
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
C257S123000, C257S125000, C257S135000
Reexamination Certificate
active
06380565
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to making, in monolithic form, bidirectional switches of medium power.
2. Discussion of the Related Art
Conventional static bidirectional switches are triacs. A triac corresponds to the antiparallel association of two thyristors. It can thus be directly connected in an A.C. network, for example, the mains. The gate of a conventional triac corresponds to the cathode gate of one, at least, of the two thyristors forming it and is referenced on the electrode located on the front surface of this triac, that is, the surface that includes the gate terminal, while the other triac surface is typically connected to a heat sink or to the ground.
Bidirectional switches of the type described in European patent application No. 0 817 277, the triggering of which is ensured by applying a voltage between a control electrode located on the front surface of the component and a main electrode located on the opposite surface of the component, will more specifically be considered hereafter.
FIG. 1
shows an equivalent schematic diagram of such a bidirectional switch. A control electrode G of the bidirectional switch is connected to the emitter of a bipolar transistor T, the collector of which is connected to the anode gates of first and second thyristors Th
1
and Th
2
placed in antiparallel between two terminals A
1
and A
2
. Terminal A
1
corresponds to the anode of thyristor Th
1
and to the cathode of thyristor Th
2
. Terminal A
1
is also connected to the base of transistor T. Terminal A
2
corresponds to the anode of thyristor Th
2
and to the cathode of thyristor Th
1
.
FIG. 2A
is a simplified cross-section view of an example of a monolithic embodiment of the bidirectional switch described in relation with FIG.
1
. Transistor T is formed in the left-hand portion of the drawing, thyristor Th
1
at the center, and thyristor Th
2
to the right thereof. As will be seen hereafter, this does not correspond to the effective arrangement of the various components, an example of which will be given in relation with the top view of
FIG. 2B
, but is only intended for explaining the operation of the structure.
The structure of
FIG. 2A
is formed from an N-type lightly doped semiconductor substrate
1
. The anode of thyristor Th
1
corresponds to a P-type layer
2
that is formed on the rear surface side of substrate
1
. Its cathode corresponds to an N-type region
3
formed on the front surface side in a P-type well
4
. The anode of thyristor Th
2
corresponds to a P-type well
5
formed on the front surface side and its cathode corresponds to an N-type region
6
formed on the rear surface side in layer
2
. The periphery of the structure is formed of a heavily-doped P-type layer
7
extending from the front surface to P-type layer
2
. Conventionally, region
7
is obtained by drive-in from the two substrate surfaces. The rear surface is coated with a metallization M
1
corresponding to first terminal A
1
of the bidirectional switch. The upper surfaces of regions
3
and
5
are coated with a second metallization M
2
corresponding to second terminal A
2
of the bidirectional switch. An N-type region
8
is formed, on the front surface side, in a P-type well
9
in contact with peripheral region
7
. The surface of region
8
is contacted by a metallization M
3
connected to control terminal G of the bidirectional switch. A metallization M
4
may be formed on the upper surface of peripheral region
7
. Metallization M
4
is connected to no external terminal. As an alternative, well
9
may be separated from peripheral region
7
and electrically connected thereto via metallization M
4
.
The operation of this bidirectional switch is the following.
When terminal A
2
is negative with respect to terminal A
1
, thyristor Th
1
is capable of being on. If a sufficiently negative voltage with respect to metallization M
1
is applied to gate G, the base-emitter junction of transistor T is forward biased and this transistor turns on. A vertical current ic shown in dotted lines in
FIG. 2A
thus flows from metallization M
1
, through the forward junction between layer
2
and substrate
1
, then into regions
1
,
9
and
8
corresponding to transistor T. Carriers are thus generated at the level of the junction between substrate
1
and well
9
near the junction between substrate
1
and well
4
, and thyristor Th
1
is turned on. It can also be considered that an auxiliary vertical NPNP thyristor Tha including regions
8
-
9
-
1
-
2
, region
9
of which forms the cathode gate region, has been triggered.
When terminal A
2
is positive with respect to terminal A
1
, thyristor Th
2
is capable of being on. Applying a negative voltage on terminal G turns on transistor T. The carriers present in the vicinity of the junction between substrate
1
and layer
2
turn on thyristor Th
2
, as will be better understood by referring to the simplified top view of
FIG. 2B
in which it can be seen that the region corresponding to transistor T neighbors a portion of each of thyristors Th
1
and Th
2
.
As can also be seen in the top view of
FIG. 2B
, triggering transistor T (that forms a portion of auxiliary thyristor Tha) is arranged to face a portion of vertical thyristor Th
1
and a portion of vertical thyristor Th
2
. More specifically, thyristor Th
1
must be very sensitive in the vicinity of its triggering area, that is, it must include no short-circuit region between its cathode and its cathode gate. Thus, metallization M
2
, not shown in
FIG. 2B
, which is in contact with region
3
and well
5
, is in contact with region
4
in a region opposite to the triggering area only.
A disadvantage of the structure shown in
FIG. 2
is that it has a poor switching breakdown voltage characteristic in the presence of an inductive load, that is, when the conduction of the bidirectional switch is desired to be interrupted, said switch, and more specifically thyristor Th
1
, risks turning back on while its control electrode is no longer activated.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel embodiment, in monolithic form, of a bidirectional switch of the above mentioned type that has a better switching breakdown voltage, especially on an inductive load.
To achieve this and other objects, the present invention provides a monolithic bidirectional switch formed in a semiconductor substrate of a first conductivity type having a front surface and a rear surface, including a first main vertical thyristor, the rear surface layer of which is of the second conductivity type, a second main vertical thyristor, the rear surface layer of which is of the first conductivity type, and structures for triggering each of the first and second main thyristors arranged to face regions mutually distant from the two main thyristors, the neighboring portions of which correspond to a region for which, for the first main thyristor, a short-circuit area between cathode and cathode gate is formed.
According to an embodiment of the present invention, the bidirectional switch includes a first auxiliary vertical thyristor, the rear surface layer of which is of the second conductivity type and is common with that of the first main thyristor, a second auxiliary vertical thyristor, the rear surface layer of which is of the second conductivity type and is common with that of the first thyristor, the main upper surface terminals of the first and second auxiliary thyristors forming a same control terminal, a peripheral region of the second conductivity type connecting, in particular, the rear surface layer of the auxiliary thyristors to the gate layers of these auxiliary thyristors located on the other side of the substrate, a first rear surface metallization, a second front surface metallization connecting the front surface regions of the first and second thyristors.
According to an embodiment of the present invention, the bidirectional switch includes an additional region that isolates the rear surface of the first auxiliary thyristor
Duclos Franck
Ladiray Olivier
Simonnet Jean-Michel
Bhagawan Venkatesha S.
Morris James H.
STMicroelectronics S.A.
Wolf Greenfield & Sacks P.C.
LandOfFree
Bidirectional switch with increased switching breakdown voltage does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Bidirectional switch with increased switching breakdown voltage, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bidirectional switch with increased switching breakdown voltage will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2914197