Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device – Combined with field effect transistor
Reexamination Certificate
2001-02-02
2002-06-11
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
Combined with field effect transistor
C257S144000
Reexamination Certificate
active
06403988
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device having reverse conducting faculty comprising a switching element including a semiconductor substrate of a first conductivity type having first and second major surfaces, a first main electrode region of the first conductivity type formed on the first major surface of the semiconductor substrate, a second major electrode region of a second conductivity type formed on the second surface of the semiconductor substrate, and a control electrode region of the second conductivity type for controlling a current passing between the first and second main electrode regions.
2. Description of the Related Art
As a voltage supply source for a pulse laser and pulse discharge device, there has been used a voltage supply source generating a pulse having a high voltage and a large current. FIG. I shows an example of a known pulse generating circuit used as a voltage supply source for use in a pulse laser. In this pulse generating circuit, between output terminals
14
a
and
14
b
of a charging circuit
14
including a DC power sur)ply source
11
, a switch
12
and a current limiting resistor
13
, is connected a static induction thyristor
15
(herein after abbreviated as SIThy). In parallel with the SIThy
15
, there are connected resonance coil
16
and capacitor
17
. Furthermore, in parallel with the capacitor
17
are connected a capacitor
18
and a coil
19
having a large inductance, and a discharge gap
20
is connected across the coil
19
as a load.
Under a non-conductive condition of the SIThy
15
, at first the switch
12
is closed to charge the capacitor
17
through the resistor
13
and coil
16
. During this charging process, an impedance of the coil
19
at a lower frequency is low, and thus the capacitor
18
is also charged through the coil
19
. Now an output voltage of the DC power supply source
11
is denoted by E. After charging the capacitors
17
and
18
up to E, the SIThy
15
is turned-on by means of a gate driving circuit
21
. Then, charge stored in the capacitor
17
is discharged through the SIThy
15
in accordance with a resonance characteristic determined by the coil
16
and capacitor
17
, and the capacitor
17
is charged in a reverse polarity to a polarity in which the capacitor
17
is charged up to substantially −E. Charge stored in the capacitor
18
is also discharged through the SIThy
15
and coil
19
. Since an impedance of the coil
19
is very high for a high frequency, the discharge is conducted very slowly. Therefore, a voltage of about −2E will be applied across the discharge gap
20
. When a discharge occurs, charge stored in the capacitors
17
and
18
disappears by discharge at the discharge gap
20
. And the switch
12
is closed to initiate the charging operation again.
In the above mentioned pulse generating circuit, if the discharging operation is carried out correctly between the discharge gap
20
when a voltage of −2E is applied across the discharge gap, charge stored in a resonance circuit consisting of the coil
16
and capacitor
17
disappears. Therefor, as shown by a solid line in
FIG. 2
, no current flows through the SIThy
15
in the reverse direction. However, if discharge does not occur correctly due to any reason, a ringing current occurs in the resonance circuit and a large current flows through the SIThy
15
in the reverse direction as illustrated by a broken line in FIG.
2
.
FIG. 3
is a graph showing a voltage across the anode-cathode path of the SIThy
15
. When discharge does not occurs correctly, a reverse voltage is applied to the SIThy
15
. In this case, a reverse current flows from the cathode to the gate of the SIThy
15
, and this results in application of an excessive high reverse voltage like as a reverse recovery phenomenon of the diode.
In order to protect the static induction thyristor from the breakdown when the large reverse current flows through the anode-cathode path of the thyristor, it has been proposed to flow the reverse current through a diode connected in anti-parallel with the static induction thyristor. The static induction thyristor having such a diode is generally called a reverse conducting static induction thyristor. In the reverse conducting static induction thyristor, in order to make a wiring inductance as small as possible, it has been proposed to form the diode by a common semiconductor substrate together with the static induction thyristor in a preliminary thesis issued for 1999 Conference of the Electric Engineering Society by Shimizu et al., “4000V Class Reverse Conducting SI Thyristor(
1
)”.
FIG. 4
is an equivalent circuit of the above mentioned reverse conducting static induction thyristor. A diode
32
is connected in anti-parallel with a static induction thyristor (SIThy)
31
such that an anode of the diode is connected to a cathode of the SIThy and a cathode of the diode is connected to an anode of the SIThy. The anode of the diode
32
is further connected to a gate of the SIThy
31
by means of a resistor
33
, and the gate of the SIThy is connected to a gate driving circuit (GC)
34
which controls the turn-on/turn-off of the SIThy. When a main power supply source
35
is connected across the anode-cathode path of the SIThy
31
as shown by a solid line in
FIG. 4
, a current I
T
flows through the SIThy, and when a voltage supply source
36
is connected in a reverse polarity as depicted by a broken line in
FIG. 4
, a current I
R
flows through the diode
32
to protect the SIThy
31
from being breakdown.
FIG. 5
is a cross sectional view showing the structure of the above mentioned known reverse conducting static induction thyristor. In one major surface of an n
−
silicon substrate
41
there is formed a p
+
gate regions
42
, and p
+
buried gate regions
43
are formed within a channel region. A gate electrode
45
is provided on the gate region
42
via a conductive layer
45
a
. The buried gate regions
43
are formed as a comb shape to be surrounded by the gate region
42
. Above the channel region, there are formed n
+
cathode regions
46
which are electrically connected to a cathode electrode
47
via a conductive layer
47
a
. On the other major surface of the silicon substrate
41
, an anode electrode
52
is provided via a conductive layer
52
a
. In this manner, a thyristor section
44
is constructed by the gate region
42
, buried gate regions
43
, channel region, cathode regions
46
. Furthermore, a diode section
49
is formed to surround the thyristor section
44
via a separation band
48
. The diode second includes a p
+
anode region
50
and a cathode region
41
a
formed by a part of the n
−
silicon substrate
41
. The anode region
50
is electrically connected to the cathode electrode
47
of the static induction thyristor via a conductive layer
47
a
and the cathode region
41
a
is connected to an anode electrode
52
of the static induction thyristor by means of n
+
contact region
51
and conductive layer
52
a.
In the above explained reverse conducting static induction thyristor, when a reverse voltage is applied across the anode-cathode main current path, the diode section
49
is made conductive to prevent the thyristor section
44
from the breakdown. However, when the known reverse conducting thyristor is used in the above mentioned pulse generating circuit shown in
FIG. 1
, the static induction thyristor is often broken by the ringing current generated in the resonance circuit by failure of discharge. In order to investigate a mechanism of such a phenomenon, the inventors have conducted a detailed analysis about the influence of the application of the reverse voltage across the anode-cathode path of the reverse conducting static induction thyristor.
FIGS. 6
,
7
and
8
are graphs showing the operation of the static induction thyristor used in the pulse generating circuit upon occurrence of discharge failur
Iida Katsuji
Imanishi Yuichiro
Sakuma Takeshi
Shimizu Naohiro
Burr & Brown
Meier Stephen D.
NGK Insulators Ltd.
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