JPS60106170A - Thyristor with overvoltage protective function - Google Patents

Abstract

PURPOSE:To enable to realize the titled thyristor posessing a higher resistivity of di/dt, which can be safely turned to ON and OFF against impression of overvoltage without damaging the resistivity of dv/dt of the first pilot thyristor, by a method wherein a breakdown voltage region, whose forward stopping voltage is lower than that of other regions, is provided at the inner peripheral part of the first pilot thyristor. CONSTITUTION:Breakdown current to generate by breakdown voltage runs to the lateral direction of the P type layer 23 of a first pilot thyristor PT1, and after the breakdown current ran through collectors 25 provided on the P type base layer 23, the breakdown current runs in a cathode electrdoe 37 through short-circuit parts 39 provided between the P type base layer 23 and the cathode electrode 37. As a result, the breakdown current makes a potential difference generate to the lateral resistance of the P type base layer 23 of the PT1 region and the N type emitter layer 24a of the PT1 is biased in the forward direction. When the value of voltage biased in the forward direction approaches the diffusion potential value of the junction part between the N type emitter layer 24a and the base layer 23, the injection of electrons, which are injected from the N type emitter layer 24a, is abruptly increased an the PT1 is turned-ON to overvoltage. This ON-state current of the PT1 runs to the P type base layer 32 of a second pilot thyristor PT2 as gate current through wirings 36 and the PT2 is made to turn-ON.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a thyristor with an overvoltage protection function that can safely trigger a voltage l when an overvoltage that exceeds the breakdown voltage is applied between an anode and a cathode.

[Technical background of the invention and its problems] When an overvoltage that causes a breakdown voltage is applied between the anode and cathode of a thyristor, the thyristor is destroyed by a minute breakdown current of several mA to several tens of mA. In order to prevent the element from being destroyed due to erroneous firing due to the application of overvoltage, a thyristor with a rated voltage two to three times the power supply voltage is generally used. However, in devices that use a large number of thyristors connected in series, such as thyristor valves for DC power transmission, if one of the thyristors fails to turn on, an overvoltage of several times the rated voltage or more will be applied to a small number of thyristors. Therefore, overvoltage breakdown cannot be prevented by the method of looking for a margin in the rated voltage as described above. Therefore, an external protection circuit is required to prevent the application of overvoltage. Under these circumstances, there has been a strong desire for a thyristor with an overvoltage protection function that will not break down even if an overvoltage is applied.

FIG. 1 is a schematic cross-sectional view of a thyristor previously proposed by the present inventors in order to solve such problems.

In the figure, a P emitter layer 11, an N base layer 12, a P
P with a four-layer structure consisting of a base layer 13 and an N emitter layer 14
An anode electrode 15 is provided on the surface of the emitter layer 11, and
A cathode electrode 15 is arranged on the surface of the short-circuited N emitter layer 14 to constitute the main thyristor MT. In the inner peripheral part of the main thyristor MT, the P emitter layer 11, the N base layer 12, and the P base layer 13 are shared, and an auxiliary N emitter layer 17 and an auxiliary electrode 18 are provided to form the pilot thyristor PT.
is formed. Further, a P base layer 20 having a curved portion 19 is disposed on the inner peripheral portion of the pilot thyristor PT. This structure can be achieved, for example, by removing the P base layer 13 by etching into a well shape, and then thermally diffusing P type impurities again.
This can be realized by forming the base layer 20, etc. Alternatively, a similar structure can be obtained by etching an N-type wafer into a well shape and diffusing P-type impurities from both sides thereof. Furthermore, in this 4R construction, the auxiliary N emitter layer 17 of the pilot thyristor PT is formed by diffusion deeper than the N emitter layer 14 of the main thyristor MT, thereby greatly increasing the lateral resistance of the P base layer of the pilot thyristor PT.

In such a structure, when an overvoltage is applied in the forward direction between the anode and cathode electrodes, the electric field concentrates on the curved part 19, and the breakdown current generated near the curved part 19 causes the pilot thyristor PT and the main thyristor MT to
are turned on sequentially.

According to experiments conducted by the inventors, the conditions for safely turning on the pilot thyristor due to forward breakdown current generated by overvoltage are as shown in FIG. In the figure, the horizontal axis is the breakdown current IR when voltage triggered, which is the minimum gate trigger current (■) of the pilot thyristor PT. The value is equal to ■. The vertical axis represents the di/dt tolerance of each test sample with respect to the breakdown current (=1°) upon voltage triggering. As is clear from the figure, a thyristor having a high-sensitivity pilot thyristor with a small IGT has a large amount of old /dtit when the voltage is triggered. But I. For any thyristor with a pilot thyristor that draws 45 mA, the di/dti1 amount suddenly drops and voltage triggering becomes impossible. In the test sample used in the experiment, this is I
This is because when R>45 mA, the bending portion 19 exceeds the allowable breakdown current value, and the bending portion 19 is destroyed before the pilot thyristor PT is turned on.

As described above, in order to safely turn on the thyristor when an overvoltage is applied to the thyristor, the gate sensitivity of the pilot thyristor PT must be increased.

However, when the gate sensitivity of the pilot thyristor is increased, the thyristor becomes more likely to malfunction when a noise voltage with a high voltage increase rate is applied to the thyristor. In other words, d
v/dt tolerance decreases. Therefore, with the conventional structure, there is a limit to increasing the gate sensitivity of the pilot thyristor PT, and it has been difficult to significantly improve the di/dt tolerance.

[Objective of the Invention] The present invention has been made in consideration of the above circumstances, and its purpose is to provide a high DI that can be turned on safely against the application of overvoltage without impairing the dv/dt withstand capability.
An object of the present invention is to provide a thyristor with an overvoltage protection function having a /dt withstand capability.

[Summary of the Invention] The present invention provides a plurality of pylons 1 to thyristors arranged so as to be surrounded by current collecting electrodes formed on a base layer, and a plurality of pylons 1 to thyristors arranged on the base layer surrounded by the emitter layer of the pilot thyristors, respectively. The gate electrode of each of these pilot thyristors is sequentially electrically connected to the emitter electrode provided on the emitter layer of the pilot thyristor in the previous stage, and the emitter electrode of the pilot thyristor in the final stage is connected to the collector electrode. The present invention is characterized in that it is configured to be common, and that a voltage breakdown region in which the forward blocking voltage is lower than other regions is provided in the inner peripheral portion of the first batch-rot thyristor.

[Effects of the Invention] According to the present invention, it is possible to increase the gate sensitivity of the pilot thyristor without reducing the dv/dt withstand capability, so that the di/dt withstand capability can be significantly improved, and when an overvoltage is applied, the thyristor can be turned on safely. In addition, in the present invention, since the on-current of the pilot thyristor in the previous stage is suppressed by the P base resistance of the pilot thyristor in the latter stage, the inrush current flowing to the first pilot thyristor at the early stage of turn-on is significantly reduced, and the di/d
The withstand capability is further improved and the safety during overvoltage turn-on is increased.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings. 3 and 4 show the configuration of a thyristor according to an embodiment of the present invention, and FIG. M3 is a plan view thereof, and FIG.
The figure is a sectional view thereof.

P emitter layer 21, N base layer 22, P base layer 23,
A collector electrode 25 is formed on the surface of the P base layer 23 adjacent to the N emitter layer 24f of the main thyristor MT, which is made up of four stacked semiconductor layers of the N emitter layer 24f. A plurality of pilot thyristors are formed. Here, a total of five pilot thyristors PTs, from the first pilot thyristor PT1 to the fifth pilot thyristor PTs whose emitter electrode is shared with the current collecting electrode 25, are shown.
pilot thyristors P'' [t~PTs are formed.A main thyristor MT
is formed. The first pilot thyristor PT1 is
An N emitter layer 24a is formed in an annular shape, and on its surface,
It is configured by arranging an emitter electrode 27. In addition, the second to fifth pilot thyristors PT2 to PTs are P
N emitter layers 24b, 24c, 24d, and 24e are formed in the base layer 23, surrounded by the current collecting electrode 25, and these N emitter layers 24b, 24c.

Emitter electrodes 28°29 on 24d, 24e, respectively.
．． 30 and 31, and gate electrodes 32, 33, 34, and 35 are also formed on the P base layer 23. Among these, the emitter electrode 31 of the fifth pilot thyristor PTs is shared with the current collecting electrode 25. Therefore, the pilot thyristors PT2, P of each stage
T3, PT4.

Each gate electrode 32, 33, 34, 35 of the PTs is connected to the pilot thyristor PT1゜PT2, PT of the previous stage, respectively.
3.Each emitter electrode of PT4 27゜28.29.30
They are sequentially electrically connected to each other by lead wiring 36 such as a single wire.

Further, a P base layer 41 having a curved portion 40 on the inner peripheral portion of the first pilot thyristor PTI is formed by the method explained in FIG. 37 is a cathode electrode, 38 is an anode electrode, and 39 is a P base short circuit.

FIG. 5 shows the equivalent circuit of this thyristor. In the figure, Cj is the junction capacitance of the central junction J2, and D1 to D5 are the first
~Fifth pilot 1~Thyristor N emitter 24a~2
4e and P base 23; DM is a diode consisting of N emitter 24f of the main thyristor between collector electrode 25 and short circuit 39 and P base 23; R1
-R5 represents the lateral resistance of the P base layer 23 of the first to fifth pilot thyristors, and RM represents the lateral resistance of the P base layer 23 of the main thyristor located between the current collecting electrode 25 and the short circuit portion 39. Further, A is an anode electrode 38, K is a cathode electrode 37, and is a current collecting electrode 25.

Now, when a forward overvoltage is applied between the anode electrode 38 and the cathode electrode 37 of the present thyristor configured in this manner, the electric field is concentrated at the curved portion 40 and a voltage drop occurs. A breakdown current IR generated by this voltage breakdown flows laterally through the P base layer 32 of the first pilot thyristor PT1,
After passing through the current collecting electrode 25 provided on the P base layer 23, P
It flows into the cathode electrode 37 via a short circuit 39 provided between the base layer 23 and the cathode electrode 37.

As a result, a potential difference is generated in the lateral resistance of the P base layer 23 in the breakdown current IRtJ of the first pilot thyristor PT area, and the N emitter layer 24a of the first pilot thyristor PTI is biased in the forward direction. When this forward bias voltage level approaches the diffusion potential value of the junction between the N emitter layer 24a and the P base layer 23, the injection of electrons from the N emitter layer 24a increases rapidly, and the first pilot thyristor PT1 turns on overvoltage. The on-current of the first pilot thyristor PTl flows as a gate current to the gate electrode 32 of the second pilot thyristor PT2 via the wiring 36, and
Turn on 2.

Similarly, the third to fifth pilot thyristors PT3~
The PTs are turned on sequentially. The turn-on current of the fifth pilot thyristor PTs flows from the current collecting electrode 25 to the cathode electrode 37 via the short-circuit portion 39 as the gate current of the main thyristor MT, turning on the main thyristor.

In addition, in this thyristor, each pilot thyristor PTi~
In the process of turning on the PTs, the pilot thyristor in the preceding stage (the first pilot thyristor is the preceding stage to the second pilot thyristor, and similarly, the PT2
, PTs with respect to PT4, PT4 with respect to PTs in the previous stage) flows to the gate electrode of the pilot thyristor in the latter stage, a potential difference is generated in the lateral resistance of the P base layer 23 of the pilot thyristor in the latter stage, It functions to forward bias the N emitter layer of the pilot thyristor in the previous stage and reverse bias the N emitter layer of the pilot thyristor in the preceding stage. For this reason, this previous stage N
The injection of electrons from the emitter layer is suppressed, which works to suppress the rapid outflow of on-current. As a result, the first pilot thyristor PT, which has a narrow initial firing region at the early stage of turn-on,
The inrush current flowing through 1 can be significantly reduced.

Next, the case where a large noise voltage of dv/dtli is applied to this thyristor will be considered with reference to FIG. When a noise voltage is applied between A and Cj shown in the figure, a displacement current is generated at Cj. This displacement current is caused by the lateral resistance R1 of the P base layer 23 of each pilot thyristor PTI to PTs.
After passing through R5, the current flows to the cathode electrode 37 via the current collecting electrode 25 and the short circuit portion 39. At this time, the displacement current is R1-R
5, a voltage drop of V1 to 5 is generated, and D1 to D5 are biased in the forward direction. The bias voltages applied to D1 to D5 are each V. 1. VO2, VO2゜Vo+, Voi
Then, it becomes as follows.

Vot=VI V2 = (R1-R2) -Cj -dv/dtVo 2
=V2-V3 = (R2-R:l) -Cj -dv/dtVo
3 = V3-V4 = (R3-R4) ・Cj -dv/dtVo 4
=V4-V5=(R4-Rs) ・Cj-dv/dtVos
=Vs =Rs ・Cj -dv/dtThis ■. 1~
When any value of Vos exceeds the diffusion potential of D1 to D5, the injection of electrons from the N emitter layer rapidly increases, and this thyristor turns on dv/dt. The dvl dt value of the noise voltage at this time becomes the dvl dt resistance of this thyristor. Here, Vot+Vo 21 Vo 3+ Vo
The value of 4 is V. If R1-R5 is designed to be equal to 5, (R1-R2) = (R2-R3) = (R
B −R4) = (R4−Rs), and R1=5
Rs, R2=4Rs.

R3=3Rs and R4=2Rs. That is, the dvl dt'#4m of this thyristor is determined by the setting of the lateral resistance R5 of the P base layer 23 of the fifth pilot thyristor PT S, and the lateral resistance R1 of the P base layer 23 of the first pilot thyristor PT1 is determined by the setting of the lateral resistance R1 of the P base layer 23 of the first pilot thyristor PT1. It can be multiplied by 5 times.

The gate sensitivity of the first pilot thyristor PT1 at this time is the dvl dt tolerance value of this thyristor.
5 of the gate sensitivity of the conventional thyristor, which is equal to the withstand value.
It's double.

As explained above, according to the thyristor of this embodiment, dv
Since the gate sensitivity of the pilot thyristor can be greatly increased without impairing the l dti41, and the inrush current of the pilot thyristor at the initial stage of turn-on can be reduced, di/dtilit can be significantly improved.

Therefore, it is possible to provide a thyristor with an overvoltage protection function that can be safely turned on when overvoltage is applied.

To give a specific example, a curved part 40 with a diameter of 0.5M is provided on the inner circumference of the first pipe thyristor, and the gate sensitivity is set to I.

■ When set to = 1.5mA, dvl dt tolerance is 3000
V/, czs or more, di/dt is 3 from an overvoltage of 6kV
It was possible to turn on safely at 00A/μS or more.

In this embodiment, an example has been described in which the P base layer 41 having the curved portion 40 is provided as the voltage breakdown region, but this voltage breakdown region may be provided by other methods. For example, a method may be used in which a part of the N base layer protrudes into the P base layer and a curved portion is provided at a part of the junction, or a method in which the impurity concentration or carrier lifetime of the N base layer is made larger than in other regions. But that's fine. Further, the number of pilot thyristors and their arrangement are not limited to the embodiments. In short, P
In the thyristors in which a plurality of pilot thyristors are arranged so as to be surrounded by current collecting electrodes provided on the base layer and electrically connected in sequence by the method described above, the breakdown voltage value is set at the inner circumference of the first pilot thyristor. It is only necessary to provide an area lower than the area of . Furthermore, in the thyristor of the present invention, it is also possible to turn on the thyristor by irradiating an optical trigger signal near the exposed portion of the P base in the region of the first pilot thyristor, or to turn it on by providing a gate electrode and using an electric trigger or signal. It is.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional thyristor, FIG. 2 is a diagram showing the relationship between gate sensitivity and di/dt tolerance, FIG. 3 is a plan view of an embodiment of the present invention, and FIG. 4 is a cross-sectional view thereof. Figure 5 is its equivalent circuit diagram. MT... Main thyristor, PTr~PTs... Pilot thyristor, 21... P emitter layer, 22.
...N base layer, 23.41...P base layer, 24a
~24f...N emitter layer, 25...Collecting electrode, 4
0...Curved portion.

Claims (1)

[Claims] (1) A base layer of a main thyristor consisting of four semiconductor layers laminated with alternating conductivity types shares three semiconductor layers other than the emitter layer of the main thyristor. In a thyristor in which the emitter layers of a plurality of pilot thyristors are formed to have the same conductivity type as the emitter layer of the main thyristor, each of the pilot thyristors is provided on a base layer adjacent to the emitter layer of the main thyristor, a current collecting electrode. A gate N pole is formed on the base layer which is arranged inside the pilot thyristor and surrounded by the emitter layer of each pilot thyristor, and the gate electrode of each of these pilot thyristors is sequentially provided on the emitter layer of the preceding pilot thyristor. The emitter electrode of the final stage pilot thyristor is electrically connected to the emitter electrode of the pilot thyristor in the final stage, and the emitter electrode of the final stage pilot thyristor is shared with the current collecting electrode. A thyristor with an overvoltage protection function, characterized by having a voltage breakdown region where the blocking voltage value is lower than other regions. (a) In the region of low voltage breakdown, part of the P base layer is
2. The thyristor with an overvoltage protection function according to claim 1, wherein the thyristor has a curved portion protruding into the base layer and provided at a part of the junction thereof. (3) The thyristor with an overvoltage protection function according to claim 1, wherein a first pilot thyristor among the plurality of pilot thyristors is driven to fire by a light 1 to RIGA signal. (4) The thyristor with an overvoltage protection function according to claim 1, wherein the low voltage breakdown region is configured to have a longer N-based carrier lifetime than other regions. (5) The low voltage breakdown region is constructed by protruding a part of the N base layer into the P base layer and providing a curve in a part of the junction thereof. Thyristor with overvoltage protection function as described in . (6) The thyristor with an overvoltage protection function according to claim 1, wherein the region where the voltage breakdown is low is configured to have a higher N-based impurity concentration than the other regions.