JPS5989462A - Thyristor - Google Patents

Abstract

PURPOSE:To increase photo sensitivity and a di/dt capability by arranging a plurality of pilot thyristors so as to be surrounded by current collecting electrodes formed to a base layer and connecting the gate electrodes of each pilot thyristor to the emitter electrodes of the thyristors at preceding stages in succession. CONSTITUTION:The current collecting electrodes 25 are formed to the surface of a P base layer 23 adjoining to the N emitter layers 24f of the main thyristor MT consisting of a semiconductor layer on which four of a P emitter layer 12, an N base layer 22, the P base layer 23 and the N emitter layers 24f are laminated, and a plurality of the pilot thyristors are formed surrounded by the current collecting electrodes 25. The pilot thyristors are formed by five thyristors from the fifth pilot thyristors PT5, the emitter electrode thereof is shared together with the current collecting electrode 25, from the first pilot thyristor PT1 with a light-receiving section 26. The gate electrodes of these each pilot thyristor are connected electrically to the emitters of the thyristors at preceeding stages in succession.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a thyristor with increased di/dt resistance and high sensitivity.

[Technical background of the invention and its problems]

As the capacity and voltage of power conversion devices such as thyristor valves for DC power transmission become larger and higher, there is a strong demand for replacing the thyristors in use with optically triggered thyristors. When using a light-triggered thyristor in a high-voltage power odor change device,
Since electrical isolation between the main circuit and control circuit is improved and countermeasures against inductive disturbances are facilitated, the equipment can be made significantly smaller and lighter.

However, the optical trigger energy that is currently available is weaker than the electrical trigger energy, so the optical sensitivity of the optical trigger thyristor is compared to the gate sensitivity of the electrically triggered thyristor.
In terms of this, it was necessary to increase the size by several tens of times. in general,
When the gate sensitivity of a thyristor is increased, the thyristor becomes more likely to malfunction due to voltage noise with a steep rise that enters from the main circuit side, such as lightning surges.

d is the allowable voltage increase rate that will not cause malfunction even if overvoltage is applied.
It is called v/dt tolerance. Reduce the area of the light receiving part,
If the displacement current generated in this part is reduced, the dv/dt tolerance can be increased without sacrificing photosensitivity, but if the light receiving area is reduced, the conduction area at the early stage of turn-on will be reduced, resulting in a steep rise at the early stage of turn-on. The withstand capacity (di/at, withstand capacity) with respect to the rising on-current decreases.

An important technical challenge is to realize a photo-triggered thyristor with high photosensitivity without sacrificing major thyristor characteristics such as dv/dt and di/dt tolerance.

FIG. 1 shows a cross-sectional view of a typical optically triggered thyristor.

Four semiconductor layers of different conductivity types are formed on a semiconductor wafer such as silicon, where I is called a P emitter layer, 2 is called an N base layer, 3 is called a P base fi, and 4 is called an N emitter layer. There is. In the center of the semiconductor wafer, a pilot thyristor consisting of an N emitter layer 4a is disposed in a circular shape, and in the center, a light receiving part 5 is formed with the P base layer 3 exposed.
It is said that An electrode 5a made of a vapor-deposited layer of aluminum or the like is formed on the N emitter layer 4a. A main thyristor L is formed in a circular shape corresponding to the pilot thyristor, and a cathode electrode 5b is deposited on the N emitter 4b of the main thyristor L. A short circuit portion 7 is provided in the N emitter layer 4b, and the P base layer 3 and the cathode electrode 5b are short-circuited at a predetermined interval. A dv/dt compensation electrode 8 is provided on the outer periphery of the main screen, and the dv/dt compensation electrode 8 is electrically coupled to the electrode 5a by a conductor 9. P emitter 1 threat
An anode electrode 6 made of a metal such as tungsten is attached by a method such as an alloy method.

When an optical trigger signal with a certain amount of light is irradiated to the light receiving part 5 of the optical trigger syringe configured in this way, N
Photocurrent Iph mainly generated in the depletion layer regions on both sides of the central junction J2 formed by the base layer 2 and the P base layer 3
begins to flow. The photovoltaic power plant ph shown by the broken line in Figure 1
flows laterally through the P base layer 3, passes through the short-circuit section 7 provided in the main thyristoro, and the cathode electrode 5b, and is then applied to the load 12.
and flows to an external circuit consisting of a power supply 13.

The voltage drop v1 generated across the P base lateral resistance R□ of the P base layer 3 through which the photocurrent Iph flows biases the junction J consisting of the P base layer 3 and the N emitter layer 4a in the forward direction. When the voltage v1 at the inner peripheral part 4a' of the deepest N emitter 4a with a 1 sail bias becomes larger than the diffusion potential of J3, the injection of electrons from the 4a' part increases rapidly, and the pilot thyristor 10 injects light from the 4a' part. Turn on. This turn-on current Ip is 4a-5e--9-8-3-7
-5b and flows out to the external circuit. Ip functions as a gate current for the main thyristor U, and Ip turns on the main thyristor U, which turns on the original trigger thyristor. As is clear from the above explanation, the photosensitivity of the phototriggered thyristor is determined by the P base lateral resistance R
1, and the larger R1 is, the higher the photosensitivity becomes.

Next, consider a case where voltage noise with a sudden and hard rise is applied between the anode electrode 6 and the cathode electrode 5b of the photo-triggered thyristor. When a photo-trigger signal is irradiated to the light-receiving section, and voltage noise is applied between the anode electrode 6 and the cathode electrode 5b of the photo-trigger thyristor, the displacement current Id flows through the entire junction area of the photo-trigger thyristor.

If the junction capacitance of the central junction J2 directly below the light receiving part is C1, the displacement current Id flowing through C1 is the junction N C2
The displacement current Id2 flowing through the main thyristor 1 flows through a short circuit 7 provided in the main thyristor 1. The equivalent circuit of the original trigger thyristor at this time is shown in FIG. Point A corresponds to the cathode electrode 5b. Pilot thyristor 1
The bias voltage Vj of the diode D consisting of the N emitter layer 4a of 0 and the P base layer 3 is the voltage v across R1 and R2;
, v,' can be expressed as the difference v1'-■2'.

When the value of V j = Vr - V2' crosses the diffusion potential of J3, the pilot thyristor 10 triggers (dv/dt).

In this case, by adjusting the value of R2 and keeping the Vj O value low, J will not be forward biased even if voltage noise is applied.
<No, the dv/dt resistance of the pilot thyristory is R.
It is possible to improve the relationship to a value of 1.

By the above-described method, the conventional photo-triggered thyristor has been designed to improve the photosensitivity and the dv/dt tolerance.

However, conventional optically triggered thyristors have the following drawbacks.

That is, in conventional optical trigger thyristors, increasing R1 and R2 increases the light sensitivity and dv/dt tolerance by using the effect of the dv/dt compensation electrode, but this is unnecessary [increasing R2 causes the main thyristor The gate sensitivity of
There was a problem in that the dv/dt tolerance of the main thyristoro was reduced. As is clear from the equivalent circuit in FIG. 2, R2 is equal to the P base layer resistance R2/ below the groove 14 in FIG. Since the bias pressure of the junction J3' formed by the N emitter 4a' and the P base layer 3 is determined by R, //, the trench 14 is deepened and R2'
By increasing the value of R2, the light sensitivity of the pilot thyristor can be increased without reducing the dv/dt tolerance of the main thyristor. However, the gate sensitivity of the main thyristor U is reduced, so the pilot There was a problem in which the turn-on of the main thyristaro was delayed compared to the turn-on of the thyristari. As a result, the on-current of the first light turn-on is concentrated on the pilot thyristor, di/at,
My tolerance level is about to drop to 1 level. In this way, dv/d
Conventional thyristors have limitations in improving photosensitivity without changing t, di/dt tolerance.

[Object of the invention] The present invention was made in consideration of the above circumstances, and
The purpose of this is to improve light sensitivity (gate sensitivity) and di
An object of the present invention is to provide a highly practical thyristor with significantly improved /dt tolerance.

[Keystone of invention]

In the present invention, a plurality of pilot thyristors are arranged so as to be surrounded by current collecting electrodes formed on a base layer, gate electrodes are respectively formed on a pace layer surrounded by an emitter layer of the pilot thyristors, and each of these pilot thyristors is The gate electrodes of the thyristors are successively connected to the emitter electrodes of the pilot thyristors in the previous stage, and the emitter electrode of the pilot thyristor in the final stage is shared with the current collecting electrode to prevent leakage current and overvoltage. It is characterized in that the cathode emitter bias voltage of the final stage of the pilot thyristor, which is generated by the displacement current accompanying the application, and the cathode emitter bias voltages of the other pilot thyristors are made smaller or equal to each other.

〔Effect of the invention〕

According to the present invention, the gate sensitivity of each pilot thyristor can be increased without reducing the dv/dt withstand capability, and the diameter of the light receiving section can also be increased by 2 to 3 times or more compared to the conventional one.

As a result of increasing the size of the light receiving section, it is possible to significantly improve photosensitivity and optical coupling efficiency. Furthermore, if the diameter of the light receiving part is increased, the leakage current generated in this part generally increases by 1, which tends to lower the withstand voltage during high temperature operation, but in the present invention, the leakage current follows the same path as the displacement current. It is also effective in preventing erroneous birds due to leakage current. Furthermore, in the present invention, since the number of pilot thyristors are turned on sequentially, the current flowing through the first pilot thyristor at the initial stage of turn-on decreases in proportion to the number of pilot thyristors in the subsequent stage. The drop in turn-on current can be reduced, and the di/dt discharge resistance can be greatly expanded without impairing the d■/dt resistance.

[Example of the present invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIGS. 3 and 4 show the configuration of a SIRISK according to an embodiment of the present invention, with FIG. 3 being a plan view of the gate electrode, and FIG. 4 being a sectional view.

P emitter 121, N base layer 22, P base layer 23,
The above N emitter layer 24ftl of the main thyristor 1viT consisting of four stacked semiconductor layers of the N emitter layer 24f
A current collecting electrode 25 is formed on the surface of the P base layer 23 adjacent to C, and a plurality of pilot thyristors are formed surrounded by this current collecting electrode 25. Here, the light receiving section 2
A first pilot thyristor PT comprising 6.

A total of five pilot thyristors p'r, -PT are formed, including the fifth pilot thyristor PT whose emitter electrode is shared with the current collecting electrode 25. Current collection′
Around the pole 25, each pilot thyristor PT
A main thyristor MT is formed around the periphery of PT to PT. The first pilot thyristor PT is configured by forming an N emitter layer 24a in an annular shape around the light receiving portion 26, and disposing an emitter conductor 27 on the surface of the N emitter layer 24a.

In addition, the pilot thyristor PT2 in the imperial edict 2 to 51
~PT, is P base, "During signal 23, M is attached to current collecting electrode 25.
N emitter layers 24b and 24c.

24d and 24e, respectively, and emitter electrodes 28, 29, and 30° 31 are formed on these N emitter layers 24b, 24c, 24d, and 24e, respectively, and gate electrodes 32, 33, and 31 are formed on P base layer 23, respectively. 34.35. Among these, the emitter electrode 31 of the fifth pilot thyristor PT is shared with the current collecting type @25. Thus, the pilot thyristors P T2 , P T3 r P T4 . Each gate electrode 32, 33, 34.35 of PT5 is connected to the pilot thyristor PT, +P T2 rp'r of the previous stage, respectively.
3. Each emitter electrode of p'r4 27, 28, 29° 30
are sequentially electrically connected to each other via a wiring layer 36 such as an Aj' line. Therefore, the pilot thyristor p'r of each stage
21PT31PT, PT are the pilot thyristors PT, PT2゜PT3 + PT4 in the previous stage, respectively
The turn-on operation is performed by receiving the turn-on current as the gate current. 37 and 38 are a cathode electrode and an anode electrode, respectively.

Now, the light receiving section 26 of this Cyrisk configured in this way
When the optical gate signal hv is applied to the first pilot thyristor PT, the photocurrent pfi generated mainly in the depletion layer region of the central junction of the first pilot thyristor PT flows into the P base layer 23. This photocurrent Iph flows laterally through the P base layer 23, passes through the collector electrode 25 provided with the knee of the P base 1231g, and then passes through the short circuit portion 39 provided between the P base layer 23 and the cathode electrode 37. and flows into the cathode electrode 37. As a result, the photocurrent Iph generates a lateral potential difference in the P base layer 23 of the first pilot thyristor PT,
Thereby, the N of the first pilot thyristor PT,
Emitter t' 524a will be forward biased. When the deepest potential of this forward bias voltage approaches the value of the diffusion potential at the junction between the N emitter core 24a and the P base layer 23, this causes the N emitter core 24a to
The injection of electrons from 4a into the P base layer 23 increases rapidly, and the first thyristor PT is turned on from the junction. This m 1 pilot thyristor PT.

The turn-on current is applied as a gate current to the gate electrode 32 of the second pilot thyristor PT2 via the wiring layer 36, thereby turning on the second pilot thyristor PT2. By turning on the pilot thyristor PT2 at the same 6k, the third to
The fifth pilot thyristors PT3 to PT are turned on in sequence. The turn-on current of the fifth pilot thyristor PT flows from the current collector 25 to the cathode electrode 37 via the short circuit 39, and at this time, the turn-on current functions as a gate current of the main thyristor IJT. The main thyristor uT will turn on.

By the way, in order to increase the photosensitivity (gate sensitivity) of the thyristor, the P base layer 2 directly below the N emitter layer 24a of the first pilot thyristor PT that is turned on first is generally used.
The lateral resistance of No. 3 may be increased. However, in the thyristor having the structure according to the present invention, in addition to this, the gate electrode 32 of the second pylon thyristor PT2 and the current collecting electrode 250
It is better to reduce the value of the resistance value R1)2 between 1 and 2. Figure 5 shows the relationship between the minimum optical trigger power φ of the first pilot thyristor PT and Rp2, which was performed by the inventors. It can be seen that when Pp2>100Ω, φ8 increases rapidly and the photosensitivity decreases. This means that a part of the photocurrent Iph is transferred to the first pilot thyristor PT, the N emitter layer 24 a% wiring 1@36, the second pilot thyristor P
Gate electrode 32 of T2, second pilot thyristor PT
As a result, a voltage that biases the N emitter 24b in the opposite direction flows between the current collecting electrode 25 and the gate' polarization 32 through the P base layer 23 directly under the N emitter layer 24b of No. 2. This is because it occurs. Therefore, gate electrode 3
The photosensitivity is improved as the resistance Rpx between the N emitter rd 24 and the current collecting electrode 25 is made smaller and the reverse bias voltage applied to the N emitter rd 24 b is made smaller. Next, consider a case where voltage noise with a large dN'/dt value is applied between the anode and cathode of a thyristor having such a structure. FIG. 6 shows an equivalent circuit of a thyristor according to the present invention. N emitters 24 a + 24 from the first pilot thyristor PT with the light receiving section to the fifth pilot thyristor PT5
b + 24 c.

The junction capacitances that supply the displacement current flowing through the P base layer 23 directly under 24d and 24e are respectively represented by 01 to C6. CM is a junction portion that supplies a current of about f flowing into a short-circuit portion 39 arranged around the inner circumference of the main thyristor MT.

Diodes D1 to D are each pilot thyristor PT,
~This is a diode formed from the N emitter layer of PT5 and the P base layer 23. Similarly, DM represents a diode formed from the N emitter layer z4r and the P base layer 23 of the main thyristor MT.

In the figure, A represents an anode electrode, K represents a cathode electrode, B represents a light receiving portion, and C-F represents gate electrodes 32 to 35, respectively. H again.

~H3 corresponds to the current collecting electrode 25. Each junction capacitance C1
~ If the density of the displacement current flowing through C'M is Jd, then as the displacement current is generated, the current collecting electrodes H1 to H3 and the light receiving part B
and the potential difference generated between gate electrodes C to F ■1 to ■
, is proportional to Jd. Let each proportionality constant be R1 (==V1/
Jd), R2(=:v2/Jd), R3(=
Vs/Jd), R4 (=V4/Jd).

It is expressed as R5 (=Vs/Jd).

The maximum value of the forward bias of each pilot thyristor PT, ~PT, is the voltage across the diodes D1~D in FIG. Forward bias applied across D1 to D, V 121 V23 + V45 and V, is R1 and R2 + R'2 and R3 ° R3 and R4 + R4
can be expressed by the difference between the voltages across R3 and the voltage across R9. Jd is junction capacitance Cj and dv/d
Since it is a product of t pieces, ■I 2 + V23 r V34
r v45 and V, are as follows.

V, 2. : V, -V2=(R1-R2)・Cj-H"
'(11v V23 = V2 Vs = (R2-R3) ・C
j−π−(21V V34=Vs V4=(R3R4)・Cj−,,−
(31V45:=V4 V5-(R4R11) ・C
j 'at'' (4) V5 = V5 = Rs
・Cj −πN' l 2 + V23 + VB2
+ V45 and V, the values of each diode D, %D,
When the diffusion potential reaches dv/dt), the injection of electrons from the pilot thyristor increases rapidly, and the pilot thyristor whose bias voltage exceeds the diffusion potential first becomes dv/dt) I).

In case of false accusation, VI 2 r ”23 + VB2 +
Select the values of R and %R so that they are equal to the value of v45 75EV, 21"V
231 v3. l If V45 is designed so that it is equal to V, R, = R, -R, = R, -R, = R2 - R
3=R, -R2 and from these rA relations, R,=R
The relationship 4/2 = Rs/3 = R2/4 = Rt15 is underestimated. Therefore, to satisfy the above-mentioned conditions, at least Rs 〉R4/2 + R5〉Rs/3 r R,〉
R2/41 R5〉R4/! R so that the relationship of 5 is satisfied.
A value of 1 to R3 must be selected.

In addition, in the present invention, as described above, it is necessary to set the resistance value between the gate electrode 32 of the second viroft thyristor PT and the current collecting electrode 250 to 100Ω or less to prevent a decrease in photosensitivity. While R2 depends on the N emitter width of the second pilot thyristor PT2, the resistance value between the gate electrode 32 and the current collecting electrode 25 can be lowered by increasing the N emitter length. Therefore, the above-described conditions of R1-R3 and the conditions of the resistance value between the current collecting electrode 25 and the gate electrode 32 can be realized without contradiction.

By the way, in such a structure, the dv/dt tolerance is equal to the P base effective resistance Rn of the final stage pilot thyristor PT5.
determined by As shown in the embodiment, when the pilot thyristor has five stages, KR may be determined so as to satisfy the dv/dt value of the predetermined specifications. At that time, RI is R6
It can be made up to 5 times larger. When trying to increase the diameter of the light receiving part in order to increase the optical sensitivity of the first pilot thyristor PT, where the light receiving part is located, or to increase the optical coupling efficiency with the optical signal transmission system, it is generally necessary to increase R1. There is. In the present invention, KR1 can be easily increased without sacrificing dv/dt tolerance, so photosensitivity and optical coupling efficiency can be significantly improved. For example, 4KV
According to experiments using a light-triggered thyristor, the light reception ff
14 diameter d = 1.5rttmφ, dv/d
At t = 1500V/ltS, the minimum optical trigger power φ = 4mw in the conventional example is now 5 mw according to the present invention.
In the optically triggered thyristor of the stage pilot thyristor, φ
It is possible to make *=2mw. Also the same φ岑=4 mw
Comparing with , if the present invention is implemented, a 4 a m
It was possible to improve uφ by a factor of two.

When a light-emitting diode is used as a light source in an optical signal transmission system consisting of a bundled optical fiber with a diameter of 1.57mm and one with a diameter of 3mm, the optical output of the light-emitting diode and the optical coupling efficiency of the bundled optical fiber are improved by more than three times. can do. In either case, the driving current of the light emitting diode can be significantly improved by π.

Since the driving current value of the light emitting diode greatly affects the life of the light emitting diode, by implementing the present invention, the reliability of the optical trigger system can be greatly improved. In particular, when the original trigger thyristor of the present invention is installed in a thyristor valve for direct current power transmission, etc., where high reliability is required for the optical trigger system, great effects will be exhibited. In addition, when the diameter of the light receiving part is increased, the leakage current generated in this part increases, and the withstand voltage tends to decrease during high temperature operation. However, since the leakage current flows along the same path as the displacement current, the present invention The implemented thyristor is also effective in preventing false triggering due to leakage current. As a result, a thyristor with excellent forward closing voltage characteristics at high temperatures can be realized.

Further, in the present invention, the following effects can be obtained by the current collecting electrode. As shown in Fig. 2, in the conventional example, R, IR
2 are electrically coupled via canned electrodes, and the voltage generated at R1 due to the displacement current is canceled out by the voltage generated at both ends of R2, thereby improving the dv/dt withstand capability. However, as described above, if an attempt was made to prevent a decrease in the dv/dt withstand capacity of the main thyristor, the di/at withstand capacity would decrease, which caused a further problem.

On the other hand, in the present invention, since R1 to Rf are electrically coupled via the current collecting electrode, the number of pilot thyristor stages can be easily increased.

Since the current that flows through the first pilot thyristor PT, which has the light receiving section, at the initial turn-on stage is smaller than the number of pilot thyristors in the subsequent stage, the thyristor according to the present invention can be used at the turn-on stage of the first pilot thyristor PT. It can reduce concentration of flow. In addition, in the thyristor of the present invention, the light-receiving area can be easily adjusted without sacrificing photosensitivity or dv/dt resistance, so the initial turn-on area is expanded and the on-current density at the initial turn-on stage can be greatly reduced. It can be lowered. For this reason,
In the present invention, according to the comparison with the conventional example, the thyristor of the embodiment has a di/dt>600A, which is 2~2~600A compared to the conventional row.
We were able to achieve three times the di/dt tolerance.

In this way, this embodiment allows di/d
It is possible to realize a high-performance and highly practical thyristor with dramatic improvements in durability and light sensitivity (gate production reduction).

FIG. 7 shows a schematic plan view of another embodiment of the present invention. First pilot thyristor P with light receiving part in the center
T1 is formed, and three second pilot thyristors PT21 to PT2° and three third pilot thyristors PT2I to p'r2. are arranged in an alternating radial pattern.

Three protrusions are provided on the outer periphery of the N emitter of the first pilot thyristor PT, and an N emitter electrode is also provided here, and these protrusions and the second pilot thyristor PT21
The gate electrodes of ~PT23 are connected by bonding with aluminum wires. Also, the second pilot thyristor PT2. A protrusion is also provided on the N emitter layer of ~Pr23, and an N emitter electrode is also provided on this, and this protrusion and the third pilot thyristor PT, ~PT3. Each gate electrode is connected by bonding with an aluminum wire. Third pilot thyristor PT31-PT3
s, the radially arranged current collecting electrodes 40 also serve as emitter electrodes, as in the previous embodiment. Each pilot thyristor and live thyristor MT is
1>i, and N of each pilot thyristor
The peripheral length direction of the emitter and current collecting electrode 400 is the crystal axis (0
11), [011), (110), (1-cho 0), [10
They are arranged in the (101) direction. Half of the perimeter length of each N emitter and %40 is (011).

The (110) and [101) crystal axes are in this direction, and the crystal axes in this direction are suitable for maintaining a conductive region at the initial stage of turn-on, and reliable turn-on can be achieved.

However, the present invention is not limited to the above embodiments. In the embodiment, an optical thyristor is exemplified, but the present invention can be similarly applied to an electric tri-type thyristor in which a gate electrode is formed in a light receiving part. In addition, the number of stages of pilot thyristors and their arrangement can be determined according to the specifications, and in short, each pilot thyristor is arranged so as to be surrounded by the current collecting electrode provided on the base, and the above-mentioned arrangement is performed. Depending on the method, electrical connections may be made sequentially.

[Brief explanation of the drawing]

The first mountain is a configuration diagram showing an example of a conventional O thyristor, FIG. 2 is an equivalent circuit diagram thereof, FIG. 3 is a plan view of a thyristor according to an embodiment of the present invention, FIG. 4 is a sectional view of the thyristor, 5
The figure is also a diagram for explaining the operating characteristics of the thyristor, Figure 6 is an equivalent circuit diagram of the thyristor, and Figure 7 is a diagram for explaining the operating characteristics of the thyristor.
The figure is a schematic plan view of a thyristor according to another embodiment of the present invention. MT...Main thyristor, ST1-ST,...Pilot thyristor, 24a-24f...N8 milling layer, 25...Collecting electrode, 26...Light receiving part, 27-31
...Emitter electrode, 32-35...Gate electrode, 3
6... Wiring, 37... Cathode electrode, 38... Anode electrode.

Claims (4)

[Claims] (1) A plurality of nozzles 44 that share three semiconductor layers other than the emitter layer of the main thyristor in the base layer of the main thyristor, which is composed of four semiconductor layers laminated with alternating conductivity types. In a thyristor in which a thyristor layer is formed to have the same conductivity type as an emitter layer of the main thyristor, each of the thyristors is provided on a base layer adjacent to the emitter layer of the main thyristor, and a collector electrode is formed on the base layer adjacent to the emitter layer of the main thyristor. Gate electrodes are respectively formed on the base layer arranged inside and surrounded by the emitter layer of each pilot thyristor, and the gate electrodes of these pilot thyristors are sequentially connected to the emitter layer of the preceding pilot thyristor. The cathode of the final stage pilot thyristor is electrically connected to the emitter electrode provided above, and the emitter electrode of the final stage pilot thyristor is shared with the current collecting electrode, and the cathode of the final stage pilot thyristor is generated by leakage current or displacement current due to overvoltage application. - A thyristor characterized in that the forward bias voltages of the cathodes and emitters of other pilot thyristors are set to be smaller but equal to the forward bias voltage of the emitter. (2) The thyristor according to claim 1, wherein the gate electrode of the second stage pilot thyristor among the plurality of pilot thyristors and the bar of the current collecting electrode have a resistance value of 100Ω or less. (3) The emitter layer of the plurality of pilot thyristors and a part of the emitter electrode thereon are provided with a protrusion for electrically connecting it to the gate electrode of an adjacent pilot thyristor. A thyristor according to claim 1. (4) The thyristor according to claim 1, wherein the first stage pilot thyristor among the number of pilot thyristors is fired and driven by an optical trigger signal.