JPH0576786B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a thyristor that can be gate-controlled by an optical signal, and in particular has a high ignition sensitivity by the optical signal and provides a sufficiently large rate of increase in critical off-voltage. This invention relates to a light-driven thyristor that is capable of

[Background of the invention]

Thyristors, which are switching elements with a four-layer structure, are widely used for switching from small to large amounts of power, but in recent years, in addition to the conventionally known thyristors, which can be called electrical signal-triggered types, optical With the advent of light-driven thyristors that can be triggered directly by energy, their applications continue to expand.

This light-driven thyristor is basically the same as an electrical signal-triggered thyristor, with at least a pnpn
It consists of four semiconductor layers and a pair of main electrodes in ohmic contact with both outer layers.
There is no trigger terminal, and the device can be turned on by irradiating a predetermined portion of the semiconductor layer with light. Therefore, (1) there is no connection between the main circuit and the control circuit; Electrical isolation with high voltage resistance is easy, and there is no risk of the control circuit becoming complicated even if the voltage of the main circuit becomes high.

(2) It is resistant to nozzles caused by electromagnetic induction, and there is little risk of malfunction.

Therefore, in recent years, there have been many expectations for its application to thyristor conversion devices for high-voltage DC power transmission.

By the way, one of the challenges facing thyristor elements in such applications is how to increase the light ignition sensitivity without impairing the critical off-voltage rise rate (abbreviated as dv/dt withstand capability). There is.

FIG. 1 shows an example of a light-driven thyristor.

In FIG. 1, an optical thyristor (light-driven thyristor) 100 includes an n base layer 1, a p
base layer 2, p emitter layer 3, n emitter layer 4,
An anode electrode 5 in ohmic contact with the n emitter layer 3, a cathode electrode 6 in ohmic contact with the n emitter layer 4, each of the n emitter layers 40 and 400 provided separately from the n emitter layer 4, and the p base layer. electrodes 60, 600 which are in ohmic contact with each other and connect them with low resistance;
The light guide 7 irradiates a predetermined surface area of the ace layer 2 with an optical signal.

When a forward voltage is applied between the electrodes 5 and 6 and an optical signal is sent by the light guide 7 to the optical thyristor 100 which is in the off state, the p base layer 2, the n base layer 1, and the p emitter layer 3 A photocurrent I _b is generated in the region and flows into the cathode electrode 6 as shown by the arrow. And as a result, p
A potential gradient is generated in the lateral direction in the base layer 2 , and a positive potential V ₀ is generated in the p base layer 2 immediately below the inner periphery of the n emitter layer 400 .

The magnitude of this potential V ₀ is given by the product of the lateral resistance R _pB of the p base layer 2 and the generated photocurrent I _b ,
When this potential V ₀ approaches the built-in voltage of the junction between the n emitter layer 400 and the p base layer 2, the n
Ignition begins from the inner peripheral portion of the emitter layer 400, and the optical thyristor 100 is ignited.

The above is the firing operation of the optical thyristor. On the other hand, when the optical thyristor 100 is in the off state, the pn
A forward voltage v is applied to the junction, and this pn junction is in a reverse bias state. In this state, when a change dv/dt is generated in the forward voltage v by a nozzle, etc., a displacement current (current flowing through the capacitor) I _d appears in this p-n junction, but this displacement current I _d has the polarity of the photocurrent described above. Ib is the same as _Ib , and therefore, if this displacement current _Id becomes large, the optical thyristor 100 will also be fired by this current _Id , resulting in erroneous firing.

Therefore, the difficulty in causing ignition due to the change in forward voltage v dv/dt is called the dv/dt tolerance, and if this is small, false ignition is likely to occur due to noise etc. A larger dt tolerance is desirable.

However, as is clear from the above, this dv/dt tolerance is determined by the lateral resistance R _pB of the p base layer 2, etc., as well as the light ignition sensitivity. Therefore, in the optical thyristor 100 shown in FIG.
When trying to increase the light ignition sensitivity, erroneous ignition is likely to occur due to the change in dv/dt, and the disadvantage is that it is difficult to simultaneously improve the light ignition sensitivity and improve the dv/dt tolerance. be.

FIG. 2 shows an example of an optical thyristor 110 in which the light ignition sensitivity can be improved independently of the dv/dt tolerance.This optical thyristor 110 is different from the optical thyristor 100 shown in FIG. The electrode 600 for the layer 400 and the p base layer 2 is divided into separate electrodes 601 and 602, and the point where they are connected by the resistor 8 and the irradiation position of the optical signal applied by the light guide 7 are the n emitters. This point is the surface area of layer 400.

When a forward voltage is applied to this optical thyristor 110 and an optical signal is irradiated from the light guide 7, a photocurrent I _b is generated inside the optical thyristor 110, which is similar to the optical thyristor 100 shown in FIG. In 110, the light passes through the n emitter layer 400 and enters, so the n emitter layer 400 and the p
A photovoltaic effect operates at the junction (J3 junction) of the base layer 2, and a voltage is generated at this junction J3. On the other hand, correspondingly, the electrode 600 has two electrodes 601 and 60.
2 and connected by resistor 8, the voltage generated at the J3 junction described above causes the n emitter layer 400 → J3 junction → p base layer 2 → electrode 602 → resistor 8 → electrode 601 → A photovoltaic current I _p circulates in the direction of the n-emitter layer 400 .

Since this photovoltaic current I _p flows in the same direction as the above-mentioned photocurrent I _b in the p base layer 2, it acts to further increase the above-mentioned voltage V ₀ and to increase the ignition sensitivity.

Furthermore, since the resistor 8 is inserted, a voltage drop due to the photocell current I _p occurs across this resistor 8, but this voltage drop is in the direction of forward biasing the J3 junction, so this also increases the ignition sensitivity. is improved.

On the other hand, this photovoltaic current I _p only appears when the optical signal is irradiated, and does not occur at all depending on the variation dv/dt.

Therefore, the effect of improving the ignition sensitivity due to the photocell current I _p appears only when a regular optical signal is incident, and the ignition sensitivity is sufficiently improved, but dv/dt
Since this optical thyristor 110 has no effect at all to reduce the withstand capacity, in the end, according to this optical thyristor 110,
This means that the ignition sensitivity can be sufficiently improved without reducing the dv/dt tolerance.

Separately, regarding optical thyristors that can improve dv/dt tolerance without affecting ignition sensitivity, for example
It is disclosed in specification No. 4122480.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a photothyristor that can increase ignition sensitivity through photovoltaic action and further improve dv/dt tolerance. There is something to do.

[Summary of the invention]

To achieve this objective, the present invention supplies a portion of the displacement current generated by the change in forward voltage to the resistance of the external conductive path used to improve the ignition sensitivity by photovoltaic action. This is characterized in that the ignition sensitivity is suppressed when a displacement current appears.

[Embodiments of the invention]

Hereinafter, the optical thyristor according to the present invention will be explained in detail with reference to illustrated embodiments.

Figures 3 and 4 show one embodiment of the present invention;
The figure is a plan view, and FIG. 4 is a cross-sectional view taken along line A-A' in FIG. This is the same as the optical thyristor 110 shown in FIG. Note that the entire optical thyristor of the present invention shown in FIGS. 3 and 4 is 1
Represented by 20.

The p base layer 20 is formed in the n base layer 1 completely independently of the original p base layer 2, and the isolation between the p base layers 20 and 2 at this time is It is adapted to be provided by a pn junction with layer 1.

The electrode 61 is connected to the electrode 601 by a low-resistance external conductive path c, which serves to connect the p-base layer 20 and the portion of the p-base layer 2 below the electrode 602 via the resistor 8. do.

Next, the operation of this embodiment will be explained.

First, the operation at the time of ignition using an optical signal will be explained.

As shown in FIG. 4, when an optical signal is irradiated from the light guide 7 to the n-emitter layer 400, the p-base layer 2, the n-base layer 1, the p-emitter A photocurrent I _b is generated in the region of the layer 3, which flows laterally through the p base layer 2 to the cathode electrode 6, and between the n emitter layer 400 and the p base layer 2, which serves as the light receiving part of the optical signal. The emitter junction of is forward biased to activate the dotting action.

On the other hand, in parallel with this, the n emitter layer 400 and the p emitter layer 400 are similar to the optical thyristor 110 in FIG.
A photovoltaic current I _p is generated due to the photovoltaic effect at the pn junction consisting of the base layer 2, and this current I _p is
It circulates along the path of emitter layer 400→p base layer 2, and acts to forward bias this pn junction to further facilitate spotting.

Therefore, the optical thyristor 120 according to this embodiment
According to the invention, high ignition sensitivity can be provided, and ignition using an optical signal can always be performed reliably.

Note that the optical thyristor 120 according to this embodiment is provided with a conductive path c, which allows the electrode 6 to
01 and 602 are conductively coupled from the electrode 61 to the p base layer 20. However, the photovoltaic current I _p generated during the ignition operation by the above optical signal is
It does not flow into the p-base layer 20 from there. The reason is as follows. That is, in the state where ignition is about to occur, that is, in the forward blocking state,
This is because a voltage is applied such that the cathode terminal K becomes negative and the anode terminal A becomes positive, so that the junction between the p base layer 20 and the n base layer 1 is in a reverse bias state. As a result, due to the presence of the conductive path c, the ignition operation by the optical signal is not affected at all, and the above-mentioned ignition sensitivity can be improved.

Next, the change in forward voltage v due to the nozzle etc.
The operation when dv/dt is ignited will be explained with reference to FIG.

When a forward voltage change dv/dt appears between the anode terminal A and the cathode terminal K, a displacement current flows near the junction between the P base layer 2 and the N base layer 1.
I _d0 is generated almost uniformly and flows laterally through the p base layer 2 into the cathode electrode 6 . Then, when the value of this displacement current I _d0 exceeds a certain level,
When the magnitude of the voltage drop due to the lateral resistance of the p base layer 2 directly under the n emitter 400 approaches the diffusion potential at the junction between the n emitter layer 400 and the p base layer 2, this optical thyristor 12
0 starts firing and causes false firing.

Therefore, the optical thyristor 12 according to this embodiment
0, a p base layer 20 is provided which is isolated from the original p base layer 2 by an n base layer 1 and exists independently, and the above-mentioned displacement current I _d0 appears. In such a state, a displacement current I _d1 similarly appears near the junction between the p base layer 20 and the n base layer 1, and this current I _d1 flows from the electrode 61 through the conductive path c and the resistor 8. to the electrode 602, and this electrode 602
It enters the p base layer 2 from there, merges with the displacement current I _d0 , and flows into the cathode electrode 6. In addition,
It is unnecessary to explain that the displacement currents I _d0 and I _d1 at this time are generated at approximately the same current density.

In this way, the displacement current from the n base layer 20
When I _d1 flows through the resistor 8, a voltage with the polarity shown is generated in the resistor 8, and this voltage is applied to the electrodes 601 and 6.
02, thereby putting the emitter-base junction between the n-emitter layer 400 and the p-base layer 2 in a reverse bias state, and acting to lower the ignition sensitivity.

Therefore, the optical thyristor 120 according to this embodiment
According to , when a forward voltage change dv/dt is applied, the ignition sensitivity is kept low only at that time, and it is possible to have a large dv/dt tolerance. It becomes possible to provide large dv/dt tolerance while maintaining high ignition sensitivity.

When compared by an experimental example, the firing sensitivity of the optical thyristor 120 according to an embodiment of the present invention to an optical signal is 1.4 with respect to that of the embodiment of FIG.
On the other hand, the dv/dt tolerance was improved by about 1.7 times compared to the optical thyristor 110 shown in FIG.

FIG. 6 shows an optical thyristor 130 according to another embodiment of the present invention.
30 is the optical thyristor 12 in the embodiment of FIG.
The only difference from No. 4 is that a mode groove M is used as a means for providing the p base layer 20 independently from the original p base layer 2, and the other structure and overall functions are the same as No. 4. This is the same as the embodiment shown in the figure.

〔Effect of the invention〕

As explained above, according to the present invention, the dv/dt tolerance of the optical thyristor, which is designed to improve the ignition sensitivity due to the photovoltaic action with respect to the ignition operation by an optical signal, is
Since it can be operated independently of improving the ignition sensitivity, it eliminates the drawbacks of conventional technology and easily provides an optical thyristor that has both the high optical ignition sensitivity and sufficient DV/DT tolerance required for an optical thyristor. can do.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing a conventional example of a light-driven thyristor, Fig. 2 is a sectional view showing an example of a light-driven thyristor with improved light ignition sensitivity, and Fig. 3 is a sectional view of a light-driven thyristor according to the present invention. A plan view showing one embodiment; FIG. 4 is a sectional view taken along line A-A' in FIG. 3;
FIG. 5 is an explanatory diagram showing the operation of the optically driven thyristor shown in FIGS. 3 and 4, and FIG. 6 is a sectional view showing another embodiment of the present invention. 1...n base layer, 2,20...p base layer,
3...p emitter layer, 4, 40, 400...n emitter layer, 5, 6, 60, 61, 601, 602
...Ohmic electrode, 7...Light guide, 8...
…resistance.

Claims (1)

[Claims] 1. A first emitter layer of a first conductivity type, a first base layer of a second conductivity type, a second base layer of the first conductivity type, and a selected portion of the surface of the second base layer. a semiconductor substrate having a four-layer structure consisting of a second emitter layer of a second conductivity type formed in the semiconductor substrate, an independent part of the surface of the second emitter layer serving as a light-receiving surface for a gate optical signal; In the light-driven thyristor, an external conductive path having a predetermined resistance value is formed between the second emitter layer serving as the light-receiving surface and a selected part of the surface area of the second base layer. A second base layer of the first conductivity type independent of the second base layer of the first conductivity type is provided, and between this independent second base layer and the second emitter layer of the second conductivity type which serves as the light-receiving surface. A light-driven thyristor characterized in that an external conductive path is formed in the thyristor. 2. In claim 1, the independent second base layer of the first conductivity type is formed by isolation using a pn junction between the independent second base layer of the second conductivity type. A light-driven thyristor characterized by: 3. In claim 1, the independent second base layer of the first conductivity type is formed by isolation using a moat groove provided on the surface of the second base layer of the first conductivity type. A light-driven thyristor characterized by: