JPH0136263B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thyristor with increased di/dt tolerance and high sensitivity.

A thyristor is composed of four semiconductor layers of alternating conductivity types, with an anode electrode and a cathode electrode attached to the front and back semiconductor layer surfaces, and generally includes a P emitter layer, an N base layer, and a cathode electrode from the anode side.
It has a structure including a P base layer and an N emitter layer. However, in this thyristor, by applying a trigger signal to the gate electrode provided on the P base layer, a small area near the gate is first turned on, and as time passes, the entire junction area is turned on. The area expands and becomes conductive. For this reason,
If the inrush current increase rate di/dt at turn-on is large, the current will concentrate in a limited conduction area near the gate in excess of the device's ability, and as a result, thermal damage may occur due to a local temperature rise.

Therefore, in recent years, as thyristors have become higher in voltage and capacity, there has been a desire for a thyristor that has a large di/dt capability during switching and has a gate control current that is as small as possible. However, there is generally a contradictory problem in that increasing the di/dt tolerance increases the gate control current. Recently, optical thyristors have been developed that control switching operation using optical signals instead of gate currents, but there is a limit to the usable optical energy and high gate drive is difficult, so di/dt I was unable to increase the tolerance level. Therefore, there has been a strong desire to develop a high-voltage, large-capacity thyristor that can improve gate sensitivity without compromising di/dt capability.

FIG. 1 schematically shows the cross-sectional structure of an optical thyristor constructed to solve such problems. In the figure, 4 layers consisting of a P emitter layer 1, an N base layer 2, a P base layer 3, and an N emitter layer 4 are shown.
An anode electrode 5 is provided on the surface of the P emitter layer 1 and a cathode electrode 6 is provided on the surface of the N emitter layer 4 of the thyristor consisting of two semiconductor layers, forming a main thyristor. Above N
The emitter layer 4 is formed in an annular shape on the outer peripheral side of the P base layer 3. Further, in the P base layer 3 of this main thyristor, emitter layers 7a, 7b, and 7c forming a plurality of pilot thyristors are formed in concentric circles spaced apart from each other, and a light receiving part 8 is formed in the center of the emitter layers 7a, 7b, and 7c. ing.

Now, however, when the light-receiving part 8 of this thyristor is irradiated with an optical trigger signal h, the photocurrent I _ph generated by this flows laterally through the P base layer 3 and is connected to the N emitter layer 4 of the main thyristor. The current flows to the cathode electrode 6 via the short-circuit portion 9 . At this time, the lateral potential difference generated in the P base layer 3 by the photocurrent I _ph biases the N emitter layers 7a, 7b, 7c of the pilot thyristor in the forward direction. The deepest part of this forward bias, that is, the voltage of the light receiving section 8 is the voltage between the P base layer 3 and the N emitter layer 7.
When the value of the built-in potential of the junction formed between N emitter layers 7a, 7b, and 7c approaches the value of It turns on from the area of the light receiving section 8. This turn-on current flows to the next-stage pilot thyristor via the electrode 10a, and serves as a high gate drive current to turn on the pilot thyristor under optimal conditions. Similarly, by turning on the pilot thyristor, the third stage pilot thyristor is driven, which in turn turns on the main thyristor.

By dispersing the excessive power loss that occurs at the initial stage of turn-on to each pilot thyristor by using the pilot thyristors configured in multiple stages in this way, it is possible to prevent the occurrence of hot spots and improve di/dt tolerance. It is being done.

However, such a conventional thyristor having a multi-stage amplification gate structure has the following drawbacks.

That is, by increasing the resistance value of the P base layer 3 of the first-stage pilot thyristor and increasing the lateral potential difference of the P base layer 3 generated by the photocurrent I _ph , the photosensitivity (gate sensitivity) can be improved. However, on the other hand, erroneous firing is likely to occur due to voltage noise mixed in from the thyristor main circuit. In other words, when voltage noise with a steep voltage increase rate is applied between the anode electrode 5' and the cathode electrode 6, the displacement current generated by this passes through the same path as the photocurrent I _ph , resulting in a decrease in photosensitivity. If it is set too high, erroneous ignition is more likely to occur due to voltage noise. Maximum allowable value to prevent false ignition due to this voltage noise
The dv/dt value is called dv/dt tolerance.

On the other hand, the radius R of the N emitter layer 7a of the first stage pilot thyristor is reduced to suppress the amount of displacement current generated in this region, and the N emitter layer 7a is
By increasing the resistance value of the P base layer 3 immediately below, it is possible to improve the photosensitivity without impairing the above-mentioned dv/dt tolerance. However, at this time,
In order to prevent the di/dt tolerance from decreasing, it is necessary to reduce the switching loss that occurs in the first stage pilot thyristor. In this regard, as mentioned above, by increasing the number of stages of pilot thyristors, the switching loss in each stage can be reduced, but unlike the photocurrent I _ph , the displacement current spreads over the entire area of the junction region. Since the current flows, the short circuit part 9 of the N emitter layer 4 of the main thyristor
Its value increases as it approaches . For this reason,
When the number of stages of pilot thyristors is increased, a new problem arises in that erroneous firing due to voltage noise becomes more likely to occur in the pilot thyristor and main thyristor in the subsequent stages.

Furthermore, as the number of pilot thyristor stages increases, the minimum anode voltage required for turn-on, ie, the finger voltage, tends to increase. For example, when thyristors with large finger voltages are operated in parallel, the anode voltage applied to both ends of each thyristor operated in parallel is determined by the on-voltage of the thyristor that is turned on first.
A problem arises in that other thyristors with higher finger voltages no longer turn on. These various problems exist not only in the above-mentioned optical thyristor but also in ordinary electrically triggered thyristors.

The present invention was made in consideration of these circumstances, and its purpose is to improve photosensitivity (gate sensitivity) and di An object of the present invention is to provide a thyristor with excellent characteristics that can improve the /dt withstand capacity.

That is, the present invention defines the current direction in the initial firing region of the pilot thyristor and the current direction in each initial firing region of the pilot thyristors other than the first stage pilot thyristor and the main thyristor to the respective optimum crystal axis directions. The above-mentioned object is effectively achieved by restricting the current direction by the groove provided in the base layer.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a plan view of the thyristor according to the embodiment, and FIG. 3 is a cross-sectional view of the thyristor. This thyristor, like the thyristor of the conventional structure shown in FIG.
2, 3, and 4 are stacked with alternating conductivity types,
The main thyristor is formed on the outermost periphery, and the first to third pilot thyristors are formed from the inside. Therefore, the P base layer 3 has grooves 11a, 11b, 11c that define the initial firing current direction from the pilot thyristor to the main thyristor.
is formed by, for example, chemical etching, and the P in the grooves 11a, 11b, 11c is
The base resistance is set higher than other P base layers 3. Each N emitter layer of the pilot thyristor, which is separated from the N emitter layer 4 of the main thyristor and is formed to have the same conductivity type, is arranged so that the current direction in the initial turn-on region is in the predetermined crystal axis direction as follows. It is provided to define the length direction. That is, the grooves 11a, 11b,
The first stage pilot thyristors 12a, 12b, 12c of each row divided into three pilot thyristor rows by 11c are connected to the N emitter layer 13.
The longitudinal directions of a, 13b, and 13c are preferably set to the crystal axes [011], [110], and [101] directions surrounding the light receiving part 14, so that in each pilot thyristor 12a, 12b, and 12c, In each case, the initial turn-on current flows in a direction perpendicular to the crystal axis direction. In addition, the second and third stage pilot thyristors 15a,
15b, 15c, 16a, 16b, 16c are the N emitter layers 17a, 17b, 17c, 18a,
The longitudinal direction of 18b and 18c is the crystal axis [011],
The [110] and [101] directions are preferably determined, so that, together with the grooves 11a, 11b, 11c, the first stage pilot thyristors 12a, 12
An initial turn-on region is formed so that the current from b and 12c flows in a direction perpendicular to each crystal axis direction. The main thyristor 19 then transfers the above current to the third stage pilot thyristor 16.
A short circuit portion 21 is formed in the current collecting electrode 20 so that the current flows in the same direction as a, 16b, and 16c. still,
In the figure, 22 indicates the N emitter layer of the main thyristor 19, and 23 indicates the P base layer.
Therefore, in this thyristor, the initial turn-on current generated by irradiating the light-receiving section 14 with the optical trigger signal flows through the grooves 11a and 11, as shown by the thick arrow in the figure.
Pilot thyristors 12a, 12b, 12c, 15a, 15b, divided by b, 11c,
The current flows to the main thyristor 19 through each row of 15c, 16a, 16b, and 16c.

That is, to explain its operation in a one-dimensional and simplified manner with reference to the cross-sectional structure shown in FIG. The photocurrent I _ph flows into the P base layer 3 . This photocurrent I _ph is
The current direction is regulated by the high resistance layer formed by the grooves 11a, 11b, and 11c, and the current flows through the P base layer 3 of the pilot thyristor in each row to the main current. Flows into the thyristor. In this main thyristor, the current flows to the cathode electrode 4 via the short-circuit portion 21 that short-circuits the P base layer 3 and the cathode electrode 4. Therefore, the photocurrent I _ph which flows in the P base layer 3 in the lateral direction and whose current direction is defined in each row of pilot thyristors is:
A lateral potential difference is generated in the P base layer 3, and the N emitters of each pilot thyristor are biased in the forward direction. As a result, each pilot thyristor is turned on in sequence in the same way as the thyristor of the conventional structure shown in FIG. 1, and this turn-on current turns on the main thyristor 19 as a high gate drive current.

Incidentally, the conduction state of the initial turn-on region in a thyristor differs depending on the crystal axis direction. For example, the following document Solid-State Electronics “Ohservation of the Initial Phases of
As introduced in "Thyristor TURN-ON" 1974.Vol 17 pp 879-880, in a pilot thyristor with a ring-shaped N emitter, the ring-shaped conduction region turns on after 1 to 2 μsec after turn-on, and the crystal axis changes. A conductive region remains in the [011][110][101] direction, and the crystal axis [011][110][1
01] direction suddenly disappears. However, the thyristor of this structure effectively solves the problems of the conventional structure by actively utilizing this anisotropy in the crystal axis direction.

That is, in this thyristor, the length direction of the initial turn-on region of the first-stage pilot thyristors 12a, 12b, and 12c is the crystal axis [011][110]
N emitter layer 13a, 1 preferably in the [101] direction
3b and 13c are determined, therefore, these first stage pilot thyristors 1
2a, 12b, 12c turn on the second and third stage pilot thyristors of each column, and the initial conduction regions of the first stage pilot thyristors 12a, 12b, 12c rapidly disappear. As a result, excessive power loss that occurs at the initial stage of turn-on occurs in the first pilot thyristor 1.
2a, 12b, and 12c is prevented or significantly reduced. Therefore, the first stage (first) pilot thyristor 12a, 12b,
The initial turn-on region of 12c can be made sufficiently small. Also, this initial turn-on region is
It is mainly determined by the lengths of the N emitter layers 13a, 13b, and 13c. Therefore, by reducing the length of the N emitter layers 13a, 13b, and 13c, the amount of displacement current generated at the current collecting electrode 23 can be reduced, as is clear from the planar configuration shown in FIG. Can be made smaller. Therefore, the P base layer 3 under the N emitter layers 13a, 13b, 13c
Even if the sensitivity to the photocurrent I _ph is increased by increasing the resistance, the dv/dt tolerance is not impaired by this, which is a remarkable effect. Furthermore, since the displacement current generated in the base layer 3 under the grooves 11a, 11b, and 11c hardly flows through the P base layer 3 region of each pilot thyristor, even if the number of stages of the pilot thyristor is increased. However, the dv/dt tolerance of the outermost periphery, that is, the rear-stage pilot thyristor, is not sacrificed. Therefore, it becomes possible to design the specifications of the pilot thyristor very easily. Furthermore, according to this structure, there is no need to increase the number of pilot thyristor stages more than necessary in order to increase the di/dt withstand capability, and therefore the increase in finger voltage due to the improvement of the di/dt withstand capability can be minimized. It has great effects such as:

Note that the present invention is not limited only to the above embodiments. In the embodiment, an optical thyristor is illustrated, but an electrically triggered type in which a gate electrode is provided on the P base layer of the light receiving section 14 can be similarly applied. Further, the shape and depth of the grooves, their number, and the number of stages of the pilot thyristor may be determined according to the specifications. Furthermore, in the embodiment, only the length direction of the initial turn-on region of the first pilot thyristor was set in the crystal axis [011][110][101] direction, but the second stage pilot thyristor was also formed in the same direction. You may also do so.

Note that the effects of the present invention do not depend on the number of divisions of the pilot thyristor. For example, even when the number of divisions is "1" as shown in FIGS. 4a and 4b, the effects of the present invention do not change. In the same figure, when the switch 31 is closed and a gate signal is applied to the gate electrode 32, the gate current i _g is blocked by the groove 33, so it passes through the current collecting electrode 34 and the P-based cathode electrode short circuit 35. It flows. When the pilot thyristor section 36 is turned on by the gate current, the turn-on current flows through the current collecting electrode 34, the short circuit section 35, and the cathode electrode 37, which functions as the gate electrode of the main thyristor section 38. . In this case, the effect of the present invention can be obtained by setting the length direction of the pilot thyristor 36 facing the gate electrode in the [110] direction and the length direction of the main thyristor 38 facing the current collecting electrode in the [110] direction. In short, the present invention can be implemented with various modifications without departing from the gist thereof.

As described in detail above, according to the present invention, di/dt withstand capability and gate sensitivity can be significantly improved without impairing major characteristics such as finger voltage and dv/dt withstand capability. Moreover, by simply defining the length direction of the initial turn-on region of the pilot thyristor and defining the current direction by the groove, the above object can be achieved extremely effectively, and great practical advantages can be achieved.

[Brief explanation of drawings]

Figure 1 is a configuration diagram showing a thyristor with a conventional structure.
FIG. 2 is a plan configuration diagram of a thyristor according to an embodiment of the present invention, FIG. 3 is a cross-sectional configuration diagram of the thyristor of the same embodiment, and FIGS. 4a and 4b are configuration diagrams showing another embodiment of the present invention. be. 3...P base layer, 4...N emitter layer, 6...cathode electrode, 11a, 11b, 11c...groove, 12
a, 12b, 12c...first pilot thyristor, 13a, 13b, 13c...N emitter layer, 1
4... Light receiving section, 15a, 15b, 15c, 16a,
16b, 16c...second and third pilot thyristors, 17a, 17b, 17c, 18a, 1
8b, 18c... N emitter layer, 19... Main thyristor, 20, 23... Current collecting electrode, 21... Short circuit part,
22...N emitter layer.

Claims (1)

[Scope of Claims] 1. A pilot which shares three semiconductor layers other than the emitter layer of the main thyristor in the base layer of a main thyristor consisting of four semiconductor layers laminated with alternating conductivity types. In a thyristor in which the emitter layer of the thyristor is separated from the emitter layer of the main thyristor and formed to have the same conductivity type as the emitter layer of the main thyristor, the current direction in the initial firing region of the pilot thyristor is set to the crystal axis [ 011], [110], [1
01], and the current direction in the initial firing region of the main thyristor driven by the firing of this pilot thyristor is set perpendicular to the crystal axis [01].
1], [110], and [101] directions perpendicular to the directions. 2. The current direction in the initial ignition region is determined by regulating the direction of current flow by the longitudinal direction of the emitter layer formed in the base layer and the groove provided in the base layer. Thyristor according to item 1. 3. A patent claim in which the pilot thyristors are provided in a plurality of rows facing the main thyristor, and each row of the pilot thyristors is separated from each other by a groove provided in the base layer. The thyristor according to item 1. 4. A plurality of pilot thyristors are formed toward the main thyristor and are fired sequentially from the first stage pilot thyristor, and the current direction in the initial firing region is the crystal axis [011], [11].
The pilot thyristors defined in the direction perpendicular to the [0], [101] directions are at least the first-stage pilot thyristors, and the current direction in the initial firing region of the remaining pilot thyristors is along the crystal axes [011], [011] and [101] along with the main thyristor. The thyristor according to claim 1, which is defined in a direction perpendicular to the [110] and [101] directions. 5. The thyristor according to claim 4, wherein the first-stage pilot thyristor is activated in response to an optical trigger signal.