JPS5895865A - Gate turn off thyristor - Google Patents

Abstract

PURPOSE:To increase a current cutoff limit at which the turn OFF operation can be performed safely, by providing a rectangular shape of the main surfaces of a semiconductor pellet so that one side of the rectangle is longer than the opposite side, and aligning the longitudinal direction of each emitter belt shaped region with the longitudinal direction of the main surfaces. CONSTITUTION:The pellet 21 of the thyristor has a four layer structure pE, nB, pB, and nE between a pair of the main surfaces 211 and 212 which are located at opposing sides each other. The nE layer and pE layers are exposed in one main surface 211, and the pE layer is exposed in the other main surface 212. The nE layer comprises a plurality of long belt shaped regions 213 which are arranged so that their longitudinal direction is aligned with the longitudinal direction of the main surfaces. Each emitter belt shaped region 213 has a width of about 0.3mm. and a length of about 4.0mm.. Two emitter belts shaped regions are provided. A cathode electrode 22 is contacted with the two emitter belt shaped regions 213 at a low resistance. A gate electrode 23 is contacted with the surface of the pB layer surrounding the emitter belt shaped regions 213 at a low resistance. An anode electrode 24 is contacted with the surface of the opposite pE layer at a low resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an element structure of a gate turn-off thyristor, and more particularly to a notch arrangement and a shape of a semiconductor pellet suitable for improving the current cutoff limit performance of a small to medium capacitance element.

Since a gate turn-off thyristor (hereinafter abbreviated as GTO) is turned off by a negative gate signal, the emitter layer on the cathode side generally has an elongated rectangular shape, and the unit element surrounded by the gate electrode is called GT.
It has a structure in which a plurality of them are arranged in parallel in a number corresponding to the current capacity of O. In this case, the length of the unit element is not necessarily constant within one GTO, but it is desirable that it be constant from the viewpoint of uniformity of operation. Now, the conventional small and medium capacity G
The shape of a TO semiconductor pellet is generally a so-called square shape in which the lengths of the vertical and horizontal sides are approximately equal. it is,
(1) Taking as many pellets as possible from the round silicone Ueno, which is commonly used in the manufacturing process, (2) Since the longest part of the pellet only needs to be 1 times the same size, it is possible to solder it to the base electrode etc. This is because the mechanical stress can be reduced during the process, and (3) pelletizing from silicon wafers can be done more easily than with round shapes.

FIG. 1 shows a conventional GTO with a controllable current of 2OA class. −
Inside a square silicone pellet 1 with sides of about 4.0 cm, there is a silicone pellet with a length of about 2.0 cm. Four elongated emitter strips 2 each having a width of about 0.2 ttm are arranged in parallel, and are provided with a cathode electrode 3 in ohmic contact with them and a meshing shape 4, and further connected to these electrodes by wire bonding with an aluminum wire. Cathode IJ-do respectively5. A gate lead 6 is attached. As seen in this example, the length of the emitter strip 2 is approximately half the length of the bullet side in order to secure the wire pumping area (part of 3 and 4) of the cathode lead 5 and gate lead 6 facing each other. It is limited to a short length. This is because the outer shape of the GTO pellet is square. FIG. 2 is an example of a GTO pellet having a larger capacity with a controllable current of 60 A class. - A total of 12 emitter strips 2 having a square shape with a side length of about 6B and a length of about 1.5 fins are arranged in two rows. In this case, two cathode leads 5 and two gate leads 6 are each connected. In GTOs in which the current flow rate is increased and the pellet size is increased, a method is generally adopted in which the emitter strips 2 are arranged in two or more rows as shown in this example.

One of the reasons for this is that when the emitter strip becomes longer, non-uniformity of operation within the strip occurs due to the lateral resistance of the omic electrode 3 above it.

By the way, the inventors have discovered that the conventional GTO pellet has the following drawback regarding the current cutoff limit. In other words, the limit withstand capacity that allows the GTO to safely cut off current without being destroyed is an important performance imposed on the GTOK, but we found that this limit value does not improve correspondingly no matter how much the number of emitter strips is increased. It was. Figure 3 shows the voltage at which the GTO can safely turn off.

The measurement result of the current limit (the area within this limit is called the safe operating area) shows the safe operating area when the length of the emitter strips is constant and the number of emitter strips is changed to 1, 4, 8. . The left side of each line is a safe area, and indicates the boundary where the GTO will immediately break down if the voltage and current locus at turn-off go to the right side of this line. As can be seen from the figure, in a region where the voltage is low, the limiting current increases according to the number of emitter strips, but as the voltage increases, the GTO will break down at a low current regardless of the number of emitter strips. This seems to be because when the voltage is high, a significant current concentration phenomenon occurs at turn-off. When used with a power supply voltage of 200V, this limit voltage is preferably 400V or more, and at such high voltages, the upper limit of the current that can be safely cut off even if the number of emitter strips with short longitudinal dimensions in parallel is increased, as in the conventional example. The problem was that it did not increase.

The purpose of the present invention is to increase the current cutoff limit for safe turn-off operation, and to expand the safe operation area.
The goal is to provide TO.

The GTO of the present invention that achieves this purpose is characterized in that the main surface of the semiconductor pellet has a rectangular shape in which one opposite side is longer than the other opposite side, and the longitudinal direction of the emitter strip is made to coincide with the longitudinal direction of the main surface. It is in. A preferred feature of the practical example is that a plurality of emitter strips are arranged in parallel in a direction perpendicular to the longitudinal direction of the main surface, and are not arranged in parallel in the longitudinal direction, but are made as long as possible.

In order to achieve the object of the present invention more reliably, the cathode electrode has approximately the same shape as the emitter strip, and the first conductive member bonded to each emitter strip is electrically connected to the first conductive member. The gate electrode is made up of a first conductive member bonded to a layer adjacent to the emitter strip along the periphery of the emitter strip, and a second conductive member bonded thereon. is desirable.

Other objects and features of the invention will become apparent from the following description of the embodiments.

FIG. 3 shows an embodiment in which the present invention is applied to a GTO with a controllable current of 20 A class. The GTO pellet 21 made of silicon has one opposite side approximately 6. Otm.

It has a rectangular shape with the other opposite side being about 2.0.

The pellet 21 has a pair of main surfaces 2 located on opposite sides of each other.
PK, nB, Pal, n between 11,212
It has a four-layer structure of nE and one main surface 211 has nE.
The PB layer is exposed on the other main surface 212, respectively. n, the layer is a plurality of elongated strip regions 21 arranged side by side with their longitudinal directions matching the longitudinal direction of the main surface.
It consists of 3 (referred to as emitter strips). In the figure, this emitter strip 213 has a width of about 0.3 m and a length of about 4.0 m.
Two pieces are arranged side by side with simple dimensions. 2 emitter strips 2
13, a cathode electrode 22 is in low resistance contact, a gate electrode 23 is in low resistance contact with the surface of the PB layer surrounding the emitter strip 213, and an anode electrode 24 is in low resistance contact with the opposite surface of the PG layer. These cathode electrodes 22. The gate electrode 23 has a cathode lead 2 made of, for example, an aluminum wire.
5. A gate lead 26 is attached. Such G
The TO pellet 21 is assembled by soldering to a package paste (not shown) via the anode electrode 24. 2
7 is glass attached to an annular groove 214 provided on the periphery of the pellet 21.

FIG. 5 shows the safe operation area at turn-off of the embodiment shown in FIG. 4 (solid line) in comparison with the conventional example shown in FIG. 1 (dotted line). As is clear from the figure, the anode voltage 4
The maximum breaking current without destruction at 00V is approximately 10O
This was a dramatic increase compared to A and 3OA of the conventional example. In this way, although the GTO pellet has a continuous controllable current and the effective area of the nE layer is almost the same, the high voltage current flow and breaking performance is significantly improved. With this improvement, protection circuits such as the current-limiting inductance and CR of the snubber circuit, which are used when an abnormal current flows through the GTO, can be made significantly smaller and cheaper, contributing to the smaller size and lower cost of the device, as well as improving reliability. It is possible to improve the Now, the direct cause of this improvement in the cutoff resistance is that the length of the emitter strip is increased. According to other experiments, it has been confirmed that further improvement can be achieved when the length of the emitter strip is further increased. The reason for this is thought to be that even when a large number of emitter strips are arranged side by side, the anode current during turn-off ultimately concentrates on one strip, which exceeds a limit value and is destroyed. Therefore, it is only necessary to increase the current interruption resistance per emitter strip. In other words, at turn-off, no interaction to alleviate current concentration can be expected between emitter strips arranged in parallel, but this interaction can be expected within the same emitter strip. According to experiments conducted by the inventors, it has been found that the withstand capacity per strip of emitter increases as the length of the emitter becomes longer, provided that the width of the emitter is constant.

FIG. 6 shows another embodiment in which the present invention is applied to a GTO with a larger current capacity, and is a GTO with a controllable current similar to that shown in FIG. In this case, four emitter strips 213 each having a length of approximately 4.0 mm are juxtaposed, and the pellet has a rectangular shape with one opposite side being approximately 6.0 mm long and the other opposite side being approximately 4.0 mm long. The maximum current that can be cut off by this GTO at a clamp voltage of 400V is about 10OA.

FIG. 7 shows another further improved embodiment of the present invention.

Inside the silicon pellet 21, about 5.8 mm long
Four emitter strips 213 with a width of about 0.3 mm are arranged in parallel, and an ohmic electrode layer 221 with a thickness of about 4 μm made of chromium, nickel, and silver is connected to the surface with low resistance. A gate electrode layer 231 with a thickness of about 0.2 mm and a length of about 5.8 m forms an emitter strip 213.
It is set up in a narrow shape. Copper electrode leads 222 and 232 are further soldered onto these ohmic electrode layers 221 and 231. These electrode leads 222 and 232 are connected to the electrode layer 221 and the gate electrode layer 231 on the surface of the emitter strip on the pellet using copper foil with a thickness of about 30 to 50 μm.
They are each formed into a comb shape according to the shape of , and connected to them via solder. In this case, the electrode layers 221 provided on each emitter strip are electrically connected to each other by electrode leads 222 and drawn out to the outside.

In an embodiment of such a configuration, the lateral electrode resistance along the electrode layer on the emitter strip as well as the gate electrode layer is significantly reduced by a copper foil several tens of micrometers thick that is oxidized on top of each; The non-uniformity of operation due to the potential drop within the electrode layer is significantly improved. As a result, the length of the emitter strip is not only 5.8 in this embodiment, but also 7.8 in length.
It is also possible to make the length longer than rrrm, and the current cutoff limit can be further improved. This improved embodiment also eliminates the area occupied by the bonding ink hat required for wire bonding aluminum wires, as shown in the embodiments of FIGS. 4 and 6, so that the bullet size is approximately 7.
There is an economic advantage in that it can be reduced to 5%. In this example, the current cutoff limit at a clap voltage of 400V was significantly improved to about 25OA.

As explained above, according to the present invention, the safe operation area of the GTo is expanded, and the current and voltage that determine the destruction limit when the element current is cut off are increased, which is an effect of improving performance.・This improved performance also simplifies the GTO protection circuit for abnormalities such as arm short circuits when the GTO is used in actual circuits such as inverters. That is, G.T.
The current-limiting inductance, which serves to limit the current flowing through o, can be made smaller and cheaper, and the abnormality detection and command circuits can be simplified. Furthermore, since a current of 25 OA or more can be safely cut off with a clamp voltage of 400 V, the snubber circuit such as a 0.1 to 0.2 μF snubber capacitor or polarized diode that was conventionally required to protect the GTO can be omitted. , the economic effects of GTo application equipment such as smaller size, simplicity, and lower cost are enormous.

Furthermore, since the GTO pellet of the present invention always has a rectangular shape, it becomes easy to detect nine positions of the pellet in each direction, and there are also side effects such as easy automatic mounting, sorting, etc.

[Brief explanation of the drawing]

1 and 2 are a plan view and a sectional view showing a conventional example of a conventional GTO, FIG. 3 is a characteristic diagram showing a safe operating area of a conventional GTO, and FIG. 4 is an example of an embodiment of the present invention. FIG. 5 is a characteristic diagram showing the safe operation area of the GTO shown in FIG. 4, and FIGS. 6 and 7 are schematic diagrams showing other embodiments of the present invention. 21... Pellet, 211... Emitter strip, 22
...Cathode electrode, 23...Gate electrode, 24...
・Anode Figure 1 ((L) (b) (C1,) → Anode °Electric IE HiA (V) 4th
Figure (b)

Claims (1)

[Claims] 1. A pair of main surfaces located on opposite sides each have a rectangular shape with one opposite side longer than the other opposite side, and have four consecutive layers of PNP between the pair of main surfaces, An outer N layer and an intermediate P layer adjacent thereto are exposed on one main surface, at least an outer P layer is exposed on the other main surface, and the outer N layer extends longitudinally toward one main surface. A semiconductor pellet consisting of a plurality of strip-shaped regions arranged in parallel along the longitudinal direction; a cathode electrode in low resistance contact with the outer N layer on one main surface; A gate comprising: a gate electrode in low resistance contact with the intermediate P layer along the periphery of the N layer; and an anode electrode in low resistance contact with at least the outer P layer on the other main surface. turn-off thyristor. 2. In claim 1, the cathode electrode has substantially the same shape as the strip-shaped region of the cathode layer, and includes a plurality of first conductive members adhered to the strip-shaped region; a second conductive member that electrically connects the conductive members to each other;
A gate turn-off thyristor comprising a conductive member and a second conductive member bonded thereon. 3. The gate turn-off thyristor according to claim 2, wherein the first conductive member of the cathode electrode and the first conductive member of the gate electrode are made of copper foil.