JP3109796B2 - Self-extinguishing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-extinguishing device capable of significantly improving a breaking ability.

[0002]

2. Description of the Related Art Inverters have been used in many fields at present, but gate turn-off thyristors (hereinafter referred to as GTO) for large-sized devices, and insulated gate bipolar transistors (hereinafter referred to as IGBTs) for small-sized devices. Is used exclusively.

Generally, a device capable of turning on and off a main current at a gate (sometimes called a base) is called a self-extinguishing device. A self-extinguishing device has a thyristor operation such as GTO, and an IGB
Some perform a transistor operation such as T. For the former, as long as the main current once supplied does not decrease below a certain value,
It keeps on even after removing the gate current and voltage. In the latter case, it is necessary to always apply a gate current / voltage to keep the main current flowing. Exceptionally, some devices, such as SIT, require a voltage to be applied to the gate to maintain the off state.

The inside of a power self-extinguishing device is composed of a segment on one chip, or an aggregate of many segments called cells, which are self-extinguishing devices themselves. In the case of GTO, it is called a segment, and in many other self-extinguishing devices, it is more often called a cell, but here it is called a segment without distinction.

[0005] A GTO of 1000 A guarantees that the gate can be turned off if the main current flowing to the anode is within 1000 A, which is called a maximum turn-off current or a maximum controllable current. If the current exceeding the threshold is turned off at the gate, the GTO may be destroyed. In a device using the GTO, the following relationship is generally established between the rated current peak value A, the overload current peak value B, the protection level C, and the maximum turn-off current D of the GTO.

If A <B <C <DD is 1000A, C is 800A and B is 700A.
About. The value of the overload is determined by the type of load. If this value is set to 150%, the rated value A is 467 A and the effective value is 330 A. In semiconductor devices, the current value that can flow is often determined from the limit of the temperature rise value.
Is a value determined from the maximum turn-off current independent of the thermal constraint. If the maximum turn-off current of this GTO is high, the rated current can be higher and therefore
There is a possibility that a large capacity device can be manufactured at the same cost. Therefore, various measures have been taken to increase the maximum turn-off current.

Seki / Kurata / Takeuchi ed., "Turn-off thyristor", Denki Shoin, page 46, published in April 1983, states that the maximum turn-off current does not increase in proportion to the number of segments. That is, even when hundreds or thousands of segments are operated in parallel, current concentration occurs in a limited number of segments at the final stage of turn-off. It is said that the reason why the GTO is broken when the current exceeding the maximum turn-off current is cut off is that avalanche breakdown occurs inside the segment where the current concentration occurs.

The most effective means to increase the maximum turn-off current of the GTO as far as possible are miniaturization of the segment and reduction of the gate resistance. Toshiba Review, 1992,
VOL. 47, NO. FIG. 7 on pages 1, 29 and FIG. 7 shows how the maximum turn-off current increases due to miniaturization and reduction in gate resistance. However, the increase in the maximum turn-off current is limited only by miniaturization and reduction of the gate resistance.

Further, the GTO always requires a snubber circuit. FIG. 5 shows a typical snubber circuit. In the figure, 1 is a snubber capacitor, 2 is a snubber diode, 3
Denotes a discharge resistance, and 4 denotes a GTO. When the GTO 4 is turned off, the anode current i that has been flowing through the GTO 4 until then is transferred to the snubber capacitor 1.

FIG. 6 shows waveforms of the anode current i and the anode voltage VAK when the GTO 4 is turned off. The instantaneous power corresponding to the product of the current of the segment turned off last and the voltage applied to both ends of the GTO 4 is the generated loss P of the segment. There is a correlation between the generated loss P and the destruction due to the failure of the GTO 4 to be turned off. When P exceeds a certain value, the destruction occurs. P is substantially proportional to the spike voltage Vdsp shown in FIG. Since the spike voltage Vdsp can be easily observed, the spike voltage Vdsp is managed so as not to exceed a certain value. The factors that determine the spike voltage Vdsp are the stray inductances Ls and di / d existing in the closed circuit of the snubber capacitor 1, snubber diode 2, and GTO4.
t. In order to reduce the stray inductance Ls, parts having the least stray inductance Ls are selected and wiring is devised.

The eleventh of the aforementioned "turn-off thyristor"
FIG. 5 ・ 24 on page 5 states that the maximum turn-off current increases when the snubber capacitor capacity is increased. Although generally in the snubber capacitor capacitance increases the maximum turn-off current increases, in the snubber circuit of Figure 5 once per cycle of the GTO on and off, roughly loss of CV ^2/2 is consumed by the snubber resistor. Here, C is a snubber capacitor capacity, and V is a snubber capacitor voltage. In the case of a high-voltage, high-current GTO, the loss of one snubber reaches several tens of kilowatts.

In response to this, the second part of the aforementioned Toshiba Review
On page 8, it is described that miniaturization and formation of a low-resistance layer in the gate portion were used as means for reducing the snubber capacitor capacitance. FIG. 7 is an enlarged view of a part of the GTO on the cathode side. In the figure, 12 is a cathode electrode, 13 is a gate electrode, and 16 is an insulating resin film. The GTO is generally made by forming P-type silicon and N-type silicon in the order of PENBPBNE, but the PE layer on the anode side is omitted in FIG. Here, the suffix E is conventionally attached to the emitter layer, and B is used to indicate the base layer and the operation role thereof. The cathode electrode 12 is located at a hill-like portion called a mesa. The miniaturization here means that the width Ws of the NE layer below the cathode electrode shown in FIG.
2 to 160 μm, which reduces the distance between the center of the segment and the gate electrode. In addition, the gate part low resistance layer means that P ⁺ B
This means that a layer having a high impurity concentration called a layer is provided. These means have the effect of reducing the variation in operation between segments and reducing the capacitance of the snubber capacitor. The result appears in the turn-off waveform as shown in FIG.
That is, FIG. 8A shows a waveform in the case of the conventional structure, and FIG. 8B shows a waveform in the case where the structure is improved and the variation in operation between segments at the time of turn-off is reduced. Although the spike voltage Vdsp increases after the improvement, the loss per segment decreases because the variation is reduced.

A self-extinguishing device that performs a transistor operation is composed of segments that are much finer than a GTO. It does not matter if the device is a monopolar device that uses either electron or hole carriers, such as a MOSFET.However, in a bipolar device that uses two carriers, electrons and holes, the current between the segments is more or less unamped. To balance. IGBT with high breakdown strength
In this case, the current concentration at the time of turn-off is not completely absent, and the withstand capability is defined by the segment whose turn-off is delayed. Accordingly, various studies have been made to reduce the variation of the turn-off, but in all cases, means based on semiconductor physics such as miniaturization and reduction of resistance are taken.

[0014]

If many of the segments can be turned off at the same time, the turn-off capability is improved in proportion to the number of segments, and the capacity of the snubber capacitor can be reduced. Not only can be reduced, but also the size and cost of the device can be reduced.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a self-extinguishing device in which the current balance between segments is improved and the maximum turn-off current value is high.

[0016]

According to the present invention, there is provided a self-extinguishing device according to the first aspect of the present invention.
In a self-extinguishing device comprising a parallel circuit of a plurality of segments, this is achieved by arranging a magnetic material having a high relative permeability around a main electrode close to a gate for each segment or segment group. .

According to a second aspect of the present invention, there is provided a self-extinguishing device comprising a parallel circuit of a plurality of mesa-type segments, wherein each mesa-type segment or each segment group has a side closer to the gate. This is achieved by arranging a magnetic material having a high relative permeability around the main electrode.

Further, in the self-extinguishing device according to the third aspect, in the planar type self-extinguishing device comprising a parallel circuit of a plurality of segments, the main electrode closer to the gate is provided for each segment or segment group. And a magnetic material having a high relative magnetic permeability is arranged inside the trench.

Further, the self-arc-extinguishing device according to claim 4 is characterized in that a capacitor or a material having a capacitor function is provided between the main electrodes of the self-extinguishing device according to claim 1, 2, or 3. This is achieved by placing them in close proximity.

[0020]

According to the configuration described above, current concentration on a small number of segments at the end of turn-off can be suppressed, and as a result, the maximum turn-off current can be dramatically increased and the capacitance of the snubber capacitor can be reduced.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the block diagram of FIG. FIG. 1 shows a cross section of a GTO to which the present invention is applied. Although it is composed of many segments, only two segments a and b are handled here for simplicity. In the figure, 11 is a cathode electrode, 12 is a segment cathode electrode, 13 is a segment gate electrode, and 14 is an anode electrode. Reference numeral 15 denotes a magnetic material having a large relative magnetic permeability, for example, about 10 ⁵ , and 16 denotes an insulating resin film for surface protection. Incidentally, the conventional GTO does not have 15 parts. The cathode electrode 11 connects the cathode electrodes 12 of the segments to each other and is connected to a cathode electrode communicating with the outside of the GTO. The gate electrodes 13 of the segments are connected to each other at a location (not shown) and are connected to a gate electrode communicating with the outside of the GTO. The anode electrode 14 is connected to an anode electrode connected to the outside of the GTO via a molybdenum plate or the like (not shown).

Next, the operation of the GTO of the present invention having the above configuration will be described. In the GTO of the present invention, a magnetic material 15 having a high relative permeability is provided around the cathode electrode 12 of the segment.
(Hereinafter, simply referred to as a magnetic material). As a result, a magnetic flux is generated in the magnetic material 15 by the main current flowing through the cathode electrode 12 of each segment.
Occurs in the E layer. This magnitude is proportional to the change in current, and the proportional constant is called inductance. The effect of this inductance being arranged in each segment will be described below.

FIG. 2A shows a GTO of the present invention, and FIG.
Shows an equivalent circuit of the conventional GTO. As can be seen at a glance, in the GTO of the present invention, the inductances Lka and Lkb are added to the cathodes 12 of the segments a and b. In any case, the segment a has a characteristic that the turn-off is faster than the segment b by Δt. The anode current of each segment is represented by Ia, Ib
In a steady state, Ia = Ib = I.

First, in FIG. 2B, when the segment a is turned off first, the current Ia which has been flowing through the segment a immediately shifts to the segment b.
a + Ib = 2I. Thus, segment b must turn off twice the current. Actually, the current of many segments concentrates on one segment, so the current value becomes several tens to several hundred times.

Next, in the case of the present invention shown in FIG. 2 (a), when the segment a is to be turned off first, a voltage is generated as shown in the drawing to prevent the current from changing due to the action of the inductances Lka and Lkb. Abrupt movement from segment a to segment b is suppressed.

The voltage of the inductance Lka also serves as a voltage for suppressing the gate current of the segment a, and has an effect of delaying turn-off. [It is known that the turn-off time (the sum of the accumulation time and the fall time) changes depending on the gradient of the gate current, as shown in FIG. 3/14 on page 71 of the aforementioned “turn-off thyristor”. On the other hand, the voltage of the gate of the segment b is such that the turn-off is accelerated.

By arranging the magnetic material 15 as described above, it is possible to suppress variations in the turn-off of the segments and prevent the current from being concentrated on one segment. This increases the maximum turn-off current value. By decreasing the current value at which the segment turns off,
Since the power loss per segment is naturally reduced, the capacitance of the snubber capacitor can be reduced.

FIG. 3 is a diagram showing the arrangement of the gate electrode 12 and the magnetic material 15 of the segment. The horizontal width of the cathode electrode 12 of the segment is Ws, the vertical width is WL, and the magnetic material 15 is as shown in FIG. The width of the magnetic material 15 is L, the height of the magnetic material 15 is H (shown in FIG. 1), the average magnetic path length around the segment is Wo, H is 20 μm, L is 100 μm (half of 50 μm per segment). ), When Wo is 10 ^-2 m and the size of the inductance of the segment is roughly calculated, the sectional area of the magnetic circuit is (20 × 50) = 10 ^-9 m ² , and the inductance is 13 nH.

As shown in another embodiment of FIG. 4, by increasing the thickness of the metal portion of the cathode electrode 12 of the segment and disposing the magnetic material 15 also around the metal portion,
, An inductance of several hundred nH is obtained. The size of the inductance can be selected to an optimum value by providing a gap in addition to the thickness of the electrode portion, or by using a material such as magnetic powder, which has a gap between grains by itself. This is not limited to the magnitude of the inductance, but it is important that the inductance does not saturate below a certain current value, so a gap is required.

In the case of a planar type self-extinguishing device, a cathode (sometimes called an emitter or a source)
Since the portion is raised, it is necessary to make the electrode portion thick. In addition, although the effect is slightly diminished, aluminum electrodes are collectively provided in units of a plurality of segments (the number varies depending on the degree of miniaturization, so the area is about 0.1 cm ² ), and some aluminum electrodes are provided. There is also a method of increasing the thickness and depositing a magnetic material around the thickness. There is also a method of digging a trench and embedding a magnetic material therein.

When a large number of segments are simultaneously turned off according to the present invention, Vdsp shown in FIG. 6 increases. As described above, this is because the voltage (Lsdi / dt) of the inductance of the snubber circuit increases. The instantaneous power (product of Vdsp and segment current) of each segment is V
Even if dsp increases, the instantaneous power is reduced overall because the segment current decreases, but it is desirable that Vdsp be low.

To suppress Vdsp, the stray inductance of the snubber circuit may be reduced. However, since there is a limit to this, a small-capacity capacitor is connected as close to the self-extinguishing device as possible separately from the snubber circuit. It is better to arrange between the cathodes. For this purpose, it is preferable to put a capacitor or a material having the same function as the capacitor inside the outer package.

[0033]

As described above, according to the present invention,
Since the current concentration at the time of turn-off between a large number of segments or between a large number of segment groups is reduced, (1) the maximum turn-off current that can be obtained with the same pellet size increases. (2) The capacity of the snubber capacitor when turning off the same current is reduced. As a result, it is possible to reduce the size, increase the efficiency, and reduce the cost of a semiconductor conversion device such as an inverter using the same.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a self-extinguishing device showing one embodiment of the present invention.

FIG. 2 is an equivalent circuit of a self-extinguishing device, (a) is an equivalent circuit of a self-extinguishing device to which the present invention is applied, and (b) is an equivalent circuit of a conventional self-extinguishing device.

FIG. 3 is a view showing an arrangement relationship between a cathode electrode of a segment and a magnetic material in the self-extinguishing device of the present invention.

FIG. 4 is a partial cross-sectional view of a self-extinguishing device showing another embodiment of the present invention.

FIG. 5 shows a snubber circuit associated with a self-extinguishing device.

FIG. 6 is a waveform diagram of an anode voltage and a current when the self-extinguishing device is turned off.

FIG. 7 is a partially enlarged cross-sectional view on the cathode side of the self-extinguishing device.

FIGS. 8A and 8B are waveform diagrams of an anode voltage and a current when the self-extinguishing device is turned off. FIG. 8A shows a characteristic when the operation between segments is uneven, and FIG. 8B shows a characteristic when the operation is uniform.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Snubber capacitor 2 ... Snubber diode 3 ... Discharge resistance 4 ... GT
O 11 cathode electrode 12 segment cathode electrode 13 segment gate electrode 14 anode electrode 15 magnetic material having a large relative magnetic permeability 16 insulating resin film for surface protection

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 29/744

Claims (4)

(57) [Claims] In a self-extinguishing device comprising a parallel circuit of a plurality of segments, a magnetic material having a high relative permeability is arranged around a main electrode close to a gate for each segment or segment group. Self extinguishing device. 2. A self-arc-extinguishing device comprising a parallel circuit of a plurality of mesa-type segments, wherein each mesa-type segment or each segment group has a high magnetic permeability around a main electrode near a gate. Self-extinguishing device with material placed. 3. A planar self-extinguishing device comprising a parallel circuit of a plurality of segments, wherein a trench is provided around a main electrode near a gate for each segment or segment group, and a high ratio is provided inside the trench. A self-extinguishing device in which a magnetic material having magnetic permeability is arranged. 4. The method according to claim 1, 2 or 3.
5. A self-extinguishing device, wherein a capacitor or a material having a capacitor function is disposed close to a main electrode of the self-extinguishing device according to 1.