JPH0691247B2 - Bidirectional semiconductor device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an AC switching semiconductor device (hereinafter, abbreviated as “TRIAC”) having a five-layer structure of alternating conductivity types among bidirectional semiconductor devices. In particular, the present invention relates to a gate structure having improved ignition characteristics.

[Technical Background of the Invention and Problems Thereof] A triac is a semiconductor switching element capable of bidirectionally controlling an alternating current by a positive or negative gate signal.
FIG. 4 is a plan view of a conventional triac, and FIG. 3 shows a sectional view of a broken line segment XX of the same triac. Its cross section is n-p-
It has a five-layer structure of npn. 1 is the first main electrode T ₁ (T ₁
2 is an n-emitter N _E1 connected to T ₁ , 9 is a second main electrode T ₂ , 8 is an n-emitter N _E2 connected to T ₂ , 3 is a gate electrode G 4, and 4 is a gate electrode G 4. N emitter N _EG , which is connected to G. 5, 6 and 7 are p-base P _B and n-base respectively
N _B and p emitter P _E. The firing mode of this triac is the bias direction between T _{1 and} T ₂ (positive and negative 2 directions), and T ₁
There are four types of combinations in the bias directions (two directions) between −G. That (if to T ₁ at the same time by applying a positive bias to T ₂ to T ₁ of a positive bias is applied to the G) I mode, (T ₂ positive with respect to T _1, G negative) I mode, III
There are four modes: a mode (T ₂ negative, G positive with respect to T ₁ ) and a III mode (T ₂ negative, G negative with respect to T ₁ ). In the I mode, the electrode T ₂ is the anode and the electrode T ₁ is the cathode P _{EN B} P _B
This is the case where the four-layer thyristor part of N _E1 turns on, and in the III mode, the four-layer thyristor part of P _B N _B P _E N _{E 2} with electrode T ₁ as the anode and electrode T ₂ as the cathode turns on. This is the case. Figure 5 (a) and (b) for the to is a plan view clarity for explaining a region where initial electron injection occurs in each mode N _E2
Is omitted. In the case of FIG. 5 (a), when a positive voltage is applied to the gate G with respect to T ₁ , a gate current flows from (a) to (b) in the direction of the arrow in the figure. The gate current path is not offset to n emitter side in contact with the second N _E1 namely T ₁ electrode, potential drop occurs in the p base P _B region sandwiched between N _EG of N _E1 and 4.

As a result, the region shown in the figure is first forward-biased, and is the part where the initial injection of electrons is performed. This initial implantation region contributes in I mode and III mode. That is, in the I mode, this causes P _E N _B N _E1
The thyristor structure part is turned on, and the main current conducting region I shown by 10 is formed (the region shown by diagonal lines). In the case of III mode, this electron injection turns on the thyristor structure part of P _B N _B P _E N _E2 , and the main current conducting region II indicated by 11
I is formed. In the I mode, the initial injection region and the main current conduction region I are close to each other and the turn-on process is similar to that of a normal thyristor, so that the turn-on is easily performed. In the case of the III mode, since this region is separated from the main current conducting region III, it takes time for the ignition region to move, and the process is complicated, so that the ignition characteristics deteriorate.

Considering the case where a negative voltage is applied to the gate electrode 3 shown in FIG. 5 (b), it is changed from (b) to (a) in the direction of the arrow shown in FIG.
The gate current flows to. The potential distribution generated by this current causes the first electron injection region in the region shown in FIG. This initial implantation region contributes in I mode and III mode. Since this region is close to the main current conducting region III for III mode, it is relatively easy for P _B N _B P
The thyristor structure of _E N _E2 can be turned on. In the case of the I mode, the initial injection region is separated from the main current conducting region I, but the N _B P _B junction is reverse biased and the ignition process is simpler in the I mode than in the III mode. Not affected.

The triac is used as an AC switching element, and the firing mode used in that case is a combination of two of the three firing modes except the III mode. The reason why the III mode is not used is that the firing characteristics are poor as described above, and the gate current required for firing is much larger than the other three modes. The state of the ignition will be described. In FIG.
Electrons are injected from N _E1 to P _B which is forward biased by the gate current flowing from the main electrode to the main electrode T ₁ (region of FIG. 5 (a)).

In FIG. 3, these electrons are accumulated in n base N _{B of} 6 and N _B
As a result of lowering the potential of, holes are injected from P _B to N _B.
This hole flows through N _B from the p emitter P _{E of} 7 to the T ₂ electrode of 9, but at this time, a potential drop occurs in P _E , which is
The injection of electrons from _E2 is promoted and finally the main current conduction region II
I is formed. In this process, the III mode is ignited, but the pattern arrangement of the n emitters N _EG and P _{B in the} gate G part and the partial overlap of N _E1 and N _E2 influence the superiority and inferiority of this ignition characteristic. To do. Among these, it is considered that the gate current path is restricted by the pattern arrangement of N _EG of the gate so that the electron injection from N _E1 occurs efficiently, which contributes to the improvement of the III mode characteristics. In the conventional gate pattern, the gate current path from the gate G to the T ₁ electrode is 1
Depending on the ignition mode, there is a case where the place where the initial electron injection occurs and the main current conducting region that finally conducts are separated. The III mode is exactly in this state, which is considered to be one of the reasons for the deterioration of the ignition characteristics.

As described above, it is a drawback and a problem of the conventional triac that the region where the initial electron injection occurs is at an extremely inappropriate position depending on the ignition mode.

[Object of the Invention] Among the triacs having four ignition modes, the present invention improves the III mode, which has conventionally been very poor in ignition characteristics as compared with the other three modes, and allows all four modes to be freely set. It is intended to be usable.

[Outline of the Invention] In the present invention, for each mode of the triac, the region where the initial electron injection occurs is one place or two or more places, and this initial injection region is arranged at the position closest to the main current conducting region of each mode. By doing so, the problem is solved.

That is, in the present invention, (a) np- whose conductivity types are alternately different
A semiconductor and a substrate having a five-layer structure of npn, (b) an n-type N _EG (first surface layer) on one surface side of the substrate, N _E3
(Second surface layer) and N _EG (third surface layer), and (c)
A first intermediate layer adjacent to each of N _E1 , N _E3 and N _EG, a part of which is exposed on the surface to separate the above three n emitters from each other, and a p-type base layer P _B ; ) and N _E1 and the third electrode T ₃ which is provided in contact with the surface exposed surfaces of the P _B of the first main electrode T ₁ and N _E3 provided in contact with the surface exposed surfaces adjacent thereto P _B adjacent thereto , N _EG and its adjacent P
_A gate electrode G provided in contact with the exposed surface of _B ,
(E) n-type N _E2 (fourth surface layer) on the other surface side of the substrate, and (f) P of the p-type body 2 intermediate layer adjacent to N _e2 and part of which is exposed on the surface. _E , and (g) N _E2 and a second main electrode T ₂ provided in contact with the exposed surface of P _E , and N _E2
Is a triac having a structure that at least partially overlaps each layer of N _E1 , N _E3, and N _EG as seen in a plane, and (a) N _E3 is arranged so as to surround N _EG , and (b) N _E3 and N _EG are arranged.
And each of which is provided with one or a plurality of openings so that the region where the initial carrier injection occurs is as close as possible to the main current conducting region, and the position of the opening is the first main current conducting region I of N _E1 . Regarding the bisector that divides the elongated region sandwiched by the second main current conducting region III of P _B exposed on the surface into approximately two equal parts, the position of the opening is (b-1) when there is one opening. Is arranged in a region on the bisector and close to both the first and second main current conducting regions. (B-2) When there are a plurality of openings, at least two of them are A triac characterized in that one is arranged in a region close to the first main current conducting region and the other one is arranged in a region close to the second main current conducting region on opposite sides with respect to the straight line. is there.

The region where the initial electron injection occurs is T in the opening of N _E3.
3 P _B N _EG Junction area or N facing the contact part between electrode and P _B
The P _B N _EG junction region facing the contact portion between the gate electrode G and P _{B in} the opening of the _EG . The main current conduction area is T ₁ , T
₂ P _E N _B P _B N _E sandwiched by both electrodes The first main current conduction region forming a thyristor structure with four layers of P _E N _B P _B N _{E 1} and P _B N _B P _E N sandwiched between both T ₁ and T ₂ electrodes It is a second main current conducting region that forms a thyristor structure with four layers of _E2 . In addition, the first main current conducting region means a geometric region where six of the T ₁ electrode, N _E1 layer, P _B layer, N _B layer, P _E layer and T ₂ electrode overlap with each other when viewed from the surface. In fact, the final conduction area of the main current does not completely match the geometrical area due to the end effect of the electrodes and the layers.

As a preferred embodiment when considering the balance of the ignition characteristics and the productivity in each mode, the position of the opening is on an equal straight line and symmetrically divided by this straight line when there is one opening. In addition, in a region close to both the first and second main current conducting regions, and when there are a plurality of openings, at least two of them are symmetrical with respect to the straight line, and the first and second main currents are located. It is arranged in a region close to one of the energization regions.

[Embodiment of the Invention] FIGS. 1 (a) and 1 (b) are plan views of an embodiment of a triac according to the present invention set forth in claim 3 as viewed from the first main surface side. In order to make the drawing easier to see, the same figure (a) is the N _E2 layer 8, and the same figure (b) is the first main electrode 1,
The description of the third electrode 15 and the gate electrode 3 is omitted.
As shown in FIG. 3B, N _E2 (fourth surface layer) 8 is a part of N _E1 (first surface layer) 2, N _E3 (second surface layer) 16 and N _EG (third surface layer).
It overlaps with the surface layer 4 when seen in a plane. N _E3 is N _EG
N _E3 has one opening 18 and N _EG
Has two openings 17. FIGS. 2A and 2B are plan views for explaining the initial electron injection region of the triac of the present invention. In FIG. 10A, a shaded area 10 is a first main current conducting area (operating in the I mode),
Reference numeral 11 indicates a second main current conducting region (operating in III mode).
The straight line Y-Y is a straight line that divides the elongated portion sandwiched between the regions 10 and 11 into two equal parts. In the figure, (a) shows the gate current flowing out from each of the two gate openings 17 even when a positive voltage is applied to the gate electrode (G) 3 with respect to the first main electrode (T ₁ ) 1. Thus, it flows through the gate current path limited by N _EG 4 and N _E3 16 and is collected at the third electrode 15 in contact with the opening 18 of N _E3 . This current causes a potential distribution in each part of the gate current path that drops along the gate openings 17 to 18, and forward biases each part of the N _E3 P _B junction in contact with this potential distribution. The most forward-biased region is the N _E3 P _B junction facing the opening 17. Therefore, the first electron injection occurs in the region shown in the figure. Similar electron injection also occurs in the N _E3 P _B junction region ′ facing the other opening arranged symmetrically with respect to the straight line YY. In order to ignite the I mode, injected electrons in a region near the main current conducting region I, and III
In order to ignite the mode, injected electrons in a region 'close to the main current conducting region III are used. FIG. 2 (b) shows the first
When a negative voltage is applied to the gate electrode (G) 3 with respect to the main electrode (T ₁ ) 1, the gate current is N _E3 1 as shown by the arrow in the figure.
From the portion of the third electrode 15 which is in contact with the opening 18 of 6, the shunt is made in two directions and flows into the two openings 17 of the N _EG 4. This gate current causes a potential drop from the opening 18 toward the opening 17 in the P _B region of the gate current path surrounded by N _EG 4 and N _E3 16, and the parts of the P _B N _EG junction in contact with this are sequentially connected. Varius. Among them, the region where the bias is particularly strong is the P _B N _EG portion facing the opening 18. Therefore, the first electron injection occurs from the region shown in the figure. In this case, the injection region is located on the bisector YY and is close to both of the two main current conducting regions. Therefore, the I-mode and the III-mode are symmetrically initiated by the injected electrons in this region.

As is apparent from the above-described embodiment, the region where the initial electron injection occurs is P _B N _E3 facing the opening of N _EG (gate current outflow end) having a high potential when the gate potential is in the mode.
P _B N, which is the junction and _faces the opening of N _E3 (the gate current outflow end) where the potential is high when the gate potential is in the mode.
_{It is the EG} junction. N _E3 16 is a part of N _E12, but the reason why it is separated by the region 19 of P _B 5 is mainly the main current conducting region.
The effect of the N _E3 portion close to the N _E3 16 parts and main current region I adjacent to III is shunt with each P region is to increase the ease of manufacturing in the same level. N _E3 is P _B
It is considered that the first main electrode 1 and the third electrode 15 are connected via the region 19 of P _B and are approximately at the same potential, though they are separated from N _E1 by.

In the present embodiment, the double pattern of N _E3 and N _EG is divided into equal straight lines YY.
However, the present invention is not limited to this. When the shapes of the main current conducting regions I and III are different and the above-mentioned straight line cannot be determined, for example, two openings are provided in N _EG , one of which is the region I and the other is the region.
Place them closest to III respectively (function in positive gate mode). One opening is provided in N _{E3 and} it is arranged at a position close to both regions I and III.

In this case, two gate current paths are formed, but the balance of the firing current is such that the resistance of the gate current path from the opening of N _{E3 to} the opening of N _EG is equal to each other (for example, Of the gate electrode in the opening of the N _EG to the opposing N _E3 of the N _EG so that the spreading resistances of P _B become equal to each other (for example, this portion has the same shape). Good.

EFFECTS OF THE INVENTION According to the present invention, the initial electron injection region of the triac is _NEG
And the position of the opening of N _E3 can be changed intentionally. In the conventional triac, the initial electron injection region and the main current conducting region III in the III mode are distant from each other and the ignition characteristics are deteriorated.However, according to the present invention, it becomes possible to provide both regions close to each other. The characteristics were also improved. Whereas the conventional triac used only three modes, it can now use all four modes.

Further, by arranging the pattern of the N region of the gate symmetrically and setting the gate current path symmetrically, the asymmetry of the generation of the injection region due to the asymmetry of the gate pattern is eliminated. As a result, the imbalance of the gate current depending on the mode in the ignition characteristic is reduced, and the degree of freedom in designing the electric circuit using the triac is increased.

[Brief description of drawings]

1 (a) and 1 (b) are partial plan views of the triac according to the present invention, and FIGS. 2 (a) and 2 (b) are plan views for explaining an initial electron injection region of the triac according to the present invention. 3 and 4 are a cross-sectional view and a plan view, respectively, of a conventional triac, and FIGS. 5 (a) and 5 (b) are plan views for explaining an initial electron injection region of the conventional triac. 1 ... First main electrode (T ₁ ), 2 ... First surface layer (N _E1 ), 3 ...
Gate electrode (G), 4 ... Third surface layer ( _NEG ), 5 ... First
Intermediate layer (P _B ), 7 ... Second intermediate layer (P _E ), 8 ... Fourth surface layer (N _E2 ), 9 ... Second main electrode (T ₂ ), 10 ... First main current conducting region (I ), 11 ... Second main current conducting region (III), 15 ... Third electrode (T ₃ ), 16 ... Second surface layer (N _E3 ), 17, 18 ... Opening, YY ...

Claims (2)

[Claims] 1. A semiconductor substrate having a five-layer structure in which conductivity types are alternately different from each other, and a first surface type first surface layer, a second surface layer and a third surface layer of the first conductivity type on the first main surface side of the substrate. A first intermediate layer adjacent to each of the first, second and third surface layers, a part of which is exposed on the first major surface to separate the three surface layers from each other; A first intermediate layer, a first main electrode provided in contact with the first surface layer and an exposed surface of the first intermediate layer adjacent thereto, a second surface layer and a first adjacent to it
A third electrode provided in contact with the exposed surface of the intermediate layer, a gate electrode provided in contact with the exposed surface of the third surface layer and a first intermediate layer adjacent thereto, and a first electrode on the second main surface side of the base. A conductive-type fourth surface layer, a second conductive-type second intermediate layer that is adjacent to the fourth surface layer and a part of which is exposed to the second main surface; a fourth surface layer, and a second intermediate-layer exposed surface; And a second main electrode provided in contact with the second main electrode, and having a structure in which the fourth surface layer at least partially overlaps each of the first, second and third surface layers when seen in a plan view. And (a) the second surface layer is arranged so as to surround the third surface layer, and (b) the main current conducting region is formed in each of the second surface layer and the third surface layer where the initial carrier injection occurs. One or a plurality of openings are provided so that they are as close as possible to the first main surface of the first surface layer. The region between the flow collector region and a second main current conducting region of the first intermediate layer exposed surface substantially 2
Regarding the equally dividing straight line, (b-1) When there is one opening, the region on the straight line is close to both the first and second main current conducting regions, and (b-2) ) When there are a plurality of openings, at least two of them are arranged on mutually opposite sides with respect to the straight line and in a region close to either of the first and second main current conducting regions. Bidirectional semiconductor device. 2. The bidirectional semiconductor device according to claim 1, wherein the positions of the openings are arranged symmetrically with respect to the straight line.