JPH03155674A - Bidirectional 2-pole thyristor - Google Patents

Abstract

PURPOSE:To obtain a bidirectional 2-pole thyristor which can be mass-produced stably with a high yield rate and has a large withstanding current for a surge by providing a region in which the overlapping distance of P (N) layers is relatively small in comparison with the one of the other region in the overlapping part of P (N) layers on both surfaces of the thyristor. CONSTITUTION:While the overlapping width of a P1 and P2 layer in a usual thyristor is d over the whole length of an overlapping part, a region C in which the overlapping width shown as d' is made to be small is locally provided in the central region part of the element and in this region, and the distance in the lateral direction between an N1 and N2 layer is shortened by (d-d'). Thereby, the positional distributions of current amplification factors alphaN, alphaP become the ones in that (alphaN+alphaP) expressing a turn-on condition is forced to exhibit a maximum peak concentrated near the region C and this corresponds equivalently making base widths WN and WP small. Therefore, the withstanding current for a lightning surge can be improved decreasing an electric power loss in a turn-on region.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a PNPNP (NPNPN) type bidirectional two-terminal thyristor, and is concerned with improving its lightning surge current withstand capability and manufacturing yield. be.

(Prior art and its problems to be solved) Fig. 1 (
A two-terminal silicon risk having a P, N+ P Nz Pg type structure, as shown in the cross-sectional view and plan view with the upper metal electrode omitted, shown in a) Cb) is widely used. (In the figure, M + 9M z is a metal electrode, 11 is an insulating film, for example, a 330g film, and d is P, and the overlap width of PtN.) In addition, recently, wires that are small and inexpensive, have high surge current resistance, and have two terminals Because it is easy to use, it is widely used for lightning surge protection in communication lines and other areas.

However, due to the structure of current thyristors, it is unreasonable to expect any further improvement in their ability to withstand current surges with a steep rise, such as surges, especially lightning surges. Moreover, it is impossible to prevent variations in the surge current resistance due to the large influence of variations in the vertical structure of the SIRISK, the impurity temperature and thickness of each layer, and even the geometrical position of each structure. Therefore, efforts are being made to eliminate the above-mentioned effects as much as possible by applying advanced process technology, but since there are limits to improving the accuracy of process technology, it is difficult to mass produce by reducing the variation in current withstand capacity. There are difficulties. Therefore, depending on the conventional structure, it is difficult to produce a bidirectional two-terminal circuit with high lightning surge current resistance with a high yield.

The reason for this will be explained below with reference to FIG. 2 regarding the normal bidirectional two-terminal risk related to the present invention shown in FIG.

In FIG. 2(a), which shows a cross-sectional view of the essential parts of the bidirectional two-terminal thyristor shown in FIG. As shown in step 1 of FIG. 2(b) showing the voltage-current characteristics, almost no current I flows. When the voltage reaches and exceeds the breakover voltage VIO of junction J, the current I
increases. Then, the amount of electrons injected from the N1 layer increases as indicated by the broken line arrow in FIG. 2(a). For this reason N
The current amplification factor α8 of the IPNz transistor increases due to its current dependence.

On the other hand, the current component flowing laterally through the N2 layer causes a voltage drop due to the lateral resistance of the N2 layer, which applies a forward bias to the junction J4. For this reason, hole injection occurs as shown by the solid arrow in FIG. 2(a), and the current amplification factor α of the transistors P, N, and
increases. As a result, αN + αP-1 becomes the junction J,
is no longer able to maintain the reverse direction breakdown voltage, it passes through step 3, which is the turn-on transition region in FIG. Due to the diffusion of carriers, the device spreads over the entire surface of the device and turns on.

As described above, the thyristor shown in Fig. 1 performs a turn-on operation, but the withstand capability against a steeply rising current surge such as a lightning surge is limited to a certain step 2.3 in the turn-on transition region shown in Fig. 2 (a). That is, it is determined by the power loss that occurs during turn-on and the speed at which the initial ignition at the - point spreads to the entire turn-on area, with the former being particularly important.

Therefore, the operation in step 2.3 showing the turn-on transition region in FIG. 2(b) will be explained in more detail with reference to FIG.

That is, the density of the current flowing across the junction J in step 2 of FIG. 2(b), and therefore the density of the current I flowing across the junction J2, is determined by the overlap of the Pt and Pg layers shown in FIG. 2(C). As shown by curve (1) in the relationship between distance Become.

(In addition, if negative resistance is shown in step 2 of FIG. 2(b), this tendency of current concentration becomes even stronger.) As a result, the current flowing through the N2 layer is the curve (n )
The voltage drop caused by this current, that is, the forward bias of junction J4 in FIG. 2(a), is as shown in FIG. 2(C).
As shown in the middle curve (I[), it increases rapidly up to the vicinity of point A,
After that, the increase slows down. Therefore, a forward current flows through the junction J4 due to this forward bias voltage, but the density of the current flow is as shown by the curve (IV) in Figure 2 (C).
It is maximum at point B, which is far from the center 0 of the element, as shown in FIG.

Here, the current amplification factor α4. is related to the turn-on condition α8+αp=1. α2 depends on the current distribution of the current 11+I2 based on the short-circuited emitter structure of the bidirectional thyristor, and the degree of dependence varies depending on the vertical structure and Nr P r N
z It varies greatly depending on the impurity concentration, thickness, lifetime, etc. of the P layer, as well as the positional non-uniformity of each structure. Therefore, the current amplification factor α8 corresponds to the dependence as shown in Fig. 2(d).
As shown in the relationship between distance On the other hand, corresponding to the dependence on the current amplification factor α, it reaches a maximum at point B, as shown in FIG. 2(d), and decreases as the distance from this point increases. Therefore, the maximum points of α8 and α2 have a positional deviation, and this positional deviation varies, but this qualitatively corresponds to changing the base widths WN and W, as shown in FIG. For example, the base widths WN and W are increased as point B is separated from point A, and the turn-on condition α8+
Current amplification factor α8 at αP-1. This corresponds to effectively reducing α. Therefore, considering the time course of the turn-on phenomenon, the turn-on time is increased, and the power loss during the turn-on transition is increased. That is, with the conventional thyristor structure, it is impossible to hope for any further improvement in surge current withstand capability.

In addition to this, effective α8. The degree of decrease in α and increase in turn-on time is affected by variations in the vertical structure during manufacturing, etc., which causes variations in the initial ignition position and the speed at which the turn-on area spreads after turn-on. Let me use it.

Therefore, depending on the conventional structure, it is not possible to manufacture a bidirectional two-terminal circuit with a high yield with a current surge resistance with a steeper rise than the current one.

(Objective of the Invention) The purpose of the present invention is to provide a means for stably mass-producing a bidirectional two-terminal circuit with excellent surge current resistance with high yield by using conventional manufacturing methods such as impurity diffusion. It is.

(Means of the present invention for solving the problem) The present invention was conceived based on the result of elucidating that the cause of the decrease and variation in the surge current withstand capacity is due to the relative positional deviation between α8 and α. According to the present invention, the current distribution is forcibly changed by planar structure means, and the current amplification factor α8. α
By localizing the positional distribution of , as shown in Figure 5,
This is an attempt to solve the problems of the prior art by reducing the positional deviation between the maximum points of α and α. Next, the present invention will be explained by examples.

(Embodiment) FIGS. 4(a) and 4(b) are cross-sectional views showing the structure of an embodiment of the present invention, and upper metal electrode M1. This is a plan view in which the insulating film I7 is not shown (the same reference numerals as in FIGS. 1 and 2 indicate the same parts), and the features of the present invention are as follows.

PI+P! in the conventional thyristor shown in FIG. The overlapping width of the layers is d in the total length of the overlapping part, but in the present invention, a region C where the overlapping width is locally reduced is provided in the center of the element as shown in d'' in FIG. ,
N in this part.

This is characterized in that the lateral distance of the Nt layer is shortened by dd'.

2, the current in step 2, which is the turn-on transition region in FIG. 2(a), flows concentratedly in region C as shown in FIG. 4 as indicated by lI. As a result, the current density in the CeI region becomes large, making the current amplification factor α8 near the C region extremely thick for the same current I.

On the other hand, the forward bias of the junction J4, that is, the lateral voltage drop of the N2 layer, compensates for the small overlap radiation d of the P+ and Pg layers because the current concentrates in the Cf and p regions as described above.
The values are approximately equal along the bottom of the boundary of the PiNi layer. As a result, due to the injection of holes from the 22nd layer, the current is distributed almost uniformly like I2, and the current amplification factor α is also approximately equal along the bottom of the boundary of the PiNt layer. Therefore, the current amplification factor α2
．． The position distribution of αP is as shown by the solid line in the relationship between the lateral distance X and the current amplification factor shown in FIG. α indicates the turn-on condition (position distribution of amplification thickness α8 and α)
8+α, is forcibly localized to the vicinity of the C area and becomes the maximum, and the base width WN explained in FIG.
This corresponds to making W and smaller. Therefore, power loss in the turn-on region can be reduced and lightning surge current resistance can be improved. Further, the initial firing position is also forcibly localized to the C9JI area, which acts as a firing pole. Therefore, variations in the initial ignition position are less likely to occur, and mass production with high yield is possible.

The action of the present invention explained above is based on the PNPNP type bidirectional 2
Since the structure of the terminal thyristor is symmetrical, the same results can be obtained when the current is passed in the opposite direction.

Therefore, according to the present invention, a bidirectional two-terminal thyristor with high resistance to surge currents with a steep rise such as lightning surges can be manufactured with high yield and economically by using manufacturing methods such as impurity diffusion that are unchanged from conventional manufacturing methods. become a target.

In addition, although the PNPNP conductivity type has been described above, the same effect can be achieved by applying it to a bidirectional two-terminal thyristor of the NPNPN conductivity type, or even to a composite thyristor having a PNPNP (NPNPN) structure in a part thereof. be able to.

In addition, although the above description has been explained using a schematic structural diagram to make the explanation easier to understand, it goes without saying that normally necessary means such as a channel stopper, for example, may be used to ensure reliability of the element.

(Effects of the Invention) As is clear from the above description, according to the present invention, a mere geometrical surface is provided in which an overlapping region of P (N) layers on both sides of the element has a shorter overlapping distance than other overlapping regions. By simply changing the structure, it is possible to completely eliminate conventional problems such as impurity diffusion.
This method has an excellent effect in that a bidirectional two-terminal thyristor having a large surge current resistance with a steep rise can be manufactured with high yield using the same manufacturing method.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are explanatory diagrams of conventional elements; Figure 4;
FIG. 5 is an explanatory diagram of one embodiment of the present invention.

Claims (1)

[Claims] A PNPNP (NPNPPN) type bidirectional two-terminal thyristor, characterized in that an area where the P(N) layers on both sides overlap is provided with a region where the overlap distance is relatively small compared to other parts. Tropical two-terminal thyristor.