JPH03215978A - Bidirectional diode-thyristor - Google Patents

Abstract

PURPOSE:To enable a thyristor to be easily manufactured, easily controlled in a holding current, and improved in cutoff characteristic by a method wherein an emitter and an exposed base region are shortcircuited to each other to constitute an electrode on both the sides of a substrate. CONSTITUTION:A P-type substrate is used as a common substrate, and an N1 layer is formed on one of the sides of the substrate and an N2 layer is formed on the other side. Rectangular P1 and P2 layers are provided onto the N1 and the N2 layer respectively so as to enable the exposed N1 layer and the exposed N2 layer to partially overlap each other and to be arranged in gridirons to form two-terminal thyristors T1 and T2. On both the sides, the P1 layers and the exposed N1 layer and the P2 layers and the exposed N2 layer are shortcircuited with metal electrodes M1 and M2 to constitute an electrode on each side of the substrate, so that elements located at a region where the N1 and the N2 layer are exposed are constituted in an NPNP layer of four- layered structure and elements located at the other region are constituted in a PNPNP layer of five-layered structure. By this setup, a thyristor of this design can be easily manufactured, easily controlled in a holding current, and can be improved in cutoff characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a bidirectional two-terminal thyristor that has excellent interrupting performance and is easy to manufacture.

(Prior art and problems to be solved) Plan views shown in FIGS. 1(a) and (b) (metal electrode M +
, M 2 insulating film I (not shown) and PNPNP (NPNPN) structure as shown in the cross-sectional view are small, inexpensive, and easy to use, so they are highly effective against lightning surges, etc. Widely used as a surge protection device. For example, as shown in Figure 2 (a), a two-terminal thyristor Z is connected between the input circuits L+ and Lz of protected electronic circuit A, and as shown in Figure 2 (b), lightning surge voltage exceeding its withstand voltage VBO enters. In this method, the lightning surge is turned on immediately when a lightning surge occurs, thereby protecting the protected electronic device A from the lightning surge as a bypass. In this case, after the lightning surge has passed, the bidirectional two-terminal thyristor Z has a circuit voltage E as shown in FIG. 2(b).

It is necessary to shut off the surge and return to the state before the surge. For this purpose, when the circuit impedance is R as shown in FIG. 2(a), the holding current Il+ of the two-terminal thyristor Z in FIG. 2(b) is E0? ■〉R? I have to be satisfied.

By the way, in the normal thyristor structure shown in FIG.
, P2, etc., the impurity concentration of each layer, layer thickness, carrier lifetime, etc., but usually precise control of the manufacturing process is required to satisfy the above conditions and keep it within the required range. It is not easy to achieve this goal since there are variations in the results.

(Objective of the Invention) The present invention provides a new holding current IH control means using a novel surface (electrode) structure to facilitate manufacturing.
This is intended to improve the interrupting characteristics by making it possible to obtain a large holding current value.

(Means of the present invention to solve the problem) Figure 3 (a)
(b) (C) (d) and (e) are plan views showing embodiments of the present invention (in the figure, the upper insulating layer and metal electrode M are removed), and a cross section taken along line A-A'. The present invention is characterized by the following points.

That is, a P-type substrate is used as a common substrate, and as shown in FIG. 3(b), an N2 layer (Heath) is provided on one surface and an N2 layer (Heath) is provided on the other surface. Further, in the N1 layer and the N2 layer, the N layer and the N2 layer are exposed on the - surface and the other surface, and the third
As shown in Figures (a) and (b), the exposed areas on the - side partially overlap with the exposed areas on the other side, forming a plurality of exposed areas in a checkerboard pattern (Figure 3 (a)).
, the solid line square is the exposed area of N1, and the dotted line square is the exposed area of N2.
2-terminal zyristors TT 2 and T 3 '''-'- are formed by providing rectangular P layers (emitters) and P2 layers (emitters) so as to be alternately arranged (representing the region of 1).

And on both sides, the above P layer and exposed Nl layer, respectively.
layer and P2 layer and exposed N2 are connected to metal electrodes M,,M2
are short-circuited to form one electrode, respectively, so that the exposed regions of N and N2 have a four-layer structure of NPNP layers, and the other parts have a five-layer structure of PNPNP layers. That is.

In this way, as shown in the enlarged view of the two-terminal thyristor T, T2 shown in FIG.
Since it is the same as the normal bidirectional two-terminal thyristor shown in the figure, it operates in the same way. For example, when a voltage is applied in the direction of the solid arrow I shown in FIG. 3(C), the two-terminal thyristor T2 turns on first.

That is, in this structure, adjacent two-terminal thyristors form a normal bidirectional two-terminal thyristor, and this relationship is exactly the same for the combination of two-terminal thyristors T 2 and T 3, for example. Moreover, each two-terminal thyristor has metal electrodes M + and M on both sides, respectively.
2, so when a voltage is applied, the one that is easiest to turn on among the two-terminal thyristors turns on first, and this causes a gate to be applied to the N2 and P layers of the other two-terminal thyristors adjacent to each other. 1. Since current flows in and out, this also turns on, and thereafter the turn-on region gradually spreads over the entire surface of the element. For example, in Figure 3 (a
) The unidirectional two-terminal thyristor T. ,T. In the cross-sectional view including 2-terminal thyristor T2, if we consider the case where it is turned on first, a lateral resistance is added to the N2 layer and P layer of unidirectional 2-terminal thyristor T3 as shown in the equivalent circuit diagram of FIG. 3(e). Since the gate current 9 flows in and out through , the unidirectional two-terminal thyristor T3 is also turned on.

Since the above is true in any part of the plan view of FIG. 3(a), if a part is turned on as described above, the turn-on region will spread over the entire surface. Further, when a reverse voltage is applied as indicated by the dotted arrow I in FIG. 3(C), the unidirectional two-terminal Zyrister T2 turns first, and then T1 operates, which is exactly the same operation.

Therefore, it is clear that the structure of the present invention operates as a bidirectional two-terminal Zyristor, and by using the structure of the present invention, it is possible to easily control the holding current, which is greatly related to the interrupting characteristics targeted by the present invention. .

Next, the usefulness of the structure of the present invention for controlling the holding current will be explained using a partially simplified diagram of the device of the present invention shown in FIG. 4(a) and a diagram showing the balance between electrons and holes in a conductive state. do.

In Fig. 4(a), L is P,,N, the length of the shorted part of the layer, ! Let be the effective distance affected by the shorted part.

In addition, in Fig. 4(b), I is the total current flowing through the unidirectional two-terminal thyristor, It is the current flowing in the short circuit, Ico is the leakage current, α8, α2 are the transistors N,, P, Let N2 and P 2+ N Z+ be the current amplification factors of the P layer.

Therefore, considering the balance between the electron current (solid line in Figure 4(b)) and hole current (dotted line in Figure 4(1)) in the N2 layer, the structure of the present invention (1-αP )(I lx)-αJ−T Z +
I co, and rearranging this, I(1-(α, (1-1) ten α.))-r,.

■ (1). On the other hand, in the case of a two-terminal Xyrisk with no short circuit, I(1-(α,]-α-)) = T CO '-
``'-'-'' (2) It is also known that the current amplification factor α, , α1, depends on the current I and decreases as the current decreases, and furthermore, α, + αN = 1 is maintained. It is also known that the current that cannot be used is I.

Therefore, as can be seen by comparing equations (1) and (2) in consideration of the above, in the case of the present invention, the current amplifier ratio αP is 1! It can be seen that the current amplification factor α, decreases by (1--,), that is, as a function of It/I.

From the above, it is clear that the current amplification factor α, decreases as a function of I t /I, and the holding current IH increases. The current I flowing through the short circuit is proportional to the sum of the areas of the short circuit parts.
! is the length of the boundary of the shorted part and the effective distance from the shorted part! (Related to, for example, the lateral resistance of the N2 layer in FIG. 4(a)).

Therefore, once the impurity distribution and thickness of each layer are determined, the holding current I
The increase in II will be proportional to L.

The above means that the present invention can maintain the same effective area and current capacity while maintaining the effective length L of the short-circuited portion, for example, N in FIG.
It can be said that this structure is effective for controlling the holding current Il+ by increasing the total exposed area of the layers, and from now on, precise process technology will no longer be required as in the past. A surge protection element with good performance can be provided.

In addition to this, in the structure of the present invention as shown in FIG.
Compared to the conventional structure shown in FIG. 1, the conduction areas are dispersed in the case of conduction in one direction. In the case of the present invention, this results in dispersion of power loss during conduction, resulting in an advantage of increasing current capacity.

The present invention has been explained above using one embodiment, but for example, the fifth embodiment
As shown in the plan view of another embodiment of the present invention shown in the figure (illustration of the insulating film 1, metal electrodes M, M2, etc. is omitted) and the cross-sectional view taken along the line A-A', the present invention is The shape, number, etc. of the exposed portions may be changed, and the conductivity type may be reversed, without departing from the scope of the invention.

Further, in the above description, the exposed base region on one side partially overlaps with the base region on the other side, but the exposed base region on one side may overlap with the base area on the other side.

In addition, it goes without saying that a structure commonly used for ensuring reliability can be applied to an actual element.

(Effects of the Invention) As is clear from the above description, according to the present invention, it is possible to easily manufacture an element with good interrupting characteristics suitable as a surge protection element against lightning surges and the like.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are a plan view and a cross-sectional view of a conventional element,
Figures 2(a) and 2(b) are a circuit diagram showing an example of surge protection, an example diagram of the voltage-current characteristics of a surge protection element, and Figure 3(a).
) ■ 0 (b) (C) (d) (e) is a plan view showing one embodiment of the present invention, a sectional view taken along line A-A', an enlarged cross-sectional view of essential parts, plan view, and B-B' Partial sectional view and equivalent circuit diagram, 4th
Figures (a) and (b) are perspective views and sectional views of essential parts for explaining the operation of the device of the present invention, and Figures 5 (a) and 5 (b) are plan views showing other embodiments of the present invention and their A -A' section sectional view.

Claims (2)

[Claims] (1) A P(N) type semiconductor is used as a common substrate, an N(P) base and a P(N) emitter are provided on both sides of the common substrate, and a part of the N(P) base is located at multiple locations in the P(N) ) The emitters are penetrated through the emitter and exposed on the surface, and are arranged alternately so that the exposed region on one side partially overlaps the exposed region on the other surface, and the emitter and the exposed base region are short-circuited and unified on each surface. A bidirectional two-terminal thyristor comprising two electrodes. (2) The bidirectional two-terminal thyristor according to claim 1, characterized in that the exposed base region on one side does not overlap with the exposed base region on the other side.