JP2724898B2 - Bidirectional 2-terminal thyristor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a bidirectional two-terminal thyristor having excellent breaking performance and easy to manufacture.

(Problems to be Solved with Conventional Technique) Plan views shown in FIGS. 1A and 1B (metal electrodes M ₁ , M ₂
Insulation film I is not shown) and PNPNP (N
A bidirectional two-terminal thyristor having a (PNPN) structure is widely used as a surge protection element for lightning surge or the like because of its small size, low cost, and simple use. In addition,
In accordance with commonly used terminology in this field, if one of P and N is of the first conductivity type, the other is of the second conductivity type. For example, as shown in FIG.
A two-terminal thyristor Z is connected between the input circuits L ₁ and L _{2 of} FIG. 1 to turn on immediately when a lightning surge voltage exceeding its withstand voltage V _BO enters as shown in FIG. Protected electronic device A is protected as a bypass. By the way, in this case, bidirectionality after the passage of lightning surge 2
Terminal thyristor Z, it is necessary to return to break the circuit voltage E ₀ of FIG. 2 (d) to the state before the surge intrusion. For this purpose, the circuit impedance is set to R as shown in FIG.
, The two-terminal thyristor Z in FIG.
Holding current I _H Must be satisfied.

Incidentally, in the ordinary thyristor structure shown in FIG. 1, as is well known, the holding current I _H is determined by the impurity concentration, layer thickness, carrier lifetime, etc. of each layer such as P ₁ , N ₁ , P, N ₂ and P _2. Normally, in order to satisfy the above-mentioned conditions, it is not easy to achieve the required range, because precise control in the manufacturing process is required, and there are variations in raw materials.

(Object of the Invention) The present invention provides a new means for controlling the holding current I _H by a novel surface (electrode) structure to facilitate the manufacture,
This is to improve the cutoff characteristics by obtaining a large holding current _IH value.

(Means for Solving the Problems of the Present Invention) FIGS. 3 (a), (b), (c), (d) and (e) are plan views showing an embodiment of the present invention (in the figure, an insulating layer on the upper surface). I, and removing the metal electrodes M _1), the a-a 'sectional view, A-
Enlarged view of a main part of a cross-sectional view of A 'part, and B-
The B 'part sectional view and the equivalent circuit, which are features of the present invention, are as follows.

That Figure 3 a P-type substrate as a common substrate N ₁ layer to the one surface thereof as (b) N ₂ layer on the other surface provided (base) (base)
Is provided. Further, a P ₁ layer (emitter) and a P ₂ layer (emitter) are provided on the N ₁ layer and the N ₂ layer, respectively. Then, the N ₁ layer
N ₂ layers, at a plurality of positions of _one layer, respectively abacus P or P ₂ layer, to expose the respective surfaces penetrates in a condition in which the P ₁ layer or P ₂ layers are integrally formed without being separated, Figure 3 (a) and (b) without overlapping with each other and the exposed area of the exposed region and the N ₂ layers of N ₁ layer in a direction perpendicular to both surfaces of the common substrate as a plurality foundation th form ( Figure 3 the exposed region of the solid squares N ₁ layer (a), the dotted line box indicates the region of the N _2-layer) so as to be disposed alternately diode thyristor
T ₁ , T ₂ , T ₃ ... Are formed.

And the P ₁ layer which is integrally formed without being separated on both surfaces and the exposed region of the N ₁ layer which is exposed at a plurality of places on the surface, and the P ₂ layer which is integrally formed without being separated as described above. the exposed region of the P ₂ layer exposed at a plurality of locations on the surface,
Each of the electrodes is short-circuited by the metal electrodes M ₁ and M ₂ to form one electrode. In the exposed region of the N ₁ layer and the N ₂ layer, the four-layer structure of the NPNP layer is used, and in the other part, the PNP NP A device having a layered structure is characterized.

In this way, the structure is the same as that of the ordinary two-way thyristor shown in FIG. 1 as shown in the enlarged view of the two-terminal thyristors T ₁ and T ₂ shown in FIG. 3 (c). perform the same operation from, for example, when the voltage in the direction of solid arrow I shown in FIG. 3 (c) is applied, the two-terminal thyristor T ₂ is first turned on.

That is, in this structure, adjacent two-terminal thyristors form a normal bidirectional two-terminal thyristor, for example, at T ₁ and T ₂ , and each two-terminal thyristor is short-circuited by a metal electrode M ₁ and M _{2 on the} screen. Therefore, when a voltage is applied, one of the two-terminal thyristors which is most likely to be turned on first turns on first, which causes the gate current to flow to the N ₂ and P layers of the adjacent circumferential two-terminal thyristors, respectively. Is turned on, so that the turn-on region sequentially spreads over the entire surface of the device. For example, the unidirectional two-terminal thyristors T ₂ and T ₃ shown in FIG.
In FIG. 3 (d), a two-terminal thyristor
Considering the case where T ₂ is first turned on, the third view unidirectional as an equivalent circuit diagram of (e) 2-terminal thyristor T ₃
To the N ₂ layer and the P layer, the gate current I ₉ via the lateral resistance flows in and out unidirectional diode thyristor T ₃ 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 extends over the entire surface. Further, even when an opposite voltage is applied as shown by a dotted arrow I in FIG. 3 (c), the same operation is performed because the structure is symmetric.

Therefore, it is clear that the structure of the present invention operates as a two-way two-terminal thyristor, and by using the structure of the present invention, it is possible to easily control the holding current largely related to the cutoff characteristic aimed at by the present invention.

Next, the fact that the structure of the present invention is useful for controlling the holding current will be described with reference to FIG. 4 (a), which is a partial simplified diagram of the device of the present invention and a diagram showing the balance between electrons and holes in a conductive state.

In FIG. 4 (a), L is the length of the short-circuit portion of the P ₁ and N ₁ layers, and l is the effective distance affected by the short-circuit portion. The fourth
Total current flowing through the unidirectional diode thyristor to I in FIG. (B), the current flowing through the short to I _l, the leakage current I _CO, alpha _N, constitute the alpha _P transistors N _1, P, N ₂ and P ₂ ,
N _{2 is} the current amplification factor of the P layer.

Therefore, considering the balance between the electron current (solid line in FIG. 4 (b)) and the hole current (dotted line in FIG. 4 (b)) in the N ₂ layer, the structure of the present invention requires (1-α) _P ) (I−I _l ) = α _N I−I _l + I _CO . Becomes On the other hand, in the case of a two-terminal thyristor without a short circuit, Given by It is known that the current amplification factors α _P and α _N depend on the current I and decrease as the current decreases.
It is also known that the current that cannot maintain α _P , α _N = 1 is I _H.

Therefore, as can be seen by comparing the expressions (1) and (2) in consideration of the above, in the case of the present invention, the current amplification factor α _P is larger than that of the two-terminal thyristor having no short-circuit portion. It can be seen that the current amplification factor α _P decreases as a function of I _l / I.

From the above, the current amplification rate α _P decreases as a function of I _l / I,
Obviously, the holding current I _H increases, but the total current I _H
For example N ₁ layer of FIG. 1 (a) is proportional to the sum of the area of the portion exposed on the surface, the current I _l flowing through the short, the effective distance from the length L and the short-circuit portion of the boundary of the short-circuit portion determined by the product of the l (e.g. FIG. 4 (relating to lateral resistance of N ₂ layer a)). Therefore impurity distribution of each layer, the increase in the holding current I _H If the thickness or the like Sadamare is proportional to L.

The above is based on the fact that the present invention makes the effective area and therefore the current capacity the same, and the effective length L of the short-circuit portion, for example, N _{1 in} FIG.
And the sum of the exposed areas of the layer to a large holding current I be said to be an effective structure for controlling the _H, interrupting performance I _H not be required and the like from now as in the prior art precision process technology as a large A good surge protection element can be provided.

In addition, as shown in FIG. 3, in the structure of the present invention, as compared with the structure of the ordinary structure shown in FIG. In the case of the present invention, this results in the dispersion of the power loss at the time of conduction, so that there is an advantage that the current capacity can be increased.

Above While the present invention has been an exemplary embodiment described, for example, another embodiment of a plan view of the invention shown in FIG. 5 (insulating film I, not shown, such as metal electrodes M _1, M ₂₎ and its A-A As shown in the cross-sectional view of the 'part, the shape and number of the exposed portions can be changed and the conductivity type can be reversed without departing from the gist of the present invention.

In the above description, the exposed base region on one surface is not overlapped with the exposed base region on the other surface in a state of being seen through from the electrode surface. The parts may overlap.

Needless to say, a structure usually used for securing reliability and the like can be applied to an actual device.

(Effects of the Invention) As is clear from the above description, according to the present invention, it is possible to easily manufacture an element having good cutoff characteristics suitable as a surge protection element for a lightning surge or the like.

[Brief description of the drawings]

1 (a) and 1 (b) are a plan view and a sectional view of a conventional element,
FIGS. 2 (a) and 2 (b) are circuit diagrams showing an example of surge protection, and voltage / current characteristics of a surge protection element, and FIG. 3 (a).
(B), (c), (d), and (e) are plan views showing an embodiment of the present invention, a sectional view taken along the line AA ', an enlarged sectional view of a main portion thereof, a plan view, a sectional view taken along the line BB'. 4 (a) and 4 (b) are perspective views for explaining the operation of the device of the present invention and sectional views of main parts thereof, and FIGS. 5 (a) and 5 (b) are other embodiments of the present invention. And a sectional view taken along line AA 'of FIG.

Claims (1)

(57) [Claims] A first conductive type semiconductor layer used as a common substrate; a second conductive type first base layer formed on one side of the common substrate; and a first base layer. First on
And a second emitter of a second conductivity type formed on both sides of the other side of the common substrate.
And a second emitter layer of a first conductivity type is formed on the second base layer, and the first base layer is integrally formed without separating the first emitter layer. A plurality of exposed regions are formed penetrating the first emitter layer so that the second emitter layer is maintained, and the second base layer is integrally formed without separating the second emitter layer. A plurality of exposed regions penetrating the second emitter layer so as to be integrally formed without being separated from the plurality of exposed regions of the first base layer on the one surface side One electrode is formed so as to be in contact with the first emitter layer, and the other side is integrally formed with the plurality of exposed regions of the second base layer without being separated from each other. In contact with the second emitter layer One electrode of the first base layer, the plurality of exposed regions in contact with the one electrode, and the plurality of exposed regions in contact with the other electrode of the second base layer, A bidirectional two-terminal thyristor configured so as not to overlap with each other in a direction perpendicular to one surface and the other surface of the common substrate.