JP2003051591A - Two-terminal thyristor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-terminal thyristor in which the surge withstand strength is improved. SOLUTION: The two-terminal thyristor comprises an n-type first semiconductor region 2 formed on the main surface of a p-type semiconductor substrate 1, a p-type second semiconductor region 3 formed in the first semiconductor region 2, a first short-circuiting region 4 surrounded by the second semiconductor region 3, an n-type third semiconductor region 5 formed at the position opposing the second semiconductor region 3 on the second main surface, and a second short-circuiting region 8 surrounded by the third semiconductor region 5. The semiconductor regions and the short-circuiting regions are polygonal having at least five sides, oval, elliptical, or circular in plain view, resulting in improved surge withstand strength of the two-terminal thyristor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-terminal thyristor suitable for surge protection of communication circuits and the like.

[0002]

2. Description of the Related Art In a communication circuit, a large surge voltage may occur due to direct hit or induction of natural lightning. In order to protect various devices and equipment connected to a communication circuit, a small, inexpensive, high-speed, two-terminal thyristor type surge protection element is used. This thyristor is connected and used between the lines of the protected circuit of the communication circuit, and when the surge voltage that penetrates between the lines exceeds the withstand voltage of the element, it turns on and applies a current to the element, and the protected circuit has a voltage higher than the withstand voltage. Make sure no voltage is applied. When the current flowing through the element decreases and falls below the holding current of the element, the current is shut off and the normal state, that is, the off state is returned to perform an operation for the next surge.

In order to perform better protection using the two-terminal surge protection element, it is necessary to increase the holding current and satisfy the conditions for increasing the surge resistance. For this reason, a reverse conduction type element that can design a large holding current is used.

FIG. 3 shows a two-terminal thyristor according to the prior art, and FIG. 3 (b) shows a cross section taken along the line AA of FIG. 3 (a). The two-terminal thyristor according to the related art is an n-type first semiconductor region 2 formed on the first main surface side of a p-type semiconductor substrate 1 and a p-type first semiconductor region 2 formed in the first semiconductor region 2. A second semiconductor region 3, a first short-circuit region 4 surrounded by the p-type second semiconductor region 3 and extending from the first main surface to the n-type first semiconductor region 2, and a p-type semiconductor substrate. An n-type third semiconductor region 5 formed at a position facing the p-type second semiconductor region 3 on the side of the second main surface opposite to the first main surface of 1.
A second short-circuit region surrounded by the third semiconductor region 5 of the mold and extending from the second main surface side to the p-type semiconductor substrate 1, and a second semiconductor region 3 formed on the first main surface side. First short circuit area 4
The first electrode 6 on the first main surface connected to the second main surface and the second main surface connected to the third semiconductor region 5 and the second short-circuit region 8 formed on the second main surface side. The second upper electrode 7 is provided, and the n-type first semiconductor region 2, the p-type second semiconductor region 3, the n-type third semiconductor region 5, the first short-circuit region 4 and The planar shape of the second short-circuit region 8 viewed from the first main surface or the second main surface is rectangular.

In the conventional two-terminal thyristor formed on the p-type semiconductor substrate 1 in FIG. 3, the direction of application of the voltage for making the first electrode 6 a positive potential with respect to the second electrode 7 is the forward direction, The application direction of the voltage that makes the first electrode 6 have a negative potential with respect to the second electrode 7 is the opposite direction.

When a voltage is applied in the forward direction, it is formed by the p-type second semiconductor region 3, the n-type first semiconductor region 2, the p-type semiconductor substrate 1 and the n-type third semiconductor region 5. When a current flows in the pnpn thyristor portion in the peripheral portion of the element to be applied and a voltage is applied in the opposite direction, the pn junction in the central portion of the element formed by the p-type semiconductor substrate 1 and the n-type first semiconductor region 2 Current flows through the diode section.

When a voltage is applied in the forward direction of the two-terminal thyristor, the pn junction J1 formed by the n-type first semiconductor region 2 and the p-type semiconductor substrate 1 is reverse biased. When the applied voltage reaches the breakdown voltage V1 of the pn junction J1, this p
A current I1 flows through the n-junction J1 to turn on a pnp transistor formed by the p-type second semiconductor region 3, the n-type first semiconductor region 2 and the p-type semiconductor substrate 1, and further the n-type semiconductor region. 2. The npn transistor formed by the p-type semiconductor substrate 1 and the n-type third semiconductor region 4 is turned on, and the pnpn thyristor is turned on.

In practice, the n-type first semiconductor region 2 and p
The pn junction J1 formed by the semiconductor substrate 1 of the type causes a uniform breakdown phenomenon, and I1 does not flow uniformly. The corner portion of the n-type first semiconductor region 2 easily breaks down, and the thyristor is turned on by the voltage due to the product of the base resistance of the pnp transistor from the corner portion to the electrode 6 and the current I1 flowing due to the breakdown phenomenon. Therefore, the surge current tends to concentrate on the corners.

In a two-terminal thyristor according to the prior art, n
The first semiconductor region 2 of the type is rectangular, and the base resistance of the pnp transistor from the first semiconductor region 2 of the n type to the first short-circuit region 4 is not uniform. Furthermore, the junctions at the corners at the four corners of the n-type semiconductor region 2 shown in FIG. 3A are spherical junctions, the electric field is likely to be high, and breakdown occurs at the four corners before the other portions. Therefore, an ON state is also likely to occur in this portion, an extreme current concentration occurs, a temperature rise locally occurs, and a surge is easily destroyed.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and an object thereof is to eliminate the unevenness of the breakdown voltage due to the pattern shape of the semiconductor diffusion region and to improve the surge withstand capability. It is to realize an improved two-terminal thyristor.

[0011]

According to a first aspect of the present invention, there is provided a first conductivity type semiconductor substrate 1 having a second conductivity type opposite to the first conductivity type formed on the first main surface side. One semiconductor region 2
And a second semiconductor region 3 of the first conductivity type formed in the first semiconductor region 2 from the first main surface side, and surrounded by the second semiconductor region 3 from the first main surface to the first main surface. A first short-circuit region 4 extending to one semiconductor region 2 and a first short-circuit region 4 formed at a position facing the second semiconductor region 3 on the second main surface side opposite to the first main surface of the semiconductor substrate 1. Second conductivity type third semiconductor region 5
A second short-circuit region 8 surrounded by the third semiconductor region 5 and extending from the second main surface side to the semiconductor substrate 1, a second semiconductor region 3 formed on the first main surface side, and a second semiconductor region 3 One short-circuit area 4
The first electrode 6 on the first main surface connected to the second main surface, the third semiconductor region 5 and the second short-circuit region 8 formed on the second main surface side.
In a two-terminal thyristor comprising a second electrode on the second main surface connected to the first semiconductor region 2, the second semiconductor region 3, the third semiconductor region 5, the first short-circuit region 4 and the second semiconductor region 3. A two-terminal thyristor characterized in that the planar shape of the second short-circuit area 8 viewed from the first main surface or the second main surface is a polygon having five or more sides, an ellipse, an ellipse, or a circle. It is provided.

The invention according to claim 2 provides the two-terminal thyristor according to claim 1, wherein the second electrode 7 is connected to the semiconductor substrate 1 surrounding the third semiconductor region 5 on the second main surface. It is provided.

According to a third aspect of the present invention, the first semiconductor region 2, the second semiconductor region 3, the third semiconductor region 5, the first short circuit region 4 and the second short circuit region 8 are provided.
2. The planar shape viewed from the first main surface or the second main surface of is arranged concentrically.
Alternatively, the two-terminal thyristor according to claim 2 is provided.

[0014]

1 shows a two-terminal thyristor according to a first embodiment of the present invention, and FIG.
The cross section in AA of (a) is shown. A circular mask is used on the first main surface side of the p-type semiconductor substrate 1 to diffuse n-type impurities to form an n-type first semiconductor region 2, and a donut-shaped mask is used from the first main surface side. A p-type impurity is diffused in the n-type first semiconductor region 2 to form a p-type second semiconductor region 3. A portion of the n-type first semiconductor region 2 surrounded by the p-type second semiconductor region 3 and exposed on the first main surface becomes the first short-circuit region 4. Using a donut-shaped mask, n-type impurities are diffused from the second main surface side of the p-type semiconductor substrate 1 to a position on the first main surface side facing the p-type second semiconductor region 3. A third semiconductor region 5 is created. A p-type semiconductor substrate 1 surrounded by an n-type third semiconductor region 5 and exposed on the second main surface
The second area becomes the second short-circuit area 8. On the first main surface side, a first electrode 6 that is vapor-deposited with a metal film and connected to the n-type second semiconductor region 3 and the first short-circuit region 4 is patterned by etching using photographic technology, Next, a metal film is vapor-deposited on the second main surface side to form the second electrode 7 on the second main surface, which is connected to the n-type third semiconductor region 5 and the second short-circuit region 8.

In this embodiment, the n-type first semiconductor region 2, the p-type second semiconductor region 3, the n-type third semiconductor region 5, the first short-circuit region 4 and the second short-circuit region are The planar shape viewed from the first main surface or the second main surface is preferably concentric, but may be a polygon having five or more sides, an ellipse, or an ellipse. Also, a combination of these may be used.

FIG. 2 shows a two-terminal thyristor according to a second embodiment of the present invention, and FIG. 2B shows a cross section taken along the line AA in the figure. In the formation of the second electrode 7 in the first embodiment, the second electrode 7 includes the second short-circuit region 8 and the n-type third semiconductor region 5 on the second main surface, and the n-type. P-type first semiconductor region 1 surrounding the third semiconductor region 5 of
And connect. In the present embodiment, the n-type first semiconductor region 2, the p-type second semiconductor region 3, the n-type third semiconductor region 5, the first short circuit region 4 and the second short circuit region 8 are The planar shape viewed from the one main surface or the second main surface is preferably concentric, but may be a polygon having five or more sides, an ellipse, or an ellipse. Also, a combination of these may be used.

In the above description, the n-type first semiconductor region 2 has been described as having a planar structure in which it is diffused from the first main surface. However, the n-type layer has a circular shape or the entire surface from the first main surface side. And the periphery of this diffusion region is etched into a groove shape or a moat shape with a depth equal to or larger than the diffusion depth.
May be formed. By filling the groove with glass, a two-terminal thyristor exhibiting stable characteristics with respect to the external atmosphere can be manufactured.

Although the p-type substrate has been described above, an n-type substrate may be used.

[0019]

According to the present invention, it is possible to obtain a two-terminal thyristor which is strong against surges and has a large holding current and which is suitable for surge protection.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a form of a two-terminal thyristor according to a conventional technique.

[Explanation of symbols]

1 p-type semiconductor substrate 2 n-type first semiconductor region 3 p-type second semiconductor region 4 First short circuit area 5 n-type third semiconductor region 6 First electrode 7 Second electrode 8 Second short circuit area

Claims (3)

[Claims] 1. A semiconductor substrate of a first conductivity type, a first semiconductor region of a second conductivity type opposite to the first conductivity type formed on the first main surface side of the semiconductor substrate, A second semiconductor region of the first conductivity type formed in the first semiconductor region from one main surface side, and surrounded by the second semiconductor region, the first main surface to the first A first short-circuit region extending to a semiconductor region, and a second conductivity type formed at a position facing the second semiconductor region on the second main surface side opposite to the first main surface of the semiconductor substrate. A third semiconductor region, a second short circuit region surrounded by the third semiconductor region and extending to the semiconductor substrate from the second main surface side, and the second short-circuit region formed on the first main surface side. A semiconductor region, a first electrode on the first main surface connected to the first short circuit region, and the first electrode formed on the second main surface side. A two-terminal thyristor comprising a third electrode and a second electrode on the second main surface connected to the second short-circuit region, wherein the first semiconductor region, the second semiconductor region, and the third Of the semiconductor region, the first short-circuit region and the second short-circuit region, the planar shape of the first main surface or the second main surface when viewed from the side is a polygon having five or more sides, an ellipse, an oval. Or a two-terminal thyristor characterized by being circular. 2. The two-terminal thyristor according to claim 1, wherein the second electrode is connected to the semiconductor substrate surrounding the third semiconductor region on the second main surface. 3. The first main surface of the first semiconductor region, the second semiconductor region, the third semiconductor region, the first short-circuit region and the second short-circuit region or the first short-circuit region. The two-terminal thyristor according to claim 1, wherein the two-dimensional thyristor is concentrically arranged when viewed from the second main surface.