JPH02174263A - Semiconductor protective element - Google Patents

Abstract

PURPOSE:To enable breakdown voltage of a semiconductor protective element to be determined only through reverse withstand voltage of a PN junction formed from a first semiconductor region and a third semiconductor region by forming a fifth semiconductor region in the semiconductor protective element consisting of the first through fourth semiconductor regions. CONSTITUTION:An N-type impurity is implanted into a part of a second semiconductor region 2 from the surface thereof until it reaches a first semiconductor region 1 to form a fifth semiconductor region 5, and an anode electrode 6 is formed in ohmic contact with both of the fifth semiconductor region 5 and the second semiconductor region 2. Namely, the anode electrode 6 is in ohmic contact not only with the second semiconductor region 2 but also with the first semiconductor region 1. In such a structure, the voltage applied across the anode electrode 6 and the cathode electrode 7 in an off state is directly applied to a PN junction formed by the first semiconductor region 1 and the third semiconductor region 3. Therefore, the reverse withstand voltage of this PN junction is the breakdown voltage of the semiconductor protective element as it is, and can be determined regardless of the second semiconductor region 2.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor protection device, and particularly to a semiconductor protection device for protecting wired communication equipment from abnormal voltages that enter through communication cables when the communication equipment is in the dark. Regarding.

[Conventional technology]

Conventionally, this type of semiconductor protection element has a second semiconductor region 2 and a third semiconductor region 3 made of a P-type semiconductor material, and a first semiconductor made of an N-type semiconductor material, as shown in the cross-sectional view of FIG. A four-layer PNPN layer including the region 1 and the fourth semiconductor region 4 is provided to short-circuit the third semiconductor region 3 and the fourth semiconductor region 4 in order to increase the forward blocking voltage increase rate dv/dt of the element. The image electrode is formed in an opening provided in the SiO □ film 8 .

In a conventional semiconductor protection element having such a device structure, an abnormal voltage exceeding the reverse withstand voltage of the PN junction consisting of the first semiconductor region 1 and the third semiconductor region 3 is applied between the anode electrode 6 and the cathode electrode 7. Then, after passing through an avalanche breakdown state in which current flows in the three layers of PNP consisting of the second semiconductor region 2, first semiconductor region 1, and third semiconductor region 3, the second semiconductor region 2 and the first semiconductor region 1 The thyristor, which is made up of four PNPN layers including the third semiconductor region 3 and the fourth semiconductor region 4, enters the on state and absorbs the abnormal voltage.

[Problem to be solved by the invention]

In the conventional semiconductor protection element described above, the breakdown voltage VBR was thought to be determined by the breakdown voltage of the PN junction formed by the first semiconductor region 1 and the third semiconductor region 3.

However, in reality, as can be seen from the device structure shown in FIG. 4, the anode electrode 6 and the cathode electrode 8i!
The voltage applied across 7 is applied not only to the PN junction consisting of the first semiconductor region 1 and the third semiconductor region 3 but also to the PNP three layers including the second semiconductor region 2.

Therefore, if the breakdown voltage of the PN junction consisting of the first semiconductor region 1 and the third semiconductor region 3 is V2C, then the breakdown voltage V8R of this semiconductor protection element is generally V8R.
The value is expressed as BR = V zo "! Go] 1. Here, n is a constant, which is usually 3 in St. Also, α
F is the forward current transfer rate when the three PNP layers are considered as a transistor.

In other words, in the semiconductor protection element with the conventional structure, the breakdown voltage is not only the breakdown voltage of the PN junction between the first semiconductor region 1 and the third semiconductor region 3, but also the breakdown voltage of the PNP three layer including the second semiconductor region 2. It will also be affected by transistor characteristics.

Moreover, the voltage-current characteristics in the conventional avalanche breakdown state are
Since it has a negative resistance characteristic as shown in the graph of Figure 5, it enters the ON state at a voltage limited by the breakdown voltage VBR in response to an abnormal voltage with a slow rise speed, but it enters the ON state at a voltage limited by the breakdown voltage VBR, but in response to an abnormal voltage with a fast rise speed. The disadvantage is that the breakdown voltage VBR cannot be maintained and the ON state is entered at a voltage limited by the breakover voltage Bo, which means that the limiting voltage that enters the ON voltage becomes bipolarized depending on the rising speed of the applied voltage. There is also.

[Means to solve the problem]

The present invention includes a first semiconductor region formed of an N-type semiconductor material, one surface of both surfaces of the first semiconductor region, and a P
a second semiconductor region formed of a P-type semiconductor material forming an N-junction; and a third semiconductor formed of a P-type semiconductor material forming a PN-junction with the other of both surfaces of the first semiconductor region. a fourth semiconductor region formed of an N-type semiconductor material forming a PN junction with a portion of the surface of the third semiconductor region, an anode electrode having ohmic contact with the second semiconductor region, and the third semiconductor region. and a cathode electrode having ohmic contact with both the fourth semiconductor region and the fourth semiconductor region, the N-type semiconductor material penetrating the second semiconductor region and short-circuiting the anode electrode and the first semiconductor region. It is a semiconductor protection element provided with a formed fifth semiconductor region.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view of a semiconductor protection element showing an embodiment of the present invention. A fifth semiconductor region 5 is formed in a part of the second semiconductor region 2 by pushing N-type impurities from the surface until it reaches the first semiconductor region 1, and ohmic contact is made with both the fifth semiconductor region 5 and the second semiconductor region 2. The anode electrode 6 is made so as to have the following properties.

That is, in the semiconductor protection device of the present invention, the anode voltage f
i6 has ohmic contact not only with the second semiconductor region 2 but also with the -th semiconductor region 1. In this structure,
The voltage applied to the anode electrode 6 and the cathode electrode 7 in the on state is directly applied to the PN junction formed by the first semiconductor region 1 and the third semiconductor region 3 in the opposite direction.

Therefore, the reverse breakdown voltage of this PN junction directly becomes the breakdown voltage VBR of the semiconductor protection element, and can be determined independently of the second semiconductor region 2. FIG. 2 is a graph showing the voltage-current characteristics of the semiconductor protection device of the present invention. As shown in Figure 2, the avalanche breakdown state also has the reverse voltage-current characteristics of a PN junction, so it does not have a negative resistance characteristic, so the limiting voltage at which the semiconductor protection device turns on is only the breakover voltage VBO. There is no obvious polarization.

In addition, since the semiconductor protection device of the present invention has diode characteristics with respect to reverse voltage, if you want to obtain the bidirectional characteristics necessary for a protection device, simply connect this device in series in the opposite direction to obtain the bidirectional characteristics. You can also get

FIG. 3 is a sectional view showing an example of application of the present invention.

In this application example, first semiconductor region 1 and third semiconductor region 3
A sixth semiconductor region 9 in which N-type impurities are pushed is formed in the surface part of the PN junction formed by the PN junction formed by the first semiconductor region 1 and the third semiconductor region 3 due to the impurity concentration in this part. This makes it possible to control the reverse breakdown voltage of the semiconductor protection element, that is, the breakdown voltage of the semiconductor protection element.

〔Effect of the invention〕

As explained above, the present invention provides 1. a. The breakdown voltage of the semiconductor protection element is determined only by the reverse withstand voltage of the PN junction formed by the first semiconductor region and the third semiconductor region, and it enters the ON state at a certain limited voltage even for applied voltages that rise quickly. This has the effect of making it possible to

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a graph showing voltage-current characteristics of a semiconductor protection element of the present invention, FIG. The figure is a cross-sectional view of a conventional semiconductor protection element, and FIG. 5 is a graph showing voltage-current characteristics of the conventional semiconductor protection element. 1... First semiconductor region, 2... Second semiconductor region, 3
... third semiconductor region, 4... fourth semiconductor region, 5.
...Fifth semiconductor region, 6... Anode electrode, 7...
Cathode electrode, 8...5i02 film, 9...6th semiconductor region.

Claims (1)

[Claims] a first semiconductor region formed of an N-type semiconductor material; a second semiconductor region formed of a P-type semiconductor material forming a PN junction with one of both surfaces of the first semiconductor region;
a third semiconductor region formed of a P-type semiconductor material forming a PN junction with the other of both surfaces of the first semiconductor region; and an N-type semiconductor region forming a PN junction with a portion of the surface of the third semiconductor region. a fourth semiconductor region formed of a type semiconductor material, an anode electrode having ohmic contact with the second semiconductor region, and a cathode electrode having ohmic contact with both the third semiconductor region and the fourth semiconductor region. 1. A semiconductor protection element, further comprising a fifth semiconductor region made of an N-type semiconductor material that penetrates through the second semiconductor region and short-circuits the anode electrode and the first semiconductor region.