JPH065884A - Diode - Google Patents

Abstract

PURPOSE:To provide a diode with stable surge withstand voltage by replacing the P<+> layer of an N<+>-N<->-P<->-P<+> diode by an N<+> region with opposite conductivity type. CONSTITUTION:An impurity out of a surface of an N<-> silicon layer 3 with low impurity density is diffused to form a P<+> layer 4 with low impurity density on an N<+> silicon substrate with high impurity density. Impurity diffusion is carried out through a window part in an SiO2 film 6 to form a circular P<+> region 5 with high impurity density. Impurity diffusion is carried out again at a central part thereof to form a circular N<+> region 8 with high impurity density. When an electrode 7 is positively and an electrode 1 is negatively biased, the electrons injected from the N<+> substrate 2 into a P<-> layer 4 is caused to flow through the N<+> region 8 and reach the electrode 7. Then, when a negative overvoltage is applied to the electrode 7 and a positive voltage to the electrode 1, an avalanche breakdown is caused at a junction between an N<-> layer 3 and the P<+> layer 4, but an NPN structure formed with the N<+> region 8 is put in an on-state. Consequently, an overvoltage is absorbed and the surge withstanding voltage can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diode utilizing the rectifying function of a semiconductor pn junction.

[0002]

2. Description of the Related Art Recently, higher efficiency and higher frequency of power supplies have been further advanced. A diode suitable for this requirement is required to have a short reverse voltage recovery time _trr , a low forward voltage V _F , and a high surge resistance against induced noise in a power supply wiring path. On the other hand, as shown in FIG. 2, an N ⁻ layer 3 of the same conductivity type and a low impurity concentration is formed on an N ⁺ substrate 2 of a high impurity concentration, and an N ⁻ layer 3 of the opposite conductivity type and a low impurity concentration is formed in this N ⁻ layer. The P ⁻ layer 4 is formed, and the P ⁺ layer 5 having a high impurity concentration is further provided in the P ⁻ layer. The cathode electrode 1 is formed on the surface of the N ⁺ substrate 2 and the oxide film 6 is formed on the surface of the P ⁺ layer. It is possible to manufacture a diode having a relatively small V _{F in} which the anode electrode 7 is in contact with each other.

[0003]

However, the structure as shown in FIG. 2 is difficult to shorten _trr and is inconvenient for increasing the frequency of the power source. Further, in order to improve the surge withstand capability, the diode is not used. There was a problem that the volume had to be increased. The object of the present invention is to solve the above problems,
An object of the present invention is to provide a diode which can cope with high efficiency and high frequency of a power supply.

[0004]

In order to achieve the above object, the diode of the present invention comprises a layer of high impurity concentration on one side and a layer of low impurity concentration on the other side of the first conductivity type layer. A second conductivity type layer is provided, and a first conductivity type region having a high impurity concentration and a second conductivity type region are provided adjacent to each other on the surface layer of the second conductivity type layer, and the surfaces of both regions are provided. The electrodes are commonly in contact with. Then, the first conductivity type region may be surrounded by the annular second conductivity type region, or the second conductivity type region may be surrounded by the annular first conductivity type region.

[0005]

When a forward bias is applied to the PN junction between the first conductivity type layer and the second conductivity type layer, the first conductivity type high impurity concentration layer passes through the low impurity concentration layer Since the minority carriers injected into the layer having the conductivity type impurity concentration reach the electrode from the first conductivity type high impurity concentration region having no barrier, V _F becomes small. At the time of off, there is no accumulation of minority carriers, and since the second conductivity type region and the first conductivity type region having a high impurity concentration are in contact with the same electrode, the operating resistance becomes small and _trr becomes short. When an overvoltage reverse bias is applied to the PN junction between the first-conductivity-type layer and the second-conductivity-type layer to cause avalanche breakdown, the second-conductivity-type layer and the first-conductivity-type layer are NPN structure or P formed by interposing in the area
Since the NP structure breaks over and is turned on, the overvoltage is absorbed and the surge withstand capability is improved.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawing in which the same reference numerals are given to the same parts as in FIG. In the embodiment shown in FIG. 1, the N ⁺ silicon substrate 2 having a high impurity concentration is used.
After a low impurity concentration P ⁻ layer 4 having a depth of 10 to 20 μm is formed by the impurity diffusion from the surface of the low impurity concentration N ⁻ silicon layer 3 formed by the epitaxial method, a SiO ₂ film covering the surface is formed. 5 due to impurity diffusion from the window of 6
Circular high impurity concentration P ⁺ with a diameter of 0.7 mm at a depth of 10 μm
Region 5 was formed, and impurity diffusion was performed again to the central portion to form a circular N ⁺ region 8 having a high impurity concentration and having a diameter of 0.05 to 0.1 mm. Anode electrode 7 is P ⁺ region 5 and N
⁺ Commonly touches the area 8. When a positive bias voltage is applied to the electrode 7 of the diode and a negative bias voltage is applied to the electrode 1, the electrons injected from the N ⁺ substrate 2 into the P ⁻ layer 4 are N ^+.
The electrode 7 is reached through the region 8. Then, a negative overvoltage is applied to the electrode 7 and a positive overvoltage is applied to the electrode 1, so that the N ⁻ layer 3
When the avalanche breakdown occurs at the junction between the P + layer 4 and the P ⁻ layer 4, the NPN structure formed by the N ⁺ region 8 is turned on.

In the embodiment shown in FIG. 3, the N ⁺ region 8 is formed in an annular shape and surrounds the P ⁺ region 5. This is because the reverse current bias is applied and the short-circuit current flowing in the N ⁺ region 8 is distributed to the outer peripheral portion when the NPN structure is turned on, whereby current concentration is improved and heat dissipation is also improved. Therefore, the breakdown voltage is improved and stabilized.

[0008]

According to the present invention, N ⁺ -N ^-- P ^-- P
By replacing a part of the P ⁺ layer or the N ⁺ layer of the diode having the ⁺ structure with the N ⁺ region or the P ⁺ region of the reverse conductivity type, the V _F is low, the _trr is short, and the surge withstand capability is further improved. A stable diode was obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a diode according to an embodiment of the present invention.

FIG. 2 is a sectional view of a conventional diode.

FIG. 3 is a sectional view of a diode according to another embodiment of the present invention.

[Explanation of reference numerals] 1 cathode electrode 2 N ⁺ substrate 3 N ⁻ layer 4 P ⁻ layer 5 P ⁺ region 7 anode electrode 8 N ⁺ region

Claims (3)

[Claims] 1. A layer of the first conductivity type having a high impurity concentration layer on one side, and a layer of the second conductivity type having a low impurity concentration on the other side.
A region of the first conductivity type and a region of the second conductivity type each having a high impurity concentration are provided adjacent to each other on the surface layer of the layer of the second conductivity type, and the electrodes commonly contact the surfaces of both regions. A diode characterized by. 2. The diode according to claim 1, wherein the first conductivity type region is surrounded by the annular second conductivity type region. 3. The diode according to claim 1, wherein the second conductivity type region is surrounded by an annular first conductivity type region.