JPS59119873A - Punch-through type constant-voltage element - Google Patents

Abstract

PURPOSE:To generate a punch-through extending over the whole region of a depletion layer, and to obtain low stable voltage characteristics by forming a junction between one conduction type layer under a reverse bias contributing to a punch-through phenomenon and the other conduction type layer into a torus shape. CONSTITUTION:The lateral fringe of an n<-> layer 10 is surrounded by a torus- shaped p<+> layer 15 in impurity concentration equal to a P<+> layer 8 so that the spreads of depletion layers in the lateral section 10'' of the n<-> layer 10 and the p<+> layer 8 are made the same as a section 10' immediately under the junction. When an electrode 13 is brought to positive poatential and an electrode 9 to negative potential in the punch-through type constant-voltage element constituted in this manner, the p-n junction 6 between a p<+> layer 11 and the n<-> layer 10 is brought to a forward bias, and the depletion layer 17 of the junction is narrowed. On the other hand, the p-n junction 18 among the torus-shaped p<+> layer 15 and the p<+> layer 8 and the n<-> layer 10 is brought to a reverse bias, a depletion layer 19 expands, the section 10' immediately under the junction on the n<-> layer 10 side and the lateral section 10'' are extended remarkably more than the p<+> layer 8, and the punch-through phenomenon is generated particularly in a region of the lateral section 10''. Accordingly, currents relaxed to uniform density are flowed, and low voltage is easily controlled particularly by stable breakdown voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to improving the constant voltage characteristics of a punch-through type constant voltage element having a sandwich-type PN structure whose structure is similar to a transistor.

BACKGROUND ART Conventionally, as a constant voltage element, a so-called Zener diode, which causes a collapse phenomenon due to a quantum mechanical tunnel effect in a depletion layer of a PN junction, has been put into practical use. However, with this Zener diode, constant voltage characteristics can only be obtained in a range where the reverse breakdown voltage is relatively high, and even if a low constant voltage can be obtained, the operating resistance increases and the temperature of the PN junction increases. However, it also has the disadvantage of generating noise. Therefore, instead of the above-mentioned Zener diode, nine layers 2 are formed on two layers 1 as shown in FIG.
A device has been proposed in which layer 3 is selectively diffused to form a pnp sandwich-inch structure.

This element is called a punch-through type constant voltage element, and is as thin as the total number of μm in the base case W of n~2, and by setting the resistivity of the nine layers 2 to be high, the two layers 1') positive, When the second layer 3 is negatively biased, the depletion layer 5 near the reverse biased pn junction 4 is expanded within nj so 2 and reaches the depletion layer of the positive pn junction 6. This is a unique use of the ``Unogunchisuru'' phenomenon. However, this constant voltage constant voltage element also has the following problems. That is, generally the P layer j in the n layer 2
Since the spread resistance is uneven between the sound IS2' directly below 3' and the horizontal part 2', the corresponding part 5' and the sound IS5' directly below the depletion layer 5 are Disclosure of the Invention This invention was proposed in response to the above circumstances, and is a 7-point through-type constant voltage that is different from the previous one. In order to solve the problem of the device's output, the junction between the layer of one conductivity type and the layer of the other conductivity type with reverse bias, which contributes to the phenomenon of "no-kunchi-through", is set in an annular shape. According to this invention, this invention provides stable voltage characteristics that are low and do not cause "gunchi-through" (over the entire depletion layer). It also has the advantage of contributing to D2 defense.

The best embodiment for carrying out the invention No. 2 (2) is a cross-sectional view of a switch-through type constant voltage element showing an embodiment of the invention, which is different from the conventional one in that it has a pip-type switch structure. The device is similar to the device, but the reverse biased PN junction structure and the direction of the noise are different. In Figure 2, 8 is a P+14 layer with a negative electrode 9 formed on its back surface, 10 is a layer epitaxially grown and grown on the P'' layer 8, and 11 is an N layer diffused into the layer 10. 12 is an oxide film that provides insulation protection on the surface, and 13 is a positive electrode that is connected to the second layer 11 by opening the part of the oxide film 12 corresponding to the P+ layer 11. Now, as is clear from FIG. 3, which shows the plane with the oxide film 12 and the positive electrode 13 removed, the negative side (biased p+111g) is the lateral WIIO'' of the n layer 10. P
In order to spread the depletion layer 14 in the layer 8 to the same extent as in the directly lower part 10', the lateral edge of the ni@lo is formed by forming a ring 4 P+ layer 15 with an impurity concentration equal to that of the P+ layer 8. surrounded by

Therefore, in the nomanthyl constant voltage element having the above structure, if the electrode 13 is set to a positive potential and the electrode 9 is set to a negative potential, P
PN junction 161″1 between the + layer 11 and the n layer 10 becomes forward biased, and its depletion layer 17 is narrow, and conversely, the annular P+ layer 1
The PN junction 18 between the 5 and P'' layer 8 and the n layer 1.0 becomes reverse biased, and the depletion layer 19 expands, and the depletion layer 19 expands, compared to the P layer 8, at the immediate lower part IQ' and the lateral portion lO'' on the n layer lO side. The elongation becomes significant, and a punch-through phenomenon occurs particularly in the region of the ItJ section 10//, resulting in a situation similar to a yield state. The basis for this situation can be understood from the following explanation. That is, this element has n layers 10 and lateral portions l.
Since o y is surrounded by the annular P+ layer 15, assuming a minute fan-shaped area 120 in FIG.
Comparing the area S1 of 5 and the area +8S2 of 7q%lO,
There is a constant relationship K' S+ > 82, and since the impurity concentration is naturally lower in the lateral part lO'' in the n layer, the lateral part
This is because o// forms a so-called bevel structure in which the withstand voltage in the vicinity of the PN junction surface is fully strengthened, and the elongation of the depletion layer 19 becomes remarkable. Therefore, in this punch-through type constant voltage element, thin arrow lines 21, 21 .・・・・・・
As shown in Figure 2, a relaxed current flows in a uniform density, making it easy to control particularly low voltages with a stable breakdown voltage, and good characteristics are obtained in which hot spots do not spread all over due to current concentration. It will be done.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional punch-through type constant voltage element, FIG. 2 is a longitudinal cross-sectional view of a punch-through type constant voltage element showing an embodiment of the present invention, and FIG. FIG. 3 is a cross-sectional view when an oxide film is removed. 8... P seed (- conductivity type), lO... n single layer (other conductivity type), 11...
P+ layer (=conductive type), -15... annular P+ layer. Patent applicant ShinNippon Electric Co., Ltd.

Claims (1)

[Claims] Form a type layer on the one conductivity type layer, and then
A layer of one conductivity type is formed on a layer of one conductivity type to form a sandwich structure, and with respect to the layer that causes the bunch-through phenomenon in the layer of the other conductivity type that serves as the base region of the sandwich structure, the reverse effect that contributes to the punch-through phenomenon is On one conductivity type layer of bias (l
1. A punch-through type constant voltage element characterized in that the junction with the f4 conductivity type layer is set in an annular shape.