JP2000156509A - Multielement compound zener diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower manufacturing cost and realize miniaturization by forming a multiplicity of Zener diodes in a single chip. SOLUTION: A backside of a P type silicon substrate 1 is used as a common anode, and a plurality of N+ type zones 2 for formation of PN junctions 4 are formed in parallel in the vicinity of a main surface of the substrate 1. N+ type guard rings 5 are provided to the N+ type zones 2 as overlapped therewith. A distance between the rings 5 of the adjacent PN junctions 4 is set at about 70 μm, and a P+ type isolation 6 is provided in between the adjacent zones 2. As a result, when a rated Zener voltage is applied to the adjacent junctions 4, the junctions are electrically isolated from each other in such an extent that the voltage does not effect Zener breakdown.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-element composite type in which a plurality of PN junctions serving as Zener diode elements are provided in parallel on the main surface of a P-type semiconductor substrate, with the back surface of the P-type semiconductor substrate serving as a common anode. It relates to a Zener diode.

[0002]

2. Description of the Related Art A Zener diode is a diode utilizing a breakdown phenomenon (Zener breakdown) in which a current starts to flow rapidly at a certain voltage when a reverse voltage is applied to a PN junction. In the range where Zener breakdown occurs, the Zener diode is used as a constant voltage element because it has a characteristic that the voltage is maintained at a constant value only by increasing the current. The voltage at which Zener breakdown starts is called the Zener voltage (Vz).

FIG. 5 is a sectional view of a general zener diode. A P ⁺ -type region 3 is provided at the center of the main surface of an N-type silicon substrate 1 to form a PN junction 4 serving as a Zener diode element. A P-type guard ring 5 is formed in an annular shape so as to overlap with the outer peripheral edge of the P ⁺ -type region 3 to prevent the PN junction 4 from deteriorating. The main surface of the silicon substrate 1 excluding the central surface of the P ⁺ type region 3 is covered with a silicon oxide film 7, and the P ⁺ type region 3 exposed on the main surface of the silicon substrate 1 has an anode electrode 8 made of an Al layer or the like. Is provided. On the back surface of the silicon substrate 1, a cathode electrode 9 made of a Ni-Au layer or the like is provided.

[0004] Some recent information terminal devices are provided with a large number of external terminals for the purpose of data communication. There is an increasing demand for a Zener diode used as a surge protection element for preventing an electronic circuit from being damaged by static electricity or the like applied to the external terminal. When used for such an application, the same number of Zener diodes as external terminals are required. However, miniaturization is indispensable in portable information devices, and there is often no room for mounting space for electronic components. For this reason, a multi-chip composite type Zener diode having two or more chips mounted in one package is used. FIG. 6 is a diagram showing an example of such a case. Chips 21, 21 each having a Zener diode element formed thereon are mounted on cathode terminals 23, 23, respectively.
A common anode terminal 22 is connected to an anode electrode (not shown) provided on the main surfaces of
, And sealed in the resin package 25.

[0005]

In the above-mentioned conventional multi-chip composite type Zener diode, a die bonding process is required for the number of chips mounted on one package, which causes an increase in manufacturing cost. Was. In addition, since a plurality of chips are mounted on a plane, the space occupied by the plane is large, and it is difficult to reduce the size of the package.

[0006] The present invention is to solve the above problems,
It is an object of the present invention to provide a multi-element composite Zener diode that can be manufactured at low cost and can be downsized.

[0007]

According to the present invention, there is provided a P-type semiconductor substrate comprising a back surface of a P-type semiconductor substrate as a common anode, and a PN junction serving as a Zener diode element connected in parallel to the main surface of the P-type semiconductor substrate. A plurality of multi-element composite type Zener diodes, wherein when a rated Zener voltage is applied to parallel PN junctions, a leakage current generated from the PN junction affects the Zener breakdown of adjacent PN junctions. The parallel PN junctions are electrically separated to the extent that they are not present.

[0008] A chip of such a multi-element composite type Zener diode is mounted on a common anode terminal, and a plurality of cathode electrodes and a plurality of cathode terminals formed in parallel on the chip main surface are connected to each other to form one package. In this case, it can be used as an anode common type multi-element composite type Zener diode. In the past, multiple chips were required to obtain a multi-element composite type Zener diode, but this allows one chip to perform the function of multiple elements, so the die bonding process of mounting the chip on the terminal is one time In addition, manufacturing costs can be reduced. Further, the package size can be reduced.

In the multi-element composite type Zener diode of the present invention, the extent that the Zener breakdown of the adjacent PN junction is not affected is defined as a condition that a forward current of 10 mA flows through the first PN junction. When a reverse voltage lower than the rated Zener voltage is applied to the PN junction of
And the leakage current flowing from the PN junction to the first PN junction is 50 nA or less. The reverse voltage applied to the second PN junction is 60% of the rated zener voltage.
The degree is preferred.

In addition, the extent that the Zener breakdown of the adjacent PN junction is not affected is defined as a state where the depletion layers extending from the adjacent PN junctions do not contact each other when a rated Zener voltage is applied to the parallel PN junctions. It was done.

With such a multi-element composite Zener diode, a plurality of Zener diode elements formed on one chip can be used as independent Zener diodes without affecting the Zener breakdown of each other.

In order to realize these characteristics, the present invention provides:
A P ⁺ -type isolation is formed between the parallel PN junctions. The impurity concentration of the P-type semiconductor substrate is 1 × 1
In the case of 0 ¹⁷ to 1 × 10 ²⁰ cm ³ and the rated Zener voltage is 50 V or less, the impurity concentration of this P ⁺ type isolation should be set in the range of 1 × 10 ¹⁹ to 1 × 10 ²⁰ cm ^3. Thus, the parallel Zener diode elements can be electrically separated.

The impurity concentration of the P-type semiconductor substrate is 1 ×
10 ¹⁷ -1 × 10 ²⁰ cm ³ , rated zener voltage is 50V
In the following cases, the parallel Zener diode elements can be electrically separated by setting the distance between the adjacent PN junctions to 50 to 100 μm.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a multi-element composite type Zener diode according to an embodiment of the present invention. As shown in FIG. 1, two N ⁺ -type regions 2 and 2 are formed in parallel on the main surface of a P-type silicon substrate 1 to form PN junctions 4 and 4 serving as Zener diode elements. On the outer peripheral edge of each of the N ⁺ -type regions 2, annular guard rings 5, 5 composed of N-type regions are formed so as to overlap. An isolation 6 composed of a P ⁺ type region is formed between the parallel PN junctions 4. The main surface of the silicon substrate 1 excluding the central surface of the N ⁺ -type regions 2 and 2 is covered with a silicon oxide film 7, and the N ⁺ -type regions 2 and
In two parts, each cathode electrode 9 made of an Al layer,
9 are provided. On the back surface of the silicon substrate 1, a common anode electrode 8 made of a Ni-Au layer is provided.

As described above, a multi-element composite Zener in which PN junctions 4 and 4 serving as Zener diode elements are provided in parallel on the main surface of the silicon substrate 1 with the back surface of the P-type silicon substrate 1 serving as a common anode electrode 8. Constitutes a diode.

In this embodiment, the silicon substrate 1 has an impurity concentration of about 4.5 × 10 ¹⁸ cm ³ and a specific resistance of 20Ωc.
m and a PN junction 4
Forming an N ⁺ -type region 2 is an impurity concentration of 5 × 10 ¹⁹ cm
Phosphorus was doped so that the specific resistance was about ³ and the specific resistance was about 1.5 mΩcm. In addition, N forming the guard ring 5
The type region is doped with boron so as to have an impurity concentration of about 1.8 × 10 ¹⁹ cm ³ and a specific resistance of about 4 mΩcm, and the P ⁺ type region forming the isolation 6 has an impurity concentration of 1.5 × 10 ¹⁹ cm ^3. cm ³ , specific resistance 7.5mΩ
cm, and the rated zener voltage (Vz) was set to 8.2 V.

FIG. 2 is a schematic view of a package of the multi-element composite type Zener diode described above. The chip 21 is mounted on a common anode terminal 22 and each cathode electrode (not shown) provided on the main surface of the chip 21. ) And the cathode terminals 23, 23 are sealed in a resin package 25 in a state where they are connected by wires 24, 24. In this embodiment, the chip size is 0.4 mm square, and the resin package has a length of 1.6 mm and a width of 0.8 mm. FIG. 3 is a circuit diagram showing this state.

When a rated Zener voltage is applied to such a multi-element composite Zener diode, it is necessary that adjacent PN junctions are electrically separated to such an extent that they do not affect each other's Zener breakdown. Specifically, when a rated Zener voltage is applied to the PN junction, the depletion layers extending from the PN junction do not come into contact with each other, and the surface of the silicon substrate between adjacent PN junctions is inverted to N-type, and the leakage current is reduced. The condition is that adjacent PN junctions are electrically separated to such an extent that the Zener breakdown of the junction is not affected.

The extent to which the adjacent PN junctions described above do not affect the Zener breakdown of each other can be defined by a measurement method described below.

FIG. 4 shows a method of measuring a leak current generated between adjacent PN junctions. Since the multi-element composite Zener diode according to the present invention is structurally the same as an NPN transistor, the back surface of the P-type silicon substrate 1 is used as a base, the first N ⁺ -type region 2a is used as an emitter, and the second N ⁺ -type region is used. 2b assuming collector, and the collector current I _C at the time of applying a collector-emitter voltage V _CE while flowing the base current I _B is measured on the assumption that the leakage current. That is, with a forward current of 10 mA (arrow a) flowing through the first PN junction 4a, a reverse voltage (arrow b) lower than the rated Zener voltage, preferably a rated Zener voltage, is applied to the second PN junction 4b. When a reverse voltage of about 60% of is applied,
A leak current (arrow c) flowing from the second PN junction 4b to the first PN junction 4a is read by the ammeter 31, and if this leak current is 50 nA or less, the Zener breakdown of the adjacent PN junction is affected. The PN junction can be kept electrically isolated so that the PN junction can operate without being given.

In order to realize this condition, when the impurity concentration of the P-type semiconductor substrate is 1 × 10 ¹⁷ to 1 × 10 ²⁰ cm ³ , when a maximum zener voltage of 30 V is applied, an adjacent PN junction In the structure described with reference to FIG. 1, the distance d between the guard rings is desirably 50 to 100 μm, preferably about 70 μm.

If the distance between the guard rings of the parallel PN junctions is at least 50 μm, the guard ring and the depletion layer extending from the isolation will not contact each other. If this distance is 50 μm or less, when a rated Zener voltage is applied, the adjacent PN junctions will affect each other's Zener breakdown, and if it is 100 μm or more, the chip size will increase, and the package size will decrease. Cannot be realized.

In this embodiment, the description has been limited to the case of the two-element composite type, but the same effect can be obtained even with the four-element composite type or a multi-element composite type Zener diode of more.

The same effect can be obtained even when the rated Zener voltage is in a range from a low voltage of about 8V to a high Zener voltage of about 50V.

Further, an epitaxial layer serving as an operation region may be formed on a silicon substrate, and a PN junction may be formed here.

[0027]

As described above, according to the multi-element composite type Zener diode of the present invention, since a multi-element Zener diode element is formed on one chip, the die bonding process of the chip can be performed only once, and the manufacturing is completed. Cost can be reduced.

Further, since a plurality of elements can be formed in one chip, the package size can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a multi-element composite type Zener diode according to the present invention.

FIG. 2 is a schematic view of a package of a multi-element composite Zener diode according to the present invention.

FIG. 3 is a package circuit diagram of a multi-element composite Zener diode according to the present invention.

FIG. 4 is a schematic diagram showing a state in which a leak current is measured.

FIG. 5 is a cross-sectional view of a general zener diode.

FIG. 6 is a schematic view of a package of a conventional multi-chip composite Zener diode.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 silicon substrate 2 N ⁺ type region 2 a first N ⁺ type region 2 b second N ⁺ type region 3 P ⁺ type region 4 PN junction 4 a first PN junction 4 b second PN junction 5 guard ring 6 isolation Reference Signs List 7 silicon oxide film 8 anode electrode 9 cathode electrode 21 multi-element composite type Zener diode chip 22 anode terminal 23 cathode terminal 24 bonding wire 25 resin package 31 ammeter

Claims (6)

[Claims] 1. A multi-element composite Zener diode in which a plurality of PN junctions serving as Zener diode elements are provided in parallel on the semiconductor substrate using the back surface of a P-type semiconductor substrate as a common anode. The parallel PN junctions are electrically separated to such an extent that the leakage current generated from the PN junction does not affect the Zener breakdown of adjacent PN junctions when a rated Zener voltage is applied to the PN junctions. A multi-element composite type Zener diode characterized by the above-mentioned. 2. The condition that the Zener breakdown of the adjacent PN junction is not affected is defined as 10 mA for the first PN junction.
When a reverse voltage slightly lower than the rated Zener voltage is applied to the second PN junction with the forward current of
2. The multi-element composite type Zener diode according to claim 1, wherein a leakage current flowing from said second PN junction to said first PN junction is 50 nA or less. 3. The degree to which the Zener breakdown of the adjacent PN junction is not affected is such that when a rated Zener voltage is applied to the parallel PN junctions, depletion layers extending from the adjacent PN junctions do not contact each other. 2. The multi-element composite type Zener diode according to claim 1, wherein the Zener diode is in a state. 4. The multi-element composite Zener diode according to claim 1, wherein a P ⁺ -type isolation is formed between said parallel PN junctions. 5. An impurity concentration of the P-type semiconductor substrate is 1 ×.
10 ¹⁷ -1 × 10 ²⁰ cm ³ , rated zener voltage is 50V
5. The multi-element composite Zener diode according to claim 4, wherein in the following cases, the impurity concentration of the P ⁺ -type isolation is in a range of 1 × 10 ¹⁹ to 1 × 10 ²⁰ cm ³ . 6. The P-type semiconductor substrate having an impurity concentration of 1 ×
10 ¹⁷ -1 × 10 ²⁰ cm ³ , rated zener voltage is 50V
The distance between the adjacent PN junctions is 50 to 100 μm in the following cases:
6. The multi-element composite type Zener diode according to items 5 to 5.