JPH0992430A - Surge absorbing element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize a discharge start voltage and extend a life by using a surge absorbing cell containing an electric field emission material for a flat insulating body using a ceramic material. SOLUTION: In a surge absorbing element 10 constituted by sealing a surge absorbing cell 40 into a glass tube 20 with a pair of sealing electrodes 52, 54, the cell 40 has a flat and thin plate-like insulating body, for instance, a ceramic body 42 which makes a base, and a material containing an electric field emission material in itself is used for the body 42. As a result, creeping discharge is stabilized by the existence of an electric field emission material, thereby being able to obtain a stable discharge start voltage. Further, metal scatter preventive layers 58, 60 are formed in the exposed end surface inside a tube of the sealing electrodes 52, 54, thereby being able to effectively prevent the constituent substance of the electrodes 52, 54 from being scattered inside a tube at every time of discharging. Therefore, a discharge start voltage can be much more stabilized and the life of the element 10 can be extended and at the same time a withstand surge current can be increased by providing end surface electrodes 48, 49.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surge absorbing element for protecting circuit elements used in electronic equipment from inductive lightning and static electricity. More specifically, by including a field emission substance as a thin plate-shaped insulator forming a surge absorption cell or forming a field emission layer having a field emission substance, it can be used particularly for low voltage surge voltage protection. At the same time, the long-life and stable discharge starting voltage can be maintained.

[0002]

2. Description of the Related Art As is well known, a surge absorbing element instantly absorbs an abnormal voltage (excessive voltage) such as an inductive lightning surge or an electrostatic surge that reaches a circuit system used in an electronic device,
It is used as a protection element for preventing circuit elements, especially semiconductor elements, from being destroyed.

As the surge absorbing element, a semiconductor element, a varistor element, a glass tube arrester, a micro gap absorbing element, etc. are known depending on the application. These do not all have the same characteristics and properties, and for example, semiconductor elements and varistor elements are superior in response speed, and varistor elements, gas tube arresters, microgap absorption elements, etc. are superior in surge current withstand capability.
Further, gas tube arresters, microgap absorbers, and the like are known as those having a small capacitance.

There are two types of surge absorbing elements of this type, one in which both ends of the surge absorbing element are short-circuited when a surge occurs, and the other in which the surge absorbing element is restored as an insulating element after a momentary short circuit. A discharge type surge absorbing element that recovers after an instantaneous short circuit is safer in use.

The surge absorber 10 shown in FIG. 9 is a conventional discharge type device that recovers after an instantaneous short circuit. This surge absorbing element 10 is disclosed in, for example, Japanese Patent Publication No. 63-57918. Surge absorber 10 disclosed in the publication
Is configured as shown in FIG.

The surge absorbing element 10 shown in the figure comprises a cylindrical resistor 12 sealed inside a glass tube 20. Ring electrodes 14 and 16 are fitted at both ends of the resistor 12, and further A lead wire 18 is connected to the electrodes 14 and 16 and is sealed and fixed in a glass tube 20. The glass tube 20 is filled with an inert gas that functions as a discharge gas.

A single groove 24 is formed in the central portion of the cylindrical resistor 12 so as to make one round, and the groove 24 functions as a microgap. The discharge starting voltage mainly changes depending on the width (microgap width) and depth of the ring-shaped groove 24. The microgap width is 30 to 50 μm.

[0008]

In the surge absorber 10 shown in FIG. 9, a ring-shaped groove 24 for a micro gap is provided.
Is often formed by a cutting process such as irradiation with a laser beam (laser light). It is known that the laser beam cannot be narrowed down too small as is well known and the amount of laser light is not constant, so that the microgap width varies in the range of 30 μm to 50 μm as described above. The edge part that has been cut is often bent instead of being flat.

If the microgap width cannot be accurately cut, the discharge start voltage varies greatly. It is known that commercially available products have a variation of about ± 20%. Therefore, at present, the circuit system is designed with reference to the one having the lower discharge starting voltage.

Between the resistor 12 and the electrodes 14 and 16,
In many cases, solder or the like is interposed in order to improve contact, but when a surge current (discharge current) flows, the solder flux or solder is decomposed and these may be scattered in the glass tube 20. When the solder or the solder flux is scattered, a part of the solder or the solder flux is deposited in the ring-shaped groove 24, which deteriorates the insulating property of the microgap,
It affects the life of the surge absorbing element 10.

As another surge absorbing element, the technique disclosed in Japanese Patent Laid-Open No. 62-237686 is known. This is configured as shown in FIG. As a surge absorption cell, a pair of resistors 3 such as silicon Si
0 and 32, which are united with the insulating layers 34 and 36 through the phosphorus glass layer 38 for adhesion, are sealed in the glass tube 20 with both ends crimped and sandwiched by the electrodes 14 and 16, respectively. Be stopped. The glass tube 20 is filled with a discharge gas.

In this structure, a pair of resistors 30, 3
A microgap is formed by the insulating layers 34 and 36 and the phosphor glass layer 38 sandwiched by two. The sealing electrodes 14 and 16 are made of Ni in consideration of the coefficient of thermal expansion with the glass tube 20.
A Dumet electrode formed by depositing Cu and CuO on the surface of —Fe is used.

In such a case, in the structure shown in FIG. 11, substances such as Cu14a and CuO14b leak and scatter into the glass tube 20 due to discharge, and a part of the substance adheres to the microgap to insulate the microgap. It caused the problem of deterioration of sex.

Therefore, the present invention solves the above-mentioned conventional problems, and is particularly suitable for a low-voltage discharge starting voltage, and has a stable discharge starting voltage and a long life. This is a proposal for a surge absorbing element that is designed to be highly functional.

[0015]

In order to solve the above-mentioned problems, in the surge absorbing element according to the present invention as set forth in claim 1, one of the high resistance layers adhered to one surface of the insulator is formed. It has a surge absorption cell in which a micro-gap is formed by cutting off the part, and the insulator used is one containing a field emission substance or one having one or both sides of the insulator coated with a field emission substance. In addition, the electrode layers formed on both ends of the surge absorption cell are sealed in a glass tube in a state of being pressure-bonded by a pair of sealing electrodes or sealing electrodes having a metal scattering prevention layer. To do.

In the surge absorbing element according to claim 2, the field emission material is MgO, BaO, CaO, Sc ₂ O ₃ , Sr.
₂ O ₃ , LaB ₆ , BaTiO ₃ , SrTiO ₃ , BaSr
It is characterized by being any one of TiO ₃ .

According to another aspect of the surge absorbing element of the present invention, SnO ₂ , C, Si, Ti, Ni, and
W, Ta, Zr, and their nitrides and carbides (SnO
₂ , except Ni, C) is used.

The surge absorbing cell is sealed in a glass tube together with a discharge gas, and a surge voltage is applied to the sealing electrodes at both ends. When this reaches a discharge start voltage, discharge is generated between the micro gaps formed in the high resistance layer. Occur. When the discharge is completed, it returns to the original state.

The discharge start voltage per gap can be lowered by narrowing the width of the microgap. For example, it can be lowered to about 200 to 250 volts.

As the insulator, one containing a field emission substance is used, or otherwise, a field emission substance (also referred to as a field emission layer) is formed on one side or both sides of this insulator. Stuff used. The presence of this field emission substance lowers the value of the discharge starting voltage, smoothes the creeping discharge, and stabilizes the discharge starting voltage.

Since the metal scattering prevention layer is provided, not only the constituent material (metal) of the sealing electrode but also the metal scattering from the oxide layer can be prevented, so that a stable discharge can be obtained, and the scattering material can form a micro gap. Since it does not adhere inside, the discharge life is extended. That is, the life of the element can be extended.

Since the plating layer is formed as the electrode layer and the high resistance layer is partially covered,
The contact state between the electrode layer and the high resistance layer is stabilized, and thus, it is prevented from being destroyed even by a large surge current.
Therefore, the surge current withstand capability is improved.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of a surge absorbing element according to the present invention will be described in detail with reference to the drawings.

In the present invention, a microgap is formed in a part of the high resistance layer formed on the insulator, and the insulator itself contains a field emission substance, or one surface or both surfaces of the insulator. It is formed by forming a field emission material on a cell and used as a surge absorption cell. This surge absorption cell is structured to be sealed in the glass tube. FIG. 1 shows an embodiment in which the insulator itself contains a field emission material.

The surge absorbing element 10 of the present invention shown in FIG.
Is constructed by sealing the surge absorption cell 40 in the glass tube 20 with a pair of sealing electrodes 52, 54.

The surge absorbing cell 40 has a flat base serving as a base.
It has a thin plate-shaped insulator, for example, a ceramic body 42. As the insulator 42, one in which a field emission substance is contained is used. For example, (Al ₂ O ₃ : BaO: CaO) and the like are preferable. Insulator 41 exhibits an insulation resistance of 10 ¹³ MΩ-cm. Other field emission materials include Sc ₂ O ₃ ,
Sr ₂ O ₃ , LaB ₆ , BaTiO ₃ , SrTiO ₃ , Ba
SrTiO ₃ or the like can be used.

A high resistance layer 44 is deposited on one surface (the upper plane in the example of the figure) of the insulator 42. High resistance layer 44
The thickness is selected so that the resistance value is about 500Ω. Carbon C and titanium carbide T as high resistance materials
iC or the like can be used.

Two line cutting parts 46 and 47 are formed at a predetermined position of the high resistance layer 44, in this example, substantially in the center part. The line cutting portions 46 and 47 form a micro gap. The width of the cut portions 46 and 47 becomes the microgap width, and the value of the discharge start voltage is mainly determined by the width. The discharge start voltage value decreases as the width becomes narrower. In this example, the microgap width and the like are selected so that the discharge start voltage is about 400 to 500 volts.

Electrode layers 48, 4 are formed on the left and right end surfaces of the insulator 42.
9 is deposited. These electrode layers 48, 49 are used to improve the bonding state with the sealing electrodes 52, 54 described later. The upper part of the electrode layers 48 and 49 is a high resistance layer 44.
Is formed so as to cover a part of. A part of the high resistance layer 44 is covered so that the upper end faces of the electrode layers 48 and 49 are end faces of the high resistance layer 44 even when the sealing electrodes 52 and 54 are pressure-bonded (this is also a cut end face by dicing). This is to prevent peeling from the surface. If peeled off, disconnection or poor contact will result.

Surge absorption cell 4 constructed as described above
0 is sealed in the glass tube 20 while being crimped by the pair of sealing electrodes 52 and 54. Sealing is heat sealing,
The temperature is in the range of 500-700 ° C. Glass tube 2
An inert gas (Ar gas etc.) as a discharge gas in 0
Is filled so that the required gas pressure is reached.

FIG. 2 is a specific example of the sealing electrodes 52 and 54, in which the electrode body 62 has a stepped portion that substantially matches the difference between the inner diameter and the outer diameter of the glass tube 20. The electrode body 62 is nickel Ni
A Dumet electrode composed of an alloy material of iron and Fe is used. A metal thin film layer 6 of copper Cu is formed on the outer surface of the electrode body 62.
4 is adhered and formed, and the surface is further subjected to oxidation treatment to form C
A uO oxidation treatment layer 66 is formed.

As described above, the Dumet electrode is used as the electrode body 62 and the surface thereof is covered with the oxidation treatment layer 66 in order to make the coefficient of thermal expansion of the glass tube 20 to be as equal as possible. This is to facilitate the sealing of the sealing electrode with the sealing electrode.

Of the surface of the oxidation treated layer 66, the glass tube 2
A metal scattering prevention layer 58 is further coated on the portion exposed inside the glass tube 20 when 0 is sealed, that is, on the surface side facing the surge absorption cell 40. The metal scattering prevention layer 58 is the material metal (Ni, F) of the electrode body 62.
This is to prevent e) and the constituent metal (Cu) of the metal thin film layer 64 from scattering or spattering into the glass tube 20 and being leaked due to discharge.

When such a metal is scattered in the glass tube 20 at each high-voltage discharge, a part of the metal adheres to the inner surfaces of the high resistance layer 44 and the cut portions 46 and 47 formed on the high resistance layer 44. The insulation deteriorates, which causes fluctuations such as a lower discharge start voltage. Fluctuations in the discharge starting voltage also lead to deterioration of the element itself, and eventually shorten the life of the element.

In this example, titanium nitride TiN is used as the metal scattering prevention layer 58, but in addition to this, tungsten W, titanium Ti, silicon Si, zirconium Zr,
Nickel Ni, tin oxide SnO ₂ , carbon C, tantalum T
It is possible to use a and their nitrides and carbides (excluding C, SnO ₂ , and Ni).

The surge absorbing element 10 thus configured
As an example of the usable dimensions of the glass tube 20, a glass tube 20 having an outer diameter of 2.6 mm and an inner diameter of 1.5 mm is used. The insulator 42 is a flat plate type and has a size of 2 mm × 1 mm and a thickness of 0.6 mm. The thickness of the high resistance layer 44 is 20
00 Angstroms and electrode layer 48 is selected to have a thickness of 5000 Angstroms. The metal scattering prevention layer 58 has a thickness of 0.25 μm. Therefore, the surge absorbing element 10 itself is a very small and lightweight element.

FIG. 3 shows an example of a method of manufacturing the surge absorption cell 40. A ceramic substrate (substrate before dicing) 42 'as an insulator contains the above-mentioned field emission material. (A in the figure). The ceramic substrate 42 'is fired at a temperature of 1400 ° C in a firing furnace. A high resistance layer 44 'using TiC or C is formed on one surface of the rectangular ceramic substrate 42' by sputtering so that the resistance value is 500Ω in this example (FIG. 9B). At this time, the temperature of the ceramic substrate is set to 100 ° C., and the grown film thickness is about 2000 Å.

Then, as shown in FIG. 6C, a photoresist layer 70 is coated and exposed so that a predetermined microgap is obtained. The shaded area is the exposed area. After the exposure processing, the unnecessary portion is removed using a dry etching device, so that a pair of cutting portions 46 and 47 having a predetermined width as shown in FIG. The pair of cutting portions 4647 form a microgap.

Next, with respect to the ceramic substrate 42 ',
In this example, using a dicer, 2 mm x 1 mm x 0.6 m
m. Cut chip or insulator 4
The size of 2 is shown in Figure D. Then, after cleaning the insulator 42, metal films 48a and 49a of Cr and Ni were formed by sputtering so as to cover the left and right end surfaces of the insulator 42 as shown in FIG. The substrate temperature at this time was 100 ° C., and Ar gas was used under a gas pressure of 4 mTorr. The metal films 48a and 49a are formed up to the upper end surface so as to cover a part of the high resistance layer 44.

After forming the metal films 48a and 4a9, the insulator 42 is immersed in an electroless Ni plating bath for 5 to 30 minutes to form Ni plating layers 48b and 49b having a thickness of 1 to 30 μm. Even in this case, the upper end faces of the plated layers 48b and 49b are part of the high resistance layer 44, and thus the metal films 48a and
It is formed so as to cover the upper end face side of 49a. The electrode layers 48 and 49 are formed by the metal layer having the two-layer structure and the plating layer.

By covering the left and right end surfaces of the high resistance layer 44 with the electrode layers in this manner, the connection between the electrode layers 48 and 49 and the high resistance layer 44 becomes good. Without such a coating treatment, it is likely to cause disconnection or poor contact. As shown in FIG. 3, the high resistance layer 44 is formed by dicing.
Since the corners of the cut end face of are in a standing state,
Sealing electrodes 52, 54 when sealing the glass tube 20
This is because the end surface of the high resistance layer 44 may be partly peeled off by the pressing. If partial peeling occurs, the element may be destroyed when a large surge current flows, and as a result, the surge current withstand capability decreases.

The Dumet electrode, which is the above-mentioned sealing electrode, was used after being preliminarily washed and then TiN was sputtered to form a film having a thickness of 3000 angstroms only on the exposed end face to form the metal scattering preventing layers 58 and 60.

One surge absorbing cell 40 formed as shown in FIG. 3 is put in the glass tube 20 and the pair of sealing electrodes 5 is inserted.
Clamp and pinch with 2,54. After that, an inert gas (Ar gas, Ne, He,
N ₂ gas etc.) is filled and sealed. The sealing temperature is about 700 ° C.

The surge absorbing element 10 manufactured by the above manufacturing method can be represented by an equivalent circuit as shown in FIG. That is, the surge absorber 10 has a resistance R (R
a, Rb, Rc) and the gap G (Ga, Gb) in series, the resistance R is the resistance of the high resistance layer 44, and the gap G corresponds to the cutting portions 46 and 47. The width of the gap G (microgap width) is the cutting portions 46, 47.
Determined by the cutting width of.

A surge absorbing element 10 using an insulator containing a field emission substance as shown in FIG.
If a DC voltage is applied between both lead terminals 18, 18,
It was found to discharge at 00V ± 10%.

On the other hand, it was found that the discharge starting voltage when using the surge absorbing element using the insulator containing no field emission material was about 230 V ± 20%. Therefore, it has been found that the surge absorbing element 10 according to the present invention can obtain a more stable discharge starting voltage.

Further, as the sealing electrodes 52 and 54, the metal discharge preventing layers 58 and 60 coated on the exposed end surfaces in the tube are used, so that the constituent substances of the metal layer formed on the end surfaces are scattered into the tube each time discharge occurs. Disappears and the high-voltage discharge becomes stable. If there is metal scattering, the insulation property of the surge absorption cell 40 itself deteriorates, but this can be confirmed by measuring the insulation resistance value at both ends of the sealing electrode.

As shown in FIG. 5, the relationship between the number of discharges and the insulation resistance at that time is as shown in FIG.
In the case where 8 and 60 are formed, it is very stable as shown by the curve Lb. On the other hand, in the surge absorbing element in which the metal scattering prevention layers 58 and 60 are not formed, it is found that the insulation resistance decreases from around 100 times of discharge as shown by the curve La. As a result, according to the configuration of the present invention, the discharge starting voltage can be further stabilized. Since metal scattering in the tube is prevented, the discharge characteristics are not deteriorated, and as a result, the life of the device is extended.

FIG. 6 shows another embodiment of the present invention. In FIG. 6, a normal ceramic material containing no field emission material is used as the insulator 42. Therefore insulator 4
The field emission layer 7 has a predetermined thickness on one surface 2
2 is deposited and a high resistance layer 44 as shown in FIG. 1 is formed on the upper surface thereof. As described above, the strip-shaped cutting portions 46 and 47 are formed at predetermined positions of the high resistance layer 44. And these cutting parts 46 and 47 function as a micro gap.

FIG. 7 shows an example of a method of manufacturing the surge absorption cell 40. A field emission layer 72 was formed on a substrate of a planar insulator 42 using a ceramic material by sputtering using a sintered target using BaO as a field emission material until the film thickness became about 2000 angstroms (the same figure). A). Other field emission materials include MgO and C
aO and further Sc ₂ O ₃ , Sr ₂ O ₃ , LaB ₆ and BaTi
It is also possible to use a sintering target such as O ₃ , SrTiO ₃ , or BaSrTiO ₃ .

Then, a high resistance layer (TiC or C) is connected and connected.
44 was formed into a film (FIG. 9B). After forming the high resistance layer 44, a resist layer 70 is applied and exposed to a predetermined pattern, and after the post-baking, the high resistance layer 44 is etched by dry etching to form cutting layers 46 and 47 (FIGS. 6C and D). .
Next, after removing the resist layer 70, the resist layer 70 was cut into a predetermined size by a dicer (D in the same figure).

After cutting, Ti and N are applied to both left and right end surfaces of the insulator 42.
The metal films 48a and 49a are continuously sputtered in the order of i (FIG. 8E), and the Ni plating layer 48 is further formed on the surface thereof.
b and 49b were formed to complete the surge absorption cell 40 (F in the same figure).

The surge absorbing cell 40 is connected to the glass tube 20.
Then, the electrodes were sealed by using sealing electrodes (Dumet electrodes) 52 and 54 having a pair of metal scattering prevention layers 58 and 60 attached to their end faces. The glass tube 20 is filled with an inert gas as a discharge gas. The sealing work is performed using a sealing device.

A surge absorbing element 1 constructed as shown in FIG.
When the characteristics were measured for 0, almost the same result as that of the surge absorber of FIG. 1 was obtained.

In the structure shown in FIG. 6, the field emission layer 72 is formed only on the upper surface of the insulator 42, but as shown in FIG. 8, the field emission layer 74 is formed on the lower surface (back surface) of the insulator 42 as well. be able to. The field emission material of the field emission layer 74 formed on the lower surface is BaO, MgO, or CaO described above.
Etc. can be used, and about 200 can be obtained by sputtering.
A film having a film thickness of about 0 Å is used.

Therefore, the final surge absorbing element 10 shown in FIG. 8 is formed by using the insulator 42 'having the field emission layer formed on the lower surface in advance and applying the manufacturing method shown in FIG. It was found that the discharge characteristics were further stabilized by forming the field emission layer 74 even on the lower surface in this manner.

[0057]

As described above, according to the present invention, the flat-plate insulator itself made of a ceramic material contains the field emission material, or the field emission layer is formed on one side or both sides of the insulator. The surge absorbing cell is constructed by using the surge absorbing cell.

According to this, the creeping discharge is stabilized in the presence of the field emission substance, and a stable discharge starting voltage can be obtained. Further, since the metal scattering prevention layer is formed on the exposed end surface of the sealing electrode inside the tube, it is possible to effectively prevent the constituent substances of the sealing electrode from scattering into the tube each time a discharge occurs. The scattered metal adheres to the inside of the microgap, which causes a change in the discharge start voltage and also affects the life of the device. In the present invention, this factor can be eliminated, so that the discharge start voltage can be stabilized and the life of the device can be extended.

Further, since the electrode layer (end face electrode) is formed so as to cover a part of the high resistance layer, disconnection, contact failure, etc. are prevented, and the element is destroyed even if a large surge current flows. Not that. Therefore, the present invention has the practical advantage of being able to provide a flat plate type surge absorbing element having a high surge current withstanding capability.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts showing an embodiment of a surge absorber according to the present invention.

FIG. 2 is a cross-sectional view showing an example of a sealing electrode used for a surge absorbing element.

FIG. 3 is a process drawing showing an example of a manufacturing process of a surge absorption cell used for a surge absorption element.

FIG. 4 is an equivalent circuit of a surge absorbing element.

FIG. 5 is a curve diagram showing the relationship between the number of discharges and insulation resistance.

FIG. 6 is a cross-sectional view of essential parts showing another embodiment of the surge absorber according to the present invention.

FIG. 7 is a manufacturing process drawing thereof.

FIG. 8 is a cross-sectional view of essential parts showing another embodiment of the surge absorber according to the present invention.

FIG. 9 is a cross-sectional view of essential parts showing a conventional example of a surge absorber.

FIG. 10 is a cross-sectional view of essential parts showing a conventional example of a surge absorber.

FIG. 11 is a partially enlarged cross-sectional view thereof.

[Explanation of symbols]

 10 Surge Absorption Element 20 Glass Tube 40 Surge Absorption Cell 42 Insulator 48,49 Electrode Layer (End Face Electrode) 52,54 Sealing Electrode 58,60 Metal Scattering Prevention Layer 72,74 Field Emission Layer

Claims (3)

[Claims] 1. A surge absorbing cell having a microgap formed by cutting out a part of a high resistance layer formed on one surface of an insulator, wherein the insulator contains a field emission material. One or both sides of the surge absorbing cell are used, and the electrode layers formed on both ends of the surge absorbing cell are a pair of sealing electrodes or a metal scattering prevention layer. A surge absorbing element, wherein the surge absorbing element is sealed in a glass tube in a state of being pressure-bonded by a sealing electrode having. 2. The field emission material is MgO, BaO,
CaO, Sc ₂ O ₃ , Sr ₂ O ₃ , LaB ₆ , BaTiO ₃ ,
The surge absorber according to claim 1, which is one of SrTiO ₃ and BaSrTiO ₃ . 3. The metal scattering prevention layer comprises SnO ₂ ,
The surge absorbing element according to claim 1, wherein C, Si, Ti, Ni, W, Ta, Zr, and their nitrides and carbides (excluding SnO ₂ , Ni, C) are used.