JP3213248B2 - Method for manufacturing field electron emission type surge absorbing element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for protecting an electronic circuit of an electronic device from an overvoltage such as a surge that enters through a power line or a communication line, or between lines or between each line and a ground. In particular, the present invention relates to a method for manufacturing a surge absorbing element using a field electron emission phenomenon.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 12, between a line L1, L2 such as a power supply line and a communication line leading to an electronic circuit 60 of an electronic device,
Alternatively, a surge absorbing element 62 is connected between each line and GND (ground) to protect the electronic circuit 60 from a surge such as an induced lightning. That is, when a surge voltage higher than the rating of the surge absorbing element 62 is applied between the lines L1 and L2 or between the lines L1 and L2 and GND, the surge absorbing element 62 conducts and bypasses the surge. This is a mechanism for protecting the electronic circuit 60.

As such a surge absorbing element 62, a gas arrester utilizing a discharge phenomenon in a discharge gap, a varistor which is a high-resistance element having a nonlinear voltage characteristic, or an avalanche (electron avalanche) of a pn junction type semiconductor is used. There are various types such as silicon surge absorbers utilizing the effect, but recently a surge absorbing element using a field electron emission phenomenon has been newly added.

[0004] A surge absorbing element using this field electron emission phenomenon is described in Japanese Patent Application No. 8-132728. As shown in FIG. 1, a field electron emission type surge absorbing element 10 disclosed therein includes a first substrate member 12 made of an n-type semiconductor.
And a second substrate member 14 are opposed to each other at a predetermined distance, and the inner peripheral edge of both members is hermetically sealed via a frame member 16 also serving as a spacer.
The envelope 18 is maintained in a high vacuum state of 10 ^-6 to 10 ^-8 Torr. On the inner surface of the first substrate member 12, a large number of emitters made of an n-type semiconductor are provided.
The cones 20 are protruded at predetermined intervals. The emitter cone 20 has a pointed cone or pyramid shape, with the tip facing the inner surface of the second substrate member 14. The inner surface of the first substrate member 12 including the surface of the emitter cone 20 and the inner surface of the second substrate member 14 include Nb,
W, Mo, Cr, Ti, Th, Si, Ni, La, G
e, a thin film made of Al or the like, a two-layer structure of W and Zr, or a protective film 22 made of a carbide, oxide, nitride, or inorganic compound containing at least one of the above substances. Have been. The first substrate member 12 and the second
A first external electrode 24 and a second external electrode 26 are formed on the outer surface of the substrate member 14, respectively. A cathode terminal 28 and an anode terminal 30 are connected to each external electrode. Then, by connecting the terminals 28, 30 to the lines L1, L2 or GND, the above-mentioned field emission type surge absorbing element 10 is connected.
Is inserted and connected between the lines L1 and L2 or between the lines L1 and L2 and GND, as shown in FIG.

The line L1 and L2 or the line L
1. When an overvoltage exceeding a rating such as a surge is applied between L2 and GND, and strong electric field concentration occurs at the tip 20a of the emitter cone on the cathode side, electrons in the n-type semiconductor are caused by a quantum mechanical tunnel effect. A so-called field electron emission phenomenon that is emitted into a vacuum beyond the potential barrier occurs. The emitted electrons are captured on the anode side of the high potential, that is, on the inner surface of the second substrate member 14, so that a precursor discharge in which a current flows between the second substrate member 14 and the first substrate member 12 is generated. The precursor discharge then shifts to a vacuum spark discharge (vacuum arc discharge). The following is conceivable as a mechanism in which the precursor discharge shifts to a vacuum spark discharge. That is, due to the effect of thermal energy generated by increasing the current density at the tip of the emitter cone due to electron emission during the precursor discharge, metal vapor is generated from the metal constituting the protective film 22 covering the surface of the emitter cone. Also, due to thermal energy generated as a result of electrons colliding with the anode side due to the precursor discharge, a metal vapor is similarly generated from the metal of the protective film 22 covering the inner surface of the second substrate member 14, and these charged metal vapors Becomes the element that forms a current, and a vacuum spark discharge is generated. Further, it is practically difficult to make the inside of the envelope 18 a complete vacuum, and gas molecules are slightly adsorbed or adhered to the surface of the material constituting the discharge space. Is released into the space by the impact of the precursor discharge, and the ionized gas molecules serve as elements for forming a current. This is also a factor promoting vacuum spark discharge.

The above-mentioned field electron emission phenomenon occurs only when the electric field intensity concentrated on the emitter cone 20 becomes higher than a predetermined value. This occurs when a voltage higher than a predetermined value is applied between both electrodes. Only means that a current flows between both electrodes. In other words, since a nonlinear relationship appears between the value of the voltage applied between the two electrodes and the flowing current, surge absorption occurs only when an overvoltage exceeding the rated voltage is applied and the overvoltage is bypassed. The function can be exerted.

Furthermore, compared with the speed of electrons in a semiconductor, electrons in a vacuum travel without being scattered, so that the field emission type surge absorbing element 10 can operate at an extremely high speed. Further, since the semiconductor device does not have a junction structure between the p-type semiconductor and the n-type semiconductor, there is no problem that the capacitance is increased unlike the silicon surge absorber.

FIG. 13 shows the surge absorption characteristics of such a field electron emission type surge absorbing element 10.
It is a graph which shows the surge absorption waveform with respect to the original surge waveform whose peak voltage value is 3 kV. As shown in the figure, when a surge voltage is applied, a precursor discharge having a peak of about 2.32 kV is instantaneously generated.
A state in which a stable surge absorption waveform of 0 V is obtained is shown.

The emitter cone 20, which is the most important component of the field electron emission type surge absorbing element 10, is:
It was formed as follows. First, as shown in FIG. 14, an n-type Si substrate 42 is oxidized in an oxidizing atmosphere, and a surface of about 150 to 3000 angstroms thick
An O ₂ thin film 44 is formed. Then, a photoresist process, about the diameter on the surface of the SiO ₂ thin film 44 3 to 10 [mu] m
The circular oxide film mask 54 is formed by selectively etching the SiO ₂ thin film 44 by BHF (wet etching using buffered hydrofluoric acid) as shown in FIG.

Next, as shown in FIG.
Is anisotropically wet-etched on the surface to erode the surface other than the oxide film mask 54, and this etching is stopped immediately before the oxide film mask 54 is separated. This produces an undercut 58, creating a prototype emitter cone with a flat tip. Since the tip of the emitter cone cannot be sharpened by this alone, as shown in FIG. 17, the surface is oxidized again to form the SiO ₂ thin film 44, and then the SiO ₂ thin film 44 is removed by wet etching to remove the tip 2.
0a forms a sharp emitter cone 20 (FIG. 1).
8).

[0011]

The operating voltage (rated voltage) of the field emission type surge absorbing element 10 is as follows.
The degree of vacuum in the envelope 18, the work function of the surface of the emitter cone 20, the distance between the emitter cone tip 20a and the inner surface of the second substrate member 14, or the emitter cone tip 20
It is determined by the sharpness of a. That is, when it is necessary to set the operating voltage of the field electron emission type surge absorbing element 10 relatively low, a method of increasing the degree of vacuum in the envelope 18, a method of reducing the work function of the emitter cone 20,
Although a method of shortening the distance between the emitter cone tip 20a and the inner surface of the second substrate member 14 or a method of sharpening the emitter cone tip 20a is theoretically conceivable. There is a certain limit in improving the degree of vacuum inside the envelope 18 and reducing the work function of the emitter cone 20, and the tip 20a of the emitter cone and the second
It is extremely difficult to control the positional relationship with the substrate member 14 on the order of μm, and ultimately the most realistic method is to increase the sharpness of the emitter cone tip 20a.

However, the emitter cone described above
In the method of forming 20, the angle of the tip 20a is at most 40-45.
There is a problem that it can be formed only to a degree. For this reason, in the conventional field electron emission type surge absorbing element 10, it is relatively easy to set the operating voltage to be higher, but there is a limit to setting the operating voltage to be lower.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and a field electron emission type surge capable of easily setting an operation voltage to a relatively low level by further increasing the sharpness of the tip of an emitter cone. An object of the present invention is to realize a method for manufacturing an absorbing element.

[0014]

In order to achieve the above object, a method of manufacturing a field electron emission type surge absorbing element according to the present invention is directed to an electron emission portion made of a semiconductor having a plurality of emitter cones integrally formed on one surface. A first substrate member provided with a first substrate member, a second substrate member provided with a flat portion on one surface, and a tip portion of an emitter cone of the first substrate member and a flat portion of the second substrate member. Arranged so as to face each other at a predetermined distance, the outer edges of both substrate members are hermetically sealed to form an envelope, and the inside of the envelope is in a high vacuum state, and the outer surfaces of both substrate members are In a method of manufacturing a field electron emission type surge absorbing element having external electrodes formed thereon, a step of forming a large number of oxide masks on the surface of the substrate member, and a step of forming SF ₆ and O _{2 on} the surface of the substrate member. Reactive ion etching using mixed gas Forming a column-shaped protrusion serving as a prototype of an emitter cone under the oxide film mask by performing etching to erode a portion not covered by the oxide film mask; and , KOH and H ₂
And O, the mixing ratio is to of H ₂ O 100 ml 50
g of KOH to form an anisotropic wet-etched surface, thereby eroding the surface thereof, thereby forming an emitter cone having a sharp tip. I do. Further, another method of manufacturing a field electron emission type surge absorbing element according to the present invention includes an electron emission portion made of a semiconductor having a plurality of emitter cones integrally formed on one surface, and a flat portion on which no emitter cone is formed. The first substrate member, and a large number of emitters
A second substrate member having an electron emission portion made of a semiconductor integrally formed with a cone and a flat portion on which no emitter cone is formed is connected to the tip of the emitter cone of one substrate member and the second substrate member of the other substrate member. It is arranged so that the flat portion and the flat portion face each other at a predetermined distance, and the peripheral edges of both substrate members are hermetically sealed to form an envelope, and the inside of the envelope is brought into a high vacuum state. In a method of manufacturing a field electron emission type surge absorption element formed by forming external electrodes on the outer surface of the member,
Forming a large number of oxide film masks on the surface of the substrate member, and performing reactive ion etching using a mixed gas of SF ₆ and O _{2 on} the surface of the substrate member; Erodes uncovered areas,
Thus, a step of forming a columnar protrusion serving as a prototype of the emitter cone below the oxide film mask, and for the protrusion ,
The KOH and H ₂ O, in H ₂ O of the mixture ratio of 100ml
Using a mixed aqueous solution obtained by mixing 50 g of KOH
The surface was eroded by performing anisotropic wet etching Te, characterized in that it comprises a step of leading end Te than to form a sharply pointed emitter cones.

[0015] Reactive ion etching (hereinafter abbreviated as "RIE") is classified as so-called dry etching.
A method in which a sample is placed between two parallel electrodes, a predetermined gas medium is filled in a vacuum chamber, and high-frequency plasma discharge is generated between the two electrodes to perform etching. And etching by a chemical reaction are superimposed to realize processing of the sample. For this reason, in addition to the characteristics that the etching rate is high and the substance to be etched can be selected, the etching direction is concentrated in the ion bombardment direction, and therefore, there is an advantage that anisotropy is excellent.

In wet etching, a sample is immersed in a predetermined chemical, and etching is performed by utilizing the chemical reaction. Generally, the wet etching is excellent in the selectivity of a substance to be etched, but has strong isotropy. That is, it is characterized in that it is difficult to control the etching direction and overetching easily occurs. On the other hand, in the anisotropic wet etching, by devising the selection of an etchant, the isotropic property is reduced and the etching direction is easily controlled while the wet etching is performed.

In the above-mentioned conventional method for forming an emitter cone, since the flat substrate member is subjected to wet etching from the beginning, anisotropic wet etching is said to be easy to control the etching direction. However, if erosion is used for a long time, erosion in the width direction will proceed before the height of the emitter cone is formed by over-etching, making it impossible to form an emitter cone with sufficient height and width Would. For this reason, conventionally, the anisotropic wet etching cannot be continued until the tip of the emitter cone obtains a sufficient sharpness, and it has to be rounded up in an appropriate time. Therefore, after the surface of the emitter cone was oxidized again, the tip was sharpened by removing this oxide film.However, the oxide film itself was extremely thin on the surface of the emitter cone. However, the removal of this did not make the tip much sharper.

On the other hand, in the method for forming the emitter cone according to the present invention, the RIE having more excellent anisotropy is provided.
First, a columnar protrusion is formed on a flat substrate member to secure the height and width of the emitter cone to some extent, and then the undercut by anisotropic wet etching is used to sharpen the protrusion. For this reason, the height and width of the emitter cone can be maintained at required levels even if anisotropic wet etching is performed until the tip of the projection is sufficiently sharpened. In fact, in the conventional forming method, the height of the emitter cone is at most 1 to
Although it could be formed only to a thickness of about 1.3 μm, the height of the emitter cone could be set to 5 μm or more by using the forming method according to the present invention.

In short, it is extremely difficult to sharpen the tip of a completely flat substrate member while securing the height and width simultaneously by anisotropic wet etching, but to achieve a sufficiently high height by RIE. If the anisotropic wet etching is performed after forming an emitter cone prototype having a width and a width, the tip can be sufficiently sharpened in a relatively short time.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic structure of a first field-emission type surge absorbing element 10 according to the present invention is common to the above-mentioned conventional example. That is, as shown in FIG.
The substrate member 12 and the second substrate member 14 are opposed to each other at a predetermined distance from each other, and the inner peripheral edges of the two substrate members are hermetically sealed via a frame member 16 also serving as a spacer. An envelope 18 is formed, and the inside of the envelope 18 is set to 10 ^-6 to 10 ^-8 Torr.
And maintained in a high vacuum state.

On the inner surface of the first substrate member 12, a large number of emitter cones 20 are provided projecting over substantially the entire surface at predetermined intervals. Although FIG. 1 is a cross-sectional view, only one row of emitter cones 20 is shown. However, actually, the emitter cones 20 are arranged vertically and horizontally at regular intervals. The first
The substrate member 12 is formed of an n-type semiconductor in which impurities such as P and As are mixed in Si. The emitter cone 20 is also made of an n-type semiconductor and is formed integrally with the first substrate member 12. The emitter cone 20 has a pointed cone or pyramid shape,
The tip portion 20a faces the inner surface of the second substrate member 14. However, a predetermined gap is maintained between the tip 20a of the emitter cone 20 and the inner surface of the second substrate member 14. The height of the emitter cone 20 is set to about 5 μm, the diameter of the bottom surface is set to about 3 to 10 μm, and the pitch between the emitter cones 20 is set to about 7.5 to 15 μm.

The first including the surface of the emitter cone 20
The inner surface of the substrate member 12 is coated with a protective film 22.
This protective film 22 is made of Nb, W, Mo, Cr, Ti, Th,
Thin films made of Si, Ni, La, Ge, Al, diamond (amorphous carbon), etc., a two-layer structure of W and Zr, or carbides, oxides, nitrides containing at least one of the above materials And inorganic compounds. On the outer surface of the first substrate member 12, a first layer 24a formed by evaporating Al or Cr, and the first layer 24a are formed.
A first external electrode 24 composed of a second layer 24b formed by evaporating Ni on the surface of a is formed. This first layer 24
Al or Cr constituting a and a constituting Ni for the second layer 24b were selected as those which achieve good ohmic contact.

The second substrate member 14 is made of an n-type semiconductor like the first substrate member 12 and has an inner surface similar to that covering the surface of the emitter cone 20 and the like. Is formed. Further, on the outer surface of the second substrate member 14, a first layer 26a formed by evaporating Al or Cr, and a second layer 26b formed by evaporating Ni on the surface of the first layer 26a. A second external electrode 26 is formed.

As is clear from the above, in the first field emission type surge absorbing element 10, the entire inner surface of the first substrate member 12 constitutes an electron emission portion, and The entire inner surface of the substrate member 14 constitutes a flat portion. As a constituent material of the second substrate member 14, other than the n-type semiconductor, other substances having substantially the same coefficient of thermal expansion as the first substrate member 12 can be used.
Corresponds to this.

The first external electrode 24 and the second external electrode
26 need not necessarily have a two-layer structure, and may be formed by evaporating only Ni. As the material of the frame member 16, Pyrex glass or the like having a thermal expansion coefficient close to that of the n-type semiconductor is used.

A first external electrode on the first substrate member 12 side
A cathode terminal 28 is connected to 24, and an anode terminal 30 is connected to the second external electrode 26 on the second substrate member 14 side. Then, by connecting each terminal to the line L1, L2 or GND in the same manner as shown in FIG. 12, the first field-emission type surge absorbing element 10 can be connected to the line L in the same manner as shown in FIG.
1 and L2 or between lines L1 and L2 and GND. When a surge voltage exceeding the rated voltage is applied between the lines L1 and L2 or between the lines L1 and L2 and GND, a strong electric field concentration occurs at the tip 20a of the emitter cone 20, and a quantum mechanical tunnel effect occurs. As a result, electrons pass through a potential barrier on the surface and are emitted into a vacuum. Electrons generated by this so-called field electron emission phenomenon are captured on the inner surface of the second substrate member 14, so that a precursor discharge in which a current flows between the second substrate member 14 and the first substrate member 12 is generated, The transition of the precursor discharge to the vacuum spark discharge realizes the absorption of the surge.

The life characteristics of the surge absorbing element 10 can be improved by selecting a material having a melting point as high as possible and resistant to ion bombardment as a material of the protective film 22 covering the surface of the emitter cone 20. Can be. Alternatively, the life characteristics can be improved by increasing the degree of vacuum in the envelope 18 to reduce the residual gas inside, or by increasing the area of the first substrate member 12 to increase the number of emitter cones 20 formed. It is possible to increase.

Although the size of the emitter cone 20 is emphasized in FIG. 1 for convenience of illustration, the emitter cone 20 is actually in a size of μm as described above. On the other hand, the first substrate member 12 has a size of mm unit (for example, 2 to 6 mm square), and tens to hundreds of thousands of emitter cones 20 are formed. Incidentally, the overall size of the first field emission type surge absorbing element 10 is 6 mm.
The thickness is about 0.6 mm at the corner.

FIG. 2 shows a second field emission type surge absorbing element 32 according to the present invention. In the second field emission type surge absorbing element 32, a first substrate member 12 and a second substrate member 14 made of an n-type semiconductor are arranged facing each other at a predetermined distance, and the inner peripheral edges of both members are arranged. An envelope 18 is formed by hermetically sealing with a frame member 16 interposed therebetween, and the internal space of the envelope 18 is in a high vacuum state of 10 ^-6 to 10 ^-8 Torr.

The inner surface of the first substrate member 12 includes a first electron emitting portion 34 in which a large number of emitter cones 20 are arranged in a dot matrix at a predetermined distance, and an emitter cone 20. Is maintained without being formed
And a flat portion 35 of the same. Also, the inner surface of the second substrate member 14 is formed with a second electron emitting portion 36 in which a large number of emitter cones 20 are arranged in a dot matrix at a predetermined distance, and an emitter cone. And a second flat portion 37 that maintains a flat shape. As shown, the first electron-emitting portion of the first substrate member 12
The second electron-emitting portion 36 of the second substrate member 14 is arranged so as to face the second planar portion 37 of the second substrate member 14.
The two substrate members are positioned so as to face the first flat portion 35 of the substrate member 12 of FIG. A predetermined gap is maintained between the tip 20a of the emitter cone 20 and each of the flat portions 35 and 37.

The inner surfaces of the two substrate members (first electron emitting portions 34,
Second electron emitting portion 36, first flat portion 35, second flat portion
37) includes the same substances (Nb, W, Mo, Cr,
A protective film 22 made of Ti, Th, Si, Ni, La, Ge, Al, etc.) is formed. A first layer made of Al or Cr is formed on the outer surface of the first substrate member 12.
A first external electrode 24 having a two-layer structure of a second layer 24b of Ni and a second layer 24b of Ni is formed.
24 is connected to a first external terminal 38. Further, on the outer surface of the second substrate member 14, a second external electrode 26 having a two-layer structure of a first layer 26a made of Al or Cr and a second layer 26b made of Ni is formed. A second external terminal 40 is connected to the second external electrode 26.

This second field emission type surge absorbing element
32 is provided between the first external electrode 24 and the second external electrode 26 by providing the emitter cone 20 on the first external terminal 38 side and the second external terminal 40 side as described above. It is characterized in that it has a structure capable of emitting electrons in both directions, and has the advantages that it can be used without concern for polarity and can cope with a case where an overvoltage is applied in the reverse direction for some reason.

Referring to FIGS. 3 to 11, the emitter cone 20 which is the most important element in manufacturing the first field emission type surge absorbing element 10 and the second field emission type surge absorbing element 32 will be described. The formation method will be described. First, an n-type Si substrate 42 having a resistivity of 0.01 to 5 (Ω · cm) is oxidized in an oxidizing atmosphere to form a SiO ₂ thin film 44 having a thickness of about 150 to 3000 Å on the surface (FIG. 3). Next, a photoresist 46 is uniformly applied to the entire surface of the SiO ₂ thin film 44 using a spinner (FIG. 4). Further, a photomask 50 in which a light-shielding paint 48 is applied in a circular shape is placed over the photoresist 46, and an exposure process using ultraviolet rays UV is performed. As a result, the surface of the photoresist 46 is exposed except for the part where the ultraviolet rays UV are blocked by the light-shielding paint 48. Next, the photoresist is
The exposed portion of 46 is removed, and a circular photoresist mask 52 is formed on the surface of the SiO ₂ thin film 44 (FIG. 5). Next, after removing a portion of the SiO ₂ thin film 44 that is not covered with the photoresist mask 52 by BHF (wet etching using buffered hydrofluoric acid), the photoresist mask 52 is peeled off.
A circular oxide mask 54 is formed (FIG. 6). Although only one oxide mask 54 is shown in FIG.
The oxide film masks 54 are formed corresponding to the number of the emitter cones 20, and are actually formed in a large number in a dot matrix at intervals of 15 μm. The diameter of the oxide film mask 54 is set to about 10 μm.

Next, RIE (reactive ion etching) is performed on the surface of the Si substrate 42 to form an oxide film mask.
The part not covered with 54 is eroded (FIG. 7). RIE
Discloses a method in which a sample (Si substrate 42) is placed between two parallel electrodes placed in a vacuum chamber, a predetermined gas medium is filled in the vacuum chamber, and a power of about 150 W is applied between the two electrodes. In this method, a high-frequency plasma discharge is generated, and etching is performed using the chemical action of this plasma and the physical action of ion bombardment. In this case, it is desirable to use reactive O ₂ and SF ₆ as a gas medium, and the volume ratio between them is, for example, SF ₆ : O ₂ under a pressure of 2.2 × 10 ⁻¹ Torr.
= 9: 1. Since RIE is excellent in anisotropy, the degree of undercut in which etching proceeds on the back side of the oxide film mask 54 is relatively low, and a quadrangular pyramid-shaped protrusion 56 having a flat tip is formed. (FIG. 8). This RIE is performed, for example, for 15 minutes under the above conditions.

Next, the surface of the Si substrate 42 is subjected to anisotropic wet etching to erode the surface of the protrusion 56 to sharpen the tip (FIG. 9). The etchant used for this anisotropic wet etching is, for example, KOH and H
_It consists of an aqueous solution mixed with ₂ O, and the solution temperature is set to about 50 degrees Celsius. The mixing ratio of the two is, for example, mixing 50 g of KOH with 100 ml of H ₂ O.

When the above-described anisotropic wet etching proceeds and a certain degree of undercut 58 occurs to sharpen the tip of the projection 56, the oxide film mask 54 loses stability and drops (FIGS. 10 and 10). 11). At this stage, the angle of the tip of the protrusion 56 is sharpened to 25 to 30 degrees, and the anisotropic wet etching is stopped because the emitter cone 20 is completed. The time required for the anisotropic wet etching up to here is expected to be about 8 minutes. Note that the tip of this emitter cone
20a still maintains the quadrangular pyramid state, but the foot portion is in the octagonal pyramid state.

In the above description, an example is shown in which an n-type semiconductor is used as the material of the first substrate member 12 and the second substrate member 14, but the present invention is not limited to this.
Of course, each substrate member can be made of a p-type semiconductor in which an impurity such as boron is mixed in i.

[0038]

According to the method of manufacturing a field electron emission type surge absorbing element of the present invention, first, a projection as a prototype of an emitter cone is formed by RIE which is a kind of dry etching having excellent anisotropy. After forming, anisotropic wet etching is applied to complete the emitter cone, so that the tip of the emitter cone is sharpened in a relatively short time while maintaining the height and width of the emitter cone at a certain level or more. Can be changed. Therefore, the operating voltage of the field electron emission type surge absorbing element can be set to a relatively low value by further increasing the sharpness of the tip of the emitter cone.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first field emission type surge absorbing element according to the present invention.

FIG. 2 is a sectional view showing a second field-emission-type surge absorbing element according to the present invention.

FIG. 3 is a partial cross-sectional view showing a process of forming an emitter cone.

FIG. 4 is a partial cross-sectional view showing a process of forming an emitter cone.

FIG. 5 is a partial sectional view showing a process of forming an emitter cone.

FIG. 6 is a partial cross-sectional view showing a process of forming an emitter cone.

FIG. 7 is a partial cross-sectional view showing a process of forming an emitter cone.

FIG. 8 is a partial perspective view showing a process of forming an emitter cone.

FIG. 9 is a partial cross-sectional view showing a process of forming an emitter cone.

FIG. 10 is a partial cross-sectional view showing a process of forming an emitter cone.

FIG. 11 is a partial perspective view showing a process of forming an emitter cone.

FIG. 12 is a circuit diagram showing a usage example of a surge absorbing element.

FIG. 13 is a waveform chart showing surge absorption characteristics of the field emission type surge absorbing element.

FIG. 14 is a partial cross-sectional view showing a process of forming a conventional emitter cone.

FIG. 15 is a partial cross-sectional view showing a process of forming a conventional emitter cone.

FIG. 16 is a partial cross-sectional view showing a process of forming a conventional emitter cone.

FIG. 17 is a partial cross-sectional view showing a process of forming a conventional emitter cone.

FIG. 18 is a partial cross-sectional view showing a process of forming a conventional emitter cone.

[Explanation of symbols]

 10 first field emission type surge absorbing element 12 first substrate member 14 second substrate member 16 frame member 18 envelope 20 emitter cone 20a tip of emitter cone 24 first external electrode 26 second External electrode 32 second field electron emission type surge absorbing element 34 first electron emission section 35 first plane section 36 second electron emission section 37 second plane section 54 oxide mask 56 protrusion

Continuation of front page (56) References JP-A-2-278681 (JP, A) JP-A-7-320635 (JP, A) JP-A-8-17330 (JP, A) JP-A-62-109319 (JP) JP-A-2-280323 (JP, A) JP-A-8-181087 (JP, A) JP-A-3-62432 (JP, A) JP-B-61-27471 (JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01T 1/00-21/06 H01J 1/00-21/36

Claims (2)

(57) [Claims] 1. A first substrate member provided with an electron emitting portion made of a semiconductor having a plurality of emitter cones integrally formed on one surface thereof, and a second substrate member provided with a flat surface portion on one surface thereof. The tip of the emitter cone of the substrate member and the second
Are arranged so that the flat portions of the substrate members face each other with a predetermined distance therebetween, and the peripheral edges of both substrate members are hermetically sealed to form an envelope, and the inside of the envelope is brought into a high vacuum state. In addition, in a method of manufacturing a field electron emission type surge absorbing element in which external electrodes are respectively formed on outer surfaces of both substrate members, a step of forming a large number of oxide film masks on the surface of the substrate member; , A reactive ion etching using a mixed gas of SF ₆ and O ₂ to erode portions not covered by the oxide mask, thereby forming a prototype of the emitter cone below the oxide mask. Forming a columnar protrusion, and forming KOH and H on the protrusion.
₂ O is mixed with 100 ml of H ₂ O at a mixing ratio of 50 ml.
g KOH mixed solution to form an emitter cone having a sharp tip with anisotropic wet etching to erosion the surface thereof. Of manufacturing a field electron emission type surge absorbing element. 2. A first substrate member having an electron emission portion made of a semiconductor having a plurality of emitter cones integrally formed on one surface, a first substrate member having a flat portion on which no emitter cone is formed, and a plurality of emitter cones formed on the same surface. A second substrate member provided with an electron emission portion made of a semiconductor integrally formed with a cone and a flat portion on which no emitter cone is formed is formed by combining the tip of the emitter cone of one substrate member and the other substrate member. A flat portion is disposed so as to face at a predetermined distance, and the outer edges of both substrate members are hermetically sealed to form an envelope, and the inside of the envelope is brought into a high vacuum state. In a method of manufacturing a field electron emission type surge absorbing element formed by forming an external electrode on an outer surface of a member, a step of forming a large number of oxide film masks on the surface of the substrate member;
Reactive ion etching using a mixed gas of SF ₆ and O ₂ is performed to erode portions not covered by the oxide film mask, thereby forming a prototype of the emitter cone below the oxide film mask. Forming a columnar protrusion, and applying KOH and H ₂ O to the protrusion.
50 g of KOH per 100 ml of H ₂ O
Subjecting the surface to erosion by anisotropic wet etching using a mixed aqueous solution formed by mixing to form an emitter cone having a sharp tip. Method of manufacturing type surge absorbing element.