JP2017183180A - Field emission device and device comprising field emission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a field emission element having enhanced insulation resistance and prevented from being destroyed by discharge, and to provide a device including the field emission element.SOLUTION: A field emission element includes an emitter having a tip serving as an acute electron emission end, a gate electrode for lead-out having an opening for exposing the tip of the emitter, and an emitter sidewall coating insulation layer covering the sidewall of the emitter and having an opening circumference for exposing the electron emission end of the emitter. Assuming the shortest distance of the tip of the emitter and the gate electrode for lead-out is D, and the distance of a triple point where three border lines of the emitter, emitter sidewall coating insulation layer and vacuum are superposed, and electron emission end is Lt, the structure satisfies a relation Lt<D/2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technical field of a field emission device that emits electrons from an emitter tip to which a high electric field is applied, and more particularly to a field emission device and an electric field emission device that have an effect of preventing destruction by discharge. It is related with the apparatus provided.

  Conventionally, field emission devices have been used for thin displays and the like. Recently, it is expected to apply to devices such as ultra-sensitive image sensors and image sensors with high radiation resistance by combining arrayed elements with field emission elements arranged in a matrix and photoelectric conversion film. (See Patent Document 1).

  The field emission element is mainly composed of an emitter, also called a protrusion having a sharp tip, and an extraction gate electrode that surrounds the emitter and applies an extraction voltage to emit electrons from the emitter. The apparatus including the field emission element is an apparatus including at least the field emission element and an anode (also referred to as a collector or an anode) for capturing or accelerating electrons. In the field emission device, when a voltage of about 10 to 60 volts is applied to the gate electrode, a very high electric field is generated at the tip of the emitter, and electrons are emitted from the emitter.

  An example of a field emission device is one that employs a conical emitter structure called a Spindt type (see Non-Patent Document 1).

  In addition, the group including the present inventor has conducted research and development on field emission devices (see Patent Documents 2 and 4 and Non-Patent Document 3). For example, for the purpose of focusing the electrons emitted from the emitter, a structure that obtains good focusing characteristics by stacking volcano-type gate electrodes and focusing electrodes and controlling the height of the electrodes has been disclosed (Non Patents) Reference 2). Furthermore, the structure which laminated | stacked the multilayer focusing electrode was disclosed (refer patent document 2).

  According to the prior art literature search, there was the following literature. Patent Document 3 discloses a structure in which a creeping distance is increased in a field emission device. Patent Document 5 discloses a structure in which an emitter is buried in a thermal oxide insulating film, leaving the emitter tip.

Japanese Patent No. 5167484 Patent No. 5062761 JP-A-8-32255 JP 2014-44885 A JP-A-9-204874

Journal of Applied Physics, Vol.47, No.12, p.5248, (1976). Applied Physics Express Vol.1, p.053001, 2008.

  A field emission device may break due to sudden dielectric breakdown during operation. One cause of dielectric breakdown is creeping discharge of the insulating film. The creeping discharge will be described in detail below with reference to FIG.

  In general, a point where a metal (conductive), an insulator (other than vacuum / air), and a vacuum are in contact with each other is called a triple point (hereinafter also referred to as a triple junction). The triple point is also a “point where the boundary line intersects” because there are three boundary lines and the three boundary lines intersect at one point. It is known that the electric field is extremely concentrated at the triple point.

  In FIG. 10, the triple junction 5 illustrated is a point where three boundary lines of metal, insulator, and vacuum on the cathode (emitter electrode) 1 side overlap. Originally unnecessary electron emission occurs due to field emission by a strong electric field from the triple junction. The emitted electrons are accelerated toward the anode (for example, the gate electrode) 3, and when some of them bombard the surface of the insulator 2, secondary electrons 4 are emitted. At this time, when the secondary electron emission efficiency exceeds 1, a plurality of electron emission occurs, and at the same time the electron emission portion is positively charged. When the emitted secondary electrons further impact the surface of the insulator 2, secondary electrons are further emitted. While repeating such a process, dielectric breakdown is accompanied with amplification of the number of electrons.

  The case of a Spindt-type field emission device will be described in detail with reference to FIG. FIG. 11 is a schematic diagram of a Spindt-type field emission device. A sharp emitter 11 is provided on an emitter electrode 12, and a gate electrode 31 is formed via an insulator 2 such as an insulating film. Note that the Spindt type means a structure including an emitter as shown in FIG. 11 by the following manufacturing method proposed by Mr. Spindt. After forming a laminate consisting of an emitter electrode, an insulating layer, and a gate electrode layer, a metal such as molybdenum is used as the emitter material in a high vacuum for the structure in which the gate electrode layer has a through hole and the insulating layer is etched. Vapor deposition is performed by a deposition method with high straightness such as vapor deposition. As the molybdenum entering through the through-holes is deposited on the emitter electrode layer, the diameter of the through-holes in the gate electrode layer is reduced, so that the emitter has a substantially conical shape with a sharp tip. Is formed.

  When the emitter 11 and the emitter electrode 12 are set to 0 V and a positive voltage is applied to the gate electrode 31, the electric field distribution formed between the emitter 11 and the gate electrode 31 is roughly the equipotential line 6. Here, a triple junction where three boundary lines of metal, insulator, and vacuum overlap is formed at a position of 5. When electrons are emitted from the triple junction 5, the electrons are accelerated in a direction perpendicular to the equipotential lines, and thus are accelerated in a direction substantially along the creeping surface of the insulator 2. Therefore, creeping discharge as described in FIG. 10 occurs in the structure of FIG.

  Conventionally, as one method for preventing avalanche breakdown due to electron hopping, a structure is known in which irregularities are formed on the surface of an insulating layer to increase the creepage distance (see Patent Document 3). However, in the method of Patent Document 3, the electrons emitted from the triple junction are still accelerated in the direction along the creepage surface, so the possibility of creeping discharge is reduced as the distance increases. It is not an effective solution.

  The case of a field emission device using a volcano gate electrode will be described with reference to FIG. FIG. 12 is a schematic view of a field emission device having a volcanic gate electrode and a conical emitter. A sharp emitter 11 is provided on the emitter electrode 12, and the emitter electrode 12 and the lower part of the side wall of the emitter 11 are formed. A volcanic gate electrode 31 lacking the top is formed through the covering insulator 2. When the emitter 11 and the emitter electrode 12 are set to 0 V and a positive voltage is applied to the gate electrode 31, the electric field distribution formed between the emitter 11 and the gate electrode 31 is roughly the equipotential line 6. Here, the triple junction 5 is located at a position 5 (emitter side wall) in the figure. As shown in FIG. 12, electrons are emitted from the triple junction 5, and the electrons are accelerated in a direction along the creeping surface of the insulator 2 to cause creeping discharge.

  The present invention is intended to solve these problems, and an object of the present invention is to provide a field emission device having a structure that is prevented from being destroyed by discharge, and an apparatus including the field emission device. And

The present invention has the following features in order to achieve the above object.
(1) The field emission device of the present invention exposes an emitter having a sharp electron emission end, an extraction gate electrode having an opening exposing the tip of the emitter, and an electron emission end of the emitter. An emitter sidewall covering insulating layer having an opening periphery and covering the emitter sidewall, wherein D is the shortest distance between the emitter tip and the extraction gate electrode, and the emitter, the emitter sidewall covering insulating layer, and the vacuum When the distance between the triple point where these three boundary lines overlap and the electron emission end is Lt, Lt <D / 2.
(2) In the field emission device of (1), a second insulating layer is further provided outside the emitter sidewall covering insulating layer, and a linear distance between the triple point and each portion along the surface of the insulating layer is Lo. It is more preferable that the creepage surface satisfying Lo> 2D exists. Here, the creeping surface of the insulating layer refers to the surface where the emitter sidewall covering insulating layer or the insulating layer of the second insulating layer is exposed to vacuum.
(3) The field emission device according to (1) or (2), further including a gate electrode inner wall covering insulating layer that covers a surface of the gate electrode facing the emitter, and continuous with the emitter sidewall covering insulating layer or the second insulating layer. It is more preferable that the insulating layer is formed.
(4) In the field emission device according to any one of (1) to (3), it is more preferable that the gate electrode is a volcano type or a flat plate type.
(5) An apparatus including the field emission device according to any one of (1) to (4).

  Since the field emission device of the present invention has a structure that does not generate a creeping current, the device and a device using the device can be prevented from causing dielectric breakdown due to discharge, and the withstand voltage can be improved.

  Further, in the field emission device of the present invention, the concentration of the electric field at the original electron emission end is made stronger, so that it is possible to emit electrons at a low voltage, and at the same time, the emitted electrons are directed toward the insulator. This is effective in preventing the emitted electrons from being accelerated and suppressing the emitted electrons from impacting the creeping surface of the insulating layer.

  Further, in the field emission device according to the embodiment of the present invention, when the structure of the gate electrode facing the emitter and the emitter electrode (the inner wall surface of the gate electrode) is covered with an insulating layer, the creepage distance is further increased. Therefore, the effect of preventing a decrease in the withstand voltage is great.

  In the present invention, the first insulating layer, which is the emitter side wall covering insulating layer covering the side wall of the emitter, has better heat conduction than the conventional structure in which the portion is vacuum, so that a large current flows from the tip of the emitter. By transmitting Joule heat generated in the case of emitting to the emitter substrate, it also plays a role of heat dissipation, so that it has an effect of preventing the tip of the emitter from being melted by Joule heat even during a large current operation.

It is a schematic diagram which shows an example of the field emission element in 1st Embodiment. It is a figure explaining the basic principle and effect in 1st Embodiment. It is a schematic diagram which shows the modification of the field emission element in 1st Embodiment. It is a figure explaining the manufacturing method of the modification of the field emission element in 1st Embodiment. It is a figure explaining the manufacturing method of the field emission element in 1st Embodiment. It is a schematic diagram which shows an example of the field emission element in 2nd Embodiment. It is the schematic diagram of the modification 1 of the field emission element in 2nd Embodiment. It is a schematic diagram of the modification 2 of the field emission element in 2nd Embodiment. It is a figure explaining the manufacturing method of the modification 2 of the field emission element in 2nd Embodiment. It is a figure explaining the principle of creeping discharge. It is a figure explaining the direction where the electron discharge | released from the triple junction is accelerated in the Spindt type field emission element of a prior art. It is a figure explaining the direction where the electron discharge | released from the triple junction is accelerated in the volcano type field emission element of a prior art.

  Embodiments of the present invention will be described below.

  The present inventor has conducted research and development on a field emission device by paying attention to the structure of the insulating layer, and has obtained a structure having excellent withstand voltage by suppressing creeping current.

  The field emission device according to the embodiment of the present invention has a structure in which the side wall of the emitter is covered with an insulating layer and only the tip of the emitter is exposed. By taking this structure, the triple junction can be made only in the vicinity of the original electron emission end. In order to make the triple junction only in the vicinity of the original electron emission end, the position of the triple junction needs to be less than or equal to one-half of the shortest distance D between the tip of the emitter and the gate electrode for extraction. It is. For example, when the opening diameter of the gate electrode is about 400 nm, the shortest distance between the tip of the emitter and the extraction gate electrode is 200 nm, and the position of the triple junction in that case is preferably about 10 to 100 nm lower than the tip. .

In this embodiment mode, a structure having a structure for emitting electrons is called an emitter, and a wiring portion for supplying current to the emitter is called an emitter electrode. The substrate is also an emitter electrode if it also serves to supply current to the emitter.
The emitter has a protruding shape having a sharp tip, and has a conical shape or the like.

  In the field emission device according to the embodiment of the present invention, electrons emitted from the triple junction formed on the cathode side are in a direction opposite to the creeping surface of the insulating layer when viewed from the triple junction which is the electron emission point. It is preferable that the insulating layer is provided on the emitter side wall so that the electric field is formed in the accelerated direction.

  In the field emission device according to the embodiment of the present invention, electrons emitted from the triple junction are not accelerated in the creeping direction of the insulating layer, so that the dielectric breakdown phenomenon does not occur.

  An apparatus including a field emission device of the present invention includes at least a field emission device and an anode (also referred to as a collector or an anode) for applying or applying an electric field to capture or accelerate electrons.

  In the field emission device according to the embodiment of the present invention, the surface of the gate electrode facing the emitter and the emitter electrode is covered with an insulating layer (hereinafter also referred to as a gate electrode inner wall surface insulating layer). preferable. By the gate electrode inner wall insulating layer, even if electrons are emitted from the outside of the triple junction due to some influence, the creepage distance can be increased and hopping cannot be continued.

  The material of the insulating layer of each layer is not particularly limited, and a material known as the material of the insulating layer can be used. For example, a film known in the semiconductor technology field such as a silicon nitride film, a silicon oxide film, and an aluminum oxide film can be used. The insulating layer covering the emitter side wall and the gate electrode inner wall surface insulating layer may be formed of individual films or may be formed of continuous films. An insulating layer covering the emitter sidewall and the insulating layer of the inner wall surface of the gate electrode are connected, and an intermediate insulating layer provided between these layers or in parallel is appropriately provided. Any of these insulating layers can be composed of one or two or more insulating layers, and each material can be appropriately selected.

  In the embodiment to be described later, the height of the emitter does not exceed the height of the gate electrode (the opening end thereof) or the height of the upper surface of the gate electrode, but is not limited to this. Since it is not, it can be designed arbitrarily.

(First embodiment)
In this embodiment, the case of a field emission element in which the shape of a gate electrode is a volcano type will be described with reference to FIGS.

  FIG. 1 is a schematic diagram of an example of the field emission device of this embodiment, and FIG. 2 is a diagram for explaining the principle and effect of the present invention based on FIG. The field emission device of FIG. 1 includes a cone-shaped emitter 11 provided on an emitter electrode 12 with a sharp tip, and a first insulating layer that covers only the sidewall of the emitter 1 and the emitter electrode by exposing only the tip of the emitter 11. 21, a second insulating layer 22 covering the first insulating layer, a third insulating layer 23 provided on the emitter of the gate electrode and the inner wall surface facing the emitter electrode, and an opening at the periphery of the emitter tip And a volcano gate electrode 31. The position of the triple junction 5 formed by the emitter 11, the first insulating layer 21, and the vacuum is defined by the first insulating layer 21. The position of the triple junction 5 is located in the vicinity of the electron emission end. In the figure, the triple junction 5 is located at the edge of the first insulating layer 21 covering the emitter sidewall. The second insulating layer is provided on the first insulating layer 21 at a position recessed from the covering end of the first insulating layer 21 to the lower part of the emitter as viewed from the emitter tip and from the triple junction. . By causing the second insulating layer to recede from the electron emission end as compared with the first insulating layer, the creeping surface of the second insulating layer is positioned so that electrons emitted from the triple junction cannot reach. be able to.

  The surfaces of the first insulating layer and the second insulating layer are in contact with vacuum and can be called creeping surfaces of the insulating layer.

  FIG. 2 shows an explanation of the position of the triple point and the arrangement of the insulating layer, which are features in the embodiment of the present invention.

  Lt <D, where D is the shortest distance between the tip of the emitter and the extraction gate electrode, and Lt is the distance between the triple point where the emitter, the emitter sidewall covering insulating layer and the vacuum boundary line overlap, and the electron emission end. The position of the triple point is set so as to satisfy the condition of / 2 (hereinafter also referred to as “condition 1”). When this condition is satisfied, it has been found by electron trajectory simulation or the like that electrons emitted from the triple point are not accelerated toward the gate electrode but accelerated toward the anode.

  The creepage formed by the surfaces of the emitter side wall covering insulating layer and the second insulating layer is a condition that there exists a creepage satisfying Lo> 2D when the linear distance between the triple point and each part of the creeping surface of these insulating layers is Lo. (Hereinafter also referred to as “condition 2”). Experiments have shown that when this condition is met, discharge breakdown is unlikely to occur.

  In such a condition, the electrons emitted from the triple junction are accelerated toward the anode in the direction perpendicular to the equipotential lines, like the electrons emitted from the electron emission end that is originally required. Therefore, it is not accelerated in the direction along the surface of the insulating layer and cannot cause creeping discharge.

  The material of the insulating layer of each layer is not particularly limited, and the insulating layer material known in the semiconductor technical field or the like can be used. For example, a silicon nitride film can be used as the first insulating layer, a silicon oxide film can be used as the second insulating layer, and alumina can be used as the third insulating layer. By using insulating layers made of different materials, the structure of this embodiment can be formed due to the difference in etching rate.

[Modification]
A modification of the field emission device of this embodiment is shown in FIG. In the modification, the first insulating layer 21 is gradually thinned toward the emitter tip. Even in the case of this modification, the position of the triple junction 5 is in the vicinity of the tip of the emitter, and the electrons emitted from the triple junction 5 are not accelerated in the direction along the creeping surface of the first insulating layer, and are not shown. Therefore, the same effect as described in FIG. 2 can be obtained.

[Production method]
A method for manufacturing the field emission device of the present embodiment will be described with reference to FIGS.
FIG. 4 is a diagram for explaining manufacturing steps (a) to (f) of a modified element.

(A) Step A sharp conical emitter 11 is formed on the emitter electrode 12. A known method can be adopted as a method for forming the emitter, and is not particularly limited. For example, a method of etching silicon may be used. Alternatively, it is used that the hole is gradually closed by depositing an emitter material on a two-layer organic coating film having fine holes by a film deposition method with high particle straightness such as vacuum deposition. A method of removing an unnecessary emitter material film by forming a conical emitter and then dissolving the organic coating film with an organic solvent may be used (see Patent Document 4).

(B) Process Next, the 1st insulating layer 21 is formed into a film. A known method can be adopted as the film forming method, and is not particularly limited. Since the film is formed on the structure, a method capable of forming the film conformally is more desirable. For example, there are methods such as chemical vapor deposition (CVD) and sputtering. Alternatively, SiN may be deposited by sputtering using silicon as a target and Ar and N ₂ as plasma sources. The film thickness of the first insulating layer 21 can be arbitrarily selected basically. However, in order to facilitate manufacture, the film thickness is about 10% to 20% of the second insulating layer. Good thickness.
Next, a second insulating layer 22 is formed. As the film forming method, a known method can be adopted and is not particularly limited. For example, SiO ₂ can be formed by plasma CVD using TEOS (tetraethoxysilane) gas.
Further, a third insulating layer 23 is formed. As for the third insulating layer 23, SiN can be formed by sputtering in the same manner as the first insulating layer 21.
Thereafter, a metal thin film to be the gate electrode 31 is formed. The metal type of the metal thin film can be a known material and is not particularly limited. For example, Nb, Mo, etc. can be easily etched by reactive ion etching (RIE) using a fluorine-based gas such as SF ₆ and not etched by buffered hydrofluoric acid (BHF) to be used later. So convenient.

(C) Process Next, the photoresist 41 is apply | coated to the board | substrate (emitter electrode) in which the 1st-3rd insulating layer and the gate electrode were formed into a film. The thickness of the photoresist to be applied is set to be thicker than that corresponding to the height of the emitter 11. The film thickness can be adjusted by adjusting the viscosity of the photoresist to be used or by adjusting the number of rotations in the case of spin coating.

(D) Step Next, the photoresist is etched by oxygen plasma or the like. The etching amount is adjusted so that the height of the gate electrode becomes a desired value.

(E) Process Next, the gate electrode 31 is etched using the remaining photoresist as a mask. When Nb or Mo is selected as the gate electrode, it can be etched by reactive ion etching (RIE) using SF ₆ gas. When SiN is selected as the material of the third insulating layer 23, the third insulating layer can be simultaneously etched by RIE using SF ₆ gas for etching the gate electrode 31. When a material other than SiN is selected, a process for etching the third insulating layer 23 is performed. At this time, it is necessary to use a method that does not etch the gate electrode 31.

(F) Step Next, the second insulating layer 22 is etched by buffered hydrofluoric acid (BHF). At this time, since the second insulating layer 22 is etched from the opening of the gate electrode 31, the etching proceeds in a direction along the emitter. If the second insulating layer 22 covering the emitter tip is etched, the first insulating layer 21 is exposed to BHF. When SiN is selected as the first insulating layer 21 and SiO ₂ is selected as the second insulating layer, the ratio of the etching rate by BHF is about 1:10 to 1:20. Therefore, the second insulating layer 22 is retracted. In the meantime, the emitter tip portion of the first insulating layer 21 is not etched, and the emitter can be exposed.

  The field emission device having the structure shown in FIG. 3 is obtained by the steps (a) to (f).

  FIG. 5 is a diagram for explaining a manufacturing process of the field emission device of FIG. 1 in which the shape of the first insulating layer 21 is different. When the field emission device shown in FIG. 1 is manufactured, steps (a) to (d) in FIG. 4 are performed, and then steps (e) to (h) in FIG. 5 are performed.

(E) Process As a material for the first insulating layer 21, it is necessary to select a material that is not etched at all for BHF, such as alumina. Steps (a) to (e) in FIG. 4 are performed using the material of the first insulating layer 21.

(F) Step Next, after the step (e), the second insulating layer 22 is retracted by etching with BHF, but the etching is temporarily stopped when only the first insulating layer 21 at the tip of the emitter is exposed. .

(G) Process Next, only the emitter tip portion of the first insulating layer 21 is removed by etching using an etchant or the like that can etch only the first insulating layer 21.

(H) Process Next, the BHF process for etching the second insulating layer 22 is performed again to further retract the second insulating layer 22.

  Through the above steps, the field emission device having the structure shown in FIG. 1 is obtained.

(Second Embodiment)
In this embodiment mode, a case of a field emission element having a flat gate electrode will be described with reference to FIGS. The principle and effect in the present embodiment are the same as described in the first embodiment. In the present embodiment, the triple point defined by the edge of the emitter sidewall covering insulating layer satisfies the condition 1. In the present embodiment, the insulating layer structure of the present invention is applied to a conventional Spindt-type field emission device (see FIG. 11) having a flat gate electrode. As shown in FIG. 11, the conventional example has a structure in which the side wall of the emitter and the emitter electrode are exposed to vacuum. On the other hand, in the present embodiment, the emitter side wall and the emitter electrode are covered with the first insulating layer 21, and only the electron emission end at the tip of the emitter is exposed. The triple junction 5 is formed near the electron emission end. By arranging such an insulating layer, electrons emitted from the triple junction 5 are accelerated toward the vacuum without being accelerated in the creeping direction of the insulating layer. Absent.

  FIG. 6 is a schematic diagram of an example of the field emission device of the present embodiment. The field emission device shown in FIG. 6 includes a cone-shaped emitter 11 provided on the emitter electrode 12 with a sharp tip, and a first insulating layer that covers only the sidewall of the emitter 11 and the emitter electrode by exposing only the tip of the emitter 11. 21, the emitter of the gate electrode and the third insulating layer 23 provided on the inner wall surface facing the emitter electrode, and the second insulating layer 23 disposed so as to connect the first insulating layer 21 and the third insulating layer 23. An insulating layer 22 and a flat gate electrode 31 having an opening in the periphery of the emitter tip are provided. The position of the triple junction 5 of the emitter 11, the first insulating layer 21 and the vacuum is defined by the edge of the first insulating layer 21.

  Also in the present embodiment, as in the first embodiment, the second insulating layer 22 is seen from the emitter tip and from the triple junction, and the covered end (emitter tip) of the first insulating layer 21 is seen. The first insulating layer 21 and the first insulating layer 21 are continuously provided at a position retracted from the lower part of the emitter) to the lower part of the emitter and further on the surface of the emitter electrode. Thus, by making the second insulating layer recede as seen from the electron emission end rather than the first insulating layer, the creeping surface of the second insulating layer can be set at a position where it cannot be directly seen from the triple junction. That is, the creeping surface of the second insulating layer can be at a position where electrons emitted from the triple junction cannot reach.

  Due to the retreat, the first insulating layer 21 has a surface that is not covered with the second insulating layer 22. In the present embodiment, the surface of the first insulating layer 21 and the surface of the second insulating layer 22 are in contact with vacuum, and these can be called creeping surfaces of the insulating layer. Also in this embodiment, the creepage of the insulating layer satisfies the condition 2 (there is a creepage that satisfies Lo> 2D when the linear distance between the triple point and each part of the creeping surface of the insulating layer is Lo). Since the electrons emitted from the triple junction are accelerated toward the anode in the direction orthogonal to the equipotential lines, as with the electrons emitted from the electron emission end that is originally required, the surface of the first insulating layer Will not be accelerated in the direction along the line.

  As shown in FIG. 6, the structure should be such that no gap is generated at the boundary between the first insulating layer 21 and the second insulating layer 22. In FIG. 6, if there is a gap between the insulating layer 21 and the insulating layer 22, that is, a triple junction is formed.

  As a structure in which no gap is generated at the boundary portion between the first insulating layer 21 and the second insulating layer 22, for example, there are the following modifications 1 and 2.

[Modification 1]
FIG. 7 is a schematic diagram showing a first modification. In the insulating structure of the field emission device of the first modification, a first insulating layer 21 that exposes only the tip of the emitter 11 and covers the side wall of the emitter 11 and the emitter electrode 12 is provided between the emitter electrode and the gate electrode. In this structure, the two insulating layers 22 are covered and the emitter electrode facing surface and the emitter facing surface of the gate electrode are continuously covered. The first insulating layer 21 continuously covers and insulates the emitter side wall, the emitter electrode, and the inner wall of the gate electrode, so that no gap is generated.

[Modification 2]
FIG. 8 is a schematic diagram showing a second modification. The insulation structure of the field emission device of the modification 2 includes a first insulating layer 21 that exposes only the tip of the emitter 11 and covers the side wall of the emitter 11 and the emitter electrode 12, and an inner electrode facing the emitter and emitter electrode of the gate electrode. The structure includes a third insulating layer 23 provided on the wall surface and a second insulating layer 22 sandwiched between the first insulating layer 21 and the third insulating layer 23. With this structure, the same effects as in FIGS. 6 and 7 can be obtained.

[Production method]
The field emission device of FIGS. 6 and 7 is the first insulating layer 21 after the conventional Spindt type field emission device shown in FIG. 11 is completed, that is, in a state where the second insulating layer 22 is completed. And the third insulating layer 23 can be formed by a method of forming a film at a desired position. For example, the insulating layer can be formed by a method such as a CVD method that can form a film conformally on each structural portion. The first insulating layer 21 formed on the tip of the emitter 11 can be removed only by using, for example, a focused ion beam and etching only the insulating layer at each tip of the arrayed emitter.

  A method for manufacturing the field emission device of the present embodiment will be described with reference to FIG. FIG. 9 is a diagram for explaining manufacturing steps (a) to (f) for the element of modification 2 (see FIG. 8).

(A) Process The sharp cone-shaped emitter 11 is formed on the emitter electrode 12 like the process of FIG. 4A demonstrated in 1st Embodiment.

(B) Process Next, the 1st insulating layer 21, the 2nd insulating layer 22, the 3rd insulating layer 23, and the gate electrode 31 are formed into a film continuously. At this time, the total thickness of the insulating layer and the gate electrode is designed to be larger than the height of the emitter. For the first insulating layer 21, the second insulating layer 22, and the third insulating layer 23, considering that it is necessary to be able to selectively etch in a later step, an appropriate material and film thickness are selected. select. For example, alumina can be used as the first insulating layer 21, a silicon oxide film can be used as the second insulating layer 22, and a silicon nitride film can be used as the third insulating layer 23.

(C) Process Next, the convex part on the emitter 11 is scraped off by chemical mechanical polishing (CMP). At this time, a buffer material may be deposited on the gate electrode.

(D) Process Next, as in the process of FIG. 5F, the second insulating layer 22 is retracted by etching with BHF, but once only the first insulating layer 21 at the tip of the emitter is exposed. The etching is finished.

(E) Process Next, as in the process of FIG. 5G, only the emitter tip portion of the first insulating layer 21 is removed by etching using an etchant that can etch only the first insulating layer 21. To do.

(F) Process Next, similarly to the process of FIG. 5H, the BHF process of etching the second insulating layer 22 is performed again to further retract the second insulating layer 22.
Through the above steps, the field emission device of Modification 2 having a structure in which only the tip of the emitter is exposed and the side wall is covered with the first insulating layer 21 is obtained.

  In addition, the example shown by the said embodiment etc. was described in order to make invention easy to understand, and is not limited to this form. For example, field emission elements can be appropriately formed in an array shape.

  Since the field emission device of the present invention and the device using the same have a structure that prevents dielectric breakdown, the field emission device can be widely used for devices such as a thin display, an ultrasensitive image sensor, a radiation resistant image sensor, and the like. It is useful above.

1 Cathode (emitter electrode)
2 Insulator 3 Anode (gate electrode)
4 Secondary electron emission 5 Triple point (triple junction)
6 Equipotential Line 11 Emitter 12 Emitter Electrode 21 First Insulating Layer 22 Second Insulating Layer 23 Third Insulating Layer 31 Gate Electrode 41 Photoresist P, Q, Direction of Accelerated Electrons Released from Triple Junction Representing arrow D The shortest distance between the tip of the emitter and the extraction gate electrode Lt The distance between the triple point and the electron emission end Lo The linear distance between the triple point and each part along the surface of the insulating layer

Claims (5)

An emitter whose tip is a sharp electron emission end;
An extraction gate electrode having an opening exposing the tip of the emitter;
An emitter sidewall covering insulating layer having an opening peripheral edge that exposes an electron emission end of the emitter, and covering a sidewall of the emitter;
When the shortest distance between the tip of the emitter and the extraction gate electrode is D, and the distance between the triple point where the emitter, the emitter sidewall covering insulating layer, and the vacuum boundary line overlap each other and the electron emission end is Lt. ,
Lt <D / 2
A field emission device characterized in that A second insulating layer further outside the emitter sidewall covering insulating layer;
2. The field emission device according to claim 1, wherein a creepage surface that satisfies Lo> 2D exists when a linear distance between the triple point and each portion of the creeping surface of the insulating layer is Lo.   A gate electrode inner wall covering insulating layer covering a surface of the gate electrode facing the emitter is provided, and an insulating layer is formed continuously with the emitter sidewall covering insulating layer or the second insulating layer. Item 3. The field emission device according to Item 1 or 2.   4. The field emission device according to claim 1, wherein the gate electrode is a volcano type or a flat plate type. An apparatus comprising the field emission device according to claim 1.

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