JP2019212567A - Electron emission element and manufacturing method thereof - Google Patents

Abstract

To provide an electron emission element capable of suppressing a voltage applied to an electron transmission electrode layer from being lowered due to an influence of a defect.SOLUTION: An electron emission element 100 according to the present invention includes a lower electrode substrate 101 made of metal or a semiconductor, a first insulator layer 102 formed on one main surface 101a of the lower electrode substrate, an electron transmission electrode layer 103 formed on the first insulator layer 102, and an upper electrode layer 104 formed on the electron transmission electrode layer 103, and the first insulator layer 102 has a projecting portion 102a on the upper layer side, and the upper electrode layer 104 is formed in a region overlapping the projecting portion 102a, and in a plan view from the stacking direction L of each layer, the electron transmission electrode layer 103 includes a through hole 103a at a position overlapping a defect portion P included in the first insulator layer 102.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electron-emitting device and a method for manufacturing the same.

  In recent years, attention has been focused on nanoscale electron-emitting devices. The transport medium for electrons emitted by the electron-emitting device is a vacuum. Therefore, the electron-emitting device has a feature that it can operate at high speed without electron scattering in the channel, a feature that it can operate at a low temperature to 300 ° C. or higher, and a feature that is excellent in radiation resistance. Due to these characteristics, the electron-emitting device is expected as a device that complements CMOS (see, for example, Non-Patent Document 1).

  Known electron-emitting devices include nano-sized needle-shaped metal cathode structures, MIS (Metal / Insulator / Semiconductor) structures, and planar types having MIM (Metal / Insulator / Metal) structures. (For example, refer to Patent Documents 1 to 3, Non-Patent Documents 2 and 3). The planar electron-emitting device has high stability of emitted electrons, high straightness of emitted electrons, can be operated at a low voltage of 10 V or less, can be manufactured by an existing semiconductor process, can be stably operated even at a low vacuum, It has features such as surface release.

  Under these circumstances, the present inventors have disclosed a structure of an electron-emitting device (electron source) that enables high-efficiency electron emission by using graphene as an upper electrode in Patent Document 4. . FIG. 5 is a cross-sectional view schematically showing the configuration of the electron-emitting device 400. The electron-emitting device 400 includes a lower electrode substrate 401, an insulator layer 402, and an electron transmission electrode layer 403. As the material of the electron transmissive electrode layer 403, one layer of graphene or several layers of graphite is used. The insulator layer 402 is formed so that a portion thereof has a thickness of 5 nm to 20 nm, and functions as an electron emission surface 405. The insulator layer 402 at a portion other than the electron emission surface is usually designed to be thicker than the electron emission surface, and has a thickness of about several tens to several hundreds of nanometers. An upper electrode layer 404 for applying a voltage is formed on a portion of the electron transmission electrode layer 403 that does not overlap the electron emission surface 405.

  When a voltage of about 5 V to 20 V is applied between the lower electrode substrate 401 and the upper electrode layer 404, the potential barrier formed in the insulator layer 402 becomes thin, and the electrons in the lower electrode substrate 401 cause the quantum mechanical tunnel effect. Thus, tunneling is performed to the conduction band of the insulator layer 402. Electrons emitted to the conduction band of the insulator layer 402 lose a part of energy due to scattering of lattice vibration, but electrons having an energy higher than the work function of the electron transmissive electrode layer 403 pass through the electron transmissive electrode layer 403. Are released into the vacuum. It is known that emitted electrons increase exponentially with applied voltage. In other words, the number of electrons emitted exponentially decreases even if the voltage applied to the electron transmissive electrode layer 403 is slightly lowered.

  Assuming that the total current tunneling from the lower electrode substrate 401 to the insulator layer 402 is Ic, the current recovered in the electron transmission electrode layer 303 out of the total current Ic is Id, and the current released into the vacuum is Ie, Ic = Id + Ie, and Ie / Ic is referred to as electron emission efficiency. When a defect exists in the insulator layer 402, there is a leakage current flowing through the insulator layer 402 without depending on tunneling. Although the leakage current increases Ic, the electrons constituting the leakage current do not have energy and therefore do not contribute to the emission current Ie. Therefore, when a defect exists in the insulator layer 402, the electron emission efficiency is lowered.

JP 2010-244735 A JP 2003-162956 A JP 2001-23511 A JP 2017-45639 A Japanese Patent No. 5,200,240 Japanese Patent Application No. 2017-197923

H. H. Busta, J .; Micromech. Microeng. 2, (1992) 43-74. K. Yokoo et al. , J .; Vac. Sci. Tecnol. B 11, (1993) 429-432. T.A. Kusunoki et al. , Jpn. J. et al. Appl. Phys. 32, (1993) L1695-L1697. Hiroyasu Kubota “Silicon material technology in the 65 nano-era”

  It is known that when manufacturing a device having a large area with an electron emission surface of about 10 mmφ (large area device), the yield is remarkably reduced as compared with manufacturing a device with a small area of about 100 μmφ. Yes. As a result of intensive research conducted by the present inventors, a decrease in the yield of large area devices is caused by an increase in leakage current due to defects present in the insulator layer. It was clarified that this was caused by the fact that it could not be applied and the electron emission was hindered.

When a silicon substrate is used as the lower electrode substrate and a thermal oxide film formed on the silicon substrate is used as the insulator layer, defects caused by impurities in the process of thermal oxidation become a problem. In addition, defects existing from the beginning also become a problem. As disclosed in Non-Patent Document 4, in normal silicon crystals, there are about 10 ⁸ defects / cm ³ due to oxygen precipitates generated when silicon cools from a molten state and becomes solid. Exists. When the thickness of the insulator layer 22 is 10 nm (= 10 ⁻⁶ cm), 100 defects exist per 1 cm ² .

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an electron-emitting device capable of suppressing the voltage applied to the electron-transmissive electrode layer from being lowered due to the influence of defects. .

  In order to solve the above problems, the present invention employs the following means.

(1) An electron-emitting device according to an aspect of the present invention includes a lower electrode substrate made of a metal or a semiconductor, a first insulator layer formed on one main surface of the lower electrode substrate, and the first insulator An electron transmissive electrode layer formed on the layer; and an upper electrode layer formed on the electron transmissive electrode layer, wherein the first insulator layer has a protrusion on the upper layer side, and the protrusion The upper electrode layer is formed in an overlapping region, and the electron transmission electrode layer has a through hole at a position overlapping with a defect portion included in the first insulator layer in plan view from the stacking direction of each layer.

(2) In the electron-emitting device according to (1), the defect portion is any one of a first defect portion including a single defect and a second defect portion including a plurality of defects. In plan view, it is preferable that the through hole overlaps a region where the distance from the first defect portion is 1 μm or less or a region where the distance from the two defect portions is 1 μm or less.

(3) In the electron-emitting device according to any one of (1) and (2), a second insulator layer may be formed inside the through hole.

(4) The method for manufacturing an electron-emitting device according to one aspect of the present invention is the method for manufacturing an electron-emitting device according to any one of (1) to (3), wherein one of the lower electrode substrates is provided. Forming a first insulator layer in which the electron emission region is thinner than other regions, forming an electron transmissive electrode layer on the first insulator layer, and Among them, the method includes a step of forming an upper electrode layer on a portion overlapping with the other region, and a step of applying a voltage between the lower electrode substrate and the upper electrode layer.

  In the electron-emitting device of the present invention, the electron transmissive electrode layer is formed so as to avoid a region overlapping with a defect in the insulator layer, and generation of a leak current via the defect can be suppressed. Therefore, in the electron-emitting device of the present invention, it is possible to suppress the voltage applied to the electron transmission electrode layer from being lowered due to the influence of defects.

(A) It is the top view which looked at the electron emission element which concerns on 1st embodiment of this invention from the upper electrode layer side. (B) It is sectional drawing of the electron emission element of (a). (A)-(f) It is sectional drawing in the manufacture process of the electron emission element which concerns on 1st embodiment. (A) It is the top view which looked at the electron emission element which concerns on 2nd embodiment of this invention from the upper-electrode layer side. (B) It is sectional drawing of the electron emission element of (a). It is sectional drawing of the electron emission element which concerns on 3rd embodiment of this invention. It is sectional drawing of the conventional electron emission element.

  Hereinafter, an electron-emitting device according to an embodiment to which the present invention is applied will be described in detail with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent. In addition, the materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be appropriately changed and implemented without changing the gist thereof.

<First embodiment>
(Electron emitting device)
FIG. 1A is a plan view of the electron-emitting device 100 according to the first embodiment of the present invention as viewed from the upper electrode layer side. FIG. 1B is a cross-sectional view taken along line AA ′ of the electron-emitting device 100 in FIG. The electron-emitting device 100 includes a lower electrode substrate 101, a first insulator layer 102 formed on one main surface 101a of the lower electrode substrate, an electron transmissive electrode layer 103 formed on the first insulator layer 102, And an upper electrode layer 104 formed on the electron transmissive electrode layer 103.

  The lower electrode substrate 101 is made of a metal or semiconductor material. Examples of the metal material include gold, silver, aluminum, and titanium. Examples of the semiconductor material include silicon. When a semiconductor material is used, it is desirable to select highly doped n-type silicon or the like from the viewpoint of facilitating electron emission.

The first insulator layer 102 is formed so as to cover substantially the entire one main surface 101a of the lower electrode substrate. Examples of the material of the first insulator layer 102 include SiO ₂ , Al ₂ O ₃ , and TiO ₂ .

  The first insulator layer 102 has a thin film portion in the electron emission region 105 when the electron-emitting device 100 is operated, and protrudes to the upper layer side (electron transmission electrode layer 103 side) in the region excluding the electron emission region. Part 102a. The first insulator layer 102 is formed thicker than the electron emission region in the region having the protrusion 102a.

  The thickness of the thin film portion of the first insulator layer 102 is preferably 5 nm to 30 nm, and more preferably 5 to 15 nm. In addition, the thickness of the first insulator layer 102 in the thick film portion having the protruding portion 102a is desirably 100 nm to 1000 nm, and more desirably 100 nm to 500 nm.

  By forming the thin film portion thin, it is possible to suppress scattering of electrons emitted from the lower electrode substrate 101 in the first insulator layer 102. Further, since the energy barrier is small for the emitted electrons that are to tunnel the thin film portion, the voltage required for tunneling can be lowered.

  Inside the first insulator layer 102, one or a plurality of defect portions P exist. The defect portion P is caused by defects existing in the lower electrode substrate 101, and an initial defect that occurs at an early stage of formation of the first insulator layer 102. Various processes are performed in the formation process of the first insulator layer 102. Process defects that occur due to conditions are included. The presence of these defects can be confirmed using an atomic force microscope (AFM) or the like.

  The electron transmissive electrode layer 103 is at least a surface of a portion of the thin film portion of the first insulator layer 102 excluding the defect portion P, preferably a large portion of the entire surface of the first insulator layer 102 excluding the defect portion P. It is formed so as to cover. The electron transmissive electrode layer 103 is desirably thinly formed so as to have high electron transmissive performance, more desirably has a thickness of 7 nm or less, and even more desirably about one atomic layer.

In a plan view from the stacking direction L of each layer, the electron transmissive electrode layer 103 has a through-hole 103a at a position overlapping the defect portion P included in the first insulator layer 102 and its vicinity. In the present embodiment, each of the defective portion P is assumed to be the first defective portion P ₁ comprising a defect singular. In plan view from the stacking direction L, the through hole 103a overlaps the substantially circular region where the distance from the first defective portion P ₁ is about 1μm or less.

  The electron transmissive electrode layer 103 preferably has a high electrical resistance, and more preferably has a sheet resistance of about 10 kΩ / □. In order to satisfy such an electrical resistance, the electron-transmissive electrode layer 103 is made of a polycrystal rather than a single crystal so as to cover a stepped region of the first insulator layer 102 without causing distortion or wrinkles. It is desirable that the size of one crystal (grain size) is about 200 nm to 500 nm.

  Examples of the material of the electron transmissive electrode layer 103 include polycrystalline graphene and graphite that have a high electron transmission probability and high electrical resistance.

  The upper electrode (contact electrode) layer 104 is formed outside the electron emission region, that is, on the region having the protruding portion 102a of the first insulator layer so as not to inhibit the transmission of the emitted electrons. The electron transmissive electrode layer 103 may be sandwiched between the protruding portion 102a of the first insulator layer and the upper electrode layer 104. The upper electrode layer 104 supports energization of the electron transmissive electrode 103, and suppresses a potential drop due to the influence of defects, as will be described later.

  The material of the upper electrode layer 104 is not particularly limited as long as it has high conductivity, and examples thereof include gold, silver, aluminum, chromium, titanium, nickel, and a laminate thereof.

(Method for manufacturing electron-emitting device)
An example of a method for manufacturing the electron-emitting device 100 will be described with reference to FIGS. The electron-emitting device 100 can be manufactured mainly through the following steps (A) to (F).

(A) First, as shown in FIG. 2A, a first insulator layer (insulating film) 102 having a sufficient thickness (about 300 nm) having a sufficient insulating performance is formed on one main surface 101a of the lower electrode substrate 101. Form. A method for forming the first insulator layer 102 is not particularly limited, and examples thereof include a thermal oxidation method, a chemical vapor deposition (CVD) method, and an anodic oxidation method.

For example, when highly doped n-type silicon is used for the lower electrode substrate 101, the surface of the n-type silicon substrate is thermally oxidized at a high temperature of about 800 ° C. to 1100 ° C. to form the first insulator layer 102. A dense SiO ₂ film can be formed. When an aluminum substrate is used as the lower electrode substrate 101, an alumina layer can be formed as the first insulator layer 102 by anodizing the surface of the aluminum substrate. Alternatively, the first insulator layer 102 may be formed by a known method such as sputtering.

(B) Next, a portion 102B of the first insulator layer 102 that overlaps the electron emission region 105 is etched to expose one main surface 101a of the lower electrode substrate, as shown in FIG. As an etching method, a method that does not damage the lower electrode substrate 101 serving as a base is desirable, and for example, etching with buffered hydrofluoric acid can be given.

(C) Next, the object subjected to the step (B) is subjected to a cleaning process such as RCA cleaning in order to reduce defects as much as possible, and then subjected to thermal oxidation, as shown in FIG. As described above, the thin film portion 102C (102) of the first insulator layer is formed on the exposed portion of the one main surface 101a of the lower electrode substrate. The thermal oxidation here can be performed using an electric furnace, for example, and the processing temperature and processing time are adjusted so that the thickness of the first insulator layer 102C to be formed is about 4 nm to 20 nm. It is desirable to do.

  When the first insulator layer 102C is thinner than 4 nm, a tunnel current flows between the lower electrode substrate 101 and the electron transmission electrode layer 103 to be formed later before applying a sufficient voltage. Even if a tunnel current flows in a state where the potential of the electron transmission electrode layer 103 is lower than the work function, electrons in the tunnel current have low energy and cannot pass through the electron transmission electrode layer 103. Cannot be obtained. Therefore, the thickness of the first insulator layer 102C is desirably 4 nm or more.

  When the first insulator layer 102C is thicker than 20 nm, the travel distance of tunneled electrons in the first insulator layer 102C becomes long, and energy is lost due to the influence of scattering of lattice vibration during the movement. End up. Therefore, in this case as well, electrons having energy higher than the work function are reduced, and the electron emission efficiency is deteriorated. According to the results of repeated studies by the present inventors, the thickness of the first insulator layer 102C is preferably 20 nm or less, and more preferably 10 nm or less.

  At the time when the step (C) is performed, the electron emission region 105 of the first insulator layer 102 is thinner than other regions. In other words, the first insulator layer 102 includes a thin film portion 102C that overlaps with the electron emission region and a thick film portion 102A that overlaps with an upper electrode to be formed later, with a step formed therebetween. Become. The thick film portion 102A corresponds to the protruding portion 102a shown in FIG.

(D) Next, by exposing to a mixed atmosphere of gallium vapor and methane gas, as shown in FIG. 2 (d), an electron transmission electrode is formed on the first insulator layer 102 formed through the step (C). Layer 103 is formed. The processing temperature and processing time are preferably adjusted so that the thickness of the electron-transmitting electrode layer 103 to be formed is about 0.3 nm to 10 nm.

(E) Next, as shown in FIG. 2 (e), the upper electrode 104 is formed only on the surface of the electron transmission electrode layer 103 at a position overlapping the thick film portion 102 </ b> A of the first insulator layer 102.

  There are two possible methods for forming the upper electrode 104. One is a method in which after a metal film constituting the upper electrode layer 104 is formed on the entire surface, only a portion overlapping with the electron emission region 105 is patterned and etched using photolithography. The other is a method in which a photoresist is applied on the electron emission region 105 by photolithography, a metal film constituting the upper electrode layer 104 is formed, and finally the photoresist is dissolved in a solution to form the upper electrode layer 104. This is a method of lifting off the metal film on the substrate.

  Either method may be used, but the portion of the electron transmissive electrode layer 103 that overlaps with the electron emission region 105 is very thin, so that this portion is not damaged when etching is performed. For example, when the electron transmissive electrode layer 103 is made of graphene or graphite, a method of using an acid / alkali or the like that does not etch the layer can be used. It is desirable not to perform dry etching using plasma or the like.

  On the other hand, in the lift-off method, it is desirable to completely remove the photoresist applied to the portion overlapping the electron emission region 105. When the organic substance component of the photoresist remains as a residue on the electron emission surface, the electron emission efficiency decreases. In experiments conducted by the present inventors, a normal electron emission surface in which no organic component remains is obtained by removing the photoresist with an organic solvent and then heating at about 300 ° C. in a vacuum.

  The material of the upper electrode layer 104 is not particularly limited. However, when the electron transmissive electrode layer 103 is made of graphene or graphite, it is desirable that the material has strong adhesion to the electrode layer 103, for example, when forming a graphene film. Examples of the catalytic metal include iron, cobalt, nickel and the like. In addition, materials having a strong adhesive force, such as chromium and titanium, are also included. The upper electrode 104 may have a two-layer structure in which these metal films are thinly formed only on a portion in contact with graphene and another metal film is formed thereon.

(F) Finally, a higher voltage of about 10V to 20V is applied between the lower electrode substrate 101 and the upper electrode layer 104 in the object to be processed after the step (E). Thereby, a leakage current flows only in the part 103b which overlaps the defect part P among the electron transmissive electrode layers 103, and this part 103b is locally heated and loses conductivity. Depending on the voltage applied, the portion 103b can be eliminated. FIG. 1B illustrates the state when the portion 103b disappears, but FIG. 2F illustrates the state when the portion 103b loses conductivity without disappearing. Through the steps (A) to (F), the electron-emitting device 100 of this embodiment can be obtained.

  As described above, in the electron-emitting device 100 according to the present embodiment, the electron transmissive electrode layer 103 is formed so as to avoid a region overlapping with the defect in the first insulator layer 102, and the leakage current passing through the defect is reduced. Occurrence can be suppressed. Therefore, in the electron-emitting device 100 according to the present embodiment, the voltage applied to the electron transmissive electrode layer 103 can be suppressed from decreasing due to the influence of defects.

<Second embodiment>
FIG. 3A is a plan view of the electron-emitting device 200 according to the second embodiment of the present invention as viewed from the upper electrode layer side. FIG. 3B is a cross-sectional view taken along line AA ′ of the electron-emitting device 200 in FIG.

During the first insulator layer 102 of the electron emission device 200, as a defect portion P, both of the second defect P ₂ consisting of the first defect portion P ₁ and a plurality of defects consisting defects singular (defect group) Existing. Accordingly, through holes 103a are formed in the electron transmissive electrode layer 103 at positions overlapping the first defect portion P ₁ and the second defect portion P ₂ . About another structure, it is the same as that of the structure of the electron emission element 100 mentioned above, and there can exist an effect equivalent to the electron emission element 100. FIG. The same components as those of the electron-emitting device 100 are denoted by the same reference numerals regardless of the shape.

In plan view from the stacking direction L, the through hole 103a, the region distance from the first defective portion P ₁ is 1μm or less, or overlap the region where the distance from the second defect P ₂ becomes 1μm or less It is desirable. In this case, the distance of the first defect portion P ₁ between the distance of the second defect P ₂ together, the distance between the first defective portion P ₁ and the second defect P ₂ are both a 1μm greater. Then, a plurality of distances defects that constitute the second defect P ₂ is to be less than 1 [mu] m.

In the first embodiment, the case where each of the defect portions P is the first defect portion P ₁ is exemplified, and in the present embodiment, each of the defect portions P is the first defect portion P ₁ or the second defect portion. Although the case where it is any one of P ₂ is illustrated, each of the defect portions P may be the second defect portion P ₂ .

<Third embodiment>
FIG. 4 is a cross-sectional view of an electron-emitting device 300 according to the third embodiment of the present invention. In the electron emitter 300, the second insulator layer 106 is formed inside the through hole 103a of the electron transmission electrode layer. About another structure, it is the same as that of the structure of the electron emission element 100 mentioned above, and there can exist an effect equivalent to the electron emission element 100. FIG. The same components as those of the electron-emitting device 100 are denoted by the same reference numerals regardless of the shape.

Examples of the material of the second insulator layer 106 include SiO ₂ , Al ₂ O ₃ , and TiO ₂ . The material of the second insulator layer 106 may be the same as or different from the material of the first insulator layer 102. The second insulator layer 106 can be formed using a known method such as a CVD method or a sputtering method.

100, 200, 300, 400 ... electron-emitting devices 101, 401 ... lower electrode substrate 102, 402 ... first insulator layer 102a ... projection 102A ... thick film portion 102B ... Etched portion 102C of first insulator layer ... Thin film portions 103, 403 ... Electron transmissive electrode layer 103a ... Through hole 103b ... Overlapping portions 104, 404 ... Upper electrode layer 102a ... protrusion 105,405 ... electron emission region 106 ... second insulation layer L ... stacking direction P ... defect portion _P 1 ... first defect _P 2 ... second Defective part

Claims (4)

A lower electrode substrate made of metal or semiconductor;
A first insulator layer formed on one main surface of the lower electrode substrate;
An electron transmissive electrode layer formed on the first insulator layer;
An upper electrode layer formed on the electron transmissive electrode layer,
The first insulator layer has a protrusion on the upper layer side, and the upper electrode layer is formed in a region overlapping the protrusion,
An electron-emitting device, wherein the electron-transmissive electrode layer has a through hole at a position overlapping with a defect portion included in the first insulator layer in a plan view from the stacking direction of each layer. The defect part is either a first defect part consisting of a single defect or a second defect part consisting of a plurality of defects,
In a plan view from the stacking direction, the through hole overlaps a region where the distance from the first defect portion is 1 μm or less or a region where the distance from the two defect portions is 1 μm or less. The electron-emitting device according to claim 1.   The electron-emitting device according to claim 1, wherein a second insulator layer is formed inside the through hole. A method for manufacturing an electron-emitting device according to any one of claims 1 to 3,
Forming a first insulator layer having an electron emission region thinner than the other region on one main surface of the lower electrode substrate;
Forming an electron transmissive electrode layer on the first insulator layer;
A step of forming an upper electrode layer on a portion of the electron transmissive electrode layer that overlaps with the other region;
And a step of applying a voltage between the lower electrode substrate and the upper electrode layer.

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