JP3878439B2 - Porous layer and device, and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a porous layer having pores whose density is controlled, a device including the porous layer, and a method for manufacturing the device.
[0002]
[Prior art]
Nanostructures having a fine structure have attracted a great deal of attention because they exhibit specific electrical and optical properties. Nanostructures having such a fine structure are expected to be applied to various fields such as vacuum microdevices, magnetic devices, light emitting devices, photonic devices, quantum effect devices, chemical sensors, and magnetic memories.
An alumina anodic oxide film has long been known as a nanostructure having a fine structure. An alumina anodic oxide film can form nanostructures in a self-organized manner, and is an industrially advantageous nanomaterial in that fine processing techniques such as photolithography, electron beam exposure, and X-ray exposure are unnecessary. It can be said that it is a structure.
[0003]
According to the conventionally known anodizing technique, the alumina anodized film is formed in a self-organized manner by anodizing an aluminum plate in an acidic solution such as sulfuric acid or oxalic acid. As shown in FIG. 12, the alumina anodic oxide film 2 formed on the aluminum substrate 1 has a large number of pores 3 having a diameter of about 5 to 200 nm, and the pores 3 are regularly arranged. Such an array structure having excellent regularity is derived from the fact that the alumina anodic oxide film 2 is formed by the cell structure 25. Such a cell structure 25 is easily controlled by anodic oxidation conditions such as applied voltage.
[0004]
In recent years, a technique for precisely controlling the pores of an alumina anodic oxide film has been disclosed in Japanese Patent Laid-Open No. 10-121292. According to Japanese Patent Laid-Open No. 10-121292, a substrate having a plurality of protrusions on the surface thereof is pressure-bonded to an aluminum substrate to be anodized to form a recess on the surface of the aluminum substrate, and anodization is performed starting from this recess. The pores formed in this way have a great advantage in that the roundness of the pores, the pore diameter, and the uniformity of the intervals can be improved precisely by controlling the interval and arrangement of the depressions of the substrate to be bonded.
[0005]
[Problems to be solved by the invention]
However, the porous anodized alumina film disclosed in Japanese Patent Laid-Open No. 10-121292 has a problem that the pore spacing and arrangement cannot be controlled in a large area. Further, the technique disclosed in Japanese Patent Application Laid-Open No. 10-121292 requires that a convex part having a device-designed pore diameter and interval be formed in advance on a mother substrate (mold). There was a problem of requiring.
The present invention has been made in order to solve the above-described problems of the prior art, has pores composed of nanostructures, controls the pore density easily and at low cost, and provides a large area for pore control. It is an object of the present invention to provide a porous layer that can be formed, a device including the porous layer, and a method for manufacturing the device.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the porous layer according to the present invention is basically a porous layer preferably composed of a plurality of pores having nanostructures, and has an opening on the surface and a certain depth. A first pore group that terminates at a length, and a second pore group that is continuous with a part of the first pore group in the depth direction and has a pore diameter different from at least the first pore group. It is characterized by having.
[0007]
That is, in the porous layer according to the present invention, the first pore group composed of a plurality of pores having nanostructures is thinned out at a desired interval, and the pores are thinned out with respect to the thinned pores. Provides a porous layer having a controlled effective pore density structure by continuing the second pore group having different pore diameters.
Preferably, in the porous layer according to the present invention, the first pore group and the second pore group have different cell structures. 1st pore group and 2nd pore group from which shapes, such as (pore pitch) and pore length, differ.
[0008]
In one form of the porous layer of the present invention, the pore diameter of the second pore group is larger than the pore diameter of the first pore group, and preferably, the second pore group Is a form in which the pores of the plurality of second pore groups are continuous with respect to the pores of one first pore group. In one form of the porous layer of the present invention, the second pore group has an opening on the other surface of the surface of the porous layer.
[0009]
The production method according to the present invention for producing the porous layer is basically different from the first step in which the first pore group is formed by anodizing the anodized substrate and the first step. And a step of forming a second pore group continuous with a part of the first pore group by anodizing under conditions. Therefore, preferably, the different condition is a formation voltage in the anodic oxidation, and the formation voltage in the second step is approximately an integral multiple of the formation voltage in the first step.
[0010]
This will be described more specifically. The porous layer and the manufacturing method thereof according to the present invention can be classified into two. First, a 1st porous layer and its manufacturing method are demonstrated. Here, the first pore group is outside the substrate (substantially, the first surface that is spatially exposed), and the second pore group is inside the substrate (substantially the second surface in contact with the substrate). Surface). The first pore group preferably has a fine cell structure enough to form a nanostructure. The cell structure forming the second pore group is larger than the cell structure forming the first pore group. Therefore, the pores of the second pore group are larger than the pore diameter of the pores of the first pore group, and the pore pitch is large (pore density is small). As shown in FIG. 2 to be described later, the porous layer described later as the first specific configuration has a thinned first pore 3 of the first pore group having a nanostructure. The pores 4a of the second pore group are connected to the pores 3a of the pore group.
[0011]
The method for producing the porous layer is characterized by using a multi-stage anodizing method (here, only the two-step anodizing method will be described as the simplest method). Therefore, the formation voltage for forming the second pore group is made larger than the formation voltage for forming the first pore group. When the formation voltage for forming the first pore group is V1, and the formation voltage for forming the second pore group is V2, the cell size of the first pore group and the cell size of the second pore group are The ratio is V1 / V2, and the pores of the second pore group are formed for every V2 / V1 of the pores of the first pore group. For example, if V1 = 30V and V2 = 150V, the cell size of the first pore group: cell size of the second pore group = 1: 5, and the pore size of the first pore group The pores of the second pore group are formed every five. At this time, the ratio of the pore density of the second pore group to the pore density of the first pore group is 1:25, and the fine pores penetrating from the first surface to the second surface of the porous layer. By using the pores in the device, 1/25 of the pores formed on the first surface side can be thinned, and the substantial pore density can be controlled. From the above, a porous layer having a pore density corresponding to the device design is provided by controlling the formation voltage for forming the first pore group and the formation voltage for forming the second pore group. It becomes possible.
[0012]
Next, a 2nd porous layer and its manufacturing method are demonstrated. This porous layer is completely opposite to the above-described structure of the porous layer, and the cell structure forming the first pore group is larger than the cell structure forming the second pore group. The cell structure forming the second pore group is fine, and is substantially composed of a pore aggregate (second pore group) reaching from the one pore of the first pore group to the substrate. Is done. As shown in FIG. 9 described later, in the second porous layer, the pores 3a of the first pore group thinned out by thinning out the pores 3 of the first pore group having nanostructures. Has a configuration in which a second pore group 17 composed of pore aggregates is provided, and the pores 3a of the first pore group are guided to the substrate.
[0013]
The porous layer manufacturing method is characterized by using a multi-stage anodizing method in the same manner as the first porous layer manufacturing method. There, the formation voltage for forming the second pore group is made smaller than the formation voltage for forming the first pore group. When the formation voltage for forming the first pore group is V1, and the formation voltage for forming the second pore group is V2, the pores that are thinned out every V1 / V2 to the base film (substrate) are obtained. It is formed. For example, if V1 = 40V and V2 = 20V, as shown in FIG. 9, the pore aggregate 17 of the second pore group is 1 in two of the pores 3 of the first pore group. It is formed at a rate of pieces.
[0014]
As described above, the porous layer of the present invention is composed of two different pore structures of the first pore group and the second pore group, and a part of the first pore group and the second pore group. The continuity with the pore group makes it possible to provide a porous layer having a nanostructure with a controlled pore density. In addition, such a porous layer can be easily formed at a low cost by a multi-stage anodization method using a change in formation voltage, and can be provided for a large area device.
[0015]
Accordingly, the present invention also includes any one of the porous layers described above on the electrode, and the pores of the first pore group that are continuous with the second pore group and the second pore group. The electronic device further comprising an electron emission portion provided on the electrode, wherein the electron emission portion is substantially electrically connected to the electrode. A chemical sensor section provided on the pores of the first pore group that is continuous with the second pore group and the second pore group, and the chemical sensor section Also disclosed is a chemical sensor device characterized in that is substantially electrically connected to the electrode. According to the present invention, low density nanostructures can be provided in such devices, and the characteristics of these devices can be improved.
In the present invention, “substantially electrically connected” means that, for example, even when the connection is made through a thin insulator, the movement and supply of charge from one to the other by tunneling or the like is substantially performed during operation. It is also used as including a connection mode that is typically performed.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment>
In the first embodiment, a two-stage anodic oxidation method is used, and the second-stage anodic oxidation (second-stage) is performed with respect to the formation voltage of the first-stage anodic oxidation (first pore group). A method for producing a porous layer having pores having a selected (thinned-out) pore structure by increasing the formation voltage of the pore group) will be described. 1 to 3 are process cross-sectional views illustrating a method for producing a porous layer according to the present embodiment.
[0017]
FIG. 1 is a process cross-sectional view of the porous layer after anodization in the first stage (first pore group). As shown in FIG. 1, an aluminum substrate 1 (purity is preferably 99% or more) was anodized to form an alumina anodic oxide film 2 and a pore group 3. The aluminum substrate 1 was anodized by applying a voltage of 40 V in 0.3 M oxalic acid (temperature: 16 ° C.).
FIG. 2 is a process cross-sectional view of the porous layer after the second stage (second pore group) anodizing. As shown in FIG. 2, the pores 4 of the second pore group connected to a part of the pores 3a formed of the first pore group were formed. The anodic oxidation conditions were 195 V in 0.3 M phosphoric acid (temperature: 0 ° C.).
[0018]
At this time, the selectivity (thinning rate) K (the pitch 5 of the pores of the first pore group / the pitch 6 of the pores of the second pore group) is the first stage (the first pores). Group) anodization applied voltage: V1, second stage (second pore group) anodization applied voltage: V2,
K ≒ V1 / V2
Can be expressed as K is approximated to an integer. In this embodiment,
K = 40/195 ≒ 1/5
Can be calculated. That is, the pores penetrating the aluminum substrate (the pores formed from the pores of the first pore group and the second pore group) are the pores formed after the first stage anodization. Thus, a structure in which four (4) of these were selected (thinned out) could be formed. At this time, the pore density of the pores penetrating the aluminum substrate is 1/25 ((V1 / V2) of the pore density of the pores of the first pore group. ² ). Moreover, the pore diameter and the cell size increased to 5 times (V2 / V1) those of the pores of the first pore group.
[0019]
As described above, the device design can be achieved by controlling the applied voltage for anodization in the first stage (first pore group) and the applied voltage for anodization in the second stage (second pore group). The fine pores of the second fine pore group are provided in the fine pores of the first fine pore group selected (decimated) according to the thickness, and penetrate through from one surface of the anodic oxide film 2 to the other surface. The density of the holes became controllable.
[0020]
FIG. 3 is a process cross-sectional view of the porous layer after the current recovery process for bringing the pores 4 of the second pore group into contact with the aluminum substrate 1. As shown in FIG. 3, dendritic micropores 7 were formed at the bottom of the pores 4 of the second pore group. By forming such fine holes 7, the through-holes formed from the selected pores 3 of the first pore group and the pores 4 of the second pore group are in contact with the aluminum substrate 1. It becomes possible. In such a current recovery process, the applied voltage is decreased by 10 V (195 V → 185 V → 175 V →… →→→) in the second 0.3 M phosphoric acid (temperature: 0 ° C.) with respect to 195 V. Was achieved. When the contact with the aluminum substrate 1 is insufficient, the anodic oxide film 2 (alumina; Ar) in the vicinity of the fine holes 7 is obtained by leaving it in a sulfuric acid solution for several hours. ₂ O _Three ) Is removed by etching, and the contact with the aluminum substrate 1 is sufficient. Such a contact needs to be substantially electrically connected to the aluminum substrate 1. The substantial electrical connection means that the barrier layer at the bottom of the pores 3 is preferably completely removed, but the barrier layer may not be completely removed as long as conductivity is ensured. means. That is, when the barrier layer is sufficiently thin, it is possible to ensure conductivity by tunneling.
[0021]
4A to 4C show process cross-sectional views of a porous layer in which the through pores formed in FIGS. 1 to 3 are used and the through pores are filled with a filling material. Such a manufacturing method can be applied to vacuum micro devices, magnetic devices, light emitting devices, photonic devices, quantum effect devices, chemical sensors, magnetic memories, and the like. In this embodiment, a chemical sensor will be described as a representative example.
In FIG. 4A, pores 3 of the first pore group, pores 4 of the second pore group, and dendritic micropores 7 are provided on the aluminum substrate 1 formed as shown in FIG. Process sectional drawing of the porous layer which isolate | separated the anodic oxide film 2 and provided the electrode material 8 on the surface on the opposite side to the aluminum substrate of a 1st pore group is shown.
[0022]
The anodic oxide film 2 from the aluminum substrate 1 is separated by either removing the aluminum substrate 1 by etching or reversing the potential at the time of anodic oxidation. The electrode material 8 is formed using a sputtering method or a vapor deposition method. The film thickness of the electrode material 8 is preferably about 0.5 to 1 μm. If the film thickness is thin, the surface of the anodic oxide film 2 cannot be sufficiently covered. On the other hand, if the film thickness is large, there is a problem that it is difficult to form a thin film.
[0023]
FIG. 4 (b) shows the selective sensing of the pores of the first pore group connected to the second pore group by removing the barrier layer of the dendritic micropores 7 formed on the aluminum substrate 1 side. Process sectional drawing of the porous layer filled with the material 10 is shown. The barrier layer of the dendritic micropores 7 was removed using dilute hydrofluoric acid having a concentration of about 0.5 to 1%. By removing the barrier layer of the dendritic micropores 7 in this way, the opening 9 is formed, and the pore 3 of the first pore group connected to the pore 4 of the second pore group is selected. Will be spatially exposed. Subsequently, the sensing material 10 is selectively filled in the pores 3 of the first pore group exposed spatially by an electrical deposition method, for example, an electroplating method.
[0024]
FIG. 4C is a process cross-sectional view of the porous layer in which the tip of the sensing material 10 filled in the pores 3 of the first pore group thinned out (selected) is exposed to the space. Here, the anodic oxide film portion of the second pore group is removed. The removal of the anodic oxide film is performed by an etching removal method or a chemical / mechanical polishing (CMP) method. In terms of ease of production, an etching method, specifically, a wet etching method is preferable, and hydrofluoric acid, phosphoric acid / hydrochloric acid mixed acid, sodium hydroxide, and the like can be used. As shown in FIG. 4C, the porous layer has an applied voltage for anodization in the first stage (first pore group) and an applied anodization in the second stage (second pore group). The sensing material is filled in the through-holes with a selectivity (decimation rate) determined by the voltage. In the present embodiment, a porous layer filled with every five pores of the first pore group was formed.
Unlike the conventional chemical sensor, the chemical sensor using the nanostructure manufactured in this way has a configuration in which the density of the nanostructure is controlled and the sensing material filled in the nanostructure is moderately scattered. Therefore, the sensing characteristics of chemical sensors have been greatly improved.
[0025]
<Second Embodiment>
In the present embodiment, a porous layer manufacturing method using the two-step anodizing method described in the first embodiment and using a supporting substrate such as a glass substrate or a silicon substrate will be described with reference to FIGS. I will explain. A device using a porous layer having such a structure has a structure widely used for devices at present, and can be widely applied to various electronic devices, optical devices, and the like. In this embodiment, an electronic device will be described as a representative example.
[0026]
FIG. 5A shows a process cross-sectional view of the porous layer after the first stage (first pore group) anodization. As the support substrate 11, a glass substrate, a silicon substrate, or the like is preferable. When a glass substrate is used, it is necessary to form an electrode material on the support substrate 11. In the present embodiment, a silicon substrate is used. An aluminum deposition film 12 is formed on the silicon substrate 11 by sputtering, vapor deposition, or the like. The thickness of the aluminum deposition film 12 is preferably about 2 to 4 μm. When the film thickness is thin, pore formation is inhibited, whereas when the film thickness is thick, the manufacturing process becomes severe. The surface of the aluminum deposited film 12 is indispensable to be flat, and is preferably a mirror surface in visual inspection.
[0027]
The aluminum deposition film 12 thus formed was subjected to anodic oxidation at the first stage (first pore group) as in FIG. The anodizing conditions were 0.3M oxalic acid, temperature: 16 ° C., and applied voltage: 40V. As shown in FIG. 5A, the anodic oxide film 2 was formed on the surface portion of the aluminum deposition film 12 on the silicon substrate 11, and the pores 3 of the first pore group were formed.
[0028]
FIG. 5B shows a process cross-sectional view of the porous layer after the second stage (second pore group) anodization. Similarly to the case of FIG. 2, the pores 4 of the second pore group connected to the partial pores 3a formed of the first pore group were formed. The anodizing conditions were 0.05M oxalic acid, temperature: 16 ° C., and applied voltage: 80V. As shown in FIG. 5B, the barrier layer 13 is present at the bottom of the pores 4 of the second pore group (the pore bottom on the silicon substrate 11 side).
[0029]
FIG. 6A shows a process cross-sectional view after removing the barrier layer 13 at the bottom of the pores 4 of the second pore group. The barrier layer 13 on the silicon substrate could be easily removed by performing anodic oxidation as shown in FIG. Thus, by controlling the anodic oxidation time, the barrier layer 13 at the bottom of the pores 4 of the second pore group was removed, and the exposed portion 14 of the silicon substrate was formed. As shown in FIG. 6A, the pores having the exposed portion 14 of the silicon substrate 11 are selected (thinned out). By using the pores thus selected (thinned out), fine pores are obtained. A porous layer having a controlled pore density can be provided.
[0030]
FIG. 6B shows a process cross-sectional view after filling the filling material 15 into the pores selected (thinned out) in FIG. The method for filling the selected (decimated) pores with the filling material 15 is preferably electrochemical deposition, that is, electroplating. As shown in FIG. 6B, the filling material 15 was selectively filled into the pores from which the silicon substrate 11 was exposed by electroplating, and as a result, the pores of the first pore group were thinned out.
Thus, it can be confirmed that the porous layer of the present invention can be formed not only on an aluminum substrate but also on a silicon substrate and a glass substrate, and can be mounted on various devices such as an electronic device and an optical device. It was.
[0031]
<Third Embodiment>
In the present embodiment, as in the second embodiment, a method for manufacturing a porous layer using a support substrate 11 such as a silicon substrate will be described with reference to FIG. In this embodiment, a vacuum microdevice will be described as a representative example. In particular, a method for manufacturing a carbon nanotube electron source will be described as an example of a method for manufacturing an electron source that can be driven at a low voltage. However, the electron source material of the present invention is not limited to such a carbon material.
[0032]
FIG. 7A shows a process after forming a pore structure on the support substrate 11 by the two-step anodic oxidation method and forming the carbon nanotube 16 using the pore structure as a template in the same manner as FIG. 6A. A cross-sectional view is shown. The carbon nanotube 16 can be formed by a CVD (Chemical I Vapor Deposition) method. As a method for forming such a carbon nanotube 16, a metal catalyst is disposed on the support substrate exposed portion 14 at the bottom of the pore 4 of the second pore group, and the carbon nanotube is formed using this metal catalyst as a growth starting point. (See the carbon nanotube formation method of Japanese Patent No. 3008852). As shown in FIG. 7A, the carbon nanotube 16 has the pore 3 of the first pore group, and the pore 3 of the first pore group and the pore 4 of the second pore group connected to each other. Formed in each of the through-holes formed.
[0033]
FIG. 7B shows a process cross-sectional view after exposing the tips of the selected (thinned-out) pores. A wet etching method was used to expose the tips of the carbon nanotubes 16 from the anodic oxide film 2. As the etching for removing the anodic oxide film 2, hydrofluoric acid, phosphoric acid, sodium hydroxide, phosphoric acid / hydrochloric acid or the like is used. When such wet etching is performed, as shown in FIG. 7B, the pores other than the through-holes formed by connecting the pores 3 of the first pore group and the pores 4 of the second pore group are connected. The carbon nanotubes 16a formed in the pores 3 are lifted off together with the etching of the anodic oxide film 2, and only the carbon nanotubes 16 formed in the through pores remain. As a result, the carbon nanotubes 16 to be formed are thinned out, and the density of the carbon nanotubes 16 is reduced.
[0034]
However, in the case of the carbon nanotube production method by the CVD method using the pore structure as a template described with reference to FIG. 7A, not only the inner walls of the pores 3 and 4, but also the carbon film on the surface of the anodic oxide film 2 Therefore, it is necessary to remove the carbon film on the surface of the anodic oxide film 2. The carbon film on the surface of the anodic oxide film 2 can be easily removed by oxygen plasma etching using RIE (Reactive Ion Etching). As described above, by using the two-step anodic oxidation method, the density of the carbon nanotubes was reduced, and by exposing the tips of the carbon nanotubes, the electric field concentration was increased and low voltage emission was enabled.
[0035]
<Fourth Embodiment>
In the fourth embodiment, a method for producing a porous layer using another two-stage anodizing method will be described. The difference from the first embodiment is that the formation voltage of the second stage anodic oxidation (second pore group) is different from the formation voltage of the first stage anodic oxidation (first pore group). Is reduced to produce a porous layer having pores of a selected (thinned-out) pore structure. 8-9 is process sectional drawing which shows the manufacturing method of the porous layer of this embodiment.
[0036]
FIG. 8 is a process cross-sectional view after the first stage anodization is performed on the aluminum substrate 1 as in FIG. The anodizing conditions were 0.3M oxalic acid, temperature: 16 ° C., and applied voltage: 40V. As shown in FIG. 8, the anodic oxide film 2 was formed on the aluminum substrate 1, and the pores 3 of the first pore group were formed.
FIG. 9 is a process cross-sectional view after performing the second stage anodization. The anodizing conditions were 0.3 M oxalic acid, temperature: 16 ° C., applied voltage: 20 V, and the pores (pore aggregates) of the second pore group obtained by thinning out the pores 3 a of the first pore group. ) 17 formed.
[0037]
At this time, the selectivity (thinning rate) K (the pitch 18 of the pores of the first pore group / the pitch 19 of the pores formed by the pore aggregates of the second pore group) is the first stage. The applied voltage of anodic oxidation of (first pore group): V1, and the applied voltage of anodic oxidation of second stage (second pore group): V2,
K ≒ V2 / V1
Thus, in the present embodiment, it becomes 1/2. That is, one of two pores of the first pore group forms a pore (pore aggregate) 17 of the second pore group. At this time, the pore density of the pores penetrating the anodic oxide film 2 was reduced to ¼ of the pores of the first pore group.
[0038]
As described above, as in the first embodiment, the applied voltage of the first stage (first pore group) anodization and the second stage (second pore group) anodization are applied. By controlling the voltage, the pores of the second pore group (pore aggregate) are provided in the pores of the first pore group selected (decimated) according to the device design, and the anodized film The density of penetrating pores penetrating from one surface of 2 to the other surface can now be controlled.
[0039]
Next, representative examples for applying the porous layer having such a configuration to a device will be described with reference to FIGS. 10 (a) to 10 (c) are typical examples (configurations applicable to chemical sensors) when an aluminum substrate is used, and FIGS. 11 (a) to 11 (c) illustrate a glass substrate, a silicon substrate, and the like. This is a typical example (configuration applicable to an electron source) when the support substrate 11 is used.
[0040]
FIG. 10A shows a process cross-sectional view after removing the aluminum substrate 1 and providing the electrode 20 with respect to the porous layer shown in FIG. The aluminum substrate 1 was removed by etching with a mixed acid of phosphoric acid / nitric acid / acetic acid. The electrode 20 was deposited by sputtering or vapor deposition.
FIG. 10B is a process cross-sectional view after filling the thinned pores with the sensing material 22 after removing the barrier layer of the pore aggregate 17 of the second pore group. The barrier layer was removed with hydrofluoric acid, and an opening 21 was provided in the pore assembly 17.
FIG. 10C shows a process cross-sectional view after the front end of the filled sensing material 22 is exposed. The anodic oxide film 2 was removed by wet etching or chemical / mechanical polishing. By removing the anodic oxide film 2, the tip of the sensing material 22 filled only in the pores of the first pore group formed by the pore aggregate of the second pore group was exposed.
[0041]
Next, another application example of the device will be described. In FIG. 11A, as described in the second embodiment, the aluminum deposition film 2 is formed on the silicon substrate 11, and the first and second stages of anodic oxidation are performed as shown in FIGS. The process cross-sectional view after applying and depositing the carbon film 16 on the inner walls of the pores 3 and 17 by the CVD method is shown. The aluminum deposition film 2 was formed on the silicon substrate 11 by 2 μm by sputtering. In addition, the first stage anodic oxidation is performed in 0.3 M oxalic acid (temperature: 16 ° C.) at 40 V, and the second stage anodic oxidation is performed in 0.3 M oxalic acid (temperature: 16 ° C.) at 20 V. went. The carbon film (carbon nanotube) was formed by circulating propylene (2.5% in nitrogen) at 800 ° C. for 3 hours in a quartz reaction tube.
[0042]
FIG. 11B is a process cross-sectional view after the carbon nanotubes 16 are exposed to the space. The tip of the carbon nanotube is exposed by etching away the anodic oxide film 2 with hydrofluoric acid or the like. At this time, the exposed carbon nanotubes are the carbon nanotubes 23 formed in the through-holes including the pores 3 of the first pore group and the pore aggregates 17 of the second pore group, and the first pores. Although the carbon nanotubes 24 are formed in the pores of the group alone, the carbon nanotubes 24 are electrically floating, so that only the carbon nanotubes 23 are substantially active as a device. Therefore, as a result, the pores formed by the first stage anodic oxidation were thinned, and the pore density (carbon nanotube density) was reduced. However, when the carbon nanotube 24 has a problem in the device structure, it is necessary to lift off by removing the unnecessary carbon nanotube 24 by over-etching the anodic oxide film 2.
[0043]
As described above, by using the two-stage anodization method, the formation voltage of the second-stage anodization is made smaller than the formation voltage of the first-stage anodization, thereby forming the first-stage anodization. By reducing the density of the carbon nanotube electron source that is substantially formed by thinning out the pores, the electric field concentration is increased, and an electron source capable of low voltage emission can be provided.
[0044]
【The invention's effect】
As described above, since the porous layer of the present invention is obtained by thinning out the first pore group having a nanostructure at a desired interval, the porous layer having a simple structure can be obtained as desired. A controlled pore density can be easily obtained.
In addition, since the method for producing a porous layer according to the present invention is based on changing the formation voltage in multi-step anodization, it is possible to form a porous layer with a large area, and at the same time, it can be finely processed and is expensive. No need for manufacturing equipment.
Furthermore, the porous layer according to the present invention provides a structure advantageous to a device having a low-density nanostructure, and in particular, improved device characteristics of chemical sensors and electron sources.
[Brief description of the drawings]
FIG. 1 is a process cross-sectional view of a porous layer in a first embodiment.
FIG. 2 is a process cross-sectional view of the porous layer in the first embodiment.
FIG. 3 shows process cross-sectional views of the porous layer in the first embodiment.
FIG. 4 is a process sectional view of a chemical sensor using a porous layer according to the first embodiment.
FIG. 5 is a process cross-sectional view of an electronic device using a porous layer in a second embodiment.
FIG. 6 is a process cross-sectional view of an electronic device using a porous layer in a second embodiment.
FIG. 7 is a process sectional view of a carbon nanotube electron source using a porous layer according to a third embodiment.
FIG. 8 is a process cross-sectional view of a porous layer in a fourth embodiment.
FIG. 9 is a process cross-sectional view of a porous layer in a fourth embodiment.
FIG. 10 is a process cross-sectional view of a chemical sensor using a porous layer in a fourth embodiment.
FIG. 11 is a process sectional view of a carbon nanotube electron source using a porous layer according to a fourth embodiment.
FIG. 12 is a perspective view of an alumina anodic oxide film.
[Explanation of symbols]
1 Aluminum substrate
2 Anodized film
3, 3a Pore of first pore group
4 Pore of the second pore group
5 Pitch pitch of the first pore group
6 Pitch pitch of the second pore group
7 micropores
8 electrodes
9 Opening at the bottom of the pores of the second pore group
10 Sensing materials
11 Support substrate
12 Aluminum deposited film
13 Barrier layer of pores of second pore group
14 Contact portion of bottom of pore of second pore group
15 Filling material
16 carbon nanotubes
17 Pore aggregate
18 Pore pitch of the first pore group
19 The pitch of the pores of the first pore group formed by the pore aggregate of the second pore group
20 electrodes
21 Opening at the bottom of the pore assembly
22 Sensing materials
23 Carbon nanotubes in contact with the underlayer
24 Floating carbon nanotubes

Claims (7)

A first pore group composed of a plurality of pores, having an opening on the first surface and terminating at a certain depth, and a portion of the first pore group and continuing in the depth direction; In a porous layer comprising at least a second pore group having a pore diameter different from that of the first pore group,
A carbon nanotube electron source, wherein carbon nanotubes are formed using the pore structure as a template.   2. The carbon nanotube electron source according to claim 1, wherein the pore diameter of the second pore group is larger than the pore diameter of the first pore group.   The carbon nanotube electron source according to claim 1 or 2, wherein a tip of the carbon nanotube is exposed. Carbon nanotube electron source according to claim 1 or 2, characterized by having an opening on the second surface the second pore group is the other surface of the first surface of the porous layer . A first step of anodizing an anodized substrate on a support substrate to form a first pore group, and anodization under conditions different from those of the first step are performed. Forming a second pore group continuous with the portion;
Disposing a metal catalyst on a support base exposed portion at the bottom of the pores of the second pore group, and forming carbon nanotubes based on the metal catalyst;
A method for producing a carbon nanotube electron source, comprising: The remaining carbon nanotubes in the first pores are selectively left by wet etching, leaving the carbon nanotubes having the second pore groups formed continuously with a part of the first pore groups. 6. The method of manufacturing a carbon nanotube electron source according to claim 5 , further comprising a step of removing the tip of the carbon nanotube to expose the tip of the carbon nanotube. 7. The carbon nanotube according to claim 5, wherein the different condition is a formation voltage in anodization, and the formation voltage in the second step is substantially an integer multiple of the formation voltage in the first step. Manufacturing method of electron source.

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