JP2001351506A - Field emission cold cathode device - Google Patents

Abstract

(57) [Problem] To provide a field emission cold-cathode device with high electron emission efficiency and high stability used for a flat display device and an imaging device. SOLUTION: In using a metal / insulator thin film heterostructure as a cold cathode material constituting a field emission device, any one of diamond, AlN, and c-BN is used as an insulator layer, and Cu, Sn- is used as a metal layer. Pb, Al, Ag,
One of Au and W is used. As a result, high efficiency and high stability of electron emission can be realized. By arranging a large number of the field emission cold cathode devices in a plane and forming a matrix electrode structure, a large screen flat display device can be realized. In this case, a high-resolution image sensor with low power consumption can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field emission cold-cathode device used for a flat display device or an image pickup device using a field emission cold-cathode array, and more particularly, to a field emission cold-cathode device with high efficiency and stable electron emission. It relates to a cathode device.

[0002]

2. Description of the Related Art At present, various flat panel displays (flat panel type display devices) such as a liquid crystal display and a plasma display are trying to establish a position as a main device in the multimedia age by making use of their characteristics. Among them, a field emission cold cathode array (FE)
A: A flat display element (F) using a field emission array
ED (Field Emission Display) is based on the principle of CRT
It has the same display characteristics as a CRT in terms of brightness, gradation, viewing angle, high definition, etc., as well as (CRT), because it emits phosphors by electron beam excitation. Therefore, it has been expected as a flat panel display.

In order to commercialize an FED (Field Emission Cold Cathode Device), a high-performance electron source, a phosphor, and a substrate spacing of 0.1 are required.
There are many problems such as realization of a high vacuum hermetic space in a narrow space of mm to several mm. Therefore, various research institutions and the like have reported research on new electron sources that may fundamentally improve the characteristics of FEDs. For example, a field emission device using a diamond thin film, which is expected to have an effect of negative electron affinity (NEA: Negative Electron Affinity), MI
M (Metal-Insulator-Metal) cathode, Surface Conduction Electron Emitter (SCE),
There are electron sources using carbon nanotubes (CNT: Carbon Nano Tube). However, none of these newly proposed electron sources have characteristics sufficient for practical use.

FIGS. 1A and 1B are schematic diagrams of electron energy distribution in the vicinity of metal and semiconductor surfaces. FIG. 1A shows a metal, FIG. 1B shows a semiconductor with a positive electron affinity, and FIG. 1C shows a semiconductor with a negative electron affinity. (NEA semiconductor). here,
E _vac vacuum level, E _F is the Fermi energy, E _c is the conduction band minimum, E _v is the valence band upper end. (A), (b) of FIG.
As shown in FIG. 1, in a normal metal cold cathode or a semiconductor having a positive electron affinity, electrons are emitted by tunneling through a surface barrier with the help of an electric field. However, as shown in FIG. In addition, in the NEA semiconductor, the conduction band lower end E _c is a vacuum level.
Since it is above _Evac , conduction electrons are likely to be emitted to the vacuum side.

FIG. 2 shows an example of the structure of a conventional thin film type cold cathode device using diamond having NEA characteristics. In the figure, 21 is a silicon substrate, 22 is a p-type diamond formed on the substrate, 23 is a NEA surface formed by hydrogen termination formed on the open surface of the diamond, 24 is an Al electrode formed on the silicon substrate 21, 25 Is an Al electrode formed on the back side of the diamond, and 26 is an Al electrode 24,
This is a power supply that connects between 25 and performs electron injection. The thin-film cold-cathode device has electron emission characteristics as a cold cathode which are not only emitted from the surface 23 based on the NEA characteristics, but also the Al electrode 25.
Is highly influenced by the efficiency of electron injection from the back surface through the substrate. Therefore, the key is to produce diamond having a high electron concentration, that is, a diamond exhibiting good quality n-type.
At present it is not successful.

FIG. 3 shows an example of a semiconductor material exhibiting NEA characteristics. Here, as a semiconductor material exhibiting NEA characteristics,
Diamond, AlN (aluminum nitride), and c
-BN (cubic-form boron nitride). Note that a black circle indicates a positive electron affinity, and a white circle indicates a negative affinity (however, the size is unknown).

[0007]

As can be seen from the above discussion with reference to FIG. 2, while maintaining the NEA characteristic in which conduction electrons are easily emitted to the vacuum side, the electron injection efficiency from the back surface is sufficiently large and stable. It is considered to be a major task in the future to invent a new semiconductor material structure capable of obtaining emitted electrons.

For this purpose, it is conceivable to increase the amount of supplied electrons by doping a semiconductor material such as diamond, AlN, c-BN or the like having the NEA characteristics shown in FIG. 3 with an n-type impurity. . However, these semiconductors generally have a large band gap, and it is difficult to dope with a shallow n-type impurity energy level. Generally, these semiconductors are p-type or insulator.

As a method of supplying electrons from the back surface of a semiconductor such as diamond, AlN / n-SiC, Al _0.9 G
a _0.1 N / n-GaN / n-SiC thin-film cold cathodes have also been trial manufactured, but no performance utilizing the NEA characteristics has been obtained.

At present, the most developed electron source is shown in FIG.
This is a so-called Spindt-type FEA having a conical electron emitting portion 41 as shown in FIG. Mo (molybdenum) is used for the electron emission portion 41. Also,
Reference numeral 42 denotes a Si (silicon) substrate, 43 denotes Th-SiO ₂ (trough-silicon dioxide) formed on the Si substrate so as to surround the electron emission portion 41, and 44 denotes an opening above the electron emission portion 41 and Th-SiO 2. is Nb provided on ₂ 42 (niobium).

However, a Spindt-type FE as shown in FIG.
Problems A include (1) reduction in driving voltage, (2) higher efficiency of electron emission, (3) uniform electron emission characteristics, and (4).
Stabilization of electron emission needs to be solved. Further, it has been pointed out that it is difficult to produce a large number of cold cathode chips in a large area with good uniformity in the Spindt-type FEA.

On the other hand, thin-film cold cathodes are relatively easy to increase in area, and are regarded as promising as electron sources for future large displays.

The present invention has been made in view of the above points, and an object of the present invention is to use a thin-film cold cathode whose area can be relatively easily increased to achieve an electric field with high efficiency and high electron emission. An emission cold cathode device is provided.

[0014]

In order to achieve the above object, the invention of claim 1 provides a high electron injection efficiency from the back surface while maintaining NEA characteristics as an electron emission layer of a field emission cold cathode device. In addition, as a semiconductor material structure capable of stably obtaining emitted electrons, a field emission cold cathode device using a metal / insulator ultra-thin heterostructure as a cold cathode material is characterized.

An example in which a metal / insulator ultra-thin heterostructure is applied to an electronic device such as a transistor has already been reported (Reference 1: Y. Nakata, M. Asada and Y. Suema).
tsu; IEEE Quantum Electron. QE-22, pp. 1880 (198
6)), (Reference 2: Masahiro Watanabe, Takashi Suemasu, Masahiro Asada; Applied Physics Vol. 63, No. 2, pp. 124 (1994)). However, in these reports, CaF ₂ is used for the insulating layer. Therefore, as shown in FIG. 5, the electron affinity is about 3 eV, and the NEA characteristics cannot be utilized.

On the other hand, according to the invention of claim 2, as shown in FIG. 3, the lower end of the conduction band of the insulating layer is substantially equal to the vacuum level of diamond, AlN, c-BN (cubic crystal-boron nitride). One of them is used as an insulating layer, and the metal layer is made of Cu,
It is characterized in that one of Sn-Pb, Al, Ag, Au and W is used. In such a metal / insulator ultra-thin film heterostructure, a so-called electron quantum confinement effect occurs.

The third aspect of the present invention is to provide a superlattice structure when a metal / insulator ultra-thin film heterostructure is used as a cold cathode material constituting a field emission cold cathode device, as shown in FIG. As shown in FIG. 9, MOC is used as a cold cathode material.
It is characterized by using a cold cathode material having a superlattice structure 84 formed on a Si substrate 81 by a VD (metal organic metal vapor phase epitaxy) method or a MOMBE (organic metal molecular beam epitaxy) method.

FIG. 6 is an electron energy distribution diagram of a metal / insulator ultra-thin film heterostructure when the present invention is carried out. Calculating with a metal / insulator ultra-thin heterostructure as shown in the figure,
As shown in the figure, a first quantum mini-band 61 and a second quantum mini-band 62 are generated. By processing the metal / insulator ultra-thin film heterostructure shown in FIG. 6, an element structure as shown in FIG. 8 is formed, and an electric field is applied. Then, a band structure as shown in FIG. 7 is obtained.

As apparent from FIG. 7, according to the present invention, a field emission cold cathode device having a sufficiently high electron injection efficiency from the back surface while maintaining the NEA characteristic in which conduction electrons are easily emitted to the vacuum side is maintained. It can be seen that it can be obtained. Moreover,
The electron has a certain quantum level of energy,
Stable emitted electrons can be obtained.

The field emission cold-cathode device structure shown in FIG. 8 is a three-terminal device, and the device manufacturing process becomes somewhat complicated as described later. Here, 81 is a Si substrate, 82 is a metal copper single crystal thin film (Cu), 83 is an insulator layer, 84 is a superlattice, and 85 and 86 are power supplies for electron injection.

On the other hand, since the element structure shown in FIG. 9 is a two-terminal element, the process is simplified. FIG. 10 shows a band structure when an electric field is applied to the structure shown in FIG. Also in this case, it is expected that a large amount of electrons will be supplied from the metal layer forming the superlattice structure on the back surface while maintaining the NEA characteristic in which conduction electrons are easily emitted to the vacuum side, so that the electron injection efficiency is sufficiently large. I understand.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIG. 8 shows a field emission cold cathode device (three-terminal device) using a metal / insulator ultra-thin film structure according to a first embodiment of the present invention, and FIG. FIG. 2B is a sectional view.

In order to realize the present invention, it is necessary to form a cold cathode device structure as shown in FIG. For that purpose, it is most important to produce the superlattice structure shown in FIG. Hereinafter, a method of manufacturing the superlattice structure will be described in detail.

First, ordinary metal organic chemical vapor deposition (MOCV
By D) method, Si (111) (lattice constant a = 5.43)
1Å) The substrate 81 is maintained at about 600 to 700 ° C., and a methyl copper (CuCH ₃ ) gas containing an organometallic gas containing Cu is supplied with a high vacuum chamber of 10 ⁻⁷ Torr or more (not shown).
The gas is introduced through a nozzle (not shown) from a gas cylinder onto the Si substrate 81 in the inside. Methyl copper is thermally decomposed on the Si substrate 81, and a metallic copper (lattice constant a = 3.615 °) single crystal thin film 82 grows. At this time, the thickness of the metal copper single crystal thin film 82 is 1000 °.

Next, methane (CH ₃ ) and carbon dioxide (CO ₂ ) gas raw materials are introduced into the vacuum chamber through a nozzle by a chemical vapor deposition (CVD) method, and the copper single crystal film 8 is formed.
Spray on 2. At this time, the substrate temperature is set to about 600 to 70
Keep at 0 ° C. Then, the gas is decomposed on the copper film 82, and a diamond (lattice constant a = 3.567 °) thin film 83 is obtained. At this time, the thickness of the diamond thin film 83 is set to 10 °.

Further, a copper thin film 82 is grown to a thickness of 10 ° by the above-described method by introducing a methyl copper gas. This process is repeated ten times to produce a superlattice structure 84 having ten layers. The top layer terminates in a 100 ° copper layer 82 to take the electrodes.

Next, a case where AlN is grown on the copper film 82 of FIG. 8 will be described. The method for producing the copper single crystal thin film is as described above. AlN is produced by a CVD method.
Trimethyl Al [Al (CH ₃ ) ₃ ], ammonia (NH
₃ ) A gas raw material is introduced into a vacuum chamber through a nozzle, and is sprayed on a copper single crystal thin film heated to about 600 to 700 ° C. The gas is thermally decomposed on the high-temperature substrate to grow an AlN compound crystal film to a thickness of 10 °. Then 10
The layer process is the same as for the diamond thin film.

In the case of producing a c-BN (cubic-type boron nitride) film, the temperature is kept high (about 60) using a boron (B) gas raw material and an ammonia (NH ₃ ) gas raw material.
(0-700 ° C.) A gas is blown onto the substrate 81 to produce a c-BN single crystal growth film by thermal decomposition and chemical reaction.
In the subsequent steps, as described above, ten superlattice films 84 are formed.

Although the method of forming the metal layer has been described for the case of copper, the Sn—Pb, Al, Ag, Au, and W layers are also formed by using the above-mentioned organometallic gas source and using a high-temperature Si placed in a vacuum chamber. A single crystal thin film can be formed over a substrate.

FIG. 6 shows an electron energy distribution diagram of the metal / insulator ultra-thin film heterostructure manufactured as described above. As can be seen from FIG. 6, the insulator layer 83
Since the material having NEA characteristics is used, it is considered that the lower end of the conduction band is equal to the vacuum level. The Fermi level of the electrons in the metal layer 82 (the maximum electron energy level where most of the electrons are present) is about 4 eV for a normal metal. According to the theory of quantum mechanics, if the metal layer 82 has a so-called quantum well structure with a thickness of about several hundreds of square meters or less and both sides surrounded by a forbidden band, electrons having energy higher than the Fermi level have discrete energy values. Will be. This size is defined as the effective mass of electrons m ^* = 0.1 m ₀ (m
_When calculated as ₀ (mass of free electrons), the first quantum level is 1.04 eV. The insulating layer 83 serving as a barrier layer
When the thickness is less than several tens of millimeters, an electron tunneling effect occurs.

Summarizing the above results, first and second minibands 61 and 62 are generated as shown in FIG. The electrons move through the mini-bands 61 and 62.

When electric fields 85 and 86 as shown in FIG. 8 are applied to the superlattice thin film 84 having such an electron energy distribution, an electron energy distribution diagram as shown in FIG. 7 is obtained.
As is apparent from FIG. 7, a large amount of electrons 64 are supplied to the first and second miniband levels 61 and 62 from the metal layer 82 'on the back surface. Further, when the electrons 64 are emitted into a vacuum, the electron energy is higher than the vacuum level, and the effect of the negative electron affinity (NEA) is realized.

As described above, the fact that the electrons 64 are sufficiently supplied from the back surface and have NEA characteristics means that the field emission cold cathode device according to the present invention has highly efficient electron emission characteristics. . Furthermore, electrons have only the energy of the first and second minibands 61 and 62, which means that the electron emission characteristics of the device can be stabilized.

Next, a method of processing the superlattice thin film manufactured as described above into an element structure as shown in FIG. 8 will be described.

Using a photomask, a 10-layer superlattice thin film 82 on a Si substrate 81 is formed into a square shape using sulfuric acid,
Etching is performed with a nitric acid-based etchant until the silicon substrate 81 is reached, as shown in FIG. Next, the lowermost metal layer 8
2 and the electrode lead wire 87 are connected. Thereafter, the SiO ₂ insulating film is formed by sputtering using a photomask.
Laminate to a thickness of 010 °. Further, using the same photomask, an 80 ° metal layer 82 ′ is deposited on the periphery of the square. Finally, as shown in FIG.
8 and 89 connected, field emission cold cathode device (3 terminal device)
To complete.

(Second Embodiment) FIG. 9 shows a field emission cold cathode device (two-terminal device) using a metal / insulator ultra-thin film structure according to a second embodiment of the present invention. FIG. 2B is a sectional view. When an electric field is applied to the element structure shown in FIG. 9, a large amount of electrons are supplied from the metal layer thin film 82 forming the superlattice 84. Also in this case, the electrons 64 emitted into the vacuum have the NEA effect.
It is clear from the electron energy distribution diagram of FIG.

The structure shown in FIG. 9 is easier to process than the structure shown in FIG. After the superlattice thin film 84 is etched in a square shape, the metal layer 82 'is
Deposit around the square to a thickness of 090 °. Then 2
The electrode lead wires 91 and 92 may be connected.

(Other Embodiments) In the above-described embodiment of the present invention, the MOCVD (Metal Organic Chemical Vapor Deposition) method is used.
Although a superlattice structure is formed on an i-substrate, the present invention is not limited to this. For example, a superlattice structure may be formed on a Si substrate by using a MOMBE (organic metal molecular beam epitaxy) method.

[0040]

As described above, according to the present invention, the efficiency of electron emission can be improved by using a metal / insulator ultra-thin film heterostructure as a cold cathode material constituting a field emission cold cathode device.
High stability can be achieved.

Actually, the copper / AlN superlattice thin film described in the section of the embodiment of the present invention is prepared, the device structure shown in FIG. 8 is formed, and the device is put in a vacuum vessel. Then, a voltage of about 1 kV was applied between the cathode and the anode, and the gate voltage versus the emission current was measured.
It was found that it was improved by one digit or more compared to the conventional element. In addition, it was also found that the time variation of the emission current was constant and high stability was maintained.

If a large number of field emission cold cathode devices according to the present invention are arranged in a plane to form a matrix electrode structure, a large-screen flat display device (FED), which has been difficult to realize so far, can be realized. Further, if applied to an image sensor, an image sensor with low power consumption and high resolution can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an electron energy distribution near a metal and semiconductor surface.

FIG. 2 is a cross-sectional view showing a structural example of a conventional thin film cold cathode device using a NEA diamond thin film.

FIG. 3 is a characteristic diagram showing a relationship between an electron affinity of a semiconductor and a band gap.

FIG. 4 is a cross-sectional view illustrating a structure of a conventional Spindt-type field emission device.

FIG. 5 is a conceptual diagram showing a conduction band profile at a CoSi ₂ / CaF ₂ heterojunction interface according to a conventional technique.

FIG. 6 is an electron energy distribution diagram of a metal / insulator ultra-thin film heterostructure according to an embodiment of the present invention.

FIG. 7 is an electron energy distribution diagram when an electric field is applied to a metal / insulator ultrathin film heterostructure (three-terminal device) according to an embodiment of the present invention.

8A and 8B are a plan view and a cross-sectional view, respectively, showing a configuration of a field emission cold cathode device (three-terminal device) using a metal / insulator ultrathin film heterostructure according to an embodiment of the present invention.

FIG. 9 is a plan view (a) and a sectional view (b) showing a configuration of a field emission cold cathode device (two-terminal device) using a metal / insulator ultrathin heterostructure in another embodiment of the present invention. is there.

FIG. 10 is an electron energy distribution diagram when an electric field is applied to the metal / insulator ultra-thin film heterostructure (two-terminal element) in FIG. 9;

[Explanation of symbols]

 Reference Signs List 61 first mini band 62 second mini band 63 conduction band lower end 64 electron 81 Si substrate 82 metal layer 83 insulator layer 84 superlattice 85, 86 power supply 87, 88, 89 electrode lead wire 91, 92 electrode lead wire

Claims (3)

[Claims] 1. A field emission cold cathode device comprising a metal / insulator ultra-thin heterostructure as a cold cathode material constituting a field emission cold cathode device. 2. The method according to claim 1, wherein the insulating layer is diamond or Al.
2. The field emission device according to claim 1, wherein one of N and c-BN is used, and one of Cu, Sn-Pb, Al, Ag, Au and W is used as the metal layer. Cold cathode device. 3. A cold cathode material having a superlattice structure formed on a Si substrate by MOCVD (metal organic chemical vapor deposition) or MOMBE (metal organic molecular beam epitaxy). 3. The field emission cold cathode device according to item 1.