JP3390495B2 - MIM structure element and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention is used in MIM structure electronic devices, such as electron sources, which require high quality insulating layers.

[0002]

2. Description of the Related Art A laminated structure of metal-insulating layer-metal is MI
It is a key part in the M diode, the MIM electron-emitting device, etc., and in particular, it is required to improve the film quality of the insulating layer to reduce the leak current and to increase the withstand voltage. The conventional technique will be described below by taking an electron-emitting device as an example.

FIG. 2 shows a principle diagram when the MIM structure is operated as an electron-emitting device. Upper electrode 11 and lower electrode 1
When a voltage is applied to the insulating layer 12, electrons near the Fermi level in the lower electrode 13 pass through the barrier due to the tunnel phenomenon due to the electric field in the insulating layer 12, and the insulating layer 12 and the upper electrode 11
Appear in the conduction band of. Of these electrons, the upper electrode 1
Electrons having an energy equal to or higher than the work function φ of 1 will be emitted into a vacuum. To date, Au-Al ₂
Electron emission based on this principle has been observed in the O ₃ -Al structure. This electron source has excellent properties as an electron source such that even if the surface of the upper electrode 11 is contaminated by adhesion of environmental gas and the work function φ changes, the electron emission characteristics are not significantly affected. , Is expected as a new type electron source.

When manufacturing this electron source, the manufacturing of the insulating layer is an important point. As the method for producing the insulating layer, a method of oxidizing the lower electrode 11 by an anodic oxidation method in an oxidizing solution is used in addition to the vapor deposition of the insulating layer constituent material and the reactive vapor deposition method of metal vapor deposition in an oxygen gas atmosphere. ing. Au-A
When forming an electron-emitting device having an l ₂ O ₃ -Al structure by an anodizing method, the formation current density that determines the anodizing rate is 0.25 A.
It has been reported that the electron emission characteristics are improved by reducing the value to / m ² . (Vid Cousche Mans, 45
Volume 253, pp. 233-249, 1990,
Vide CouchesMinces, Vol. 45, No. 253, pp. 233 − 2
49 (1990)).

[0005]

As a characteristic showing the performance of the MIM electron-emitting device, when a diode voltage is applied between the upper electrode 11 and the lower electrode 13, the upper electrode 11-
A current (diode current I
d) and the emission current I emitted from the upper electrode 11 into the vacuum
There is a ratio (emission ratio) with e, Ie / Id. The higher the emission ratio, the more efficient the electron-emitting device. However, in the MIM electron-emitting device obtained by the above manufacturing method, (1/1
Only a low emission ratio of 0 ⁵ ) order was obtained.

As described above, the cause of the low emission ratio is that most of the electrons transmitted through the barrier at the interface between the lower electrode 13 and the insulating layer 12 by tunneling pass through the conduction band in the insulating layer 12. This is because energy is lost due to scattering with the crystal lattice and the barrier (work function φ) between the upper electrode 11 and the vacuum interface cannot be exceeded. Further, when the film quality of the insulating layer 12 is further deteriorated, leak current flows in addition to the permeation by tunneling. Since the leak current flows ohmicly through the conductive path in the insulating layer 12,
It has low kinetic energy and does not contribute to electron emission. As described above, the reason why the emission ratio in the MIM electron-emitting device is low is that the film quality of the insulating layer is poor.

It is an object of the present invention to improve the film quality of the insulating layer so as to increase the emission ratio in the electron-emitting device and improve the device characteristics such as reduction of the leak current in other MIM structure devices.

[0008]

[Means for Solving the Problems] The formation current density during anodization is set to 0.1 A / m ² or less, and the oxidation rate is set to 0.2 nm / m.
By setting it to be in or less, the film quality of the insulating layer can be improved. When this is applied to the MIM electron-emitting device, the emission ratio becomes 1 × (1/10 ³ ) and can be increased by one digit as compared with the conventional one.

[0009]

Using Al as the lower electrode 13, it is anodized to form the insulating layer 12 made of Al ₂ O ₃ , and further the upper electrode 11 is formed to produce the MIM electron-emitting device. The thickness of each of the lower electrode 13 and the upper electrode 11 is 1
It is about 5 and 10 nm. It goes without saying that this film thickness is an example. The film thickness of the insulating layer 12 is about 3 to 10 nm.

This anodic oxidation process will be described in detail. As the chemical conversion liquid, for example, a 1 to 3% tartaric acid aqueous solution neutralized with aqueous ammonia and diluted with ethylene glycol is used. An Al lower electrode 13 is used as an anode and a platinum wire is inserted as a cathode in this chemical conversion liquid, and a constant current I ₀ is flown between them. I ₀ divided by the area S of the lower electrode 13 immersed in the chemical conversion liquid (that is, the area to be oxidized), J ₀ = I ₀ / S
The rate of oxidation is governed by (formation current density).

FIG. 3 shows the relationship between the anode-cathode voltage (formation voltage V) and the current flowing between the anode and the cathode during anodization. The vertical axis represents the formation current density J. At the initial stage of oxidation, the formation current density J is kept at J ₀ in the external circuit. Then,
The formation voltage V continues to rise. When the formation voltage V reaches the voltage value corresponding to the desired film thickness (point A in FIG. 3), the external circuit is switched from the constant current circuit to the constant voltage circuit. Then, the formation current density J gradually decreases. When J is small enough, the anodization process is terminated.

Here, the reaction on the surface of the anode during the anodic oxidation will be described by taking the case of using Al as the anode. The oxidant Ox in the chemical conversion liquid extracts electrons from Al by the following reaction.

[0013]

[Chemical 1]

Here, (Al +) is not a free Al + ion but an atom in a state of lacking electrons on the electrode. Then, by reaction with various chemical species in the chemical conversion liquid,
A compound represented by Al _x O _y (OH) _z (x, y, z are integers or decimals) is produced. Further electrode reaction:

[0015]

[Chemical 2]

By the above, Al is further oxidized. By repeating this process, when Al is trivalent, it becomes Al ₂ O ₃ , which is thermodynamically stable. Therefore, if the oxidation process proceeds slowly enough,
Although thermodynamically stable Al ₂ O ₃ can be obtained, if the speed is high, an imperfect compound of Al _x O _y (OH) _z remains in the oxide film. This deteriorates the film quality. Further, if the oxidation rate is increased, pinholes and the like are likely to be formed in the oxide film. This increases the leak current between the upper metal 11 and the lower electrode 13.

When the reactions of (Chemical formula 1) and (Chemical formula 2) occur, A
Since electrons move from the 1-electrode to the chemical conversion liquid, a current flows between the anode and the cathode. Conversely, unless a current is applied to the external circuit, the reactions of (Chemical formula 1) and (Chemical formula 2) do not occur, so
The oxidation process does not proceed. This is the formation current density J _0.
It is the principle that the oxidation rate is slowed down by improving the film thickness to improve the film quality.

FIG. 4 shows the result of measuring the emission ratio of the electron-emitting device manufactured by the above method. The horizontal axis represents the formation current density J ₀ . As is clear from this figure, when J ₀ > 0.1 A / m ² , there are many variations in the emission ratio and the values are low. When J ₀ ≦ 0.1 A / m ² , variations in the emission ratio are small, and a high emission ratio of 1 × (1/10 ⁴ ) or more can be obtained with good reproducibility. Furthermore, a high emission ratio of 1 × (1/10 ³ ) may be obtained. This indicates that when J ₀ ≦ 0.1 A / m ² , the oxidation rate is sufficiently slow, and the situation is close to that of thermodynamics, so there is little variation and a high-quality insulating film can be formed. There is.

FIG. 5 shows the relationship between the formation current density J ₀ and the oxidation rate. Here oxidation rate and is, t ₁ the time from after the start oxidized to time A in FIG. 3, when the oxide thickness was d, is defined as d / t _1. As expected from the above mechanism, the oxidation rate and the formation current density are almost proportional. As can be seen from FIG. 5, J ₀ <
The condition of 0.1 A / m ² is that the oxidation rate is 0.2 nm / min.
It is nothing but the following.

Since J ₀ and the oxidation rate are almost proportional, J 0
_{When 0} = 0.0001 A / m ² , the oxidation rate is 0.00
It becomes 02 nm / min, and it takes 160 hours to oxidize 2 nm. If anodic oxidation is continued for such a long time, the quality of the film deteriorates due to the influence of residual impurities in the chemical conversion solution. Therefore, the formation current density is 0.
It is preferable to set it in the range of 0001 <J ₀ <0.1 A / m ² .

Since the oxidation rate is controlled by the current flowing from the electrode, that is, the current flowing through the external circuit as described above, the data shown in FIG. 3 does not depend on the type of the chemical conversion liquid used. Therefore, the conditions of the chemical conversion current density are the same when an aqueous solution of ammonium tartrate, an aqueous solution of ammonium citrate, an aqueous solution of ammonium oxalate or the like is used as the chemical conversion liquid.

As described above, the emission ratio in the MIM electron-emitting device is also an index showing the quality of the insulating layer film. Therefore, the MIM structure device made by the present invention is
The characteristics can be improved even in the case of an MIM diode or the like other than the electron-emitting device.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG.
15 n of Al is used as the lower electrode 13 on the insulating substrate 14.
m. For example, RF magnetron sputtering is used to form Al. This is put in a chemical conversion solution having the above-mentioned composition, and anodization is performed using a platinum wire as a cathode. The formation current density J ₀ is limited to 0.05 A / m ² . The insulating layer 12 can be formed by this anodic oxidation. Next, SiO ₂ and Al
An insulator such as ₂ O ₃ is vapor-deposited with a film thickness of about 50 nm by a chemical vapor deposition method (CVD method) or the like to form the protective layer 15.
Then, Au is deposited to a thickness of about 5 nm by RF magnetron sputtering or vapor deposition to form the upper electrode 11. Further, Au, Al or the like having a thickness of about 50 nm is vapor deposited to form the electrode terminal 16. The MIM type electron-emitting device manufactured in this manner is placed in a vacuum chamber having a vacuum degree of 1 × (1/10 ⁷ ) Torr, and the lower electrode 13 is set to the ground potential.
6, that is, when a voltage of about +5 to 7 V is applied to the upper electrode 11, a tunnel current flows from the lower electrode 13 toward the upper electrode 11, and electron emission occurs in vacuum. In the present embodiment, as the lower electrode 13, a highly oriented film,
Alternatively, when a single crystal film is used, the characteristics of the insulating layer 12 formed by anodic oxidation of the single crystal film are further improved, and a higher performance electron-emitting device can be obtained.

Since the insulating layer produced by the method of the present invention has excellent film quality, it can be operated as an electron-emitting device even if the film thickness is thin. Since the MIM electron-emitting device utilizes the tunnel current due to the high electric field applied in the insulating layer 12, if the insulating layer thickness is reduced, the voltage (diode voltage) applied between the upper electrode 11 and the lower electrode 13 is reduced. Even if Vd) is reduced, a sufficient electric field is applied in the insulating layer, so that a sufficient emission current can be obtained.

The insulating layer 12 is formed by the method described in the above embodiment.
When the film thickness of is 5 nm, the upper electrode 11-the lower electrode 13
The electric field in the insulating layer when a voltage of 5 V is applied between them is 1 MV /
cm and electron emission occurs. When the diode voltage is lowered as described above, there is an advantage that the energy dispersion of the emitted electrons becomes small.

When Au is used for the upper electrode 11, the barrier (work function) at the interface between the upper electrode 11 and the vacuum is 4.7.
Since it is about V 2, when operating at Vd = 5V, the energy dispersion becomes small at about 0.3V. in this way,
Although there is a great merit in setting the film thickness of the insulating layer 12 to 6 nm or less, the conventional method for forming an insulating layer requires a film thickness of about 10 nm to 20 nm because the withstand voltage is insufficient.

Journal of Applied Physics, Vol. 45, No. 1, pp. 119-125, 197.
4 years (Journal of Applied Physics, Vol. 45, No. 1,
pp.119-125 (1974)), a MIM electron-emitting device with a film thickness of 6.5 nm is reported.
Although it operates at the following low temperatures, when it is operated at room temperature, it forms immediately and becomes an unstable operation mode in which the current amount of emitted electrons includes noise.

On the other hand, when the MIM electron-emitting device having the thickness of the insulating layer 12 of 5.5 nm is manufactured by the method described in the above embodiment, it is operated at Vd = 5.5V at room temperature. Stable electron emission was also observed, and an electron beam with low energy dispersion could be obtained.

[0029]

As described above, in the insulating film forming process by the anodic oxidation method, the formation current density is 0.1 A / m ²
By limiting to the following and slowing the oxidation rate, the quality of the insulating layer film can be improved and the performance of the MIM structure element can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of an electron-emitting device manufactured according to the present invention.

FIG. 2 is an explanatory diagram of an operating principle of the MIM type electron-emitting device.

FIG. 3 is a characteristic diagram showing changes in formation current and formation voltage during anodization.

FIG. 4 is a characteristic diagram showing a correlation between a chemical conversion current density and an emission ratio.

FIG. 5 is an explanatory diagram showing the relationship between the formation current density and the oxidation rate.

[Explanation of symbols]

10 ... Vacuum, 11 ... Upper electrode, 12 ... Insulating layer, 13 ... Lower electrode, 14 ... Substrate, 15 ... Protective layer, 16 ... Electrode terminal,
20 ... power supply.

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Susumu Sasaki 1-280 Higashi Koikekubo, Kokubunji City, Tokyo Inside Hitachi Central Research Laboratory (72) Inventor Tomio Yaguchi 1-280 Higashi Koikeku, Tokyo Kokubunji City Hitachi Ltd. Central Research Laboratory (72) Inventor Tadashi Seisei 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi, Ltd. Central Research Center (72) Inventor Emiko Yamada 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi Ltd. Central Research Center (56) References JP-A-2-121227 (JP, A) JP-A-5-289113 (JP, A) JP-A-7-45950 (JP, A) JP-B-40-10338 (JP, B1) (JP 58) Fields investigated (Int.Cl. ⁷ , DB name) H01J 9/02 H01J 1/30

Claims (4)

(57) [Claims] 1. A structure in which a metal 1 layer, an insulating layer, and a metal 2 layer are laminated in this order, and the metal 1 layer and the metal 2 are laminated.
In the method of manufacturing an MIM structure element in which electrons are emitted from the surface of the metal 2 layer into a vacuum by applying a voltage between the layers of
A method of manufacturing a MIM structure element, characterized in that the insulating layer is formed by anodizing the metal 1 constituting the layer of the metal 1 at a formation current density of A / m 2 or less. 2. A structure in which a metal 1 layer, an insulating layer, and a metal 2 layer are laminated in this order, and the metal 1 layer and the metal 2 are laminated.
In the method of manufacturing an MIM structure element in which electrons are emitted from the surface of the metal 2 layer to a vacuum by applying a voltage between the layer and the layer of 0.002 nm or more and 0.2 nm or less per minute. A method of manufacturing an MIM structure element, characterized in that the insulating layer is formed by anodizing the metal 1 constituting the layer of the metal 1 at a speed. 3. The MI according to claim 1, wherein aluminum (Al) is used as the metal 1.
Manufacturing method of M structure element. 4. The method of manufacturing an MIM structure element according to claim 1, wherein tantalum (Ta) or titanium (Ti) is used as the metal 1.