JPH11149858A - Field emission type cold cathode and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of an emission characteristic, especially the generation of gate leakage current, and at the same time lower electric power consumption, prolong life, and enhance the reliability by covering the surface of an emitter with a protective film made of a high resistance material or an insulating material. SOLUTION: An emitter 5a having a sharp tip end, a gate electrode 3a, and an insulating film 2 are formed on a silicon substrate 1, and furthermore the emitter 5a and the exposed silicon substrate 1 surface are coated with a protective film 6 made of a semi-insulating film such as a diamond film. The electrons emitted from the emitter 5a have tracks within a certain spread and the residual gas ionized by collision of the electrons moves in the emitter 5a direction along the potential distribution. Although the ions generated in close proximity to the emitter 5a move towards the tip of the emitter 5a since the ions generated at remote positions have energy in the vertical direction, the ions enter in the sidewall of the emitter 5a. As a result, the generation of gate leakage current can be prevented.

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, and more particularly to a field emission cold cathode having a sharp emitter.

[0002]

2. Description of the Related Art A field emission type cold cathode has a sharp cone-shaped emitter and a submicron-order opening, and a gate electrode formed close to the emitter concentrates a high electric field at the tip of the emitter. An element that emits electrons from the tip and receives the electrons at the anode electrode. However, strictly speaking, even in a vacuum, residual gas at an extremely low pressure remains in the operating environment. Further, when an electron flow enters the anode electrode or the like, degassing occurs, and the degree of vacuum may decrease.

[0003] In such a vacuum environment, the residual gas is ionized positively by electrons, which is incident on the emitter and sputters the emitter material. For this reason, the current may fluctuate due to deformation of the emitter shape. Further, the sputtered emitter material may deposit on the side wall of the insulating film between the gate electrode and the emitter electrode, causing current leakage between the emitter and the gate. When such a leakage current occurs, the effective emitter-gate voltage is reduced due to the excess current, and the emission current value is also reduced, thereby shortening the lifetime.

To prevent this leakage current, it is effective to prevent the emitter material from being sputtered. Therefore,
A method of covering the emitter with a material having high sputtering resistance has been proposed.

[0005] A field emission type cold cathode of this type is disclosed, for example, in Japanese Patent Application Laid-Open No. 7-192604. As shown in FIGS. 8 (cross-sectional view) and FIG. 9 (plan view), a projection-shaped emitter 5a is formed on a silicon substrate 1 serving as a support substrate, and an insulating film 2 made of an oxide film having an opening on the emitter 5a. And an electrode film 3 formed thereon, and a structure in which an organometallic compound 8 such as an organosilicon compound is formed so as to cover the emitter 5a and the silicon substrate 1 exposed in the opening of the insulating film 2. Had become. By forming a conductive film having high sputter resistance as the emitter protective film in this manner, the life can be improved.

[0006]

As described above, by using a material having higher sputter resistance than the emitter material, the fluctuation of the anode current is reduced and the life is improved. However, when a conductive metal compound is used as the protective film, in a case where high-energy ions are incident, the organic metal compound serving as the protective film is sputtered and deposited on the side wall of the insulating film, thereby causing a problem that a gate leak path occurs between the emitter and the gate. is there.

[0007] Forty as tested in the above publication.
The sputterability of ions generated at a gate voltage of about V is small, and it is considered that the effect of improving the life is large in the evaluation at such a low voltage. However, in an actual evaluation environment, a high voltage of 1000 V or more is applied as an anode electrode. May be done. Generally, the sputtering rate increases while showing a tendency of saturation from an energy of 1000 V or more. For this reason, in an environment where a high voltage is applied, a metal compound serving as an emitter protective film is also sputtered, and eventually, a current may decrease due to gate leakage. Furthermore, the generation of the gate leak current generates excess power, which hinders low power operation.

SUMMARY OF THE INVENTION The present invention has been made in view of the problems in the related art, and prevents deterioration of emission characteristics, particularly generation of gate leakage current, low power consumption, long life, and high reliability of field emission. It is an object of the present invention to provide a cold cathode and a manufacturing method thereof.

[0009]

According to the present invention, there is provided a field emission type comprising a sharp-pointed emitter formed on a substrate and a gate electrode provided close to the emitter and having an opening in the emitter. In the field emission cold cathode, the surface of the cold cathode is covered with a protective film made of a high resistance material or an insulating material.

The present invention is also directed to a field emission cold cathode having a sharp tip-shaped emitter and a gate electrode provided in close proximity to the emitter and having an opening in the emitter portion. The field emission type cold cathode is characterized in that the electron emission region is exposed and the side wall surface other than the electron emission region is covered with a protective film made of a high-resistance material or an insulating material.

According to the present invention, by forming a protective film made of a high-resistance material or an insulating material on the surface of the emitter, the emitter material is prevented from being sputtered even when the ionized residual gas enters the emitter. Further, even if the sputtered protective film adheres to the side wall of the insulating film, a gate leak current that leads to a decrease in the emission current between the emitter and the gate electrode does not flow. Further, there is no generation of excess power due to the generation of a gate leak current, which is effective for low power operation.

[0012]

FIG. 1 shows an example of an embodiment of the present invention. Emitter 5a having a sharp tip on silicon substrate 1, gate electrode 3a formed so as to surround it
And an insulating film 2, and a protective film covering the emitter 5 a and the exposed surface of the silicon substrate 1. In this figure, the protective film 6 is also formed on the gate electrode 3a and the insulating film 2, but these are not necessarily required.

FIG. 2 is a plan view of this embodiment. FIG.
FIG. 3 is a sectional view taken along a line AB in FIG. As shown in FIG.
The protective film 6 formed on the surface has at least the gate electrode 3
In the part of the electrode take-out part 11 shown in FIG.

FIG. 7 schematically shows the trajectories of the emission electrons from the emitter and the residual gas ionized by the electrons, and the effect of the present invention will be described. As shown in FIG. 7, the electrons emitted from the emitter 5a show a locus having a certain spread (indicated by a dotted line). The residual gas ionized by the collision of the electrons travels toward the emitter along the potential distribution. Here, ions (thin solid line) generated in the vicinity of the emitter are directed toward the tip of the emitter, while ions (thick solid line) generated at a distant position have energy in the vertical direction, and are incident on the side wall of the emitter. .

In the conventional field emission type cold cathode, the emitter is sputtered by the incidence of such ions, and a gate leak current path is formed by the emitter material deposited on the side wall of the insulating film 2 in the vicinity.

However, when an insulating emitter surface protective film is formed as in the present invention, even if it is sputtered by ions and deposited on the side wall of the insulating film, only a nonconductive emitter surface material is deposited. No gate leak path is formed between the gate electrodes.

The volume resistivity of the protective film is 10 Ω · cm.
And preferably at least 10 ⁵ Ω · cm.

As shown in FIG. 1, when the entire surface of the emitter is covered with a protective film, the thickness of the protective film is such that electrons are easily emitted from emitter 5a by tunneling, for example, about 10 nm. The following is desirable.

In the present invention, as shown in FIG. 4C, it is preferable that the electron emission region of the emitter 5a is exposed without being covered with a protective film.

Further, by using a material having a low sputtering rate for the protective film, the surface of the emitter can be further protected, and the emitter itself is not damaged.

Examples of the material used as the protective film include diamond, diamond-like carbon, a silicon oxide film, a silicon nitride film, and graphite. Among them, diamond, diamond-like carbon, and silicon oxide film are preferable.

By using the field emission cold cathode of the present invention for a display element, an excellent display device with stable luminance can be obtained.

In particular, in the case of a flat panel display in which a large number of field emission cold cathodes are formed so as to face an anode electrode, if the amount of emission current decreases due to the incidence of positive ions on the emitter, the difference between the brightness of the surroundings and the brightness is reduced. Occurs or remains as a dark spot. However, when the field-emission cold cathode of the present invention is used, a plurality of field-emission cold cathodes operate without current fluctuation and a long-life display operation can be performed.

Further, when the field emission cold cathode of the present invention is applied to a cathode ray tube (CRT) for a display, a device having stable current characteristics can be realized.

[0025]

Next, the present invention will be described more specifically with reference to examples.

[Embodiment 1] FIGS. 3A to 3D are sectional views in the order of steps of a first embodiment of the present invention. First, FIG.
As shown in (a), n having an impurity concentration of about 10 ¹⁵ cm ^-3
An insulating film 2 having a thickness of about 500 nm, such as an oxide film formed by thermal oxidation, is formed on the surface of a mold silicon substrate 1. Subsequently, an electrode film 3 made of a metal film such as tungsten is deposited to a thickness of about 200 nm by a method such as sputtering.

Next, as shown in FIG. 3B, the electrode film 3 is selectively etched using a mask such as a resist to form a gate electrode 3a, and further patterned by photolithography using the resist as a mask. Gate electrode 3a
And the insulating film 2 are subjected to reactive ion etching (RI
Etching is performed by the method E) to form an opening exposing the silicon substrate 1 in the emitter formation region.

Next, as shown in FIG. 3C, the sacrificial layer 4 made of, for example, aluminum is made about 100 nm in an oblique direction inclined at a predetermined angle from the vertical direction by electron beam evaporation.
Deposits thick. In this step, since the sacrificial layer is deposited obliquely from above, the sacrificial layer is not formed on the exposed silicon substrate 1 serving as an emitter formation region, but is formed on the upper surface and the side wall of the insulating layer 2 and on the gate electrode 3a. You.

Next, an emitter material layer 5 of, for example, Mo
Is deposited from the vertical direction by an electron beam evaporation method. In this step, the emitter material layer 5 is deposited on the upper surface of the sacrifice layer 4 and, at the same time, the emitter material layer 5 is deposited and grown in a cone shape on the silicon substrate 1 in the emitter formation region to form the emitter 5a.

Next, as shown in FIG. 3D, the sacrificial layer 4 is removed by etching with phosphoric acid or the like. As a result, the emitter material layer 5 on the sacrificial layer 4 is lifted off to expose the emitter 5a.

Thereafter, a protective film 6 made of a semi-insulating film such as a diamond film is formed by a CVD method or the like from 5 nm to 20 nm.
After depositing over the entire surface to a thickness of m, the protective film 6 in a predetermined area for pad formation is removed to obtain the field emission cold cathode of the first embodiment shown in FIG.

According to this method, a desired protective film can be simply formed in the final step of forming the field emission cold cathode.

When the life of the field emission type cold cathode was evaluated in a vacuum environment of 10 ⁻⁶ Pa, in the conventional field emission type cold cathode with the exposed emitter, the gate leakage current gradually increased after 100 hours, and the emission current was increased. However, no leakage current was observed in the device of the present invention.

[Embodiment 2] Next, a second embodiment of the present invention will be described. FIGS. 4A to 4C are sectional views in the order of steps in a second embodiment of the present invention.

As shown in FIG. 4A, the emitter material layer 5 is deposited on the upper surface of the sacrificial layer 4 and the emitter 5a is formed at the same time as in the first embodiment.

Thereafter, as shown in FIG. 4B, the sacrificial layer 4 is etched with phosphoric acid or the like, unnecessary emitter material layers 5 are lifted off, and diamond-like carbon (DLC) of about 10 ⁹ Ω · cm is removed. After a 10 nm thick film is deposited on the entire surface by the CVD method and a flat film such as a resist is applied, O ₂
The resist is etched back in the plasma and the emitter 5a is etched.
The resist 7 remains only in the opening in which is formed, and the tip of the emitter is exposed from the resist.

Thereafter, the exposed portion of the DLC film is etched to remove the resist, leaving the DLC film on the side wall of the emitter 5a and exposing the emitter material such as Mo at the tip as shown in FIG. 4C. A field emission cold cathode is completed.

In this embodiment, since the tip of the emitter is exposed, there is no need to tunnel the protective film when electrons are emitted, and operation at a low voltage is possible.

As described above, even when the tip of the emitter is exposed, the high-energy ions are far from the emitter, so that the probability of being incident on the tip of the emitter is low. The possibility of forming a leakage current path on the side wall of the second is extremely low.

That is, in this embodiment, it is possible to obtain a long-life and high-reliability field emission type cold cathode which can be driven at a low voltage.

Third Embodiment Next, a third embodiment of the present invention will be described. FIGS. 5A to 5E are process sectional views of a third embodiment of the present invention. First, as shown in FIG. 5A, an insulating film 21 such as an oxide film having a thickness of about 200 nm is formed on the silicon substrate 1 by a method such as a thermal oxidation method.

Next, as shown in FIG.
The silicon substrate 1 is etched into a convex shape by a dry etching method using a gas such as SF ₆ using the mask as a mask.

Next, as shown in FIG. 5C, the exposed silicon substrate 1 is subjected to thermal oxidation to form an oxide film 2 having a thickness of about 200 nm.
2 and silicon substrate 1 for emitter formation at the same time
Is processed into a sharp conical shape to form the emitter 5a. Further, an insulating film 2 such as an oxide film is formed by an electron beam evaporation method.
3 is formed to a thickness of about 300 nm, and an electrode film 3 made of a metal film such as tungsten is formed to a thickness of about 200 nm.

Next, as shown in FIG. 5D, after the electrode film 3 is patterned by photolithography, the insulating film 21, the insulating film 23 and the oxide film 22 are etched with a hydrofluoric acid solution or the like. As a result, the surplus electrode film 3 on the emitter is lifted off and removed to form a gate electrode 3a.

Next, as shown in FIG. 5E, the exposed surface of the emitter 5a is oxidized to form a protective film 6 made of an oxide film of 5 to 10 nm.

As described above, in the method of forming the emitter by sharpening the silicon substrate by etching or the like, it is possible to easily form the protective film by oxidizing the surface of the emitter thinly. In this method, a material such as a DLC film may be deposited.

[Embodiment 4] Next, a fourth embodiment will be described. FIG. 6 is a sectional view of the fourth embodiment. About 10
^A conical emitter 5a is formed on the surface of an n-type silicon substrate 1 having a concentration of ¹⁵ cm ^-3 , and an oxide film 22 or 3 having a thickness of about 200 nm, for example, an oxide film formed by thermal oxidation.
Field emission type cold cathode emitter 5 comprising a 00 nm thick insulating film 23 and a gate electrode 3a made of, for example, tungsten.
The structure is such that a protective film 6 made of, for example, an oxide film is formed in a region excluding the tip of a.

In order to form such a structure, the structure up to FIG.
After applying a flat film such as resist in the same manner as above, etch back the resist so that the tip of the emitter is exposed from inside the resist, etch the exposed silicon oxide film, and then remove the resist. As shown in 6, a structure in which silicon is exposed at the tip of the emitter and the side wall of the emitter is covered with a protective film made of a silicon oxide film is completed.

As described above, even with the emitter made of silicon, it is possible to protect the sputter of the emitter in a state where the tip is exposed and emission characteristics are improved. This method is effective when a material having a high work function and relatively low emission efficiency, such as an oxide film, is used as a protective film.

[0050]

According to the present invention, it is possible to provide a field emission type cold cathode which has a low power consumption, a long service life and a high reliability by preventing the deterioration of the emission characteristic, in particular, the occurrence of a gate leak current. .

Further, according to the present invention, low voltage operation is possible.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one example of a field emission cold cathode according to the present invention.

FIG. 2 is a plan view showing one example of a field emission cold cathode of the present invention.

FIG. 3 is a cross-sectional view in the order of steps of the first embodiment of the present invention.

FIG. 4 is a cross-sectional view in the order of steps of a second embodiment of the present invention.

FIG. 5 is a sectional view in order of steps of a third embodiment of the present invention.

FIG. 6 is a sectional view of a fourth embodiment of the present invention.

FIG. 7 is an explanatory diagram of trajectories of electrons emitted from a field emission type cold cathode and ions irradiated to the cold cathode.

FIG. 8 is a sectional view of a conventional field emission cold cathode.

FIG. 9 is a plan view of a conventional field emission cold cathode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Insulating film 3 Gate electrode material 3a Gate electrode 4 Sacrificial layer, 5 Emitter material layer 5a Emitter 6 Protective film 7 Resist 8 Organometallic compound 21 Insulating film 22 Oxide film 23 Insulating film

Claims (10)

[Claims] 1. A field emission cold cathode comprising: a sharp-pointed emitter on a substrate; and a gate electrode provided close to the emitter and having an opening in the emitter portion. Characterized by being covered with a protective film made of a high-resistance material or an insulating material. 2. A field emission cold cathode having a sharp tip-shaped emitter and a gate electrode provided adjacent to the emitter and having an opening in the emitter portion, wherein the electron emission region at the tip of the emitter is provided. Wherein the surface of the side wall other than the electron emission region is covered with a protective film made of a high resistance material or an insulating material. 3. The field emission cold cathode according to claim 1, wherein the protective film is a diamond film, a diamond-like carbon film, or a silicon oxide film. 4. A step of forming an insulating film and an electrode film in this order on a silicon substrate, processing the electrode film into a gate electrode shape, and providing an opening at an emitter forming position of the insulating film and the electrode film; Exposing the silicon substrate; forming a sacrificial layer on a surface other than the inside of the opening by oblique vapor deposition; depositing an emitter material layer on the surface of the sacrificial layer;
A step of forming an emitter electrode in the opening in a cone shape; a step of etching the sacrificial layer to lift off an emitter material layer on the sacrificial layer; and forming a high-resistance material or an insulating material on the surface of the cone-shaped emitter. Forming a protective film by filming.
A method for producing a field emission cold cathode as described in the above. 5. A step of forming an insulating film and an electrode film in this order on a silicon substrate; processing the electrode film into a gate electrode shape; and providing an opening at an emitter forming position of the insulating film and the electrode film. Exposing the silicon substrate; forming a sacrificial layer on a surface other than the inside of the opening by oblique vapor deposition; depositing an emitter material layer on the surface of the sacrificial layer;
A step of forming an emitter electrode in a cone shape in the opening; a step of etching off the sacrificial layer to lift off an emitter material layer on the sacrificial layer; and forming a high-resistance material or an insulating material on the surface of the cone-shaped emitter. A step of forming a protective film by filming, a step of exposing the tip of the emitter from the resist by forming a resist on the entire surface and then performing an etch back, and a step of removing the protective film at the tip of the emitter. 3. The method for producing a field emission cold cathode according to claim 2, comprising: 6. A step of forming a first insulating film at an emitter forming position on a silicon substrate, isotropically etching the silicon substrate using the first insulating film as a mask, and subsequently thermally oxidizing the silicon substrate. Forming a silicon oxide film on the surface of the silicon substrate and simultaneously processing the silicon substrate under the first insulating film into a sharp shape to form an emitter; and forming a second insulating film and subsequently an electrode film Removing the first insulating film, the second insulating film, and the electrode film formed on the emitter by photolithography, and oxidizing the surface of the silicon emitter exposed on the surface to form a protective film The method for producing a field emission cold cathode according to claim 1, comprising: 7. A step of forming a first insulating film at a position where an emitter is formed on a silicon substrate, isotropically etching the silicon substrate using the first insulating film as a mask, and subsequently thermally oxidizing the silicon substrate. Forming a silicon oxide film on the surface of the silicon substrate and simultaneously processing the silicon substrate under the first insulating film into a sharp shape to form an emitter; and forming a second insulating film and subsequently an electrode film Removing the first insulating film, the second insulating film, and the electrode film formed on the emitter by photolithography, and oxidizing the surface of the silicon emitter exposed on the surface to form a protective film Subsequently, a step of exposing the tip of the emitter from the resist by etching back after forming a resist on the entire surface, and a step of removing the protective film at the tip of the emitter. The method for producing a field emission cold cathode according to claim 2. 8. A display device using the field emission cold cathode according to claim 1. 9. A flat panel display using the field emission cold cathode according to claim 1. 10. A display cathode tube using the field emission cold cathode according to claim 1.