Etching a substrate: processes – Forming or treating an article whose final configuration has...
Reexamination Certificate
1999-12-13
2001-12-11
Mills, Gregory (Department: 1763)
Etching a substrate: processes
Forming or treating an article whose final configuration has...
C445S051000, C445S024000, C438S020000
Reexamination Certificate
active
06328904
ABSTRACT:
This application is based on Japanese Patent Application HEI 10-354850, filed on Dec. 14, 1998, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a manufacture method of a field emission element, and more particularly to a method of manufacturing a field emission element emitting electrons from a sharp tip of an emitter.
b) Description of the Related Art
A field emission element emits electrons from a sharp tip of an emitter by utilizing electric field concentration. For example, a flat panel display can be structured by using a field emitter array (FEA) having a number of emitters disposed in array. Each emitter controls the luminance of a corresponding pixel of the display.
In a field emission element, a gate electrode is configured near an emitter electrode. By applying positive potential to the gate electrode, the emitter electrode can emit electrons to an anode electrode.
Providing that an emitting current is same or increases, the field emission element is desired to have such properties as a decreased threshold voltage between the gate electrode and emitting electrode, fast drive and reduced power consumption. Consideration in choosing a structure and shape of the element is required to obtain those properties. In addition, for a steady and easy manufacture of such element, special consideration is necessary for the manufacturing process.
The shape of the emitter electrode especially influences on the above-listed properties. Most importantly, the emitter electrode should have a fine tip. By making an apex angle of the emitter electrode as small as possible, electric field at the tip will be strong enough to reduce the threshold voltage between the gate electrode and emitting electrode. Therefore, provided that the emitting current obtained is the same, it is possible to reduce the threshold voltage. Provided that the threshold voltage is the same, it is possible to obtain a larger emitting current by the same threshold voltage between the gate electrode and emitting electrode than using the emitter electrode with a larger apex angled tip. Therefore, it is important to utilize a manufacturing method that easily enables sharpening the tip of the emitting electrode.
Especially, as shown in
FIGS. 10A and 10B
, a composite-shaped emitter electrode, which has an outline composed of two parts of lines (straight lines as shown in
FIG. 10A
or curves as shown in FIG.
10
B), has a fine tip and good electrical properties. At meantime, the emitter electrode has a wide base, and so the casting of material for electrode to an emitter mold can be easily performed.
Some manufacturing methods of the composite-shaped emitter electrode have been provided conventionally.
For example, the assignee of this application discloses a manufacturing method of the emitter electrode in JP-A HEI 09-274846. The method includes steps of forming an overhung gate electrode, depositing a sacrificial film to an overhanging portion of the gate electrode by a deposition method having good step coverage, performing a wet oxidation process to the sacrificial film for volume expansion after diffusing impurities to a portion corresponding the tip of the emitter electrode. In the same processing time, a region with diffused impurities expands more likely than a region without diffused impurities. Therefore, the wet oxidation process of the sacrificial film will form an emitter electrode mold that has the composite-shaped cross-section including two different degrees of volume expansion.
Moreover, JP-A HEI 09-17335 discloses another manufacturing method of the composite-shaped emitter electrode. In the method, an emitter electrode is formed by following steps. At first, on a substrate having concaves is formed a gate oxide film having smaller openings than the concaves on the substrate. Then, an electrode material is deposited on the gate oxide film by sputtering to form gate electrodes on the gate oxide film and emitter electrodes on the concaves under the openings of the gate oxide film.
In the prior art, it is difficult to control over the oxidation process and film thickness of the gate film. Moreover, it is impossible to make an insulating film thick, and therefore, a distance between emitter gates will be too short causing low insulation-resistant, and fast drive is limited due to high capacitance.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a field emission element having an emitter electrode with a fine tip and method of manufacturing the field emission element.
According to one aspect of the present invention, there is provided a method of manufacturing a field emission element comprising the steps of forming, on a substrate, a base layer comprising a gate film formed of a conductive material which is capable of chemical reaction accompanying volume expansion, forming an insulating film on said base layer, forming a taper-shaped first hole in said insulating film, forming a second hole in said gate film by anisotropically etching said gate film using said insulating film as a mask, reacting a part of a surface layer of said gate film to form a volume-expanded film by chemical reaction, forming an emitter film made of an electrically conductive material on said insulating film and said expanded film, and exposing said emitter film and said gate film by removing unnecessary parts comprising said substrate and said expanded film.
Volume expansion of the gate film by the chemical reaction makes it possible to obtain the chemically reacted film that expands toward the center of the opening. A mold of an emitter electrode with a fine tip can be obtained by using the chemically reacted film. In addition, a step of diffusing impurities will not be required.
According to another aspect of the present invention, there is provided a field emission element comprising a gate electrode having a gate hole, and overhanging toward a center of the gate hole, an emitter electrode whose tip is extending near said gate hole, and an insulating film formed between said gate electrode and said emitter electrode.
Because the mold of the emitter electrode is formed by the volume expansion caused by the chemical reaction of the gate film on both or either of up and down side of which the insulating film or a reaction inhibitive film is deposited, a gorge formed by the expansion can be used as the mold of the fine tip of the emitter electrode.
Further, forming the emitter electrode into the composite-shape makes it easy to fill the material into the mold. A beak-shaped tip of the gate electrode formed by the chemical reaction prevents concentration of stress at the gate, and therefore, it can prevent generation of a short circuit or leak between the emitter and the gate.
REFERENCES:
patent: 5795208 (1998-08-01), Hattori
patent: 9-17335 (1997-01-01), None
patent: 9-274846 (1997-10-01), None
Hattori Atsuo
Iriguchi Chiharu
Hassanzadeh P.
Mills Gregory
Ostrolenk Faber Gerb & Soffen, LLP
Yamaha Corporation
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