Electric lamp and discharge devices – Discharge devices having a multipointed or serrated edge...
Reexamination Certificate
1997-11-28
2001-02-13
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Discharge devices having a multipointed or serrated edge...
C313S306000, C313S311000, C313S336000, C313S351000, C313S34600R, C313S495000, C313S496000, C313S497000
Reexamination Certificate
active
06188167
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to electron beam sources and more particularly to a micro-electron gun known also as micro-field emission gun and a fabrication process thereof.
2. Description of the Related Art
Micro-field emission guns have been studied originally in the purpose of breaking through the limit of operational speed of solid-state devices. In such a study, attempts have been made to fabricate integrated circuits of vacuum tubes by using the microfabrication technology developed in the art of semiconductor fabrication. Recently, however, intensive efforts are being made to construct a flat panel display by arranging such micro-field emission guns in a two-dimensional plane, such that an image is formed on a screen opposing such a field emitter array by the electron beams emitted from the micro-field emission guns forming the field emitter array. It should also be noted that such micro-field emission guns are advantageous in the point that one can produce a high energy electron beam without using bulky columns conventionally used for producing such a high energy electron beam. Thus, the possibility has now emerged to construct very compact electron microscopes or other analyzing tools that use such accelerated electron beams by using the micro-field emission guns.
FIG. 1
shows the construction of a conventional micro-field emission gun.
Referring to
FIG. 1
, the micro-field emission gun is constructed on a semiconductor substrate
11
such as Si and includes a sharply pointed conical emitter
12
, wherein the emitter
12
is surrounded by a gate electrode
13
. The gate electrode
13
induces an electric field between the gate electrode
13
and the emitter
12
such that the electrons are emitted from the emitter
12
as a result of field emission. The emitter
12
may have a diameter of 2 &mgr;m and is formed in a hole
14
a
that is formed in an insulation film
14
of SiO
2
or SiO covering the surface of the substrate
11
such that the hole
14
a
exposes the surface of the substrate
11
. Typically, a number of such
14
a
are formed in rows and columns in the insulation film
14
with a pitch of about 300 &mgr;m, and accordingly, the emitters
12
are also formed in rows and columns with a corresponding pitch of about 300 &mgr;m. In such a construction, a large electric field is induced in response to the control voltage applied to the gate electrode
13
, while such a large electric field causes a deformation in the surface potential barrier of the conductor material such as Si or W that forms the emitter
12
. Thereby, the electrons are emitted to the exterior of the emitter
12
by passing through the deformed surface potential barrier by tunneling effect. The structure shown in
FIG. 1
can be fabricated easily by the microfabrication technology used in the production of semiconductor devices.
FIGS. 2A-2D
show the fabrication process of the micro-field emission gun of FIG.
1
.
Referring to
FIGS. 2A-2D
, a mask pattern
12
a
of SiO
2
is provided in the step of
FIG. 2A
on a part of the silicon substrate
11
on which the emitter
12
is to be formed, and a reactive ion etching process (RIE) is conducted in the step of
FIG. 2B
upon the substrate
11
while using the pattern
12
a
as a mask. Thereby, the RIE process is set such that the etching proceeds obliquely to the surface of the substrate
11
, and one obtains a truncated-conical region
12
b
in correspondence to the mask
12
a.
Next, the surface of the substrate
11
is subjected to oxidation while leaving the mask
12
a
such that an oxide film
12
c
is formed on the inclined, conical surface of the region
12
b.
Further, an insulation layer
14
of SiO and a layer of Cr to be used for the gate electrode
13
, are deposited consecutively upon the silicon oxide film
12
c
on the substrate
11
. Thereby, one obtains a structure shown in FIG.
2
C.
Further, by removing the mask pattern
12
a,
a structure of
FIG. 2D
is obtained. In the structure of
FIG. 2D
, it should be noted that one can form a sharply pointed structure by removing the oxide film
12
c.
In the micro-field emission gun of the structure of
FIG. 1
or
FIG. 2D
, an acceleration voltage of several hundred volts is applied across the gate electrode
13
and the substrate
11
, and an electron beam of several hundred electron volts is obtained. On the other hand, this means that an acceleration voltage of several thousand kilovolts has to be applied across the substrate
11
and the gate electrode
13
in order to obtain an accelerated, high energy electron beam of several kilo-electron volts, which are required in electron microscopes or other various analyzing tools. As the insulation layer
14
has a thickness of about 1 &mgr;m or less, such an application of high acceleration voltage results in a formation of a very high electric field in the order of 10
9
V/m in the insulation layer
14
. Thereby, a leakage current of several micro-amperes cannot be avoided in the insulation layer
14
.
In order to reduce the level of the leakage current, it is necessary to increase the thickness of the insulation layer
14
to be larger than 10 &mgr;m, while the formation of such a thick insulation layer by means of conventionally used semiconductor fabrication processes such as CVD or sputtering is difficult. It is, of course, possible to bond a thick glass slab upon the gate electrode and provide an acceleration electrode upon such a glass slab by means of adhesives, while such a use of adhesives raises a problem in that the gas released from the adhesives may cause a contamination of the field emitter guns and hence undesirable deterioration of the emission characteristics thereof.
SUMMARY OF THE INVENTION
Accordingly, it is a general object of the present invention to provide a novel and useful micro-field emission gun and a fabrication process thereof wherein the foregoing problems are eliminated.
Another and more specific object of the present invention is to provide a micro-field emission gun having an acceleration electrode on a gate electrode with a separation therefrom, for producing a high energy electron beam, and a fabrication process thereof.
Another object of the present invention is to provide a method for fabricating a micro-field emission gun, the micro-field emission gun having an emitter provided on a substrate, an insulator layer surrounding said emitter, and a gate electrode provided on said insulator layer so as to surround said emitter, the micro-field emission gun thereby emitting an electron beam from said emitter in response to a control voltage applied to said gate electrode, the method comprising the steps of:
providing an insulator slab, formed with a penetrating hole acting as a passage of the electron beam, upon the gate electrode, such that the penetrating hole is aligned with the emitter of the field emission gun;
bonding the insulator slab upon the gate electrode by means of an anodic bonding process; and
providing an acceleration electrode on the insulator slab such that the acceleration electrode covers a surface of the insulator slab facing away from the gate electrode, except for a passage of the electron beam.
Another object of the present invention is to provide a micro-field emission gun, comprising:
a substrate;
an emitter provided on a surface of the substrate, said emitter emitting electrons in response to a gate electric field applied thereto;
a first insulation layer provided on the surface of the substrate, the first insulation layer carrying thereon a first penetrating hole in alignment with the emitter as a passage of the electrons;
a gate electrode layer provided on a surface of the first insulation layer, the gate electrode carrying thereon a first opening in alignment with the first penetrating hole and acting as a passage of the electrons, the gate electrode being applied with a gate voltage and creating the gate electric field in response thereto;
a second insulation layer provided on a surface of the gate electr
Endo Yasuhiro
Goto Shunji
Honjo Ichiro
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Haynes Mack
Patel Nimeshkumar D.
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