Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material
Reexamination Certificate
1999-08-10
2001-10-23
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
C445S024000
Reexamination Certificate
active
06306740
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a filed emission element and more particularly to a field emission element having a field emission cathode whose tip emits electrons and its manufacture method.
b) Description of the Related Art
A field emission element emits electrons from a sharp tip of an emitter (field emission cathode) 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 on a substrate. Each emitter controls the luminance of a corresponding pixel of the display.
FIGS. 15A
to
15
F schematically illustrate a conventional method of manufacturing a field emission element.
As shown in
FIG. 15A
, a conductive gate electrode
62
is formed on a substrate
61
. For example, the conductive gate electrode
62
is made of polysilicon doped with impurities. On the conductive gate electrode
62
, a resist film
63
having a predetermined pattern is formed through photolithography.
Next, by using the resist pattern
63
as a mask, the gate electrode
62
is anisotropically etched to leave as shown in
FIG. 15B
a gate electrode
62
a
having a gate hole
67
having a circular flat shape (as viewed from the top). This etching thins the resist pattern
63
and a thin resist pattern
63
a
is left.
As shown in
FIG. 15C
, after the resist pattern
63
a
is removed, a sacrificial film
64
is isotropically deposited on the gate electrode
62
a
and on the exposed substrate
61
.
Next, as shown in
FIG. 15D
, the sacrificial film
64
is anisotropically etched to leave a sacrificial film (side spacer)
64
a
on the side wall of the gate hole
67
of the gate electrode
62
a.
Next, as shown in
FIG. 15E
, an insulating film
65
is formed on the whole upper surface of the substrate and a conductive emitter electrode
66
is formed on the insulating film
65
.
Next, as shown in
FIG. 15F
, the whole of the substrate
61
and side spacer
64
a
and part of the insulating film
65
are etched to leave a peripheral portion of the insulating film
65
a
between the gate electrode
62
a
and emitter electrode
66
.
As a positive potential is applied to the gate electrode to concentrate an electric field upon the tip of the emitter electrode (cathode)
66
, electrons can be emitted from the emitter electrode
66
toward an anode electrode (not shown).
FIG. 16
is a cross sectional view of a flat panel display using such field emission elements.
Each field emission element is manufactured by the above-described method, and has an emitter electrode
44
and a gate electrode
45
. Formed on a support substrate
41
made of insulating material are a wiring layer
42
made of Al, Cu, or the like and a resistor layer
43
made of polysilicon or the like. On the resistor layer
43
, a number of emitter electrodes
44
having a sharp tip are disposed to form a field emitter array (FEA). Each gate electrode
45
has a small opening (gate hole) near at the tip of each emitter electrode
44
and a voltage can be applied independently to each gate electrode although not specifically shown in
FIG. 16. A
plurality of emitter electrodes
44
can also be independently applied with a voltage.
Facing an electron source including the emitter electrode
44
and gate electrode
45
, an opposing substrate is disposed including a transparent substrate
46
made of glass, quartz, or the like. The opposing substrate has a transparent electrode (anode electrode)
47
made of ITO or the like disposed under the transparent electrode
46
and a fluorescent member
48
disposed under the transparent electrode
47
.
The electron source and opposing substrate are joined together via a spacer
50
made of a glass substrate and coated with adhesive, with the distance between the transparent electrode
47
and emitter electrode
44
being maintained about 0.1 to 5 mm. The adhesive may be low melting point glass.
Instead of the spacer
50
of a glass substrate, a spacer
50
made of adhesive such as epoxy resin with glass beads being dispersed therein may be used.
An air exhaust pipe
49
is coupled in advance to the opposing substrate. By using this air exhaust pipe
49
, the inside of the flat display panel is evacuated to about 1×10
−5
Torr to 1×10
−9
Torr (about 1×10
−5
×133.3 Pa to 1×10
−9
×133.3 Pa), and then the air exhaust pipe
49
is sealed by using a burner or the like. Thereafter, the anode electrode (transparent electrode)
47
, emitter electrode
44
, gate electrode
45
are wired to complete the flat panel display.
The anode electrode (transparent electrode)
47
is always maintained at a positive potential. Pixels are selected two-dimensionally by emitter wiring lines and gate wiring lines. Field emission elements are selected disposed at each cross point of voltage applied emitter and gate wiring lines.
The emitter electrode is applied with a negative potential and the gate electrode is applied with a positive potential. Electrons are emitted from the emitter electrode toward the anode electrode. When electrons are bombarded with the fluorescent member
48
, fluorescence is radiated from the bombarded area (pixel).
In order to maintain the inside of the flat panel display at a high vacuum degree, a getter member
51
is provided at the corner in the flat panel display. For example, the getter member
51
is made of Ti, Ta, Zr, Al, Mg, or the like. After the air exhaust pipe
49
is sealed, the getter member
51
is activated by heating it with a lamp or laser beam to adsorb ambient molecules therein. The initial vacuum degree in the flat panel display can therefore be improved.
Other molecules such as He passing through the transparent substrate
46
and support substrate
41
and entering the inside of the flat panel display or other molecules such as H
2
O, O
2
, and N
2
emitted in the flat panel display are also adsorbed by the getter member
51
. As a result, the vacuum degree in the flat panel display is prevented from being lowered and the flat panel display is prolonged its lifetime.
The getter member
51
is disposed at the corner in the flat panel display so as not to obstruct electrons to be emitted from the emitter electrode
44
toward the transparent electrode
47
. The getter member
51
is therefore placed at the position remote from the emitter electrodes
44
. As the getter member
51
is placed remotely from the emitter electrodes
44
, the function of the getter member
51
cannot be sufficiently demonstrated and the following disadvantages may occur.
(1) Molecules described above are attached to the surface of the emitter electrode
44
in a high electric field, before they are adsorbed by the getter member
51
. Radiation current (electron flow) from the emitter electrode
44
therefore reduces.
(2) As molecules attach to or emit from the surface of the emitter electrode
44
, a magnitude of the radiation current from the emitter electrode
44
fluctuates and becomes unstable.
(3) As the emitter electrode
44
is bombarded with ions, the emitter electrode
44
is sputtered and the tip of the emitter electrode
44
deforms. As the tip of the emitter electrode
44
is rounded, an electric field is hard to be concentrated and the performance of the field emission element is degraded.
(4) In order to maintain a high vacuum degree during the long span of one to ten years, a getter member
51
having a large area is required. As the large area getter member
51
is used, the flat panel display becomes large and the fluorescence radiation area (display area) becomes relatively small.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a field emission element and a manufacture method thereof capable of improving the vacuum degree in the flat panel display and preventing molecules from being attached to the emitter surface.
According to one aspect of the present invention, there is provided a method of manufacturing a field emission element incl
Nelms David
Ostrolenk Faber Gerb & Soffen, LLP
Vu David
Yamaha Corporation
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