U.S. patent application number 09/131339 was filed with the patent office on 2001-11-15 for electron emission device and display device using the same.
Invention is credited to CHUMAN, TAKASHI, ITO, HIROSHI, IWASAKI, SHINGO, NEGISHI, NOBUYASU, OGASAWARA, KIYOHIDE, SAKEMURA, KAZUTO, YAMADA, TAKASHI, YANAGISAWA, SHUUICHI, YOSHIKAWA, TAKAMASA, YOSHIZAWA, ATSUSHI.
Application Number | 20010040430 09/131339 |
Document ID | / |
Family ID | 16667276 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010040430 |
Kind Code |
A1 |
ITO, HIROSHI ; et
al. |
November 15, 2001 |
ELECTRON EMISSION DEVICE AND DISPLAY DEVICE USING THE SAME
Abstract
An electron emission device exhibits a high electron emission
efficiency. The device includes an electron-supply layer of metal
or semiconductor, an insulator layer formed on the electron-supply
layer, and a thin-film metal electrode formed on the insulator
layer. The insulator layer has a film thickness of 50 nm or
greater. The electron-supply layer has a silicide layer. When an
electric field is applied between the electron-supply layer and the
thin-film metal electrode, the electron emission device emits
electrons.
Inventors: |
ITO, HIROSHI;
(TSURUGASHIMA-SHI, JP) ; OGASAWARA, KIYOHIDE;
(TSURUGASHIMA-SHI, JP) ; YOSHIKAWA, TAKAMASA;
(TSURUGASHIMA-SHI, JP) ; CHUMAN, TAKASHI;
(TSURUGASHIMA-SHI, JP) ; NEGISHI, NOBUYASU;
(TSURUGASHIMA-SHI, JP) ; IWASAKI, SHINGO;
(TSURUGASHIMA-SHI, JP) ; YOSHIZAWA, ATSUSHI;
(TSURUGASHIMA-SHI, JP) ; YAMADA, TAKASHI;
(TSURUGASHIMA-SHI, JP) ; YANAGISAWA, SHUUICHI;
(TSURUGASHIMA-SHI, JP) ; SAKEMURA, KAZUTO;
(TSURUGASHIMA-SHI, JP) |
Correspondence
Address: |
MORGAN LEWIS & BOCKIUS
1800 M STREET NW
WASHINGTON
DC
20036
|
Family ID: |
16667276 |
Appl. No.: |
09/131339 |
Filed: |
August 7, 1998 |
Current U.S.
Class: |
313/496 ;
313/310; 313/495 |
Current CPC
Class: |
H01J 1/312 20130101;
B82Y 10/00 20130101 |
Class at
Publication: |
313/496 ;
313/310; 313/495 |
International
Class: |
H01J 001/62; H01J
063/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 8, 1997 |
JP |
9-215134 |
Claims
What is claimed is:
1. An electron emission device comprising: an electron-supply layer
made of metal or semiconductor; an insulator layer formed on the
electron-supply layer; and a thin-film metal electrode formed on
the insulator layer and facing a vacuum space, characterized in
that said insulator layer has a film thickness of 50 nm or greater,
and said electron-supply layer has a silicide layer, whereby the
electron emission device emits electrons when an electric field is
applied between the electron-supply layer and the thin-film
metal.
2. An electron emission device according to claim 1, wherein said
electron-supply layer is disposed on an ohmic electrode and said
silicide layer is disposed at an interface between the ohmic
electrode and said electron-supply layer.
3. An electron emission device according to claim 1, wherein said
silicide layer is disposed at an interface between the insulator
layer and said electron-supply layer.
4. An electron emission device according to claim 1, wherein said
silicide layer is disposed at an mediate region of said
electron-supply layer.
5. An electron emission device according to claim 1, wherein a
plurality of said silicide layer and said electron-supply layer are
alternately layered by in the thickness direction.
6. An electron emission device according to claim 5, wherein a
plurality of said layered silicide layers have thicknesses
gradually descended in the thickness direction.
7. An electron emission device according to claim 5, wherein a
plurality of said layered silicide layers have thicknesses
gradually ascended in the thickness direction.
8. An electron emission display device comprises: a pair of first
and second substrates facing each other with a vacuum space in
between; a plurality of electron emission devices provided on the
first substrate: a collector electrode provided in the second
substrate; and a fluorescent layer formed on the collector
electrode, each of the electron emission devices comprising an
electron-supply layer of metal or semiconductor; an insulator layer
formed on the electron-supply layer; and a thin-film metal
electrode formed on the insulator layer and facing a vacuum space,
wherein said insulator layer has a film thickness of 50 nm or
greater, and said electron-supply layer has a silicide layer.
9. An electron emission display device according to claim 8,
wherein said electron-supply layer is disposed on an ohmic
electrode and said silicide layer is disposed at an interface
between the ohmic electrode and said electron-supply layer.
10. An electron emission display device according to claim 8,
wherein said silicide layer is disposed at an interface between the
insulator layer and said electron-supply layer.
11. An electron emission display device according to claim 8,
wherein said silicide layer is disposed at an mediate region of
said electron-supply layer.
12. An electron emission display device according to claim 8,
wherein a plurality of said silicide layer and said electron-supply
layer are alternately layered by in the thickness direction.
13. An electron emission display device according to claim 12,
wherein a plurality of said layered silicide layers have
thicknesses gradually descended in the thickness direction.
14. An electron emission display device according to claim 12,
wherein a plurality of said layered silicide layers have
thicknesses gradually ascended in the thickness direction.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electron emission device
and an electron emission display device using the same.
[0003] 2. Description of the Related Art
[0004] In field electron emission display apparatuses, a Field
Emission Display (FED) is known as a planar emission display device
equipped with an array of cold-cathode electron emission source
which does not require cathode heating. The emission principle of,
for example, an FED using Spindt-type cold cathodes of minute
protrusions is as follows: Its emission principle is like a Cathode
Ray Tube (CRT), although this FED has a cathode array of
Spindt-type protrusions which is different from that of CRT. In the
FED, electrons are drawn into a vacuum space by means of each gate
electrode spaced apart from the Spindt-type cathode, and the
electrons are made to impinge upon the fluorescent substance that
is coated on a transparent anode, thereby causing light
emission.
[0005] This FED, however, has a problem of low production yield
because the manufacture of the minute Spindt-type emitter arrays as
a cold cathode is complex and involves many processes.
[0006] There also exists an electron emission device with a
metal-insulator-metal (MIM) structure as a planar electron emission
source. The electron emission device with the MIM structure
comprises an Al underlayer as a base electrode, an Al.sub.2O.sub.3
insulator layer with about 10 nm thickness, and an Au overlayer, as
a top electrode with about 10 nm thickness which are formed in
order on the substrate. In the case that this MIM device is placed
under an opposing electrode in a vacuum, when a voltage is applied
between the Al underlayer and the Au overlayer and, at the same
time, an acceleration voltage is applied to the opposing electrode,
then some of electrons emit out of the Au overlayer and reach the
opposing electrode. Even the electron emission device with the MIM
structure does not yet provide a sufficient amount of emitted
electrons.
[0007] To improve these disadvantages of emission of the MIM
device, it is conventionally considered that there is a necessity
to make the Al.sub.2O.sub.3 insulator layer thinner by about
several nanometers and make the Al.sub.2O.sub.3 insulator layer
with a uniform quality so that the interface between the
Al.sub.2O.sub.3 insulator layer and the Au overlayer is more
uniform.
[0008] To provide a thinner and more uniform insulator layer, for
example, an attempt has been made to control the anodized current
by using an anodization method thereby to improve the electron
emission characteristics, as in the invention described in Japanese
Patent Application kokai No. Hei 7-65710.
[0009] However, even an electron emission device with the MIM
structure which is manufactured by this anodization method ensures
an emission current of about 1.times.10.sup.-5 A/cm.sup.2 and an
electron emission efficiency of about 1.times.10.sup.-3.
OBJECTS AND SUMMARY OF THE INVENTION
[0010] Accordingly, it is an object of the present invention to
provide an electron emission device with a high electron emission
efficiency capable of stably emitting electrons with a low applied
voltage thereto and an electron emission display apparatus using
the same.
[0011] In consideration to a universal application of this electron
emission device, the usage of silicon (Si) for an electron-supply
layer in the electron emission device is effective to improve the
stability of electron emission in the device and also the use of an
amorphous silicon (a-Si) layer deposited by a sputtering method is
effective in a high productivity and therefore is very useful.
Since the heat treatment is necessary for vacuum-packaging of the
device, the device suffers from the inevitable radiant heat
occurred during vacuum sealing. However there is a problem that the
property of the a-Si layer is apt to deteriorate due to a heat
treatment thereto, because an alloy layer are generated at the
interface between e.g., an Al ohmic electrode and a Si
electron-supply layer by the diffusion thereof. The alloy layer may
alter the internal stress and electric resistance value of the
electron emission device display, so that durability of the device
becomes poor because its electric properties such as electron
emission efficiency and negative resistance are changed as well as
its mechanical properties. Accordingly, it is another object of the
present invention to provide an electron emission device with a
high stability at a high temperature and an electron emission
display apparatus using the same.
[0012] In order to overcome the foregoing and other problems, the
object of the invention are realized by an electron emission device
in accordance with embodiments of this invention, wherein the
device according to the invention comprises:
[0013] an electron-supply layer made of metal or semiconductor
disposed on an ohmic electrode;
[0014] an insulator layer formed on the electron-supply layer;
and
[0015] a thin-film metal electrode formed on the insulator layer
and facing a vacuum space,
[0016] characterized in that said insulator layer has a film
thickness of 50 nm or greater, and said electron-supply layer has a
silicide layer, whereby the electron emission device emits
electrons when an electric field is applied between the
electron-supply layer and the thin-film metal.
[0017] In the electron emission device according to the invention,
said electron-supply layer is disposed on an ohmic electrode and
said silicide layer is disposed at an interface between the ohmic
electrode and said electron-supply layer.
[0018] In the electron emission device according to the invention,
said silicide layer is disposed at an interface between the
insulator layer and said electron-supply layer.
[0019] In the electron emission device according to the invention,
said silicide layer is disposed at an mediate region of said
electron-supply layer.
[0020] In the electron emission device according to the invention,
a plurality of said silicide layer and said electron-supply layer
are alternately layered by in the thickness direction.
[0021] In the electron emission device according to the invention,
a plurality of said layered silicide layers have thicknesses
gradually descended in the thickness direction.
[0022] In the electron emission device according to the invention,
a plurality of said layered silicide layers have thicknesses
gradually ascended in the thickness direction.
[0023] Moreover a display device using an electron emission device
according to the invention comprises:
[0024] a pair of first and second substrates facing each other with
a vacuum space in between:
[0025] a plurality of electron emission devices provided on the
first substrate:
[0026] a collector electrode provided in the second substrate;
and
[0027] a fluorescent layer formed on the collector electrode,
[0028] each of the electron emission devices comprising an
electron-supply layer of metal or semiconductor; an insulator layer
formed on the electron-supply layer; and a thin-film metal
electrode formed on the insulator layer and facing a vacuum space,
wherein said insulator layer has a film thickness of 50 nm or
greater, and said electron-supply layer has a silicide layer.
[0029] In the electron emission display device according to the
invention, said electron-supply layer is disposed on an ohmic
electrode and said silicide layer is disposed at an interface
and/or between the ohmic electrode and said electron-supply
layer.
[0030] In the electron emission display device according to the
Invention, said silicide layer is disposed at an interface and/or
between the insulator layer and said electron-supply layer.
[0031] In the electron emission display device according to the
invention, said silicide layer is disposed at an mediate region of
said electron-supply layer.
[0032] In the electron emission display device according to the
invention, a plurality of said silicide layer and said
electron-supply layer are alternately layered by in the thickness
direction.
[0033] In the electron emission display device according to the
invention, a plurality of said layered silicide layers have
thicknesses gradually descended in the thickness direction.
[0034] In the electron emission display device according to the
invention, a plurality of said layered silicide layers have
thicknesses gradually ascended in the thickness direction.
[0035] According to the electron emission device of the invention
with the above structure, the thermal stability of the device is
improved since the silicide layer has a thermal stability in the
device. In applications of a display device based on the electron
emission device, there is obtained a stable high luminance electron
emission display durable against the vacuum-packaging Moreover,
through-bores are not likely to be produced in the insulator layer
because of its relatively thick thickness and therefore its
production yield is improved.
[0036] The electron emission device of the invention is a planar or
spot-like electron emission diode and can be adapted to high speed
devices such as a source of a pixel vacuum tube or bulb, an
electron emission source of a scanning or transmission electron
microscope, a vacuum-micro electronics device and the like. In
addition, this electron emission device can serve as a minute
microwave tube or a diode which emits electromagnetic waves with
millimeter or sub-millimeter wavelength, and also can serve as a
high speed switching device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is a schematic cross-sectional view of an electron
emission device according to the invention;
[0038] FIG. 2 is a partially enlarged cross-sectional view showing
an electron emission device of an embodiment according to the
invention showing an adjacent region of the silicide layer;
[0039] FIG. 3 is a graph showing a relationship between the
emission current of the electron emission device with the layer
{W.sub.0.35Si.sub.0.65(3 )/Si(6 nm)}.sub.2 and the temperatures at
which the devices are baked or heated in the process for
manufacturing the electron emission display device according to the
invention;
[0040] FIG. 4 is a graph showing a relationship between the
electron emission efficiency of the electron emission device and
the temperatures at which the devices are baked or heated in the
process for manufacturing the electron emission display device
according to the invention:
[0041] FIG. 5 is a graph illustrating a dependency of the emission
current on the film thickness of an insulator layer in an electron
emission device embodying the invention;
[0042] FIG. 6 is a graph showing a dependency of the electron
emission efficiency on the film thickness of the insulator layer in
the electron emission device embodying the invention;
[0043] FIG. 7 is a graph showing a relationship between the
emission current of the electron emission device with the layer
{W(3 nm)/Si(5 nm)}.sub.2 and the temperatures at which the devices
are baked or heated in the process for manufacturing the electron
emission display device according to the invention;
[0044] FIG. 8 is a graph showing a relationship between the
electron emission efficiency of the electron emission device and
the temperatures at which the devices are baked or heated in the
process for manufacturing the electron emission display device
according to the invention;
[0045] FIG. 9 is a graph illustrating a dependency of the emission
current on the film thickness of an insulator layer in an electron
emission device embodying the invention;
[0046] FIG. 10 is a graph showing a dependency of the electron
emission efficiency on the film thickness of the insulator layer in
the electron emission device embodying the invention;
[0047] FIGS. 11 to 15 are partially enlarged cross-sectional views
each showing an electron emission device of another embodiment
according to the invention showing an adjacent region of the
silicide layer; and
[0048] FIG. 16 is a schematic perspective view showing an electron
emission display device according to one embodiment of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0049] Preferred embodiments according to the present invention
will be described in more detail with reference to the accompanying
drawings.
[0050] As shown in FIG. 1, an electron emission device embodying
the invention has an electron-supply layer 12 of silicon (Si), an
insulator layer 13 of silicon dioxide (SiO.sub.2) and a thin-film
metal electrode 15 of gold (Au) facing a vacuum space which are
layered or deposited in turn on an electrode surface of a device
substrate 10 of glass on which an ohmic electrode 11 of tungsten
(W) is previously formed. Particularly, in the electron-supply
layer 12, a silicide layer 14 is disposed at an mediate region
thereof, which is a thermally stable intermetallic compound. The
insulator layer 13 is deposited in relatively thicker thicknesses
so as to have a thickness of 50 nm or greater. A second substrate 1
is fixed to the first substrate 10 so as to sandwich a vacuum space
therebetween. Ceramics such as Al.sub.2O.sub.3, Si.sub.3N.sub.4 and
BN etc. may be used for the material of the device substrate 10
instead of glass.
[0051] This electron emission device can be regarded as a diode of
which the thin-film metal electrode 15 at its surface is connected
to a positive applied voltage Vd and the back i.e., ohmic electrode
11 is connected to a ground potential. When the voltage Vd e.g. 90V
is applied between the ohmic electrode 11 and the thin-film metal
electrode 15 to supply electrons into the electron-supply layer 12,
a diode current Id flows. Since the insulator layer 13 has a high
resistance, most of the applied electric field is applied to the
insulator layer 13. The electrons travel In the conduction band in
the insulator layer 13 toward the thin-film metal electrode 15.
Some of the electrons that reach near the thin-film metal electrode
15 tunnel through the thin-film metal electrode 15, due to the
strong electric field, to be emitted out into the vacuum space.
[0052] The electrons e (emission current Ie) discharged from the
thin-film metal electrode 15 by the tunnel effect are soon
accelerated by a high voltage Vc, which is applied to an opposing
collector electrode (transparent electrode) 2, and is collected at
the collector electrode 2. If a fluorescent substance is coated on
the collector electrode 2, corresponding visible light is
observed.
[0053] The silicide layer 14 is deposited as a thin film and made
by alloying of a semiconductor Si with a transition metal such as
W, Mo, Ti, Cr, V, Co, Fe, Ta, Nb, Hf, Zr, Mn, Re, Ru, Os, Rh, Ir,
Ni, Pd, and Pt and disposed at an mediate region of the
electron-supply layer 12. Instead of the mediate, the silicide
layer 14 may be formed at least one of interfaces both between the
insulator layer 13 and the electron-supply layer 12 and between the
ohmic electrode 11 and the electron-supply layer 12. The silicide
layer 14 may be formed with an artificial layered structure, e.g.,
W/Si layer. In addition to a single layer structure of silicide,
plural silicide layers 14 may be formed as a superlattice
consisting of metal and Si atoms or a multilayer structure.
Moreover the film thickness of these structures of the single
layer, superlattice and multilayer is ranging from several
nano-meters to tens nano-meters.
[0054] Silicon oxide SiO.sub.x (wherein subscribed x represents an
atomic ratio) is effective as the dielectric material of the
insulator layer 13 and, metal oxides or metal nitrides such as
LiO.sub.x, LiN.sub.x, NaO.sub.x, KO.sub.x, RbO.sub.x, CsO.sub.x,
BeO.sub.x, MgO.sub.x, MgN.sub.x, CaO.sub.x, CaN.sub.x, SrO.sub.x,
BaO.sub.x, ScO.sub.x, YO.sub.x, YN.sub.x, LaO.sub.x, LaN.sub.x,
CeO.sub.x, PrO.sub.x, NdO.sub.x, SmO.sub.x, EuO.sub.x, GdO.sub.x,
TbO.sub.x, DyO.sub.x, HoO.sub.x, ErO.sub.x, TmO.sub.x, YbO.sub.x,
LuO.sub.x, TiO.sub.x, TiN.sub.x, ZrO.sub.x, ZrN.sub.x, HfO.sub.x,
HfN.sub.x, ThO.sub.x, VO.sub.x, VN.sub.x, NbO.sub.x, TaO.sub.x,
TaN.sub.x, CrO.sub.x, CrN.sub.x, MoO.sub.x, MoN.sub.x, WO.sub.x,
WN.sub.x, MnO.sub.x, ReO.sub.x, FeO.sub.x, FeN.sub.x, RuO.sub.x,
OsO.sub.x, CoO.sub.x, RhO.sub.x, IrO.sub.x, NiO.sub.x, PdO.sub.x,
PtO.sub.x, CuO.sub.x, CuN.sub.x, AgO.sub.x, AuO.sub.x, ZnO.sub.x,
CdO.sub.x, HgO.sub.x, BO.sub.x, BN.sub.x, AlO.sub.x, AlN.sub.x,
GaO.sub.x, GaN.sub.x, InO.sub.x, SiN.sub.x, GeO.sub.x, SnO.sub.x,
PbO.sub.x, PO.sub.x, PN.sub.x, AsO.sub.x, SbO.sub.x, SeO.sub.x,
TeO.sub.x and the like can be used as well. Furthermore, metal
complex oxides such LiAlO.sub.2, Li.sub.2SiO.sub.3,
Li.sub.2TiO.sub.3, Na.sub.2Al.sub.22O.sub.34, NaFeO.sub.2,
Na.sub.4SiO.sub.4, K.sub.2SiO.sub.3, K.sub.2TiO.sub.3,
K.sub.2WO.sub.4, Rb.sub.2CrO.sub.4, Cs.sub.2CrO.sub.4,
MgAl.sub.2O.sub.4, MgFe.sub.2O.sub.4, MgTiO.sub.3, CaTiO.sub.3,
CaWO.sub.4, CaZrO.sub.3, SrFe.sub.12O.sub.19, SrTiO.sub.3,
SrZrO.sub.3, BaAl.sub.2O.sub.4, BaFe.sub.12O.sub.19, BaTiO.sub.3,
Y.sub.3Al.sub.5O.sub.12, Y.sub.3Fe.sub.5O.sub.12, LaFeO.sub.3,
La.sub.3Fe.sub.5O.sub.12, La.sub.2Ti.sub.2O.sub.7, CeSnO.sub.4,
CeTiO.sub.4, Sm.sub.3Fe.sub.5O.sub.12, EuFeO.sub.3,
Eu.sub.3Fe.sub.5O.sub.12, GdFeO.sub.3, Gd.sub.3Fe.sub.5O.sub.12,
DyFeO.sub.3, Dy.sub.3Fe.sub.5O.sub.12, HoFeO.sub.3,
Ho.sub.3Fe.sub.5O.sub.12, ErFeO.sub.3, Er.sub.3Fe.sub.5O.sub.12,
Tm.sub.3Fe.sub.5O.sub.12, LuFeO.sub.3, Lu.sub.3Fe.sub.5O.sub.12,
NiTiO.sub.3, Al.sub.2TiO.sub.3, FeTiO.sub.3, BaZrO.sub.3,
LiZrO.sub.3, MgZrO.sub.3, HfTiO.sub.4, NH.sub.4VO.sub.3,
AgVO.sub.3, LiVO.sub.3, BaNb.sub.2O.sub.6, NaNbO.sub.3,
SrNb.sub.2O.sub.6, KTaO.sub.3, NaTaO.sub.3, SrTa.sub.2O.sub.6,
CuCr.sub.2O.sub.4, Ag.sub.2CrO.sub.4, BaCrO.sub.4,
K.sub.2MoO.sub.4, Na.sub.2MoO.sub.4, NiMoO.sub.4, BaWO.sub.4,
Na.sub.2WO.sub.4, SrWO.sub.4, MnCr.sub.2O.sub.4, MnFe.sub.2O.sub.4,
MnTiO.sub.3, MnWO.sub.4, CoFe.sub.2O.sub.4, ZnFe.sub.2O.sub.4,
FeWO.sub.4, CoMoO.sub.4, CoTiO.sub.3, CoWO.sub.4,
NiFe.sub.2O.sub.4, NiWO.sub.4, CuFe.sub.2O.sub.4, CuMoO.sub.4,
CuTiO.sub.3, CuWO.sub.4, Ag.sub.2MoO.sub.4, Ag.sub.2WO.sub.4,
ZnAl.sub.2O.sub.4, ZnMoO.sub.4, ZnWO.sub.4, CdSnO.sub.3,
CdTiO.sub.3, CdMoO.sub.4, CdWO.sub.4, NaAlO.sub.2,
MgAl.sub.2O.sub.4, SrAl.sub.2O.sub.4, Gd.sub.3Ga.sub.5O.sub.12,
InFeO.sub.3, MgIn.sub.2O.sub.4, Al.sub.2TiO.sub.5, FeTiO.sub.3,
MgTiO.sub.3, NaSiO.sub.3, CaSiO.sub.3, ZrSiO.sub.4,
K.sub.2GeO.sub.3, Li.sub.2GeO.sub.3, Na.sub.2GeO.sub.3,
Bi.sub.2Sn.sub.3O.sub.3, MgSnO.sub.3, SrSnO.sub.3, PbSiO.sub.3,
PbMoO.sub.4, PbTiO.sub.3, SnO.sub.2-Sb.sub.2O.sub.3, CuSeO.sub.4,
Na.sub.2SeO.sub.3, ZnSeO.sub.3, K.sub.2TeO.sub.3, K.sub.2TeO.sub.4,
Na.sub.2TeO.sub.3, Na.sub.2TeO.sub.4 and the like can be used as
well and still furthermore. sulfides such as FeS, Al.sub.2S.sub.3,
MgS, ZnS and the like, fluorides such as LiF, MgF.sub.2, SmF.sub.3
and the like, chlorides such as HgCl, FeCl.sub.2, CrCl.sub.3 and
the like, bromides such as AgBr, CuBr, MnBr.sub.2 and the like,
iodide such as PbI.sub.2, CuI, FeI.sub.2 and the like and metal
oxidized nitrides such as SiAlON and the like can be used as well
for the insulator layer.
[0055] Moreover, carbon such as diamond, Fullerene (C.sub.2n) and
the like or metal carbide such as Al.sub.4C.sub.3, B.sub.4C,
CaC.sub.2, Cr.sub.3C.sub.2, Mo.sub.2C, MoC, NbC, SiC, TaC, TiC, VC,
W.sub.2C, WC, ZrC and the like are also effective as the dielectric
material of the insulator layer 13. Fullerene (C.sub.2n) consists
of carbon atoms. The representative C.sub.60 is a spherical surface
basket molecule as known a soccer ball molecule. There is also
known C.sub.32 to C.sub.960 and the like. The subscribed x in
O.sub.x, N.sub.x and the like in the above chemical formulas
represent atomic ratios and also herein after.
[0056] The film thickness of the insulator layer 13 may be 50 nm or
greater preferably in ranging from 100 to 1000 nm.
[0057] While Si is particularly effective as a material for the
electron-supply layer 12 of the electron emission device, an
elemental semiconductor or a compound semiconductor of an element
of a group IV, a group III-V, a group II-VI or the like, such as a
germanium (Ge), germanium silicon compound (Ge-Si), silicon carbide
(SiC), gallium arsenide (GaAs), indium phosphide (InP), or cadmium
selenide (CdSe) or CuInTe.sub.2 can be used as well.
[0058] While metals such as Al, Au, Ag and Cu are effective as the
electron supplying material, Sc, Ti, V, Cr, Mn. Fe, Co, Ni, Zn, Ga,
Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Cd, Ln, Sn, Ta, W, Re, Os, Ir, Pt,
Tl, Pb, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu
and the like can be used as well.
[0059] Metals Pt, Au, W, Ru and Ir are effective as the material
for the thin-film metal electrode 15 on the electron emission side.
In addition, Al, Sc, Ti, V, Cr. Mn, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr,
Nb, Mo, Tc, Rh, Pd, Ag, Cd, Ln, Sn, Ta, Re, Os, Ti, Pb, La, Ce. Pr,
Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and the like can be
used as well for the thin-film metal electrode.
[0060] Although sputtering is particularly effective in the
fabrication of those layers and the substrate, vacuum deposition,
CVD (Chemical Vapor Deposition), laser ablation, MBE (Molecular
Beam Epitaxy) and ion beam sputtering are also effective.
[0061] Electron emission devices according to the invention
comprising electron-supply layers each having a silicide layer were
fabricated as first embodiments and their characteristics were
examined concretely.
[0062] First, as shown in FIG. 2, an electron-supply layer 12 of
2.5 .mu.m thick Si was deposited by sputtering, on an electrode
surface 11 of each device substrate of glass on which an ohmic
electrode 11 of 300 nm thick W was previously deposited by
sputtering. A plurality of preliminary substrates of this type were
similarly prepared.
[0063] Next a W/Si silicide layer 14 ranging from
W.sub.0.35Si.sub.0.65 to WSi.sub.2 was deposited with thick of 3 nm
on each Si electron-supply layer 12 and then a 6 nm thick Si layer
12a was deposited on this W/Si silicide layer 14 per one
preliminary substrate. A set lamination of the suicide layer 14 and
the Si layer 12a is referred as {W.sub.0.35Si.sub.0.65(3 nm)/Si(6
nm)} implying {silicide (thickness)/silicon(thickness)}
hereinafter.
[0064] Then {W.sub.0.35Si.sub.0.65(3 nm)/Si(6 nm)} were deposited
again on the Si layer 12a. The two sets of lamination of
{W.sub.0.35Si.sub.0.65(3 nm)/Si(6 nm)} of the silicide layer 14 and
the Si layer 12a are referred as {W.sub.0.35Si.sub.0.65(3 nm)/Si(6
nm)}.sub.2 implying {silicide (thickness)/ silicon(thickness)} the
set number subscribed hereinafter.
[0065] After that, an electron-supply layer 12 of 2.5 .mu.m thick
Si was deposited again on the Si layer 12a. Subsequently, an
insulator layer 13 of 400 nm thick SiO.sub.x was deposited on the
electron-supply layer per one of the preliminary substrates. In
this way, the first embodiments of the devices were manufactured in
which a multilayer of silicide 14 was sandwiched by the two
equivalent thickness electron-supply layers 12. In addition, the
comparative electron emission devices were prepared in the same
manner as the first embodiments excepting that an electron-supply
layer 12 with thick of 5 .mu.m was deposited without any multilayer
of silicide per one of the comparative devices. Thus a plurality of
second preliminary substrates were provided. Each layer was
deposited by sputtering by using a gas of Ar, Kr or Xe or a mixture
thereof, or a gas mixture essentially consisting of one of those
rare gases with O.sub.2, N.sub.2 or the like mixed therein, under
the sputtering conditions of a gas pressure of 0.1 to 100 mTorr,
preferably 0.1 to 20 mTorr and the depositing rate of 0.1 to 1000
nm/min, preferably 0.5 to 100 nm/min.
[0066] Finally, a thin-film metal electrode of Pt was deposited
with thick of 10 nm on the surface of the amorphous SiO.sub.x layer
of each substrate by sputtering, thus providing plural device
substrates.
[0067] Meanwhile, transparent substrates were prepared, each of
which has an ITO collector electrode formed inside a transparent
glass substrate and has a fluorescent layer of a fluorescent
substance corresponding to R, G or B color emission formed on the
collector electrode by the normal scheme.
[0068] Electron emission devices of the first embodiments were
assembled in each of which the device substrate and the transparent
substrate are supported apart from one another by 10 mm in parallel
by a spacer in such a way that the thin-film metal electrode 15
faced the collector electrode 2, with the clearance therebetween
made to a vacuum of 10.sup.-7 Torr or 10-5 Pa.
[0069] Next, the resultant electron emission devices were heated or
baked at temperatures of 25.degree. C., 100.degree. C., 200.degree.
C., 300.degree. C., 400.degree. C., 500.degree. C., 600.degree. C.,
700.degree. C., 800.degree. C., 900.degree. C., and 100.degree. C.
in a vacuum atmosphere for one hour respectively.
[0070] Then, the diode current Id and the emission current Ie of
the heated and cooled plural devices corresponding to the baked
temperatures were measured while an applied voltage Vd of 0 to 200
V was applied to the prepared electron emission devices. The
results are shown in FIGS. 3 and 4.
[0071] FIGS. 3 and 4 show the variations of the emission current Ie
and the maximum electron emission efficiency (Ie/Id) respectively
with respect to the temperatures at which the devices were baked or
heated in the manufacturing process. In FIGS. 3 and 4, plots of
.circle-solid. represent the emission current values and the
electron emission efficiencies of the first embodiment devices
having {W.sub.0.35Si.sub.0.65(3 nm)/Si(6 nm)}.sub.2. The reductions
of emission current and emission efficiency of the first embodiment
devices are smaller than those the comparative devices represented
by plots of .largecircle.. In the comparative devices, the emission
current and emission efficiency thereof rapidly decrease as the
baked temperature rises. The first embodiment devices keep the
electron emission efficiency of 1.times.10.sup.-6 or more even
after the heating treatment of the 25.degree. C. to 1000.degree. C.
temperature.
[0072] Next, the second embodiments of electron emission devices
each having a {W.sub.0.35Si.sub.0.65(3 nm)/Si(6 nm)}.sub.2 were
deposited in the same manner as the first embodiments excepting
that an insulator layer 13 of SiO.sub.x was deposited while
changing the film thickness thereof in a range from 50 nm to 1000
nm.
[0073] Then, the electron emission devices of the second
embodiments were heated or baked at temperatures of 500.degree. C.
in a vacuum atmosphere for one hour respectively. Several devices
was remained as comparative devices without heated.
[0074] After that, the diode current Id and the emission current Ie
in the heated and cooled plural devices were measured
correspondingly to the thicknesses of insulator layer, when a
driving voltage Vd of 0 to 200 V was applied to the prepared
electron emission devices. The results are shown in FIGS. 5 and
6.
[0075] FIGS. 5 and 6 show the variations of the maximum emission
current Ie and the maximum electron emission efficiency (Ie/Id)
respectively with respect to the film thickness of the insulator
layer of the devices. As apparent from Figures, the variations of
the emission current Ie and the electron emission efficiency
(Ie/Id) of the devices with a {W.sub.0.35Si.sub.0.65(3 nm)/Si(6
nm)}.sub.2 have a similar electrical properties to those of the
comparative devices as far as the devices each comprising the
insulator layer having thickness of 300 nm, 400 nm, and 550 nm
respectively, even after the heating treatment of the 500.degree.
C. temperature. Particularly, there is little variation in the
electron emission efficiency in both kinds devices. It is
understood from those results that by applying a voltage of 200 V
or lower, the emission current of 1.times.10.sup.-6 A/cm.sup.2 or
greater can be acquired from an electron emission device which has
a insulator layer with a 50 nm thickness or greater, preferably 50
to 1000 nm in thickness.
[0076] Next, the third embodiments of electron emission devices
each having a {W(3 nm)/Si(5 nm)}.sub.2 were fabricated in the same
manner as the first embodiments excepting that, instead of a
W.sub.0.35Si.sub.0.65 silicide layer 14, a tungsten metal layer 14B
was formed for an artificial lattice as a whole.
[0077] Then, the electron emission devices of the third embodiments
were heated or baked at the same temperature range as the first
embodiments in a vacuum atmosphere for one hour respectively.
[0078] After that, the diode current Id and the emission current Ie
of the heated and cooled plural devices were measured
correspondingly to the heating temperatures, when a driving voltage
Vd of 0 to 200 V was applied to the prepared electron emission
devices. The results are shown in FIGS. 7 and 8 illustrating the
variations of the emission current Ie and the maximum electron
emission efficiency (Ie/Id) respectively with respect to the
temperatures at which the devices were baked or heated in the
manufacturing process. As seen from Figures, the reductions of
emission current and emission efficiency plotted by .circle-solid.
of the third embodiment devices with {W(3 nm)/Si(5 nm)}.sub.2 are
smaller than those the comparative devices represented by plots of
.largecircle.. The third embodiment devices keep the electron
emission efficiency values of 1.times.10.sup.-6 or more even after
the heating treatment of the 25.degree. C. to 1000.degree. C.
temperature.
[0079] Furthermore, the fourth embodiments of electron emission
devices each having a {W(3 nm)/Si(5 nm)}.sub.2 were formed in the
same manner as the first embodiments excepting that, a tungsten
metal layer 14B was formed for an artificial lattice as a whole
instead of a W.sub.0.35Si.sub.0.65 silicide layer 14 and that an
insulator layer 13 of SiO.sub.x was deposited while changing the
film thickness thereof in a range from 50 nm to 1000 nm.
[0080] Then, the electron emission devices of the fourth
embodiments were heated or baked at temperatures of 500.degree. C.
in a vacuum atmosphere for one hour respectively. Several devices
was remained as comparative devices without heated.
[0081] After that, the diode current Id and the emission current Ie
of the heated and cooled plural devices were measured
correspondingly to the thicknesses of insulator layer, when a
driving voltage Vd of 0 to 200 V was applied to the prepared
electron emission devices. The results are shown in FIGS. 9 and
10.
[0082] FIGS. 9 and 10 show the variations of the maximum emission
current Ie and the maximum electron emission efficiency (Ie/Id)
respectively with respect to the film thickness of the insulator
layer of the devices. As apparent from Figures, the variations of
the emission current Ie and the electron emission efficiency
(Ie/Id) of the devices having a {W(3 nm)/Si(5 nm)}.sub.2 have a
similar electrical properties to those of the comparative devices
as far as the devices each comprising the insulator layer having
thickness of 300 nm, 400 nm, and 550 nm respectively, even after
the heating treatment of the 500.degree. C. temperature.
Particularly, there is little variation in the electron emission
efficiency in both kinds devices. It is understood from those
results that by applying a voltage of 200 V or lower, the electron
emission efficiency of 1.times.10.sup.-3 or greater can be acquired
from an electron emission device which has a insulator layer with a
50 nm thickness or greater, preferably 50 to 1000 nm in
thickness.
[0083] As results from various experiments of such devices in which
a multilayer composed of an artificial lattice layer with range
{W.sub.0.35Si.sub.0.65(2-4 nm)/Si(1-6 nm)}.sub.2-3 was deposited
between the W ohmic electrode and the Si electron-supply layer per
each device by sputtering, there is little variation in the
electric properties, particularly, electron emission efficiency in
both kind of devices before and after the heating treatment, even
after the heating treatment of the 500.degree. C. temperature.
Typically, in the silicide layer, each WSi.sub.2 layer have a
thickness of 2.5 nm and each Si layer have a thickness of 5.5 nm
and the total thickness is 12 to 15 nm. In view of the crystalline
structure, the multi {WSi/Si} layers of artificial lattice before
heating in the first and second embodiments were in an amorphous
structure, and after heated, the amorphous structures of the layer
were kept. However, although the multi layers {WSi/Si} of
artificial lattice before heated in the third and fourth
embodiments were in an amorphous structure, after heated at
500.degree. C., the crystal structure of the layer was changed from
the amorphous structure to the bcc structure of W. In case of the
W-Si diode structure of the layer, the barrier height of the
interface is constant and the tungsten silicide of WSi is
formed.
[0084] Moreover, other comparative devices having multi-layers
{Mo(2-8 nm)/Si(1.5-7 nm)} which are referred as the device A and
{MoSi.sub.2(2-8 nm)/Si(1.5-7 nm)} which are referred as the device
B were manufactured in the same manner as the above embodiments
excepting that molybdenum (Mo) was used for the device instead of
tungsten (W). Although, after the heating treatment of 300.degree.
C. for 30 minutes, the diffusion occurred within the {Mo/Si} layer
in the device A, there was not observed any diffusion within the
{MoSi.sub.2/Si} layer in the device B.
[0085] It is understood that the good results are obtained from the
device comprising the electron-supply layer having silicide layer
and the insulator layer with a 50 nm thickness or greater.
[0086] With a voltage of approximately 4 kV applied between the
fluorescent-substance coated collector electrode and the thin-film
metal electrode of one embodiment of the above devices whose
insulator layers have thicknesses of 50 nm or greater, a uniform
fluorescent pattern corresponding to the shape of the thin-film
metal electrode was observed. This indicates that the electron
emission from the amorphous SiO.sub.x layer is uniform and has a
high linear movement, and that those devices can serve as an
electron emission diode, or a light-emitting diode or a laser diode
which emits electromagnetic waves with millimeter or sub-millimeter
wavelength and also a high speed switching device.
[0087] By a scanning electron microscope (SEM), there were
observations of the surface of the SiO.sub.x insulator layer
resulted from the sputtering during the above deposition process,
microstructures composed of grain surface each having about 20 nm
diameter appeared. The microstructures composed of grain structure
of SiO.sub.x of the insulator layer seems to cause the peculiar
phenomena that the tunnel current flows through the insulator layer
which has a thickness of 50 nm or greater. While SiO.sub.x is an
insulator by nature, multiple bands with low potentials are caused
by the occurrence of defects adjacent thereto or impurities in the
forbidden band of the insulator layer. It is assumed that electrons
tunnel-pass through multiple bands with the low-potential one after
another, and thus pass through the insulator layer of 50 nm or
greater in thickness as a consequence.
[0088] In addition that two of the silicide layers are disposed at
an mediate region of the electron-supply layer as shown in the
above embodiments, as shown in FIG. 11, a single or plural silicide
layers 14 may be disposed at an interface between the ohmic
electrode 11 and the electron-supply layer 12. As shown in FIG. 12,
a single or plural silicide layers 14 may be disposed at an
interface between the insulator layer 13 and the electron-supply
layer 12.
[0089] Further, as shown in FIG. 13 illustrating a partially
enlarged cross section view of the device, two or more of the
silicide layers 14 may be disposed within the electron-supply layer
12 to be divided into three portions as a multi-layered structure.
In other words, a plurality of the silicide layer and the
electron-supply layer are alternately layered by in the thickness
direction of the device. In addition, a plurality of layered
silicide layers 14 may be formed so as to have their interval
gradually descended (or ascended) in the thickness direction
upward.
[0090] As shown in FIG. 14, a plurality of layered suicide layers
14 may be formed within the electron-supply layer 12 so as to have
their thicknesses gradually descended (or ascended) in the
thickness direction upward.
[0091] Furthermore, other embodiments are shown in FIG. 15 the
silicide layer 14 may be formed, by sputtering, within the
electron-supply layer 12 so as to be a dispersion region of dopants
of a high conductive material. This silicide region also can serve
to facilitate to promote the transport of electrons from the ohmic
electrode 11 to the electron-supply layer 12. In addition, the
silicide region 14 may be formed to have a incline density of
dopants so that as the higher or lower density of silicide dopants
is provided as the silicide region 14 is closer to the thin-film
metal electrode 15.
[0092] It is understood from those results that the electron-supply
layer having silicide layer is effective for the electron emission
device capable of driving in a stable emission current with a low
applied voltage comprising; the electron-supply layer made of metal
or semiconductor; the insulator layer with a 50 nm thickness or
greater; and the thin-film metal electrode facing a vacuum space,
so that the electron emission device emits stably electrons when
applying a relatively low voltage across the electron-supply layer
and the thin-film metal electrode.
[0093] FIG. 16 shows an electron emission display device according
to one embodiment of the invention. This embodiment comprises a
pair of the transparent substrate 1 and the device substrate 10,
which face each other with a vacuum space 4 in between. In the
illustrated electron emission display apparatus, a plurality of
transparent collector electrodes 2 of, for example, an indium tin
oxide (so-called ITO), tin oxide (SnO), zinc oxide (ZnO) or the
like, are formed in parallel on the inner surface of the
transparent glass substrate 1 or the display surface (which faces
the back substrate 10). The collector electrodes 2 may be formed
integrally. The transparent collector electrodes which trap emitted
electrons are arranged in groups of three in association with red
(R), green (G) and blue (B) color signals in order to provide a
color display panel, and voltages are applied to those three
collector electrodes respectively. Therefore, fluorescent layers
3R, 3G and 3B of fluorescent substances corresponding to R, G and B
color emissions are respectively formed on the three collector
electrodes 2 in such a way as to face the vacuum space 4.
[0094] A plurality of ohmic electrodes 11 are formed in parallel on
the inner surface of the device substrate 10 of glass or the like
which faces the transparent glass substrate 1 with the vacuum space
4 in between (i.e., said inner surface faces the transparent glass
substrate 1) via an auxiliary insulator layer 18. The auxiliary
insulator layer 18 is comprised of an insulator such as SiO.sub.2,
SiN.sub.x, Al.sub.2O.sub.3 or AlN, and serves to prevent an adverse
influence of the device substrate 10 on the device (such as elution
of an impurity such as an alkaline component or a roughened
substrate surface). A plurality of electron emission devices S are
formed on the ohmic electrodes 11. In order that adjoining
thin-film metal electrodes 15 are electrically connected to each
other, a plurality of bus electrodes 16 are formed on parts of the
thin-film metal electrodes 15, extending in parallel to one another
and perpendicular to the ohmic electrodes 11. Each electron
emission device S comprises the electron-supply layer 12 having the
silicide layer 14, the insulator layer 13 and the thin-film metal
electrode 15 which are formed In order on the associated ohmic
electrode 11, The thin-film metal electrodes 15 face the vacuum
space 4. A second auxiliary insulator layer 17 with openings Is
formed to separate the surfaces of the thin-film metal electrodes
15 into a plurality of electron emission regions. This second
auxiliary insulator layer 17 covers the bus electrodes 16 to
prevent unnecessary short-circuiting.
[0095] The material for the ohmic electrodes 11 is Au, Pt, Al, W or
the like which is generally used for the wires of an IC, and has a
uniform thickness for supplying substantially the same current to
the individual devices.
[0096] From the principle of electron emission, it is better that
the material for the thin-film metal electrode 15 has a lower work
function .phi. and is thinner. To increase the electron emission
efficiency, the material for the thin-film metal electrode 15
should be a metal of the group I or group II in the periodic table;
for example, Mg. Ba, Ca, Cs, Rb, Li, Sr, and the like are effective
and alloys of those elements may be used as well. To make the
thin-film metal electrode 15 very thin, the material for the
thin-film metal electrode 15 should be chemically stable with a
high conductivity; for example, single substances of Au, Pt, Lu, Ag
and Cu or alloys thereof are desirable, It is effective to coat or
dope a metal with a low work function as described above on or in
those metals.
[0097] The material for the bus electrodes 16 can be Au, Pt, Al or
the like which is generally used for the wiring of an integrated
circuit IC, and should have a thickness enough to supply
substantially the same potential to the individual devices,
adequately of 0.1 to 50 .mu.m. A simple matrix system or an active
matrix system may be employed as the driving system for the display
device of the invention.
* * * * *