BACKGROUND OF THE INVENTION
Field of the Invention:
[0001] The present invention relates to an electron emitter including a first electrode
and a second electrode formed on an emitter section. A slit is formed between the
first electrode and the second electrode.
Description of the Related Art:
[0002] In recent years, electron emitters having a cathode electrode and an anode electrode
have been used in various applications such as field emission displays (FEDs) and
backlight units. In an FED, a plurality of electron emitters are arranged in a two-dimensional
array, and a plurality of fluorescent elements are positioned at predetermined intervals
in association with the respective electron emitters.
[0003] Conventional electron emitters are disclosed in Japanese laid-open patent publication
No. 1-311533, Japanese laid-open patent publication No. 7-147131, Japanese laid-open
patent publication No. 2000-285801, Japanese patent publication No. 46-20944, and
Japanese patent publication No. 44-26125, for example. All of these disclosed electron
emitters are disadvantageous in that since no dielectric body is employed in the emitter
section, a forming process or a micromachining process is required between facing
electrodes, a high voltage needs to be applied between the electrodes to emit electrons,
and a panel fabrication process is complex and entails a high panel fabrication cost.
[0004] It has been considered to make an emitter section of a dielectric material. Various
theories about the emission of electrons from a dielectric material have been presented
in the documents: Yasuoka and Ishii, "Pulsed electron source using a ferroelectric
cathode", J. Appl. Phys., Vol. 68, No. 5, p. 546 - 550 (1999), V.F. Puchkarev, G.A.
Mesyats, "On the mechanism of emission from the ferroelectric ceramic cathode", J.
Appl. Phys., Vol. 78, No. 9, 1 November, 1995, p. 5633 - 5637, and H. Riege, "Electron
emission ferroelectrics - a review", Nucl. Instr. and Meth. A340, p. 80 - 89 (1994).
[0005] In the conventional electron emitters, electrons trapped on the surface of the dielectric
material, at the interface between the dielectric material and the upper electrode,
and in the dielectric material by the defect level are released (emitted) when polarization
reversal occurs in the dielectric material. The number of the electrons emitted by
the polarization reversal does not change substantially depending on the voltage level
of the applied voltage pulse.
[0006] However, the electron emission is not performed stably, and the number of emitted
electrons is merely tens of thousands. Therefore, conventional electron emitters are
not suitable for practical use.- Advantages of an electron emitter having an emitter
section made of a dielectric material have not been achieved.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to provide an electron emitter having an
emitter section made of a dielectric material in which a first electrode is not damaged
easily due to the emission of electrons, so that the electron emitter has a long service
life and high reliability.
[0008] According to the present invention, an electron emitter comprises an emitter section
made of a dielectric material, a first electrode formed in contact with the emitter
section, and a second electrode formed in contact with the emitter section. A slit
is formed between the first electrode and the second electrode. A drive voltage is
applied between the first electrode and the second electrode to induce polarization
reversal at least at a portion of the emitter section which is exposed through the
slit, for emitting electrons. A charging film is formed at least on a surface of the
second electrode.
[0009] In the electron emitter, the emitter section may be made of a piezoelectric material,
an anti-ferroelectric material, or an electrostrictive material.
[0010] Polarization reversal may occur in an electric field E of the emitter section represented
by E= Vak/d, where d is a width of the slit, and Vak is a voltage applied between
the first electrode and the second electrode. In this case, preferably, the voltage
Vak is less than a dielectric breakdown voltage of the emitter section. The thickness
d may be determined so that the voltage Vak applied between the first electrode and
the second electrode has an absolute value of less than 100V.
[0011] The principle of exponential increase of electrons in the electron emission, and
the affect of the electron emission to the first electrode will be described. Firstly,
a drive voltage is applied between the first electrode and the second electrode such
that the first electrode has a potential lower than a potential of the second the
second electrode to reverse polarization of at least a portion of the emitter section
which is exposed through the slit. The polarization reversal causes emission of electrons
in the vicinity of the first electrode. The polarization reversal generates a locally
concentrated electric field on the first electrode and the positive poles of dipole
moments in the vicinity the first electrode, emitting primary electrons from the first
electrode. The primary electrons emitted from the first electrode impinge upon the
emitter section, causing the emitter section to emit secondary electrons.
[0012] When the first electrode, the portion of the emitter section which is exposed through
the slit, and a vacuum atmosphere define a triple point, primary electrons are emitted
from a portion of the first electrode in the vicinity of the triple point. The emitted
primary electrons impinge upon the emitter section to induce emission of secondary
electrons from the emitter section.
The secondary electrons include electrons emitted from the solid emitter section under
an energy that has been generated by a coulomb collision with primary electrons, Auger
electrons, and primary electrons which are scattered in the vicinity of the surface
of the emitter section (reflected electrons). In particular, if the first electrode
is very thin, having a thickness of 10 nm or less, electrons are emitted from the
interface between the first electrode and the emitter section.
[0013] Since the electrons are emitted according to the principle as described above, the
electron emission is stably performed, and the number of emitted electrons would reach
2 billion or more. Thus, the electron emitter is advantageously used in the practical
applications. The number of emitted electrons is increased substantially proportional
to the drive voltage applied between the first electrode and the second electrode.
Thus, the number of the emitted electrons can be controlled easily.
[0014] When the electron emitter is used as a pixel of a display, a third electrode is provided
above the emitter section at a position facing the slit. The third electrode is coated
with a fluorescent layer. Some of the emitted electrons are guided to the collector
electrode to excite the fluorescent layer to emit fluorescent light from the fluorescent
layer to the outside. Some of the emitted electrons are guided to the second electrode.
[0015] When the emitted electrons are guided to the second electrode, the gas near the second
electrode or floating atoms (generated by evaporation of the electrode) near the second
electrode are ionized into positive ions and electrons by the emitted electrons. The
electrons generated by the ionization ionize the gas and the atoms of the electrode.
Therefore, the electrons are increased exponentially to generate a local plasma in
which the electrons and the positive ions are neutrally present.
[0016] Then, the voltage Vak applied between the first electrode and the second electrode
is decreased at the time of electron emission to a level in which electric discharge
is maintained in a substantially short circuited condition.
[0017] The positive ions generated by the ionization may impinge upon the first electrode,
possibly damaging the first electrode.
[0018] In order to solve the problem, in the present invention, a charging film is formed
at least on a surface of the second electrode. As described above, when some of the
electrons emitted from the emitter section are guided toward the second electrode,
the surface of the charging film is charged negatively. Therefore, the positive polarity
of the second electrode is weakened, and the intensity of the electric field between
the first electrode and the second electrode is reduced. The ionization stops instantly.
The voltage change between the first electrode and the second electrode is very small
at the time of the electron emission. Thus, almost no positive ions are generated,
preventing the first electrode from being damaged by positive ions. This arrangement
is thus effective to increase the service life of the electron emitter.
[0019] The charging film may be made of a piezoelectric material, an electrostrictive material,
an anti-ferroelectric material, or a material having a low dielectric constant. For
example, SiO
2, or a metal oxide film such as MgO, or a glass may be used as the material having
a low dielectric constant. Alternatively, the charging film may be made of the same
dielectric material as that of the emitter section.
[0020] Preferably, the charging film formed on the surface of the second electrode has a
thickness in the range of 10 nm to 100 µm. If the charging film is too thin, durability
of the charging film may not be good and the charging film may have handling problems.
If the charging film is too thick, the distance between the first electrode and the
second electrode, i.e., the width of the slit is not small. Therefore, sufficient
electric field for emitting electrons may not be generated.
[0021] A protective film may be formed on the surface of the first electrode. In the electron
emitter, the protective film and the charging film may be made of a same material.
The protective film may be made of an insulator or a highly resistive conductor having
a low sputtering yield and a high evaporation temperature in vacuum. Preferably, the
protective film formed on the first electrode has a thickness in the range of 10 nm
to 100 nm. If the protective film is too thin, durability of the protective film may
not be good and the protective film may have handling problems. If the protective
film is too thick, the electrons emitted from the electric field concentration point
or the interface between the first electrode and the emitter section may not pass
through the protective film.
[0022] In the present invention, preferably, the voltage change between the first electrode
and the second electrode at the time of electron emission is 20V or less.
[0023] In the present invention, the first electrode and the second electrode may be formed
on an upper surface of the emitter section, and the slit may be a gap.
[0024] The first electrode may be formed in contact with one side of the emitter section,
and the second electrode may be formed in contact with the other side of the emitter
section such that the emitter section is positioned in the slit.
[0025] If the slit is a gap, the width of the slit may be increased due to the damages of
the first electrode, and the drive voltage may not be low voltage. Therefore, the
emitter section is positioned in the slit so that the width of the slit does not change
even if the first electrode is damaged. Consequently, the electron emission is stably
performed at a constant voltage, and the electrode has a long service life.
[0026] Further, since the emitter section is sandwiched between the two electrodes, the
polarization is performed perfectly in the emitter section, and the electron emission
is stably performed by the polarization reversal.
[0027] In particular, if the emitter section is formed in a tortuous pattern, the area of
contact between the first electrode and the emitter section and the area of contact
between the second electrode and the emitter section are increased for efficiently
emitting electrons.
[0028] In one embodiment, the emitter section is provided on an upper surface of a substrate,
the first electrode is formed in contact with one side of the emitter section, the
second electrode is formed in contact with the other side of the emitter section,
the emitter section is formed in the slit, a third electrode is provided above the
substrate, and the third electrode is coated with a fluorescent layer.
[0029] The above and other objects, features, and advantages of the present invention will
become more apparent from the following description of preferred embodiments when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030]
FIG. 1 is a view showing an electron emitter according to a first embodiment;
FIG. 2 is a plan view showing electrodes of the electron emitter according to the
first embodiment;
FIG. 3 is a waveform diagram showing a drive voltage outputted from a pulse generation
source;
FIG. 4 is a view illustrative of operation when a first voltage is applied between
a cathode electrode and an anode electrode;
FIG. 5A is a view illustrative of operation of emission of primary electrons when
a second voltage is applied between the cathode electrode and the anode electrode;
FIG. 5B is a view illustrative of operation of emission of secondary electrons induced
by emission of the primary electrons;
FIG. 6 is a view showing relationship between the energy of the emitted secondary
electrons and the number of emitted secondary electrons;
FIG. 7A is a waveform diagram showing an example of a drive voltage;
FIG. 7B is a waveform showing the change of the voltage applied between the cathode
electrode and the anode electrode in which no charging film is formed on the anode
electrode;
FIG. 8 is a view illustrative of operation when the second voltage is applied between
the cathode electrode and the anode electrode of the electron emitter according to
the first embodiment;
FIG. 9A is a waveform diagram showing an example of a drive voltage;
FIG. 9B is a waveform diagram showing the change of the voltage applied between the
cathode electrode and-the anode electrode of the electron emitter according to the
first embodiment;
FIG. 10 is a view showing a modification of the electron emitter according to the
first embodiment;
FIG. 11 is a view showing main components of an electron emitter according to a second
embodiment;
FIG. 12 is a plan view showing a first modification of the electron emitter according
to the second embodiment;
FIG. 13 is a cross sectional view taken along a line XIII-XIII shown in FIG. 12;
FIG. 14 is a cross sectional view showing a second modification of the electron emitter
according to the second embodiment;
FIG. 15 is a cross sectional view showing a third modification of the electron emitter
according to the second embodiment; and
FIG. 16 is a plan view showing the third modification of the electron emitter according
to the second embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] Electron emitters according to embodiments of the present invention will be described
below with reference to FIGS. 1 through 16.
[0032] Electron emitters according to the embodiments of the present invention can be used
in displays, electron beam irradiation apparatus, light sources, alternatives to LEDs,
and electronic parts manufacturing apparatus.
[0033] Electron beams in an electron beam irradiation apparatus have a high energy and a
good absorption capability in comparison with ultraviolet rays in ultraviolet ray
irradiation apparatus that are presently in widespread use. Electron emitters are
used to solidify insulating films in superposing wafers for semiconductor devices,
harden printing inks without irregularities for drying prints, and sterilize medical
devices while being kept in packages.
[0034] The electron emitters are also used as high-luminance, high-efficiency light sources
such as a projector having a high pressure mercury lamp. The electron emitter according
to the present embodiment is suitably used as a light source. The light source using
the electron emitter according to the present embodiment is compact, has a long service
life, has a fast response speed for light emission. The electron emitter does not
use any mercury, and the electron emitter is environmentally friendly.
[0035] The electron emitters are also used as alternatives to LEDs in indoor lights, automobile
lamps, surface light sources for traffic signal devices, chip light sources, and backlight
units for traffic signal devices, small-size liquid-crystal display devices for cellular
phones.
[0036] The electron emitters are also used in apparatus for manufacturing electronic parts,
including electron beam sources for film growing apparatus such as electron beam evaporation
apparatus, electron sources for generating a plasma (to activate a gas or the like)
in plasma CVD apparatus, and electron sources for decomposing gases. The electron
emitters are also used as vacuum micro devices such as high speed switching devices
operated at a frequency on the order of Tera-Hz, and large current outputting devices.
Further, the electron emitter are used suitably as parts of printers, such as light
emitting devices for emitting light to a photosensitive drum, and electron sources
for charging a dielectric material.
[0037] The electron emitters are also used as electronic circuit devices including digital
devices such as switches, relays, and diodes, and analog devices such as operational
amplifiers. The electron emitters are used for realizing a large current output, and
a high amplification ratio.
[0038] As shown in FIG. 1, an electron emitter 10A according to the first embodiment comprises
an emitter section 14 formed on a substrate 12, a first electrode (cathode electrode)
16 and a second electrode (anode electrode) 20 formed on one surface of the emitter
section 14. A slit 18 is formed between the cathode electrode 16 and the anode electrode
20. A pulse generation source 22 applies a drive voltage Va between the cathode electrode
16 and the anode electrode 20 through a resistor R1. In FIG. 1, the anode electrode
20 is connected to GND (ground) and hence set to a zero potential. However, the anode
electrode 20 may be set to a potential other than the zero potential.
[0039] For using the electron emitter 10A as a pixel of a display, a third electrode (collector
electrode) 24 is provided above the emitter section 14 at a position facing the slit
18, and the collector electrode 24 is coated with a fluorescent layer 28. A bias voltage
source 102 (having a bias voltage Vc) is connected to the collector electrode 24 through
a resistor R3.
[0040] The electron emitter 10A according to the first embodiment is placed in a vacuum
space. As shown in FIG. 1, the electron emitter 10A has electric field concentration
points A, B. The point A can also be defined as a triple point where the cathode electrode
16, the emitter section 14, and a vacuum are present at one point. The point B can
also be defined as a triple point where the anode electrode 20, the emitter section
14, and a vacuum are present at one point.
[0041] The vacuum level in the atmosphere should preferably in the range from 10
2 to 10
-6 Pa and more preferably in the range from 10
-3 to 10
-5 Pa.
[0042] The range of the vacuum level is determined for the following reason. In a lower
vacuum, (1) many gas molecules would be present in the space, and a plasma can easily
be generated and, if the plasma were generated excessively, many positive ions would
impinge upon the cathode electrode 16 and damage the cathode electrode 16, and (2)
emitted electrons would impinge upon gas molecules prior to arrival at the collector
electrode 24, failing to sufficiently excite the fluorescent layer 28 with electrons
that are sufficiently accelerated under the collector potential (bias voltage Vc).
[0043] In a higher vacuum, though electrons are smoothly emitted from the electric field
concentration points A and B, structural body supports and vacuum seals would be large
in size, posing difficulty in making a small electron emitter.
[0044] The emitter section 14 is made of a dielectric material. The dielectric material
should preferably have a high relative dielectric constant (relative permittivity),
e.g., a dielectric constant of 1000 or higher. Dielectric materials of such a nature
may be ceramics including barium titanate, lead zirconate, lead magnesium niobate,
lead nickel niobate, lead zinc niobate, lead manganese niobate, lead magnesium tantalate,
lead nickel tantalate, lead antimony stannate, lead titanate, lead magnesium tungstenate,
lead cobalt niobate, etc. or a material whose principal component contains 50 weight
% or more of the above compounds, or such ceramics to which there is added an oxide
of lanthanum, calcium, strontium, molybdenum, tungsten, barium, niobium, zinc, nickel,
manganese, or the like, or a combination of these materials, or any of other compounds.
[0045] For example, a two-component material nPMN-mPT (n, m represent molar ratios) of lead
magnesium niobate (PMN) and lead titanate (PT) has its Curie point lowered for a larger
relative dielectric constant at room temperature if the molar ratio of PMN is increased.
[0046] Particularly, a dielectric material where n = 0.85 - 1.0 and m = 1.0 - n is preferable
because its relative dielectric constant is 3000 or higher. For example, a dielectric
material where n = 0.91 and m = 0.09 has a relative dielectric constant of 15000 at
room temperature, and a dielectric material where n = 0.95 and m = 0.05 has a relative
dielectric constant of 20000 at room temperature.
[0047] For increasing the relative dielectric constant of a three-component dielectric material
of lead magnesium niobate (PMN), lead titanate (PT), and lead zirconate (PZ), it is
preferable to achieve a composition close to a morphotropic phase boundary (MPB) between
a tetragonal system and a quasi-cubic system or a tetragonal system and a rhombohedral
system, as well as to increase the molar ratio of PMN. For example, a dielectric material
where PMN : PT : PZ = 0.375 : 0.375 : 0.25 has a relative dielectric constant of 5500,
and a dielectric material where PMN : PT : PZ = 0.5 : 0.375 : 0.125 has a relative
dielectric constant of 4500, which is particularly preferable. Furthermore, it is
preferable to increase the dielectric constant by introducing a metal such as platinum
into these dielectric materials within a range to keep them insulative. For example,
a dielectric material may be mixed with 20 weight % of platinum.
[0048] The emitter section 14 may be in the form of a piezoelectric/electrostrictive layer
or an anti-ferroelectric layer. If the emitter section 14 is a piezoelectric/electrostrictive
layer, then it may be made of ceramics such as lead zirconate, lead magnesium niobate,
lead nickel niobate, lead zinc niobate, lead manganese niobate, lead magnesium tantalate,
lead nickel tantalate, lead antimony stannate, lead titanate, barium titanate, lead
magnesium tungstenate, lead cobalt niobate, or the like or a combination of any of
these materials.
[0049] The emitter section 14 may be made of chief components including 50 weight % or more
of any of the above compounds. Of the above ceramics, the ceramics including lead
zirconate is most frequently used as a constituent of the piezoelectric/electrostrictive
layer of the emitter section 14.
[0050] If the piezoelectric/electrostrictive layer is made of ceramics, then oxides of lanthanum,
calcium, strontium, molybdenum, tungsten, barium, niobium, zinc, nickel, manganese,
or the like, or a combination of these materials, or any of other compounds may be
added to the ceramics.
[0051] For example, the piezoelectric/electrostrictive layer should preferably be made of
ceramics including as chief components lead magnesium niobate, lead zirconate, and
lead titanate, and also including lanthanum and strontium.
[0052] The piezoelectric/electrostrictive layer may be dense or porous. If the piezoelectric/electrostrictive
layer is porous, then it should preferably have a porosity of 40 % or less.
[0053] If the emitter section 14 is in the form of an anti-ferroelectric layer, then the
anti-ferroelectric layer may be made of lead zirconate as a chief component, lead
zirconate and lead stannate as chief components, lead zirconate with lanthanum oxide
added thereto, or lead zirconate and lead stannate as components with lead zirconate
and lead niobate added thereto.
[0054] The anti-ferroelectric layer may be porous. If the anti-ferroelectric layer is porous,
then it should preferably have a porosity of 30 % or less.
[0055] Strontium bismuthate tantalate is used suitably for the emitter section 14. The emitter
section 14 made of strontium bismuthate tantalate is not damaged by the polarization
reversal easily. For preventing damages due to the polarization reversal, lamellar
ferroelectric compounds represented by a general formula (BiO
2)
2+ (A
m-1B
mO
3m+1)
2- are used. The ionized metal A includes Ca
2+, Sr
2+, Ba
2+, Pb
2+, Bi
3+, La
3+, and the ionized metal B includes Ti
4+, Ta
5+, Nb
5+.
[0056] Piezoelectric/electrostrictive/anti-ferroelectric ceramics is mixed with glass components
such as lead borosilicate glass or other compounds having a low melting point such
as bismuth oxide to lower the firing temperature. Thus, the emitter section 14 is
formed easily on the substrate 12.
[0057] The emitter section 14 may be made of a material which does not contain any lead,
i.e., made of a material having a high melting temperature, or a high evaporation
temperature. Thus, the emitter section 14 is not damaged easily when electrons or
ions impinge upon the emitter section 14.
[0058] The emitter section 14 may be formed on the substrate 12 by any of various thick-film
forming processes including screen printing, dipping, coating, electrophoresis, etc.,
or any of various thin-film forming processes including an ion beam process, sputtering,
vacuum evaporation, ion plating, chemical vapor deposition (CVD), plating, etc.
[0059] In the first embodiment, the emitter section 14 is formed on the substrate 12 suitably
by any of various thick-film forming processes including screen printing, dipping,
coating, electrophoresis, etc.
[0060] These thick-film forming processes are capable of providing good piezoelectric operating
characteristics as the emitter section 14 can be formed using a paste, a slurry, a
suspension, an emulsion, a sol, or the like which is chiefly made of piezoelectric
ceramic particles having an average particle diameter ranging from 0.01 to 5 µm, preferably
from 0.05 to 3 µm.
[0061] In particular, electrophoresis is capable of forming a film at a high density with
high shape accuracy, and has features described in technical documents such as "Electrochemistry
Vol. 53. No. 1 (1985), p. 63 - 68, written by Kazuo Anzai", and "The 1
st Meeting on Finely Controlled Forming of Ceramics Using Electrophoretic Deposition
Method, Proceedings (1998), p. 5 - 6, p. 23 - 24". The piezoelectric/electrostrictive/anti-ferroelectric
material may be formed into a sheet, or laminated sheets. Alternatively, the laminated
sheets of the piezoelectric/electrostrictive/anti-ferroelectric material may be laminated
on, or attached to another supporting substrate. Any of the above processes may be
chosen in view of the required accuracy and reliability.
[0062] The width d of the slit 18 between the cathode electrode 16 and the anode electrode
20 is determined so that polarization reversal occurs in the electric field E represented
by E= Vak/d (Vak is a voltage measured between the cathode electrode 16 and the anode
electrode 20 when the drive voltage Va outputted from the pulse generation source
22 is applied between the cathode electrode 16 and the anode electrode 20). If the
width d of the slit 18 is small, the polarization reversal occurs at a low voltage,
and electrons are emitted at the low voltage (e.g., less than 100V).
[0063] The cathode electrode 16 is made of materials as described below. The cathode electrode
16 should preferably be made of a conductor having a small sputtering yield and a
high evaporation temperature in vacuum. For example, materials having a sputtering
yield of 2.0 or less at 600 V in Ar
+ and an evaporation pressure of 1.3 × 10
-3 Pa at a temperature of 1800 K or higher are preferable. Such materials include platinum,
molybdenum, tungsten, etc. The cathode electrode 16 is made of a conductor which is
resistant to a high-temperature oxidizing atmosphere, e.g., a metal, an alloy, a mixture
of insulative ceramics and a metal, or a mixture of insulative ceramics and an alloy.
Preferably, the cathode electrode 16 should be composed chiefly of a precious metal
having a high melting point, e.g., platinum, iridium, palladium, rhodium, molybdenum,
or the like, or an alloy of silver and palladium, silver and platinum, platinum and
palladium, or the like, or a cermet of platinum and ceramics. Further preferably,
the cathode electrode 16 should be made of platinum only or a material composed chiefly
of a platinum-base alloy. The electrode should preferably be made of carbon or a graphite-base
material, e.g., diamond thin film, diamond-like carbon, or carbon nanotube. Ceramics
to be added to the electrode material should preferably have a proportion ranging
from 5 to 30 volume %.
[0064] Further, preferably, organic metal pastes which produce a thin film after firing,
such as platinum resinate paste are used. Further, for preventing damages due to polarization
reversal, oxide electrode is used. The oxide electrode is made of any of ruthenium
oxide, iridium oxide, strontium ruthenate, La
1-xSr
xCoO
3 (e.g., x=0.3 or 0.5), La
1-xCa
xMnO
3, La
1-xCa
xMn
1-yCO
yO
3 (e.g, x=0.2, y=0.05).
Alternatively, the oxide electrode is made by mixing any of these materials with platinum
resinate paste, for example.
[0065] The cathode electrode 16 may be made of any of the above materials by an ordinary
film forming process which may be any of various thick-film forming processes including
screen printing, spray coating, dipping, coating, electrophoresis, etc., or any of
various thin-film forming processes including sputtering, an ion beam process, vacuum
evaporation, ion plating, CVD, plating, etc. Preferably, the cathode electrode 16
is made by any of the above thick-film forming processes. Dimensions of the cathode
electrode 16 will be described with reference to FIG. 2. In FIG. 2, the cathode electrode
16 has a width W1 of 2 mm and a length L1 of 5 mm. Preferably, the cathode electrode
16 has a thickness of 20 µm or less, or more preferably 5 µm or less.
[0066] The anode electrode 20 is made of the same material by the same process as the cathode
electrode 16. Preferably, the anode electrode 20 is made by any of the above thick-film
forming processes. As shown in FIG. 2, as with the cathode electrode 16, the anode
electrode 20 has a width W2 of 2 mm and a length L2 of 5 mm.
[0067] In the first embodiment, the width d of the slit between the cathode electrode 16
and the anode electrode 20 is 70 µm.
[0068] The substrate 12 should preferably be made of an electrically insulative material
in order to electrically isolate the line electrically connected to the cathode electrode
16 and the line electrically connected to the anode electrode 20 from each other.
[0069] The substrate 12 may be made of a highly heat-resistant metal or a metal material
such as an enameled metal whose surface is coated with a ceramic material such as
glass or the like. However, the substrate 12 should preferably be made of ceramics.
[0070] Ceramics which the substrate 12 is made of include stabilized zirconium oxide, aluminum
oxide, magnesium oxide, titanium oxide, spinel, mullite, aluminum nitride, silicon
nitride, glass, or a mixture thereof. Of these ceramics, aluminum oxide or stabilized
zirconium oxide is preferable from the standpoint of strength and rigidity. Stabilized
zirconium oxide is particularly preferable because its mechanical strength is relatively
high, its tenacity is relatively high, and its chemical reaction with the cathode
electrode 16 and the anode electrode 20 is relatively small. Stabilized zirconium
oxide includes stabilized zirconium oxide and partially stabilized zirconium oxide.
Stabilized zirconium oxide does not develop a phase transition as it has a crystalline
structure such as a cubic system.
[0071] Zirconium oxide develops a phase transition between a monoclinic system and a tetragonal
system at about 1000°C and is liable to suffer cracking upon such a phase transition.
Stabilized zirconium oxide contains 1 to 30 mol % of a stabilizer such as calcium
oxide, magnesium oxide, yttrium oxide, scandium oxide, ytterbium oxide, cerium oxide,
or an oxide of a rare earth metal. For increasing the mechanical strength of the substrate
12, the stabilizer should preferably contain yttrium oxide. The stabilizer should
preferably contain 1.5 to 6 mol % of yttrium oxide, or more preferably 2 to 4 mol
% of yttrium oxide, and furthermore should preferably contain 0.1 to 5 mol % of aluminum
oxide.
[0072] The crystalline phase may be a mixed phase of a cubic system and a monoclinic system,
a mixed phase of a tetragonal system and a monoclinic system, a mixed phase of a cubic
system, a tetragonal system, and a monoclinic system, or the like. The main crystalline
phase which is a tetragonal system or a mixed phase of a tetragonal system and a cubic
system is optimum from the standpoints of strength, tenacity, and durability.
[0073] If the substrate 12 is made of ceramics, then the substrate 12 is made up of a relatively
large number of crystalline particles. For increasing the mechanical strength of the
substrate 12, the crystalline particles should preferably have an average particle
diameter ranging from 0.05 to 2 µm, or more preferably from 0.1 to 1 µm.
[0074] Each time the emitter section 14, the cathode electrode 16, or the anode electrode
20 is formed, the assembly is heated (sintered) into a structure integral with the
substrate 12. After the emitter section 14, the cathode electrode 16, and the anode
electrode 20 are formed, they may simultaneously be sintered so that they may simultaneously
be integrally coupled to the substrate 12. Depending on the process by which the cathode
electrode 16 and the anode electrode 20 are formed, they may not be heated (sintered)
so as to be integrally combined with the substrate 12.
[0075] The sintering process for integrally combining the substrate 12, the emitter section
14, the cathode electrode 16, and the anode electrode 20 may be carried out at a temperature
ranging from 500 to 1400°c, preferably from 1000 to 1400°C. For heating the emitter
section 14 which is in the form of a film, the emitter section 14 should be sintered
together with its evaporation source while their atmosphere is being controlled.
[0076] The emitter section 14 may be covered with an appropriate member for preventing the
surface thereof from being directly exposed to the sintering atmosphere when the emitter
section 14 is sintered. The covering member should preferably be made of the same
material as the substrate 12.
[0077] The principles of electron emission of the electron emitter 10A will be described
below with reference to FIGS. 1 through 6. As shown in FIG. 3, the drive voltage Va
outputted from the pulse generation source 22 has repeated steps each including a
period in which a first voltage Va1 is outputted (preparatory period T1) and a period
in which a second voltage Va2 is outputted (electron emission period T2). The first
voltage Va1 is such a voltage that the potential of the cathode electrode 16 is higher
than the potential of the anode electrode 20, and the second voltage Va2 is such a
voltage that the potential of the cathode electrode 16 is lower than the potential
of the anode electrode 20. The amplitude Vin of the drive voltage Va can be defined
as the difference (= Va1 - Va2) between the first voltage Va1 and the second voltage
Va2.
[0078] The preparatory period T1 is a period in which the first voltage Va1 is applied between
the cathode electrode 16 and the anode electrode 20 to polarize the emitter section
14, as shown in FIG. 4. The first voltage Va1 may be a DC voltage, as shown in FIG.
3, but may be a single pulse voltage or a succession of pulse voltages. The preparatory
period T1 should preferably be longer than the electron emission period T2 for sufficient
polarization. For example, the preparatory period T1 should preferably be 100 µsec.
or longer. This is because the absolute value of the first voltage Va1 for polarizing
the emitter section 14 is smaller than the absolute value of the second voltage Va2
to reduce the power consumption at the time of applying the first voltage Va1, and
to prevent the damage of the cathode electrode 16.
[0079] Preferably, the voltage levels of the first voltage Va1 and the second voltage Va2
are determined so that the polarization to the positive polarity and the negative
polarity can be performed reliably. For example, if the dielectric material of the
emitter section 14 has a coercive voltage, preferably, the absolute values of the
first voltage Va1 and the second voltage Va2 are the coercive voltage or higher.
[0080] The electron emission period T2 is a period in which the second voltage Va2 is applied
between the cathode electrode 16 and the anode electrode 20. When the second voltage
Va2 is applied between the cathode electrode 16 and the anode electrode 20, as shown
in FIG. 5A, the polarization of at least a portion of the emitter section 14 which
is exposed through the slit 18 is reversed. Because of the reversed polarization,
a locally concentrated electric field is generated on the cathode electrode 16 and
the positive poles of dipole moments in the vicinity thereof, emitting primary electrons
from the cathode electrode 16. As shown in FIG. 5B, the primary electrons emitted
from the cathode electrode 16 impinge upon the emitter section 14, causing the emitter
section 14 to emit secondary electrons.
[0081] With the electron emitter 10A having the triple point A where the cathode electrode
16, the emitter section 14, and the vacuum are present at one point, primary electrons
are emitted from the cathode electrode 16 near the triple point A, and the primary
electrons thus emitted from the triple point A impinge upon the emitter section 14,
causing the emitter section 14 to emit secondary electrons. If the thickness of the
cathode electrode 16 is very small (up to 10 nm), then electrons are emitted from
the interface between the cathode electrode 16 and the emitter section 14.
[0082] The principle of exponential increase of electrons in the electron emission, and
the affect of the electron emission to the cathode electrode 16 will be described.
Firstly, when the negative voltage Va2 is applied to the cathode electrode 16, secondary
electrons are emitted from the emitter section 14 as described above.
[0083] Of the emitted secondary electrons, some are emitted to the collector electrode 24
to excite the fluorescent layer 28, which produces a fluorescent emission directed
outwardly. Other secondary electrons and the primary electrons are emitted to the
anode electrode 20.
[0084] A distribution of emitted secondary electrons will be described below. As shown in
FIG. 6, most of the secondary electrons have an energy level near zero. When the secondary
electrons are emitted from the surface of the emitter section 14 into the vacuum,
they move according to only an ambient electric field distribution. Specifically,
the secondary electrons are accelerated from an initial speed of about 0 (m/sec) according
to the ambient electric field distribution. Therefore, as shown in FIG. 5B, if an
electric field E is generated between the emitter section 14 and the collector electrode
24, the secondary electrons has their emission path determined along the electric
field E. Therefore, the electron emitter 10A can serve as a highly straight electron
source. The secondary electrons which have a low initial speed are electrons which
are emitted from the solid emitter section 14 under an energy that has been generated
by a coulomb collision with primary electrons.
[0085] As can be seen from FIG. 6, secondary electrons having an energy level which corresponds
to the energy E
0 of primary electrons are emitted. These secondary electrons are primary electrons
that are emitted from the cathode electrode 16 and scattered in the vicinity of the
surface of the emitter section 14 (reflected electrons).
[0086] If the thickness of the cathode electrode 16 is greater than 10 nm, then almost all
of the reflected electrons are directed toward the anode electrode 20. The secondary
electrons referred herein include both the reflected electrons and Auger electrons.
[0087] If the thickness of the cathode electrode 16 is very small (up to 10 nm), then primary
electrons emitted from the cathode electrode 16 are reflected by the interface between
the cathode electrode 16 and the emitter section 14, and directed toward the collector
electrode 24.
[0088] The electrons emitted to the anode electrode 20 ionize a gas or atoms of the anode
electrode 20 which are present mainly in the vicinity of the anode electrode 20 into
positive ions and electrons. The atoms of the anode electrode 20 are present in the
vicinity of the anode electrode 20 as a result of evaporation of part of the anode
electrode 20. The atoms float in the vicinity of the anode electrode 20. Since electrons
produced by the ionization further ionize the gas and the atoms, the electrons are
increased exponentially. As exponential increase of the electrons goes on until electrons
and positive ions are present neutrally, a local plasma is generated.
[0089] The electrons guided to the anode electrode 20 impinge upon the emitter section 14
for causing emission of secondary electrons. The gas near the anode electrode 20 or
the floating atoms (generated by evaporation of the electrode) near the anode electrode
20 are ionized into positive ions and electrons by the emitted electrons.
[0090] As shown in FIG. 7A, for example, the drive voltage Va applied between the cathode
electrode 16 and the anode electrode 20 has a first voltage Va1 of 50 V, and a second
voltage va2 of -100V. In FIG. 7B, the voltage Vak between the cathode electrode 16
and the anode electrode 20 has a peak at the time P1 when electrons are emitted. Then,
by the progress of the ionization, the voltage Vak is decreased to a level Vb in which
electric discharge is maintained in a substantially short circuited condition. The
voltage level Vb may be higher than or smaller than the coercive voltage (e.g., -20V)
of the dielectric material (the emitter section 14). The voltage change ΔVak of the
voltage between the cathode electrode 16 and the anode electrode 20 is about 50V.
[0091] Preferably, the dielectric breakdown voltage of the emitter section 14 is at least
10kV/mm or higher. In the embodiment, when the width d of the slit 18 is 70 µm, even
if the drive voltage of -100V is applied between the cathode electrode 16 and the
anode electrode 20, the portion of the emitter section 14 which is exposed through
the slit 18 does not break down dielectrically.
[0092] The positive ions generated by the ionization may impinge upon the cathode electrode
16, possibly damaging the cathode electrode 16.
[0093] In order to solve the problem, in the first embodiment, as shown in FIGS. 1 and 8,
a charging film 40 is formed on a surface of the anode electrode 20.
[0094] Thus, when some of the electrons emitted from the emitter section 14 are guided to
the anode electrode 20, as shown in FIG. 8, the surface of the charging film 40 is
charged negatively. Therefore, the positive polarity of the anode electrode 20 is
weakened. and the intensity of the electric field E between the cathode electrode
16 and the anode electrode 20 is reduced. Thus, the ionization stops instantly. In
FIG. 9A, for example, the drive voltage Va applied between the cathode electrode 16
and the anode electrode 20 has a first voltage Va1 of 50 V, and a second voltage va2
of -100V. The change ΔVak of the voltage between the cathode electrode 16 and the
anode electrode 20 at the time P1 (peak) the electrons are emitted is 20V or less
(about 10 V in the example of FIG. 9B), and very small. Consequently, almost no positive
ions are generated, thus preventing the cathode electrode 16 from being damaged by
positive ions. This arrangement is thus effective to increase the service life of
the electron emitter 10A.
[0095] Preferably, the charging film 40 formed on the surface of the anode electrode 20
has a thickness t1 in the range of 10 nm to 100 µm. If the charging film 40 is too
thin, durability of the charging film 40 may not be good and the charging film 40
may have handling problems. If the charging film 40 is too thick, the distance between
the cathode electrode 16 and the anode electrode 20, i.e., the width d of the slit
is not small. Therefore, sufficient electric field for emitting electrons may not
be generated. In the first embodiment, the thickness t1 of the charging film 40 is
45 µm.
[0096] The charging film 40 is made of a piezoelectric material, an electrostrictive material,
an anti-ferroelectric material, or a material having a low dielectric constant. For
example, SiO
2, or a metal oxide film such as MgO, or a glass may be used as the material having
a low dielectric constant. Alternatively, the charging film 40 may be made of the
same dielectric material as that of the emitter section 14.
[0097] FIG. 10 is a view showing an electron emitter 10Aa in a modification. The electron
emitter 10Aa includes a protective film 42 formed on the surface of the cathode electrode
16. The protective film 42 may be formed on the same material as that of the charging
film 40. The protective film 42 may be made of an insulator or a highly resistive
conductor having a low sputtering yield and a high evaporation temperature in vacuum.
[0098] Preferably, the protective film 42 has a thickness in the range of 10 nm to 100 nm.
If the protective film 42 is too thin, durability of the protective film 42 may not
be good and the protective film 42 may have handling problems. If the protective film
42 is too thick, the electrons emitted from the electric field concentration point
A or the interface between the cathode electrode 16 and the emitter section 14 may
not pass through the protective film 42. The protective film 42 may be made of the
same material as the charging film 40. Thus, the charging film 40 and the protective
film 42 can be formed in a single process, and the fabrication process is simplified.
[0099] The pattern or the potential of the collector electrode 24 may be changed suitably
depending on the application. If a control electrode (not shown) or the like is provided
between the emitter section 14 and the collector electrode 24 for arbitrarily setting
the electric field distribution between the emitter section 14 and the collector electrode
24, the emission path of the emitted secondary electrons can be controlled easily.
Thus, it is possible to change the size of the electron beam by converging and expanding
the electron beam, and to change the shape of the electron beam easily.
[0100] As described above, the electron source emitting a straight electron beam is produced,
and the emission path of emitted secondary electrons is controlled easily.
Therefore, the electron emitter 10A according to the first embodiment can be utilized
advantageously as a pixel of a display with an aim to decrease the pitch between the
pixels.
[0101] Next, an electron emitter 10B according to a second embodiment will be described
with reference to FIG. 11.
[0102] As shown in FIG. 11, the electron emitter 10B according to the second embodiment
includes an emitter section 14 having a width d in the range of 0.1 to 50 µm. A cathode
electrode 16 is formed on one side of the emitter section 14, and an anode electrode
20 is formed on the other side of the emitter section 14. The emitter section 14 is
formed in a slit 18 between the cathode electrode 16 and the anode electrode 20, and
the emitter section 14 is sandwiched between the cathode electrode 16 and the anode
electrode 20.
[0103] As with the first embodiment, a charging film 40 is formed on the surface of the
anode electrode 20. As shown in FIG. 11, a protective film 42 may be formed on the
cathode electrode 16.
[0104] In the electron emitter 10B according to the second embodiment, as with the electron
emitter 10A according to the first embodiment, damages to the cathode electrode 16
are prevented. Since the emitter section 14 is made of a dielectric material, and
sandwiched between the cathode electrode 16 and the anode electrode 20, the polarization
in the emitter section 14 is carried out completely, and the electron emission by
the polarization reversal can be performed stably and efficiently.
[0105] Next, three modifications of the electron emitter 10B according to the second embodiment
will be described with reference to FIGS. 12 to 16.
[0106] The electron emitter 10Ba in the first modification is based on the same concept
as the electron emitter 10B according to the second embodiment, but differs from the
electron emitter 10B in that the emitter section 14 is formed in a tortuous pattern
in a plan view, as shown in FIGS. 12 and 13.
[0107] If the emitter section 14 is formed in a tortuous pattern, the area of contact between
the cathode electrode 16 and the emitter section 14 and the area of contact between
the anode electrode 20 and the emitter section 14 are increased for efficiently emitting
electrons. Also in this modification, a charging film 40 is formed on the surface
of the anode electrode 20. As shown in FIGS. 12 and 13, a protective film 42 may be
formed on the cathode electrode 16.
[0108] As shown in FIG. 14, an electron emitter 10Bb according a second modification has
an emitter section 14 made of a dielectric material on the substrate 12, and a cathode
electrode 16 and an anode electrode 20 which are embedded in windows defined in the
emitter section 14. The cross-sectional areas of the cathode electrode 16 and the
anode electrode 20 are thus increased to reduce the resistance of the cathode electrode
16 and the anode electrode 20 for suppressing the generation of the Joule heat. That
is, the cathode electrode 16 and the anode electrode 20 can be protected. Also in
this modification, a charging film 40 is formed on the surface of the anode electrode
20. As shown in FIG. 14, a protective film 42 may be formed on the cathode electrode
16.
[0109] In the second modification, the thickness of the cathode electrode 16 and the thickness
of the anode electrode 20 are the same as the thickness of the emitter section 14.
In an electron emitter 10Bc according to a third modification, and the thickness of
the cathode electrode 16, the thickness of the anode electrode 20 are thinner than
the thickness of the emitter section 14 as shown in FIGS. 15 and 16. As with the electron
emitter 10B according to the second embodiment shown in FIG. 11, the cathode electrode
16 and the anode electrode 20 are formed in contact with side walls of the emitter
section 14 in the slit 18. Also in this modification, a charging film 40 is formed
on the surface of the anode electrode 20. As shown in FIG. 15, a protective film 42
may be formed on the cathode electrode 16.
[0110] In the third modification, the amount of metals needed for the cathode electrode
16 and the anode electrode 20 is small as with the first modification. Therefore,
a precious metal such as platinum or gold can be used as a material forming the cathode
electrode 16 and the anode electrode 20, and the characteristics of the electrodes
are improved.
[0111] In the electron emitters 10A and 10B according to the first and second embodiments
(including the modifications), the collector electrode 24 is coated with the fluorescent
layer 28 for use as a pixel of a display. The displays of the electron emitters 10A
and 10B offer the following advantages:
(1) The displays can be thinner (the panel thickness = several mm) than CRTs.
(2) Since the displays emit natural light from the fluorescent layer 28, they can
provide a wide angle of view which is about 180° unlike LCDs (liquid crystal displays)
and LEDs (light-emitting diodes).
(3) Since the displays employ a surface electron source, they produce less image distortions
than CRTs.
(4) The displays can respond more quickly than LCDs, and can display moving images
free of after image with a high-speed response on the order of µsec.
(5) The displays consume an electric power of about 100 W in terms of a 40-inch size,
and hence is characterized by lower power consumption than CRTs, PDPs (plasma displays),
LCDs, and LEDs.
(6) The displays have a wider operating temperature range (- 40 to + 85°C) than PDPs
and LCDs. LCDs have lower response speeds at lower temperatures.
(7) The displays can produce higher luminance than conventional FED displays as the
fluorescent material can be excited by a large current output.
(8) The displays can be driven at a lower voltage than conventional FED displays because
the drive voltage can be controlled by the polarization reversing characteristics
and film thickness of the piezoelectric material.
[0112] Because of the above various advantages, the displays can be used in a variety of
applications described below.
(1) Since the displays can produce higher luminance and consume lower electric power,
they are optimum for use as 30- through 60-inch displays for home use (television
and home theaters) and public use (waiting rooms, karaoke rooms, etc.).
(2) Inasmuch as the displays can produce higher luminance, can provide large screen
sizes, can display full-color images, and can display high-definition images, they
are optimum for use as horizontally or vertically long, specially shaped displays,
displays in exhibitions, and message boards for information guides.
(3) Because the displays can provide a wider angle of view due to higher luminance
and fluorescent excitation, and can be operated in a wider operating temperature range
due to vacuum modularization thereof, they are optimum for use as displays on vehicles.
Displays for use on vehicles need to have a horizontally long 8-inch size whose horizontal
and vertical lengths have a ratio of 15 : 9 (pixel pitch = 0.14 mm), an operating
temperature in the range from - 30 to + 85°C, and a luminance level ranging from 500
to 600 cd/m2 in an oblique direction.
[0113] Because of the above various advantages, the electron emitters can be used as a variety
of light sources described below.
(1) Since the electron emitters can produce higher luminance and consume lower electric
power, they are optimum for use as projector light sources which are required to have
a luminance level of 200 lumens.
(2) Because the electron emitters can easily provide a high-luminance two-dimensional
array light source, can be operated in a wide temperature range, and have their light
emission efficiency unchanged in outdoor environments, they are promising as an alternative
to LEDs. For example, the electron emitters are optimum as an alternative to two-dimensional
array LED modules for traffic signal devices. At 25°C or higher, LEDs have an allowable
current lowered and produce low luminance.
1. An electron emitter comprising:
an emitter section (14) made of a dielectric material;
a first electrode (16) formed in contact with said emitter section (14);
a second electrode (20) formed in contact with said emitter section (14), wherein
a slit (18) is formed between said first electrode (16) and said second electrode
(20);
a drive voltage (Va) is applied between said first electrode (16) and said second
electrode (20) to induce emission of electrons from at least a portion of said emitter
section (14) which is exposed through said slit (18); and
a charging film (40) is formed at least on a surface of said second electrode (20).
2. An electron emitter according to claim 1, wherein said emitter section (14) is made
of a piezoelectric material, an anti-ferroelectric material, or an electrostrictive
material.
3. An electron emitter according to claim 1 or 2, wherein polarization reversal occurs
in an electric field E applied to said emitter section (14) represented by E= Vak/d,
where d is a width of said slit (18), and Vak is a voltage applied between said first
electrode (16) and said second electrode (20).
4. An electron emitter according to claim 3, wherein said voltage Vak is less than a
dielectric breakdown voltage of said emitter section (14).
5. An electron emitter according to claim 3 or 4, wherein the width d of said slit (18)
is determined so that the voltage Vak applied between said first electrode (16) and
said second electrode (20) has an absolute value of less than 100V.
6. An electron emitter according to any one of claims 1 to 5, wherein said charging film
(40) is made of a piezoelectric material, an electrostrictive material, an anti-ferroelectric
material, or a material having a low dielectric constant.
7. An electron emitter according to claim 6, wherein said material having a low dielectric
constant is an oxide or a glass.
8. An electron emitter according to any one of claims 1 to 7, wherein said charging film
(40) and said emitter section (14) are made of a same dielectric material.
9. An electron emitter according to any one of claims 1 to 8, wherein said charging film
(40) has a thickness in the range of 10 nm to 100 µm.
10. An electron emitter according to any one of claims 1 to 9, wherein a protective film
(42) is formed on a surface of said first electrode (16).
11. An electron emitter according to claim 10, wherein said protective film (42) and said
charging film (40) are made of a same material.
12. An electron emitter according to claim 10 or 11, wherein said protective film (42)
is made of an insulator or a highly resistive conductor having a low sputtering yield
and a high evaporation temperature in vacuum.
13. An electron emitter according to any one of claims 10 to 12, wherein said protective
film (42) has a thickness in the range of 10 nm to 100 nm.
14. An electron emitter according to any one of claims 1 to 13, wherein the change of
the voltage applied between said first electrode (16) and said second electrode (20)
at the time of electron emission is 20V or less.
15. An electron emitter according to any one of claims 1 to 14, wherein said first electrode
(16) and said second electrode (20) are formed on an upper surface of said emitter
section (14), and said slit (18) is a gap.
16. An electron emitter according to any one of claims 1 to 14, wherein said first electrode
(16) is formed in contact with one side of said emitter section (14), said second
electrode (20) is formed in contact with the other side of said emitter section (14),
and said emitter section (14) is formed in said slit (18).
17. An electron emitter according to claim 16, wherein said emitter section (18) is formed
in a tortuous pattern.
18. An electron emitter according to any one of claims 1 to 17, wherein said drive voltage
(Va) is applied between said first electrode (16) and said second electrode (20) such
that said first electrode (16) has a potential lower than a potential of said second
electrode (20) to reverse polarization of at least a portion of said emitter section
(14) which is exposed through said slit (18); and
the polarization reversal causes emission of electrons in the vicinity of said
first electrode (16).
19. An electron emitter according to any one of claims 1 to 18, wherein said drive voltage
(Va) is applied between said first electrode (16) and said second electrode (20) to
reverse polarization of a portion of said emitter section which is exposed through
said slit (18);
the polarization reversal causes positive poles of dipole moments in the vicinity
of said first electrode (16) to be oriented toward said first electrode (16), inducing
emission of primary electrons from said first electrode (16); and
said emitted primary electrons impinge upon said emitter section (14) to induce
emission of secondary electrons from said emitter section (14).
20. An electron emitter according to claim 19, wherein said first electrode (16), a portion
of said emitter section (16) which is exposed through said slit (18), and a vacuum
atmosphere define a triple point; and
primary electrons are emitted from a portion of said first electrode (16) in the
vicinity of said triple point, and said emitted primary electrons impinge upon said
emitter section (14) to induce emission of secondary electrons from said emitter section
(14).
21. An electron emitter according to any one of claims 1 to 20, wherein a third electrode
(24) is provided above said emitter section (14) at least at a portion facing said
slit (18), and said third electrode (24) is coated with a fluorescent layer (28).
22. An electron emitter according to any one of claims 16 to 20, wherein
said emitter section (14) is provided on an upper surface of a substrate (12);
said first electrode (16) is formed in contact with one side of said emitter section
(14);
said second electrode (20) is formed in contact with the other side of said emitter
section (14);
said emitter section (14) is formed in said slit (18);
a third electrode (24) is provided above said substrate (12); and
said third electrode (24) is coated with a fluorescent layer (28).