Electron beam apparatus and method of driving the same

An electron beam apparatus comprises an electron-emitting device, an anode separated from the electron-emitting device by a distance H (m), means for applying a voltage Vf (V) to the device, and means for applying a voltage Va (V) to the anode. The device has an electron-emitting region arranged between a lower potential side electroconductive thin film which is connected to a lower potential side electrode and a higher potential side electroconductive thin film which is connected to a higher potential side electrode. The device also has a film containing a semiconductor substance with a thickness not greater than 10 nm. The semiconductor-containing film extends on the higher potential side electroconductive thin film from the electron-emitting region toward the higher potential side electrode over a length L (m). The above Vf, Va, H and L satisfy the relationship L.gtoreq.(1/.pi.).multidot.(Vf/Va).multidot.H.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an electron beam apparatus using 
electron-emitting devices and it also relates to a method of driving such 
an apparatus. 
2. Related Background Art 
There have been known two types of electron-emitting device: the thermionic 
type and the cold cathode type. Of these, the cold cathode type refers to 
devices including field emission type (hereinafter referred to as the FE 
type) devices, metal/insulation layer/metal type (hereinafter referred to 
as the MIM type) electron-emitting devices and surface conduction 
electron-emitting devices. Examples of FE type devices include those 
proposed by W. P. Dyke & W. W. Dolan, "Field Emission", Advances in 
Electron Physics, 8, 89 (1956) and C. A. Spindt, "physical Properties of 
Thin-Fields Field Emission Cathodes thin-film field emission cathodes with 
Molybdenum Cones", J. Appl. Phys., 47, 5248 (1976). 
Examples of MIM devices are disclosed in various papers including C. A. 
Mead, "Operation of Tunnel-Emission Devices", J. Appl. Phys., 32, 646 
(1961). 
Examples of surface conduction electron-emitting devices include one 
proposed by M. I. Elinson, Radio Eng. Electron Phys., 10 (1965). A surface 
conduction electron-emitting device is realized by utilizing the 
phenomenon that electrons are emitted out by a small thin film formed on a 
substrate when an electric current is forced to flow in parallel with the 
film surface. While Elinson proposes the use of an SnO.sub.2 thin film for 
a device of this type, the use of an Au thin film is proposed in G. 
Dittmer, "Thin Solid Films", 9, 317 (1972), whereas the use of In.sub.2 
O.sub.3 /SnO.sub.2 and of carbon thin film are discussed respectively in 
M. Hartwell and C. G. Fonstad, "IEEE Trans. ED Conf.", 519 (1975) and H. 
Araki et al., "Vacuum", Vol. 26, No. 1, p. 22 (1983). 
FIG. 26 of the accompanying drawings schematically illustrates a typical 
surface conduction electron-emitting device proposed by M. Hartwell. In 
FIG. 26, reference numeral 121 denotes a substrate. Reference numeral 122 
denotes an electroconductive thin film normally prepared by producing an 
H-shaped thin metal oxide film by means of sputtering, part of which 
eventually makes an electron-emitting region 123 when it is subjected to a 
current conduction treatment referred to as "energization forming" as will 
be described hereinafter. In FIG. 26, the narrow film arranged between a 
pair of device electrodes has a length G of 0.5 to 1 mm and a width W' of 
0.1 mm. 
Conventionally, an electron emitting region 123 is produced in a surface 
conduction electron-emitting device by subjecting the electroconductive 
thin film 122 of the device to a preliminary treatment, which is referred 
to as "energization forming". In an energization forming process, a 
constant DC voltage or a slowly rising DC voltage that rises typically at 
a rate of 1 V/min. is applied to given opposite ends of the 
electroconductive thin film 122 to partly destroy, deform or transform the 
film and produce an electron-emitting region 123 which is electrically 
highly resistive. Thus, the electron-emitting region 123 is part of the 
electroconductive thin film 122 that typically contains a fissure or 
fissures therein so that electrons may be emitted from the fissurer. Note 
that, once subjected to an energization forming process, a surface 
conduction electron-emitting device comes to emit electrons from its 
electron emitting region 123 whenever an appropriate voltage is applied to 
the electroconductive thin film 122 to make an electric current run 
through the device. 
Known surface conduction electron-emitting devices include, beside the 
above-described device of M. Hartwell, one comprising an insulating 
substrate, a pair of oppositely disposed device electrodes of an 
electroconductive material formed on the substrate and a thin film of 
another electroconductive material arranged to connect the device 
electrodes. An electron-emitting region is produced in the 
electroconductive thin film when the latter is subjected to energization 
forming. Techniques that can be used for energization forming include that 
of applying a slowly rising voltage as described above and the one with 
which a pulse voltage is applied to an electron-emitting device and the 
wave height of the pulse voltage is gradually raised. 
The intensity of the electron beam emitted from an electron-emitting device 
can be remarkably raised by carrying out an activation process on the 
electron-emitting device that has been subjected to an energization 
forming process. In an activation process, a pulse voltage is applied to 
the device that is placed in a vacuum chamber so that carbon or a carbon 
compound may be produced on the device by deposition at a location close 
to the electron-emitting region from an organic substance existing in the 
vacuum of the vacuum chamber. 
Japanese Patent Application Laid-Open No. 6-141670 discloses a surface 
conduction electron-emitting device, its configuration and a method of 
manufacturing such a device. 
However, when surface conduction electron-emitting devices are used in a 
flat type image-forming apparatus, the ratio of the electric current 
generated as a result of electron emission (emission current Ie) from the 
device to the electric current running through each device (device current 
If) is preferably made as large as possible in order to improve the 
electron emission efficiency of the device from the viewpoint of achieving 
a good quality for displayed images and, at the same time, reducing the 
power consumption rate of the device. A large emission current to device 
current ratio is particularly important for a high definition 
image-forming apparatus comprising a large number of pixels and is 
realized by arranging a large number of electron-emitting devices because 
such an apparatus inevitably consumes power at an enhanced rate and a 
considerable portion of the substrate of the apparatus that carries the 
electron-emitting devices thereon is occupied by wires connecting the 
devices. If each of the electron-emitting devices shows an excellent 
electron-emitting efficiency and consumes little power, smaller wires can 
be used, to provide a higher degree of freedom in designing the overall 
image-forming apparatus. 
Further, in order to produce bright and clear images, not only the 
electron-emitting efficiency but also the emission current Ie of each 
device has to be improved. 
Finally, each electron-emitting device is required to maintain its good 
performance of electron emission for a prolonged period in order for the 
image-forming apparatus comprising such devices to operate reliably for a 
long service life. 
SUMMARY OF THE INVENTION 
In view of the above identified technological problems, it is, therefore, 
an object of the present invention to provide an electron beam apparatus, 
or an image-forming apparatus in particular, comprising one or more 
electron-emitting devices having an improved electron-emitting efficiency. 
Another object of the present invention is to provide an electron beam 
apparatus, or an image-forming apparatus in particular, comprising one or 
more electron-emitting devices having an improved emission current. 
Still another object of the present invention is to provide a method of 
driving an electron beam apparatus, or an image-forming apparatus in 
particular, comprising one or more electron-emitting devices that can 
improve the electron-emitting efficiency of the electron-emitting devices. 
A further object of the present invention is to provide a method of driving 
an electron beam apparatus, or an image-forming apparatus in particular, 
comprising one or more electron-emitting devices that can improve the 
emission current of the electron-emitting devices. 
According to a first aspect of the invention, there is provided an electron 
beam apparatus comprising an electron-emitting device, an anode, means for 
applying a voltage Vf (V) to said electron-emitting device and means for 
applying another voltage Va (V) to said anode, said electron-emitting 
device and said anode being separated by a distance H (m), wherein said 
electron-emitting device has an electron-emitting region arranged between 
a lower potential side electroconductive thin film connected to a lower 
potential side electrode and a higher potential side electroconductive 
thin film connected to a higher potential side electrode and also has a 
film containing a semiconductor substance and having a thickness not 
greater than 10 nm, said semiconductor-containing film extending on said 
higher potential side electroconductive thin film from said 
electron-emitting region toward said higher potential side electrode over 
a length L (m) satisfying the relationship expressed by formula (1) below: 
##EQU1## 
According to a second aspect of the invention, there is provide a method of 
driving an electron beam apparatus comprising an electron-emitting device 
having an electron-emitting region arranged between a lower potential side 
electroconductive thin film connected to a lower potential side electrode 
and a higher potential side electroconductive thin film connected to a 
higher potential side electrode and also having a film containing a 
semiconductor substance and having a thickness not greater than 10 nm, 
said semiconductor-containing film extending on said higher potential side 
electroconductive thin film from said electron-emitting region toward said 
higher potential side electrode over a length L (m), and an anode disposed 
as separated from said electron-emitting device by a distance H (m), 
wherein the electron beam apparatus is driven in such a way that voltage 
Vf (V) applied to said electron-emitting device and voltage Va (V) applied 
to said anode satisfies the relationship expressed by formula (1) below: 
##EQU2##

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1A and 1B schematically illustrate a surface conduction 
electron-emitting device prepared according to a first mode of realizing 
the present invention. It comprises an electron-scattering plane forming 
layer 6 arranged on the higher potential side electroconductive thin film 
5 and, if necessary, also on the higher potential side device electrode of 
the device in order to provide a highly efficient electron-scattering 
plane that elastically scatters electrons striking the device from 
outside. FIG. 1A is a plane view and FIG. 1B is a cross-sectional side 
view taken along line 1B--1B in FIG. 1A. Reference numeral 1 denotes an 
insulating substrate, reference numerals 2 and 3 respectively denote lower 
and higher potential side device electrodes, reference numeral 4 denotes a 
lower potential side electrode, and reference numeral 7 denotes an 
electron-emitting region. 
The electron-scattering plane is a boundary plane of two different 
substances at which incident electrons are elastically scattered in a 
highly efficient way. The electron-scattering plane is formed on the 
higher potential side electroconductive thin film 5 and, if necessary, 
also on the higher potential side device electrode 3 and extending from 
the electron-emitting region 7 toward the higher potential side device 
electrode 3 over a length L that preferably satisfies the relationship 
expressed by formula (1) below: 
##EQU3## 
where Vf is the voltage (device voltage) applied between the oppositely 
disposed device electrodes 2 and 3 of the surface conduction 
electron-emitting device 8, Va is the voltage applied between the surface 
conduction electron-emitting device 8 and an anode 9, which will be 
described below, and H is the distance between the electron-emitting 
device and the anode. Referring to FIG. 2, an anode 9 is arranged 
vis-a-vis the surface conduction electron-emitting device 8 in order to 
effectively capture electrons coming from the electron-emitting device 
when the latter is driven to emit electrons. 
The effect of an electron-scattering plane for efficiently scattering 
electrons may be given rise to in a manner as described below by referring 
to FIG. 4. In FIG. 4, reference 25 denotes a vacuum space and external 
electrons come to strike the electron-scattering plane forming layer by 
way of this space. Reference numeral 26 denotes the surface of an 
electron-scattering plane forming layer that reflects and scatters part of 
incident electrons to give rise to their respective tracks, only one of 
which is shown there, indicated by reference numeral 28. A boundary plane 
is formed under the surface and operates as an electron-scattering plane 
27. This plane is defined as a boundary plane of either of the first and 
second layers of an electron-scattering plane forming layer or an 
electron-scattering plane forming layer and the higher potential side 
electroconductive thin film, although its function is the same in both 
cases. Some of the electrons passing through the surface 26 of the 
electron-scattering plane forming layer are reflected and scattered by 
this electron-scattering plane to fly into the vacuum space to give rise 
to their respective tracks, only one of which is shown there, indicated by 
reference numeral 29. The remaining electrons that pass through the 
electron-scattering plane 27 will eventually lose the energy they have and 
will not fly back into the vacuum space, as indicated by reference numeral 
30. Thus, it will be safe to assume that an electron-scattering plane 27 
effectively and efficiently produces scattered electrons that fly back 
into the vacuum space. 
If the distance, or the depth, of the electron-scattering plane 27 from the 
surface 26 of the electron-scattering plane forming layer is too large, 
electrons can lose the energy they have while they are traveling 
therebetween to reduce the electron scattering efficiency of the 
electron-scattering plane. 
If the electron-scattering plane forming layer has a double-layered 
configuration, the first and second layers are prepared from different 
materials in order to produce a good electron scattering effect. 
Preferably, the materials of the two layers are so selected as to make the 
electron-scattering plane show a large potential difference. A large 
potential difference may be obtained when both the electronegativities and 
the work functions of the two materials show a large difference. As will 
be described hereinafter, a favorable effect can be achieved when 
semiconductor substances, specifically Si and B, are used for the first 
layer and metals of the IIIb group, specifically La and Sc, or those of 
the IIa group, specifically Sr and Ba, are used for the second layer. 
However, materials that can be used for these two layers are not limited 
to those listed above, and many other materials may be used if they 
produce a highly efficient elastic electron scattering effect on the 
electron scattering plane. 
Now, a surface conduction electron-emitting device that can be used for the 
purpose of the invention will be described in greater detail. 
Materials that can be used for the substrate 1 include quartz glass, glass 
containing impurities such as Na to a reduced concentration level, soda 
lime glass, a glass substrate realized by forming an SiO.sub.2 layer on 
soda lime glass by means of sputtering, and ceramic substances such as 
alumina, as well as Si. While the oppositely arranged lower and higher 
potential side device electrodes 2 and 3 may be made of any highly 
conducting material, preferred candidate materials include metals such as 
Ni, Cr, Au, Mo, W, Pt, Ti, Al, Cu and Pd and their alloys, printable 
conducting materials made of a metal or a metal oxide selected from Pd, 
Ag, Au, RuO.sub.2, Pd-Ag, etc., in combination with glass, transparent 
conducting materials such as In.sub.2 O.sub.3 --SnO.sub.2 and 
semiconductor materials such as polysilicon. 
Referring to FIGS. 1A and 1B, the gap length G separating the device 
electrodes 2 and 3, the length W of the device electrodes, the contours of 
the lower and higher potential side electroconductive films 4 and 5 and 
other factors for designing a surface conduction electron-emitting device 
according to the invention may be determined depending on the-application 
of the device. The gap length G separating the device electrodes 2 and 3 
is preferably between hundreds of nanometers and hundreds of micrometers 
and, still preferably, between several micrometers and several tens of 
micrometers. 
The length W of the device electrodes 2 and 3 is preferably between several 
micrometers and several hundreds of micrometers depending on the 
resistance of the electrodes and the electron-emitting characteristics of 
the device. The film thickness d of the device electrodes is between tens 
of several tens of nanometers and several micrometers. 
A surface conduction electron-emitting device according to the invention 
may have a configuration other than the one illustrated in FIGS. 1A and 1B 
and, alternatively, it may be prepared by laying electroconductive thin 
films 4 and 5 on a substrate 1 and then oppositely disposed lower and 
higher potential side device electrodes 2 and 3. 
The electroconductive thin films 4 and 5 are preferably fine particle films 
in order to provide excellent electron-emitting characteristics. The 
thickness of the electroconductive thin films is determined as a function 
of the stepped coverage of the electroconductive thin films on the device 
electrodes 2 and 3, the electric resistance between the device electrodes 
2 and 3 and the parameters for the forming operation that will be 
described later as well as other factors and preferably between several 
tenths of a nanometers and several hundreds of nanometers and more 
preferably between a nanometer and fifty nanometers. The electroconductive 
thin films 4 and 5 normally show a sheet resistance Rs between 10.sup.2 
and 10.sup.7 .OMEGA./.quadrature.. Note that Rs is the resistance defined 
by R=Rs(l/w), where t, w and l are the thickness, the width and the length 
of a thin film respectively and R is the resistance determined along the 
longitudinal direction of the thin film. Also note that, while the forming 
process is described in terms of current conduction treatment for the 
purpose of the present invention, it is not limited thereto and may 
include a variety of processing steps where a fissure is formed in the 
thin film to produce a high resistance state there. 
The electroconductive thin films 4 and 5 are made of fine particles of a 
material primarily selected from metals such as Pd, Pt, Ru, Ag, Au, Ti, 
In, Cu, Cr, Fe, Zn, Sn, Ta, W and Pb, oxides such as PdO, SnO.sub.2, 
In.sub.2 O.sub.3, PbO and Sb.sub.2 O.sub.3, borides such as HfB.sub.2, 
ZrB.sub.2, LaB.sub.6, CeB.sub.6, YB.sub.4 and GdB.sub.4, carbides such 
TiC, ZrC, HfC, TaC, SiC and WC, nitrides such as TiN, ZrN and HfN, and the 
like. 
The term a "fine particle film" as used herein refers to a thin film 
constituted of a large number of fine particles that may be loosely 
dispersed, tightly arranged or mutually and randomly overlapping (to form 
an island structure under certain conditions). The diameter of fine 
particles to be used for the purpose of the present invention is between 
tenths of a several nanometers and several hundreds of several nanometers 
and preferably between a nanometer and twenty nanometers. 
Since the term "fine particle" is frequently used herein, it will be 
described in greater depth below. 
A small particle is referred to as a "fine particle" and a particle smaller 
than a fine particle is referred to as an "ultrafine particle". A particle 
smaller than an "ultrafine particle" and constituted by several hundred 
atoms is referred to as a "cluster". 
However, these definitions are not rigorous and the scope of each term can 
vary depending on the particular aspect of the particle to be dealt with. 
An "ultrafine particle" may be referred to simply as a "fine particle" as 
in the case of this patent application. 
"The Experimental Physics Course No. 14: Surface/Fine Particle" (ed., Koreo 
Kinoshita; Kyoritu Publication, Sep. 1, 1986) describes as follows: 
"A fine particle as used herein refers to a particle having a diameter 
somewhere between 2 to 3 .mu.m and 10 nm and an ultrafine particle as used 
herein means a particle having a diameter somewhere between 10 nm and 2 to 
3 nm. However, these definitions are by no means rigorous and an ultrafine 
particle may also be referred to simply as a fine particle. Therefore, 
these definitions are a rule of thumb in any means. A particle constituted 
of two atoms to several tens or hundreds of atoms is called a cluster." 
(Ibid., p.195, 11.22-26) 
Additionally, "Hayashi's Ultrafine Particle Project" of the New Technology 
Development Corporation defines an "ultrafine particle" as follows, 
employing a smaller lower limit for the particle size: 
"The Ultrafine Particle Project (1981-1986) under the Creative Science and 
Technology Promoting Scheme defines an ultrafine particle as a particle 
having a diameter between about 1 and 100 nm. This means an ultrafine 
particle is an agglomerate of about 100 to 10.sup.8 atoms. From the 
viewpoint of atom, an ultrafine particle is a huge or ultrahuge particle." 
("Ultrafine Particle-Creative Science and Technology": ed., Chikara 
Hayashi, Ryoji Ueda, Akira Tazaki; Mita Publication, 1988, p.2, 11.1-4) "A 
particle smaller than an ultrafine particle and constituted by several to 
several hundred atoms is referred to as a cluster. (Ibid., p.2, 11.12-13) 
Taking the above general definitions into consideration, the term "a fine 
particle" as used herein refers to an agglomerate of a large number of 
atoms and/or molecules having a diameter with a lower limit between a 
tenth of several nanometers and a nanometer and with an upper limit of 
several micrometers. 
The electron-emitting region 7 is formed between the lower potential side 
and higher potential side electroconductive thin films 4 and 5 and 
comprises an electrically highly resistive fissure, although its 
performance is dependent on the thickness, the nature and the material of 
the electroconductive thin films 4 and 5 and the energization forming 
process which will be described hereinafter. The electron emitting region 
7 may contain in the inside electroconductive fine particles having a 
diameter between a tenth of several nanometers and tens of several 
nanometers. The material of such electroconductive fine particles may 
contain all or part of the materials that can be used to prepare the 
electroconductive thin films 4 and 5 including the electron emitting 
region. 
Subsequently, an electron-scattering plane forming layer 6 is produced. 
This will be described in terms of an electron-scattering plane forming 
layer having a double-layered configuration. (FIG. 17A schematically 
illustrates such a double-layered configuration.) 
Firstly the second layer of an electron-scattering plane forming layer 6 is 
produced on the higher potential side electroconductive thin film 5. 
Techniques that can be used for this operation include vacuum evaporation 
and sputtering as well as chemical techniques such as MOCVD (metal organic 
chemical vapor deposition). Two or more than two such techniques may be 
used in combination. 
If the technique of vacuum evaporation or sputtering is used, a patterning 
operation has to be conducted in order to form a film only in necessary 
areas. If the technique of MOCVD is used, to the contrary, a film can be 
formed selectively on the higher potential side device electrode 3 and the 
higher potential side electroconductive thin film 5, although the produced 
films may not necessarily show a desired profile because there may be 
areas where a film can easily grow and areas where a film cannot easily 
grow depending on surface configuration or other factors of the device. If 
such is the case, MOCVD may be used for areas near the electron-emitting 
region 7, while vacuum evaporation or sputtering may be used for the 
remaining areas. 
Materials that can be used for the second layer include metals of the 2a 
and 3a groups, specifically Sr, Ba, Sc and La. Any of these substances can 
be used in combination with one of the materials that can be used for the 
first layer, which will be described hereinafter. Source gases that can be 
used for CVD for the second layer include Sr(C.sub.11 H.sub.19 
O.sub.2).sub.3, Ba(C.sub.11 H.sub.19 O.sub.2).sub.3, Sc(C.sub.11 H.sub.19 
O.sub.2).sub.3 and La(C.sub.11 H.sub.19 O.sub.2).sub.3. 
Note that the second layer is not necessary if the boundary plane of the 
first layer and the electroconductive thin film is used for an 
electron-scattering plane. (FIG. 17B schematically illustrates such a 
single-layered configuration.) 
Then, the first layer is formed. The methods that can be used for forming 
the second layer can also be used for the first layer. While materials 
that can be used for the first layer include semiconductor substances, the 
use of Si or B is preferable. The film thickness of the first layer has to 
be rigorously controlled to less than 10 nm, preferably less than 5 nm, 
because the film thickness of the first layer significantly affects the 
efficiency of elastic electron-scattering of the device. Source gases that 
can be used for CVD for the first layer include SiH.sub.4 and B(C.sub.2 
H.sub.5).sub.3. 
Note that the two component layers of an electron-scattering plane forming 
layer having a double-layered configuration are not necessarily arranged 
continuously and they may be layered in a discontinuous manner. 
Now, the right side of formula (1) will be described below. 
For driving a surface conduction electron-emitting device to emit 
electrons, values for Vf, H and Va are selected respectively from 
somewhere between ten and several tens of volts (V), 2 and 8 millimeters 
(mm) and 1 and 10 kilovolts (kV). By looking into the electric field 
formed by the electron-emitting device and the anode under these 
conditions, it will be found that electrons in a region above the higher 
potential side electroconductive thin film 5 are subjected to a downward 
force directed to the higher potential side electroconductive thin film 5 
or the device electrode 3. FIG. 3 schematically illustrates such a region 
indicated by oblique lines and denoted by reference numeral 10. In this 
region, electrons are subjected to a downward force due to the electric 
field generated there. 
The region extends from the electron-emitting region toward the higher 
potential side device electrode for a distance of 
##EQU4## 
which is the same as the right side of formula (1). 
Most of the electrons emitted from the electron-emitting region cannot 
leave the slashed region of FIG. 3 immediately because of the downward 
force of the electric field applied to them and strike the 
electron-scattering plane forming layer. The incident electrons are 
scattered and/or absorbed by the layer. Electrons are scattered either 
elastically without losing the energy they have or non-elastically, losing 
part of the energy they have. Further, secondary electrons may be emitted 
by incident electrons. Since the energy level of electrons scattered 
non-elastically and those energized and emitted secondarily by incident 
electrons is lower than that of elastically scattered electrons, they 
cannot overcome the downward force exerted by the electric field and hence 
cannot leave the slashed region so that they are eventually absorbed by 
the higher potential side electroconductive thin film 5 or the device 
electrode 3 and take part in the device current If. Thus, only electrons 
that are elastically scattered can overcome the downward force of the 
electric field and eventually leave the region to produce an emission 
current. 
Electrons emitted from the electron-emitting region 7 show a certain spread 
angle. While some of them may immediately get out of the slashed region of 
FIG. 3 and fly toward the anode 9 as indicated by trajectory a, most of 
them are pulled back by the downward force of the electric field existing 
there and enter the electron-scattering plane forming layer 6. A given 
portion of these electrons are elastically scattered and eventually leave 
the slashed region 10 to get to the anode 9. Once they leave the 
electron-emitting region by the distance expressed by formula 2, the force 
applied to them by-the electric field is directed upward so that they may 
produce their respective trajectories that get to the anode such as 
trajectory b illustrated in FIG. 3. 
Electrons emitted from the electron-emitting region may be elastically 
scattered by the electroconductive thin film 3 with a non-zero probability 
if an electron-scattering plane forming layer 6 is not provided. However, 
the probability with which electrons are elastically scattered is 
remarkably increased by arranging an electron-scattering plane forming 
layer 6 to increase the ratio of "surviving" electrons and hence the 
electron emitting efficiency of the device. Preferably, the 
electron-scattering plane forming layer 6 is made to entirely cover the 
higher potential side electroconductive thin film 5 that is directly 
neighboring the slashed region 10 of FIG. 3 and, if the region 10 gets to 
the surface of the higher potential side device electrode 3 that does not 
carry thereon any electroconductive thin film, it may preferably be 
extended to the surface of the electrode 3 or made longer than the length 
expressed by formula (2). 
A surface conduction electron-emitting device prepared according to a 
second mode of realizing the present invention comprises, in addition to 
the components of a device of the first mode of realization, a low work 
function material layer 83 arranged on the lower potential side 
electroconductive thin film 4 at least in an area close to the 
electron-emitting region 7. With such an arrangement, the emission current 
Ie of the device can be significantly increased. 
Materials that can be used for the low work function material layer 83 
include metals of the IIa and IIIb groups, which may also be used for one 
of the double layers constituting the electron-scattering plane forming 
layer 6, if the latter has a double-layered configuration. In other words, 
the two layers can be produced in a single manufacturing step and, 
therefore, an electron-emitting device according to the first mode and a 
device according to the second mode of realizing the present invention can 
be manufactured with a same number of manufacturing steps, although they 
may alternatively be manufactured with different manufacturing steps. 
A surface conduction electron-emitting device prepared according to a third 
mode of realizing the present invention comprises, in addition to the 
components of a device of the first mode of realization, a high melting 
point substance layer 84 arranged on the lower potential side 
electroconductive thin film 4 at least in an area close to the 
electron-emitting region 7. 
If the high melting point substance layer 6 is made of a material that is 
also used in the electron-scattering plane forming layer 6 like the case 
of a device according to the second mode of realizing the invention, the 
above manufacturing method as described for the second mode of realization 
may also be used. Materials of the high melting point substance layer, 
however, is generally different from that of the electron-scattering plane 
forming layer. A high melting point substance layer 84 may well be formed 
by deposition in an area of the electron-emitting region located close to 
the lower potential side electroconductive thin film by applying a 
positive pulse voltage to the lower potential side electroconductive thin 
film, which is opposite to the case of driving the device, and using a CVD 
technique in an atmosphere containing an appropriate source gas. 
Materials that can be used for the high melting point substance layer 84 
include the metals of the IVb, Vb, VIb, VIIb and VIII groups in the fifth 
and sixth periods, any of which may be used as an independent metal, as an 
alloy or as a mixture thereof. More specifically, any of Nb, Mo, Ru, Hf, 
Ta, W, Re, Os and Ir may be used as an independent metal because they show 
a melting point higher than 2,000.degree. C. Either of Zr and Rh may also 
be used as an independent metal because they have a melting point close to 
2,000.degree. C. For the purpose of the present invention, the temperature 
at which the material for the high melting point substance layer gives 
rise to a vapor pressure of 1.3.times.10.sup.-3 Pa (10.sup.-5 Torr) is of 
particular interest from the viewpoint that the film may be partly 
sublimated as it is heated to degrade its performance. While Pd gives rise 
to the above vapor pressure at 1,100.degree. C., the corresponding 
temperatures of W, Ta, Re, Os and Nb are respectively 2,570.degree. C., 
2,410.degree. C., 2,380.degree. C., 2,330.degree. C. and 2,120.degree. C. 
and, therefore, any of these substances may preferably be used for the 
purpose of the invention. Particularly, the use of W is most preferable 
because its melting point is 3,380.degree. C. which is higher than those 
of the other metals. 
Source gases that can be used to deposit these metals by CVD include 
NbF.sub.5, NbCl.sub.5, Nb(C.sub.5 H.sub.5)(CO).sub.4, Nb(C.sub.5 
H.sub.5).sub.2 Cl.sub.2, OsF.sub.4, Os(C.sub.3 H.sub.7 O.sub.2).sub.3, 
Os(CO).sub.5, Os.sub.3 (CO).sub.12, Os(C.sub.5 H.sub.5).sub.2, ReF.sub.5, 
ReCl.sub.5, Re(CO).sub.10, ReCl(CO).sub.5, Re(CH.sub.3)(CO).sub.5, 
Re(C.sub.5 H.sub.5)(CO).sub.3, Ta(C.sub.5 H.sub.5)(CO).sub.4, Ta(OC.sub.2 
H.sub.5).sub.5, Ta(C.sub.5 H.sub.5).sub.2 Cl.sub.2 Ta(C.sub.5 
H.sub.5).sub.2 H.sub.3, WF.sub.5, W(CO).sub.6, W(C.sub.5 H.sub.5).sub.2 
Cl.sub.2, W(C.sub.5 H.sub.5).sub.2 H.sub.2 and W(CH.sub.3).sub.6. 
With the arrangement of a high melting point substance layer, possible 
reduction with time of the emission current of a surface conduction 
electron-emitting device can be significantly suppressed. 
The electron-emitting performance of an electron-emitting device prepared 
according to any of the first through third modes of realizing the present 
invention as described above will now be described by referring to FIG. 7 
and FIGS. 8A and 8B. 
FIG. 7 is a schematic block diagram of an arrangement comprising a vacuum 
chamber that can be used as a gauging system for determining the 
performance of an electron emitting device of the type under 
consideration. Referring to FIG. 7, the gauging system includes a vacuum 
chamber 16 and a vacuum pump 17. An electron-emitting device is placed in 
the vacuum chamber 16. The device comprises a substrate 1, lower and 
higher potential side device electrodes 2 and 3, lower and higher 
potential side thin films 4 and 5 and an electron-emitting region 7. 
Although not shown in FIG. 7, the device additionally comprises an 
electron-scattering plane forming layer, a low work function material 
layer and/or a high melting point substance layer. Otherwise, the gauging 
system has a power source 11 for applying a device voltage Vf to the 
device, an ammeter 12 for metering the device current If running through 
the thin films 4 and 5 between the device electrodes 2 and 3, an anode 15 
for capturing the emission current Ie produced by electrons emitted from 
the electron-emitting region 7 of the device, a high voltage source 13 for 
applying a voltage to the anode 15 of the gauging system and another 
ammeter 14 for metering the emission current Ie produced by electrons 
emitted from the electron-emitting region 7 of the device. For determining 
the performance of the electron-emitting device, a voltage between 1 and 
10 kV may be applied to the anode, which is spaced apart from the electron 
emitting device by distance H which is between 2 and 8 mm. 
Instruments including a vacuum gauge and other pieces of equipment 
necessary for the gauging system are arranged in the vacuum chamber 16 so 
that the performance of the electron-emitting device or the electron 
source in the chamber may be properly tested under desired atmosphere. The 
vacuum pump 17 may be provided with an ordinary high vacuum system 
comprising a turbo pump and a rotary pump and an ultra-high vacuum system 
comprising an ion pump. The entire vacuum chamber containing an electron 
source substrate therein can be heated to 250.degree. C. by means of a 
heater (not shown). Thus, this vacuum processing arrangement can be used 
for the "forming" process and the subsequent processes. Reference numeral 
18 denotes a substance source for storing a substance to be introduced 
into the vacuum chamber whenever necessary. It may be an ampule or a 
cylinder. Reference numeral 19 denotes a valve to be used to regulate the 
rate of supplying the substance into the vacuum chamber. 
FIG. 8A shows a graph schematically illustrating the relationship between 
the device voltage Vf and the emission current Ie and the device current 
If typically observed by the gauging system of FIG. 7. Note that different 
units are arbitrarily selected for Ie and If in FIG. 8A in view of the 
fact that Ie has a magnitude by far smaller than that of If. Note that 
both the vertical and transversal axes of the graph represent linear 
scales. 
As seen in FIG. 8A, an electron-emitting device according to the invention 
has three remarkable features in terms of emission current Ie, which will 
be described below. 
(i) Firstly, an electron-emitting device according to the invention shows a 
sudden and sharp increase in the emission current Ie when the voltage 
applied thereto exceeds a certain level (which is referred to as a 
threshold voltage hereinafter and indicated by Vth in FIG. 8A), whereas 
the emission current Ie is practically undetectable when the applied 
voltage is lower than the threshold value Vth. Differently stated, an 
electron-emitting device according to the invention is a non-linear device 
having a clear threshold voltage Vth to the emission current Ie. 
(ii) Secondly, since the emission current Ie increases monotonically 
dependent on the device voltage Vf, the former can be effectively 
controlled by way of the latter. 
(iii) Thirdly, the emitted electric charge captured by the anode 35 is a 
function of the duration of time of application of the device voltage Vf. 
In other words, the amount of electric charge captured by the anode 15 can 
be effectively controlled by way of the time during which the device 
voltage Vf is applied. 
Because of the above remarkable features, it will be understood that the 
electron-emitting behavior of an electron source comprising a plurality of 
electron-emitting devices according to the invention and hence that of an 
image-forming apparatus incorporating such an electron source can easily 
be controlled in response to the input signal. Thus, such an electron 
source and an image-forming apparatus may find a variety of applications. 
On the other hand, the device current If either monotonically increases 
relative to the device voltage Vf (as shown in FIG. 8A, a characteristic 
referred to as "MI characteristic" hereinafter) or changes to show a curve 
specific to a voltage-controlled-negative-resistance characteristic (a 
characteristic referred to as "VCNR characteristic" hereinafter) as shown 
in FIG. 8B. These characteristics of the device current are dependent on 
the manufacturing method. 
Now, some examples of the usage of electron-emitting devices, to which the 
present invention is applicable, will be described. 
According to a fourth mode of realizing the invention, an electron source 
and hence an image-forming apparatus can be realized by arranging on a 
substrate a plurality of electron-emitting devices according to any of the 
above described first through third modes of realizing the present 
invention, and including the thus obtained electron source and an 
image-forming member within a vacuum container. 
Electron-emitting devices may be arranged on a substrate in a number of 
different modes. 
For instance, a number of electron-emitting devices may be arranged in 
parallel rows along a direction (hereinafter referred to row direction), 
each device being connected by wires at opposite ends thereof, and driven 
to operate by control electrodes (hereinafter referred to as grids) 
arranged in a space above the electron-emitting devices along a direction 
perpendicular to the row direction (hereinafter referred to as 
column-direction) to realize a ladder-like arrangement. Alternatively, a 
plurality of electron-emitting devices may be arranged in rows along a 
X-direction and columns along an Y-direction to form a matrix, the X- and 
Y-directions being perpendicular to each other, and the electron-emitting 
devices on a given row are connected to a common X-directional wire by way 
of one of the electrodes of each device while the electron-emitting 
devices on a given column are connected to a common Y-directional wire by 
way of the other electrode of each device. The latter arrangement is 
referred to as a simple matrix arrangement. Now, the simple matrix 
arrangement will be described in detail. 
In view of the above described three basic characteristic features (i) 
through (iii) of a surface conduction electron-emitting device, to which 
the invention is applicable, it can be controlled for electron emission by 
controlling the wave height and the wave width of the pulse voltage 
applied to the opposite electrodes of the device above the threshold 
voltage level. On the other hand, the device does not practically emit any 
electrons below the threshold voltage level. Therefore, regardless of the 
number of electron-emitting devices arranged in an apparatus, desired 
surface conduction electron-emitting devices can be selected and 
controlled for electron emission in response to an input signal by 
applying a pulse voltage to each of the selected devices. 
FIG. 9 is a schematic plan view of the substrate of an electron source 
realized by arranging a plurality of electron-emitting devices, to which 
the present invention is applicable, in order to exploit the above 
characteristic features. In FIG. 9, the electron source comprises a 
substrate 21, X-directional wires 22, Y-directional wires 23, surface 
conduction electron-emitting devices 24 and connecting wires 25. 
There are provided a total of m X-directional wires 22, which are denoted 
by Dx1, Dx2, . . . , Dxm and made of an electroconductive metal produced 
by vacuum evaporation, printing or sputtering. These wires are so designed 
in terms of material, thickness and width that, if necessary, a 
substantially equal voltage may be applied to the surface conduction 
electron-emitting devices. A total of n Y-directional wires 23 are 
arranged and denoted by Dy1, Dy2, . . . , Dyn, which are similar to the 
X-directional wires 23 in terms of material, thickness and width. An 
interlayer insulation layer (not shown) is disposed between the m 
X-directional wires 22 and the n Y-directional wires 23 to electrically 
isolate them from each other. (Both m and n are integers.) 
The interlayer insulation layer (not shown) is typically made of SiO.sub.2 
and formed on the entire surface or part of the surface of the insulating 
substrate 21 to show a desired contour by means of vacuum evaporation, 
printing or sputtering. For example, it may be formed on the entire 
surface or part of the surface of the substrate 21 on which the 
X-directional wires 22 have been formed. The thickness, material and 
manufacturing method of the interlayer insulation layer are so selected as 
to make it withstand the potential difference between any of the 
X-directional wires 22 and any of the Y-directional wires 23 observable at 
the crossing thereof. Each of the X-directional wires 22 and the 
Y-directional wires 23 is drawn out to form an external terminal. 
The oppositely arranged paired electrodes (not shown) of each of the 
surface conduction electron-emitting devices 24 are connected to related 
one of the m X-directional wires 22 and related one of the n Y-directional 
wires 23 by respective connecting wires 25 which are made of an 
electroconductive metal. 
The electroconductive material of the device electrodes and that of the 
connecting wires 25 extending from the wire 22 and 23 may be same or 
contain a common element as an ingredient. Alternatively, they may be 
different from each other. These materials may be appropriately selected 
typically from the candidate materials listed above for the device 
electrodes. If the device electrodes and the connecting wires are made of 
the same material, they may be collectively called device electrodes 
without discriminating the connecting wires. 
The X-directional wires 22 are electrically connected to a scan signal 
application means (not shown) for applying a scan signal to a selected row 
of surface conduction electron-emitting devices 24. On the other hand, the 
Y-directional wires 23 are electrically connected to a modulation signal 
generation means (not shown) for applying a modulation signal to a 
selected column of surface conduction electron-emitting devices 24 and 
modulating the selected column according to an input signal. Note that the 
drive signal to be applied to each surface conduction electron-emitting 
device is expressed as the voltage difference of the scan signal and the 
modulation signal applied to the device. 
With the above arrangement, each of the devices can be selected and driven 
to operate independently by means of a simple matrix wire arrangement. 
Now, an image-forming apparatus comprising an electron source having a 
simple matrix arrangement as described above will be described by 
referring to FIGS. 10, 11A, 11B and 12. FIG. 10 is a partially cut away 
schematic perspective view of the image forming apparatus and FIGS. 11A 
and 11B are schematic views, illustrating two possible configurations of a 
fluorescent film that can be used for the image forming apparatus of FIG. 
10, whereas FIG. 12 is a block diagram of a drive circuit for the image 
forming apparatus of FIG. 10 that operates for NTSC television signals. 
Referring firstly to FIG. 10 illustrating the basic configuration of the 
display panel of the image-forming apparatus, it comprises an electron 
source substrate 21 of the above described type carrying thereon a 
plurality of electron-emitting devices, a rear plate 31 rigidly holding 
the electron source substrate 21, a face plate 36 prepared by laying a 
fluorescent film 34 and a metal back 35 on the inner surface of a glass 
substrate 33 and a support frame 32, to which the rear plate 31 and the 
face plate 36 are bonded by means of frit glass. Reference numeral 37 
denote an envelope, which is baked to 400.degree. to 500.degree. C. for 
more than 10 minutes in the atmosphere or in nitrogen and hermetically and 
airtightly sealed. 
In FIG. 10, reference numeral 24 denotes the electron-emitting devices and 
reference numerals 22 and 23 respectively denotes the X-directional wire 
and the Y-directional wire connected to the respective device electrodes 
of each electron-emitting device. 
While the envelope 37 is formed of the face plate 36, the support frame 32 
and the rear plate 31 in the above described embodiment, the rear plate 31 
may be omitted if the substrate 21 is strong enough by itself because the 
rear plate 31 is provided mainly for reinforcing the substrate 21. If such 
is the case, an independent rear plate 31 may not be required and the 
substrate 31 may be directly bonded to the support frame 32 so that the 
envelope 37 is constituted of a face plate 36, a support frame 32 and a 
substrate 21. The overall strength of the envelope 37 may be increased by 
arranging a number of support members called spacers (not shown) between 
the face plate 36 and the rear plate 31. 
FIGS. 11A and 11B schematically illustrate two possible arrangements of 
fluorescent film. While the fluorescent film 34 (FIG. 10) comprises only a 
single fluorescent body if the display panel is used for showing black and 
white pictures, it needs to comprise for displaying color pictures black 
conductive members 38 and fluorescent bodies 39, of which the former are 
referred to as black stripes or members of a black matrix depending on the 
arrangement of the fluorescent bodies. Black stripes or members of a black 
matrix are arranged for a color display panel so that the fluorescent 
bodies 39 of three different primary colors are made less discriminable 
and the adverse effect of reducing the contrast of displayed images of 
external light is weakened by blackening the surrounding areas. While 
graphite is normally used as a principal ingredient of the black stripes, 
other conductive material having low light transmissivity and reflectivity 
may alternatively be used. 
A precipitation or printing technique is suitably be used for applying a 
fluorescent material to the glass substrate regardless of black and white 
or color display. An ordinary metal back 35 is arranged on the inner 
surface of the fluorescent film 34. The metal back 35 is provided in order 
to enhance the luminance of the display panel by causing the rays of light 
emitted from the fluorescent bodies and directed to the inside of the 
envelope to turn back toward the face plate 36, to use it as an electrode 
for applying an accelerating voltage to electron beams and to protect the 
fluorescent bodies against damages that may be caused when negative ions 
generated inside the envelope collide with them. It is prepared by 
smoothing the inner surface of the fluorescent film (in an operation 
normally called "filming") and forming an Al film thereon by vacuum 
evaporation after forming the fluorescent film. 
A transparent electrode (not shown) may be formed on the face plate 36 
facing the outer surface of the fluorescent film 34 in order to raise the 
conductivity of the fluorescent film 34. 
Care should be taken accurately to align each set of color fluorescent 
bodies and an electron-emitting device, if a color display is involved, 
before the above-listed components of the envelope are bonded together. 
Now, a method of manufacturing an image-forming apparatus as illustrated in 
FIG. 10 will be described below. 
FIG. 13 shows a schematic block diagram of a vacuum processing system that 
can be used for manufacturing an image-forming apparatus according to the 
invention. In FIG. 13, an image-forming apparatus 51 is connected to the 
vacuum chamber 53 of the vacuum system by way of an exhaust pipe 52. The 
vacuum chamber 53 is further connected to a vacuum pump unit 55 by way of 
a gate valve 54. A pressure gauge 56, a quadrupole mass (Q-mass) 
spectrometer 57 and other instruments are arranged within the vacuum 
chamber 53 to measure the internal pressure and the partial pressures of 
the gases within the chamber. Since it is difficult to directly gauge the 
internal pressure of the envelope 37 of the image-forming apparatus 51, 
the parameters for the manufacturing operation are controlled by gauging 
the internal pressure of the vacuum chamber 53 and other measurable 
factors. 
A gas feed line 58 is connected to the vacuum chamber 53 in order to 
introduce a gaseous substance necessary for the operation and control the 
atmosphere within the chamber. The gas feed line 58 is, at the other end, 
connected to a substance source 60, that may be an ampule or a cylinder 
containing a substance to be supplied to the vacuum chamber. A feeding 
rate control means 59 is arranged on the gas feed line in order to control 
the rate at which the substance in the source 60 is fed to the chamber. 
More specifically, the feeding rate control means may be a slow leak valve 
that can control the rate of leaking gas or a mass flow controller 
depending on the type of the substance to be fed. 
After evacuating the inside of the envelope 37 by means of an arrangement 
as shown in FIG. 13, the image forming apparatus is subjected to a forming 
process. This process may be carried out by connecting the Y-directional 
wires 23 to common electrode 61 and applying a pulse voltage to the 
electron-emitting devices connected to each of the X-directional wires 22 
on a wire by wire basis as shown in FIG. 14. The wave form of the pulse 
voltage to be applied, the conditions under which the process is 
terminated are other factors concerning the process may be appropriately 
selected by referring to the above description on the forming process for 
a single electron-emitting device. In FIG. 13, reference numeral 63 
denotes a resistor for gauging an electric current running therethrough 
and reference numeral 64 denotes an oscilloscope for gauging an electric 
current. 
After the completion of the forming process, an electron-scattering plane 
forming layer is produced. 
In this process of producing an electron-scattering plane forming layer, a 
source gas selected appropriately depending on the material of the layers 
to be formed within the envelope is introduced and a pulse voltage is 
applied to each electron-emitting device by means of CVD. The wiring 
arrangement used for the forming process may also be used for this 
process. 
If a low work function material layer or a high melting point substance 
layer is produced on the lower potential side electroconductive thin film 
after the completion of producing an electron-scattering plane forming 
layer, an appropriate source gas good for the process is introduced and a 
pulse voltage as described above is applied. Note, however, that the 
polarlity of the pulse voltage to be applied is inverted from the one used 
above. 
Note also that at least part of the forming process down to the process of 
producing a low function material layer or a high melting point substance 
layer may be carried out before the preparation and hermetical sealing of 
the envelope. 
The envelope 37 is evacuated by means of the vacuum pump unit 55 such as an 
oil free pump unit consisting of an ion pump and a sorption pump that does 
not involve the use of oil by way of the exhaust pipe 52, while it is 
being heated to 80.degree. to 250.degree. C., until the atmosphere in the 
inside is reduced to a sufficiently low pressure and the organic 
substances contained therein are satisfactorily eliminated, when the 
exhaust pipe is heated to melt by a burner and then hermetically sealed. 
Then, a getter process may be conducted in order to maintain the achieved 
degree of vacuum in the inside of the envelope 37 after it is sealed. In a 
getter process, a getter (not shown) arranged at a predetermined position 
in the envelope 37 is heated by means of a resistance heater or a high 
frequency heater to form a film by evaporation immediately before or after 
the envelope 37 is sealed. A getter typically contains Ba as a principal 
ingredient and can maintain a degree of vacuum within the envelope 37 by 
the adsorption effect of the film deposited by evaporation. 
Now, a drive circuits for driving a display panel comprising an electron 
source with a simple matrix arrangement for displaying television images 
according to NTSC television signals will be described by referring to 
FIG. 12. In FIG. 12, reference numeral 41 denotes a display panel. 
Otherwise, the circuit comprises a scan circuit 42, a control circuit 43, 
a shift register 44, a line memory 45, a synchronizing signal separation 
circuit 46 and a modulation signal generator 47. Vx and Va in FIG. 11 
denote DC voltage sources. 
The display panel 41 is connected to external circuits via terminals Dox1 
through Doxm, Doy1 through Doym and high voltage terminal Hv, of which 
terminals Dox1 through Doxm are designed to receive scan signals for 
sequentially driving on a one-by-one basis the rows (of N devices) of an 
electron source in the apparatus comprising a number of surface-conduction 
type electron-emitting devices arranged in the form of a matrix having M 
rows and N columns. 
On the other hand, terminals Doy1 through Doyn are designed to receive a 
modulation signal for controlling the output electron beam of each of the 
surface-conduction type electron-emitting devices of a row selected by a 
scan signal. High voltage terminal Hv is fed by the DC voltage source Va 
with a DC voltage of a level typically around 10 kV, which is sufficiently 
high to energize the fluorescent bodies of the selected surface-conduction 
type electron-emitting devices. It is an accelerating voltage for giving 
energy to electron beams emitted from the surface conduction 
electron-emitting devices at a rate sufficient to energize the fluorescent 
body of the image-forming apparatus. 
The scan circuit 42 operates in a manner as follows. The circuit comprises 
M switching devices (of which only devices S1 and Sm are specifically 
indicated in FIG. 13), each of which takes either the output voltage of 
the DC voltage source Vx or 0V! (the ground potential level) and comes to 
be connected with one of the terminals Dox1 through Doxm of the display 
panel 41. Each of the switching devices S1 through Sm operates in 
accordance with control signal Tscan fed from the control circuit 43 and 
can be prepared by combining switching devices such as FETs. 
The DC voltage source Vx of this circuit is designed to output a constant 
voltage such that any drive voltage applied to devices that are not being 
scanned is reduced to less than threshold voltage due to the performance 
of the surface conduction electron-emitting devices (or the threshold 
voltage for electron emission). 
The control circuit 43 coordinates the operations of related components so 
that images may be appropriately displayed in accordance with externally 
fed video signals. It generates control signals Tscan, Tsft and Tmry in 
response to synchronizing signal Tsync fed from the synchronizing signal 
separation circuit 46, which will be described below. 
The synchronizing signal separation circuit 46 separates the synchronizing 
signal component and the luminance signal component from an externally fed 
NTSC television signal and can be easily realized using a popularly known 
frequency separation (filter) circuit. Although a synchronizing signal 
extracted from a television signal by the synchronizing signal separation 
circuit 46 is constituted, as well known, of a vertical synchronizing 
signal and a horizontal synchronizing signal, it is simply designated as 
Tsync signal here for convenience sake, disregarding its component 
signals. On the other hand, a luminance signal drawn from a television 
signal, which is fed to the shift register 44, is designated as DATA 
signal. 
The shift register 44 carries out for each line a serial/parallel 
conversion on DATA signals that are serially fed on a time series basis in 
accordance with control signal Tsft fed from the control circuit 43. (In 
other words, a control signal Tsft operates as a shift clock for the shift 
register 44.) A set of data for a line of one image that have undergone a 
serial/parallel conversion (and correspond to a set of drive data for N 
electron-emitting devices) are sent out of the shift register 44 as n 
parallel signals Id1 through Idn. 
The line memory 45 is a memory for storing a set of data for a line of one 
image, which are signals Id1 through Idn, for a required period of time 
according to control signal Tmry coming from the control circuit 43. The 
stored data are sent out as Id'1 through Id'n and fed to the modulation 
signal generator 47. 
Said modulation signal generator 47 is in fact a signal source that 
appropriately drives and modulates the operation of each of the 
surface-conduction type electron-emitting devices and output signals of 
this device are fed to the surface-conduction type electron-emitting 
devices in the display panel 41 via terminals Doy1 through Doyn. 
As described above, an electron-emitting device, to which the present 
invention is applicable, is characterized by the following features in 
terms of emission current Ie. Firstly, there exists a clear threshold 
voltage Vth and the device emits electrons only when a voltage exceeding 
Vth is applied thereto. Secondly, the level of emission current Ie changes 
as a function of the change in the applied voltage above the threshold 
level Vth. More specifically, when a pulse-shaped voltage is applied to an 
electron-emitting device according to the invention, practically no 
emission current is generated so far as the applied voltage remains under 
the threshold level, whereas an electron beam is emitted once the applied 
voltage rises above the threshold level. It should be noted here that the 
intensity of an output electron beam can be controlled by changing the 
peak level Vm of the pulse-shaped voltage. Additionally, the total amount 
of electric charge of an electron beam can be controlled by varying the 
pulse width Pw. 
Thus, either voltage modulation method or pulse width modulation method may 
be used for modulating an electron-emitting device in response to an input 
signal. With voltage modulation, a voltage modulation type circuit is used 
for the modulation signal generator 47 so that the peak level of the pulse 
shaped voltage is modulated according to input data, while the pulse width 
is held constant. 
With pulse width modulation, on the other hand, a pulse width modulation 
type circuit is used for the modulation signal generator 47 so that the 
pulse width of the applied voltage may be modulated according to input 
data, while the peak level of the applied voltage is held constant. 
Although it is not particularly mentioned above, the shift register 44 and 
the line memory 45 may be either of digital or of analog signal type so 
long as serial/parallel conversions and storage of video signals are 
conducted at a given rate. 
If digital signal type devices are used, output signal DATA of the 
synchronizing signal separation circuit 46 needs to be digitized. However, 
such conversion can be easily carried out by arranging an A/D converter at 
the output of the synchronizing signal separation circuit 46. It may be 
needless to say that different circuits may be used for the modulation 
signal generator 47 depending on if output signals of the line memory 45 
are digital signals or analog signals. If digital signals are used, a D/A 
converter circuit of a known type may be used for the modulation signal 
generator 47 and an amplifier circuit may additionally be used, if 
necessary. As for pulse width modulation, the modulation signal generator 
47 can be realized by using a circuit that combines a high speed 
oscillator, a counter for counting the number of waves generated by said 
oscillator and a comparator for comparing the output of the counter and 
that of the memory. If necessary, am amplifier may be added to amplify the 
voltage of the output signal of the comparator having a modulated pulse 
width to the level of the drive voltage of a surface-conduction type 
electron-emitting device according to the invention. 
If, on the other hand, analog signals are used with voltage modulation, an 
amplifier circuit comprising a known operational amplifier may suitably be 
used for the modulation signal generator 47 and a level shift circuit may 
be added thereto if necessary. As for pulse width modulation, a known 
voltage control type oscillation circuit (VCO) may be used with, if 
necessary, an additional amplifier to be used for voltage amplification up 
to the drive voltage of a surface-conduction type electron-emitting 
device. 
With an image forming apparatus having a configuration as described above, 
to which the present invention is applicable, the electron-emitting 
devices emit electrons as a voltage is applied thereto by way of the 
external terminals Dox1 through Doxm and Doy1 through Doyn. Then, the 
generated electron beams are accelerated by applying a high voltage to the 
metal back 35 or a transparent electrode (not shown) by way of the high 
voltage terminal Hv. The accelerated electrons eventually collide with the 
fluorescent film 34, which in turn glows to produce images. 
The above described configuration of image forming apparatus is only an 
example to which the present invention is applicable and may be subjected 
to various modifications. The TV signal system to be used with such an 
apparatus is not limited to a particular one and any system such as NTSC, 
or SECAM may feasibly be used with it. It is also suited for TV 
signals involving a larger number of scanning lines (typically of a high 
definition TV system such as the MUSE system). 
Now, an electron source comprising a plurality of surface conduction 
electron-emitting devices arranged in a ladder-like manner on a substrate 
and an image-forming apparatus comprising such an electron source will be 
described by referring to FIGS. 15 and 16. 
Firstly referring to FIG. 15 schematically showing an electron source 
having a ladder-like arrangement, reference numeral 21 denotes an electron 
source substrate and reference numeral 24 denotes a surface conduction 
electron-emitting device arranged on the substrate, whereas reference 
numeral 22 denotes (X-directional) wires Dx1 through Dx10 for connecting 
the surface conduction electron-emitting devices 24. The electron-emitting 
devices 24 are arranged in rows (to be referred to as device rows 
hereinafter) on the substrate 21 to form an electron source comprising a 
plurality of device rows, each row having a plurality of devices. The 
surface conduction electron-emitting devices of each device row are 
electrically connected in parallel with each other by a pair of common 
wires so that they can be driven independently by applying an appropriate 
drive voltage to the pair of common wires. More specifically, a voltage 
exceeding the electron emission threshold level is applied to the device 
rows to be driven to emit electrons, whereas a voltage below the electron 
emission threshold level is applied to the remaining device rows. 
Alternatively, any two external terminals arranged between two adjacent 
device rows can share a single common wire. Thus, for example, of the 
common wires Dx2 through Dx9, Dx2 and Dx3 can share a single common wire 
instead of two wires. 
FIG. 16 is a schematic perspective view of the display panel of an 
image-forming apparatus incorporating an electron source having a 
ladder-like arrangement of electron-emitting devices. In FIG. 16, the 
display panel comprises grid electrodes 71, each provided with a number of 
bores 72 for allowing electrons to pass therethrough and a set of external 
terminals 73, or Dox1, Dox2, . . . , Doxm, along with another set of 
external terminals 74, or G1, G2, . . . , Gn, connected to the respective 
grid electrodes 71 and an electron source substrate 31. The image forming 
apparatus differs from the image forming apparatus with a simple matrix 
arrangement of FIG. 10 mainly in that the apparatus of FIG. 16 has grid 
electrodes 71 arranged between the electron source substrate 21 and the 
face plate 36. 
In FIG. 16, the stripe-shaped grid electrodes 71 are arranged 
perpendicularly relative to the ladder-like device rows for modulating 
electron beams emitted from the surface conduction electron-emitting 
devices, each provided with through bores 72 in correspondence to 
respective electron-emitting devices for allowing electron beams to pass 
therethrough. Note that, however, while stripe-shaped grid electrodes are 
shown in FIG. 16, the profile and the locations of the electrodes are not 
limited thereto. For example, they may alternatively be provided with 
mesh-like openings and arranged around or close to the surface conduction 
electron-emitting devices. 
The external terminals 73 and the external terminals 74 for the grids are 
electrically connected to a control circuit (not shown). 
An image-forming apparatus having a configuration as described above can be 
operated for electron beam irradiation by simultaneously applying 
modulation signals to the rows of grid electrodes for a single line of an 
image in synchronism with the operation of driving (scanning) the 
electron-emitting devices on a row by row basis so that the image can be 
displayed on a line by line basis. 
Thus, a display apparatus according to the invention and having a 
configuration as described above can have a wide variety of industrial and 
commercial applications because it can operate as a display apparatus for 
television broadcasting, as a terminal apparatus for video 
teleconferencing, as an editing apparatus for still and movie pictures, as 
a terminal apparatus for a computer system, as an optical printer 
comprising a photosensitive drum and in many other ways. 
EXAMPLES 
Now, the present invention will be described by way of examples. 
Examples 1-3, Comparative Examples 1 and 2 
FIG. 17A schematically illustrates the configuration of the surface 
conduction electron-emitting devices prepared in these examples. 
Referring to FIG. 17A, the illustrated device comprises a substrate 1, 
device electrodes 2 and 3, electroconductive thin films 4 and 5, an 
electron-scattering plane forming layer 6 and an electron-emitting region 
7. 
In each of these examples, an electron-scattering plane forming layer 6 has 
a double-layered configuration of a first layer 81 and a second layer 82 
formed on the electroconductive thin film 5. 
The process employed for manufacturing each of the electron-emitting 
devices will be described by referring to FIGS. 18A through 18F. 
Step a: 
After thoroughly cleansing a soda lime glass substrate 1 by means of a 
neutral detergent, pure water and an organic solvent, a Ti film and an Ni 
film were sequentially formed to respective thicknesses of 5 nm and 100 nm 
by vacuum evaporation. Thereafter, photoresist (AZ1370: available from 
Hoechst Corporation) was applied and baked to produce a resist layer. 
Then, using a photomask, it was exposed to light and photochemically 
developed to produce a pattern for a pair of device electrodes 2 and 3 
separated by a distance (gap length) G of 3 .mu.m and having a length W 
(See FIG. 1A) of 300 .mu.m. (FIG. 18A) 
Step b: 
A Cr film was formed to a film thickness of 100 nm by vacuum evaporation 
and then photoresist (RD-2000N-41: available from Hitachi Chemical Co., 
Ltd.) was applied thereto and baked to form a resist layer. Thereafter, 
using a photomask, it was exposed to light, photochemically developed and 
an opening corresponding to the pattern of an electroconductive thin film 
was formed there. After removal of the Cr film of the areas for the 
electroconductive thin film by wet etching, the resist layer was removed 
by dissolving it into acetone to produce a Cr mask 83. (FIG. 18B) 
Step c: 
A Pd amine complex solution (ccp4230: available from Okuno Pharmaceutical 
Co., Ltd.) was applied to the Cr mask by means of a spinner and baked at 
300.degree. C. for 10 minutes in the atmosphere to produce a PdO fine 
particle film. Then, the Cr mask 83 was removed by wet-etching and the PdO 
fine particle film was lifted off to obtain an electroconductive thin film 
86 having a desired profile. (FIG. 18C) 
Step d: 
The device was placed in the vacuum chamber of a vacuum processing system 
as schematically illustrated in FIG. 7 and the vacuum chamber 16 of the 
system was evacuated to a pressure of 2.7.times.10.sup.-3 Pa. 
Subsequently, a pulse voltage was applied between the device electrodes 2 
and 3 to flow an electric current through the electroconductive thin film 
and thereby carry out an energization forming process. 
The pulse voltage used for the forming process was a triangular pulse 
voltage whose peak value gradually increased with time as shown in FIG. 
6B. The pulse voltage had a pulse width of T1=1 msec and a pulse interval 
of T2=10 msec. During the energization forming process, an extra pulse 
voltage of 0.1 V (not shown) was inserted into intervals of the forming 
pulse voltage in order to determine the resistance of the 
electroconductive thin film and the energization forming process was 
terminated when the resistance exceeded 1 M.OMEGA.. As a result, a fissure 
7 constituting an electron-emitting region was formed in part of the 
electroconductive thin film, which was consequently divided into a thin 
film 4 and another thin film 5. (FIG. 18D) 
Step e: 
Subsequently, a second layer 82 of an electron-scattering plane forming 
layer was formed on the electroconductive thin film 5 by MOCVD. Then, the 
device was heated to 150.degree. C. in the vacuum chamber 16 of FIG. 7. A 
triangular pulse voltage with a wave height of 16 V, a pulse width of T1=1 
msec. and a pulse interval of T2=10 msec. was applied to the device. Then, 
La(C.sub.11 H.sub.19 O.sub.2).sub.3 was introduced into the vacuum chamber 
16 as a source gas from the substance source 18 of the system to produce a 
pressure between 10.sup.-2 Pa to several Pa in the vacuum chamber by 
controlling the valve 19. 
This process was continued for 30 minutes to produce the second layer 82 of 
the electron-scattering plane forming layer consisting of La. The film 
thickness was about 70 nm. (FIG. 18E) 
Step f: 
Thereafter, a first layer 81 of the electron-scattering plane forming layer 
was produced. 
After removing the La(C.sub.11 H.sub.19 O.sub.2).sub.3 introduced in the 
above step and remaining in the vacuum chamber, an identical pulse voltage 
was applied to the device and (C.sub.2 H.sub.5).sub.3 B was introduced 
into the vacuum chamber to produce the first layer of the 
electron-scattering plane forming layer consisting of B. (FIG. 18F) 
Note that in Examples 1, 2 and 3, the first layers of the 
electron-scattering plane forming layers of the prepared devices were made 
equal to 3 nm, 5 nm and 10 nm respectively by appropriately selecting the 
durations of this step. For the purpose of comparison, the steps up to 
Step-e of Examples 1, 2 and 3 were followed for and an ordinary activation 
process was carried out on the device of Comparative Example 1 and, in 
Step-f, the first layer of electron-scattering plane forming layer was 
made equal to 20 nm for the device of Comparative Example 2. 
Each of the sample devices was then tested for electron-emitting 
performance by driving it with a gauging system of FIG. 7. A pulse voltage 
was applied to the device in such a way that the device electrodes 2 and 3 
were respectively made to be lower and higher potential side device 
electrodes (and therefore the electroconductive thin film 4 and the 
electroconductive thin film 5 on which an electron-scattering plane 
forming layer 6 had been formed were respectively made to be lower and 
higher potential side electroconductive thin films). The wave height of 
the applied pulse voltage was 16 V. The distance H between the device and 
the anode was 4 mm and the potential difference between them was 1 kV. 
Table 1 below shows the emission current Ie, the device current If and the 
electron emission efficiency .eta. observed on each of the sample devices. 
After the measurement, each of the devices was observed through a scanning 
electron microscope (SEM) to find out that, while the electron-scattering 
plane forming layer of the device of Example 3 had a relatively continuous 
layered structure, that of the device of Example 1 had a discontinuous 
structure. 
In each of the devices of Examples 1 through 3, it was found that the 
electron-scattering plane forming layer 6 was extended by a distance of 
about L=50 .mu.m (FIG. 17A) from the electron-emitting region 7. 
TABLE 1 
______________________________________ 
first film 
layer thickness 
Ie If .eta. 
device (nm) (.mu.A) (mA) (%) 
______________________________________ 
Example 1 3 7.0 2.8 0.25 
Example 2 5 6.6 3.0 0.22 
Example 3 10 3.1 3.1 0.10 
Comparative 
0 1.2 2.5 0.048 
Example 1 
Comparative 
20 1.2 3.0 0.04 
Example 2 
______________________________________ 
Examples 4 through 6 
FIG. 17C schematically illustrates the configuration of the surface 
conduction electron-emitting devices prepared in these examples. In each 
of these examples, steps a through d, or steps down to the energization 
forming process, of Example 1 were followed. Thereafter, the following 
steps were carried out. 
Step e: 
A pair of La thin films 82 and 83 were formed respectively on the 
electroconductive thin films 4 and 5 by MOCVD. 
Then, the device was heated to 150.degree. C. in the vacuum chamber 16 of 
FIG. 7. A triangular pulse voltage having an alternating polarity as shown 
in FIG. 6C with a wave height of 16 V, a pulse width of T1=1 msec. and a 
pulse interval of T2=10 msec. was applied to the device. Then, La(C.sub.11 
H.sub.19 O.sub.2).sub.3 was introduced into the vacuum chamber 16 as a 
source gas from the substance source 18 of the system to produce a 
pressure between 10.sup.-2 Pa to several Pa in the vacuum chamber by 
controlling the valve 19. 
This process was continued for 30 minutes to produce La thin films 
respectively on the electroconductive thin films 4 and 5. The film 
thickness was about 40 nm. 
Step f: 
Thereafter, a first layer 81 of the electron-scattering plane forming layer 
consisting of B was produced on one of the electroconductive thin films, 
or electroconductive thin film 5, as in the case of step f of Example 1. 
Note that in Examples 4 through 6, the B layers of the prepared devices 
were made equal to 3 nm, 5 nm and 10 nm respectively by appropriately 
selecting the durations of this step. 
As in the case of Examples 1 through 3, each of the sample devices was then 
tested for electron-emitting performance by driving it with a gauging 
system of FIG. 7. A pulse voltage was applied to the device in such a way 
that the device electrodes 2 and 3 were respectively made to be lower and 
higher potential side device electrodes (and therefore the 
electroconductive thin film 4 on which the La thin film 83 had been formed 
and the electroconductive thin film 5 on which the electron-scattering 
plane forming layer 6 constituted of the second layer of La thin film 82 
and the first B layer 81 had been formed were respectively made to be 
lower and higher potential side electroconductive thin films). 
In each of the above devices, the La thin film 83 operates as a low work 
function material layer. Table 2 below shows the performance of each of 
the sample devices of these examples observed in a test. After the 
measurement, each of the devices was observed through a scanning electron 
microscope (SEM) to find out that the electron-scattering plane forming 
layer 6 was extended by a distance of about L=50 nm (FIG. 17C) from the 
electron-emitting region 7. 
TABLE 2 
______________________________________ 
first film 
layer thickness 
Ie If .eta. 
device (nm) (.mu.A) (mA) (%) 
______________________________________ 
Example 4 3 7.4 3.1 0.24 
Example 5 5 7.4 3.2 0.23 
Example 6 10 3.3 3.0 0.11 
______________________________________ 
Examples 7 through 12 
For each of the devices prepared in these examples, the first layer 81 and 
the second layer 82 of the electron-scattering plane forming layer 6 were 
respectively made of Si and La. Otherwise, the manufacturing steps of 
Examples 1 through 6 were followed. SiH.sub.4 was used for the source gas 
of Si. 
Examples 13 through 24 
For each of the devices prepared in Examples 13 through 18, the first layer 
81 and the second layer 82 of the electron-scattering plane forming layer 
6 were respectively made of B and Sc. Otherwise, the manufacturing steps 
of Examples 1 through 6 were followed. Likewise, for each of the devices 
prepared in Examples 19 through 24, the first layer 81 and the second 
layer 82 of the electron-scattering plane forming layer 6 were 
respectively made of Si and Sc. Otherwise, the manufacturing steps of 
Examples 1 through 6 were followed. Sc(C.sub.11 H.sub.9 O.sub.2).sub.3 was 
used for the source gas of Sc. 
Examples 25 through 48 
For each of the devices prepared in Examples 25 through 30, the first layer 
81 and the second layer 82 of the electron-scattering plane forming layer 
6 were respectively made of B and Sr. Otherwise, the manufacturing steps 
of Examples 1 through 6 were followed. Sr(C.sub.11 H.sub.19 O.sub.2).sub.3 
was used for the source gas of Sr. 
Likewise, for each of the devices prepared in Examples 31 through 36, the 
first layer 81 and the second layer 82 of the electron-scattering plane 
forming layer 6 were respectively made of Si and Sr. SiH.sub.4 was used 
for the source gas of Si. 
Similarly, for each of the devices prepared in Examples 37 through 42, the 
first layer 81 and the second layer 82 of the electron-scattering plane 
forming layer 6 were respectively made of B and Ba. Ba(C.sub.11 H.sub.19 
O.sub.2).sub.3 was used for the source gas of Ba. 
In a similar way, for each of the devices prepared in Examples 43 through 
48, the first layer 81 and the second layer 82 of the electron-scattering 
plane forming layer 6 were respectively made of Si and Ba. SiH.sub.4 was 
used for the source gas of Si and Ba(C.sub.11 H.sub.19 O.sub.2).sub.3 was 
used for the source gas of Ba. 
Each of the sample devices was then tested for electron-emitting 
performance by driving it with a gauging system of FIG. 7, using the 
conditions of Examples 1 through 3. A pulse voltage was applied to the 
device in such a way that the device electrodes 2 and 3 were respectively 
made to be lower and higher potential side device electrodes (and 
therefore the electroconductive thin film 4 and the electroconductive thin 
film 5 on which an electron-scattering plane forming layer 6 had been 
formed were respectively made to be lower and higher potential side 
electroconductive thin films). Table 3 below shows the performance of each 
of the sample devices of these examples observed in a test. 
In Table 3, "type 1" denotes a device having an electron-scattering plane 
forming layer on the higher potential side and no low work function 
material layer on the lower potential side (FIG. 17A), whereas "type 2" 
denotes a device having an electron-scattering plane forming layer on the 
higher potential side and a low work function material layer on the lower 
potential side (FIG. 17C). 
After the measurement, each of the devices was observed through a scanning 
electron microscope (SEM) to find out that the electron-scattering plane 
forming layer 6 was extended by a distance of about L=50 nm from the 
electron-emitting region 7. 
TABLE 3 
______________________________________ 
#1 layer 
device #1 layer 
thickness 
#2 layer 
Ie If .eta. 
Example 
type material 
(nm) material 
(.mu.A) 
(mA) (%) 
______________________________________ 
7 1 Si 3 La 5.1 2.7 0.19 
8 1 Si 5 La 4.8 2.8 0.17 
9 1 Si 10 La 2.9 2.9 0.10 
10 2 Si 3 La 6.0 3.0 0.20 
11 2 Si 5 La 5.1 3.0 0.17 
12 2 Si 10 La 3.2 3.2 0.10 
13 1 B 3 Sc 5.4 2.7 0.20 
14 1 B 5 Sc 4.6 2.7 0.17 
15 1 B 10 Sc 2.8 2.8 0.10 
16 2 B 3 Sc 5.1 3.0 0.17 
17 2 B 5 Sc 4.5 3.0 0.15 
18 2 B 10 Sc 2.8 3.1 0.09 
19 1 Si 3 Sc 3.5 2.7 0.13 
20 1 Si 5 Sc 3.5 2.7 0.13 
21 1 Si 10 Sc 3.0 2.8 0.11 
22 2 Si 3 Sc 3.7 2.7 0.14 
23 2 Si 5 Sc 2.9 2.7 0.12 
24 2 Si 10 Sc 2.4 2.8 0.085 
25 1 B 3 Sr 6.8 2.7 0.25 
26 1 B 5 Sr 5.9 2.7 0.22 
27 1 B 10 Sr 2.8 2.8 0.10 
28 2 B 3 Sr 7.8 2.9 0.27 
29 2 B 5 Sr 5.9 2.8 0.22 
30 2 B 10 Sr 3.0 2.8 0.11 
31 1 Si 3 Sr 5.1 2.7 0.19 
32 1 Si 5 Sr 3.9 2.6 0.15 
33 1 Si 10 Sr 2.5 2.7 0.093 
34 2 Si 3 Sr 5.2 2.9 0.18 
35 2 Si 5 Sr 4.3 2.5 0.17 
36 2 Si 10 Sr 2.8 2.7 0.10 
37 1 B 3 Ba 7.8 2.9 0.27 
38 1 B 5 Ba 7.0 2.8 0.25 
39 1 B 10 Ba 3.1 3.2 0.097 
40 2 B 3 Ba 9.0 3.2 0.28 
41 2 B 5 Ba 7.4 3.1 0.24 
42 2 B 10 Ba 3.3 3.2 0.10 
43 1 Si 3 Ba 6.4 2.9 0.22 
44 1 Si 5 Ba 5.1 2.7 0.19 
45 1 Si 10 Ba 3.0 3.0 0.10 
46 2 Si 3 Ba 6.5 3.1 0.21 
47 2 Si 5 Ba 5.2 2.9 0.18 
48 2 Si 10 Ba 3.1 3.1 0.10 
______________________________________ 
Examples 49 through 51, Comparative Examples 3 through 5 
FIG. 17B schematically illustrates the configuration of the surface 
conduction electron-emitting devices prepared in these examples. 
In each of the sample devices prepared in these examples, the 
electron-scattering plane forming layer 6 had a single-layered 
configuration. 
The surface conduction electron-emitting devices of these examples were 
prepared in a manner as described below. 
For each of the devices prepared in these examples, steps a through c of 
Example 1 were followed. The subsequent steps will be described by 
referring to FIGS. 20D through 20F. 
Step d: 
A thin film 85a of B was formed by high frequency sputtering on the part of 
the electroconductive thin film 86 located on the device electrode 3. The 
thickness of the formed film was about 3 nm. For this step, the device was 
covered by a metal mask to make the distance L' between the outer edge of 
the B thin film 85a and the center of the gap separating the device 
electrodes (which was substantially equal to the length L of the 
electron-scattering plane forming layer to be prepared) equal to a desired 
value. (FIG. 20D) 
Step e: 
The device was put in the vacuum chamber of a vacuum processing system as 
illustrated in FIG. 7 and subjected to a forming treatment similar to step 
d of Example 1 to produce an electron-emitting region 7. (FIG. 20E) 
Step f: 
As in step e of Example 1, another B thin film 85b was formed between the 
electron-emitting region 7 and the B thin film 85a by deposition. A pulse 
voltage was applied to the device for 10 minutes before terminating this 
step. The period of 10 minutes was the time predetermined to deposit B to 
a thickness of 3 to 5 nm at a position between the electron-emitting 
region and the B thin film 85a formed in step d. While additional B might 
have been deposited on part of the B thin film 85a formed in step d, the 
overall thickness of the B thin film 85a did not exceed 6 nm at any 
position thereof. 
With the above steps, an electron-scattering plane forming layer 6 having 
an intended length of L was produced. Note that the devices of these 
examples were made different in the length L from each other. 
Also note that step d was omitted and an electron-scattering plane forming 
layer of B was produced only by means of Step-f for the device of 
Comparative Example 3. 
Each of the sample devices was then tested for electron-emitting 
performance by driving it with a gauging system of FIG. 7. The distance 
between the device and the anode was equal to H=4 mm and the electric 
potential of the anode relative to the device was equal to Va=1 kV. The 
pulse voltage applied to the device had a rectangular waveform with a 
pulse wave height of 16 V, a pulse width of T1=1.0 msec. and a pulse 
interval of T2=16.7 msec. The pulse voltage was applied to the device in 
such a way that the device electrodes 2 and 3 were respectively made to be 
lower and higher potential side device electrodes (and therefore the 
electroconductive thin film 5 on which the electron-scattering plane 
forming layer 6 had been formed was made to be a higher potential side 
electroconductive thin film). 
Table 4 below shows the performance of each of the sample devices of these 
examples observed in a test. 
TABLE 4 
______________________________________ 
L Ie If .eta. 
device (.mu.m) 
(.mu.A) (mA) (%) 
______________________________________ 
Comparative 2 0.25 0.25 0.10 
Example 3 
Comparative 7 0.30 0.25 0.12 
Example 4 
Comparative 12 0.38 0.25 0.15 
Example 5 
Example 49 22 0.50 0.25 0.20 
Example 50 32 0.55 0.25 0.22 
Example 51 42 0.58 0.25 0.23 
______________________________________ 
After the measurement, each of the devices was observed through a scanning 
electron microscope (SEM) to see the length L of the electron-scattering 
plane forming layer 6. For each of the devices, the right side of formula 
(1) was about 20 .mu.m. Note that the devices of Examples 49 through 51 
showed a remarkable improvement in the electron-emitting efficiency 
.eta.(%) as compared with those of Comparative Examples 3 through 5 having 
a value less than 20 .mu.m for L. 
Example 52 
FIG. 19 schematically illustrates a cross sectional view of the surface 
conduction electron-emitting device prepared in this example. 
The surface conduction electron-emitting device of this example was 
prepared by following steps a through f of Example 1 and subsequently 
carrying out step g as described below. 
Step g: 
The vacuum chamber 16 was evacuated again and then W(CO).sub.6 was 
introduced, controlling the partial pressure thereof to get to 
1.3.times.10.sup.-1 Pa. Subsequently, a pulse voltage used in Step-f of 
Example 1 but having an inverted polarity was applied to the device for 5 
minutes to cause W to be deposited near the electron-emitting region 7 on 
the electroconductive thin film 4 to produce a high melting point 
substance layer 84. 
Then, the device was tested for electron-emitting performance by means of 
the gauging system of Example 1. 
The pulse voltage was applied to the device in such a way that the device 
electrodes 2 and 3 were respectively made to be lower and higher potential 
side device electrodes (and therefore the electroconductive thin film 5 on 
which the electron-scattering plane forming layer 6 had been formed was 
made to be a higher potential side electroconductive thin film). 
The device of the example showed values of Ie=6.2 .mu.A, If=2.5 mA and 
.eta.=0.25%. While the value of Ie of the device was a little smaller than 
that of the device of Example 1, the both devices showed a substantially 
same electron-emitting efficiency. 
Thereafter, the devices of this example and Example 1 were driven for 
electron emission and the emission current of each of the devices was 
observed to check its change with time. As a result, it was found that the 
emission current of this device fell less with time than the than that of 
the device of Example 1. 
It may be safe to assume that the lower potential side electroconductive 
thin film 2 of the device of this examples was less deformed by Joule's 
heat and other causes in an area near the electron-emitting region because 
of the existence of a high melting point substance. 
After the measurement, the device was observed through a scanning electron 
microscope (SEM) to find out that the electron-scattering plane forming 
layer 6 was extended by a distance of about L=50 nm (FIG. 19) from the 
electron-emitting region 7. 
Example 53 
In this example, an electron source was prepared by arranging a large 
number of electron-emitting devices like those formed in the preceding 
examples and wiring them with a matrix of wires. The electron source 
comprised 300 devices on each row along the X-direction and 100 devices on 
each column along the Y-direction. 
FIG. 21 is an enlarged schematic plan view of part of the electron source 
of this example. FIG. 22 is a schematic sectional view of the electron 
source taken along line 22--22 in FIG. 21. 
In these figures, reference numeral 1 denotes a substrate and reference 
numerals 22 and 23 respectively denote an X-directional wire (lower wire) 
and a Y-directional wire (upper wire), while reference numerals 2 and 3 
denote device electrodes and reference numeral 86 denotes an 
electron-emitting thin film prepared by a patterning operation. For 
simplification, the lower potential side electroconductive thin film, the 
higher potential side electroconductive thin film, the electron-emitting 
region and the electron-scattering plane forming layer are collectively 
shown. Reference numeral 87 denotes an interlayer insulation layer and 
reference numeral 88 denotes a contact hole for electrically connecting a 
device electrode 3 and a lower wire 22. 
Now, the method used for manufacturing the image-forming apparatus will be 
described in terms of an electron-emitting device thereof by referring to 
FIGS. 23A through 23H. Note that the following manufacturing steps, or 
step A through step H, respectively correspond to FIGS. 23A. through 23H. 
Step A: 
After thoroughly cleansing a soda lime glass plate a silicon oxide film was 
formed thereon to a thickness of 0.5 .mu.m by sputtering to produce a 
substrate 1, on which Cr and Au were sequentially laid to thicknesses of 5 
nm and 600 nm respectively and then a photoresist (AZ1370: available from 
Hoechst Corporation) was formed thereon by means of a spinner, while 
rotating the film, and baked. Thereafter, a photo-mask image was exposed 
to light and photochemically developed to produce a resist pattern for 
X-directional wires (lower wires) and then the deposited Au/Cr film was 
wet-etched to actually produce X-directional wires (lower wires) 22 having 
a desired profile. 
Step B: 
A silicon oxide film was formed as an interlayer insulation layer 87 to a 
thickness of 1.0 .mu.m by RF sputtering. 
Step C: 
A photoresist pattern was prepared for producing a contact hole 88 in the 
silicon oxide film deposited in Step B, which contact hole 88 was then 
actually formed by etching the interlayer insulation layer 87, using the 
photoresist pattern for a mask. A technique of RIE (Reactive Ion Etching) 
using CF.sub.4 and H.sub.2 gas was employed for the etching operation. 
Step D: 
Thereafter, a pattern of photoresist (RD-2000N-41: available from Hitachi 
Chemical Co., Ltd.) was formed for a pair of device electrodes 2 and 3 and 
a gap G separating the electrodes and then Ti and Ni were sequentially 
deposited thereon respectively to thicknesses of 5 nm and 100 nm by vacuum 
evaporation. The photoresist pattern was dissolved into an organic solvent 
and the Ni/Ti deposit film was treated by using a lift-off technique to 
produce a pair of device electrodes 2 and 3 having a width of W1=300 .mu.m 
and separated from each other by a gap distance of G=3 .mu.m. 
Step E: 
A resist pattern was prepared for the entire area except the contact hole 
88 and Ti and Au were sequentially deposited by vacuum evaporation to 
respective thicknesses of 5 nm and 500 nm. The contact hole was buried by 
removing the unnecessary areas by means of a lift-off technique. 
Step F: 
After forming a photoresist pattern for Y-directional wires (upper wires), 
Ti and Au were sequentially deposited by vacuum evaporation to respective 
thicknesses of 5 nm and 500 nm and then unnecessary areas were removed by 
means of a lift-off technique to actually produce Y-directional wires 
(upper wires) 23 having a desired profile. 
Step G: 
Then, a Cr film 89 was formed to a film thickness of 30 nm by vacuum 
evaporation and processed to show a pattern having an opening 
corresponding to the profile of the electroconductive thin film 86. A 
solution of Pd amine complex (ccp4230) was applied to the Cr film by means 
of a spinner and baked at 300.degree. C. for 12 minutes to produce an 
electroconductive thin film 90 made of PdO fine particles and having a 
film thickness of 70 nm. 
Step H: 
The Cr film 89 was removed along with any unnecessary portions of the 
electroconductive thin film 90 of PdO fine particles by wet etching, using 
an etchant to produce an electroconductive thin film 86 having a desired 
profile. The electroconductive thin film showed an electric resistance of 
Rs=4.times.10.sup.4 .OMEGA./.quadrature. in average. 
Step I: 
This step and the subsequent steps will be described by referring to FIGS. 
10 and 11A. 
After securing an electron source substrate 21 onto a rear plate 31, a face 
plate 36 (carrying a fluorescent film 34 and a metal back 35 on the inner 
surface of a glass substrate 33) was arranged 5 mm above the substrate 21 
with a support frame 32 disposed therebetween and, subsequently, frit 
glass was applied to the contact areas of the face plate 36, the support 
frame 32 and the rear plate 31 and baked at 400.degree. C. in the 
atmosphere for 10 minutes to hermetically seal the container. The 
substrate 21 was also secured to the rear plate 31 by means of frit glass. 
While the fluorescent film 34 is consisted only of a fluorescent body if 
the apparatus is for black and white images, the fluorescent film 34 of 
this example as shown in FIG. 11A was prepared by forming black stripes 38 
in the first place and filling the gaps with stripe-shaped fluorescent 
members 39 of primary colors. The black stripes were made of a popular 
material containing graphite as a principal ingredient. A slurry technique 
was used for applying fluorescent materials onto the glass substrate 33. 
A metal back 35 is arranged on the inner surface of the fluorescent film 
34. After preparing the fluorescent film, the metal back 35 was prepared 
by carrying out a smoothing operation (normally referred to as "filming") 
on the inner surface of the fluorescent film and thereafter forming 
thereon an aluminum layer by vacuum evaporation. 
While a transparent electrode might be arranged on the outer surface of the 
fluorescent film 34 of the face plate 36 in order to enhance its 
electroconductivity, it was not used in this example because the 
fluorescent film showed a sufficient degree of electroconductivity by 
using only a metal back. 
For the above bonding operation, the components were carefully aligned in 
order to ensure an accurate positional correspondence between the color 
fluorescent members and the electron-emitting devices. 
Step J: 
The image forming apparatus was then placed in a vacuum processing system 
shown in FIG. 13 and the vacuum chamber 53 was evacuated to reduced the 
internal pressure to less than 2.6.times.10.sup.-3 Pa. FIG. 24 shows a 
diagram of the wiring arrangement used for the forming operation in this 
example. Referring to FIG. 24, a pulse generated by a pulse generator 91 
is applied to one of the X-directional wires 22 selected by a line 
selector. Both the pulse generator and the line selector are controlled 
for operation by a control unit 93. The Y-directional wires 23 of the 
electron source 94 are connected together and grounded. The thick solid 
line in FIG. 24 represents a control line, whereas thin solid lines 
represent so many wires. The applied pulse voltage had a triangular pulse 
wave form with an increasing wave height as shown in FIG. 6B. As in the 
case of Example 1, a rectangular pulse voltage having a wave height of 0.1 
V was inserted into intervals of the triangular pulse to gauge the 
resistance of each device row and the forming operation was terminated for 
the row when the resistance exceeded 3.3 k.OMEGA. for each device row (or 
1 M.OMEGA. for each device). Then, the voltage applying line was switched 
to a next line by the line selector. The pulse wave height was about 7.0 V 
for all the lines when the forming operation was terminated. 
Step K: 
La(C.sub.11 H.sub.19 O.sub.2).sub.3 was introduced into the vacuum chamber 
until the internal pressure was raised to 1.3.times.10.sup.-1 Pa. The same 
wiring arrangement as in step J was also used to apply a pulse voltage to 
each of the electron-emitting devices. The pulse wave generated by the 
pulse generator was a rectangular pulse having a pulse wave height of 18 
V, a pulse width of 100 .mu.sec. and a pulse interval of 167 .mu.sec. In 
other words, the pulse voltage applied to the X-directional wires and 
having a pulse width of T1=100 .mu.sec. and a pulse interval of T2=16.7 
.mu.sec. (or 60 Hz in terms of frequency) was switched sequentially on a 
wire by wire basis by the line selector for every 167 .mu.sec. The pulse 
generator and the line selector were driven to operate synchronously under 
the control of a control unit. 
As a result of this step, a second La layer of the electron-scattering 
plane forming layer was produced on the higher potential side 
electroconductive thin film by deposition. 
Step L: 
The envelope was once evacuated and, thereafter, (C.sub.2 H.sub.5).sub.3 B 
was introduced into the envelope and a pulse voltage same as the one used 
in Step K was applied to each device to produce a first B layer of the 
electron-scattering plane forming layer. 
The envelope was evacuated again to reduce the internal pressure to about 
10.sup.-5 Pa, while heating the entire panel to about 80.degree. C., and 
the exhaust pipe (not shown) was heated to melt by a gas burner and 
hermetically seal the envelope. Finally, the getter (not shown) arranged 
in the envelope was heated by high frequency heating to carry out a getter 
process. 
The image-forming apparatus produced after the above steps was then driven 
to operate by applying a scan signal and a modulation signal from a signal 
generator (not shown) to the electron-emitting devices by way of external 
terminals Dx1 through Dxm and Dy1 through Dyn so that 14 V was applied to 
the selected devices, which consequently emitted electrons. The emitted 
electron beams were accelerated by applying a high voltage greater than 5 
kV to the metal back 35 by way of the high voltage terminal Hv to make 
them collide with the fluorescent film 34, which was consequently excited 
and fluoresced to display images. 
Thereafter, the image-forming apparatus was broken apart and the devices 
were taken out and observed through a scanning electron microscope (SEM) 
to find out that, in each device, the first layer (B thin film) of the 
electron-scattering plane forming layer had a film thickness between 5 and 
10 nm and was extended by a distance of about L=10 to 20 .mu.m. 
FIG. 25 is a block diagram of a display apparatus realized by using a 
method according to the invention and a display panel prepared in Example 
11 and arranged to provide visual information coming from a variety of 
sources of information including television transmission and other image 
sources. 
In FIG. 25, there are shown a display panel 101, a display panel driver 
102, a display panel controller 103, a multiplexer 104, a decoder 105, an 
input/output interface circuit 106, a CPU 107, an image generator 108, 
image input memory interface circuits 109, 110 and 111, an image input 
interface circuit 112, TV signal receivers 113 and 114 and an input unit 
115. (If the display apparatus is used for receiving television signals 
that are constituted by video and audio signals, circuits, speakers and 
other devices are required for receiving, separating, reproducing, 
processing and storing audio signals along with the circuits shown in the 
drawing. However, such circuits and devices are omitted here in view of 
the scope of the present invention.) 
Now, the components of the apparatus will be described, following the flow 
of image signals therethrough. 
Firstly, the TV signal receiver 114 is a circuit for receiving TV image 
signals transmitted via a wireless transmission system using 
electromagnetic waves and/or spatial optical telecommunication networks. 
The TV signal system to be used is not limited to a particular one and any 
system such as NTSC, or SECAM may feasibly be used with it. It is 
particularly suited for TV signals involving a larger number of scanning 
lines (typically of a high definition TV system such as the MUSE system) 
because it can be used for a large display panel 101 comprising a large 
number of pixels. The TV signals received by the TV signal receiver 114 
are forwarded to the decoder 105. 
The TV signal receiver 113 is a circuit for receiving TV image signals 
transmitted via a wired transmission system using coaxial cables and/or 
optical fibers. Like the TV signal receiver 114, the TV signal system to 
be used is not limited to a particular one and the TV signals received by 
the circuit are forwarded to the decoder 105. 
The image input interface circuit 112 is a circuit for receiving image 
signals forwarded from an image input device such as a TV camera or an 
image pick-up scanner. It also forwards the received image signals to the 
decoder 105. 
The image input memory interface circuit 111 is a circuit for retrieving 
image signals stored in a video tape recorder (hereinafter referred to as 
VTR) and the retrieved image signals are also forwarded to the decoder 
105. 
The image input memory interface circuit 110 is a circuit for retrieving 
image signals stored in a video disc and the retrieved image signals are 
also forwarded to the decoder 105. 
The image input memory interface circuit 109 is a circuit for retrieving 
image signals stored in a device for storing still image data such as 
so-called still disc and the retrieved image signals are also forwarded to 
the decoder 105. 
The input/output interface circuit 106 is a circuit for connecting the 
display apparatus and an external output signal source such as a computer, 
a computer network or a printer. It carries out input/output operations 
for image data and data on characters and graphics and, if appropriate, 
for control signals and numerical data between the CPU 107 of the display 
apparatus and an external output signal source. 
The image generation circuit 108 is a circuit for generating image data to 
be displayed on the display screen on the basis of the image data and the 
data on characters and graphics input from an external output signal 
source via the input/output interface circuit 106 or those coming from the 
CPU 107. The circuit comprises reloadable memories for storing image data 
and data on characters and graphics, read-only memories for storing image 
patterns corresponding to given character codes, a processor for 
processing image data and other circuit components necessary for the 
generation of screen images. 
Image data generated by the image generation circuit 108 for display are 
sent to the decoder 105 and, if appropriate, they may also be sent to an 
external circuit such as a computer network or a printer via the 
input/output interface circuit 106. 
The CPU 107 controls the display apparatus and carries out the operation of 
generating, selecting and editing images to be displayed on the display 
screen. 
For example, the CPU 107 sends control signals to the multiplexer 104 and 
appropriately selects or combines signals for images to be displayed on 
the display screen. At the same time it generates control signals for the 
display panel controller 103 and controls the operation of the display 
apparatus in terms of image display frequency, scanning method (e.g., 
interlaced scanning or non-interlaced scanning), the number of scanning 
lines per frame and so on. 
The CPU 107 also sends out image data and data on characters and graphic 
directly to the image generation circuit 108 and accesses external 
computers and memories via the input/output interface circuit 106 to 
obtain external image data and data on characters and graphics. The CPU 
107 may additionally be so designed as to participate other operations of 
the display apparatus including the operation of generating and processing 
data like the CPU of a personal computer or a word processor. The CPU 107 
may also be connected to an external computer network via the input/output 
interface circuit 106 to carry out computations and other operations, 
cooperating therewith. 
The input unit 115 is used for forwarding the instructions, programs and 
data given to it by the operator to the CPU 107. As a matter of fact, it 
may be selected from a variety of input devices such as keyboards, mice, 
joysticks, bar code readers and voice recognition devices as well as any 
combinations thereof. 
The decoder 105 is a circuit for converting various image signals input via 
said circuits 108 through 114 back into signals for three primary colors, 
luminance signals and I and Q signals. Preferably, the decoder 105 
comprises image memories as indicated by a dotted line in FIG. 25 for 
dealing with television signals such as those of the MUSE system that 
require image memories for signal conversion. The provision of image 
memories additionally facilitates the display of still images as well as 
such operations as thinning out, interpolating, enlarging, reducing, 
synthesizing and editing frames to be optionally carried out by the 
decoder 105 in cooperation with the image generation circuit 108 and the 
CPU 107. 
The multiplexer 104 is used to appropriately select images to be displayed 
on the display screen according to control signals given by the CPU 107. 
In other words, the multiplexer 104 selects certain converted image 
signals coming from the decoder 105 and sends them to the drive circuit 
102. It can also divide the display screen in a plurality of frames to 
display different images simultaneously by switching from a set of image 
signals to a different set of image signals within the time period for 
displaying a single frame. 
The display panel controller 103 is a circuit for controlling the operation 
of the drive circuit 102 according to control signals transmitted from the 
CPU 107. 
Among others, it operates to transmit signals to the drive circuit 102 for 
controlling the sequence of operations of the power source (not shown) for 
driving the display panel in order to define the basic operation of the 
display panel. It also transmits signals to the drive circuit 102 for 
controlling the image display frequency and the scanning method (e.g., 
interlaced scanning or non-interlaced scanning) in order to define the 
mode of driving the display panel. 
If appropriate, the display panel controller 103 transmits control signals 
for controlling the quality of the image being displayed in terms of 
brightness, contrast, color tone and/or sharpness of the image to the 
drive circuit 102. 
The drive circuit 102 is a circuit for generating drive signals to be 
applied to the display panel 101. It operates according to image signals 
coming from said multiplexer 104 and control signals coming from the 
display panel controller 103. 
A display apparatus according to the invention and having a configuration 
as described above and illustrated in FIG. 25 can display on the display 
panel 101 various images given from a variety of image data sources. More 
specifically, image signals such as television image signals are converted 
back by the decoder 105 and then selected by the multiplexer 104 before 
sent to the drive circuit 102. On the other hand, the display controller 
103 generates control signals for controlling the operation of the drive 
circuit 102 according to the image signals for the images to be displayed 
on the display panel 101. The drive circuit 102 then applies drive signals 
to the display panel 101 according to the image signals and the control 
signals. Thus, images are displayed on the display panel 101. All the 
above described operations are controlled by the CPU 107 in a coordinated 
manner. 
The above described display apparatus can not only select and display 
particular images out of a number of images given to it but also carry out 
various image processing operations including those for enlarging, 
reducing, rotating, emphasizing edges of, thinning out, interpolating, 
changing colors of and modifying the aspect ratio of images and editing 
operations including those for synthesizing, erasing, connecting, 
replacing and inserting images as the image memories incorporated in the 
decoder 105, the image generation circuit 108 and the CPU 107 participate 
such operations. Although not described with respect to the above 
embodiment, it is possible to provide it with additional circuits 
exclusively dedicated to audio signal processing and editing operations. 
Thus, a display apparatus according to the invention and having a 
configuration as described above can have a wide variety of industrial and 
commercial applications because it can operate as a display apparatus for 
television broadcasting, as a terminal apparatus for video 
teleconferencing, as an editing apparatus for still and movie pictures, as 
a terminal apparatus for a computer system, as an OA apparatus such as a 
word processor, as a game machine and in many other ways. 
It may be needless to say that FIG. 25 shows only an example of possible 
configuration of a display apparatus comprising a display panel provided 
with an electron source prepared by arranging a number of surface 
conduction electron-emitting devices and the present invention is not 
limited thereto. For example, some of the circuit components of FIG. 25 
that are not necessary fo for a particular application may be omitted. To 
the contrary, additional components may be arranged there depending on the 
application. For example, if a display apparatus according to the 
invention is used for visual telephone, it may be appropriately made to 
comprise additional components such as a television camera, a microphone, 
lighting equipment and transmission/reception circuits including a modem. 
As described above in detail, by arranging an electron-scattering plane 
that elastically scatters incident electrons and has a length L defined by 
formula (1) above on the higher potential side electroconductive thin film 
of a surface conduction electron-emitting device at a depth of less than 
10 nm from the surface, the electron-emitting efficiency of the device can 
be remarkably improved. Additionally, by arranging a low work function 
material layer on the lower potential side electroconductive thin film at 
a position close to the electron-emitting region, the emission current of 
the device can be improved or, by arranging a high melting point substance 
layer, the reduction of the emission current can be suppressed.