JPH02257541A - Electron beam generating apparatus and image forming device using the same - Google Patents

Abstract

PURPOSE:To enhance performance of a thin display device in practical use by varying the area of an emitting part in accordance with dispersion of impression voltage of an electron emitting element, or by using two or more different types of materials. CONSTITUTION:Conductive paths 2a, 2b made in Au, Ag, Cu, etc., are formed on a glass base board 1, and thereover are provided a plurality of filament parts 3 which are formed from film consisting of Ta, Ta alloy, W, etc. Each filament part 3 is coated on its oversurface with material with low work function 4, 4', 4'' such as LaBe, TiC, TaC, etc. Therein the area of this covering of low work function material shall be changed element by element so that the current amount of the electron beam emitted from different elements becomes equal. Thus unevenness of image in its shade is reduced greatly, and performance of a thin display device in practical use can be enhanced to a great extent.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electron beam generator equipped with a large number of thermionic beam sources using thin films, and an image forming apparatus using the same (for example, a flat CRT, etc.). Regarding.

[Prior Art 1] Conventionally, various types of flat display devices have been proposed, but representative ones include flat display devices using electroluminescence methods, plasma methods, liquid crystal methods, etc. There is a device.

However, when trying to use the above method in display devices that require high-speed scanning and high pixel density images, such as color televisions, there is a limit to its luminous efficiency, and it is difficult to use for large screens. is also not practical. For this reason, flat display devices of the electron beam acceleration type have conventionally been used for televisions, etc., which reproduce images by accelerating electrons emitted from an electron source in a vacuum with high voltage and colliding with a phosphor to emit light. He is one of the leading candidates.

In this electron beam acceleration type flat display device,
For example, it has been considered to have a multi-electron source structure in which each pixel corresponds to an electron source on a one-to-one basis, and an example of an electron beam source in this case is disclosed in Japanese Patent Application Laid-Open No. 1987-1956. The use of thin-film thermionic beam sources has been proposed.

FIG. 15 shows a cross-sectional structure of this conventional thermionic beam source. According to FIG. 15, a glass insulating layer (supporting layer) 7 is formed on a substrate 1, and a After forming a thin tungsten film by sputtering or the like, a photolithography method is used to integrally form a thin film filament 3 that emits thermoelectrons when energized, and a conductive path 8 for energizing the thin film filament 3. Thereafter, a part of the lower part of the thin film filament 3 of the insulating layer (supporting layer) 7 is removed by wet etching to form a gap 9, thereby showing a thermionic beam source having a thin film hollow structure.

[Problems to be Solved by the Invention] By the way, when these thermionic sources are applied to an image forming apparatus, generally a large number of elements (hereinafter the thermionic sources are abbreviated as elements) are formed in an array on a substrate, Each element was electrically wired using thin-film or thick-film electrodes and used as a multi-electron beam source, but the voltage applied to each element varied due to the voltage drop caused by the wiring resistance. A phenomenon is occurring. As a result, the amount of current of the electron beam emitted from each emitting element varies, causing a problem of density unevenness in the formed image.

Figures 16 and 17 are diagrams to explain this problem in more detail. In both figures, (a) is an equivalent circuit diagram including an electron-emitting device, wiring resistance, and power supply, and (b) is an equivalent circuit diagram of each electron. A diagram showing the potentials of the positive and negative electrodes of the emitting element, and (e) a diagram showing the voltage applied between the positive and negative electrodes of each element. FIG. 16(a) shows N electron-emitting devices connected in parallel, ~D
This shows a circuit in which N and a power source Vt are connected, and the positive electrode of the power source and the positive electrode of the element are connected, and the negative electrode of the power source and the negative electrode of the element are connected. Further, it is assumed that the common wiring connecting each element in parallel has a resistance component of r between adjacent elements as shown in the figure. (In image forming devices, the pixels that are the targets of the electron beam are usually arranged at equal pitches. Therefore, the electron-emitting elements are also arranged at equal spatial intervals, and the wiring that connects them has a width and thickness. (As long as there is no variation in thickness due to manufacturing, the devices have the same resistance value.) Furthermore, all the electron-emitting devices D1 to DH have approximately the same resistance value Rd.

In the circuit diagram of FIG. 16(a), FIG. 16(b) shows the potentials of the positive and negative electrodes of each element. The horizontal axis of the figure shows the element numbers D1 to DN, and the vertical axis shows the potential.
The marks represent the positive electrode potential of each element, and the ■ marks represent the negative electrode potential.For convenience, the marks (■ marks) are connected with a solid line to make it easier to see the tendency of the potential distribution.

As is clear from this figure, the voltage drop due to the wiring resistance r does not occur uniformly; in the case of the positive electrode side, the closer it is to the element RI, the steeper it is, and conversely, on the negative electrode side, the closer it is to the element RI, the steeper it is. It has become. This is because on the positive electrode side, the closer to Dl the larger the current flows through the wiring resistance r, and on the negative electrode side, the closer to DH, the larger the current flows.

From this, the voltage applied between the positive and negative electrodes of each element is plotted in FIG. In the figure, the horizontal axis indicates the element number of -DN, and the vertical axis indicates the applied voltage, and as in (b), O is connected with a solid line for convenience to make the trend easier to see.

As is clear from the figure, in the case of the circuit shown in figure (a), a larger voltage is applied closer to the elements at both ends (D and DH), and a smaller voltage is applied to the elements near the center. Become.

Therefore, the electron beam emitted from each electron-emitting device is
The beam current increases toward the elements at both ends, which is extremely inconvenient when applied to an image forming apparatus. (For example, the image near both ends has a high density (and the image near the center has a low density.) On the other hand, what is shown in Fig. 17 is one side of an element array connected in parallel (in this figure, the image is This is the case when the positive and negative poles of the power supply are connected to the DI (side).In the case of such a circuit, as shown in the same figure (b), the closer the wiring resistance r is to the positive and negative poles of both the positive and negative poles.
The voltage drop due to

Therefore, as shown in FIG. 2C, the voltage applied to each element becomes larger as it approaches DI, which is extremely inconvenient for application as an image forming apparatus.

As shown in the above two examples, the degree of variation in the applied voltage for each element depends on the total number of elements connected in parallel N, the ratio of element resistance Rd to wiring resistance r (= Rd/r), or the power supply Although it differs depending on the connection position, in general, the larger N is and the smaller Rd/r is, the more pronounced the variation becomes.Furthermore, the connection method shown in FIG. For example, in the connection method shown in Fig. 16, when the element resistance Rd = l kΩ and r = 10 mΩ, if N = 100, comparing the element with the largest applied voltage and the element with the smallest applied voltage, V, x: V...
ll = about 102:100, but N = 100
If there is 0"t', then v,...: v111=472:
100, the rate of variation becomes large.

Also, N = 1000. Rd=1 kΩ, r=1
6 for mΩ, Il: V, , = 127
: About 100, but in the case of r = lOmΩ,
The degree of variation becomes large, such as V,,,I:V,,ll=472:100.

As explained above, when multiple electron-emitting devices with the same characteristics are connected in parallel, the effective voltage applied to each device varies from device to device due to the voltage drop caused by wiring resistance. , the amount of emitted electron beam becomes non-uniform, which is inconvenient when applied as an image forming apparatus.

Particularly, when attempting to realize a large-capacity display device with a large number of pixels (that is, a large number of N), the above-mentioned variation rate becomes remarkable, and uneven density of images becomes a major problem.

[Means and effects for solving the problem] According to the present invention, when a plurality of electron-emitting devices (thin-film thermionic sources) are wired in parallel to form a multi-electron beam source, the plurality of electron-emitting devices The amount of electron beams emitted from each element is made equal by making the electrical resistances of the elements the same, and by appropriately changing the area of the electron emitting part or the material used for the electron emitting part for each element.

More specifically, regarding the front side, the amount of electron beam is made equal by appropriately changing the surface area of the low work function material layer formed on the thin film heater for each element. When wiring is performed using the method shown in FIG. 16, the area of the electron emitting portion of the central element is made larger than that of the elements at both ends.

Furthermore, when electron-emitting devices are wired using the method shown in FIG. 17, the area of the electron-emitting portion is made larger as the device is farther from the power supply side.

Regarding the rear part, for example, it is possible to use completely different materials for the electron-emitting part, or to form the electron-emitting part from at least two kinds of materials.
A method of changing the ratio of materials used at that time was also considered.

In this case, for example, when electron-emitting devices are wired in the manner shown in FIG. Use materials with high density.

Furthermore, when the electron-emitting devices are wired in the manner shown in FIG. 17, a material having a higher thermionic emission current density is used for the devices farther from the power supply side than for the devices closer to the power supply side.

[Example] Hereinafter, the present invention will be specifically described in detail based on Examples.

Distortion 11 Figures 1 to 5 are schematic diagrams for explaining a first embodiment of the present invention. First, FIG. 1 is a partially cutaway perspective view of a multi-electron beam source to which the present invention is applied. In this figure, 1 is a glass substrate (any insulating material is fine), and on it there are (Au, Ag, Cu, Ai),
Conductive paths 2a and 2b made of at least one kind of Ni or the like are formed. Furthermore, a thin film made of tantalum, tantalum alloy, tungsten, etc.
A plurality of filament parts 3 are formed. In other words, the conductive paths 2a and 2b also have the function of a thin film support having the filament portion 3. The thickness of the paths 2a and 2b is 1 km to 300 m, and the width is 10 μm to 11000 m.
The thickness of the filament portion 3 is preferably 0.1 μm to 3ILI111, and the length of the filament portion 3 is 10 μm to 30 μm.
It is preferable that the width is 2000 gm and the width is about 1 μI11 to 50H.

Further, 4, 4', 4'' are low work function material coating parts in which the upper surface of each filament part 3 is coated with a low work function material such as Lava, Tic, TaC, SiC, etc. In the figure, the shaded area indicates the coating area. It shows.

In FIG. 1, only three elements of the thin film thermionic source are shown for the sake of simplicity, but in reality, more than 100 elements are arrayed in the same direction.

In the above electron source, by applying a voltage between the conductive paths 2a and 2b, a current flows through the filament portion 3, generating heat, and electrons are emitted from the low work function material coating portions 4.4' and 4''. be done.

Here, the feature of the present invention is as shown in FIG. 2(a).
As shown in , (b) and (c), the area of the low work function material covering portion is appropriately changed for each element to equalize the amount of current of the electron beam emitted from each element.

Therefore, for more specific explanation, a case will be described in which the electron-emitting device array shown in FIG. 1 is connected to a power source (drive circuit) by the method shown in FIG. 16. In this case, the area of the low work function material covering portion of each of the N elements connected in parallel is shown in FIG. 3, where the horizontal axis represents the element number (corresponding to the element number in FIG. 16), The vertical axis represents the area of the low work function material coating. (In this case, the area cannot be uniquely expressed as an absolute value, but is a quantity that depends on the size of the heater section, etc., so the vertical axis is expressed as the relative difference between the elements.) As is clear from the figure, in the present invention, the area of the electron emitting part is adjusted appropriately by considering in advance the variation in applied voltage to the elements that occurs when elements with equal resistance values are connected in parallel via equal wiring resistance. I'm making adjustments. In this example, as shown in FIG. 16(C), the element applied voltage is smaller in the central element than in the elements at both ends. As shown in Figure 2, the area of the electron emitting part of the center element is larger (by design (here, the maximum area is 32 and the minimum area is St).

When a conventional multi-electron beam source in which all the elements have the same emission area is applied to a display tube or the like, the characteristics are as shown in FIG. 4. In other words, when we measure the electron beam current reaching the phosphor screen while keeping the accelerating voltage applied to the phosphor screen and the modulation voltage applied to the modulation grid constant, we get:
The applied voltage is Vma. From the element with (maximum value), EB,...
, electron beams of EB arrive, but only electron beams of EB, , n reach from the element where the applied voltage is ■□n (minimum value). Therefore, the display tube has a brightness characteristic that is bright at both ends and dark at the center, which is inconvenient.

However, according to the present invention, as shown in FIG.
Since the area of the electron emitting part of the element was made to be 32, the amount of electron beams reaching the phosphor screen was equal, making it possible to realize a display tube with uniform brightness over the entire screen. . (In addition, in FIG. 5, for the sake of simplicity of explanation, only examples where the device applied voltages are Vmax and Vstn are shown, but other devices can also be set to the emission area shown in FIG. 3). Equal phosphor screen currents EB are obtained.

Next, FIGS. 6 to 8 are diagrams for explaining an embodiment of a flat panel display device to which the present invention is applied, and FIG. 6 is a partially cutaway perspective view showing the structure of the display panel. FIG. 7 is a diagram showing a block circuit for driving the panel, and FIG. 8 is a time chart showing the driving timing of each part of the panel.

The operation of this device will be explained step by step below. FIG. 6 shows the structure of the display panel. In the figure, VC is a glass vacuum container, and FP, which is a part of the vacuum container, is a face plate on the display surface side. A transparent electrode made of ITO is formed on the inner surface of the face plate FP, and red and green electrodes are formed inside the transparent electrode.

Blue phosphors are painted in a mosaic pattern, and a metal back treatment known in the field of CRTs is applied. (The transparent electrode, phosphor, and metal back are not shown.) Furthermore, the transparent electrode is electrically connected to the outside of the vacuum vessel through a terminal EV in order to apply an accelerating voltage.

Further, S is a glass substrate fixed to the bottom surface of the vacuum container VC, and an electron-emitting device (thin-film thermionic source) is mounted on the top surface of the glass substrate.
are arranged in N×β columns. (Here, N = 200 and g = 200.) The electron-emitting device groups are electrically connected in parallel in each column, and the positive electrode side wiring (negative electrode side wiring) of each column is connected to terminals D□~ D,i) (Terminals Dell to D,il) are electrically connected to the outside of the vacuum vessel. That is, in this device, two rows of elements are formed on the substrate S using the power feeding method shown in FIG. 16, which was explained in the section on conventional problems. (The number of elements per row is N.) The electrical resistance of each emitter is equal within the manufacturing error, and the electron emitting part of each emitter is as shown in Figure 3 above. Adjust the area accordingly.

Furthermore, a striped grid electrode GR is provided between the substrate S and the face plate FP. N grid electrodes GR are provided perpendicular to the element array, and each electrode is provided with a hole Gh for transmitting an electron beam. One hole Gh may be provided for each electron-emitting device as in the example shown in FIG. 6, or a large number of fine holes may be provided in a mesh shape. Each grid electrode is electrically connected to the outside of the vacuum vessel through terminals G and -G.

In this panel, an XY matrix is formed by two rows of electron-emitting device rows and N rows of grid electrode rows. By sequentially driving (scanning) the electron emission rows one by one and simultaneously applying a modulation signal for one image line to the grid electrode row, the irradiation of each electron beam to the phosphor is controlled. The image is displayed line by line.

What is shown in FIG. 7 is a block diagram of an electric circuit for driving the display panel shown in FIG.
11 is the display panel shown in FIG. 6, 12 is an element column drive circuit, 13 is a modulation grid drive circuit, and 14 is a high voltage power supply. The electrode terminal EV of the display panel 11 is connected to the high voltage power supply 1
An accelerating voltage of about 4 to 10 KV is supplied. In addition, the negative electrode side wiring terminal ([1-, ~D-12) of the electron-emitting device row
is grounded to the ground level (OV), and the wiring terminals (D, 1 to o, R) on the positive electrode side are connected to the element column drive circuit 12. Further, the grid electrode is connected to the modulation grid drive circuit 13 through terminals 61 to GN.

Signal voltages are output from the element array drive circuit 12 and the modulation grid drive circuit 13 at the timing shown in the drive time chart of FIG. In FIG. 8, (a) to (d) show the D□+Dpi of the element panel 11 from the element column drive circuit 12,
o, and the signals applied to the DpR terminals.As can be seen from the figure, Del, D□+Dpa...(D, 4
~Dp+i'-++ is shown in the figure) Drive pulses of amplitude Vi [V] are sequentially applied in the order of DpR. In synchronization with this, the modulation grid drive circuit 13 outputs terminals GI to GN.
8(e), the modulation signal (V,
(ON) or V, (OFF)) is applied.

Whether the vo (ON) level or the V, (OFF) level is applied to each terminal is determined by the pattern of the displayed image.

Before applying the present invention, when the entire screen was illuminated, brightness unevenness of nearly 20% was observed at the center and both edges of the screen, but as a result of applying the present invention, under the same display conditions, The brightness unevenness was reduced to less than 1/20 of the conventional level, and the quality of the displayed image was significantly improved.

Although the electron beam generator to which the present invention is applied and the image forming apparatus using the same have been described above, the embodiments of the present invention are not limited to those shown in FIGS. 1 to 8.

For example, when changing the area of the low work function material coating layer, the shape of the coating formed on the heater does not necessarily have to be the same as the second one.
The shape is not limited to that shown in the figure (for example, it may be circular as shown in FIG. 9).

Furthermore, the area of the covering part does not necessarily have to be changed for each element; for example, as shown in Figure 10, the area near the center where the variation in applied voltage is small may be the same across multiple elements. .

Furthermore, depending on the method of feeding power to the electron-emitting device array, the covering area of the central device may not necessarily be maximized, for example, as shown in FIG. 17 described in the prior art section. In this case, as shown in FIG. 11, it is preferable to make the area of the covering portion larger (0) as the element is farther from the power supply side.

11■Yu Next, a second example will be shown.

The feature of the present invention here is as shown in FIG. 12(a).
, (b) and (c), the current of the electron beam emitted from each element can be adjusted by appropriately changing the coating material used for the electron emitting part for each element in the array of elements connected in parallel. This reduces the variation in quantity.

In the figure, the element (a) uses Mo/Th, the element (b) uses W/Th, and the element (c) uses Ta/Th as the coating material for the electron emission region.

By arranging these elements as necessary, a multi-electron source is constructed.

For example, in the wiring method shown in FIG. 16 explained in the conventional example, when the number of elements N is 100, D1 to D2° and Dal
Mo/Th was used as the coating material for each element of "DI..., W/Th was used for each element of 021"D4° and Del"06°, and Ta/Th was used for each element of D41 to Da. Use.

In this case, D1 to D2° and Dal to D1° as explained in the conventional problem. Since a higher voltage is applied to the element group than to the element group from Da+ to D8°, the temperature of the heater section will be higher, but as mentioned above, the coating material should be selected taking into account the temperature difference in advance. By doing so, approximately the same radiation current can be obtained.

FIG. 13 is a graph for explaining this, in which the horizontal axis is the voltage applied to the electron-emitting device, and the vertical axis is the radiation current obtained from the electron-emitting device. In addition, the three types of elements in the same figure are
This corresponds to that shown in FIG. 12 above. Element (a)
Since a voltage higher than that of element (b) or element (c) is applied to element (b) or element (c) (V, > Vb > Vc), the temperature of the heater section increases, but Mo/Th is higher than W/Th or T.
Compared to a/Th, it has a characteristic that the thermionic emission current density is smaller at the same temperature, and the thermionic emission current density becomes equivalent only at a higher temperature. In addition, considering that an intermediate voltage V2 between elements (a) and (C) is applied to element (b), W/Th is an intermediate thermionic voltage between Mo/Th and Ta/Th. The material has a radiation current density.

Therefore, when 100 elements are connected in parallel as described above,
(a), (b) according to the distribution of element applied voltage.
.

By arranging the elements of (C) in advance, it became possible to significantly reduce variations in radiation current.

According to the inventors' experiments, when the same coating material (for example, Mo/Th) was used for all 100 elements, a variation of about 25% was observed in the emission current, but (a)
As a result of appropriately arranging the elements (b) and (c), it was possible to reduce the variation in radiation current to about 4%.

On the other hand, when the wiring method shown in FIG. 17 is used, a material with a high thermionic emission current density may be used for elements far from the power supply side. That is, when the number of elements N = 100, the elements of (a) above are placed in D1 to D33, and the elements in 034 to D
a? The element (b) above was added to Dam −D+o.

It is sufficient to arrange the elements of (c) above.

Further, the vine coating material used in the present invention is not limited to the above-mentioned alloys, but includes, for example, LaB5. BaBa, CaBa
Materials with relatively high thermionic emission current density, such as borides such as TaC, SiC, and TiC, carbides such as TaC, SiC, and TiC, or oxides such as Y20□, ThO□, and Laz03, can be used for the electron emission part. is possible.

The present invention also includes an embodiment as shown in FIG. In other words, this is a method in which the electron emitting portion is coated with a small number of materials (in both cases, two or more kinds of materials, and the current emitted from each element is made equal by changing the proportion of the area covered with each material. In the example, (a), (b),
The characteristics of the elements in (c) are different.

The feature of this embodiment is that, compared to the method shown in FIG. 12, it is possible to more precisely reduce the variation in radiation current of multiple elements. This is because using techniques such as photolithography etching and mask vapor deposition, it is easy to cover different materials in an arbitrary area ratio. For example, this method succeeded in reducing the variation in radiation current of 100 elements to about 1%.

Next, using this device, a flat panel display device was fabricated and driven in the same manner as in Example 1.

This device is thin and has uneven brightness, making it extremely suitable for office machines, computer terminals, home television receivers, and the like.

[Effects of the Invention] As explained above, in the present invention, the area of the electron emitting part formed on the heater of the thin film thermionic electron source differs depending on the variation in the voltage applied to each element. By changing the size, using different materials, or using two or more types of materials and changing the area covered by each material, it is possible to significantly reduce the variation in the current emitted from each element. .

As a result, image density unevenness that occurs when applying a thin film thermionic electron source to an image forming apparatus is significantly reduced, and the practical performance of, for example, a thin display apparatus can be significantly improved.

The present invention can be applied to most image forming apparatuses having an electron source section in which a large number of electron-emitting devices are connected in parallel, in addition to flat panel display devices as shown in the embodiments. It is also extremely effective in the field of image recording devices.

[Brief explanation of drawings]

1 is a partial perspective view of a multi-electron beam source according to a first embodiment of the present invention, FIG. 2 is a plan view of an element of a multi-electron beam source according to a first embodiment of the present invention, and FIG. 3 is a partial perspective view of a multi-electron beam source according to a first embodiment of the present invention. , a graph showing the area of the low work function material covering part of each element, FIG. 4 is a graph showing the current reaching the phosphor screen when the present invention is not applied, and FIG. 5 is a graph showing the current reaching the phosphor screen when the present invention is applied. A graph showing the current, FIG. 6 is a partially cutaway perspective view of an image forming apparatus to which the present invention is applied, FIG. 7 is a drive circuit block diagram of the image forming apparatus to which the present invention is applied, and FIG. 8 is a graph showing the image forming apparatus to which the present invention is applied. Time chart showing the operation timing of each part of the applied image forming apparatus, No. 9
The figure is a plan view of an element showing another embodiment of the first example, and FIGS. 10 and 11 show the area of a low work function material coating part showing another embodiment of the first example. The graph, FIG. 12, is a plan view of three types of thin film thermionic sources according to the second embodiment of the present invention, and FIG. 13 shows the characteristics of three types of thin film thermionic sources, which are the second embodiment of the present invention. Graph, FIG. 14 is a plan view of an element showing another embodiment of the second example, FIG. 15 is a cross-sectional view for explaining a conventional thin film thermionic source, FIGS. 16 and 17. 1 is a diagram for explaining the conventional problems of a multi-electron beam source in which a plurality of thin-film thermionic electron sources are connected in parallel. 1-Substrate (glass substrate) 2.3-Filament portion 4, 4', 4''-Low work function material coating portion 5-Mo/
Th coating part 6- Ta/Th coating part 7- Insulating layer
8.2a, 2b - conductive path 9 - gap
11-Display panel 12-Element column drive circuit 13-Modulation grid drive circuit 14-High voltage power supply

Claims (1)

[Scope of Claims] (1) A multi-electron beam source in which a plurality of thin-film thermionic sources are electrically connected in parallel via conductive paths, the plurality of thin-film thermionic sources are What is claimed is: 1. An electron beam generating device comprising at least two types of devices having equal resistance and different areas of electron emitting portions. (2) In the multi-electron beam source, a power supply means is provided so that a positive voltage can be applied from one end of the row of thin film thermionic sources connected in parallel and a negative voltage can be applied from the other end, and the thin film thermionic emitters are connected in parallel. 2. The electron beam generating device according to claim 1, wherein the area of the electron emitting portion of the electron source located at the center of the row is larger than that of the electron sources located at both ends of the row. (3) In the multi-electron beam source, means for supplying positive voltage and negative voltage for driving the electron sources is provided at one end of the row of thin film thermionic sources connected in parallel, and 2. The electron beam generating device according to claim 1, wherein the area of the electron emitting section is larger in the electron source located further away than in the electron source closer to one end where the power feeding means is provided. (4) The electron beam generating device according to any one of claims 1 to 3 is provided, a beam modulating means for modulating the electron beam, and a target for forming an image by being irradiated with the electron beam. An image forming apparatus characterized by: (5) A multi-electron beam source in which a plurality of thin-film thermionic electron sources are electrically connected in parallel via a conductive path, wherein the plurality of thin-film thermionic electron sources have heater parts with equal electrical resistance and An electron beam generator characterized in that the emission part is made of at least two or more materials having different thermionic emission current densities. (8) In the multi-electron beam source, a power supply means is provided so that a positive voltage can be applied from one end of the row of thin film thermionic sources connected in parallel, and a negative voltage can be applied from the other end of the row, and the thin film thermionic emitters 6. The electron beam generator according to claim 5, wherein the thermionic emission current density of the electron emitting portion of the electron source located at the center of the row is larger than that of the electron sources located at both ends of the row. Device. (7) In the multi-electron beam source, means for supplying positive voltage and negative voltage for driving the electron sources is provided at one end of the row of thin film thermionic sources connected in parallel, and 6. The electron beam generating device according to claim 5, wherein the thermionic emission current density of the electron emitting section is greater in an electron source located far away than in an electron source closer to one end where the power feeding means is provided. (8) The electron beam generating device according to any one of claims 5 to 7 is provided, a beam modulating means for modulating the electron beam, and a target for forming an image by being irradiated with the electron beam. An image forming apparatus characterized by: