JP2000251679A - Image forming device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain abnormal discharge during image formation in an image forming device provided with an anode board and a cathode board facing each other. SOLUTION: When high-resistance parts 4 on a cathode board 2 is charged by applying a voltage to a high-voltage power source 5 together with generating ions by a charging device 1, creeping discharge is generated, when there is abnormality in an electrode shape. By performing the charging process until the creeping discharge is terminated, the abnormality of the electrode shape can be corrected without causing damage to conductive parts 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and a method of manufacturing the same, and more particularly, to a flat type image forming apparatus having an anode substrate and a cathode substrate facing each other and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, a flat plate type image forming apparatus comprising an anode and a cathode has been widely researched and developed, and as an electron source used, for example, a field emission device or a surface conduction type electron emission device is used. What is constituted is mentioned. US Pat. No. 5,142,184 proposes an example using the former field emission device. U.S. Pat. No. 5,066,883 proposes an example using the latter surface conduction electron-emitting device.

[0003] Although the structure of the electron source and the driving method are different, the common features are a cathode composed of an electron source composed of a plurality of electron-emitting devices and an anode close to the cathode. It is a point which has.
The distance between the cathode and the anode is generally several hundred μm to several m.
m. Normally, the inside of the image forming apparatus is kept in a vacuum, and a high positive potential of approximately several kilovolts to several tens of kilovolts is applied to the anode to attract electrons. Therefore, a strong potential is applied between the anode and the cathode. An electric field is applied.

[0004] Usually, a phosphor is formed on the anode, and light is emitted when electrons collide with the phosphor to form an image. Therefore, in order to improve the brightness of an image, it is necessary to increase the energy of electrons, and therefore, it is preferable that the voltage applied to the anode be high. In the following description, a substrate on which an anode is formed is referred to as an anode substrate, and a substrate on which a cathode is located opposite to the anode substrate is referred to as a cathode substrate.

In the above-described conventional flat panel image forming apparatus, an abnormal discharge may occur between the anode and cathode substrates under such a strong electric field. The abnormal discharge referred to here is a large current that is related to driving and is short-circuited between the anode and the cathode, which is distinguished from the normal or predictable steady emission current emitted from the electron source. Refers to discharge accompanied by Such abnormal discharge occurs when there is insufficient vacuum between the cathode and the anode substrate, or when there is a problem that an abnormal electric field can be caused in the electrode shape or the high resistance portion on the cathode substrate. It is considered something.

[0006] Once such an abnormal discharge occurs, it depends on the magnitude of the capacitance formed between the anode and the cathode substrate. In some cases, an arc discharge in a vacuum that causes destruction of an element connected via the wiring may occur. This arc discharge results in a large current, and a large amount of Joule heat due to the current may cause the destruction of the element in the abnormal discharge part or the short-circuit of other elements or wiring due to evaporated particles. In addition, the current concentration may destabilize the potential of the cathode and the wiring for connection, and as a result, may damage elements connected via the wiring.

[0007] As an attempt to suppress the discharge in a vacuum, a "conditioning" method is required to apply a high electric field without causing abnormal discharge, that is, to increase the voltage that can be applied to the anode. There is generally known a method of performing a process referred to as a process. As this conditioning, generally, in order to change the state of the surface of the positive electrode, a high electric field is applied in advance in a high vacuum, or a process of performing a glow discharge in a low-pressure hydrogen gas is performed before use. Methods are known. For example, "The Institute of Electrical Engineers of Japan, High Voltage Engineering Second Revised Edition" (edited by the Institute of Electrical Engineers of Japan, published by Ohmsha on November 10, 1981) is a means for raising the starting voltage of spark discharge in vacuum discharge. (Page 39, lines 11-12). The abnormal discharge in the present specification includes the above-described spark discharge.

[0008]

Therefore, in a flat panel type image forming apparatus, it is required to perform a process for preventing or hardly causing an abnormal discharge which may cause a pixel defect or the like. Such abnormal discharge does not occur,
Alternatively, as a process for reducing the occurrence of such a condition, for example, a conditioning process in which an electric field is applied in advance between the anode and the cathode in a vacuum during the manufacturing process of the image forming apparatus, or a glow discharge is performed in a low-pressure hydrogen gas Can be considered. As a result, an effect of suppressing abnormal discharge can be expected especially for a cathode substrate serving as a cathode during image formation. This is presumably because the above-described conditioning makes it possible to change and substantially correct an abnormal portion such as an electrode shape on the cathode substrate.

However, in order to perform the above-described conditioning, it is necessary to evacuate the anode substrate and the cathode substrate during the manufacturing process or to perform gas replacement thereafter, which complicates the manufacturing process. There is.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem. In an image forming apparatus having a cathode substrate and an anode substrate opposed to each other, an image capable of suppressing abnormal discharge during image formation is provided. An object of the present invention is to provide a forming apparatus and a manufacturing method thereof.

[0011]

In order to achieve the above object, a method of manufacturing an image forming apparatus according to the present invention includes, for example, the following steps.

That is, a method of manufacturing a flat plate type image forming apparatus in which a cathode substrate and an anode substrate are arranged to face each other, wherein a setting step of setting a potential of a conductive portion formed on the cathode substrate; Charging the high resistance portion formed on the cathode substrate at atmospheric pressure.

Further, in the charging step, the amount of charge injected per unit area of the cathode substrate is controlled.

For example, the cathode substrate is constituted by a surface conduction electron-emitting device.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below in detail with reference to the drawings.

First Embodiment [Outline of Manufacturing Method] First, a configuration for manufacturing an image forming apparatus to which the present embodiment is applied will be described below. FIG. 1 is a diagram schematically illustrating a configuration of an image forming apparatus according to the present embodiment. In the figure, 1 is a charging device, 2 is a cathode substrate, 3 is a conductive portion such as an electrode and wiring formed on the cathode substrate 2, 4 is a high resistance portion on the cathode substrate 2, 5 is a high voltage power supply, 6 Indicates an ammeter.

As the charging device 1, a device capable of ionizing nitrogen or the like in the atmosphere and irradiating the cathode substrate 2 with a desired polarity, that is, an anion or a cation can be used. For example, there is an apparatus using corona discharge as such an apparatus, and an electric field is applied between the apparatus and the cathode substrate 2 in order to selectively irradiate a desired polarity.
To generate this electric field, five high voltage power supplies are used. Note that the magnitude of the electric field depends on the cathode substrate 2 during image formation.
Is much smaller than the electric field applied to

The current flowing as a result of the movement of ions of the desired polarity is observed by the ammeter 6, and its value is as small as several tens nA to several tens μA per square centimeter. Therefore, the act of charging itself does not damage the cathode substrate 2.
As the cathode substrate 2, a substrate on which an electron source and wiring for connection are formed, or a substrate in the process of manufacturing can be used. Further, as shown in the figure, the cathode substrate 2 may be of any type as long as it has a structure in which conductive portions 3 such as electrodes and wires are separated by high-resistance portions 4.

Next, an outline of a method of manufacturing the image forming apparatus according to the present embodiment will be described. The present embodiment is characterized in that conditioning in the manufacturing process of the image forming apparatus can be performed at atmospheric pressure. Here, conditioning refers to a process of correcting the electrode shape and the like of the cathode substrate so that a high electric field can be applied when facing the anode substrate. Below, at atmospheric pressure,
An example in which conditioning is performed in the atmosphere will be described. However, the manufacturing process of the present embodiment may be performed in a state in which a gas such as nitrogen flows instead of the air.

First, the cathode substrate 2 is set so that the potential of the conductive portion 3 can be defined. This potential is the ground potential in FIG. Subsequently, the charging device 1 is arranged to face the cathode substrate 2. At that time, the conductive portion 3
The charging device 1 is connected to a high-voltage power supply 5 so that a voltage can be applied to the charging device 1. In addition, an ammeter 6 is provided between them so that an ion current can be observed as needed.

Subsequently, a charging process is performed. That is, the charging device 1
To generate ions, and simultaneously apply a voltage to the high-voltage power supply 5. For example, when a positive voltage is applied to the high voltage power supply 5, the cathode substrate 2 is irradiated with positive ions. By irradiating the ions in this manner, the charges move to the conductive portion 3 and the high-resistance portion 4, but the charges moved to the conductive portion 3 quickly flow through the connection, and have a specified potential, in the above case, It becomes the ground potential. However, the charge that has moved to the high-resistance portion 4 cannot immediately move through the conductive portion 3 depending on its impedance, and is eventually accumulated in the high-resistance portion 4. Therefore, the potential of the high resistance portion 4 rises, that is, it is charged. This charge amount is determined by the difference between the charge moved to the high resistance portion 4 and the charge moved through the conductive portion 3.

When the high-resistance portion 4 is charged as described above, if there is an abnormality such as an electrode shape near the portion, creeping discharge may occur in the portion. This creeping discharge is caused by an abnormal electric field generated as a result of an abnormality such as an electrode shape and the like.
The electric charge accumulated in the main flow mainly flows as a discharge current. This discharge current is considerably smaller than the above-described abnormal discharge that occurs in a vacuum at the time of image formation or the like, and does not cause catastrophic damage to the conductive portion 3 formed on the cathode substrate 2 without causing fatal damage. It is possible to correct abnormalities such as shapes. This correction can be made by checking the presence or absence of creeping discharge when the above-described charging operation is performed again.

As described above, for example, by continuing the charging process until the creeping discharge stops for a desired charge amount, abnormal discharge during image formation can be suppressed. When the area that can be irradiated at a time in the charging device 1 is smaller than the area of the cathode substrate 2, the charging process is divided into a plurality of times for each location of the cathode substrate 2,
Alternatively, the relative position of the charging device 1 with respect to the cathode substrate 2 may be gradually moved. Further, when the above-described charging process is completed, an operation of removing electricity may be performed as needed.

As will be understood from the above description, the conditioning in the present embodiment can be performed extremely easily without requiring a vacuum. Further, by utilizing the creeping discharge generated on the cathode substrate 2, it is possible to correct an abnormality such as an electrode shape without causing a fatal damage to the conductive portion 3 formed on the cathode substrate 2. It is possible to provide an image forming apparatus in which abnormal discharge is suppressed.

[Details of Manufacturing Method] Hereinafter, a method of manufacturing the image forming apparatus according to the present embodiment will be described more specifically.

In the present embodiment, as described above, the charging process according to the configuration shown in FIG. 1 is performed. As the cathode substrate 2 to be processed, a cathode substrate composed of electron sources in which surface conduction electron-emitting devices are arranged in a matrix was used. FIG. 3 shows the appearance of the cathode substrate 2 on which the electron source is formed. In the same figure, 12 is an x-direction wiring, 13 is y
The direction wiring 15 is a surface conduction electron-emitting device. FIG.
Corresponds to the x-direction wiring 12, the y-direction wiring 13, the conductive part of the surface conduction electron-emitting device 15, and the like, and the high resistance portion 4 is a region where these are not formed on the substrate, It corresponds to an interlayer insulating portion (not shown) formed so as to keep electrical insulation at a portion where the x and y direction wirings 12 and 13 intersect.

In the present embodiment, the number of electron sources on the cathode substrate 2 is 120 in the y direction (n = 120) and 4 in the x direction.
A device composed of zero (m = 40) surface conduction electron-emitting devices 15 having an area of about 33 square centimeters was used. The surface conduction electron-emitting device 15 is provided with opposing device electrodes, and a conductive thin film is formed between the device electrodes. As the charging device 1, a device capable of charging an area of about 50 square centimeters at a time was used. That is, the charging device 1 can charge the entire region of the electron source portion on the cathode substrate 2 at a time.

Hereinafter, the respective steps when the image forming apparatus is actually manufactured based on the manufacturing method according to the present embodiment will be sequentially described. First, the x-direction wiring 12 and the y-direction wiring 13 of the cathode substrate 2 shown in FIG. 3 are set at the ground potential, and the high-voltage power supply 5 using the potential as a reference potential.
Is connected to the charging device 1. Since the atmosphere during the treatment was the atmosphere, the atmosphere and pressure were not particularly controlled. Further, an ammeter 6 was installed between the high-voltage power supply 5 and the charging device 1 to observe the ion current.

Then, ions were generated by the charging device 1, and at the same time, a positive potential of 4 kV was applied to the ion generator of the charging device 1 by the high voltage power supply 5. Thereby, the ammeter 6 showed a value of approximately 10 μA. When this state was maintained for about 10 seconds, weak light emission was observed several times. This light emission is considered to have been caused by creeping discharge. Therefore, once the cathode substrate 2 was neutralized by using a neutralization blower (not shown), and the charging process was performed again for 10 seconds under the above-described conditions, no light emission was observed.

Then, the cathode substrate 2
It is determined that the correction of the abnormal portion of the electrode structure in the above has been completed, and then a process for completing the electron source on the cathode substrate 2 is performed, whereby the image display unit shown in FIG. 4 is finally manufactured. . 4, FIG. 1 and FIG.
The same reference numerals are given to the same parts as those described above, and the description is omitted. 1
6 is a rear plate for supporting the cathode substrate 2, 17 is a glass substrate, 18 is a phosphor, 19 is a metal back, and 20 is a support frame for fixing the anode substrate 1 and the cathode substrate 2. The surface conduction electron-emitting device 15 is provided with opposing device electrodes. When a voltage of about 15 V is applied between the device electrodes, a device current If flows between the electrodes, and at the same time, electron emission occurs. Done.

[Evaluation Experiment] Here, in order to facilitate understanding of the characteristics of the image display unit shown in FIG. 4 manufactured according to the present embodiment, the above-described charging process was performed separately from the image display unit. The image display unit was manufactured without using the manufacturing method according to the present embodiment. Hereinafter, an image display unit manufactured according to the present embodiment is referred to as “Example”, and an image display unit manufactured without using the present embodiment is referred to as “Comparative Example”. That is, the only difference between the embodiment and the comparative example is whether or not the charging process is performed on the cathode substrate.

Hereinafter, evaluation experiments performed to evaluate the characteristics of the example and the comparative example will be described.

First, in order to evaluate the characteristics of the image display section of the embodiment, the wirings 12 in the x direction (specifically, Dox1, Dox2,... Dox (m-1), Doxm) and the y direction Wiring 13 (specifically, Doy1, Doy2,... Doy (n-1), Doy
While n) was connected to the ground, the voltage applied to the anode was increased from 10 kV to 15 kV at a rate of 20 V per second, and then held for one hour to determine the presence or absence of abnormal discharge. As a result, abnormal discharge never occurred.
Subsequently, a high voltage of 12 kV is applied to the anode to drive a driver unit (not shown) connected to the x-direction wiring 12 and the y-direction wiring 13 of the cathode substrate 2.
The image was displayed. As a result, a good image was displayed without causing abnormal discharge.

Subsequently, also for the image display section of the comparative example,
An evaluation experiment equivalent to the above-described embodiment was performed. That is, similarly to the embodiment, the x-direction wiring 12 (specifically Dox1, Dox2,... Dox (m-1), Doxm) and the y-direction wiring 13 (specifically Doy1, Doy2, … Doy (n-1), Do
With yn) connected to ground, the voltage applied to the anode was increased from 10 kV at a rate of 20 V per second, and abnormal discharge occurred at 10.8 kV. After that, when the voltage was continuously increased, abnormal discharge occurred again at 11.7 kV, and the voltage increase was stopped. Next, apply 12 kV to the anode.
Is applied, and a driver unit (not shown) connected to the x-direction wiring 12 and the y-direction wiring 13 of the cathode substrate 2 is driven to display an image. Was seen. Abnormal discharge was also observed during evaluation of the image. From these results, it can be seen that in the comparative example, the voltage of the anode at which abnormal discharge starts is lower than 12 kV, and it is therefore difficult to drive without generating abnormal discharge under the condition of the anode voltage of 12 kV.

Based on the results of the evaluation experiments described above, no abnormal discharge occurred in the image display section of the example. Therefore, the charging process in the manufacturing process of this embodiment is effective in suppressing abnormal discharge. Is understood. This is because by performing the charging process on the cathode substrate 2 of the embodiment, it is possible to correct an abnormal portion such as an electrode shape and the like, thereby improving the voltage that can be applied to the anode without causing abnormal discharge. Because it was done.

As described above, according to the present embodiment, the charging process is performed on the high resistance portion of the cathode substrate under the atmospheric pressure, so that a creeping discharge is generated in the vicinity of the charged portion and the shape of the electrode on the cathode substrate is reduced. Can be applied to correct the condition. As a result, the starting voltage of the creeping discharge generated on the cathode substrate, that is, the creepage withstand voltage is improved, and as a result, the starting voltage of the abnormal discharge generated between the anode and the cathode is improved, and the abnormal discharge during image formation can be suppressed. .

<Second Embodiment> Hereinafter, a second embodiment according to the present invention will be described.
An embodiment will be described.

[Details of Manufacturing Method] In the second embodiment,
The charging process described in the first embodiment with reference to FIG. 1 is performed by the configuration shown in FIG.

In FIG. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 2, reference numeral 9 denotes an ammeter for observing an ion current, which corresponds to the ammeter 6 in the first embodiment. The ammeter 9 includes a feedback circuit (not shown) to the high-voltage power supply 5 and the charging device 1, and controls the output voltage of the high-voltage power supply 5 and the amount of ions generated by the charging device 1 to set the ion current value to a set value. It is configured to be controllable. Therefore, by controlling the charging time and the like, the amount of charge injected per unit area of the cathode substrate 2 can be controlled. Reference numeral 7 denotes a second ammeter, and reference numeral 8 denotes discharge detection means. The discharge detection means 8 detects a current change signal from the second ammeter 7, and specifically detects a current flowing when creeping discharge occurs. Note that the same cathode substrate 2 and charging device 1 as those in the above-described first embodiment can be used.

Hereinafter, a method of manufacturing the image forming apparatus according to the second embodiment will be specifically described. In the second embodiment, the cathode substrate shown in FIG. 3 is manufactured by performing a charging process using the configuration shown in FIG. The description of each configuration in the figure has been made in the above-described first embodiment, and will not be repeated here.

First, the x-directional wiring 12 and the y-directional wiring 13 of the cathode substrate 2 schematically shown in FIG. 3 are set at the ground potential via the second ammeter 7. Subsequently, a high voltage power supply 5 having a ground potential as a reference potential is connected to the charging device 1 via an ammeter 9. Since the atmosphere during the treatment was the atmosphere, the atmosphere and pressure were not particularly controlled.

Then, the high voltage power supply 5 is controlled so that the charging device 1 generates ions and simultaneously applies a positive potential to the ion generating section of the charging device 1. At this time, the ammeter 9 controls the charging device 1 and the high-voltage power supply 5 via a feedback circuit (not shown) so that the current value becomes 20 μA. About 5 in this state
After holding for 2 seconds, six discharges were observed in the discharge observation means 8. This discharge is considered to have been caused by creeping discharge. Then, after the charge was once removed by using a charge removing blower (not shown), the charging process was performed again for 20 seconds under the above-mentioned conditions, and no discharge was observed.

Then, the cathode substrate 2
It is determined that the correction of the abnormal portion of the electrode structure in the above has been completed, and then a process for completing the electron source on the cathode substrate 2 is performed, whereby the image display unit shown in FIG. 4 is finally manufactured. . The description of each configuration shown in FIG. 4 has already been made in the above-described first embodiment, and will not be repeated here.

[Evaluation Experiment] Here, an evaluation experiment performed to evaluate the characteristics of the image display unit shown in FIG. 4 manufactured according to the second embodiment will be described.

First, a high voltage of 12 kV is applied to the anode, and the x-direction wiring 12 (specifically, Dox
1, Dox2,... Dox (m-1), Doxm) and y-direction wiring 13
(Specifically, an image is displayed by driving a driver unit (not shown) connected to Doy1, Doy2,... Doy (n-1), Doyn). As a result, a good image was displayed. Subsequently, in this state, a 300-hour durability test was performed while displaying various images. As a result, a good image was maintained without any abnormal discharge.

According to the experimental results, it was shown that the image forming apparatus manufactured by the manufacturing method according to the second embodiment is effective for suppressing abnormal discharge.

As described above, according to the second embodiment, in addition to the first embodiment, it is possible to control the amount of electric charge injected per unit area of the cathode substrate and to control the amount of electric charge accumulated in the charged portion. It becomes possible. Therefore, finer charging control is possible.

Further, by providing a means for observing discharge, it is possible to measure the number of occurrences of abnormalities in the electrode shape on the cathode substrate, and the like.

In the second embodiment, an example in which the amount of charge injected per unit area of the cathode substrate 2 is controlled has been described. In addition to this, the time change of the amount of injected charge, that is, the ion current value is controlled. It is also possible to control at the same time. For example, by setting the ion current value stepwise, the time required for the charging process can be reduced, or the charge amount can be controlled with higher precision.

In the second embodiment, an example has been described in which the discharge observing means 8 observes a change in the current flowing through the conductive portion. Good. For example, a photomultiplier tube (photomultiplier) can be used as the discharge observation means 8.

Also, in the second embodiment, the number of occurrences of abnormalities in the electrode shape or the like that cause abnormal discharge can be measured by providing the discharge observing means 8, so that the number of occurrences can be measured between a plurality of cathodes, for example. By comparing the numbers,
Variations and the like can also be monitored.

[0052]

As described above, according to the present invention, in an image forming apparatus having a cathode substrate and an anode substrate opposed to each other, abnormal discharge during image formation can be suppressed very easily.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration when an image forming apparatus according to an embodiment of the invention is manufactured.

FIG. 2 is a diagram illustrating a configuration when manufacturing an image forming apparatus according to a second embodiment;

FIG. 3 is a diagram showing a configuration of a cathode substrate manufactured according to the present invention;

FIG. 4 is a diagram illustrating a configuration of an image forming apparatus manufactured according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Charging device 2 Cathode substrate 3 Conductive part on cathode substrate 4 High resistance part on cathode substrate 5 High voltage power supply 6, 7, 9 Ammeter 8 Discharge observation means 12 X direction wiring 13 Y direction wiring 15 Surface conduction type electron emission Element 16 Rear plate 17 Glass substrate 18 Phosphor 19 Metal back 20 Support frame

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Keisuke Yamamoto, Inventor 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term in Canon Inc. (reference) 5C094 AA00 AA42 AA43 AA53 BA32 BA34 CA19 DA13 DB04 EA04 EA07 FA01 FB20 GB10 5G435 AA16 AA17 BB02 KK05 KK10

Claims (14)

[Claims] 1. A method for manufacturing a flat plate type image forming apparatus in which a cathode substrate and an anode substrate are arranged to face each other, wherein: a setting step of setting a potential of a conductive portion formed on the cathode substrate; A charging step of charging a high resistance portion formed on the cathode substrate at atmospheric pressure, the method comprising: 2. The method according to claim 1, wherein the cathode substrate includes a cold cathode. 3. The method according to claim 1, wherein the cathode substrate has a structure in which the conductive portion is separated by a high-resistance portion. 4. The method according to claim 1, wherein in the setting step, the potential of the conductive portion is set to a ground potential. 5. The method according to claim 1, wherein said charging step is performed in a nitrogen gas flow state. 6. The method according to claim 1, wherein in the charging step, an amount of charge injected per unit area of the cathode substrate is controlled. 7. The method according to claim 1, wherein in the charging step, an amount of electric charge injected per unit area of the cathode substrate and an amount of time derivative thereof are controlled. 8. The method for manufacturing an image forming apparatus according to claim 1, further comprising an observation step of observing a discharge generated in the charging step. 9. The method for manufacturing an image forming apparatus according to claim 8, wherein in the observation step, a creeping discharge generated near a high resistance portion on the cathode substrate is observed. 10. The method according to claim 8, wherein the charging step is continued until no discharge is observed in the observation step. 11. The method according to claim 9, wherein in the observing step, the creeping discharge is observed by detecting a change in a current flowing through the conductive portion. 12. The method according to claim 9, wherein in the observation step, the creeping discharge is observed by detecting light emission on the cathode substrate. 13. An image forming apparatus manufactured by the method according to claim 1. 14. The image forming apparatus according to claim 13, wherein said cathode substrate is constituted by a surface conduction electron-emitting device.