JPH02299143A - Image forming device - Google Patents

Abstract

PURPOSE:To uniform luminescence brightness by continuously changing the film thickness of the metal back of a fluorescent face in response to the degree of the discharged current decrease due to the temperature rise of an element. CONSTITUTION:The film thickness of the metal back 6 of a fluorescent face is continuously changed so that it is made thinnest at the center section and thicker toward the periphery section. When phosphors 7 are illuminated by the fixed accelerating voltage, the permeability of electrons is reduced at the thick portion of the metal back film thickness and the luminescence brightness is made low, and the permeability is increased at the thin portion and the luminescence brightness is made high. When surface conductive type electron emitting elements connected in parallel are driven, the center section has a temperature higher than that of the periphery section due to the difference of heat radiation, the electron emission characteristic is deteriorated, and the discharged current is decreased. When the metal back thickness of the fluorescent face is changed, uniform luminescence can be obtained without using special driving or constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus comprising a plurality of surface conduction electron-emitting devices and a phosphor screen.

[Prior art 1] Conventionally, as an element that can emit electrons with a simple structure,
For example, M.I. Ellingson (M, I.

A cold cathode device announced by John Elinson et al. is known. [Radio Engineering Electron Physics (Radio Eng, Elect
Ron.

Phys, ) Volume 1O, pp. 1290-1296, 19
1965] This type of electron-emitting device includes one using an 8-hole 0□ (sb) thin film developed by Ellingson et al., and one using an Au thin film [G.
Solid Films'' (G, Dittmer: T
h1nSolid Fi1ms''), vol. 9, p. 317, (1972) ITO thin film [M. Hartwell and C.G.
Fonstad: “IEEεTrans, ED
Conf, ”) p. 519, (1975)], carbon thin film [Hisashi Araki et al.: “Vacuum”
.

Vol. 26, No. 1, p. 22 (1983)].

Coupled with advances in film-forming technology and photolithography technology, it is becoming possible to form a large number of elements on a substrate, and this is expected to be applied to various image-forming devices using multiple electron sources. .

[Problems to be Solved by the Invention] However, conventional surface conduction electron-emitting devices do not require temperature rise unlike thermionic sources, but because electricity is applied to the minute electrode spacing, the emission region is extremely small. A portion of the flowing current is consumed as heat generation. Therefore, when considering an image forming apparatus in which a plurality of these elements are arranged on the same substrate, the heat generation described above becomes so large that it cannot be ignored.

Furthermore, as a result of studies conducted by the present inventors, it has been found that surface conduction type emitters are sensitive to temperature increases, and that their electron emission characteristics begin to deteriorate when the element temperature reaches about 100°C. When applied to a large-sized image forming apparatus in which a large number of emitting elements need to be arranged, there is a drawback that the emitting current is reduced due to the heat generated from the elements themselves and the heat storage effect thereof.

Furthermore, since the devices are arranged vertically and horizontally on the same board, the temperature rise of the board is not uniform within one board, but the temperature near the center is the highest (the temperature is highest near the center), and the peripheral part has good heat dissipation. Therefore, the deterioration of the element is greatest near the center, which has the disadvantage of appearing as uneven brightness when used as an image forming apparatus.

[Means and effects for solving the problem] According to the present invention, the area where a difference in emission current occurs between the center and the periphery due to the heat generated by driving the element is regarded as a steady state. By making the metal back of the phosphor screen thinner than the surrounding area, uneven brightness can be minimized.

Further, the present invention will be explained in detail using the drawings.

FIG. 2 is a schematic diagram showing the temperature distribution on the device substrate after a certain period of time when surface conduction electron-emitting devices connected in parallel in a line are driven line by line, which is used in the present invention. Since the initial characteristics of each element connected in parallel are almost uniform, the amount of heat generated per element is equal, but the temperature in the center is higher than that in the periphery due to differences in heat radiation. This is the same no matter what driving method is used as long as the power consumption per element is constant.

As an image forming apparatus, when a necessary and sufficient number of elements are arranged on an insulating substrate such as glass and driven with an applied voltage that can obtain a necessary and sufficient emission current, the temperature of the center part is 10
It has been found that the temperature exceeds 0° C., which is the temperature at which the electron emission properties begin to deteriorate.

Therefore, in an image forming apparatus in which surface conduction type emission elements are arranged vertically and horizontally, a drop in emission current near the center can be avoided.

I can't kick it. Therefore, the present invention is characterized in that the difference in emission current is absorbed by the difference in metal back film thickness Φ of the phosphor screen, and the final luminance is made uniform.

FIG. 1 is a schematic diagram showing the distribution of the thickness of the metal back 6 on the phosphor screen, which shows the features of the present invention.

The film thickness changes continuously, being the thinnest at the center and becoming thicker as it spreads toward the periphery. Therefore, when the phosphor 7 is made to emit light with a constant accelerating voltage, the transmittance of electrons decreases in the thick part of the metal back film and the emission brightness is low (in contrast, the transmittance is high in the thin part) , the luminance of light emission also increases.

The actual film thickness is determined based on the material used, the degree of reduction in emission current, the accelerating voltage, etc. In Figure 3, the acceleration voltage 8
The relationship between the aluminum metal back film thickness and electron transmittance at KV is shown. As is clear from the figure, if the emission current decreases by 50% due to an increase in the substrate temperature, for example, if the acceleration voltage is kept constant at 8KV and aluminum is used as the material, 200 people in the center and 3000 people in the peripheral area. do it.

The metal back may be formed by any commonly used method, but since it requires film thickness distribution within the same plane and controllability for 100 people, methods such as vacuum evaporation may be used. is desirable.

[Example] Examples of the present invention are shown below.

An image forming apparatus as schematically shown in FIG. 4 was manufactured as described below.

First, electrodes 2 and 3 of a surface conduction electron-emitting device were formed on a 2-inch square quartz substrate 1 which had been thoroughly degreased and cleaned using a conventional photolithography technique. The electrode material is nickel, and its film thickness is approximately 2000 mm. Also,
The interval between the minute interval portion 4 between the positive electrode 2 and the negative electrode 3 is 2Pl! !
and its width is 300 p, 11. 5 more
On the l line, 40 elements are connected in parallel at 1rBII+ pitch, and this is 15 lines, so there are 40 elements on the board l.
X 15 = 600 electron-emitting device portions were formed.

Next, an organic solvent containing an organic palladium compound (Catapaste-ccp manufactured by Okuno Pharmaceutical Co., Ltd.) was spin-coated onto this substrate l using a spin coater, and then coated at 250°C in air.
Firing was performed for 10 minutes to turn palladium into fine particles, and an element substrate was completed with the microelectrode spacing section 4 as a discontinuous film having an island structure of palladium.

In order to measure the temperature rise during driving of the thus obtained element substrate, thermocouples were placed concentrically in the center and periphery of the back surface of the substrate 1, and the entire substrate was maintained at approximately I x 10-'Torr. Electron emission experiments were conducted in a vacuum container.

The driving method is line sequential driving, and the voltage V applied to both ends of the element is varied between 10 and 14 V, and the driving frequency is set to 30 V.
KHz. As a result, when L=14V, the temperature rise was the most severe, and when a steady state was reached, the temperature was highest near the center, approximately 150°C, and the lowest temperature was approximately 100°C, near the outermost periphery. In this state, when an IKV voltage was applied to the fluorescent screen 5 provided on the top of the element substrate and the emission of electron beams was observed, the brightness at the position corresponding to the high temperature area near the center was visually observed. A clear decrease was confirmed, indicating that the emission current was decreasing.

In addition, when we measured the emission current when pulse-driven for each line, we found that the current I
□ is V, when = 14V! , = 1 to 2μ8 substrates
The emission current from the line is 1 when v = 14V.
, = 6 μA. Therefore, on average per element,
It is 50 nA at the center and 150 nA at both ends.

As a result, when the temperature of the element reaches nearly 150''C, the emission current of the element at the center is approximately 1/3 of that at both ends.

From these results, in order to make the luminance of the phosphor uniform, the thickness of the metal back in the central part should be 500 mm, and the thickness of the metal back in the peripheral area should be 20 mm.
Using the phosphor substrate 5 of 0.00 people, an experiment was conducted again to emit light over the entire surface by line driving, and visually it was found that the light emitted was uniform over almost the entire surface.

Furthermore, for application to a large-sized image forming apparatus, an element similar to that of Example 1 was fabricated using a 10-inch square glass substrate as the element substrate. III element pitch! ZOO elements were arranged in parallel and 6o lines were arranged per line.

The driving method was the same as in Example 1, but the driving voltage of each line was suppressed to a maximum of 12 V in order to avoid a temperature rise due to an increase in the number of elements. The maximum temperature in the center at this time is 120℃
On the other hand, in order to compensate for the decrease in luminance caused by the decrease in emission current due to the decrease in drive voltage, the acceleration voltage V, must be set higher (in this example, V, = 10 KV.In addition, the reduction rate of the emission current at the center of the element substrate (L+/Ieix too)
was almost 50%.

When the acceleration voltage V=10 is V, the metal back thickness at which the electron beam transmittance is at least 50% is approximately 2500, and the maximum is 100% and the film thickness effective as a metal back is approximately 30.
0, the optimum metal back thickness of the phosphor screen for this device is 300 at the center and 2500 at the periphery.

Therefore, on a phosphor screen that had been uniformly coated with phosphor and then filmed with nitrocellulose, aluminum was vapor-deposited using a vacuum evaporator with two evaporation sources. In order to form a particularly thin film in the center, a circular metal mesh was fixed and evaporated between the evaporation source and the evaporation source.

When we conducted an experiment using the fluorescent screen obtained in this way, we found that
(2) Sufficient light emission brightness was obtained even at =12V, and the light emission was uniform when visually observed.

[Effects of the Invention] As explained above, in an image forming apparatus using a surface conduction electron-emitting device, the thickness of the metal back of the phosphor screen can be adjusted continuously to match the degree of decrease in emission current due to temperature rise of the device. By providing a change in , there is an effect that uniform light emission can be obtained without using any special drive or configuration.

[Brief explanation of drawings]

Fig. 1 shows the film thickness distribution of the phosphor substrate and metal back used in the present invention, Fig. 2 shows the outline of the electron-emitting device part and the temperature distribution in the same plane used in the present invention, and Fig. 3 shows the metal back. FIG. 4, which is a diagram showing the relationship between thickness and electron beam transmittance, is a schematic diagram of the image forming apparatus manufactured in Example 1.

Claims (4)

[Claims] (1) An image forming apparatus comprising at least a plurality of surface conduction electron-emitting devices, a phosphor screen, and a metal back, characterized in that the metal back attached to the phosphor screen has a film thickness distribution. (2) The image forming apparatus according to claim 1, wherein the film thickness is thinner at the center and thicker at the periphery. (3) The image forming apparatus according to claim 2, wherein the film thickness is changed depending on the amount of current emitted from the emitting element. (4) The image forming apparatus according to claim 3, wherein the change in the emission current is due to an increase in temperature of the element.