JPH02257544A - Electron beam generating apparatus and image forming device using the apparatus - Google Patents

Abstract

PURPOSE:To uniformize electron beams emitted by a plurality of electron emitting elements and enhance the display quality by previously adjusting the electron emission characteristics of the elements in accordance with dispersion of the impressed voltage on the elements originating from voltage drop caused by the resistance of a wiring part. CONSTITUTION:A plurality of MIM type electron emitting elements and conductive paths 2a, 2b are formed on an insulative base board 1. A lower metal electrode 3, middle insulating layer 4, and upper metal electrode 5 of the element are furnished, wherein the upper metal electrode 5 is made thin partially, and a circular region 6 is provided as electron emitting part. The area of this electron emitting part 6 is varied appropriately element by element for adjustment of the emission characteristic as countermeasure for dispersion of the electron beam emission amount due to voltage drop when a pos. and a neg. voltage are fed from the mating ends of each element row at the time of driving the element row. This uniformize the electron beams emitted by the elements to lead to accomplishing a greatly enhanced performance of a large capacity display device in thin construction and with large area.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a multi-electron beam generating device in which a large number of MIM type electron-emitting devices are arranged, and an image forming device (for example, a flat CRT) using the multi-electron beam generating device. ) regarding.

[Prior Art] Various types of flat display devices have been proposed in the past, and representative ones include flat display devices using a luminescence method, a plasma method, a liquid crystal method, etc. There is.

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 one electron source corresponds to each pixel, and an MIM type electron-emitting device, for example, is known as an electron beam source in this case.

FIG. 13 is a schematic diagram showing a general configuration of an MIM type electron-emitting device.

As shown in the figure, the MIM type electron-emitting device is made of metal Ml.
It has a structure in which a thin metal M2 is laminated on top with a thin insulating layer 1 interposed therebetween. And the work function φm of metal M2
By applying a larger voltage V to the metals M1 and M2, electrons that have tunneled through the insulating layer and have energy greater than the vacuum level are emitted from the surface of the metal M2.

FIG. 14 is a schematic cross-sectional view of a conventional MIM type electron-emitting device. As shown in the figure, in the electron emission part W, the metal M2 is formed thinly.

[Problems to be Solved by the Invention] However, when applying these MIM electron-emitting devices to an image forming device, generally a large number of devices (hereinafter MIM-type electron-emitting devices are abbreviated as elements) are arranged on a substrate. It was used as a multi-electron beam source by forming electrical wiring between each element using thin-film or thick-film electrodes, but the voltage applied to each element varied due to the voltage drop caused by wiring resistance. This phenomenon occurs. 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 15 and 16 are diagrams to explain this problem in more detail. In both figures, (a) is an equivalent circuit diagram including an electron-emitting element, wiring resistance, and power supply, and (b) is an equivalent circuit diagram of each electron-emitting element. A diagram showing the potentials of the positive and negative electrodes of the elements, and (c) a diagram showing the voltages applied between the positive and negative electrodes of each element. Figure 15 (
a) is N electron-emitting devices DI, ~D connected in parallel.
, and a power source VE are connected, and the positive electrode of the power source is connected to the positive electrode of the element RI, and the negative electrode of the power source is connected to the negative electrode of the element DN. 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 elements have the same resistance value.) Furthermore, it is assumed that all the electron-emitting elements, ~D0, have approximately the same resistance value Rd.

In the circuit diagram of FIG. 15(a), FIG. 15(b) shows the potentials of the positive and negative electrodes of each element. The horizontal axis of the figure shows the element numbers D, to D, and the vertical axis shows the potential.

The ・mark represents the positive electrode potential of each element, and the ■ mark represents the negative electrode potential.For convenience, the ・mark (
■mark) are connected with a solid line.

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 element D1, the steeper it is, and conversely, on the negative electrode side, the closer it is to element DN, the steeper it is. ing. This is because on the positive electrode side, the closer to D, the thicker the current flows through the wiring resistance r (and on the negative electrode side, conversely, 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. The horizontal axis of the figure is -D,
The horizontal axis shows the applied voltage.
), ■ are connected with solid lines for convenience in order to make the trends easier to see.

As is clear from this figure, in the case of the circuit shown in (a) of the figure, a larger voltage is applied to the elements near both ends (D, and), and the applied voltage is lower to the elements near the center. becomes smaller. Therefore, the beam current of the electron beam emitted from each electron-emitting device becomes larger as the devices are located 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 light density.) On the other hand, what is shown in Fig. This is the case when the positive and negative poles of the power supply are connected to the terminals (Dt side).In the case of such a circuit, as shown in Figure (b), the closer the positive and negative poles are to DI, the higher the voltage due to the wiring resistance r. The descent is thick.

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

As shown in the two examples above, 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 power supply connection. Although it varies depending on the position, in general, the larger N is and the smaller Rd/r is, the more pronounced the variation is, and the connection method shown in FIG. 16 has a larger variation in the voltage applied to the element than the connection method shown in FIG. 15. .

For example, in the connection method shown in FIG. 15, element resistance Rd=lkΩ, r
= lOmΩ, if N = 100, comparing the element with the largest applied voltage and the element with the smallest applied voltage, V
wax: V,, 11 = about 102:100, if N = 1000, then V,, x: V,, n = 4
The dispersion ratio is 72:100.

Also, N = 1000. Rd = 1 kΩ, r = 1
For mΩ, Vaax:Vml. = 127:10
When r = 10 mΩ, V□,
:V, 1. = 472:100, the degree of variation is large.

As explained above, when multiple electron-emitting devices with the same characteristics are connected in parallel, the voltage effectively applied to each device varies 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 MIM type electron-emitting devices are wired in parallel to form a multi-electronic boom source, variations in driving voltage for each device are taken into consideration in advance. However, the electron emission characteristics of the elements are appropriately changed to form an array (thereby, the same amount of electron beam can be obtained from every element).

As a first method for changing such electron emission characteristics, we have devised a method of forming the electron emitting portion by appropriately changing the area for each element.

In addition, as a second method, we devised a method of appropriately changing the thickness of the upper metal electrode of each MIM type electron-emitting device.

In addition, as a third method, we devised a method of appropriately changing the material used for the electron-emitting portion.

The first to third methods described above may be used independently, or may be combined in some cases.

In the present invention, elements having different electron emission characteristics realized by the above method are arranged as described below, and voltages are electrically applied in parallel.

In other words, when power is supplied to a row of elements connected in parallel using the method shown in FIG. An element that can obtain the necessary beam current even with an applied voltage is placed in the center.

Furthermore, when power is supplied using the method shown in FIG.
An element that can obtain the necessary beam current even with a relatively small applied voltage is placed at a position far from the power supply side.

The method described above makes it possible to make the amount of electron beams emitted from a large number of parallel-connected MIM type electron-emitting devices uniform without variation.

[Example] The present invention will be specifically explained in detail below using examples.

1111 FIGS. 1 to 4 illustrate a first embodiment of the present invention. First, FIG. 1 is a perspective view showing a part of an electron beam generator to which the present invention is applied.

In this figure, 1 is an insulating substrate (for example, a glass plate), on which a plurality of MIM type electron-emitting devices and conductive paths 2a,
2b (electrical wiring) is formed.

Such conductive paths 2a and 2b are made of, for example, Au, Cu,
It is made of metal such as AI, Ni, Ag, etc., and 2a is for applying a positive voltage to the upper metal electrode of the element.
2b is for applying a negative voltage to the lower metal electrode of the element.

Further, 3 is a lower metal electrode of the element, 4 is an intermediate insulating layer, and 5 is an upper metal electrode.

The circular region 6 provided in a part of the upper metal electrode 5 is made of thin metal as explained in the prior art section,
This part becomes the electron emitting part.

Although only four MIM-type electron-emitting devices are shown in FIG. 1, the present invention is also effective for a larger number of device rows, and this embodiment is also applicable to Approximately 200 elements are formed.

Furthermore, in the case of this embodiment, when driving the element array, as shown in FIG. 15, positive voltage and negative voltage are respectively supplied from opposite ends of the element array.

In addition, as a measure to deal with variations in the amount of electron beam emission due to voltage drop, which is a feature of the present invention, the area of the electron emission section 6 is appropriately changed for each element to adjust the electron emission characteristics.

In order to explain this, FIG. 2 shows a cross-sectional view taken along a plane that passes through the center of the element array shown in FIG. 1 (the center of each electron-emitting section 6) and is perpendicular to the substrate 1.

In this figure, the shapes of the lower metal electrode 3 and the intermediate insulating layer 4 are the same in all elements, but the upper metal electrode 5
The area of the thin portion (constant thickness), that is, the electron emitting portion 6, differs from device to device. That is, in this embodiment, since the electron emitting part 6 is circular, d+, da, and dsd4 appearing in the cross-sectional view represent the diameter of the electron emitting part of each element, and have different sizes as appropriate for each element. There is.

(The electron-emitting part of the MIM type electron-emitting device is circular (
Of course, the present invention can also be applied to other shapes. ) Next, in order to explain the present invention in detail, FIG. 3 illustrates the difference in electron emission characteristics when the area of the electron emission section 6 is different. In the figure, the horizontal axis represents the voltage applied to the electron-emitting device, and the vertical axis represents the beam current output from the device. For example, a device with an area of electron emission part of Sl and a device with an area of 82 (however, Sl>
As a voltage is applied to S2), the electron emission characteristics become different as shown in the figure.

Therefore, in a place where it is assumed that a voltage of v1 or no voltage will be applied, an element with an emitting area of Sl is formed in advance, and at the same time, an element with an emitting area of Sl is formed in a place where it is assumed that a voltage of v2 is applied. If elements with an area of 82 are formed, beam currents of equal magnitude will be obtained from these elements.

Therefore, in the array of elements shown in Figure 1, by changing the area of the electron emitting area of each element, as shown in the graph of Figure 4, it is possible to obtain the same beam current from all elements. In Figure 15(c), the horizontal axis represents the elements corresponding to each number, and the vertical axis - represents the area of the electron emitting portion of each element.

In this example, as shown in Figure 15(c), the element applied voltage is smaller in the center element than in the elements at both ends. As shown in Figure 2, the area of the electron emitting portion is larger in the center element than in the elements at both ends.

On the other hand, when driven by the power supply method shown in Fig. 16, as shown in Fig. 5, the elements near the power supply side (0, side) can be separated from each other by reducing the electron emitting area area. Equal beam currents can be obtained.

Next, as a second example, by appropriately changing the thickness of the recessed part (electron emitting part 6) of the upper metal electrode 5, the electron emission characteristics are adjusted for each element and the output beam current is made uniform. Here are some examples.

FIGS. 6 to 8 are diagrams for explaining this embodiment.

First, FIG. 6 shows a cross-sectional view of an MIM type electron-emitting device. In this embodiment, when arranging a plurality of devices, the area and thickness of the lower metal electrode 3 and intermediate insulating layer 4 are The areas of the electron-emitting portions 6 and 6 are made equal, and only the thickness t of the electron-emitting portions 6 of the upper metal electrode 5 is changed as appropriate.

Therefore, the difference in electron emission characteristics when t is changed is illustrated in FIG. 7. When 1 + < 1 *, as the voltage applied to the device increases, electron emission starts at approximately the same voltage, but when the voltage is further increased, the device with thickness t becomes more similar to the device with thickness t2. In comparison, the output beam current increased significantly.

Therefore, as can be inferred from the first embodiment, by arranging elements with an appropriate thickness t in advance in accordance with variations in the voltage applied to the elements, it is possible to make the magnitude of the output beam current uniform.

8 and 9 show the above-mentioned FIG. 15 and 1, respectively.
6 is a diagram showing an arrangement pattern of elements having different thicknesses t when the power feeding method shown in FIG. 6 is performed, and in the figure, the horizontal axis represents the element number, and the vertical axis represents the thickness t.

In the case of this embodiment, if the thickness t is too large, sufficient output beam current cannot be obtained (on the other hand, if the thickness t is too small, the durability will be insufficient, so in general, 100 people ≦ t ≦ 500 people). It is desirable to choose within the range of people.

Furthermore, without changing the thickness t of each of the N elements, by forming a group of several to several 10 elements and changing it for each group, the variation can be reduced to some extent, and the manufacturing process can be simplified. There is.

Back 1d Nine Dans Next, a third embodiment of the present invention will be described.

In this embodiment, the first. Unlike the second embodiment, the shape and size of each element are the same, and the electron emission characteristics are changed by appropriately using different metal materials for the upper metal electrode 5.

Materials used in this case include, for example, Au and Ag.

Metals such as Cu, W, AI, Ni, Ta, Cu, Mo
Also included are alloys such as /Th, W/Th, and Ta/Th, or metal borides, carbides, or oxides.

In this embodiment, as the upper metal electrode 5 in the element array, a material with a small work function is used for elements to which an applied voltage is small, and a material with a relatively large work function is used for elements to which an applied voltage is large. In this way, by appropriately selecting and changing the material used for the upper metal electrode 5, it is possible to reduce variations in the output beam current emitted from each element.

Three embodiments of the present invention have been described above, but the basic idea of the present invention is that, in a plurality of MIM type electron-emitting devices connected in parallel, variations in device applied voltage due to voltage drop caused by wiring resistance The aim is to make the electron beams emitted from each element uniform by appropriately adjusting the electron emission characteristics of the elements in advance. Therefore, methods other than the above may be used as long as they comply with this basic idea.
Further, the above three methods may be combined.

Next, an embodiment of a flat plate image forming apparatus to which the present invention is applied will be described with reference to FIGS. 1θ to 12.

Fig. 1O is a partially cutaway perspective view showing the structure of the display panel, Fig. 11 is a diagram showing a block circuit that drives the panel, and Fig. 12 is a time chart showing the drive timing of each part of the panel. It is.

The operation of this device will be explained step by step below.

Figure 1O shows the structure of the display panel, in which VC
is a glass vacuum container, and FP, which is a part of the container, indicates the face plate on the display side.

A transparent electrode made of, for example, ITO is formed on the inner surface of the face plate FP, and a red,
Green and blue phosphors are painted separately in a mosaic pattern, and a metal back treatment known in the CRT field 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 the MIM type electron-emitting devices of the present invention are arranged in N×p rows on the top surface. The electron emitting 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 Dp+-DpR (terminal Dm
It is electrically connected to the outside of the vacuum vessel by 1-Dm#). That is, in this device, two rows of elements are formed on the substrate S using the power feeding method shown in FIG. 15 described above. (The number of elements per row is N.) Furthermore, it goes without saying that the electron emission portion of each emission element is adjusted as appropriate to the electron emission characteristics (as shown in the above embodiment).

Further, a striped grid electrode GR is provided between the substrate S and the face plate FP. N grid electrodes GR are provided perpendicularly to the element array, and each electrode has the following: Holes Gh are provided for the transmission of electron beams. One hole Gh may be provided for each electron-emitting device as shown in FIG. 1O, 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, .about.G.

In this display panel, an XY matrix is formed by four electron-emitting device columns and N grid electrode columns. By sequentially driving (scanning) the electron emission rows one by one and simultaneously applying modulation signals for 1942 images to the grid electrode row, the irradiation of each electron beam to the phosphor is controlled, and one image is created. It is displayed line by line.

What is shown in FIG. 11 is a block diagram of an electric circuit for driving the display panel shown in FIG. 1θ, in which 7 is the display panel shown in FIG. 9 is a modulation grid drive circuit; 10 is a high voltage power supply. The electrode terminal EV of the display panel 7 is supplied with an accelerating voltage of about 10 KV from a high voltage power supply IO. In addition, the negative electrode side wiring terminal (Dml-DIII) of the electron-emitting device array is
It is grounded to the ground level (0■), and the wiring terminals (Dp+ to Dpβ) on the positive side are connected to the element column drive circuit 8. Further, the grid electrode is connected to a modulation grid drive circuit 9 through terminals GI-GN.

Signal voltages are output from the element array drive circuit 8 and the modulation grid drive circuit 9 at the timing shown in the drive time chart of FIG. In Figure 12, (a) to (d) are
Dp+, DI)i of the display panel 7 from the element column drive circuit 8
, Op8. and Dpi), and as can be seen from the figure, Dp+, Dpi, Dpa,...
(Dp4 to Dp(il-1) are in the figure) Dpi' (
7) Sequentially, sequentially, amplitude V.

A drive pulse of [V] is applied. In synchronization with this, a modulation signal (V, (ON) or V. (OFF)) is applied from the modulation grid drive circuit 9 to the terminals G to GH at the timing shown in FIG. V for each terminal
.

Which of the (ON), V, and (OFF) levels is applied is determined by the pattern of the displayed image.

For example, in a panel with N=200 and fl=200,
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, As a result, the brightness unevenness can be reduced to less than '/20 of the conventional value, and the quality of displayed images can be significantly improved.

[Effects of the Invention] As explained above, in the present invention, when a plurality of MIM type electron-emitting devices are connected in parallel to form a multi-beam electron beam generating device, the voltage drop caused by the resistance of the wiring portion is By appropriately adjusting the electron emission characteristics of the device in advance depending on the voltage applied to the device, it has become possible to make the electron beam emitted from each device uniform.

This makes it possible, for example, to eliminate the uneven brightness of images that has traditionally been a problem when realizing flat CRTs, and to significantly improve the practical performance of thin, large-area, large-capacity display devices. was completed.

The present invention can be applied to most image forming apparatuses having an electron source section in which a large number of MIM type electron-emitting devices are connected in parallel, in addition to the flat image forming apparatus shown in the embodiments.
It is also extremely effective in the fields of electron beam drawing devices and image recording devices.

[Brief explanation of drawings]

FIG. 1 is a partial perspective view of an electron beam generator according to a first embodiment of the present invention, FIG. 2 is a partial cross-sectional view of an electron beam generator according to a first embodiment of the present invention, Figure 3 is a graph showing the output characteristics of MIM type electron-emitting devices with different emitter areas. Figures 4 and 5 are graphs showing the electron-emitting area of N elements connected in parallel. Figure 6 is an MIM for explaining the second embodiment of the present invention.
Figure 7 is a graph showing the output characteristics of elements with different thicknesses of the upper metal of the electron-emitting part. Figures 8 and 9 are the upper sides of N elements connected in parallel. A graph showing the thickness of metal; FIG. 10 is a partially cutaway perspective view of an image forming apparatus to which the present invention is applied; FIG. 11 is a drive block circuit diagram of the image forming apparatus to which the present invention is applied; Drive time charts showing the operation timing of each part of the image forming apparatus to which the present invention is applied, FIGS. 13 and 14
The figure is a cross-sectional view for explaining an MIM type electron-emitting device, and Figures 15 and 16 are diagrams for explaining problems that conventionally occurred when connecting multiple MIM type electron-emitting devices in parallel. . 1 - Insulating substrate 2a, 2b - Conductive path 3 - Lower metal electrode 4 - Intermediate insulating layer 5 - Upper metal electrode 6 - Electron emission section 7 - Display panel 8 - Element column drive circuit 9 - Modulation grid drive circuit l〇 −High voltage power supply

Claims (11)

[Claims] (1) In an electron beam generation source in which multiple MIM type electron-emitting devices are electrically connected in parallel, the applied voltage of each device is An electron beam generator characterized by MIM type electron-emitting devices arranged in such a way that the output beam current characteristics are adjusted to be different as appropriate. (2) The electron beam generating device according to claim 1, wherein the means for adjusting the output beam current characteristics with respect to the applied voltage appropriately changes the area of the electron emitting part of the MIM type electron emitting device. (3) The electron beam according to claim 1, wherein the means for adjusting the output beam current characteristics with respect to the applied voltage appropriately changes the thickness of the upper metal electrode which is the electron emitting part of the MIM type electron emitting device. Generator. (4) The electron beam generator according to claim 1, wherein the means for adjusting the output beam current characteristics with respect to the applied voltage appropriately changes the material of the upper metal electrode which is the electron emitting part of the MIM type electron emitting device. Device. (5) A power feeding means is provided so as to be able to apply a positive voltage from one end of a row of MIM type electron-emitting devices electrically connected in parallel and a negative voltage from the other end, and 3. The electron beam generating device according to claim 2, wherein the area of the electron emitting portion is larger in the element located at the center of the row than in the elements located at both ends of the row. (6) Means for supplying a positive voltage and a negative voltage for driving the elements is provided at one end of a row of MIM type electron-emitting devices electrically connected in parallel, and the MIM type electron-emitting devices emit electrons. 3. The electron beam generating device according to claim 2, wherein an area of an element further from one end where the power feeding means is provided is larger than an area of the element closer to one end where the power feeding means is provided. (7) A power supply means is provided so as to be able to apply a positive voltage from one end of a row of MIM type electron-emitting devices electrically connected in parallel and a negative voltage from the other end, and 4. The electron beam generating device according to claim 3, wherein the thickness of the upper metal electrode serving as the electron emitting portion is smaller in the element located at the center of the row than in the elements located at both ends of the row. . (8) Means for feeding positive voltage and negative voltage for driving the elements is provided at one end of a row of MIM type electron-emitting devices electrically connected in parallel, and the MIM type electron-emitting devices emit electrons. 4. The electron beam generating device according to claim 3, wherein the thickness of the upper metal electrode serving as a portion of the element is smaller in the element farther from the element than in the element closer to one end where the power feeding means is provided. (9) A power feeding means is provided so as to be able to apply a positive voltage from one end of a row of MIM type electron-emitting devices electrically connected in parallel and a negative voltage from the other end, and 5. The method according to claim 4, wherein the material used for the upper metal electrode serving as the electron emitting section is made of a material having a smaller work function for the elements located at the center of the row than for the elements located at both ends of the row. Electron beam generator. (10) Means for supplying a positive voltage and a negative voltage for driving the elements is provided at one end of a row of a plurality of MIM type electron-emitting devices electrically connected in parallel, and the MIM type electron-emitting devices emit electrons. 5. The electron beam generator according to claim 4, wherein the material used for the upper metal electrode serving as the part is made of a material having a smaller work function in an element further away than in an element closer to one end where the power feeding means is provided. Device. (11) The electron beam generating device according to claim 1 is provided as an electron source, and a modulating means for modulating the electron beam (electron beam) emitted from each electron emitting section, and an image is generated by irradiation with the electron beam. What is claimed is: 1. An image forming apparatus comprising: a target that forms a target;