The present invention relates to a photoconductive image pickup device which has an electron emission source array with a plurality of electron emission sources arranged on a plane, and an optoelectronic film opposed thereto. More particularly, the invention relates to an imaging apparatus which employs such an image pickup device and a magnetic field converging structure.
Electron emission source arrays with a plurality of minute electron emission sources disposed in a matrix on a substrate plane and configured to draw out electrons by applying an electric field thereto have been known as cold cathodes.
Such electron emission sources which are each drivable at a low voltage and simplified in structure have been studied for application to compact imaging devices which employ an electron emission source array.
For example, in the field of imaging devices, studies have also been conducted on such imaging devices that have a combination of the image pickup device with an electron emission source array and the magnetic field converging structure. It has been reported that electron beams can be converged by forming magnetic force lines in a direction perpendicular to the plane of the electron emission source array (in parallel to the direction of travel of electron beams from the electron emission sources). (See Patent Literature 1.)
In an imaging device combined with the conventional magnetic field converging structure, an image pickup device is disposed at the center of the hollow of a cylindrical magnet to form a magnetic field in parallel to the direction of electron emission from the electron emission source of the image pickup device. Furthermore, Patent Literature 1 suggests an imaging device which has, in addition to the cylindrical magnet surrounding the image pickup device, a disc-shaped permanent magnet disposed behind the image pickup device to be opposed to the image pickup device.
Using the hollow of the conventional cylindrical magnet requires a cylindrical magnet with an increased cylinder length and an increased cylinder diameter in order to form a magnetic field in parallel to the direction of electron emission within the range of the effective light-receiving area of the optoelectronic film.
In this context, the inventor has repeated experiments to reduce the size of the imaging device. As a result, it has been found that reducing the inner diameter of the cylindrical magnet having the magnetic field converging structure which is disposed around the conventional image pickup device would provide a nonuniform magnetic field strength and thus such a size reduction would be difficult to achieve.
For example,
In this context, by way of example, the present invention offers an imaging apparatus which provides a uniform magnetic field distribution in the image pickup device having a magnetic field converging structure and which contributes to reduction in the size of the apparatus by solving a conventional problem that a uniform magnetic field could not be obtained without increasing the inner diameter of the magnet.
The imaging apparatus of the present invention includes an electron emission source array with a plurality of electron emission sources arranged on a plane perpendicular to an optical axis, and a translucent substrate having an optoelectronic film opposed on the optical axis to the electron emission source array with a space therebetween. The imaging apparatus emits electrons to the optoelectronic film by dot sequential scanning across the electron emission sources for output as an electrical signal associated with an optical image which has been projected onto the optoelectronic film by the incidence of light through the translucent substrate. The imaging apparatus includes a magnet portion for forming in the space a magnetic field in a direction orthogonal to each principal plane of the translucent substrate and the electron emission source array, and a magnetic force line supply portion. The magnetic force line supply portion has a magnetic body which is disposed on the light incident side on the optical axis to be opposed to the translucent substrate with a space therebetween and connected to the magnet portion, and an opening which defines an optical path that will not hinder formation of the optical image.
In the aforementioned imaging apparatus, the magnet portion defines a hollow along the symmetric axis and can be a cylindrical permanent magnet which is coaxial with the optical axis and which accommodates the translucent substrate and the electron emission source array at the center of the hollow.
The aforementioned imaging apparatus can have a second magnet portion. The second magnet portion can be a disc-shaped second permanent magnet which is disposed on the optical axis opposite to the light incident side to be opposed to the electron emission source array with a space therebetween and is opposed to the electron emission source array so that the symmetric axis is coaxial with the optical axis.
In the aforementioned imaging apparatus, the second permanent magnet can have an opening which is coaxial with the optical axis.
In the aforementioned imaging apparatus, the inner diameter of the opening of the magnetic force line supply portion can be greater than the diametral size of the effective light-receiving surface of the optoelectronic film on the optical axis and less than the inner diameter of the hollow defined by the magnet portion.
As described above, the imaging apparatus of the present invention includes the image pickup device with the optoelectronic film and the electron emission source array, and the magnet portion which is disposed around the image pickup device to converge electron beams emitted from the electron emission source array. In front of the magnet portion, the magnetic force line supply portion is provided which is formed of the magnetic body that extends toward the inner diameter of the magnet portion and which also plays a role of a magnetic path. Thus, the present invention makes it possible to improve simultaneously the uniformity of the magnetic flux in an electron travelling portion in the image pickup device, reduce the leakage of magnetic flux in front of the image pickup device, make effective use of magnetic fields, and prevent internally reflected light from entering the optoelectronic film. It is thus possible to reduce the size of the imaging apparatus.
Conventionally, it has been thought to be effective that to provide a uniform magnetic field distribution in the image pickup device, the outer shape and the inner diameter of a surrounding magnet should be increased as much as possible. However, forming a magnetic path (the magnetic force line supply portion) in front of the magnet can reduce the outer shape of the magnet around the image pickup device and provide a uniform magnetic field distribution in the electron travelling region inside the image pickup device as well as magnetic shielding effects. Also provided is an aperture function for the plate-shaped magnetic force line supply portion to prevent the internal reflection of diagonally incident light upon a lens from entering the optoelectronic film.
Now, an imaging apparatus according to the embodiments of the present invention will be explained below with reference to the drawings. It is to be understood that the embodiments will be illustrated only by way of example and the present invention will not be limited thereto.
Image Pickup Device of Imaging Apparatus
With reference to
In the image pickup device 10 shown in
The optoelectronic film 11 is a light-receiving section for receiving light from an object to be imaged, and is mainly formed of amorphous selenium (Se), but may also be formed of another material, for example, a compound semiconductor such as silicon (Si), lead oxide (PbO), cadmium selenide (CdSe), or gallium arsenide (GaAs).
The electrically conductive translucent film 12 can be formed, for example, of tin oxide (SfO2), ITO (indium tin oxide), or Se—As—Te. As will be described later, the electrically conductive translucent film 12 is supplied with a predetermined positive voltage via a connection terminal T1 provided on the translucent substrate 13.
The translucent substrate 13 has only to be formed of a material which transmits the light of wavelengths at which the image pickup device 10 picks up images. For example, to pick up images by visible light, the substrate 13 is made of a material such as glass that transmits visible light, whereas to pick up images by ultraviolet light, the substrate 13 is made of a material such as sapphire or silica glass that transmits ultraviolet light. Furthermore, to pick up images by X-ray, the substrate 13 may only have to be made of a material, such as beryllium (Be), silicon (Si), boron nitride (BN), or aluminum oxide (Al2O3), which transmits X-ray.
On the electrically conductive translucent film 12 side of the optoelectronic film 11, there is provided a hole injection stopping layer such as of CeO2 for preventing holes in the electrically conductive translucent film 12 from being injected into the optoelectronic film 11. Furthermore, on the vacuum space side, there can be provided an electron injection device layer such as of Sb2S3 for preventing electrons from being injected into the optoelectronic film 11.
A mesh electrode 15 in the vacuum space is provided with a plurality of penetrating openings and is made of, for example, a well-known metal material, an alloy, or a semiconductor material. The mesh electrode 15 is supplied with a predetermined positive voltage via a connection terminal (not shown). The mesh electrode is an intermediate electrode which is provided for accelerating electrons and collecting excessive electrons. This makes it possible to improve the directivity of electron beams and thereby provide an improved resolution.
As will be described in more detail later, the electron emission source array chip 24 is configured such that the gate electrode of a metal oxide semiconductor (MOS) transistor for driving the electron emission sources is connected to an X scanning driver (horizontal scanning circuit) and the source electrode is connected to a Y scanning driver 22 (vertical scanning circuit) to perform the dot sequential scanning. The Y scanning driver and the X scanning driver are formed on the electron emission source array chip 24 on one chip integrally with the electron emission source array, and provided on a support 25 in a glass housing 10A. The signals and voltages that are required to drive the electron emission source array chip 24 are supplied through the connection terminal (not shown) that is provided in the glass housing 10A.
The electron emission source array chip 24 and the translucent substrate 13 are disposed generally in parallel to each other with the vacuum space 4 therebetween and is vacuum-sealed in the translucent substrate 13 and the glass housing 10A which are sealed with frit glass or indium metal.
As shown in
The electron emission source array 20 formed on the upper surface of the chip is constructed as an integrated active drive electric field emitter array (FEA) which has the electron emission source array directly stacked in layers on a driving circuit LSI which is formed on a Si wafer. The electron emission source array 20 can cope with a high-speed driving (for example, a driving pulse width of several tens of nano seconds for one electron emission source 31) of an image pickup operation for dot sequential scanning. The electron emission source array 20 is formed of a plurality of electron emission sources 31 which are arranged in a matrix of n rows and m columns (the number of pixels is n×m) and which are connected to n and m scanning driving lines (hereafter referred to as the scanning line) in the Y direction (the vertical direction) and the X direction (the horizontal direction), respectively.
Furthermore, the number of the electron emission sources 31 of the electron emission source array 20 is, for example, 1920×1080, with the size of one electron emission source 31 being 20×20 μm2. The surface portion of one electron emission source 31 is provided with an electron emission portion 91 which is an opening for emitting electrons. For example, on the area of 8×8 μm2 of one electron emission source 31, there are formed 3×3 electron emission portions 91 (1 μmφ) with the electron emission source having a diameter of about 1 μm. For example, one electron emission portion 91 emits an electron flow of several microamperes (μA) (with an emission current density of about 4 A/cm2). Note that the numerical values in this embodiment are shown only by way of example, and as well applicable by being modified or changed as appropriate depending on the apparatus for which the image pickup device is used, the resolution of the image pickup device, sensitivity thereof or the like.
The Y scanning driver 22 and the X scanning driver 23 perform the dot sequential scanning and drive the electron emission sources 31 on the basis of control signals from the controller 26 such as a vertical sync signal (V-Sync), a horizontal sync signal (H-Sync), and a clock signal (CLK). That is, the scanning lines (Yj, j=1, 2, . . . , n) are sequentially scanned in the Y direction, so that when one scanning line (let the line be Yk) is selected, the scanning lines (Xi, i=1, 2, . . . , m) are sequentially scanned in the X direction to selectively drive each electron emission source 31 on that scanning line (Yk), thereby performing the dot sequential scanning. Then, the electron emission source 31 is switched to emit electrons by controlling, with the scanning lines, the drain potential of the MOS transistor, that is, the potential of the lower electrode of each electron emission source 31 of the electron emission sources 31.
Upper electrodes 36 are connected, for example, to the Y scanning driver to apply a predetermined signal to each thereof. Lower electrodes 33 are connected, for example, to the X scanning driver to apply a predetermined signal to each thereof in sync with a vertical scan pulse. Since the electron emission portion 91 is disposed at the intersection between the lower electrode 33 and the upper electrode 36, in the image pickup device of the embodiment the lower electrode and the upper electrode 36 sequentially drive the electron emission portions 91 to scan the proximal optoelectronic film region with emitted electrons, and then obtain an optoelectronically converted video signal from an image formed on the optoelectronic film.
As shown in
For a plurality of MOSFETs, the silicon device substrate 30 has a device separation film 77 formed in the silicon device substrate 30. On the silicon device substrate 30 between the device separation films 77, there are formed a gate insulating film 74 and a gate electrode 75 of poly-silicon. Furthermore, with the gate electrode 75 and the device separation film 77 employed as a mask, impurities are added to the silicon device substrate 30 and then activated, thereby allowing a source electrode 72 and a drain electrode 76 to be formed in a self-aligned manner. The lower electrode 33 electrically communicates with the drain electrode 76 via metal such as tungsten in a contact hole 71 that penetrates an interlayer insulating film 70. The electron emission sources 31 are independently separated from each other for each lower electrode 33. On top of the lower electrode 33, sequentially stacked in layers are the electron supply layer 34, the insulator layer 35, and the upper electrode 36, and then the electron emission portion 91 is formed as a recessed portion and covered with the carbon layer 37. The electron emission sources 31 are separated from each other by an enlarged opening space 80 which is formed by removing the electron supply layer 34 through etching. Although like the lower electrodes 33, the electron supply layers 34 are independently separated from each other for each electron emission source 31, the upper electrode 36 has bridge portions 36a which are suspended in the space to electrically connect between the adjacent electron emission sources 31. The carbon layer 37 is deposited on the upper electrode 36 of the electron emission portion 91.
Next, a description will be made to the operation of the imaging apparatus.
In the image pickup device 10 shown in
The imaging apparatus includes a cylindrical magnet portion 5 which surrounds the image pickup device 10 and an annular plate shaped or disc shaped magnetic force line supply portion 6 which is fixedly attached and connected to the magnet portion 5. The magnetic force line supply portion 6, which is formed of a magnetic material such as soft magnetic material like permalloy, is opposed on the light incident side on the optical axis to the translucent substrate 13 with a space therebetween, and has an opening 7 on the optical axis for defining an optical path which will not hinder formation of optical images to be formed in the optoelectronic film 11.
The magnet portion 5 defines a hollow along the symmetric axis and is a cylindrical permanent magnet which is coaxial with the optical axis and accommodates the translucent substrate 13 and the electron emission source array 20 at the center of the hollow.
The imaging apparatus further includes a second magnet portion 5b. The second magnet portion 5b is a disc-shaped second permanent magnet which is disposed on the optical axis opposite to the light incident side to be opposed to the electron emission source array 20 with a space therebetween and is opposed to the electron emission source array 20 so that the symmetric axis is coaxial with the optical axis.
As shown in
Furthermore, the preferred dimensions of the members of the imaging apparatus according to the embodiment should be as shown in
In the imaging apparatus, such a space that has magnetic force lines perpendicular to the electron emission source array 20 is formed by the magnetic force line supply portion 6, thereby allowing the electron beams spread at an angle from the electron emission source array 20 to reach the optoelectronic film 11 while travelling in a spiral around the magnetic force lines due to the Lorentz force. Note that the mesh electrode 15 interposed between the optoelectronic film 11 and the electron emission source array 20 is supplied with a voltage to adjust the speed of electrons, thereby allowing for controlling the diameter of the electron beams that arrive at the optoelectronic film 11. It is also possible to form a plurality of convergence points by the voltage of the mesh electrode 15.
As described above, according to the aforementioned imaging apparatus, the magnetic path of soft magnetic material (the magnetic force line supply portion 6) is disposed on the light incident side and directs, to the center of the hollow, the magnetic force lines to be diffused, so that the magnetic field near the image pickup device 10 disposed in the vicinity of the center is made uniform and the magnetic force lines are perpendicular to the electron emission source array 20. Furthermore, the magnetic path (the magnetic force line supply portion 6) also serves as a magnetic shielding plate which attenuates magnetic fields which spread outward.
As shown in
That is, as shown in
Furthermore, as shown in
As shown in
In any of the aforementioned embodiments, the cylindrical magnet portion 5 around the image pickup device 10 and the magnetic force line supply portion 6 of a magnetic shielding plate are not limited to the cylindrical or disc shape, but may also have a rectangular or square cross-sectional shape depending on the image pickup area of the image pickup device 10, with the opening being also rectangular. This will also provide the same effects as those provided by the aforementioned embodiments. Furthermore, in any of the aforementioned embodiments, although not illustrated, the aforementioned imaging apparatus is equipped with a magnetic shielding mechanism for reducing magnetic field leakage to the surrounding.
In any of the aforementioned embodiments, the electron emission source array illustrated above has a plurality of electron emission portions disposed in a matrix with the recessed portions covered with a carbon layer, the recessed portions penetrating the insulator layer and the upper electrode down to the electron supply layer. However, the present invention is not limited thereto. The present invention is also applicable to the imaging apparatus which employs another planer type electron emission source array, such as, what is called, a Spindt electron emission source matrix array.
While the imaging apparatus according to the aforementioned embodiments has been described, the improvement in the uniformity of magnetic flux in the electron travelling portion of the electron emission source array according to the present invention and the structure for preventing the leakage of magnetic flux to the electron emission side can be applied to planer type display devices or rendering devices.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2009/062819 | 7/15/2009 | WO | 00 | 2/28/2012 |