JP2009081017A - Field emission electron source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filed emission type electron source device having improved the ability of reading signal charges by reducing the flow-in amount of a beam current to a shield electrode to increase the beam current amount irradiated to a target. <P>SOLUTION: The field emission type electron source device includes: an electron source array in which a plurality of emitters for emitting electrons are provided; a photoelectric conversion film in which a predetermined operation is performed by electron beams emitted from the electron source array; and an electrode having a plurality of through holes each of which inner wall surface is covered with a film of a secondary electron radiating material between the electron source array and the photoelectric conversion film. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a field emission imaging device using a field emission electron source.

  In recent years, with the progress of semiconductor microfabrication technology, vacuum microelectronic technology that integrates a large number of micron-order cold cathode structures on a substrate such as a semiconductor attracts attention. Field emission electron source array with a micro cold cathode structure obtained by these technologies can be expected to have planar electron emission characteristics and high current density, and does not require a heat source such as a heater unlike a hot cathode. Therefore, expectation is gathered as an electron source for low power consumption next generation flat displays, sensors, and planar imaging devices.

  FIG. 7 shows the basic configuration of an example of a planar imaging device using a field emission electron source array. A front panel 1, a back panel 2, and a side peripheral device 3 are provided, which are fixedly fixed by a sealing material 4 such as frit glass or indium, and the inside thereof is held in a vacuum. An anode electrode 5 that transmits incident light from the outside is formed on the inner surface of the front panel 1, and a photoelectric conversion film made of antimony sulfide, selenium, or the like is formed as a target 6 on the surface (for example, Patent Documents). 1).

  The inner surface of the back panel 2 has a plurality of cold cathode elements (emitters), an insulating layer formed around each cold cathode element, and a periphery including a gate electrode for applying a voltage for extracting electrons from the cold cathode element A semiconductor substrate 8 on which a field emission electron source array 7 in which elements are integrated and integrated is formed. The electron beam 9 emitted from the cold cathode device is landed on the target 6, and the spatial distribution of signal charges generated and accumulated in the target 6 by the incident light is taken out to the outside as a time-series electric signal and connected to the target 6. The imaged image can be read.

  However, since the electron beam is emitted from the cold cathode element 7 with a spread, in this configuration, the electron beam that reaches the photoelectric conversion film has a certain spread. For this reason, part or all of the scanning surface potential of the adjacent pixels on the target 6 is also read, and there is a problem that resolution degradation and false signal reading occur.

In view of this, a means has been proposed in which a shield-grid electrode having a plurality of through holes is arranged between a field emission electron source array and a target to suppress the spread of the electron beam and improve the resolution. Since the signal charge accumulated in the target is read while suppressing the spread of the electron beam from the electron emission region by the shield-grid electrode, the charge reading of the adjacent pixels is reduced and high resolution is realized. Further, damage to the emitter and the gate electrode is protected from positive ions and surplus electrons caused by the gas emitted from the photoelectric conversion film, and operation stability and low noise of the cathode array are realized (see, for example, Patent Document 2).
JP-A-6-176704 JP 2000-48743 A

  However, in the conventional configuration, when a shield-grid electrode exists between the electron source array and the target, most of the electron beams radiated from the electron source array flow into the shield-grid electrode. The current is greatly reduced. When the beam current that reaches the target decreases, the reading ability of the signal charges accumulated in the target decreases, and it becomes difficult to capture a clear image. In order to compensate for this, it is necessary to increase the amount of electron emission from the electron source array and operate with a high beam current. However, since it is necessary to apply a high voltage to the gate electrode to apply a high load to the emitter, there arises a problem that dielectric breakdown occurs between the emitter and the gate electrode and the life of the electron source is reduced. For this reason, there has been a problem that an electron beam with sufficient sensitivity cannot be irradiated onto the target.

  The present invention solves the above-mentioned conventional problems, and reduces the amount of beam current flowing into the shield electrode, thereby increasing the amount of beam current irradiated to the target and improving the signal charge reading capability. An object of the present invention is to provide a type electron source device.

  In order to solve the above-described conventional problems, a field emission electron source device according to the present invention has a predetermined operation by an electron source array provided with a plurality of emitters for emitting electrons, and an electron beam emitted from the electron source array. And an electrode having a plurality of through holes whose inner wall surface is covered with a film of a secondary electron emitting material between the electron source array and the photoelectric conversion film. To do.

According to the field emission electron source device of the present invention, electrons are emitted from the secondary electron emitting material when the electron beam collides with the side surface of the through-hole, and the electrons colliding with the side surface of the through-hole and the secondary electron emission Since electrons emitted from the material are scattered, the chance of collision of electrons with the side surface of the through hole is increased, the secondary electron multiplication factor is improved, the irradiation current to the target is increased, and the signal charge reading sensitivity of the target is increased. Can be improved and a clear image can be taken.
The secondary electron emitting material is preferably a film containing either magnesium oxide or beryllium oxide. Since these materials have a secondary electron emission ratio exceeding 1, it is possible to irradiate the target with a current higher than the beam current colliding with the side surface of the through hole.

  The through-hole is preferably a trimming type electrode in which the length of the electron beam passage path is larger than the opening diameter. As a result, electrons incident on the through hole with an oblique velocity component collide with the side surface of the through hole, the spread of the electron beam is suppressed, and the target can be irradiated with an electron beam with a small beam diameter. In addition, the chance of collision of electrons with the side surface of the through-hole is increased, and the multiplication factor of secondary electrons is improved, so that the irradiation current to the target is increased and the signal charge reading sensitivity is improved.

  Therefore, according to the present invention, the target can be irradiated with an electron beam having a higher current amount than before, so that a highly sensitive electron source device can be realized.

  Embodiments of a field emission electron source device of the present invention will be described below in detail with reference to the drawings.

(Embodiment 1)
A first embodiment of the present invention will be described with reference to the drawings. A schematic diagram of the field emission electron source device of the present invention is shown in FIG. A front panel 1, a back panel 2, and a side peripheral device 3 are provided, which are fixedly fixed by a sealing material 4 made of indium, and the inside thereof is kept in a vacuum. An anode electrode 5 that transmits incident light from the outside is formed on the inner surface of the front panel 1, and a photoelectric conversion film made of antimony sulfide is formed as a target 6 on the surface.

  On the inner surface of the back panel 2, a plurality of cold cathode elements (emitters) are applied on the cathode substrate 10, an insulating layer formed around each cold cathode element, and a voltage for extracting electrons from the cold cathode elements. A semiconductor substrate 8 on which a field emission electron source array 7 in which peripheral elements such as gate electrodes are integrated and integrated is formed. Further, an electrode support 12 on which an electrode 11 having a plurality of through holes is mounted is installed at the end of the cathode substrate 10.

FIG. 1B shows an enlarged view of the electrode 11 having a plurality of through holes. The electrode 11 is a structure having a cross beam-like through hole 13 and a length L of 1: 5 with respect to the opening diameter D of the through hole. An electrode having such a structure is called a trimming electrode. (Hereinafter, the electrode of this structure is referred to as a trimming electrode.)
FIG. 1C shows a cross-sectional view of the through hole of the trimming electrode 11. As shown in the cross-sectional view, the inner wall of the through hole has an uneven shape. Further, a magnesium oxide layer 14 as a secondary electron emitting material is formed on the surface, and the inner wall surface of the through hole is covered with an uneven magnesium oxide film. Since the side surface of the through hole of the trimming electrode 11 has irregularities, the electrons 9 incident on the through hole in an oblique direction collide with the side surface of the through hole and scatter, so the number of times of collision with the side surface of the through hole Further, since the side surface of the through hole is covered with the magnesium oxide layer 14, the number of secondary electrons emitted is also increased. As a result, the current traveling from the trimming electrode 11 to the target 6 is greater than the current incident on the through hole of the trimming electrode 11. Thereby, the electron beam with which the target 6 is irradiated is increased and the signal charge reading sensitivity on the target surface is improved, so that an imaging device with high sensitivity and high contrast can be realized.

  Further, since the trimming electrode 11 can suppress the spread of the electron beam and reduce the beam diameter, the electron beam emitted from the cold cathode element 7 is landed on the target 6 and generated in the target 6 by incident light.・ Extracting the spatial distribution of accumulated signal charges as a time-series electric signal to the outside, and when reading an image formed on the target 6, it is possible to maintain fine reading accuracy and improve the resolution of the imaging device Can do.

  Next, a method for manufacturing the trimming electrode 11 and a method for forming the magnesium oxide layer 14 will be described. FIG. 2A shows a state before the trimming electrode is processed. The trimming electrode before processing is a laminated plate in which a plurality of layers of silicon (Si) 15 and silicon oxide (SiO 2) 16 are overlapped. Etching is performed on the laminated plate to form through holes. The etching process is performed by the following wet etching process.

  In the laminated plate in which the silicon layer 15 and the silicon oxide layer 16 are overlapped, silicon nitride is formed to a thickness of 100 nm by vapor deposition or the like on the surface of the portion that is not etched to form a masking layer. Next, the laminate is immersed in an etching solution containing 50% by weight of hydrogen fluoride. By this step, the silicon layer 15 and the silicon oxide layer 16 where there is no masking layer are eroded by hydrogen fluoride, so that through holes are formed in the laminate. In this laminated board, the etching rate is slightly different between the silicon layer 15 and the silicon oxide layer 16, and the silicon oxide layer 16 is eroded slightly faster. When the laminated plate is immersed in the etching solution for 30 minutes to complete the etching process, the side surface of the through hole has an uneven shape as shown in FIG. Next, when the masking layer of silicon nitride is removed with a stripping solution such as alkylbenzene sulfonic acid, the trimming electrode 11 having through holes with unevenness on the side surface shown in FIG. 2B is completed.

  The laminated plate having a plurality of through holes is masked on portions other than the through holes on the electron beam incident side, and magnesium is deposited and deposited from an oblique direction on the electron beam incident side. A magnesium layer is formed on the side surface. Thereafter, the magnesium layer is oxidized, and as shown in FIG. 2 (c), a silicon and silicon oxide laminate having a magnesium oxide layer 14 having irregularities on the surface of the through-holes is produced. The trimming electrode 11 is completed by adhering this laminated plate to the electrode support 12 with a conductive material. By bonding with a conductive material, a uniform voltage can be applied from the top surface to the bottom surface of the trimming electrode.

  In the present embodiment, a material containing silicon as a main component is used as the material for the trimming electrode. However, the material is not particularly selected as long as it is a conductive material. However, since it is a member used in a vacuum, the thing with few emitted gas in a vacuum is preferable. In this embodiment, magnesium oxide is used as the secondary electron emitting material, but the same effect can be obtained even when beryllium oxide is used.

(Embodiment 2)
A second embodiment of the present invention will be described. A schematic diagram of the field emission type electron source device of the second embodiment is shown in FIG. The configuration of the field emission electron source device of the second embodiment is the same as that of the first embodiment shown in FIG. 1 except for the trimming electrode 17 having a plurality of through holes.
FIG. 3B shows a cross-sectional view of a trimming electrode having a through hole. The difference from the first embodiment is that the material is made of a porous metal, and the inner wall of the through hole has an uneven shape as shown in FIG. Further, a magnesium oxide layer 14 as a secondary electron emitting material is formed on the inner wall of the through hole. Even when this trimming electrode 17 is used, since the side surface of the through hole has irregularities, electrons incident on the through hole in an oblique direction collide with the side surface of the through hole and are scattered, Increases the number of collisions on the side. Further, since the side surface of the through hole is covered with the magnesium oxide layer 14, the number of secondary electrons emitted is increased, so that the current from the trimming electrode 17 to the target 6 flows into the through hole of the trimming electrode 17. It will be larger than the incident current. Thereby, the electron beam with which the target 6 is irradiated is increased and the signal charge reading sensitivity on the target surface is improved, so that an imaging device with high sensitivity and high contrast can be realized.

  Next, a method for manufacturing the trimming electrode 17 will be described. Etching is performed on the porous nickel plate 18 shown in FIG. 4A to form through holes. Porous nickel is obtained by sintering nickel particles, and there are gaps between the particles inside. The nickel particles of the porous nickel plate 18 are mainly made of spherical particles, the particle diameters thereof are in the range of 1.8 μm to 4.7 μm, and the average particle diameter is 3.0 μm. In addition, in the porous nickel plate of FIG. 4 (a), in order to simplify the description, those having the same particle diameter are regularly arranged. When the through hole is formed, as shown in FIG. 4B, the side surface of the through hole has a shape having irregularities of about 1.5 μm on average.

  The porous nickel plate 18 is etched by the following wet etching process. In the porous nickel plate 18, silicon nitride is formed to a thickness of 100 nm by vapor deposition or the like on the surface of the portion that is not etched, thereby forming a masking layer. Next, the porous nickel plate 18 is immersed in an etching solution containing 10% by weight of nitric acid. By this step, the nickel in the portion without the masking layer is eroded by nitric acid, so that through holes are formed in the porous nickel. When the porous nickel plate 18 is immersed in the etching solution for 2 hours to complete the etching process, as shown in FIG. 4B, the side surface of the through hole has an uneven shape with an average of about 1.5 μm. It becomes. Finally, when the silicon nitride masking layer is removed with a stripping solution such as alkylbenzene sulfonic acid, the trimming electrode 17 having through holes with unevenness on the side surface as shown in FIG. 4B is completed.

  For a porous nickel plate with a plurality of through holes, mask the portions other than the through holes on the electron beam incident side, and deposit and deposit magnesium from the oblique direction on the electron beam incident side. Then, a magnesium layer is formed on the side surface of the through hole. Thereafter, the magnesium layer is oxidized to produce a porous nickel plate in which a magnesium oxide layer 14 having irregularities on the surface of the through-holes is formed as shown in FIG. 4C. The trimming electrode 17 is completed by adhering this porous nickel plate to the electrode support 12 with a conductive material.

  In the second embodiment, porous nickel is used as the material for the trimming electrode. However, the material is not particularly selected as long as it is a conductive porous material. However, since it is a member to be used in a vacuum, it is preferable that the gas released in vacuum is small, and it is necessary that it is not oxidized in the magnesium oxidation step. Therefore, as the porous metal, nickel or copper is used. preferable.

(Embodiment 3)
A third embodiment of the present invention will be described with reference to the drawings. A schematic diagram of the field emission electron source device of the present invention is shown in FIG. The configuration of the field emission electron source device of the third embodiment is the same as that of the first embodiment shown in FIG. 1 except for the trimming electrode 19 having a plurality of through holes.

  FIG. 5B shows an enlarged cross-sectional view of the trimming electrode portion having a through hole. Similar to the trimming electrode 11 in the first embodiment, the trimming electrode 19 in the third embodiment has a cross-shaped through hole, and has a structure in which the length L is 1: 5 with respect to the opening diameter D of the through hole. Is the body. The side surface of the through hole of the trimming electrode 19 in the third embodiment has a shape with irregularities by forming a layer 20 of fine particles of magnesium oxide as a secondary electron emitting material on a flat electrode substrate. Yes.

  Even when this trimming electrode 19 is used, since the side surface of the through hole is uneven due to the fine particles of magnesium oxide, electrons incident obliquely to the through hole collide with the side surface of the through hole. The number of times of scattering and collision with the side surface of the through hole increases. At the same time, since the magnesium oxide fine particles emit secondary electrons, the current directed to the target 6 is larger than the current incident on the through hole of the trimming electrode 19. As a result, as in the first embodiment, the number of electron beams applied to the target 6 increases, and the signal charge reading sensitivity on the target surface is improved, so that a high-sensitivity and high-contrast imaging device can be realized. it can.

  Next, a method for producing the trimming electrode 19 and a method for forming the magnesium oxide fine particle layer 20 will be described. FIG. 6A shows a state before the trimming electrode is processed. The trimming electrode before processing is a single substrate 21 made of silicon. Etching is performed on the silicon substrate 21 to form through holes.

  The etching process is performed by the following wet etching process. In the silicon substrate 21, silicon nitride is formed with a thickness of 100 nm by vapor deposition or the like on the surface of the portion that is not etched, thereby forming a masking layer. Next, the silicon substrate 21 is immersed in an etching solution containing 30% by weight of potassium hydroxide. Through this step, the silicon without the masking layer is eroded by potassium hydroxide, so that through holes are formed in the silicon substrate. When the silicon substrate 21 is immersed in the etching solution for 30 minutes to complete the etching process, a through-hole having a flat side surface is formed as shown in FIG. Next, the silicon nitride masking layer is removed with a stripping solution such as alkylbenzene sulfonic acid to produce a silicon substrate 21 having a plurality of through holes.

  Next, the silicon substrate 21 having a plurality of through holes is immersed in a mixed liquid in which a highly dispersed solvent and fine particles of magnesium oxide having a particle diameter of 1 μm or less are mixed to give charges to the silicon substrate, thereby Then, a layer 20 of magnesium oxide fine particles having a thickness of about 2 μm is electrodeposited and formed. Next, the magnesium oxide fine particle layer on the front surface and the back surface of the silicon substrate is removed, and the fine particle layer 20 of the magnesium oxide is left only on the side surface of the through hole of the silicon substrate, as shown in FIG. A silicon substrate having a fine particle layer 20 of magnesium oxide formed on the hole surface is produced. The trimming electrode 19 is completed by adhering this silicon substrate to the electrode support 12 shown in FIG.

  In the third embodiment, silicon is used as the material for the trimming electrode. However, the material is not particularly selected as long as it is a conductive substance, as in the case of the first embodiment. In addition, although the magnesium oxide fine particle layer is formed on the side surface of the through hole of the trimming electrode, the same effect can be obtained by forming a beryllium oxide fine particle layer. In the third embodiment, the electrodeposition method is used as the method for forming the layer of the magnesium oxide fine particles. However, the formation method is not particularly limited. For example, the magnesium oxide fine particles can be formed using a slurry coating method. The layer can be formed.

  The field of application of the present invention can be used as a field emission electron source imaging device, particularly as a high-sensitivity and high-resolution imaging device such as a night vision camera.

Sectional drawing of the field emission type electron source device concerning Embodiment 1 of this invention The figure which shows the production method of the trimming electrode used for the field emission type electron source device concerning Embodiment 1 of this invention. Sectional drawing of the field emission type electron source device concerning Embodiment 2 of this invention The figure which shows the production method of the trimming electrode used for the field emission type electron source device concerning Embodiment 2 of this invention. Sectional drawing of the field emission type electron source device concerning Embodiment 3 of this invention The figure which shows the production method of the trimming electrode used for the field emission type electron source device concerning Embodiment 3 of this invention. Sectional view of a field emission electron source device using a conventional field emission electron source array

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Front panel 2 Back panel 3 Side surface peripheral device 4 Sealing member 5 Anode electrode 6 Target 7 Field emission type electron source array 8 Semiconductor substrate 9 Electron beam 10 Cathode substrate 11 Trimming electrode 12 Electrode support 13 Through-hole 14 Magnesium oxide layer 15 Silicon layer 16 Silicon oxide layer 17 Trimming electrode 18 Porous nickel plate 19 Trimming electrode 20 Magnesium oxide particulate layer 21 Silicon substrate

Claims (9)

An electron source array provided with a plurality of emitters for emitting electrons;
A photoelectric conversion film that performs a predetermined operation by an electron beam emitted from the electron source array;
An electrode having a plurality of through-holes whose inner wall surface is covered with a film of a secondary electron emitting material between the electron source array and the photoelectric conversion film;
A field emission electron source device. The field emission electron source device according to claim 1, wherein the electron source array includes a plurality of emitters that emit electrons. The field emission electron source device according to claim 1, wherein the surface of the film of the secondary electron emitting material covered by the through hole is uneven. The electron source device according to claim 1, wherein the secondary electron emitting material is a thin film containing either magnesium oxide or beryllium oxide. The electron source device according to claim 1, wherein the secondary electron emitting material is a fine particle of magnesium oxide or beryllium oxide. The electron source device according to claim 1, wherein the through hole has a length larger than an opening diameter. The electron source device according to claim 1, wherein the electrode is made of a laminated plate of silicon and silicon oxide. 4. The electron source device according to claim 1, wherein the electrode having the plurality of through holes is made of a porous metal. 6. The electron source device according to claim 5, wherein the porous metal is made of nickel or copper.

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