JP2008084681A - Field emission type electron source element, and imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a field emission type electron source element capable of stably emitting electrons even in high-speed drive required for an imaging operation, and high in image quality. <P>SOLUTION: This field emission type electron source element is provided with cathode electrodes 3 with a plurality of emitters 2 of a conductive minute structure projected from a substrate 1 formed thereon, and gate electrodes 5 electrically insulated from the cathode electrodes 3. In the field emission type electron source element, the cathode electrodes 3 and the gate electrodes 5 are arranged in a matrix-like form; an emitter group corresponding to one pixel portion is formed by the plurality of emitters 2 corresponding to an intersection part between the cathode electrode 3 and the gate electrode 5; and the emitter groups adjacent to each other are separated from each other by a low-dielectric-constant insulation film 6. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a matrix-type field emission electron source element (field emission cold cathode element) and an imaging apparatus using the same.

  Conventionally, a photoconductive imaging tube is known as an imaging device. The photoconductive imaging tube includes a photoconductive film that generates and accumulates signal charges according to the amount of incident light. Signal charges generated and accumulated in the photoconductive film can be read out to an external circuit in time series by an electron beam, and an electrical signal corresponding to the spatial distribution of the incident light quantity can be generated.

  As a means for irradiating an electron beam, an electron tube using a field emission type electron source element instead of the conventional thermoelectron type is proposed in Patent Document 1, for example. The field emission electron source device has advantages such as a higher current density than that of the hot cathode and a small velocity distribution of emitted electrons.

FIG. 3 is a plan view showing an electrode arrangement of a matrix type field emission electron source element.
A strip-shaped cathode electrode 303 extending in the horizontal axis (X-axis) direction and a strip-shaped gate electrode 304 extending in the vertical axis (Y-axis) direction orthogonal to the horizontal axis are arranged in a matrix.

  The cathode electrode 303 is formed by using a part of the silicon substrate 301, and an emitter group 302 that is an aggregate of emitters (electron emission sources) is formed on the cathode electrode 303. The emitter group 302 is shown in a circle. In one emitter group 302, several hundred to several thousand emitters are formed.

  The gate electrode 304 is disposed by being patterned on the upper side of the cathode electrode 303. Therefore, in the example of FIG. 3, the line of the cathode electrode 303 is hidden on the lower surface of the gate electrode 304.

  By driving the cathode electrode 303 and the gate electrode 304 in matrix, electrons can be emitted from the emitter group 302 at the intersection of both electrodes. By selecting each position in the X direction and the Y direction and sequentially driving them, the accumulated charge on the photoelectron surface can be read out and used as an image sensor.

  A potential can be supplied to the gate electrode 304 and the cathode electrode 303 arranged in a matrix from a gate electrode pad 305 and an emitter electrode pad 306, respectively. Both electrode pads are provided on the upper surface side of the silicon substrate 301 which is the same as the electron emission surface of the emitter.

  The emitter group 302 corresponding to the intersection of the gate electrode 304 and the cathode electrode 303 corresponds to one pixel. The emitter group 302 is separated so that it can be individually driven in units of pixels in time series. Specifically, the gate electrode emitter groups 302 adjacent to each other on the left and right are separated by electrode patterning when the electrodes are formed, and the cathode electrode emitter groups 302 adjacent to each other on the upper and lower sides are formed on a silicon substrate. It is separated by an insulating film.

In such a configuration, when each pixel is selected and emitted in time series, one of the electrodes in the X direction and Y direction is sequentially selected in time series. By selecting the other electrode group in a time series within the time during which one electrode of the selected one electrode group is selected, it is possible to obtain an emission from the individual emitter group.
JP 2000-48743 A

  However, in an imaging apparatus equipped with a conventional field emission electron source element, when the resolution is increased, the dot clock is driven at a high speed of 11 MHz in the case of NTSC due to the dot sequential driving of the imaging tube. End up. In the case of high-definition HDTV specifications, a dot clock exceeding 60 MHz is required.

  This is because the image pickup tube has a photoconductive film that generates and accumulates signal charges according to the amount of incident light, and the signal charges generated and accumulated in the photoconductive film are time-sequentially transferred to an external circuit by an electron beam. This is based on the principle of reading out and generating an electrical signal corresponding to the spatial distribution of the incident light quantity.

  In the case where the cathode electrode separated by the insulating film is driven at high speed, a delay occurs in the voltage applied to the cathode electrode in the selected pixel. When this delay occurs, the timing of starting the operation of the next cathode electrode is reached before the matrix-driven cathode electrode reaches the potential to be applied. In this case, there is a problem that the cathode electrode does not have a potential to be originally applied, and as a result, a normal emission amount is not output.

  This means that an erroneous electric signal is sent to the original image, and as a result, an image having a luminance different from that of the original image is formed and the image quality is deteriorated. Therefore, it is required to transmit the gate electrode signal without signal delay.

  The present invention solves the conventional problems as described above, and can stably emit electrons even at a high speed required for an imaging operation, and has a high image quality field emission electron source. An object is to provide an element.

  In order to achieve the above object, a field emission electron source device according to the present invention comprises a cathode electrode having a plurality of conductive microstructure emitters protruding from a substrate, a gate electrode electrically insulated from the cathode electrode, The cathode electrode and the gate electrode are arranged in a matrix, and a plurality of emitters corresponding to intersections of the cathode electrode and the gate electrode form an emitter group corresponding to one pixel. The emitter groups of at least the adjacent cathode electrodes are separated by a low dielectric constant insulating film.

  In addition, an imaging apparatus according to the present invention includes the field emission electron source element.

  According to the present invention, high-speed driving is stable and high-quality images can be formed.

  According to the present invention, it is possible to stably emit electrons even in high-speed driving, and a high-quality image can be formed.

  In the field emission electron source device of the present invention, the low dielectric constant insulating film is preferably porous silicon oxide.

  The low dielectric constant insulating film is preferably a fluorine-added silicon oxide film.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The configuration of the electrode arrangement shown in FIG. 3 is the same in the following embodiments. Therefore, FIG. 3 is also used as an electrode arrangement diagram in the following embodiment.

(Embodiment 1)
FIG. 1 shows a cross-sectional view of a field emission type electron source device (field emission cold cathode device) according to the first embodiment. This figure corresponds to a cross-sectional view in the Y direction of FIG. The silicon substrate 1 is formed with a cathode electrode 3 from which an emitter (electron emission electrode) 2 having a conductive microstructure is projected. The emitter 2 is a tower type (cone type) having a cone shape or a polygonal pyramid shape such as a quadrangular pyramid. A gate electrode 5 is disposed on the silicon substrate 1 via an insulating layer 4 (for example, an SiO ₂ insulating layer). Each emitter 2 corresponds to a pair of openings in the gate electrode 5. More specifically, the opening of the gate electrode 5 corresponds to the periphery of the tip of the emitter 2.

  A low dielectric constant insulating film 6 is formed in the groove of the silicon substrate 1. The emitter 2 between the adjacent low dielectric constant insulating films 6 corresponds to the emitter 2 for one pixel, that is, the emitter group 302 in FIG. For simplicity, the number of emitters 2 for one pixel is omitted. In the present embodiment, the low dielectric constant insulating film 6 is made of porous silicon oxide.

  When the configuration of FIG. 1 is made to correspond to the configuration of FIG. 3, the emitter group 302 adjacent in the Y direction in FIG. 3 is separated by the low dielectric constant insulating film 6. More specifically, in FIG. 3, the emitter group 302 corresponding to one cathode electrode 303 is lower than the emitter group 302 corresponding to another adjacent cathode electrode 303. The dielectric constant insulating film 6 is separated by a line.

  A predetermined potential can be applied to the gate electrode 5. Emission can be obtained by applying a potential difference between the gate electrode 5 and the emitter 2.

  FIG. 2 is an enlarged view of a part of FIG. As shown in FIG. 2, the field emission electron source element has a fine conical emitter 2 on a silicon substrate 1 and a gate electrode 5 having a submicron size so as to surround the emitter 2 with an insulating layer 3 interposed therebetween. It is formed at intervals. When a voltage is applied between the gate electrode 5 and the cathode electrode 3 on the silicon substrate 1, an electric field is concentrated on the tip of the emitter 2, and electrons are emitted in a vacuum.

The field emission type electron source element is manufactured by a normal semiconductor process. The emitter 2 in FIG. 2 is a silicon emitter, and is processed into a trapezoid shape using a circular thermal oxide film as a mask through a photo process. At this time, anisotropic wet etching is performed by reactive ion etching using SF ₆ + O ₂ gas or KOH.

  Thereafter, an element isolation line is etched through a photo process. Next, porous silicon is filled by a conventional method, and deposition and thermal oxidation are repeated to form an insulating film and a gate electrode (silicon, Nb). Next, lift-off with BHF is completed.

  In the example shown in FIG. 3, the driving is performed in a point-sequential manner in which the X-direction gate electrode 304 is selected and the Y-direction emitter (cathode electrode 303) is sequentially driven line by line. In the case of VGA for dot-sequential driving, the dot clock must be performed at a driving frequency of 11 MHz.

  In the present embodiment, the low dielectric constant insulating film 6 is formed of porous silicon oxide to reduce the dielectric constant of a normal element isolation line. When an imaging apparatus using a field emission electron source element having this configuration was manufactured, the emitter voltage could be stably operated without delay at a drive frequency of 11 MHz. That is, since there is a drive frequency characteristic of 11 MHz, it is possible to perform a stable emission operation without delaying a signal, and it is possible to form a high-quality image. This is presumably because the parasitic capacitance between adjacent cathode electrodes was reduced by lowering the dielectric constant of the element isolation line.

(Embodiment 2)
In the first embodiment, porous silicon is used for the inter-element insulating film. However, in the second embodiment, an imaging apparatus is formed using a field emission electron source element in which the inter-element insulating film is formed of a fluorine-added silicon oxide film. Produced.

  Even in the configuration of the present embodiment, the emitter voltage can be stably operated without delay at a drive frequency of 11 MHz. Since it has a drive frequency characteristic of 11 MHz, it is possible to perform a stable emission operation without delaying a signal, and it is possible to form a high-quality image.

  Although the first and second embodiments have been described with the example in which the cathode is divided only in the column direction and driven at high speed, the effect of this example is not limited to this, and the method of dividing the elements individually is also possible. Similar effects can be obtained.

  In addition, although the example of porous silicon oxide or fluorine-added silicon has been described as the material of the inter-element insulating film, it is not limited to this, and other low dielectric constant insulating films having a relative dielectric constant of 3.0 or less are used. May be.

  As described above, the field emission type electron source element according to the present invention is useful as a field emission type electron source element for an imaging apparatus because high-speed driving is stable and a high-quality image can be formed.

1 is a cross-sectional view of a field emission type electron source device according to an embodiment of the present invention. FIG. 2 is an enlarged view of a part of FIG. 1. The top view which shows electrode arrangement | positioning of a matrix type field emission type electron source element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Emitter 3 Cathode electrode 4 Insulating layer 5 Gate electrode 6 Low dielectric constant insulating film

Claims (4)

A cathode electrode formed with a plurality of conductive microstructure emitters protruding from the substrate;
A gate electrode electrically insulated from the cathode electrode,
The cathode electrode and the gate electrode are arranged in a matrix,
An emitter group corresponding to one pixel is formed by a plurality of the emitters corresponding to the intersections of the cathode electrode and the gate electrode,
A field emission electron source device, wherein at least the emitter groups of adjacent cathode electrodes are separated by a low dielectric constant insulating film.   The field emission electron source device according to claim 1, wherein the low dielectric constant insulating film is porous silicon oxide.   The field emission electron source element according to claim 1, wherein the low dielectric constant insulating film is a fluorine-added silicon oxide film.   An imaging apparatus comprising the field emission electron source element according to claim 1.

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