Electric lamp and discharge devices – Discharge devices having three or more electrodes
Reexamination Certificate
1999-07-21
2001-08-21
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
Discharge devices having three or more electrodes
C313S309000
Reexamination Certificate
active
06278228
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a cold cathode field emission device and a cold cathode field emission display into which the cold cathode field emission device is incorporated.
Various flat type, or flat panel type displays are being studied as an image display which is to replace currently main-stream cathode ray tubes (CRT). The flat type displays include a liquid crystal display (LCD), an electroluminescence display (ELD) and a plasma display panel (PDP). Further, there is also proposed a cold cathode field emission display capable of emitting electrons into a vacuum from a solid without relying on thermal excitation, and it attracts attention from the viewpoint of a brightness on a screen and a low power consumption.
The cold cathode field emission display (to be sometimes simply referred to as “display” hereinafter) generally has a configuration in which a cathode panel and an anode panel are arranged so as to face each other through a vacuum layer. The cathode panel has electron emission portions corresponding to two-dimensionally arranged pixels having a gridiron pattern. The anode panel has a fluorescence layer which emits light by its excitation due to a collision with electrons emitted from the electron emission portions. On individual pixels on the cathode panel, generally, a plurality of electron emission portions are formed, and gate electrodes are also formed for emitting electrons from the electron emission portions. An element constituted of the above electron emission portion and the above gate electrode will be referred to as a cold cathode field emission device or a field emission device hereinafter.
In the above display, for attaining a large emission electron current with a low driving voltage, each electron emission portion is required to have a sharply pointed form, it is required to scale down electron emission portions in a block corresponding to one pixel for increasing the density of the electron emission portions, and it is required to decrease a distance between the top end portion of each electron emission portion and each gate electrode. Cold cathode field emission devices having various configurations have been so far proposed for complying with the above requirements.
As a typical example of conventional field emission devices, there is known a so-called Spindt-type field emission device having electron emission portions composed of an electrically conductive material having a conical form. On the cathode panel side of a display into which the Spindt-type field emission devices are incorporated, a cathode electrode, an insulating layer and a gate electrode are consecutively formed on a supporting substrate. Many fine opening portions having a diameter of approximately 1 &mgr;m are formed in a two-dimensional matrix form so as to penetrate through the gate electrode and the insulating layer, and the electron emission portions are formed on the cathode electrode exposed in bottoms of the opening portions. When a voltage is applied to the gate electrode constituting an edge of the opening portion, electrons are emitted from the top end portion of the electron emission portion depending upon the intensity of an electric field generated by the voltage application. Emitted electrons are drawn out of the opening portion and collide with the fluorescence layer on the anode panel side to excite the fluorescence layer and to allow the fluorescence layer to emit light, so that the electrons serve to form an intended image. The conical electron emission portion composed of an electrically conductive material is formed, in a self-aligning manner, by decreasing the amount of depositing particles of the electrically conductive material which can strike into the opening portion, with the passage of time by utilizing the shielding effect of an overhung deposit of the electrically conductive material deposited around the edge of the opening portion during the vertical deposition of the electrically conductive material.
The electron emission characteristic of the Spindt-type field emission device is largely dependent upon the distance from the edge of the gate electrode constituting the edge of the opening portion to the top end portion of the electron emission portion. Actually, however, it is difficult to form the electron emission portions having a uniform form and uniform dimensions in the entirety of the supporting substrate having a large area, and some in-plane deviation and a deviation among lots are inevitable. The deviations cause image displaying characteristics of a display, for example, a brightness of images to vary.
For overcoming the above defects of the Spindt-type field emission device, a so-called edge-type field emission device has been proposed. In one example of the edge-type field emission device, the conical electron emission portions in the Spindt-type field emission device are replaced with projections formed by consecutively forming, on an insulating substrate as a supporting substrate, a first insulating layer, an electron emission layer, a second insulating layer and a gate electrode to form a laminate, forming an opening portion in the laminate, and projecting an edge (end portion or the projection) of the electron emission layer by some method, which edge is exposed on a wall surface of the opening portion.
As a method of projecting the edges of the electron emission layer from the wall surfaces of the opening portions, generally, there is employed a method in which the above laminate is processed by combining anisotropic etching and isotropic etching. That is, the gate electrode is etched under an anisotropic condition, the second insulating layer immediately below the gate electrode is etched under an isotropic condition, the electron emission layer immediately below the second insulating layer is etched under an anisotropic condition, and the first insulating layer immediately below the electron emission layer is etched under an isotropic condition, whereby the wall surfaces of the first insulating layer and the second insulating layer are “withdrawn” more deeply than the edge of the gate electrode and the edge of the electron emission layer. In the above configuration, the distance from the edge of the gate electrode to the edge of the electron emission portion is mainly dependent upon the thickness of the second insulating layer, and it is far easier to control the above distance than to control the distance in the Spindt-type field emission device. Therefore, uniform electron emission characteristics of the electron emission portions can be accomplished even on the supporting substrate having a large area, and a uniform brightness of an image on a display can be also accomplished.
U.S. Pat. No. 5,214,347 discloses a structure in which not only a gate electrode is formed on the upper side of the electron emission layer but also a gate electrode is formed on the lower side of the electron emission layer so that a more intense electric field can be applied to the electron emission layer. That is, as shown in
FIG. 18
, a conductive layer
101
, a first insulating layer
102
, a lower gate electrode
103
, a second insulating layer
104
, an electron emission layer
105
, a third insulating layer
106
and an upper gate electrode
107
are consecutively formed on a supporting substrate
100
to form a laminate, and an opening portion
108
is formed which penetrates through all the layers excluding the conductive layer
101
and has the conductive layer
101
exposed on a bottom thereof. Predetermined voltages are applied to the lower gate electrode
103
, the electron emission layer
105
and the upper gate electrode
107
to generate an electric field, and due to the electric field, electrons e are emitted from the edge of the electron emission layer
105
projected on the wall surface of the opening portion
108
. The emitted electrons are introduced out of the opening portion
108
. The top of the edge of the electron emission layer
105
has its radius of curvature decr
Iwase Yuichi
Okita Masami
Day Michael H.
Kananen Ronald P.
Rader Fishman & Grauer
Sony Corporation
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