Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1996-05-28
2002-10-29
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
Reexamination Certificate
active
06473063
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electron source comprising a large number of electron-emitting devices arranged in a matrix array, an image-forming apparatus comprising such an electron source and a method of driving such an image-forming apparatus.
2. Related Background Art
In recent years, there have been a number of studies on cold cathode type electron-emitting devices, trying to use them for image-forming apparatuses. A surface conduction electron-emitting device is a cold cathode type electron-emitting device. A surface conduction electron-emitting device is realized by utilizing the phenomenon that electrons are emitted out of a small thin film formed on a substrate when an electric current is forced to flow in parallel with the film surface.
A surface conduction electron-emitting device typically comprises an electrically insulating substrate, a pair of device electrodes arranged on the substrate and an electroconductive thin film containing an electron emitting region and arranged between the device electrodes to electrically connect them. The electron emitting region is produced by subjecting the electroconductive thin film, which is typically made of a metal oxide, to a current conduction treatment referred to as energization forming. In an energization forming process, a constant DC voltage or a slowly rising DC voltage that rises typically at a rate of 1V/min. is applied to given opposite ends of the electroconductive thin film to partly destroy, deform or transform the film and produce an electron-emitting region which is electrically highly resistive. When a voltage is applied to an electroconductive thin film where such an electron emitting region is formed in order to make an electric current flow therethrough, the electron emitting region starts emitting electrons.
A surface conduction electron-emitting device having a configuration as described above is advantageous in that it is structurally simple and can be manufactured easily so that a large number of such devices can be arranged over a large area in a simple manner at low cost. Studies have been made to exploit this advantage, and known applications of such devices include image-forming apparatuses including display apparatuses.
The performance of a surface conduction electron-emitting device will be described below by referring to
FIG. 19
of the accompanying drawings.
The electric current (If) that flows through a surface conduction electron-emitting device when a voltage (Vf) is applied thereto cannot be uniquely defined. A surface conduction electron-emitting device may operate typically in either of two different ways. Firstly, the electric current flowing through the device (If) may increase in the initial stages as the applied voltage (Vf) is raised from 0[V] but falls thereafter before it gets to a plateau that may be slightly inclined upward. Alternatively, the electric current flowing through the device (If) may monotonically increase as the applied voltage (Vf) is raised from 0[V].
For the sake of convenience, hereinafter, the first characteristic of performance will be referred to as the static characteristic, whereas the second one will be referred to as the dynamic characteristic.
In
FIG. 19
, the broken line indicates the static characteristic that appears when a voltage sweep speed of less than about 1V/min. is used. More specifically, in the first voltage region of Vf=0 to V
1
(I region), the electric current flowing through the device (If) monotonically increases with the increase of the voltage (Vf). In the succeeding voltage region of Vf=V
1
to V
2
(II region), the electric current flowing through the device (If) decreases with the increase of the voltage (Vf). This characteristic is referred to as a voltage-controlled-negative-resistance characteristic (hereinafter referred to as a “VCNR characteristic” hereinafter). In the third voltage region of Vf=V
2
to Vd (III region), the electric current flowing through the device (If) practically does not change relative to the increase of the voltage (Vf). Note that V
1
represents the voltage when the electric current flowing through the device (If) is maximized and V
2
represents the voltage corresponding to the Vf axis intercept of the tangent line to the If curve at the maximum gradient point in the If decreasing resion (II region). Meanwhile, the emission current (Ie) of the device increases as the voltage (Vf) is raised with regard to a threshold voltage Ve.
In
FIG. 19
, the solid line indicates the dynamic characteristic of the device when the voltage sweep speed is greater than about 10V/sec. More specifically, if the maximum voltage is swept with Vd (If (Vd) line in FIG.
19
), the electric current flowing through the device (If) gradually increases and its line comes to agree with the If line for the static characteristic at Vd. If, on the other hand, the maximum voltage is swept with V
2
(If (V
2
) line in FIG.
19
), the line of the electric current flowing through the device (If) also gradually increases and its line comes to agree with the If line for the static characteristic at V
2
. If the maximum voltage is swept with a voltage of the I region, electric current flowing through the device (If) changes substantially along the If line.
While the above described static and dynamic characteristics for the I-V relationship can be varied by changing the material, the profile and/or the other factors of the device or depending on the vacuum atmosphere, a surface conduction electron-emitting device that operates in a desired way typically shows the above three regions, or the regions I through III, of performance.
Different electron sources comprising a large number of surface conduction electron-emitting devices arranged in the form of X-Y matrix have been proposed in order to exploit the above described characteristics for flat panel CRTs and other displays.
A matrix type electron source is realized by arranging M×N surface conduction electron-emitting devices and electrically connecting them by wires XE
1
through XEN and YE
1
through YEM as illustrated in FIG. of the accompanying drawings. When such an electron source is used for an image-forming apparatus, e.g. a flat panel CRT, the pixels on the screen and the surface conduction electron-emitting devices are arranged on a one-to-one correspondence basis and the latter are driven to operate according to a given pattern.
Two drive modes are known to date; point-by-point sequential scanning for exciting the screen on a pixel by pixel basis and line-by-line sequential scanning for exciting the screen on a pixel line by pixel line basis. (Each line has M pixels in the arrangement of
FIG. 20.
) The line-by-line sequential scanning system is normally used as it is advantageous particularly from the viewpoint of the speed of driving each surface conduction electron-emitting device and the momentary current generated by the emitted electron beam because a longer operating time is allocated to each pixel.
Meanwhile, these known scanning systems are accompanied by a problem of high power consumption rate because a large electric current is made to flow to those surface conduction electron-emitting devices that are not currently emitting electron beams and hence staying idle when a large number of surface conduction electron-emitting device are driven either by line-by-line sequential scanning or by point-by-point sequential scanning.
This problem will be discussed below in greater detail by referring to
FIGS. 21 through 23
of the accompanying drawings.
FIG. 21
is a schematic plan view of an electron source that comprises only 6×6 surface conduction electron-emitting devices arranged in a simple matrix arrangement for the sake of simplicity. The surface conduction electron-emitting devices are denoted by D(
1
,
1
), D(
1
,
2
), . . . , D(
6
,
6
), using the popular (x,y) coordinate system. If such an electron source is used for a flat panel CRT and each surface conductio
Hamamoto Yasuhiro
Nakamura Naoto
Nomura Ichiro
Suzuki Hidetoshi
Takeda Toshihiko
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hjerpe Richard
Laneau Ronald
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