Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2000-07-10
2002-02-12
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169100, C315S169200, C315S169400, C313S310000, C313S311000
Reexamination Certificate
active
06346776
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to field emission displays (FEDs) and more specifically to a light modulator technology that employs a field emitter array (FEA) to address a deformable light valve modulator of reflective operation.
2. Description of the Related Art
Image displays are used to convert electrical signals into viewable images. The most common technology used in both projection and direct-view displays is the cathode ray tube (CRT), in which a scanning electron gun shoots one or several beams of electrons across a vacuum to scan a phosphor-coated anode. The electrons penetrate the individual phosphors causing them to emit light and taken together produce a direct view image. By necessity, the gun must sit far from the anode to raster scan the phosphor screen, a distance similar to the width of the display area. As a result, high-resolution large area direct-view displays are correspondingly very large and very heavy.
During the past 40 years numerous attempts have been made to construct a “Flat-CRT”, which can overcome the length and weight limitations of the conventional CRT without sacrificing performance. With few exceptions, these efforts have failed commercialization due to serious complexities in the electron source and mechanical structure, but a new alternative called the Field Emission Display (FED) has recently appeared that has shown promise in overcoming these barriers. The FED utilizes a matrix addressed cold cathode array, spacers to support the atmospheric pressure, and cathodoluminescent phosphors for efficient conversion of the electron beams into visible light. The non-linearity of the current/voltage relationship permits matrix addressing of high information content displays while providing high contrast ratio.
The FED combines the best properties of CRTs (full color, full grayscale, brightness, video rate speeds, wide viewing angle and wide temperature range) with the best attributes of Flat Panel technology (thin and light weight, linearity and color convergence). However, the current production FEDs have limited display sizes, 10 inch diagonal or less, due to the fabrication and vacuum packaging problems. Since the primary motivation for Flat-CRTs was to overcome the size and weight limitations of the conventional CRT for large display sizes, this is a serious problem to successful commercialization of the FED technology.
To appreciate FEDs, one must understand the physics of field emission. The potential barrier at the surface of a metallic conductor binds electrons to the bulk of the material. This potential barrier is called the work function, and is defined as the potential difference between the Fermi level and the height of the barrier. For an electron to leave the material, the electron must gain an energy that exceeds the work function. This can be accomplished in a number of ways, including thermal excitation (thermionic emission), electron and ionic bombardment (secondary emission), and the absorption of photons (photoelectric effect). Fowler-Nordheim emission or field emission differs from these other forms of emission in that the emitted electrons do not gain an energy that exceeds the material work function.
Field emission occurs when an externally applied electric field at the material surface thins the potential barrier to the point where electron tunneling occurs, and thus differs greatly from thermionic emission. Since there is no heat involved, field emitters are a “cold cathode” electron source. One needs to apply an electric field on the order of 30-70 MV/cm at the surface of a metallic conductor to produce significant tunneling current. For example, if an electrode were placed 1 &mgr;m from the surface of a conductor it would take 1000 V between the electrode and cathode to induce significant current flow. Obviously, a flat-panel display (FPD) that is addressed at 1000 V is of little use. Therefore, “field enhancement” is used to lower the necessary addressing voltages.
A field emitter is a sharp point, or whisker, with a connecting cathode electrode, a dielectric layer, and an isolated extraction gate in close proximity. If a positive potential is applied between the gate and cathode, a uniform electric field is produced in the dielectric. But the presence of the sharp tip emitter produces a compression of the equipotential lines at the tip, and thus a high electric field. Field enhancement is a geometric property and is strongly dependent on the sharpness of the tip. Note that the dielectric must hold off the unenhanced field, so field enhancement is essential for operation of field emitters. With field enhancement, a reasonable voltage applied to the extraction gate results in electron emission at the point.
As shown in
FIG. 1
, a vacuum packaged FED
10
includes a matrix-addressed cold cathode array
12
, spacers
14
that support atmospheric pressure and a cathodoluminescent anode
16
. Cathode array
12
is composed of row and column conductors separated by an insulating layer (not shown) with interspersed field emitter tips
17
. These layers are deposited on an insulating substrate
18
, such as glass. The locations where the rows and column cross define a pixel. The row conductors serve as the extraction gate and the column conductors connect to the cathodes.
Anode
16
is the phosphor screen and is composed of phosphor powders
20
, which are typically deposited within a black matrix on a glass substrate
22
. The entire anode
16
is covered with a thin aluminum layer, which acts both as a reflector to enhance brightness and as an anode voltage stabilizer by prevent charging of the phosphor powders. The cathode and screen, along with spacer materials, are aligned, sealed, and evacuated to complete the vacuum package.
Electron emission from each pixel is controlled by a forward bias between the gate and cathode. Once released from the confines of the bulk material, the emitted electrons are accelerated toward the phosphor screen. A focusing grid (not shown), which is biased at a negative potential with respect to the cathode, is often used to focus the electrons as they are accelerated toward the screen. The voltage applied to the screen must be higher than the cathode voltage or the emitted electrons. The screen voltage must also be high enough so that most of the electrons' energy remains once they penetrate the aluminum layer covering the phosphor particles.
As shown in FIG.
1
and in more detail in
FIG. 2
, drive electronics
24
are needed to control operation of the vacuum packaged FED, specifically the cathode array
12
. The drive electronics subsystems include a power module
26
, a video controller
28
, panel controller
30
, and row and column drivers
32
and
34
, respectively. The component subsystems will differ depending on whether the input is analog or digital.
For an analog composite video signal containing red, green, and blue (RGB) information and timing signals, video controller
28
samples the analog video signal, digitizes it, and separates it into RGB components. Horizontal and vertical timing information is also extracted from the composite input. Video controller
28
then presents the digitized video information to panel controller
30
in the form required by a standard digital video interface specification. This standard specifies digital RGB data up to 18 bits in parallel, horizontal and vertical sync, a pixel clock, and a data valid signal. Other processing that may be required in the video controller are gamma correction and adjustment of color saturation, brightness, and contrast.
In order to keep the FED compatible with other FPD technologies that accept digital input, panel controller
30
must accept the standard digital-interface signals and extract the signals necessary to drive the FED row and column drivers
32
and
34
. In most cases, the signals appearing at the digital interface are used directly by the row and column drivers, and the functionality of the panel controllers is minimal. However, depending on the dr
Boysel Robert Mark
Robinson William P.
MEMSolutions, Inc.
Vu Jimmy T.
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