Electric lamp and discharge devices – With luminescent solid or liquid material – Vacuum-type tube
Reexamination Certificate
1997-12-04
2001-07-03
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Vacuum-type tube
C313S309000, C313S336000, C313S351000, C313S306000, C313S307000, C313S308000
Reexamination Certificate
active
06255771
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to field emitter arrays having an insulator structure surrounding each field emitter, groups of field emitters, or the perimeter of a field emitter group array. The invention also relates to methods of making such insulator structures.
BACKGROUND OF THE INVENTION
Microminiature field emitters are well known in the microelectronics art. These microminiature field emitters are finding widespread use as electron sources in microelectronic devices. For example, field emitters may be used as electron guns in flat panel displays for use in aviation, automobiles, workstations, laptops, head wearable displays, heads up displays, outdoor signage, or practically any application for a screen which conveys information through light emission. Field emitters may also be used in non-display applications such as power supplies, printers, and X-ray sensors.
When used in a display, the electrons emitted by a field emitter are directed to an cathodoluminescent material. These display devices are commonly called Field Emitter Displays (FEDs). A field emitter used in a display may include a microelectronic emission surface, also referred to as a “tip” or “microtip”, to enhance electron emissions. Conical, pyramidal, curved and linear pointed tips are often used. Alternatively, a flat tip of low work function material may be provided. An emitting electrode typically electrically contacts the tip. An extraction electrode or “gate” may be provided adjacent, but not touching, the field emission tip, to form an electron emission gap therebetween. Upon application of an appropriate voltage between the emitting electrode and the gate, quantum mechanical tunneling, or other known phenomena, cause the tip to emit electrons. In microelectronic applications, an array of field emission tips may be formed on the horizontal face of a substrate such as a silicon semiconductor substrate, glass plate, or ceramic plate. Emitting, electrodes, gates and other electrodes may also be provided on or in the substrate as necessary. Support circuitry may also be fabricated on or in the substrate.
The FEDs may be constructed using various techniques and materials, which are only now being perfected. Preferred FED's may be constructed of semiconductor materials, such as silicon. There are two predominant processes for making field emitters; “well first” processes, and “tip first” processes. In well first processes, such as a Spindt process, wells are first formed in a material, and tips are later formed in the wells. In tip first processes, the tips are formed first, and the wells are formed around the tips. There are multitudes of variations of both the well first and the tip first processes. The present invention is equally applicable to field emitters made by any process, whether it be well first, tip first, or some other type of process.
The electrical theory underlying the operation of an FED is similar to that for a conventional CRT. Electrons supplied by a cathode are emitted from the tips in the direction of the display surface. The emitted electrons strike phosphors on the inside of the display which excites the phosphors and causes them to momentarily luminesce. An image is produced by the collection of luminescing phosphors on the inside of the display screen. This process is a very efficient way of generating a lighted image.
In a CRT, a single electron gun is provided to generate all of the electrons which impinge on the display screen. A complicated aiming device, usually comprising high power consuming electromagnets, is required in a CRT to direct the electron stream towards the desired screen pixels. The combination of the electron gun and aiming device behind the screen necessarily make a CRT display. prohibitively thick.
FEDs, on the other hand, may be relatively thin. Each pixel of an FED has its own electron source, typically an array or grouping of emitting microtips. The voltage difference between the cathode and the gate causes electrons to be emitted from the microtips which are in electrical proximity with the cathode. The FEDs are thin because the microtips, which are the equivalent of an electron gun in a CRT, are extremely small. Further, an FED does not require an aiming device, because each pixel has its own electron gun (i.e. an array of emitters) positioned directly behind it. The emitters need only be capable of emitting electrons in a direction generally normal to the FED substrate.
With reference to
FIG. 1
, a basic FED emitter device
10
may include a glass substrate
100
with a cathode line
200
provided thereon. A current limiter
300
may be provided on the cathode line
200
, and emitters
500
may be provided on the current limiter
300
. The current limiter
300
may include an insulating or near insulating layer
310
and a resistive layer
350
. By way of example, the resistive layer
350
may comprise an 8%-50% chromium—silicon oxide mixture.
The emitters
500
, are preferably shaped to have a fine point
510
which enhances the electron emission capability of the emitters. The emitters
500
may be provided in wells
410
formed in a layer of insulator material
400
. A gate line
600
may be provided over the insulator layer
500
with holes in the gate line above the emitters
500
. The edges of the holes in the gate lines may be referred to as the gates
610
for the respective emitters. Plural emitters
500
may be arranged into groups
520
having a square, rectangular, circular, or some other geometric pattern as viewed from above.
With reference to
FIG. 2
, a plan view of several groups
520
of emitters are shown as arranged over adjacent cathode lines
200
and in adjacent gate lines
600
. The cross section A—A identified in
FIG. 2
can be viewed in detail in FIG.
1
. The cathode lines or columns
200
and the gate lines or rows
600
typically run across the display perpendicular to one another. Each grouping (or pixel)
520
may contain hundreds or even thousands of individual emitters
500
. Only four (
4
) emitters are shown per grouping in
FIG. 2
for ease of illustration. Plural cathode lines
200
may be arranged in parallel vertical columns, and plural gate lines
600
may be arranged in parallel horizontal rows to form a matrix of “columns” and “row”.
The emitters
500
of the grouping
520
may emit electrons when an intersecting cathode line
200
and gate line
600
are both activated. Activation of the gate lines may be achieved simply by periodically applying a voltage to each of the gate lines in sequence in accordance with a raster scan using simple drivers. For example, in a 480 row FED, each gate line or row may expect to be “on” for {fraction (1/480)} of the time. Activation of the cathode line is produced by selectively lowering the voltage of the cathode line to increase the potential difference between the cathode line and the gate line or row. The selective decrease in the cathode line voltage allows for the provision of a gray scaled display with more colors than might be expected. Drivers with gray level capability are only required for the cathode lines because they are the only lines which require selective variation of the voltages thereon.
Referring back to
FIG.1
, emission of electrons from the tips
510
is brought about by generating an electrical field at the tips which is conducive to electron emission. The fine point of the tips concentrates the electric field at the tips and enhances the likelihood that electrons will tunnel from the tips in a generally upward direction. To achieve emission, this electric field must be generated in conjunction with the application of a particular voltage to the cathode line
200
underlying the emitter tips
510
. The electrical field may be generated by increasing the positively charged voltage applied to the gate line
600
. Consequently, the electrons are induced to tunnel from the tips
510
and travel upwards under the influence of the positively charged gates
610
toward a much more positively biased anode
700
(not shown in
Howard Webster E.
Jones Gary W.
Lloyd Stewart
Zimmerman Steven M.
Collier Shannon Scott PLLC
eMagin Corporation
Haynes Mack
Patel Nimeshkumar D.
Yohannan David R.
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