Patent for “Amorphic diamond film flat-field emission cathode”

Nanotechnology – Nalin Kumar, Chenggang Xie, Applied Nanotech Holdings Inc

Search Patent for “Amorphic diamond film flat-field emission cathode”

Abstract for “Amorphic diamond film flat-field emission cathode”

A field emission cathode is described that comprises a layer made of conductive material and an amorphic layer of diamond film. These layers act as low-effective work-function materials. They are deposited on top of the conductive material to create emission sites. Each emission site contains at least two sub-regions with differing electron affinity. The cathode can be used to create a computer screen or a fluorescent light source.

Background for “Amorphic diamond film flat-field emission cathode”

Field emission refers to a phenomenon where an electric field near the surface of an emitting material narrows the width of a potential barrier at the surface. This allows for a quantum tunnelling effect, in which electrons pass through the potential barrier and are released from the material. This is in contrast to thermionic emissions, which is when electrons are ejected from a material by heating it. Field emission is a quantum mechanical phenomenon while thermionic emissions is a classical phenomenon.

The field strength needed to cause field emission of electrons from a material’s surface depends on its effective “work function”. Many materials have a positive function, and therefore require an intense electric field to induce field emission. Some materials have a low electron affinity or a work function and therefore do not require strong fields to cause emission. These materials can be deposited on a conductor as a thin film. This creates a cathode that has a low threshold voltage to emit electrons.

“In the prior art devices it was possible to increase field emission of electrons through providing for a cathode geo that focused electron emission at one, relatively sharp point at the tip of a conical Cathode (called micro-tip cathode). These cathodes have been used for many years with extraction grids located near the cathodes.

“For example, U.S. Pat. No. No. 4,857 799 was issued to Spindt and al. on August 15, 1989. It is directed at a matrix-addressed flatpanel display using field emission cathodes. The cathodes are integrated into the display backing structure and activate the corresponding cathodoluminescent zones on a faceplate. In the preferred embodiment, the face plate is placed 40 microns away from the cathode arrangement. A vacuum is also provided between the plate (and cathodes) in this space. The spacing is maintained by spacers that look like legs interspersed between the pixels. Electrical connections to the bases of the cathodes can be diffused sections through a backing structure. Spindt et al. Spindt et al. employ a number of micro-tip field emission capacitors in a matrix arrangement with the tips aligned with apertures in the extraction grid above the cathodes. The display described by Spindt and al. can be made with an anode added to the extraction grid. It is a three-terminal (triode) display.

Micro-tips are difficult to make because they have intricate geometries. If the micro-tips do not have the same geometry throughout the display, there will be variations in the emission from tip to tip, which can lead to uneven illumination. These micro-tip displays can be expensive because of the tight tolerances involved in manufacturing.

“For many years, others have concentrated considerable effort on solving the problem of mass-producing cathodes to tight tolerances. This allows them to perform with precision and accuracy. One of the objectives of prior art inventions was to use emission materials with a low effective work function in order to reduce extraction field strength.

“An example of such an effort is found in U.S. Pat. No. No. 3,947 716 was issued on March. 3,947,716, which was issued on Mar. A vacuum is created by heating pulses within an electrostatic field. This creates thermal field buildup in a chosen plane. The emission patterns of this plane are then observed. Once the desired plane is identified, the heating process within the electrostatic field continues until the tip is heated to the desired temperature. The tip is then vaporized with the adsorbent. This process results in a faceted tip. The emitting surface has a lower work function, while the non-emitting surface has a higher work function. The tip is then coated with a metal adsorbent, which results in significantly improved emission characteristics. These micro-tip cathodes can be expensive to make due to their intricate geometries. Because emission comes from a very sharp tip, it can be a little inconsistent between cathodes. These disadvantages are more severe when many cathodes have to be used in large numbers, such as in flat panel displays for computers.

“As you can see in the cathode structure above, a key attribute of a good cathode design consists of minimizing the cathode’s work function. Some substances, such as elemental carbon in diamond crystals form and alkali metals, have a low effective function. Many inventions have been made to find suitable geometries that can be used as cathodes with negative electron affinity substances as a cathode coating.

“For instance, U.S. Pat. No. No. 3,970,887 was issued on Jul. 3,970,887 was issued on Jul. To form micro-anode structures, an insulating and overlying conductor layer can be formed over the semiconductor substrate in the following order. Electrical isolation can be achieved by appropriately doping the semiconductor substrate in order to create opposite conductivity-type areas at each field emission location and forming the appropriate conductive layer. Smith and colleagues. Smith et al. Smith et al. Fraser, Jr. et. al. has the same drawbacks.”

“U.S. Pat. No. No. 4,307.507 was issued Dec. 29, 1981 to Gray et. It describes a method for manufacturing a field emitter array cathode structure. In this process, a substrate of single-crystalline material is selectively mask so that islands are created on the substrate. The single crystal material under the unmasked areas is orientation-dependent etched to form an array of holes whose sides intersect at a crystal graphically sharp point.”

“U.S. Pat. No. No. Busta et al. disclose a method for manufacturing. This allows for a sharp-tipped capode.”

U.S. Pat. No. No.

“Yet another sharply-tipped emission cathode has been disclosed in U.S. Pat. No. No. Gray et al. Gray et al. describe a method for fabricating soft aligned field emitter arrays by using a soft leveling planarization technique. A spin-on process

Sharp-tipped cathodes can cause major problems in flat-panel graphic displays, even though they use low-effective work-function materials to their advantage. They are expensive to produce. They are also difficult to produce with high consistency. The tip is where electron emission occurs from sharp-tipped cathodes. The tip must be made with great precision so that electron emission from sharp-tipped cathodes does not occur at the tip in a matrix of cathodes. This creates an uneven visual display. To put it another way, cathodes must also be manufactured more accurately to avoid inconsistencies in brightness along their surfaces.

“In Ser. No. No. 07/851 701, filed Mar. 16, 1992 and was entitled “Flat Panel Display Based On Diamond Thin Films”, which was refiled as a continuation of application Ser. No. No. No. No. 5,543,684 was disclosed on Aug. 6, 1996. An alternative cathode design was also first revealed. U.S. Pat. No. No. 5,543,684 describes a cathode with a relatively flat emission surface, as opposed to the micro-tip configuration. In its preferred embodiment, the cathode employs a field emission material with a low effective work function. The material is laid on top of a conductive layer to form a plurality emission sites that can emit electrons in the presence a low intensity electric field.

Flat cathodes are less costly and more difficult to make in large quantities because they lack the micro-tip geometry. In this article, we discuss the advantages of flat cathodes. U.S. Pat. No. No.

“The discovery of amorphic diamond is a relatively recent advancement in materials science. In Thin-Film Diamond (published in the Texas Journal of Science vol. ), the structure and characteristics of an amorphic diamond is discussed in detail. 41, no. 4, 1989, by C. Collins et al. Collins et al. Collins et al. describe a laser deposition method for producing an amorphic, diamond-like film. Amorphic diamond is composed of a number of micro-crystallites. Each of these structures depends on the method used to prepare the film.

“Diamond is a neutral electorate. This means that only a low electric field is needed to distort any potential barriers on the diamond’s surface. Diamond is therefore a desirable material to be used in conjunction with field emission catalysts. The prior art actually used crystalline diamond films as an emission surface for micro-tip cathodes.

S. Bajic and R. V. Latham, from the Department of Electronic Engineering and Applied Physics at Aston University, Aston Triangle in Burmingham B4 7ET received May 29, 1987. They describe a new composite resin-carbon field emitting cathode that switches on at low applied fields of approximately 1.5 MV m-1. The I-V characteristic has stable emission currents of >/=1 mA at moderate applied frequencies of usually 8 MV m-1. Direct electron emission imaging has revealed that the total externally recorded current is due to a high density and random distribution of emission sites over the cathode’s surface. The observed characteristics have been qualitatively explained by a new hot-electron emission mechanism involving a two-stage switch-on process associated with a metal-insulator-metal-insulator-vacuum (MIMIV) emitting regime. The graphite powder is mixed into a resin compound, which results in larger grains. This results in fewer emission sites, as the area of particles in the resin compound is smaller. To achieve a uniform brightness from low voltage sources, it is preferable to have a greater number of sites.

“The prior art fails to (1) exploit the unique properties and field emission cathodes of amorphic diamond; (2) allow for field emission cathodes with a greater diffused area from where field emission can occur; (3) allow for a higher concentration of emission sites (i.e. smaller particles or crystallites) in order to produce uniform electron emission from each site; however, a low voltage source is required to produce the required field to emit the electrons.

“The prior art failed to recognize that an amorphic, or a combination of different forms of diamonds, is a good emitting material. U.S. Pat. No. No. 5,543,684 was first to describe the use of amorphic diamond film as an emission material. The preferred embodiment of the invention, described herein, used amorphic diamond film in conjunction with a flat structure as an emission cathode to create a completely different field emission cathode design.

The present invention further enhances the use of amorphic diamond by depositing the diamond micro-crystallites on the cathode surface in such a way that there is a percentage of crystals that are in the SP2 configuration at each region. Another percentage emerges in the SP3 configuration. There are many discontinuities between the SP2 configurations and SP3 configurations in each region. The SP2 crystallites have different electron affinities.

“Accordingly, in order to take advantage the above-noted possibilities, it is a primary object the present invention provide an independently addressable catheter. The catheter comprises a layer conductive material and a thin layer amorphic diamond film. Each layer has a plurality distributed electron emission sites. Sub-regions have differing electron affinity between them.

“In the preferred embodiment of this invention, the amorphic diamant film is deposited as an extremely flat emission surface. Flat cashodes are simpler and therefore less costly to make and easier to control the emission from during display operation.

“The technical advantage of the invention is that it provides a cathode with emission sites having electrical properties that include discontinuous boundaries with different electron affinities.”

“Another technical advantage to the invention is to provide an emission site that contains dopant atoms.”

“Another technical advantage of the invention is that it provides a cathode in which a dopant is carbon.”

“Yet another technical advantage of this invention is that it provides a cathode in which emission sites have multiple bonding structures.”

“The present invention provides a cathode with SP3 as a bonding structure at the emission site. This is a technical advantage.”

“The present invention still has the technical advantage of providing a cathode in which each emission site has a plurality bonding orders, including SP3.

“Another technical advantage to the invention is that it provides a cathode in which emission sites contain dopants from an element other than a low-effective work-function material.” The dopant element in the case of using amorphic, or low-effective work-function materials as the cathode is not carbon.

“The present invention also provides a cathode that contains discontinuities in the crystalline structure. These discontinuities can be either line defects, point defects, or dislocations.

“The invention also includes novel operations for a flat panel LCD and the use of amorphic diamant as a coating on an electromagnetic wire screen or as an element in a cold cathode fluorescent bulb.”

“The preferred embodiment of this invention is an amorphic-diamond film cold-cathode consisting of a substrate, a layer conductive material, an electronic resistive pillar deposited above the substrate, and an amorphic-diamond film layer deposited over that conductive material. The amorphic film has a relatively flat emission area comprising multiple distributed micro-crystallite emission sites with differing electron affinity.

“The above has provided a broad overview of the technical features and advantages of the present invention so that you may better understand the detailed description that follows.”

“Additional features, advantages and a description of the invention will also be provided hereinafter. These are the subject of the claims. The inventive concept and its specific embodiment can be used to modify or design other structures. This is a benefit that should be recognized by all who are skilled in the art. Those skilled in the art should realize that similar constructions to the invention do not violate the spirit or scope of the invention, as defined in the appended claims.

“Turning now towards FIG. 1. This is a cross-sectional view of the cathode as well as the substrate according to the present invention. The cathode 10, generally referred to as 10, includes a resistive layer 11, an effective work-function emitter 12 and an intermediate layer 13. The cathode 10, which is also known as the cathode conductive 14 sits on top of a substrate 15. U.S. Pat. describes in detail the structure and function of the cathode 10, as well as the relationship between the cathode 10, conductive layer 14, and substrate 15. No. No.

“Now, turn to FIG. 2 is a top-view of the cathode 10, FIG. 1. In the preferred embodiment, the emitter layer 12 is an amorphic diamond movie that contains a number of micro-crystallites of diamonds in an overall amorphic structure. The micro-crystallites are formed when the amorphic material is deposited on to the metal layer 13. This can be done by laser plasma deposition. C. B. Collins et al. have published a paper titled “Laser Plasma Source of Amorphic Diamond”, January 1989. It discusses one such process.

“Micro-crystallites are formed with specific atomic structures that depend on the environment during deposition and a little luck. A certain percentage of crystals will form in an SP2 configuration (two-dimensional bonding carbon atoms) at a given temperature and environmental pressure. An SP3 configuration will yield a smaller percentage of crystals. An SP3 configuration has a lower electron affinity than the SP2 configuration for carbon and graphite microcrystallites. FIG. 2 shows the SP3 configuration of micro-crystallites. They have a lower electron affinity than micro-crystallites made from carbon or graphite. 2. A plurality of black spots are found in the emitter layer 12.

“The flat surface is basically a microscopically flat. However, a particular surface morphology is not necessary. However, enhancement factors can be increased by small features that are typical of any thin polycrystalline polycrystalline. This could improve emission characteristics. Some micro-tip geometries can result in a higher enhancement factor. In fact, the present invention may be used in a microtip or ‘peaked” structure.

“Turning Now to FIG. 3 shows a better view of FIG. 2. For example, there are a variety of micro-crystallites 31, 32 and 33. The micro-crystallites 31 and 33 are shown with an SP2 configuration. Micro-crystallite 34 shows an SP3 configuration. FIG. FIG. 3 shows that micro-crystallite34 is surrounded with micro-crystallites of an SP2 configuration.

“There are many randomly distributed localized emission sources per unit of surface area. These emission sites have different electronic properties than the rest of the film. These conditions could be one or more of the following:

“1) The presence of a doping element (such as carbon), in the amorphic diacritic diamond lattice.

“2: A change in the bonding structure of SP2 to SP3 within the same micro-crystallite.

“3) A change in the order in which the bonding structure is formed in the same microcrystallite.

“4) An impurity (perhaps an atom dopant) of an element other than that in the film material.

“5” is an interface between various micro-crystallites.

“6. Impurities or differences in bonding structure at the microcrystallite boundary.

“(7) Other defects, such as dislocations or point defects.”

“The art of making each of these conditions is well-known.”

Doping is one of the conditions that can create micro-crystallites with different characteristics. Interjecting elemental carbon in the diamond during deposit can be used to dop amorphic-diamond thin films. Statistics will show that micro-crystallites with different structures can be made by doping carbon. Some micro-crystallites may be n-type. A non-carbon dopant could also be used depending on the emission site characteristics and desired percentage. In flat panel displays, cathodes that have only one emission site can function well. For optimal functioning, however, it is desirable to have 1-10 n-type microcrystallites per square millimeter. The present invention produces micro-crystallites with a diameter of less than 1 micron, and more commonly, 0.1 micron.

“Emission from cathode 10, FIG. 1 is caused by a potential difference between the cathode 10, and an anode (not illustrated in FIG. 1), which is separated from the cathode 10 by a small distance. This potential is a small distance from the cathode 10.

“In the following example, we will assume that there is a condition that can create micro-crystallites with different work functions. This will be a change of the bonding structure between SP2 and SP3 within the same microcrystallite (condition #3). Referring to FIGS. FIGS. 2 and 3 show that micro-crystallites with an SP3 configuration have lower electron affinity and work-function than those with an SP2 configuration. The voltage between the anode and cathode 10 will increase until the SP3 microcrystallites begin to emit electrons. The SP3 microcrystallites present on the cathode 10 will produce enough electron emission to excite it (not shown). However, the voltage levels must be raised to sufficient to allow emission from the SP2 microcrystallite. By controlling the temperature, pressure, and method of deposition, the SP3 microcrystallites can be made large enough to produce enough electron emission.

“Now, let’s move to FIG. 4. This is a cross-sectional image of a flat panel display using the cathode according to the present invention. As shown in FIG. 10, the cathode 10 is still on its cathode-conductive layer 14 and substrate 15. 1 has been mated with an anode, commonly designated 41, and consisting of a substrate 42. In the preferred embodiment, it is glass. Indium Tin Oxide layer 43 is deposited on the substrate 42. A phosphor layer 44 is added to the anode conductive layer in order to show electron flow from the cathode 10 visually. To put it another way, electrons from the cathode will flow towards the anode 43 when there is a potential difference between them. However, the phosphor 44 will emit light through the substrate 42 and cause the phosphor to emit light. This will provide a visual indication of electron flow that can be used with other video equipment or computers. Insulated separators 45 and 46 separate the anode41. These provide separation between the anode 11 and the cathode 10. All of this is in compliance with U.S. Pat. No. 5,543,684.”

“Further,” in FIG. 4. The voltage source 47 is represented by a positive and negative poles 48 and 49. The source 47 couples the positive pole to the anode conductor layer 43. The source 47 couples the negative pole to the source 47. While the source 47 couples the negative pole to the cathodeconductive layer 14. If the voltage from the source 47 is sufficient high, the device 47 will impress a potential difference between cathode 10, and anode41. This causes electron flow between cathode 10, and anode41.

“Turning to FIG. 9 shows illustrated computer 90, which includes keyboard 93, disk drive94, hardware 92, and display 91. Display 91 may use the present invention to provide images and text. Anode 41 is all that is visible in the present invention.

“Turning to FIG. 5 shows a diagram of a coated wire matrix emitter, usually designated 51. The wire mesh 51 is made up of a number of rows and columns that are electrically connected at their intersection points. To create a wire mesh cathode, the wire mesh 51 is coated with a material with a low effective function and electron affinity such as amorphic diamant. This allows for the application of high current and potential differences to produce incandescence, and flow of electrons from a mesh to an anode. Incandescence is not necessary due to the amorphic coating of diamonds and its associated lower work functions. The wire mesh 51 cathode is therefore able to be used at room temperatures to emit electrons.

“Turning to FIG. 6 shows a cross-sectional view of a wire that has been coated with a material with low electron affinity and work-function. The wire is designated 61. It has a coating 62 that has been applied by laser plasma deposition or any other well-known technique to allow the coating 62 act as a cold catalyst in the same way as the cathodes in FIGS. 1-5.”

“Turning now, to FIG. 7 shows one use of the wire 61. The coated wire 61 acts as a conductive filament. A glass tube 72 acts as an anode, and contains an electrical contact (73). This creates a fluorescent tube. The tube works in an analogous way to the flat panel display described in FIGS. 1-5 refers to a potential difference between wire 61 (negative), and tube 72 that is sufficient to overcome the space charge between cathode wire 6 and tube anode 72. After the space-charge is overcome electrons will flow from the emission site SP3 microcrystallites within the coating 62.

“Turning to FIG. 8 is a partial end view of the Florescent Tube 71 in FIG. 7. The FIG. 61 wire and the coating 62 are again shown. 6 together form the fluorescent tube’s low-effective work-function cathode 71. FIG. 72 shows the glass tube 72. 7. The glass tube 72 of FIG. 7 consists of a glass wall 81, on which is coated an anide conductive layer (82). The anode-conductive layer 82 is electrically connected to the electrical contact (73) of FIG. 7. Finally, a layer of phosphor 83 is placed on the anode conductor layer 82. Electrons flow between the emitter layer 82 and the anode conductor layer 82 when a potential difference between the cathodewire 61 and the layer 82 is created. As shown in FIG. However, as in FIG. The fluorescent tube in FIGS. The fluorescent tube of FIGS. 7 and 8 uses a cathode with a low-effective work-function emitter such as an amorphic diamond film. This ensures that the tube doesn’t get too warm while in operation. This saves the energy that would otherwise be wasted on traditional fluorescent tubes as heat. The heat is also not generated and therefore can be removed later by air conditioning.

“Even though the advantages of the present invention have been explained in detail, it is important to understand that many modifications, substitutions, and alterations may be made without departing from its spirit and scope as described by the attached claims.”

Summary for “Amorphic diamond film flat-field emission cathode”