Patent Application
20090026944
1. Field
This disclosure relates generally to field emission cathode structures, and more specifically, to field emission cathode structures featuring blade emitters and methods of making the same.
2. Related Art
Field Emission Displays (FEDs) are a form of flat CRT (Cathode Ray Tube). Thousands of electron emitters replace the single scanning e-beam of a typical CRT and also allow for manufacturing of a very flat CRT. However, costs for manufacturing FED cathode displays have been prohibitive. The cost of manufacturing of the FED cathode is a major impediment for this technology. This cost is driven by the need to use (i) expensive and low throughput equipment, for example, high resolution scanners and evaporation tools, or (ii) exotic technologies, for example, carbon nanotubes.
In addition, one known lateral-emitter field-emission device makes use of horizontal blades. However, such horizontal blades of the lateral-emitter field-emission device are unsuitable for being subjected to a roughening treatment. In addition, a face to face surface ratio of the horizontal blades of the lateral-emitter field-emission device to a corresponding extraction grid is very high and is also very sensitive to dielectric breakdown. While such a process for making horizontal blades is low cost, the method does not sufficiently allow for manufacturing effective and reliable emitters.
Accordingly, there is a need for an improved method and apparatus for overcoming the problems in the art as discussed above.
The present invention is illustrated by way of example and is not limited by the accompanying figures, in which like references indicate similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale.
The method and apparatus according to the embodiments of the present disclosure advantageously provide a novel integration scheme that greatly reduces a cost of manufacturing of FEDs. The method and apparatus also provide for the manufacturing of effective and reliable emitters.
According to the embodiments of the present disclosure, an FED includes a structure of vertical blade emitters. In the embodiments, a process integration to achieve the vertical blade emitter structures includes steps configured to increase the Fowler Nordheim effect of the vertical blade emitters. In one embodiment, a step configured to increase the Fowler Nordheim effect includes blade sharpening and micro structuration. In another embodiment, the step configured to increase the Fowler Nordheim effect includes layering of the vertical blade in order to increase its micro roughness.
The embodiments of the present disclosure overcome problems in the art, for example, with an electron emission enhancement obtained by treating the vertical blade structure with an anisotropic plasma. Such an anisotropic plasma would be detrimental for use in the case of the known lateral emitter structures, since it would undesirably attack the horizontal surfaces of the lateral emitter structure. In addition, the vertical blade structure according to the embodiments of the present disclosure also minimizes the face to face surface of emitter and extraction grid. Accordingly, this minimizes the risk of dielectric breakdown (e.g., a reliability concern) and the capacitance effect (e.g., a lower cost of drivers).
Accordingly, the embodiments of the present disclosure provide a method for the manufacturing of low cost/high reliability field emitters. While these emitters can be used for Field Emission displays, they can also be used as generic electron sources.
Column driver metal 14 comprises any suitable conductor, for example, including but not limited to Nichol or other suitable metal. Column driver metal 14 includes a thickness on the order of 1,000 to 4,000 angstroms, or other thickness selected according to the current carrying requirements of the column driver metal for a given field emission cathode structure implementation. The column driver metal 14 can be patterned within the field emission cathode structure according to the requirements of a given field emission cathode structure application. For example, column driver metal 14 can be patterned within a given pixel to provide a desired control of a series resistance between the column driver metal, the ballast layer, and a corresponding vertical sidewall blade (as discussed further herein below).
Ballast layer 16 comprises any suitable resistive ballast material that can act as a resistor, for example, including but not limited to amorphous silicon or the like. Ballast layer includes a thickness on the order of between 1,000 and 10,000 angstroms, or other thickness selected according to the requirements of the ballast resistance for a given field emission cathode structure implementation. Dielectric layer 18 comprises any suitable dielectric, for example, including but not limited to low cost, high quality, TEOS or the like. Dielectric layer 18 includes a thickness on the order of between 5,000 and 10,000 angstroms, or other thickness selected according to the requirements of the dielectric for a given field emission cathode structure implementation.
Line driver metal 20 comprises any suitable conductor, for example, including but not limited to Nichol or other suitable metal. Line driver metal 20 includes a thickness on the order of less than 1,000 angstroms, or other thickness selected according to the current carrying requirements of the line driver metal for a given field emission cathode structure implementation. In addition, the line driver metal 20 can be patterned within the field emission cathode structure according to the requirements of a given field emission cathode structure application.
In
Subsequent to the formation of trench 22, as shown in
Following the formation of conformal spacer layer 24 and blade metal layer 26, the field emission cathode structure 10 is processed with an anisotropic blade etch. The anisotropic blade etch can include any suitable directional plasma etch, wherein horizontal components of blade metal of layer 26 are removed, leaving vertically disposed portions (28, 30) of the blade metal along sidewalls of the conformal spacer layer 24 within trench 22, as shown in
Subsequent to the anisotropic blade etch, the structure is processed via a suitable spacer etch. The spacer etch removes portions of the conformal spacer layer 24, for example, portions previously occupied within recessed regions 36 and 38 and a bottom of the trench 22, and leaves remaining portions of sidewall spacers 32 and 34, as shown in
In addition, the thickness of the spacer layer 24 as indicated by reference numeral 40 advantageously establishes a desired spacing of the vertical sidewall blade (28, 30) from the sidewall of the trench 22, as well as, spacing of the vertical sidewall blade from an edge of the line metal layer 20. The spacing is selected as a function of a voltage to be applied between the vertical sidewall blade and the line metal layer. Furthermore, during operation, the electric field at the tip of the vertical sidewall blade varies inversely with respect to the spacing.
For example, in
The total thickness of the plurality of conformal blade metal layers (62, 64, 66, 68, and 70) can be on the order of less than or equal to 1000 angstroms. The first conformal blade metal layer 62 can include, for example, molybdenum (Mo), niobium (Nb), or other suitable transition metal, having a thickness that is a first percentage of the total thickness of the plurality of conformal blade metal layers. In one embodiment, the first conformal blade metal layer 62 is formed via suitable vacuum deposition techniques. The second conformal blade metal layer 64 can include, for example, molybdenum (Mo), niobium (Nb), or other suitable transition metal, having a thickness that is a second percentage of the total thickness of the plurality of conformal blade metal layers. In one embodiment, the second conformal blade metal layer 64 comprises the same material as the first conformal blade metal layer 62; however, it is formed via suitable vacuum deposition techniques different from the first conformal blade metal layer 62 such that the second conformal blade metal layer 64 has etch characteristics different from the etch characteristics of the first conformal blade metal layer 62. For example, second conformal blade metal layer 64 could be formed via suitable vacuum deposition techniques that include the addition of oxygen to produce a slightly oxidized metal.
In a similar manner, third, fourth, and fifth conformal blade metal layers 66, 68, and 70 are formed, wherein the etch characteristics of each is different from the etch characteristics of an adjoining layer. The individual layers of the conformal blade metal of the plurality of layers can have similar thicknesses to one another or different thickness to one another. In addition, the percentage thickness of each conformal blade metal layer of the plurality of layers cumulatively adds up to one-hundred percent of the total thickness of the plurality of conformal blade metal layers.
Subsequent to the formation of the plurality of conformal blade metal layers (62, 64, 66, 68, and 70), the field emission cathode structure 60 is processed with an anisotropic blade etch. The anisotropic blade etch can include any suitable directional plasma etch, wherein horizontal components of blade metal of the plurality of conformal blade metal layers (62, 64, 66, 68, and 70) are removed, leaving vertically disposed cumulative blade 72 that includes portions (74, 76, 78, 80, and 82) of the blade metal along sidewalls of the conformal spacer layer 24 within the trench. The method of the present disclosure thus provides for a self-aligned emitter structure. That is, formation of the cumulative sidewall blade comprises a self-aligned process in the fabrication of the emitter blade structures.
The tip of the cumulative emitter blade 72 advantageously provides for enhanced electron emission. That is, the field emission cathode structure 60 features a cumulative blade emitter formed with emission enhanced blade tips, wherein the height of individual ones of the blades of the cumulative emitter blade 72 varies in a manner that provides for emission enhancement. In particular, the field emission cathode structure 60 of
Subsequent to the anisotropic blade etch, the structure 60 is processed via a suitable spacer etch. The spacer etch removes portions of the conformal spacer layer 24, for example, portions previously occupied within recessed regions and a bottom of the trench, and leaves remaining portions of the sidewall spacer 25, as shown in
Subsequent to the formation of adhesion layer 92, a conformal blade metal layer 94 is formed overlying adhesion layer 92. Conformal blade metal layer 94 includes for example, grapheme having a thickness on the order of five angstroms (5 Å), having been formed by atomic layer deposition. Subsequent to the formation of blade metal layer 94, a conformal protective cap layer 96 is formed overlying blade metal layer 94. Conformal protective cap layer 96 includes any suitable protective cap layer, for example, silicon oxide or other oxide, having a thickness on the order of ten to fifty angstroms (10-50 Å), having been formed by atomic layer deposition.
Subsequent to the formation of the protective cap layer 96, the field emission cathode structure 90 are processed with an anisotropic blade etch. The anisotropic blade etch can include any suitable directional plasma etch, wherein horizontal components of the adhesive, blade metal, and protective cap layers are removed, leaving vertically disposed cumulative sidewall blade 98 comprising portions 100, 102, and 104 of the adhesive, blade metal, and protective cap layers, respectively, along sidewalls of the conformal spacer layer 24 within the trench. The method of the present disclosure thus provides for a self-aligned emitter structure. That is, formation of the cumulative sidewall blade comprises a self-aligned process in the fabrication of the emitter blade structures.
Subsequent to the anisotropic blade etch, the structure 90 is processed via a suitable spacer etch. The spacer etch removes portions of the conformal spacer layer 24, for example, portions previously occupied within recessed regions and a bottom of the trench, and leaves remaining portions of the sidewall spacer 25, as shown in
By now it should be appreciated that there has been provided a method for making a field emission cathode structure that comprises: forming a ballast layer over a column metal layer; forming a dielectric layer over the ballast layer; forming a line metal layer over the dielectric layer; forming a trench in the line metal layer and the dielectric layer, the trench extending to the ballast layer; and forming a sidewall spacer and a sidewall blade adjacent a sidewall of the trench, wherein the sidewall spacer is between the dielectric layer and the sidewall blade, and wherein the conformal spacer is recessed as compared to the sidewall blade such that a gap is present between the sidewall blade and the line metal layer. In another embodiment, a major surface of the sidewall blade is substantially perpendicular to a major surface of the line metal layer. The method further comprises roughening a tip of sidewall blade.
In yet another embodiment, the sidewall blade comprises a first metal layer and a second metal layer, wherein the first metal layer is a different metal than the second metal layer. In addition, the first metal layer is recessed as compared to the second metal layer. The method further comprises providing a substrate, wherein the column layer is formed over the substrate, and wherein a major surface of the sidewall blade is substantially perpendicular to a major surface of the substrate. In a further embodiment, the sidewall blade can comprise one of a metal, grapheme, or diamond-like-carbon.
In another embodiment, a method for making a field emission cathode structure comprises: forming a ballast layer over a column metal layer; forming a dielectric layer over the ballast layer; forming a line metal layer over the dielectric layer; forming a trench in the line metal layer and the dielectric layer, the trench extending to the ballast layer; forming a conformal spacer layer over the line metal layer and ballast layer, wherein the conformal spacer layer is conformal to a sidewall of the trench; forming a blade metal layer over the conformal spacer layer; removing portions of the blade metal layer to form a sidewall metal blade adjacent a sidewall of the trench; and removing portions of the conformal spacer layer to form a gap between the line metal layer and the sidewall metal blade, wherein a remaining portion of the conformal spacer layer remains between the dielectric layer and the sidewall metal blade. In one embodiment, the width of the trench is on the order of at least one micron.
In another embodiment, the method further comprises providing a substrate, wherein the column metal layer is formed over the substrate, and wherein a major surface of the sidewall metal blade is substantially perpendicular to a major surface of the substrate. In another embodiment, the method further comprises roughening a tip of the sidewall metal blade, wherein the roughening the tip of the sidewall metal blade comprises performing a plasma etch or wet pitting on the sidewall metal blade after the removing portions of the conformal spacer layer to form the gap.
In one embodiment, forming the blade metal layer over the conformal spacer layer comprises forming a first blade metal layer over the conformal spacer layer and a second blade metal layer over the first blade metal layer, and wherein the removing the portions of the blade metal layer comprises removing portions of the first blade metal layer and the second blade metal layer, wherein the sidewall metal blade is further characterized as a multiple layer blade. In another embodiment, the first blade metal layer is a different metal than the second blade metal layer. Furthermore, in yet another embodiment, after the removing the portions of the first blade metal layer and the second blade metal layer, a remaining portion of the first blade metal layer has a different height than a remaining portion of the second blade metal layer.
In one embodiment, a field emission cathode structure comprises a ballast layer over a column metal layer; a dielectric layer over the ballast layer; a line metal layer over the dielectric layer; a trench extending through the line metal layer and the dielectric layer to the ballast layer; a sidewall spacer adjacent a sidewall of the trench; and a sidewall blade adjacent the sidewall spacer, wherein the sidewall spacer is between the dielectric layer and the sidewall blade, and wherein a gap is present between the line metal layer and the sidewall blade. In one embodiment, the sidewall blade comprises a material selected from a group consisting of metal, grapheme, and diamond-like-carbon. In another embodiment, the sidewall blade comprises a plurality of different metal layers.
Although the invention has been described with respect to specific conductivity types or polarity of potentials, skilled artisans appreciated that conductivity types and polarities of potentials may be reversed.
Moreover, the terms “front,” “back,” “top,” “bottom,” “over,” “under” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.
Although the invention is described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. For example, the embodiments of the present disclosure can also be used for MEMS, sensors, SMARTMOS, and the like. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. Any benefits, advantages, or solutions to problems that are described herein with regard to specific embodiments are not intended to be construed as a critical, required, or essential feature or element of any or all the claims.
The term “coupled,” as used herein, is not intended to be limited to a direct coupling or a mechanical coupling.
Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles.
Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements.
