Diamond field emission tip and a method of formation

A portion of the disclosure of this patent document contains material which is subject to copyright or mask work protection. The copyright or mask work owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright or mask work rights whatsoever.

This application is related to and claims priority from U.S. patent application Ser. No. 11/238,991, titled “Ultra-Small Resonating Charged Particle Beam Modulator,” and filed Sep. 30, 2005, the entire contents of which are incorporated herein by reference. This application is related to U.S. patent application Ser. No. 10/917,511, filed on Aug. 13, 2004, entitled “Patterning Thin Metal Film by Dry Reactive Ion Etching”; U.S. application Ser. No. 11/203,407, entitled “Method Of Patterning Ultra-Small Structures,” filed on Aug. 15, 2005; U.S. patent application Ser. No. 11/243,476, filed on Oct. 5, 2005, entitled “Structures and Methods For Coupling Energy From An Electromagnetic Wave”; and, U.S. application Ser. No. 11/243,477, titled “Electron Beam Induced Resonance,” filed on Oct. 5, 2005, all of which are commonly owned with the present application at the time of filing, and the entire contents of each of which are incorporated herein by reference.

This disclosure relates to an improved charged particle field emission tip.

Electromagnetic Radiation & Waves

Electromagnetic radiation is produced by the motion of electrically charged particles. Oscillating electrons produce electromagnetic radiation commensurate in frequency with the frequency of the oscillations. Electromagnetic radiation is essentially energy transmitted through space or through a material medium in the form of electromagnetic waves. The term can also refer to the emission and propagation of such energy. Whenever an electric charge oscillates or is accelerated, a disturbance characterized by the existence of electric and magnetic fields propagates outward from it. This disturbance is called an electromagnetic wave. Electromagnetic radiation falls into categories of wave types depending upon their frequency, and the frequency range of such waves is tremendous, as is shown by the electromagnetic spectrum in the following chart (which categorizes waves into types depending upon their frequency):

The ability to generate (or detect) electromagnetic radiation of a particular type (e.g., radio, microwave, etc.) depends upon the ability to create a structure suitable for electron oscillation or excitation at the frequency desired. Electromagnetic radiation at radio frequencies, for example, is relatively easy to generate using relatively large or even somewhat small structures.

Electromagnetic Wave Generation

There are many traditional ways to produce high-frequency radiation in ranges at and above the visible spectrum, for example, up to high hundreds of Terahertz. As frequencies increase, however, the kinds of structures needed to create the electromagnetic radiation at a desired frequency become generally smaller and harder to manufacture. We have discovered ultra-small-scale devices that obtain multiple different frequencies of radiation from the same operative layer and that these ultra small devices can be activated by the flow of beams of charged particles.

Myriad benefits and advantages can be obtained by a ultra-small resonant structure that emits varying electromagnetic radiation at higher radiation frequencies such as infrared, visible, UV and X-ray. For example, if the varying electromagnetic radiation is in a visible light frequency, the micro resonant structure can be used for visible light applications that currently employ prior art semiconductor light emitters (such as LCDs, LEDs, and the like that employ electroluminescence or other light-emitting principals). If small enough, such micro-resonance structures can rival semiconductor devices in size, and provide more intense, variable, and efficient light sources. Such micro resonant structures can also be used in place of (or in some cases, in addition to) any application employing non-semiconductor illuminators (such as incandescent, fluorescent, or other light sources).

The use of radiation per se in each of the above applications is not new. But, obtaining that radiation from particular kinds of increasingly small ultra-small resonant structures revolutionizes the way electromagnetic radiation is used in and can be used in electronic and other devices.

As used throughout this document:

The phrase “ultra-small resonant structure” shall mean any structure of any material, type or microscopic size that by its characteristics causes electrons to resonate at a frequency in excess of the microwave frequency.

The term “ultra-small” within the phrase “ultra-small resonant structure” shall mean microscopic structural dimensions and shall include so-called “micro” structures, “nano” structures, or any other very small structures that will produce resonance at frequencies in excess of microwave frequencies.

Brief Description of Figures

The invention is better understood by reading the following detailed description with reference to the accompanying drawings in which:

FIG. 1 shows a diagrammatic cross-section of a first step in the production cycle of a first embodiment of the present invention;

FIG. 2 shows a diagrammatic cross-section of the next step in the production cycle of a first embodiment of the present invention;

FIG. 3 shows a diagrammatic cross-section of the next step in the production cycle of a first embodiment of the present invention;

FIG. 4A shows the results of etching a diamond layer during the formation of diamond emission tips according to a first embodiment of the present invention;

FIG. 4B shows a completed diamond field emission tip from the structure of FIG. 4A ;

FIG. 5 shows a diagrammatic cross-section of a first step in the production cycle of a second embodiment of the present invention;

FIG. 6 shows a diagrammatic cross-section of a first step in the production cycle of a second embodiment of the present invention;

FIG. 7A shows a diagrammatic cross-section of a metal layer etching step in the production cycle of a second embodiment of the present invention;

FIG. 7B shows a completed diamond field emission tip from the structure of FIG. 7A ; and

FIG. 8 is a schematic of a charged particle modulator that velocity modulates a beam of charged particles according to embodiments of the present invention.

FIG. 9 is an electron microscope photograph illustrating an example ultra-small resonant structure according to embodiments of the present invention.

FIG. 10 is an electron microscope photograph illustrating the very small and very vertical walls for the resonant cavity structures according to embodiments of the present invention.

FIG. 11 shows a schematic of a charged particle modulator that angularly modulates a beam of charged particles according to embodiments of the present invention.

FIGS. 12( a )- 12 ( c ) are electron microscope photographs illustrating various exemplary structures according to embodiments of the present invention.

FIG. 8 depicts a charged particle modulator 200 that velocity modulates a beam of charged particles according to embodiments of the present invention. As shown in FIG. 8 , a source of charged particles 202 is shown producing a beam 204 consisting of one or more charged particles. The charged particles can be electrons, protons or ions and can be produced by any source of charged particles including cathodes, tungsten filaments, planar vacuum triodes, ion guns, electron-impact ionizers, laser ionizers, chemical ionizers, thermal ionizers, or ion impact ionizers. The artisan will recognize that many well-known means and methods exist to provide a suitable source of charged particles beyond the means and methods listed.

Beam 204 accelerates as it passes through bias structure 206 . The source of charged particles 202 and accretion bias structure 206 are connected across a voltage. Beam 204 then traverses excited ultra-small resonant structures 208 and 210 .

An example of an accretion bias structure is an anode, but the artisan will recognize that other means exist for creating an accretion bias structure for a beam of charged particles.

Ultra-small resonant structures 208 and 210 represent a simple form of ultra-small resonant structure fabrication in a planar device structure. Other more complex structures are also envisioned but for purposes of illustration of the principles involved the simple structure of FIG. 8 is described. There is no requirement that ultra-small resonant structures 208 and 210 have a simple or set shape or form. Ultra-small resonant structures 208 and 210 encompass a semi-circular shaped cavity having wall 212 with inside surface 214 , outside surface 216 and opening 218 . The artisan will recognize that there is no requirement that the cavity have a semi-circular shape but that the shape can be any other type of suitable arrangement.

Ultra-small resonant structures 208 and 210 may have identical shapes and symmetry, but there is no requirement that they be identical or symmetrical in shape or size. There is no requirement that ultra-small resonant structures 208 and 210 be positioned with any symmetry relating to the other. An exemplary embodiment can include two ultra-small resonant structures; however there is no requirement that there be more than one ultra-small resonant structure nor less than any number of ultra-small resonant structures. The number, size and symmetry are design choices once the inventions are understood.

In one exemplary embodiment, wall 212 is thin with an inside surface 214 and outside surface 216 . There is, however, no requirement that the wall 212 have some minimal thickness. In alternative embodiments, wall 212 can be thick or thin. Wall 212 can also be single sided or have multiple sides.

In some exemplary embodiments, ultra-small resonant structure 208 encompasses a cavity circumscribing a vacuum environment. There is, however, no requirement that ultra-small resonant structure 208 encompass a cavity circumscribing a vacuum environment. Ultra-small resonant structure 208 can confine a cavity accommodating other environments, including dielectric environments.

In some exemplary embodiments, a current is excited within ultra-small resonant structures 208 and 210 . When ultra-small resonant structure 208 becomes excited, a current oscillates around the surface or through the bulk of the ultra-small structure. If wall 212 is sufficiently thin, then the charge of the current will oscillate on both inside surface 214 and outside surface 216 . The induced oscillating current engenders a varying electric field across the opening 218 .

In some exemplary embodiments, ultra-small resonant structures 208 and 210 are positioned such that some component of the varying electric field induced across opening 218 exists parallel to the propagation direction of beam 204 . The varying electric field across opening 218 modulates beam 204 . The most effective modulation or energy transfer generally occurs when the charged electrons of beam 204 traverse the gap in the cavity in less time then one cycle of the oscillation of the ultra-small resonant structure.

In some exemplary embodiments, the varying electric field generated at opening 218 of ultra-small resonant structures 208 and 210 are parallel to beam 204 . The varying electric field modulates the axial motion of beam 204 as beam 204 passes by ultra-small resonant structures 208 and 210 . Beam 204 becomes a space-charge wave or a charge modulated beam at some distance from the resonant structure.

Ultra-small resonant structures can be built in many different shapes. The shape of the ultra-small resonant structure affects its effective inductance and capacitance. (Although traditional inductance an capacitance can be undefined at some of the frequencies anticipated, effective values can be measured or calculated.) The effective inductance and capacitance of the structure primarily determine the resonant frequency.

Ultra-small resonant structures 208 and 210 can be constructed with many types of materials. The resistivity of the material used to construct the ultra-small resonant structure may affect the quality factor of the ultra-small resonant structure. Examples of suitable fabrication materials include silver, high conductivity metals, and superconducting materials. The artisan will recognize that there are many suitable materials from which ultra-small resonant structure 208 may be constructed, including dielectric and semi-conducting materials.

An exemplary embodiment of a charged particle beam modulating ultra-small resonant structure is a planar structure, but there is no requirement that the modulator be fabricated as a planar structure. The structure could be non-planar.

Example methods of producing such structures from, for example, a thin metal are described in commonly-owned U.S. patent application Ser. No. 10/917,511 (“Patterning Thin Metal Film by Dry Reactive Ion Etching”). In that application, etching techniques are described that can produce the cavity structure. There, fabrication techniques are described that result in thin metal surfaces suitable for the ultra-small resonant structures 208 and 210 .

Other example methods of producing ultra-small resonant structures are described in commonly-owned U.S. application Ser. No. 11/203,407, filed on Aug. 15, 2005 and entitled “Method of Patterning Ultra-Small Structures.” Applications of the fabrication techniques described therein result in microscopic cavities and other structures suitable for high-frequency resonance (above microwave frequencies) including frequencies in and above the range of visible light.

Such techniques can be used to produce, for example, the klystron ultra-small resonant structure shown in FIG. 9 . In FIG. 9 , the ultra-small resonant klystron is shown as a very small device with smooth and vertical exterior walls. Such smooth vertical walls can also create the internal resonant cavities (examples shown in FIG. 10 ) within the klystron. The slot in the front of the photo illustrates an entry point for a charged particle beam such as an electron beam. Example cavity structures are shown in FIG. 10 , and can be created from the fabrication techniques described in the above-mentioned patent applications. The microscopic size of the resulting cavities is illustrated by the thickness of the cavity walls shown in FIG. 10 . In the top right corner, for example, a cavity wall of 16.5 nm is shown with very smooth surfaces and very vertical structure. Such cavity structures can provide electron beam modulation suitable for higher-frequency (above microwave) applications in extremely small structural profiles.

FIGS. 10 and 11 are provided by way of illustration and example only. The present invention is not limited to the exact structures, kinds of structures, or sizes of structures shown. Nor is the present invention limited to the exact fabrication techniques shown in the above-mentioned patent applications. A lift-off technique, for example, may be an alternative to the etching technique described in the above-mentioned patent application. The particular technique employed to obtain the ultra-small resonant structure is not restrictive. Rather, we envision ultra-small resonant structures of all types and microscopic sizes for use in the production of electromagnetic radiation and do not presently envision limiting our inventions otherwise.

FIG. 11 shows another exemplary embodiment of a charged particle beam modulator 220 according to embodiments of the present invention. In these embodiments, the source of charged particles 222 produces beam 224 , consisting of one or more charged particles, which passes through bias structure 226 .

Beam 224 passes by excited ultra-small resonant structure 228 positioned along the path of beam 224 such that some component of the varying electric field induced by the excitation of excited ultra-small resonant structure 228 is perpendicular to the propagation direction of beam 224 .

The angular trajectory of beam 224 is modulated as it passes by ultra-small resonant structure 228 . As a result, the angular trajectory of beam 224 at some distance beyond ultra-small resonant structure 228 oscillates over a range of values, represented by the array of multiple charged particle beams (denoted 230 ).

FIGS. 12( a )- 12 ( c ) are electron microscope photographs illustrating various exemplary structures operable according to embodiments of the present invention. Each of the figures shows a number of U-shaped cavity structures formed on a substrate. The structures may be formed, e.g., according to the methods and systems described in related U.S. patent application Ser. No. 10/917,511, filed on Aug. 13, 2004, entitled “Patterning Thin Metal Film by Dry Reactive Ion Etching,” and U.S. application Ser. No. 11/203,407, filed on Aug. 15, 2005, entitled “Method Of Patterning Ultra-Small Structures,” both of which are commonly owned with the present application at the time of filing.

Thus are described ultra-small resonating charged particle beam modulators and the manner of making and using same.

Below we describe methods for forming an improved, diamond field emission tip that will act as a source of charged particles for use with ultra-small resonant structures. A surface of a micro-resonant structure is excited by energy from an electromagnetic wave, causing the micro-resonant structure to resonate. This resonant energy interacts as a varying field. A highly intensified electric field component of the varying field is coupled from the surface. A source of charged particles, referred to herein as a beam, is provided. The beam can include ions (positive or negative), electrons, protons and the like. The beam may be produced by any source, including, e.g., without limitation an ion gun, a tungsten filament, a cathode, a planar vacuum triode, an electron-impact ionizer, a laser ionizer, a chemical ionizer, a thermal ionizer, an ion-impact ionizer.

The beam travels on a path approaching the varying field. The beam is deflected or angularly modulated upon interacting with a varying field coupled from the surface. Hence, energy from the varying field is transferred to the charged particles of the beam. Characteristics of the micro-resonant structure including shape, size and type of material disposed on the micro-resonant structure can affect the intensity and wavelength of the varying field. Further, the intensity of the varying field can be increased by using features of the micro-resonant structure referred to as intensifiers. Further, the micro-resonant structure may include structures, nano-structures, sub-wavelength structures and the like, as are described in the above identified co-pending applications which are hereby incorporated by reference.

An improved charged particle emission tip includes diamond as one of the principle tip materials, together with a highly conductive metal as an improved charged particle source.

In manufacturing such a field emission tip, a substrate material 10 , such as silicon as shown in FIG. 1 , provides a starting base layer. A diamond layer 12 is then formed on or deposited, typically by using a chemical vapor deposition (CVD) technique, on the upper surface 20 of the substrate 10 . Thereafter, a layer of photoresist 14 is formed at discrete locations on, or across the entire upper exposed surface of diamond layer 12 .

The “photoresist” layer 14 is then patterned, as shown in FIG. 2 , by using one or more etching techniques, including, for example, isotropic etching, RIE etching techniques, lift off or chemical etching techniques, to form holes having vertical sidewalls 17 . This is followed, as shown in FIG. 2 , by etching the diamond layer using, for example, a reactive ion etch that is tuned to provide an isotropic etch as is known to those skilled in the art. It is preferred to completely etch through the full height of the diamond layer 12 down to the substrate's upper surface 20 . It is also preferred to form the etched holes in the diamond layer 12 with angled side walls 18 , for example at a discrete angle to the substrate's upper surface 20 which is thereby exposed in that etched opening. This angle of side walls 18 relative to the upper surface 20 will preferably range from about 91° to about 135°, with the preferred range of angles being 95° to 120°.

A conductive material, such as, for example, silver (Ag) 22 , is then preferably electroplated into the etched patterned areas of the diamond layer 12 as shown in FIG. 3 . Other deposition techniques could be used as well, so long as the desired amount of silver, or other conductive metal, is deposited. It is preferred to have the deposited silver 22 remain within the vertical confines of the patterned areas within the diamond layer 12 and that the silver not migrate onto or across the top surface 24 of the diamond layer 12 . The silver will typically extend above the surface of the diamond layer when the hole is completely filled. It is desired to nearly fill the hole, leaving the edge 34 at least slightly exposed. That way, edge 34 will comprise the emission edge or tip. The shape of the extended portion 26 of the deposited silver 22 can be one of a variety of shapes including curved, polygonal, spherical or other shape. Regardless of the exact shape of the extending portion of the conductive material, what is desired is that some volume of the deposited material, such as the silver material 22 , extend above the horizontal level of diamond surface 24 . It is also desirable that the conductive material 22 come as close as possible to the upper edge 34 of the diamond material 12 .

Following the electroplating of the conductive material, e.g., the silver 22 , the diamond layer 12 will be further etched, for example by plasma etching, to cut away the diamond material 12 close to the deposited material thus forming the side wall 32 of the diamond layer and forming as well the shaped structure 30 . This structure 30 can be formed into a number of shapes including, for example, a circular collar or ring that extends around and is in tight contact against the conductive material, silver 22 , as is shown in FIG. 4A . As noted above, the structure 30 can be segmented rather than a continuous structure, with the segments be of any desired shape or portion of the total structure.

The outer side walls 32 of the resulting final shape 30 will preferably be formed at 90° to the surface 20 of the substrate 10 , and the upper edge 34 of the diamond structure 30 preferably extends only a part of the way up the total vertical height of the deposited silver 22 and will comprise the edge, line or tip from which emissions will occur.

Thereafter, the substrate 10 will be cut into individual, separate pieces thereby forming finished individual emission tips each of which being comprised of the silver material 22 , the diamond material 30 surrounding at least the base of the silver material 22 and the underlying substrate 10 as is shown in FIG. 4B .

A second method of forming diamond field emission tips begins with a substrate 40 of typically silicon on which a diamond layer 42 , shown by the dotted lines in FIG. 5 was formed by being deposited, for example, by CVD techniques. The diamond layer 42 is thereafter suitably patterned by depositing a layer of a photoresist or e-beam resist material, such as PMMA, and which is then patterned by one or more of the techniques mentioned above. Optionally, and intermediate hard mask of material, such as SiO 2 or metal may be used. The diamond layer is then etched by using typically oxygen plasma etching techniques. When the photoresist is removed this process will have created a plurality of vertically extending, separated, individual diamond posts 44 , shown in FIG. 5 in full line. Each diamond post 44 can have any shape that is desired and constructed by the pattern chosen, and the shape can be arbitrary as long as an edge, corner, tip or other sharp area is created from which the emissions will occur. The height can range from about 100 nm to about 1000 nm, and a width ranging from about 100 nm to about 500 nm, although these dimensions are not to be construed as limiting, but are rather only exemplary in the context of this invention.

With reference to FIG. 6 , a layer of highly conductive metal 46 , for example, silver (Ag), is then deposited or otherwise formed on and around the diamond posts 44 , for example, by employing sputter deposition process, thereby covering them with a metal layer preferably about 100 nm thick. The layer 46 can be shaped to extend around the posts 44 or layer 46 can undulate over and around the diamond posts 44 .

As shown in FIG. 7A , following the step of depositing the conductive metal layer 46 , an etching process, for example slightly anisotropic reactive ion etching, will be used to remove selected portions of metal layer 46 so that a portion 50 remains on the top surface 48 of posts 44 , and a triangular cross-sectional shaped portion 52 extends about the outer circumference of each of the posts 44 . The remaining conductive metal layer 46 preferably extends from a position adjacent the upper edge of the posts 44 , leaving the upper edge 58 of the diamond exposed, down to and in contact with the top surface of substrate 40 . It is preferred to have the outer wall 54 of the roughly triangular portion 52 form an angle between the top surface 56 of substrate 40 and the outer wall 54 ranging from about 95° to about 120°. Similarly, the metal 50 remaining on the outer ends of posts 44 can have a spherical, triangular, rounded or other shape. However, it should be understood that the metal structure 52 could have other shapes, such as, for example, and that structure could also be either fully enclosing the outer circumference of posts 44 or could extend around posts 44 in a segmented manner.

In the end, the final structure is formed as shown in FIG. 7B where the metal structure 52 is formed about the sides of the diamond posts 44 substantially in the form of a triangular cross-sectional structure, as well as a small amount of metal 50 on the exposed top surface of the posts 44 along with the exposed upper edge 58 which will act as the emission edge or area. Preferably, there will be more metal adjacent the base of the posts 44 than there is near the top of the posts.

Following the completion of the formation steps, the substrate will be cut apart thereby forming individual diamond emission tips as in FIG. 7B .

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.