A FOCAL PLANE ARRAY INCORPORATING ULTRA-SMALL RESONANT STRUCTURES

COPYRIGHT NOTICE

[0001] 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.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present invention is related to the following co-pending U.S. Patent applications which are all commonly owned with the present application, the entire contents of each of which are incorporated herein by reference:

1. U.S. Application No. 11/302,471, entitled "Coupled Nano-Resonating Energy Emitting Structures," filed December 14, 2005,

2. U.S. Application No. 11/349,963, entitled "Method And Structure For Coupling Two Microcircuits," filed February 9, 2006;

3. U.S. Patent Application No. 11/238,991 , filed September 30, 2005, entitled "Ultra-Small Resonating Charged Particle Beam Modulator";

4. U.S. Patent Application No. 10/917,511 , filed on August 13, 2004, entitled "Patterning Thin Metal Film by Dry Reactive Ion Etching";

5. U.S. Application No. 11/203,407, filed on August 15, 2005, entitled "Method Of Patterning Ultra-Small Structures";

6. U.S. Application No. 11/243,476, filed on October 5, 2005, entitled "Structures And Methods For Coupling Energy From An Electromagnetic Wave";

7. U.S. Application No. 11/243,477, filed on October 5, 2005, entitled "Electron beam induced resonance,"

8. U.S. Application no. 11/325,448, entitled "Selectable Frequency Light Emitter from Single Metal Layer," filed January 5, 2006;

9. U.S. Application No. 11/325,432, entitled, "Matrix Array Display," filed January 5, 2006,

10. U.S. Patent Application No. 11/400,280, titled "Resonant Detector for Optical Signals," filed April 10, 2006.

FIELD OF THE DISCLOSURE

[0003] This relates to micro-electromagnetic resonant detectors, and, more particularly, to using such devices in focal plane arrays.

GLOSSARY

[0004] Ultra-small resonant structure: 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.

[0005] Micro-electromagnetic resonant detector cell: detects electromagnetic radiation by angularly modulating a beam of charged particles and comprises at least a charged particle source, at least one detector and at least one ultra-small resonant structure.

INTRODUCTION & BACKGROUND

[0006] A focal plane array (FPA) is a matrix of detector cells. FPAs are frequently connected to or built on a semiconductor chip. FPA detector cells are composed of materials that are responsive to particular frequencies of electromagnetic radiation (EMR). The particular frequencies the detector cells are responsive to depends on the application. The response of all the detector cells in the array can be combined to form a composite image. One of the most common imaging application is digital photography, i.e. generating an image from detector cells that are responsive to frequencies in the visible light range. However, there is a growing market for devices that create images from detector cells that are responsive to a variety of electromagnetic frequencies including those not in the visible light spectrum.

[0007] Microbolometers have FPAs consisting of detector cells made from materials that produce a change in electrical resistivity in accordance with a temperature change i.e. a change in infrared radiation. Commercially available microbolometers have FPAs with a resolution of 320x240 and a response speed of 30 fps. Micrcobolometers are an uncooled type of bolometer as opposed to a cooled type which typically requires cryogenic cooling to minimize noise. Cooled sensors offer greater sensitivity, but are

more expensive because of the cost required to cool them. Furthermore, mircobolometers are limited by their response speed. Thus, it is desirable to produce a microbolometer type device with increased sensitivity and a better response speed, but without the added costs of temperature controls.

[0008] The more specific aspects of the various other focal point arrays and the various other devices which employ them are known to the artisan and for brevity will not be repeated herein.

[0009] U.S. Pat. Application No. 11/400,280, noted above describes various arrangements of ultra-small resonant structures that can be used to angularly modulate a beam of charged particles directed past them, when exposed to incoming or received EMR. The ultra-small structure(s) may comprise, for instance, any number of nano-sized resonant structures constructed and adapted to angularly modulate a beam of charged particles in responses to observed electromagnetic waves such that EMR can be detected e.g., as described above and/or in U.S. Patent Applications nos. 11/243,476; 11/400,280 (each described in greater detail above).

[0010] It is desirable to use one or more ultra-small resonant structures or arrays thereof, to create a FPA for use in imaging applications, in particular mircobolometery.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The following description, given with respect to the attached drawings, may be better understood with reference to the non-limiting examples of the drawing, wherein the drawings show:

[0012] Figure 1: Diagrammatically shows an imaging device; [0013] Figure 2: Shows an enlarged diagrammatic view of a micro-electromagnetic radiation detector cell; and

[0014] Figure 3: Shows an enlarged diagrammatic view of an alternative micro- electromagnetic radiation detector cell.

DESCRIPTION OF THE PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS [0015] As shown in Fig. 1, an imaging device 10 that includes a lens system 11 and at . least one Focal Point Array (FPA) 12 comprised of a plurality of micro-electromagnetic resonant detector cells, where each micro-electromagnetic resonant detector cell is

denoted as ED ₁ , ED ₂ ...ED _n . An enlarged view of the surface of the FPA 12 is shown to the right of the imaging device 10. EMR 13 is focused through the lens system 11 and is absorbed by the surface of the FPA 12. The structure set forth in Fig.l is intended to be exemplary only and is not intended to limit the ways in which a FPA can or might absorb EMR 13. It should be noted, that the FPA 12 may be capable of moving within the housing of the imaging device 10 e.g. the FPA 12 may be capable of rotating about an axis or tilting about an axis.

[0016] Each detector cell ED ₁ -ED _n includes a charged particle source, at least one detector and at least one ultra-small resonant structure. It should be noted that although the detectors cells ED _n S are shown to be rectangular in shape, this should not be viewed in any limiting way, but is used purely for exemplary purposes ED _n S could be other shapes (e.g. hexagons, etc.), or any combination of shapes, without departing from the scope of the present invention. Furthermore, although the ED _n S are shown with there faces on a single plane this is not intended to be limiting, the ED _n S may face different directions, e.g. the ED _n S may be orthogonal to each other.

[0017] Fig. 2 shows an enlarged view of an exemplary detector cell ED _n which includes a charged particle source 21 that generates a beam of charged particles 23, a detector 22, and an ultra-small resonant structure 20.

[0018] The details of detection are set forth in the above referenced U.S. Pat. Application No. 11/400,280 and will not be repeated herein. However, in brief the charged particle source 21 generates the particle beam 23 that passes along or next to at least one ultra-small resonant structure 20. The particle beam 23 may comprise any type of charged particles (such as, e.g., positive ions, negative ions, electrons, protons and the like) and the charged particle source 21 may be any desired source of charged particles such as an ion gun, a thermionic filament, tungsten filament, a cathode, a vacuum triode, a planar vacuum triode, an electron-impact ionizer, a laser ionizer, a field emission cathode, a chemical ionizer, a thermal ionizer, an ion-impact ionizer, an electron source from a scanning electron microscope, etc.

[0019] With no incoming EMR being received, the charged particle beam 23 will , simply pass by the ultra-small resonant structure to the center of the detector 22. However, the ultra-small resonant structures 20 will angularly modulate the charged

particle beam 23 when they receive EMR 13. The ultra-small resonant structure 20 may be any of the ultra-small resonant structures disclosed in the related applications. In general, the structures have one physical dimension that is smaller than the wavelength of visible light.

[0020] As described in U.S. Patent Application 11/243,476 when the energy of an electromagnetic wave 13 is absorbed by an ultra-small resonant structure 20, the transfer causes plasmons on the ultra-small resonant structure 20 to resonate. The ability of an electromagnetic wave to induce the surface plasmons to resonate is described in one or more of the above applications including No. 11/400,280 and is not repeated herein. [0021] The ultra-small resonant structures 20 will resonate in accordance with the characteristics of an incoming electromagnetic wave 13 (for example, intensity, frequency, polarization, etc.), such that the amplitude of the electric field in the ultra- small resonant structures bears a relation to a electromagnetic wave 13 characteristic. When the ultra-small resonant structures 20 resonate as a result of electromagnetic wave 13 being received the path of the particle beam 23 will be altered from its natural or normal path 23a. The amount the path of the particle beam 23a will be altered is related to the amplitude of the electrical field in the ultra-small resonant structures 20. Thus, the alteration of the particle beam from the normal or natural path 23a can be related to a characteristic of incoming electromagnetic wave 13. That is, the amplitude of a characteristic of an incoming electromagnetic wave 13 can be calculated by measuring the alteration of the particle beam path 23a. Exemplary altered paths of particle beams are shown as 23b and 23c, on both sides of 23a depending on the particular characteristics of electromagnetic wave 13.

[0022] As described in U.S. Patent Application 11/400,280, the detector 22 comprises charged particle absorption elements (e.g. receiving electrodes) that are placed at locations corresponding to altered paths 23b-23c and detector elements (e.g. differential current detector) that detect which particle absorption element absorbed particles from the particle beam 23 (i.e. to what extent was the particle beam 23 angularly modulated). Detectorportions 22 typically comprise an absorption element that receives the unaltered particle beam 23a and a series of detector elements that receive various altered particle beams 23b-23c. Further details of detecting the deflected particle beam are disclosed in

U.S. Patent Application 11/400,280 and will not be described herein. Alternative methods of detecting the deflected particle beam will be recognizable to the artisan who understands from this description the structure and purpose of the detector portion 22. [0023] Fig. 3 shows an enlarged view of an exemplary ED _n with multiple detector portions 32a-c and multiple ultra-small resonant structures 30a-c. A single beam source 31 provides particle beams 33a-c to ultra-small resonant structures 30a-c. This may be accomplished by having a beam source 31 that is capable of providing particle beams 33a-c to ultra-small resonant structures 30a-c simultaneously via beam splitters, or the like, or by having a beam source 31 that provides particle beams 33a-c to each ultra-small resonant structure 30a-c at a different time. It should be noted that although Figure 3 shows an ED _n with three ultra-small resonant structures and three detectors this is not intended to be limiting. In fact, any number of ultra-small resonant structures and corresponding detectors could be incorporated into a detector cell, so long as each ultra- small resonant structure can angularly modulate a particle beam and a the corresponding detector can detect the modulation.

[0024] The ED _n in Figure 3 functions in a similar manner to the ED _n described in accordance with Figure 2, the difference being that it uses multiple detector portions 32a- c and multiple ultra-small resonant structures 30a-c which allows the ED _n to gather more information about the incoming characteristics of the incoming electromagnetic radiation 13. For example, each ultra-small resonant structure 30a-c could be tuned to resonant at different frequencies of received EMR 13. In addition, one ultra-small resonant structure could be tuned to resonant in response to receiving EMR of a particular frequency while another ultra-small resonant structure is tuned to resonant in response to receiving EMR of a particular polarity.

[0025] The various micro-electromagnetic resonant detector cells ED _n may be made, e.g., using techniques such as described in U.S. Patent Applications Nos. 10/917,511; 11/203,407 (described in greater detail above), or in some other manner. [0026] The micro-electromagnetic resonant detectors cells ED _n of an array may all be of the same type, or each may have a unique architecture, that is each may have a unique type of electrical beam source, each may use different ultra-small resonant structures, each may have a different number of ultra-small resonant structures, each may use

US2006/024215

different types of detector portions, and each may have a different number of detector portions or any combination of the foregoing. For example, an array could contain a number of the ED _n S shown in Fig. 2 and a number of the ED _n S shown in Fig. 3 where each ED _n is responsive to a particular EMR characteristic (e.g. intensity, frequency, polarity, etc.). In the case where ED _n S of an array are responsive to the polarization of an

EMR wave, each ED _n S can respond a different type of polarization (e.g. orthogonal polarizations).

[0027] More than one array of micro-electromagnetic resonant detector cells may be used within a signal imaging device. For example, an array could be used for each type of electromagnetic characteristic. Furthermore, when an imaging device comprises multiple arrays, the arrays can be configured such a way that their faces are on the same plane or the arrays can be configured so that each array faces a different direction, e.g. the faces of the arrays may be orthogonal to one another.

[0028] The mirco-electromagnetic resonant detector cells ED _n may be formed at a linear density of 10,000 per inch.

[0029] The FPA described above may be included in any imaging device, including, without limitation, e.g. digital cameras, microbolometers and any device measuring EMR from the infrared to ultraviolet range. In theory, the present invention could be used to measure EMR throughout the EMR spectrum. It should be noted that the present invention is only limited by the degree to which a particle beam can be angularly modulated by an ultra-small electromagnetic detecting resonant structures receiving EMR and the degree to which angular modulations can be measured and correlated to characteristics of an EMR wave.

[0030] Furthermore, the FPA described in accordance with the present invention can be used in various imaging technologies such as: 3D imaging technologies that incorporate spinning arrays, imaging technologies that filter EMR before it is received by the FPA, imaging technologies that use multiple lenses and complex lens architectures, imaging technologies that use high shutter speeds, imaging technologies that measure reflected

EMR and the like.

[0031] All of the ultra-small resonant structures described are preferably under vacuum conditions during operation. Accordingly, in each of the exemplary embodiments

described herein, the entire package which includes the ultra-small resonant structures may be vacuum packaged. Alternatively, the portion of the package containing at least the ultra-small resonant structure(s) should be vacuum packaged. Our invention does not require any particular kind of evacuation structure. Many known hermetic sealing techniques can be employed to ensure the vacuum condition remains during a reasonable lifespan of operation. We anticipate that the devices can be operated in a pressure up to atmospheric pressure if the mean free path of the electrons is longer than the device length at the operating pressure.

[0032] While certain configurations of structures have been illustrated for the purposes of presenting the basic structures of the present invention, one of ordinary skill in the art will appreciate that other variations are possible which would still fall within the scope of the appended claims. 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.