Abstract:
A method for displaying and storing or otherwise recording images includes use of an image detection apparatus that includes a field emission array with an image-sensing surface, an image-displaying surface opposite the image-sensing surface, and integral signal transmission circuits. As appropriate voltages are applied and the image-sensing surface of the field emission array is exposed to an image, p-n junctions near the image-sensing surface generate electron-hole pairs, which cause electrons to be transferred to a corresponding n-well. The change in voltage may result in the emission of electrons from an emitter tip that corresponds to the n-well and, thus, the display of an image by a display panel positioned adjacent to, but spaced apart from, the image-displaying surface. Additionally, changes in voltage in the n-well may be communicated in such a way that they are stored or recorded.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a divisional of application Ser. No. 09/386,906, filed Aug. 31, 1999, pending. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an integrated apparatus that senses or detects electromagnetic radiation and displays the sensed or detected radiation. Particularly, the present invention relates to an apparatus that senses or detects electromagnetic radiation of visible or near infrared wavelengths and that displays the sensed or detected radiation in the form of a visible image. More particularly, the present invention relates to an apparatus that senses or detects electromagnetic radiation, displays an image representative of the sensed or detected radiation, and transmits signals representative of the detected radiation. The present invention also relates to devices that include the inventive apparatus.  
         [0004]     2. Background of Related Art  
         [0005]     Semiconductor devices, such as charge coupled devices (“CCDs”) have long been employed to detect radiation, such as electromagnetic radiation. Charge coupled devices typically include an array of pixels, each of which includes an n-well, which is a region of n-type or n-doped silicon, in a p-type, or p-doped, silicon substrate. N-type semiconductor regions are typically relatively negatively electrically charged and conduct current by means of electrons. P-type semiconductor regions are relatively positively electrically charged and conduct current by means of electron hole pairs. The junction between the p-type substrate and the n-well, which is also referred to as a p-n junction or as a depletion region, typically has little or no mobile electrical charge. As radiation (e.g., photons) impinges the p-n junction, electron-hole pairs proportionate to the amount of radiation are created therein. Stated another way, as the p-n junction of a pixel is irradiated, electrons, or electrical impulses, move from the p-n junction into the adjacent n-well of the pixel.  
         [0006]     Since the p-n junctions of charge coupled devices convert radiation to an electrical signal, charge coupled devices have been employed to detect radiation (e.g., electromagnetic radiation), and to transmit electrical signals representative of the detected radiation by means of circuitry associated with the pixels of these charge coupled devices. Accordingly, charge coupled devices have been used in various image detection applications, such as in digital cameras.  
         [0007]     Some field emission arrays similarly include a p-type silicon substrate with relatively electrically conductive n-wells extending therethrough and, therefore, p-n junctions. Field emission arrays have conventionally been employed in association with cathodo-luminescent display panels, in the form of field emission displays (“FEDs”), in order to display images.  
         [0008]     Typically, the field emission array of a field emission display includes an array of emission pixels, each of which includes one or more substantially conical emitter tips. Each of the emitter tips is electrically connected to a relatively negative voltage source, or an electron source, by means of a cathode conductor line, which is also typically referred to as a column line.  
         [0009]     Another set of electrically conductive lines, which are typically referred to as row lines or as gate lines, extend over the emission pixels of the field emission array. Row lines typically extend across a field emission display substantially perpendicularly to the direction in which the column lines extend. Accordingly, the paths of a row line and of a column line typically cross proximate (above and below, respectively) the location of one or more emitter tips. The row lines of a field emission array are electrically connected to a relatively positive voltage source. Thus, as a voltage is applied across both the column line and the row line that intersect at one or more emission pixels, electrons are emitted by the emitter tips of those emission pixels and accelerated through an opening in the row line.  
         [0010]     As electrons are emitted by emitter tips and accelerate past the row line that extends over the emission pixel, the electrons are directed toward a corresponding display pixel of a positively charged cathodo-luminescent panel of the field emission display, which is spaced apart from and substantially parallel to the field emission array. As electrons impact a display pixel of the cathodo-luminescent panel, the display pixel is illuminated. The degree to which the display pixel is illuminated depends upon the number of electrons that impact the display pixel.  
         [0011]     As the field emission array and its associated cathodo-luminescent display are both generally planar structures and are disposed relatively close to one another, the field emission display (“FED”) devices of which the field emission array and cathodo-luminescent display are a part are typically relatively thin, flat devices. Thus, field emission displays are compact relative to display devices that include cathode ray tubes, and have found widespread use in many types of portable electronic devices, such as portable computers and video cameras, or “camcorders”.  
         [0012]     Field emission arrays have also been employed to detect radiation (e.g., electromagnetic radiation of a visible wavelength or electrons) and to transmit electrons representative of the detected radiation. Exemplary devices which employ field emission arrays in such a manner are disclosed in U.S. Pat. No. 3,466,485 (hereinafter “the &#39;485 Patent”), issued to John R. Arthur, Jr. et al. on Sep. 9, 1969; U.S. Pat. No. 3,814,968 (hereinafter “the &#39;968 Patent”), issued to Harvey C. Nathanson et al. on Jun. 4, 1974; U.S. Pat. No. 5,804,833 (hereinafter “the &#39;833 Patent”), issued to Roger Stettner et al. on Sep. 8, 1998; and U.S. Pat. No. 5,818,500 (hereinafter “the &#39;500 Patent”), issued to Jon K. Edwards et al. on Oct. 6, 1998.  
         [0013]     The &#39;485 Patent discloses a light sensitive field emission array with emitter tips that intensify a detected light image. As light is directed toward the back side of the field emission array, photons create current in the emitter tips corresponding to the areas of the back side upon which light is directed.  
         [0014]     The &#39;968 Patent discloses a radiation sensitive field emission array that is similar to that disclosed in the &#39;485 Patent. The emitter tips of the field emission array of the &#39;968 Patent emit electrons in response to an input radiation, such as light or electrons. The emitted electrons are directed to a display screen that displays the detected image.  
         [0015]     The field emission array of the &#39;833 Patent detects and displays images in a similar manner. In addition to detecting and displaying visible light images, however, the field emission array of the &#39;833 Patent can also detect electromagnetic radiation wavelengths from visible light up to far infrared wavelengths (i.e., from about 300 nm up to about 1×10 6  nm) and display images representative of electromagnetic radiation of these wavelengths. Applicable uses of such a field emission array would be in so-called “night vision” applications.  
         [0016]     These patents do not, however, disclose field emission arrays that include components that transmit signals representative of the detected images. Thus, the radiation-sensitive field emission arrays of these patents may not be employed to detect radiation, to display images representative of the radiation, and to substantially simultaneously transmit signals representative of the radiation to another source, such as to recording componentry.  
         [0017]     Accordingly, there is a need for a field emission array that detects radiation and substantially simultaneously displays an image representative of the detected radiation and transmits detectable signals representative of the radiation. A relatively compact apparatus that detects radiation and displays images and transmits signals that are representative of the radiation is also needed.  
       SUMMARY OF THE INVENTION  
       [0018]     The integrated field emission array sensor, display, and transmitter of the present invention includes a field emission array having a semiconductor substrate with an array of n-wells and, thus, p-n junctions defined therein, an array of emitter tips adjacent and corresponding to the p-n junctions, and circuitry associated with each pixel of the array.  
         [0019]     The field emission array substrate is preferably a semiconductive material, such as silicon. The substrate may be p-type or p-doped semiconductor material, and therefore conducts current by means of electron hole pairs (i.e., the p-type semiconductor material is relatively electron deficient).  
         [0020]     Regions of conductively doped n-type semiconductive material, which are referred to herein as n-type semiconductor wells or simply as n-wells, are defined in the substrate. These n-wells may comprise the column lines of a field emission array. N-type semiconductive materials conduct current by means of the free electrons of a dopant material.  
         [0021]     The interface between each n-well and the p-type semiconductor substrate of the field emission array defines a so-called “p-n junction” or “n-p junction”. A depletion region, which includes relatively non-charged materials, exists at the p-n junction. Thus, as is known in the art, a contact potential exists at the p-n junction.  
         [0022]     The back side of the substrate (i.e., p-type semiconductor material) of the field emission array comprises a radiation detection surface, which is also referred to herein as a detection surface, as a sensor surface, or as a radiation sensitive surface. As radiation such as photons (i.e., quanta of electromagnetic radiation) enter a pixel through the radiation detection surface, the radiation impedes a p-n junction of the field emission array, and electron hole pairs are created in the p-n junction.  
         [0023]     As electron hole pairs are created in the p-n junction, a substantially proportionate number of electrons move into the n-well from the p-n junction. Thus, the voltage of the n-well decreases. The radiation detection surface is preferably shielded from further radiation until a signal representative of the radiation incident with the pixel has been transmitted.  
         [0024]     Each pixel of the inventive apparatus includes a signal transmission circuit associated with the n-well of that pixel. The signal transmission circuit includes a capacitor, a first side of which communicates with the n-well and a second side of which is a source node of a first transistor or otherwise communicates with a source node of the first transistor. The drain node of the first transistor communicates with a baseline potential (V DD ). A second transistor shares a source node with the first transistor. The drain node of the second transistor communicates with a scan circuit of a type known in the art, such as the circuits employed in digital cameras.  
         [0025]     As the voltage of the n-well of an emission pixel decreases, the voltage of the n-well is communicated to the first side of the capacitor. As the source node of the first transistor and, thus, the second side of the capacitor, is preferably charged to the baseline potential, the voltage at the second side of the capacitor and, thus, the voltage of the source node of the second transistor drops until it is substantially the same as the voltage of the n-well. Upon turning the second transistor “on” (i.e., upon opening the gate of the second transistor), the voltage is transferred to the drain node of the second transistor. The voltage of the second transistor, which is now substantially representative of the amount and type of radiation that impinged the p-n junction of the emission pixel, may then be measured by the scan circuit that communicates with the drain node of the second transistor. Upon turning the gate of the second transistor “off”, the source node of the second transistor is electrically isolated from the voltage of the n-well. A value representative of the voltage measured by the scan circuit at the drain node of the second transistor, which represents the radiation detected by the emission pixel, may then be stored, as known in the art.  
         [0026]     Each emission pixel of the field emission array further includes at least one emitter tip that protrudes from an emission surface of the field emission array located opposite the detection surface. The emission pixels are preferably disposed substantially over and in communication with the associated n-wells of the field emission array.  
         [0027]     As the gate of the first transistor is opened, the source node of the first transistor and, thus, the second side of the capacitor, is charged to the baseline potential (V DD ). As a relatively positive voltage is applied to a conductive member of an extraction grid, or grid anode, overlying the emission pixel, due to the potential difference between the grid anode and the emitter tip, electrons may be drawn from the n-well, into the associated emitter tip, and emitted from the emitter tip. As the electrons are emitted from the emitter tip and through the extraction grid, they are directed toward a corresponding display pixel of an cathodo-luminescent display and illuminate the same in a manner that represents the wavelength or intensity of radiation that impinged the emission pixel that corresponds to the display pixel upon impinging the display pixel. The n-well will then return substantially to the baseline potential. Another image may be detected and a representative signal transmitted by exposing the radiation detection surface to radiation, closing the gate of the first transistor, and repeating the process.  
         [0028]     Other features and advantages of the present invention will become apparent to those of ordinary skill in the art through consideration of the ensuing description, the accompanying drawings, and the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0029]      FIG. 1  is a schematic representation of a field emission array according to the present invention;  
         [0030]      FIG. 1A  is a schematic representation of a field emission array according to the present invention, which includes a detection enhancement material to facilitate the detection infrared and longer wavelengths of electromagnetic radiation;  
         [0031]      FIG. 2  schematically illustrates a circuit including transistors that may be employed in the field emission array according to the present invention;  
         [0032]      FIG. 2A  schematically illustrates a variation of the circuit depicted in  FIG. 2 , which includes a switch between the n-well and the capacitor;  
         [0033]      FIG. 3  is a flow chart that illustrates the method of the present invention;  
         [0034]      FIG. 4  is a schematic representation of a system wherein a field emission array according to the present invention is employed to detect radiation, to display images representative of the detected radiation; and to transmit signals representative of a magnitude or amount and a wavelength or type of the detected radiation; and  
         [0035]      FIGS. 5A and 5B  are front and rear schematic representations, respectively, of a video camera including a field emission array according to the present invention which depicts the use thereof to detect radiation, to display images representative of the detected radiation, and to transmit and record signals representative of the detected radiation. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0036]      FIG. 1  illustrates an emission pixel  14  of a preferred embodiment of a field emission array  10  according to the present invention, which includes a p-type semiconductor substrate  12 , such as p-type silicon, with an array of emission pixels  14  and a signal transmission circuit  26  associated with each emission pixel  14 .  
         [0037]     Each emission pixel  14  includes a region of n-type semiconductor material, which is also referred to herein as an n-well  16 , such as n-type silicon, proximate an active surface of substrate  12 . The interface between each n-well  16  and the surrounding p-type semiconductor material of substrate  12  defines a p-n junction  17 . Preferably, the thickness D of, or shortest distance across, the p-type region of substrate  12  between each n-well  16  and the back side of substrate  12  facilitates the creation of electron hole pairs as radiation, such as photons of electromagnetic radiation, impinge p-n junction  17 .  
         [0038]     The thickness D between the back side of substrate  12  and n-well  16  preferably facilitates the generation of electron-hole pairs in p-n junction  17  by visible wavelengths of electromagnetic radiation (i.e., visible light). Thickness D may facilitate the generation of electron hole pairs in p-n junction  17  by infrared or other wavelengths of electromagnetic radiation.  
         [0039]     Field emission array  10  also includes at least one emitter tip  18  associated with each n-well  16 . Each emitter tip  18  is laterally surrounded by and, preferably, at least partially spaced apart from a layer  20  of dielectric material. An extraction grid  22 , which is fabricated from an electrically conductive material, is disposed over layer  20  and, therefore, over a surface of field emission array  10 . Apertures  24  formed through extraction grid  22  are located substantially above each emitter tip  18 .  
         [0040]     With continued reference to  FIG. 1 , the signal transmission circuit  26  associated with each emission pixel  14  includes a first transistor  28 , or baseline potential transistor, which is illustrated in phantom since transistor  28  extends into or out of the plane of the page, and a second transistor  30 , which is also referred to herein as a signal transmission transistor. First transistor  28  and second transistor  30  may share an n-well  32 , which acts as the drain  34 , or drain node, of both first transistor  28  and second transistor  30 . First transistor  28  also includes a gate  36  and a source  38 , or source node, both of which are illustrated in phantom. Source  38  may communicate with a drain voltage, V DD . Second transistor  30  includes a gate  40  and a source  42 , which is also referred to herein as a source node. Source  42  communicates with a scan circuit  44  of a type known in the art.  
         [0041]     Although second transistor  30  is illustrated as a metal-oxide-semiconductor field-effect transistor (“MOSFET”), which is a type of insulated-gate field-effect transistor (“IGFET”), other types of transistors, such as a junction field-effect transistor (“JFET”) may also be employed as second transistor  30 . Similarly, first transistor  28  may comprise an IGFET, a JFET, or any other type of transistor.  
         [0042]     A capacitor  46  disposed between n-well  16  and signal transmission circuit  26  facilitates the generation of a current through signal transmission circuit  26 . Capacitor  46  includes a first conductive structure  48 , which is a conductive contact disposed in contact with the n-well  16  of emission pixel  14 , a second conductive component  52 , and a dielectric component  50 , such as a glass or an oxide, disposed between first conductive component  48  and second conductive component  52 .  
         [0043]     The various components of field emission array  10 , including n-wells  16 , emitter tips  18 , capacitor  46 , and signal transmission circuit  26 , may be fabricated by known semiconductor device fabrication techniques.  
         [0044]     With reference to  FIGS. 2 and 3 , and with continued reference to  FIG. 1 , a preferred embodiment of the radiation detection, display, and signal transmission process of the present invention is depicted.  FIG. 2  is a schematic representation of the circuit defined by n-well  16 , capacitor  46 , and signal transmission circuit  26 .  FIG. 3  is a flow chart illustrating an image sensing, display, and signal transmission process according to the present invention.  
         [0045]     While the processes of the present invention are occurring, an appropriate voltage or voltages are applied, at reference  100  of  FIG. 3 , to all of the components of the circuit, including extraction grid  22 , the ground reference of the circuit, the substrate bias of the circuit, the circuit voltage, and the cathodo-luminescent display panel  66  (see  FIG. 4 ), if any, is biased at a substantially constant, relatively positive voltage.  
         [0046]     The n-well  16  and drain  34  of an emission pixel  14  are each charged to a baseline potential. Accordingly, the back side  13  of substrate  12  at emission pixel  14  is shielded from radiation, such as by a shutter  54 . Alternatively, with reference to  FIG. 2A , field emission array  10  may include a shutter  45 . At reference  101  of  FIG. 3 , gate  36  of first transistor  28  is turned “on” while the back side  13  of substrate  12  at emission pixel  14  is shielded from radiation. Alternatively, with reference again to  FIG. 2A , gate  36  of first transistor  28  may be turned “on” while shutter  45  of  FIG. 2A  is in the closed position. Shielding back side  13  or closing shutter  45  permits n-well  16  to return to its original, or base, voltage, prior to detecting radiation R from a portion of an object O. This original voltage sets the voltage difference between grid  22  and emitter tips  18  below the threshold voltage that causes emitter tips  18  to emit electrons. Therefore, as shutter  45  is closed, emitter tips  18  do not emit electrons. As gate  36  of first transistor  28  is turned “on”, at reference  101  of  FIG. 3 , a substantially constant drain source voltage, which comprises the baseline potential (V DD ), is transferred from source  38  of first transistor  28  to drain  34 . Gate  36  is then turned “off”, at reference  102  of  FIG. 3 .  
         [0047]     At reference  104  of  FIG. 3 , the back side of substrate  12  is exposed to radiation, which impinges p-n junction  17 , creating electron-hole pairs representative of the intensity or type of radiation therein and causing electrons to be transferred to n-well  16 . Thus, as radiation impinges p-n junction  17 , the voltage of n-well  16  drops, or decreases, to create a voltage difference between grid  22  and emitter tips  18 , thereby facilitating the emission of electrons from emitter tips  18 . Changes in the voltage of n-well  16  are communicated to first conductive component  48  of capacitor  46 , at reference  104  of  FIG. 3 . Thus, the voltage of n-well  16  and any changes in the voltage thereof may be communicated to a first side of capacitor  46 .  
         [0048]     As the voltage on the n-well  16  side of capacitor  46 , at first conductive component  48 , drops, the voltage on the drain  34  side of capacitor  46 , at second conductive component  52 , substantially correspondingly drops. Capacitor  46  stores the voltage of drain  34  until gate  40  of second transistor  30  is turned “on”, at reference  106  of  FIG. 3 . As gate  40  of second transistor  30  is turned “on”, the reduced voltage of drain  34  is communicated or transferred to source  42  of transistor  30 , which may be scanned, at reference  108  of  FIG. 3 , to determine the intensity or type of radiation incident with emission pixel  14 .  
         [0049]     At reference  110  of  FIG.3 , gate  40  may be turned “off” while the back side  13  of substrate  12  at emission pixel  14  remains shielded from radiation. Gate  36  of first transistor  28  is turned “on” to charge drain  34  back to V DD , which permits n-well  16  to return substantially to its original, baseline potential.  
         [0050]     The process may then be repeated to detect, display, and transmit a signal representative of subsequent radiation “images”. Gate  36  of first transistor  28  may be turned “off” and radiation permitted to impinge the back side  13  of substrate  12  at emission pixel  14 , at reference  102  of  FIG. 3 , to facilitate the sensing or detecting of another image of radiation by emission pixel  14  and the transmission of a signal representative of the radiation through second transistor  30 .  
         [0051]     As the apparatus of present invention comprises a field emission array having an array of n-wells, each of the n-wells preferably has a signal transmission circuit associated therewith. Accordingly, radiation may be detected by each n-well of the apparatus, or by each emission pixel thereof, and signals representative of the radiation detected at each of the pixels may be transmitted to a scan circuit, or image processing circuit, of a type known in the art, associated with each of the signal transmission circuits. The scanned and processed data may then be recorded by known processes.  
         [0052]     With reference to  FIG. 4 , a system  60  is shown, which includes field emission array  10 , a scan circuit  62  associated with field emission array  10 , a processor  63  in communication with scan circuit  62 , a recording mechanism  64  in communication with processor  63 , a substantially flat display panel  66 , or cathodo-luminescent display, spaced apart from field emission array  10  in substantially mutually parallel relation therewith, and other components, as known in the art.  
         [0053]     Scan circuit  62  is preferably an image signal detector of a type known in the art, which detects or measures the charge or potential at source  42  (see  FIGS. 1 and 2 ) of the second transistor  30  of each of the emission pixels  14  of field emission array  10 . Processor  63 , which is preferably of a type known in the art, communicates with scan circuit  62  to convert the voltage measured at each emission pixel  14  to data representative of the wavelength or the intensity of the radiation impinging emission pixel  14 . Recording mechanism  64 , which is also preferably of a type known in the art, communicates with processor  63  and records or stores the data representative of the wavelength or intensity of radiation impinging emission pixel  14  along with the location of the emission pixel  14  from which the data was obtained.  
         [0054]     Display panel  66  includes an array of display pixels  68 , each of which are positioned to correspond to an emission pixel  14  of field emission array  10 . In use, cathodo-luminescent display panel  66  is charged to a relatively positive attraction potential, which is greater than the relatively positive potential of extraction grid  22  so as to attract electrons emitted from the emitter tips  18  of field emission array  10 , and which generates image light as electrons are attracted thereto.  
         [0055]      FIG. 4  depicts the detection of electromagnetic radiation of or reflected by an object O and the display of an image I of object O by system  60 . Preferably, electromagnetic radiation from object O is focused on back side  13  of substrate by one or more optical lenses (see, e.g., optical lens  72  in  FIGS. 1 and 5 B). As back side  13  (see  FIG. 1 ) of substrate  12  is exposed to electromagnetic radiation from object O, emission pixels  14  are exposed to different wavelengths and intensities of electromagnetic radiation from the different portions of object O to which each emission pixel  14  is exposed.  
         [0056]     The wavelength and intensity of the radiation from each portion of object O impinging a corresponding emission pixel  14  of field emission array  10  is translated to a corresponding electrical impulse in the manner described in reference to  FIGS. 2 and 3 . These electrical impulses are measured by a scan circuit  62  of a type known in the art. Processor  63  processes the measurements taken by scan circuit  62 , which may be recorded for each of the emission pixels  14  of field emission array  10  by recording mechanism  64 , as known in the art. Thus, recording mechanism  64  stores an array of information representative of the radiation from object O to which back side  13  of substrate  12  of field emission array  10  is exposed.  
         [0057]     The emitter tip or tips  18  of each emission pixel  14  emit electrons in a manner that represents the wavelength and the intensity of the portion of radiation from object O to which emission pixel  14  is exposed. These electrons are emitted upon application of a relatively positive potential to extraction grid  22 , as described above in reference to  FIGS. 2 and 3 . Thus, electrons representative of object O are emitted from the emission pixels  14  of field emission array  10  as emission pixels  14  are exposed to radiation from object O. These emitted electrons impinge display pixels  68  of display  66 , eliminating display pixels  68  that correspond to emission pixels  14  that have been exposed to a portion of the radiation from object O. Thus, display  66  displays an image I representative of object O.  
         [0058]     As an alternative to or in combination with recording mechanism  64 , system  60  may include an image transmission mechanism of a type known in the art, which transmits signals representative of radiation from object O to a storage device, an output device, a processor, or another device which may store, process, interpret, or otherwise utilize the signals of scan circuit  62 .  
         [0059]     Although system  60  is depicted in  FIG. 4  as including a display  66  associated with field emission array  10 , system  60  need not include such a display. If system  60  does not include display  66 , image I may be displayed by other components associated with scan circuit  64 .  
         [0060]     System  60  may be employed to detect a series of images and measure the wavelengths and intensities of portions of each image of the series of images incident with each emission pixel  14  of field emission array  10 . These measured wavelengths and intensities at each emission pixel  14  may be stored for each image of the series of images. Since scan circuit  62  identifies the emission pixel  14  that detects the radiation of a portion of an image, information representative of radiation impinging each emission pixel  14  of field emission array  10  is stored. Since this information may be stored on an image-by-image basis, a video representative of a series of images may be stored and played back. Thus, as shown in  FIGS. 5A and 5B , the system  60  (see  FIG. 4 ) of the present invention may be employed in a video camera  70 . Of course, video camera  70  also includes one or more optical lenses  72  that focus electromagnetic radiation from an object O onto back side  13  of substrate  12  of field emission array  10  (see  FIG. 1 ) and other components, as known in the art.  
         [0061]     If field emission array  10  is capable of detecting infrared wavelengths of electromagnetic radiation, system  60  or an image detection system similar thereto may also be used in apparatus for detecting or displaying infrared images. For example, system  60  could be used in night-vision goggles.  
         [0062]     A silicon substrate by itself has too high a band gap to detect longer wavelengths (e.g. 2,500 to 10,000 nm) of electromagnetic radiation. Accordingly, referring again to  FIG. 1 , field emission array  10  may optionally include a substrate  12  of low band gap material, which is also referred to herein as a “detection enhancement material,” of a type known in the art to enhance detection of longer wavelengths of electromagnetic radiation by field emission array  10 . Low band gap materials, such as mercury-cadmium-tellurium alloys and other materials having electrical characteristics that are more readily altered than those of silicon by electromagnetic radiation of relatively long wavelengths, may be used as substrate  12  to facilitate the detection or display infrared radiation in thermal imaging applications or longer wavelengths of electromagnetic radiation. Detection enhancement materials such as mercury-cadmium-tellurium facilitate the detection by field emission array  10  of wavelengths of electromagnetic radiation of from about 1,000 nm to about 10,000 nm and greater.  
         [0063]     Alternatively, with reference to  FIG. 1A , a field emission array  10 ′ configured to detect wavelengths of electromagnetic radiation that are longer than visible light can include a silicon substrate  12 ′ with a p-type region  76  (e.g., p-type silicon) having a p-type conductivity and an n-type region  78  (e.g., n-doped silicon) having an n-type conductivity. A diffusion region  77 , or p-n junction, is located between p-type region  76  and back side  13 ′ of substrate  12 ′ and is proximate to back side  13 ′. A coating  74 , or layer, of detection enhancement material disposed on back side  13 ′ proximate to diffusion region  77  facilitates the detection of radiation, the scanning of electrical impulses representative of the detected radiation, and the emission of electrons representative of the detected radiation in a manner similar to the detection, scanning, and emission effected by p-n junction  17  of semiconductor substrate  12 . Alternative embodiments of field emission array  10 ′, as well as examples of useful low band gap materials and dopant concentrations, are disclosed in U.S. Pat. No. 6,441,542, issued to Hush et al. on Aug. 27, 2002, the disclosure of which is hereby incorporated in its entirety by this reference.  
         [0064]     Although the foregoing description contains many specifics and examples, these should not be construed as a limiting the scope of the present invention, but merely as providing illustrations of some of the presently preferred embodiments. Similarly, other embodiments of the invention may be devised which do not depart from the spirit or scope of the present invention. The scope of this invention is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions and modifications to the invention as disclosed herein and which fall within the meaning of the claims are to be embraced within their scope.