Abstract:
In one aspect, a cathode emitter device comprises an infrared receptor having an n-type doped semiconductive region overlying a p-type doped semiconductive region. The n-type and p-type doped regions of the receptor join at a junction diode. The cathode emitter device further comprises an array of cathode emitter tips in electrical connection with the n-type region of the infrared receptor. In other aspects, the invention encompasses field emission display devices, such as, for example, devices comprising the above-described cathode emitter device. In yet other aspects, the invention encompasses methods of utilizing cathode emitter devices, such as, for example, methods of utilizing the above-described cathode emitter device.

Description:
PATENT RIGHTS STATEMENT 
     This invention was made with government support under Contract No. DABT63-94-C-0012 awarded by Advanced Research Projects Agency (ARPA). The Government has certain rights in this invention. 
    
    
     TECHNICAL FIELD 
     The invention pertains to cathode emitter devices. In particular applications, the invention pertains to devices configured to detect infrared radiation, as well as to methods of utilizing such devices. 
     BACKGROUND OF THE INVENTION 
     Many applications are known wherein it is desired to detect and/or image infrared radiation. Exemplary applications include thermo-imaging devices, such as cameras, utilized in night-vision accessories and other surveillance equipment. For instance, infrared radiation can be utilized by surveillance equipment to detect and image objects that are hotter than their surrounding environment. Such utilization takes advantage of the fact that objects naturally emanate infrared radiation when heated (so-called blackbody radiation). 
     Among the known methods for detecting and/or imaging infrared radiation are methods which take advantage of sensitivity of p-type silicon to infrared radiation. For instance, U.S. Pat. No. 3,814,968 describes a field emission display apparatus comprising an array of lower doped p-type cathode emitter devices in electrical contact with a higher doped p-type semiconductive material. The apparatus is configured such that when the higher doped p-type material is exposed to infrared radiation, the electrical properties of the material change and cause one or more electrons to be emitted from the lower doped p-type cathode array. Such electrons then impact a phosphor spaced from the array to cause a visually detectable image to occur. 
     A difficulty associated with devices such as that disclosed in U.S. Pat. No. 3,814,968 can be a lack of sensitivity of the semiconductive material to radiation having relatively long wavelengths, such as wavelengths greater than or equal to about 2,500 angstroms. For instance, if p-type doped silicon (with the dopant provided to a concentration of greater than or equal to 1×10 18 atoms/cm 3 ) is utilized as the semiconductive material, it will typically be unable to detect infrared photons at wavelengths greater than about 1,200nanometers. This causes complications for utilizing silicon detectors because many objects are not hot enough to generate a significant amount of infrared radiation having wavelengths less than or equal to 1,200 nanometers. It would therefore be desirable to develop improved methods for detecting infrared radiation. 
     SUMMARY OF THE INVENTION 
     In one aspect, a cathode emitter device comprises an infrared receptor having an n-type doped semiconductive region overlying a p-type doped semiconductive region. The n-type and p-type doped regions of the receptor join at a junction diode. The cathode emitter device further comprises an array of cathode emitter tips in electrical connection with the n-type region of the infrared receptor. 
     In another aspect, the invention encompasses a cathode emitter device. The device includes a substrate comprising an n-type doped region overlying a p-type doped region, with the n-type and p-type doped regions joining at a junction diode. The device further comprises an array of cathode emitter tips in electrical connection with the junction diode, and a receptor assembly beside the junction diode. The receptor assembly comprises a material different from that of the substrate, and comprises a p-type doped region and n-type doped region of said material. The p-type doped region of the receptor assembly contacts the p-type doped region of the substrate, and the n-type doped region of the receptor assembly contacts the n-type doped region of the substrate. 
     In other aspects, the invention encompasses field emission display devices, such as, for example, devices comprising the above-described cathode emitter device. In yet other aspects, the invention encompasses methods of utilizing cathode emitter devices, such as, for example, methods of utilizing the above-described cathode emitter device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the invention are described below with reference to the following accompanying drawings. 
     FIG. 1 is a diagrammatic, schematic, cross-sectional, fragmentary view of a first embodiment apparatus encompassed by the present invention. 
     FIG. 2 is a diagrammatic, fragmentary, schematic, cross-sectional view of a second embodiment apparatus encompassed by the present invention. 
     FIG. 3 is a diagrammatic, fragmentary, schematic, cross-sectional view of a third embodiment apparatus encompassed by the present invention. 
     FIG. 4 is a diagrammatic, fragmentary, schematic, cross-sectional view of a fourth embodiment apparatus encompassed by the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8). 
     The invention encompasses devices configured for detecting infrared radiation, and in particular embodiments encompasses devices configured to detect light having a wavelength of greater than or equal to about 2,500 nanometers. 
     A first embodiment display device  10  encompassed by the present invention is illustrated in FIG.  1 . Device  10  includes a base substrate  12  which can comprise, for example, monocrystalline silicon. To aid in interpretation of the claims that follow, the term “semiconductive substrate” is defined to mean any construction comprising semiconductive material, including, but not limited to bulk semiconductive materials, such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above. 
     A layer  14  is formed over substrate  12 . Layer  14  comprises a material having p-type doped portion  16  and an n-type doped portion  18 . The material of layer  14  is preferably chosen such that p-type doped portion  16  has electrical characteristics which are more readily altered by light having relatively long wavelengths (such as, for example, wavelengths of greater than or equal to about 2,500 nanometers) than are the electrical characteristics of p-type doped silicon. An exemplary preferred material for layer  14  is Hg—Cd—Te. Such material can be formed by, for example, chemical vapor deposition or sputter deposition. If layer  14  comprises Hg—Cd—Te, p-type doped portion  16  is preferably doped to a concentration of at least about 2.3×10 16  atoms/cm 3 , and n-type doped portion  18  is preferably doped to a concentration of at least about 6×10 15  atoms/cm 3 . A suitable p-type dopant for Hg—Cd—Te is boron, and suitable n-type dopants include phosphorus and arsenic. The Hg—Cd—Te preferable comprises Hg (l-X) Cd (X) Te, wherein x is 0.3. In a particular construction, layer  14  can consist essentially of doped Hg—Cd—Te. A junction diode  20  is defined by an interface of p-type doped portion  16  and n-type doped portion  18 . 
     Another exemplary material which can be incorporated into layer  14  is platinum silicide. If layer  14  comprises platinum silicide, portion  16  is preferably n-type doped silicon and layer  18  preferably consists essentially of platinum silicide. 
     In particular embodiments, layer  14  can comprise predominately either monocrystalline silicon or polycrystalline silicon, and can, accordingly comprise a same material as substrate  12 . In such embodiments, the silicon materials of substrate  12  and layer  14  can together define a silicon block. 
     An array of cathode emitter tips  22  is formed over material  14  and in electrical connection with n-type doped portion  18 . In the shown embodiment, cathode emitter tips  22  are in physical connection with n-type doped portion  18 . In other embodiments (not shown) another material (such as, for example, an electrically conductive material) can be provided between cathode emitter tips  22  and n-type doped portion  18 . 
     A dielectric material  24  is formed at a base of cathode emitter tips  22 , and a conductive extraction grid  26  is formed at an elevational level of the tip portions of cathode emitter tips  22 . Dielectric material  24  and grid  26  can be formed in accordance with conventional methods. 
     A phosphor-coated plate  28  is provided in spaced relation relative to the array of cathode emitter tips  22 . 
     A power source  40  is provided to charge phosphor-coated plate  28 , extraction grid  26 , and layer  14 . In alternative embodiments in which a conductive material is provided between the array of cathode emitter tips and n-type portion  18 , such conductive material can be charged instead of, or in addition to, layer  14 . 
     In operation, infrared light  50  penetrates silicon substrate  12  and impacts p-type do de portion  16  of layer  14  to change electrical characteristics of the p-type doped portion. Such change in electrical characteristics is propagated through junction diode  20  and n-type doped 
     portion  18  to cause electrons  52  to be emitted from cathode emitter tips  22 . Electrons  52  impact phosphor of plate  28  to cause an image to be displayed. 
     An advantage of the present invention over the prior art is that if the material of layer  14  is chosen to be more sensitive to light with relatively long wavelengths (such as, for example, light having wavelengths of greater than or equal to about 2,500 nanometers) than is p-type doped silicon, an apparatus of the present invention can be utilized for detecting and/or imaging radiation that could not be detected with p-type silicon alone. Such radiation can include infrared radiation naturally emanating from warm-blooded creatures. 
     A second embodiment apparatus  100  encompassed by the present invention is described with reference to FIG.  2 . Apparatus  100  comprises a substrate  112  having a p-type doped portion  116  and an n-type doped portion  118 , with a junction diode  120  defined by the interface of portions  116  and  118 . Substrate  112  can comprise, for example, silicon, and is preferably formed to a thickness “y” of less than 10 microns. If substrate  112  comprises silicon, the silicon can be in one or more of a monocrystalline or polycrystalline form. Such silicon material can comprise a p-type doped portion  116  having a dopant concentration of at least about 1×10 18  atoms/cm 3 , and an n-type doped portion  118  having a dopant concentration of at least about 1×10 18  atoms/cm 3 . 
     An array of cathode emitter tips  122  is formed over substrate  112  and in electrical connection with n-type doped portion  118 . In the shown embodiment, cathode emitter tips  122  are in physical contact with n-type doped portion  118 . In other embodiments (not shown) another material (such as, for example, a conductive material) can be placed between emitter tips  122  and n-type doped portion  118 . 
     A dielectric material  124  is formed at an elevational level of lower portions of emitter tips  122  and a conductive extraction grid  126  is formed at an elevational level of the tip portions of the emitter tips  122 . 
     A phosphor-coated plate  128  is provided to be spaced from cathode emitter tips  122 . A power source  140  is provided to charge to phosphor-coated plate  128 , extraction grid  126  and n-type doped portion  118 . In alternative embodiments wherein a conductive material is provided between cathode emitter tips  122  and n-type doped portion  118 , a charge can be provided within such conductive material, in addition to, or instead of, n-type doped portion  118 . 
     An infrared sensitive structure  170  is provided in electrical connection with p-type doped region  112  and n-type doped region  118 , with structure  170  configured to function as a receptor for receiving relatively long wavelength infrared radiation (such as infrared radiation having wavelengths greater than or equal to about 2500 nanometers). In the shown embodiment, receptor  170  comprises a material  172  having a p-type doped portion  174  and an n-type doped portion  176 . Material  172  is preferably chosen to have electrical characteristics which are more readily altered by light having a wavelength of about 2,500 nanometers or greater than are the electrical characteristics of p-type doped region  112 . Material  172  can comprise, for example, platinum silicide or Hg—Cd—Te, and can be formed by methods described above with reference to layer  14  of FIG.  1 . In particular embodiments, material  172  can consist essentially of conductively doped platinum silicide or doped Hg—Cd—Te. In the shown embodiment, material  172  physically contacts p-type region  116  and n-type region  118  of substrate  112 . In other embodiments (not shown) one or more materials (such as, for example, conductive materials) can be provided between material  172  and one or both of p-type region  116  and n-type region  118 . 
     In operation, light  190  passes through substrate  112  to strike receptor  170  and causes an electrical characteristic of material  172  to be altered. The alteration in the electrical characteristic of material  172  causes an alteration in the electrical properties of one or both of p-type doped portion  116  and n-type doped portion  118 , to cause electrons  192  to be emitted from cathode emitter tips  122 . Electrons  192  strike phosphor-coated plate  128  to cause an image to be displayed. 
     Device  100 , like the above-described device  10 , can be advantageous over prior art devices, in that device  100  can be more sensitive to light having relatively long wavelengths (such as, for example, wavelengths of greater than or equal to about 2,500 nanometers) than are prior art devices. 
     FIG. 3 illustrates an alternative embodiment of the apparatus  100  of FIG.  2 . The embodiment of FIG. 3 differs from that of FIG. 2 in that a light-blocking material  200  is provided to prevent light from reaching diode  120 . Material  200  can comprise, for example, a metal (such as, for example, tungsten or aluminum) or amorphous silicon. In particular applications in which only relatively long wavelength light (greater than or equal to about 2500 nanometers) is desired to be detected, material  200  can advantageously preclude light of relatively short wavelengths (less than or equal to about 1200 nanometers) from reaching diode  120  and causing spurious signals. 
     FIG. 4 illustrates an alternate embodiment  100 a of the present invention. In referring to FIG. 4, identical numbering to that utilized in describing FIG. 2 is used, with differences indicated by the suffix “a”. FIG. 4 is identical to FIG. 2 in all respects except that receptor  170  of FIG. 2 is replaced with a receptor  170   a  that comprises an electrical component sensitive to infrared radiation, such as, for example, a bolometer, with such electrical component being in electrical connection with one or both of p-type doped region  116  and n-type doped region  118 . 
     In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.