Abstract:
The present application is directed to a self-pixelating focal plane array and includes a photodetection portion having a body defining a self-pixelating active detection region, and a readout device in electrical communication with the photodetection portion and configured to capture electrical charges from the photodetection portion. During use, the photodetection portion is configured to operate in Geiger mode. As such, the application of one or more electrical fields to the photodetection portion results in the photodetection portion operating in a self-pixelating manner. The readout device may be used to capture the electrical charges and signals generated by the photodetection portion due to the incidence of one or more photons on the photodetection portion.

Description:
BACKGROUND 
   Optical detectors and focal plane arrays are presently used in a number of industries to capture light for analysis. Presently, there is a great deal of interest in producing optical detectors and focal plane arrays with higher sensitivity to incident light while decreasing the noise produced within the detector or focal plane array. 
   One class of device currently in use comprises a photodetection device having an active detection area which is matched to an optical readout chip. During manufacture, great care must be taken when coupling the readout chip to the photodetection device. Typically, the photodetection device and the readout chip are positioned within a high vacuum chamber and the contact surfaces of each device are cleaned to ensure the surfaces are free of molecular contaminants. Thereafter, a bonding agent may be applied to a surface of at least one of the photodetection device and/or the readout chip, thereby bonded the photodetection device and readout chip together. Typically, these devices are referred to as “flip-chip” devices. While these devices have proven useful in detecting incident radiation, a number of shortcoming have been identified. 
   During use, imaging information is derived by knowing precisely which pixel of the active detection area of the photodetection device generated an electrical signal within the readout chip. Since pixel sizes are quite small, it is imperative that the non-conducting and conducting regions of the photodetection device and readout chip overlap and maintain their position relative to each other during the manufacturing process. Typically, the manufacturing process incorporates extensive procedures to align and register the photodetection device and readout chip. As such, manufacturing yields are not high. Furthermore, the manufacturing process is quite lengthy, labor intensive, and costly. 
   Thus, in light of the foregoing, there is an ongoing need for a self-pixelating focal plane array which can be produced more efficiently. 
   BRIEF SUMMARY 
   Various embodiments of self-pixelating focal plane arrays with electronic outputs are disclosed herein. In addition, the present application discloses various methods of manufacturing various embodiments of self-pixelating focal plane arrays. 
   In one embodiment, the present application discloses a self-pixelating focal plane array and includes a photodetection portion having a body defining a self-pixelating active detection region, and a readout device in electrical communication with the photodetection portion and configured to capture electrical charges from the photodetection portion. During use, the photodetection portion is configured to operate in Geiger mode. As such, the application of one or more electrical fields to the photodetection portion results in the photodetection portion operating in a self-pixelating manner. The readout device may be used to capture the electrical charges and signals generated by the photodetection portion due to the incidence of one or more photons on the photodetection portion. 
   In another embodiment, the present application discloses a self-pixelating focal plane array and includes at least one photodiode having a body defining an active detection region, a voltage source in communication with the at least one photodiode and configured to operate the at least one photodiode in Geiger mode, and a readout device in electrical communication with the at least one photodiode. 
   In still another embodiment, the present application discloses at least one photodiode having a body defining an active detection region, the at least one photodiode configured to operate in Geiger mode, and a readout device coupled to the at least one photodiode in flip chip relation, wherein the readout chip is in electrical communication with the at least one photodiode. 
   In addition, the present application discloses various methods of manufacturing a self-pixelating focal plane array. One method of manufacturing a self-pixelating focal plane array includes providing a photodetection portion and a readout device, configuring the photodetection portion to operate in Geiger mode, coupling the readout device to the photodetection portion, creating a self-pixelating photodetection portion by operating the photodetection portion in Geiger mode, and capturing electrical charges received from the photodetection portion with the readout device. 
   In an alternate embodiment, a self-pixelating focal plane array may be manufactured by providing one or more avalanche photodiodes, providing one or more flip-chip readout devices, coupling the one or more flip-chip readout devices to the one or more avalanche photodiodes wherein the one or more flip-chip devices are in electrical communication with the one or more avalanche photodiodes, biasing the one or more photodiodes to operate in Geiger mode wherein the photodiodes become self-pixelating, and capturing electrical charges generated within the photodiodes with the readout devices. 
   Other features and advantages of the embodiments of the self-pixelating focal plane arrays with electronic outputs as disclosed herein will become apparent from a consideration of the following detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A self-pixelating focal plane array with an electronic output will be explained in more detail by way of the accompanying drawings, wherein: 
       FIG. 1  shows a cross sectional view of an embodiment of a self-pixelating focal plane array with electronic outputs; 
       FIG. 2  shows cross sectional view of an embodiment of a photodetection portion for use with a self-pixelating focal plane array; 
       FIG. 3  shows cross sectional view of an embodiment of a readout device for use with a self-pixelating focal plane array; 
       FIG. 4  shows a cross sectional view of an embodiment of a self-pixelating focal plane array during use wherein electromagnetic radiation is incident upon an embodiment of a photodetection portion; 
       FIG. 5  shows a cross sectional view of the embodiment of the self-pixelating focal plane array shown in  FIG. 4  wherein a micro-channel of avalanche-induced electrons is formed within the photodetection portion; and 
       FIG. 6  shows a cross sectional view of the embodiment of the self-pixelating focal plane array shown in  FIG. 4  wherein the readout device of the self-pixelating focal plane array is outputting an electrical signal. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows an embodiment of a self-pixelating focal plane array. In one embodiment, the self-pixelating focal plane array  10  includes a photodetection portion  12  coupled to or otherwise in communication with a readout device  14 . For example, in one embodiment, the photodetector portion  12  comprises an avalanche photodiode while the readout device  14  comprises an integrated circuit detector or readout chip. In an alternate embodiment, the self-pixelating focal plane array  10  may comprise a monolithic electromagnetic radiation detector array formed by coupling one or more readout chips to one or more avalanche photodiodes using a flip-chip manufacturing process. 
     FIG. 2  shows a cross sectional view of an embodiment of the photodetection portion  12  configured for use with the self-pixelating focal plane array. As shown, the photodetection portion  12  includes a body  16  having an active detection area  18  defined therein. In one embodiment, the photodetection portion  12  comprises an avalanche photodiode having a first layer  20 , a second layer  22 , and a third layer  24 . Optionally, the first layer  20  may comprise a positively doped semi-conductive material configured to permit an avalanche of electrons to be freed when struck with a photon. For example, in one embodiment the positively doped semi-conductive material comprises silicon. In an alternate embodiment, the first layer  20  is comprised of indium phosphide and is heavily doped with a P-type material such as zinc. As such, the first layer  20  may lose its semi-conductive properties and function similar to a conductor. Further, the second layer  22  may optionally be either a negative layer or an insulator. For example, the second layer  22  maybe manufactured without doping or with low doping. Similarly, the third layer  24  may be a negative layer. In one embodiment, the third layer  24  is moderately doped with an N-type material. In another embodiment, the third layer  24  is heavily doped with an N-type material such as sulfur, for example, such that the third layer no longer behaves as a semiconductor but instead has a reasonable good conductivity. 
   Referring again to  FIG. 2 , in one embodiment, a circuit  26  may be connected to the photodetection portion device  12  with a first and second electrode  28 ,  30 . The circuit  26  may include a voltage source  32  configured to apply a charge across the photodetection portion  12 . optionally, a circuit resistor  34  may be positioned between the voltage source  32  and at least one of the electrodes  28 ,  30 . As a result, a first electric field  36  may be created across the photodetection portion  12 . As such, the photodetection portion  12  may be configured to be operated in Gieger mode. As shown in  FIG. 2 , the first electric field  36  is substantially perpendicular to the layers ( 20 ,  22 ,  24 ) of the active detection area  18 . Optionally, a second circuit  38  may also be coupled to the photodetection portion  12 . As such, a second electric field  40  may be created within or surrounding the photodetection portion  12 . In the illustrated embodiment, the second electric field  40  is perpendicular to the first electric field  36 . Optionally, any number of electric fields or field directions may be used. Furthermore, the photodetection portion  12  may be manufactured in any number of sizes or shapes as desired. In an alternate embodiment, the photodetection portion  12  comprises any number or variety of alternate photodetection devices, including, without limitation, charge coupled devices, photo multipliers, and similar devices. 
   Optionally, the photodetection portion  12  may include a coupling layer  42  configured to electrically, mechanically, or electro-mechanically couple the photodetection portion  12  to the readout device  14 . As such, the coupling layer  42  may be formed from a conductive material, an insulating material, and/or a dielectric material. Further, the coupling layer  42  may include one or more contact areas  44  formed thereon. As such, the contact areas  44  may be formed from a conductive material, an insulating material, and/or a dielectrical material. For example, in one embodiment, the contact areas  44  comprise conductive pads configured to electrically couple the photodetection portion  12  to the readout device  14 . 
   As stated above, the photodetection device  12  may comprise one or more avalanche photodiodes configured to be operated in Geiger mode. As such, the incidence of a photon having an energy below the bandgap of the photodiode causes a chain reaction or avalanche of electrons in a photodiode material. The avalanche of electrons within the photodiode material continues until the current within the electrical field applied to the photodiode drops to zero or until the voltage falls below the breakdown voltage. Further, the avalanche of electrons may be confined within a micro-channel formed within the materials forming the photodiode. As a result, the photodiode operated in Geiger mode is self-pixelating. The one or more photodiodes used to form the photodetection portion  12  may be manufactured from any variety of material, including, without limitation, Indium Gallium Arsenide (InGaAs), Silicon (Si), Germanium (Ge), Gallium Nitride (GaN), Silicon Carbide (SiC), or any other suitable materials. 
     FIG. 3  shows a cross sectional view of an embodiment of a readout device  14  for use with various embodiments of a self-pixelating focal plane array. As shown, the readout device  14  may comprise a first layer  50 , a second layer  52 , and a substrate  54 . In one embodiment, the first layer  50  is formed from a semi-conductive material, including, for example, silicon. As shown in  FIG. 3 , the first layer  50  may include one or more integrated circuit devices  56  position thereon. Exemplary integrated circuit devices  56  may include, without limitation, amplifiers, processors, assignment specific integrated circuits, and the like. The integrated circuit devices  56  may be configured to capture, amplify, and/or read out a pixilated radiation intensity pattern from the photodetection portion  12 . (See  FIG. 2 ). As such, the readout device  14  may form a flip-chip readout chip configured to be electrically, mechanically, or electro-mechanically coupled to the photodetection portion  12 . Optionally, the first layer  50  may further include one or more bond pads, contacts, conduits, and/or leads thereby permitting the readout device  14  to be electrically coupled to the photodetection portion  12 .  FIG. 3  shows an embodiment of a readout device  14  having one or more contact pads  57  formed thereon. 
   Referring again to  FIG. 3 , the second layer  52  of the readout device  14  may comprise a compensation layer bonded or otherwise coupled to the first layer  50 . As such, the second layer  52  may provide structure support to the first layer  50 . In addition, the second layer  52  may effectuate the transfer of heat from the photodetection portion  12 , the first layer  50 , and/or the integrated circuit devices  56 . The substrate layer  54  may further assist in the transfer of heat from the various components of the self-pixelating focal plane array while further providing addition structural support thereto. In an alternate embodiment, the readout device  14  may comprise a flex circuit architecture bonded or otherwise coupled to the photodetection portion  12 . Optionally, the readout device  14  may include one or more electrical contact area formed thereon thereby permitting the readout device  14  to be electrically coupled to external circuits. 
   The readout device  14  may be coupled to the photodetection portion  12  in any variety of ways. For example, the readout device  14  may coupled to the photodetection portion  12  using methods know in the art of flip-chip fabrication. As stated above, the photodetection portion  12  may comprise one or more avalanche photodiodes configured to operate in Geiger mode, and, as such, may be self-pixelating. As a result, the self-pixelating characteristics of the photodetection portion  12  of the embodiments of the devices disclosed herein greatly reduces or eliminates the precision alignment procedures commonly required during flip-chip fabrication. Therefore, during the manufacturing process, the precise alignment and registration of individual pixels of prior art photodetectors to prior art readout chips is substantially reduced or eliminated, thereby reducing production cost while improving production yields.  FIGS. 4–6  show various views of an embodiment of the self-pixelating focal plane array during use.  FIG. 4  shows energy  70 , below the bandgap of the photodetection portion  14 , incident on the self-pixelating focal plane array. The energy  70  is applied substantially perpendicular to a top surface of the active detection area  18  so the energy  70  is applied in a direction substantially parallel to electric field  36 . (Ref.  FIG. 2 ) The incidence of this energy  70  results in the generation of electron-hole pairs comprising an avalanche of electrons confined within the material forming the photodetection portion. When operated in Geiger mode the generation of the electron-hole pairs is focused within a micro-channel of the materials forming the photodetection portion  12 .  FIG. 5  shows the formation of a micro-channel  72  within the photodetection portion  12 . As a result, an electrical signal  74  is formed within the micro-channel  72  and transmitted by the photodetection portion  12  to the readout device  14  electrically coupled thereto. Thereafter, the electrical signal  74  may be processed or otherwise modified by the readout chip  14 . For example, the electrical signal  74  may be amplified by one or more integrated circuit devices  56  included within the readout device. (see  FIG. 3 ). As shown in  FIG. 6 , the readout device  14  may output an output signal  76  to an electrical circuit or other device in electrical communication with the readout device  14 . 
   Embodiments disclosed herein are illustrative of the principles of the invention. Other modifications may be employed which are within the scope of the invention, thus, by way of example but not of limitation, alternative photodetection devices, alternative readout device configurations, and alternate integrated circuit devices positioned on the readout device. Accordingly, the devices disclosed in the present application are not limited to that precisely as shown and described herein.