Patent Publication Number: US-2011073877-A1

Title: High-current/low cost read-in integrated circuit

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of U.S. Provisional Application Ser. No. 61/246,230 filed on Sep. 28, 2010 having the same title as the present application. 
    
    
     BACKGROUND INFORMATION 
     1. Field 
     Embodiments of the disclosure relate generally to the field of read-in integrated circuits (RIIC) for infrared emitters and more particularly to embodiments for a RIIC device that incorporates a “copper overlayer” process that serves the dual purpose of providing high supply and return current to the array of unit cells and also provides good thermal conduction to help keep the operating temperature of the circuitry cool. 
     2. Background 
     Infrared detection and imaging systems are being employed to sense temperature differences to create scenes displaying various objects. To accommodate testing of such systems, scene generators must be employed which provide high temperature emitters to accurately simulate inputs for test. In current devices a “suspended bridge” emitting device is attached to the RIIC. The large expense required to attach or otherwise deposit such suspended bridge technology contributes to the sales price of full infrared emitting systems to be over $1M. Also contributing to this price is the requirement that the technology incorporates patented subject matter requiring a license for the purpose of producing that patented emitting structure. Additionally, high temperature emitters typically require higher currents than can be provided by CMOS or other standard cell technologies employed in control and operation of RIIC based scene generators. 
     It is therefore desirable to provide RIIC unit cells which provide the capability to supply high currents required for high temperature emitters while using standard CMOS circuitry for control but at a reduced cost using simplified components. It is also desirable to provide a RIIC having high current output capability for enhanced emitter operation but provide thermal conduction for temperature control in the RIIC. 
     SUMMARY 
     Exemplary embodiments provide a Read-In Integrated Circuit scene generator which incorporates an array of unit cells, with each cell having a switching control circuit. An array of emitting elements is associated with the unit cells and each element is connected with a lead to the switching control circuit of the associated cell. A first electrically conducting overlayer is deposited substantially covering the array of unit cells and connected for current supply. Each emitting element is connected to the first conducting overlayer and the first conducting overlayer includes vias through which each connecting lead from the emitting element to the switching control circuit extends. A second electrically conducting overlayer is deposited substantially covering the array of unit cells and connected for current return. Each switching control circuit is connected to the second conducting overlayer. The second conducting overlayer also has vias through which each lead from the emitting elements extends to the switching circuit. 
     In certain embodiments, the Read-In Integrated switching control circuits of the array are CMOS. 
     In an exemplary configuration, the first and second conducting overlayers are copper. 
     Additionally in certain embodiments, one or both of the conducting overlayers is thermally conductive. 
     The features, functions, and advantages that have been discussed can be achieved independently in various embodiments of the present invention or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side section schematic of a generalized unit cell of an exemplary embodiment; 
         FIG. 2  is a partial top view of an exemplary embodiment RIIC showing a subset of the array of unit cells; and, 
         FIGS. 3A-3D  are exemplary views of the RIIC of  FIG. 2  with subsets of pixels in one row of unit cells illuminated. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments described herein provide a high-current “Read-In Integrated Circuit” (RIIC) device that contains a large number of unit cell elements that will have the capability to be mated to “emitting” devices for use in infrared scene projection applications. As generally described in  FIG. 1 , a high-temperature resistive element  10  as an emitter is shown mated to an emitting unit cell  12 . For the embodiment shown, an emitter of approximately 20K ohms in resistance provides 3000K maximum temperature capability. The unit cell incorporates a CMOS control circuit  14  providing switching control for the emitter. Other example emitter technologies such as infrared (IR) light emitting diode arrays, IR laser diode arrays, IR emitting photonic crystal arrays and liquid crystal on silicon IR emitting arrays may also be mated to the unit cell in alternative embodiments. The emitting unit cells are arranged in an array as in a standard RIIC device and copper plating overlayer  16  for supply current and overlayer  18  for return current extend over the array separated by dielectric layers  17  and  19  respectively with vias  20  and  22  for circuit isolation in each cell allowing lead  23  from the resistive element  10  to pass through the overlayers for connection to the CMOS control circuit  14 . For the embodiment shown, the dielectric layers are silicon dioxide (SiO 2 ). The thickness of the copper overlayers is determined based upon the maximum amount of current required to operate the emitting devices at prescribed maximum radiance levels. 
     The copper overlayers on the wafers of the RIIC die remove the voltage drops produced within the emitting core of previous high-current scene projection devices. Additionally, the presence of the highly thermally conductive copper overlayers on the RIIC effectively limit lateral thermal migration, thus limiting the local heating spatially resulting in a predominance of infrared radiation as opposed to lateral thermal diffusion from adjacent cells. In addition, the high thermal conductivity of the copper overlayers create a condition in which the copper overlayers act as a thermal shield, isolating the underlying CMOS circuitry from high levels of thermal radiation and excessive heating. 
       FIG. 2  shows in partial view an exemplary implementation for test of the embodiment disclosed in  FIG. 1  wherein 7K ohm nichrome resistors  24  were photolithographically patterned in isolated layers on top of 256×256 RIIC devices (such as NOVA-012 RIIC devices produced by Nova Research, Solvang, Calif.) that have a 51 um emitting pixel pitch. Each unit cell  12  shows top copper overlayer  16  and the associated vias  20  and  22  in each cell. While not appropriate for high temperature emission applications, the embodiments disclosed herein could be well utilized for lower temperature (i.e., lower dynamic range than achievable when used with MWIR LED arrays, high temperature resistive emitters, photonic crystals, etc.) but high speed (up to approximately 800 Hz full frame in the analog input mode) applications at very low cost. 
       FIGS. 3A-3D  show a demonstration of the operation of the exemplary test circuit  26  shown in partial view in  FIG. 2 . A simple stimulus pattern was implemented that energizes sets of 32 pixels in an individual row until the entire row  27  (as seen in  FIG. 2 ) is “lit”. In  FIG. 3A  a first 32 pixel set  28   a  in the exemplary row is illuminated. In  FIG. 3B  a second adjacent 32 pixel set  28   b  is also illuminated. In  FIG. 3C , the third adjacent 32 pixel set  28   c  is illuminated while in  FIG. 3   d  the fourth adjacent 32 pixel set  28   d  is illuminated to complete the row. The pattern then continues to the next row and eventually addresses all pixels in the device from the top to the bottom of the device. 
     Having now described various embodiments of the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims.