Christopher L. Fletcher

Wide-FOV FPAs for a shipboard distributed aperture system

The Navy faces an ever evolving threat scenario, ranging from sub-sonic sea skimming cruise missiles to newer, unconventional threats such as that experienced by the USS Cole. Next generation naval technology development programs are developing “stealthy” ships by reducing a ships radar cross section and controlling electromagnetic emissions. To meet these threat challenges in an evolving platform environment, ONR has initiated the “Wide Aspect MWIR Array” program. In support of this program, Raytheon Vision Systems (RVS) is developing a 2560 X 512 element focal plane array, utilizing Molecular Beam Epitaxially grown HgCdTe on silicon detector technology. RVS will package this array in a sealed Dewar with a long-life cryogenic cooler, electronics, on-gimbal power conditioning and a thermal reference source. The resulting sub system will be a component in a multi camera distributed aperture situation awareness sensor, which will provide continuous surveillance of the horizon. We will report on the utilization of MWIR Molecular Beam Epitaxial HgCdTe on Silicon material for fabrication of the detector arrays. Detector arrays fabricated on HgCdTe/Si have no thermal expansion mismatch relative to the readout integrated circuits. Therefore large-area focal plane arrays (FPAs) can be developed without concern for thermal cycle reliability. In addition these devices do not require thinning or reticulation like InSb FPAs to yield the high levels of Modulation Transfer Function (MTF) required by a missile warning sensor. HgCdTe/Si wafers can be scaled up to much larger sizes than the HgCdTe/CdZnTe wafers. Four-inch-diameter HgCdTe/Si wafers are currently being produced and are significantly larger than the standard 1.7 inch x 2.6 inch HgCdTe/CdTe wafers. The use of Si substrates also enables the use of automated semiconductor fabrication equipment.

Advanced IRFPAs for next-generation sensors

Raytheon Vision Systems (RVS) has invented and demonstrated a new class of advanced focal plane arrays. These Advanced FPAs are sometimes called 3rd Generation or “Next Generation” FPAs because they have integrated onto the FPA the ability to sense multiple IR spectrums, have improved resolution and performance, and conduct image processing on the FPA ROIC. These next generation of FPAs are allowing more functionality and the detection of a more diverse set of data than previously possible with 2nd Gen FPAs. Examples and history of advanced next generation FPAs are reviewed including RVS’s Multispectral, Uncooled, Adaptive Sensors and other advanced sensors.

Megapixel and larger readouts and FPAs for visible and infrared astronomy

The desire for larger and larger format arrays for astronomical observatories -- both ground and space based -- has fueled the development of detector, readout, and hybrid Focal Plane Array (FPA) technology that has paved the way for later development of tactical and strategic arrays for military applications. Since 1994, Raytheon has produced megapixel readouts and FPAs for Infrared Astronomy. In 1999 Raytheon demonstrated a revolutionary approach to photolithography called Reticle Image Composition Lithography (RICL) that opened the door to very large format FPAs in state of the art sub-micron CMOS processes. The first readout processed using the patented RICL technique was a 4.2 megapixel readout for astronomy. We present the design and performance of several 4.2 megapixel (2048 x 2048) readout arrays for visible and infrared astronomy applications. The first of these arrays are fabricated in a workhorse 2 μm CMOS process that is optimized for low temperature operation (down to as low as 6 Kelvin). Most recently Raytheon has developed a scaleable 2,048 x 2,048 high density array for several ground based astronomical applications. This array can be manufactured in any m x n multiple of a basic 1024 (V) x 512 (H) pixel array core. The primary design is a 2 x 4 array to yield a 2,048 x 2,048 format array. This same design can be extended to at least a 4,096 x 4,096 format array -- an incredible 16.7 megapixel array! These readouts are compatible with a wide range of detector types including InSb, HgCdTe, and Si detectors. The use of hybrid technology -- even for the visible wavebands -- allows 100% optical fill factors to be achieved. The design and performance of these megapixel class detectors, readouts, and FPAs will be presented.