Abstract. There is a strong motivation for smaller pixels based on enduser demand for lower-cost, higher-resolution camera systems both for military and commercial applications. Uncooled detector technology fits the need for a low size, weight, and power system. We explore the tradeoffs and challenges to achieving pixel designs smaller than the current 17-μm state-of-the-art detectors without loss in sensitivity or resolution. For illustration we consider a 12-μm design. We also address modulation transfer function issues as the pixel size shrinks, and examine the difference between the performance of present devices and the theoretical performance limit for uncooled detectors. IntroductionFifteen to 20 years ago, developments in the semiconductor industry enabled the earlier generations of uncooled focal plane array (FPAs) and cameras with small format, 160 by 120 and then 320 by 240 array sizes with large pixels, generally in the neighborhood of 50 × 50 μm 2 . The detector material was usually vanadium oxide (VOx), alpha-silicon (a-Si) or ferroelectrics. The wave band over which the optics and detectors of a camera were generally designed to receive and respond to radiation that is approximately 7.5 AE .0.5 μm 2 to 13 AE 1 μm 2 . The user community, mainly the military at that time, specified camera operational requirements, which were typically around a 50-mK noise equivalent temperature difference (NETD), a frame rate of 30 Hz, and commensurate time constants for applications such as a thermal weapons sight or helmet-mounted goggles. The sensitivity of the detectors was far from the fundamental limits and thus drove the need for optics with an F/number near 1.0 to obtain the desired NETD. The modulation transfer function (MTF) of the system was almost never dominated by the MTF of the optics. Over the years, the semiconductor industry has made advances with ever smaller design rules, enabling the uncooled camera manufacturers to further push their designs and performance. Pixel sizes have been reduced from 50 to ∼25 μm, then to 17 μm, and today uncooled camera manufacturers are looking into developing FPAs with pixels in the range of 10 to 13 μm while also increasing the resolution of the arrays to a nominal 1 K × 1 K format.1,2 The user-desired operational specifications generally require a 35-to 50-mK NETD and a 10-to 12-ms time constant with a frame rate of 30 or 60 Hz. A nominal F/1 optic is still required to obtain this sensitivity. There is also interest in further shortening the time constant to 5 ms or less while maintaining good NETD performance for higher speed motion applications. This raises a number of considerations, practical and theoretical, related to the benefits of making uncooled detector pixels much smaller than 17 μm. This paper explores some of those considerations.
Kopin's miniature Active Matrix Liquid Crystal Displays (AMLCD's) are rapidly becoming the display technology of choice in a wide range of military head mounted and sensor viewer applications. These low power, ruggedized displays operate from -37 o C to +65 o C with excellent imaging characteristics and reliability. Kopin and the US Army Night Vision and Electronic Sensors Directorate (NVESD) are co-operatively developing high resolution, full-color displays for day/night operations and image fusion applications. Kopin is leveraging the successful development of its monochrome SXGA (1280 x 1024) AMLCD to develop a color SXGA display and a color SVGA (800 x 600) display.Color technology approaches evaluated for these new products included color filters, frame sequential color, binary optic phase plate spot sequential color, and diffractive optic column sequential color. These approaches all involve frame sequential operation with the exception of color filters. A generic color frame sequential mode was selected for the SXGA display design that will allow operations of all frame-sequentially based approaches. This display facilitates color technology changes and upgrades by replacing the backlight assembly. The color filter approach was selected for the SVGA display. Both color technologies are used for Kopin commercial display products.Performance data and specifications for Kopin's displays will be presented with reference to military (HMD and weapon sight), industrial, and commercial applications. Analytical results and data from color approaches investigated will be presented and compared. Application extensions that utilize the new color technologies developed will be highlighted.
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