Millimeter-wave (mmW)/sub-mmW/THz region of the electro-magnetic spectrum enables imaging thru clothing and other obscurants such as fog, clouds, smoke, sand, and dust. Therefore considerable interest exists in developing low cost millimeter-wave imaging (MMWI) systems. Previous MMWI systems have evolved from crude mechanically scanned, single element receiver systems into very complex multiple receiver camera systems. Initial systems required many expensive mmW integrated-circuit low-noise amplifiers. In order to reduce the cost and complexity of the existing systems, attempts have been made to develop new mmW imaging sensors employing direct detection arrays. In this paper, we report on Raytheon’s recent development of a unique focal plane array technology, which operates broadly from the mmW through the sub-mmW/THz region. Raytheon’s innovative nano-antenna based detector enables low cost production of 2D staring mmW focal plane arrays (mmW FPA), which not only have equivalent sensitivity and performance to existing MMWI systems, but require no mechanical scanning.
Transmittance spectra of solid and vapor samples of trinitrotoluene (TNT) in the spectral range 0.6 to 10 THz at
resolutions up to 1 GHz are reported. Uniform solid samples of ~100 &mgr;m thickness gave stronger absorption and more
resolved structure than previous studies. New absorption lines for TNT solid below 100 cm-1 are reported. A heated 10
m multpass White cell was used for spectroscopy of the vapor. Strong absorption bands yield unexpectedly large
absorption cross sections for the anticipated saturated vapor pressure at the cell temperature, leaving their assignment to
TNT in doubt. These results indicate that path lengths exceeding 10 m and temperatures higher than 40 C, or
significantly higher instrumental sensitivity, are needed for sensing of TNT vapor in the spectral range 0.6 to 10 THz.
The low vapor pressure and concentration of explosive such as TNT and RDX pose significant problems for the
detection of explosive vapors in the mmW bands. For the positive identification of explosive vapors using an uncooled
passive mmW imaging spectrometer with a low false alarm rate (FAR) requires an unprecedented sensitivity of <150
fW. We report on the recent development of a novel uncooled mmW antenna-coupled direct detector, which shows
promise of meeting this requirement.
The advantages and uses of infrared (IR) imaging continue to grow. As such, a new generation of requirements for IR focal plane arrays (IRFPAs) has emerged that affects the development of both the detectors and readout integrated circuits (ROICs). Because these applications have varying requirements, a universal set of FPAs cannot be made to satisfy all needs, and custom designs are needed. However, the desired capabilities follow a common theme. The industry is receiving more demands in the areas of larger formats, increased sensitivity, smaller pixels, and higher functionality. These must be met in addition to achieving production quantities at a low cost. This paper focuses on two main facets of the complex FPA, the detector and readout integrated circuit (ROIC), to address the evolving requirements. For detectors, we explore both the cooled and uncooled technologies, where HgCdTe grown by molecular beam epitaxy (MBE) and vanadium oxide (VOx) microbolometers are discussed, respectively, for the two areas. Development in ROICs expands in terms of smart features, on-chip signal processing, and on-chip analog-to-digital conversion.
KEYWORDS: Readout integrated circuits, Staring arrays, Sensors, Signal processing, Digital electronics, Filtering (signal processing), Spatial filters, Standard readout integrated circuits, Signal detection, Analog electronics
As 2nd and 3rd generation Focal Plane Arrays (FPA) become more complex, the readout integrated circuit (ROIC) has emerged as a major discriminator in system performance. The focus of development and advancement has traditionally involved the detector technology. Early ROICs were simple multiplexers that performed little if any signal processing on the detector diode signal. Advances in silicon fabrication processes for analog integrated circuits have opened a new era in IRFPAs where signal digital functions can be achieved on the focal plane. We present an overview of significant advances in the area of mixed mode ROIC designs that enable greater functionality and performance of the sensor chip assembly. Innovations, continuing progress in CMOS technology, and greater foundry access have allowed enhancements in practically every aspect of the ROIC, from sophisticated unit cells to lower noise and lower power signal paths to highly programmable digital support circuitry. Denser detector input circuits with active amplifiers (FEDI or CTIA) have been implemented in unit cells as small as 27 micrometer X 27 micrometer. In addition, multiple gain, temporal filtering, or spatial filtering capabilities have been incorporated into these small unit cells. Significant reductions in focal plane power have been fabricated and demonstrated enabling a factor of 2 increase in frame rates for very large staring FPAs and a factor of 4 increase in line rates for scanning FPAs. Other developments include, but are not limited to, alternative schemes for time-delayed integration (TDI) and breakthroughs for uncooled applications. As the chip designs increase in capability, greater systems on a chip are feasible, especially with more programmable features provided by the on-chip digital circuitry.
Conference Committee Involvement (8)
Infrared Technology and Applications LI
14 April 2025 | Orlando, Florida, United States
Infrared Technology and Applications L
21 April 2024 | National Harbor, Maryland, United States
Infrared Technology and Applications XLIX
30 April 2023 | Orlando, Florida, United States
Infrared Technology and Applications XLVIII
3 April 2022 | Orlando, Florida, United States
Infrared Technology and Applications XLVII
12 April 2021 | Online Only, Florida, United States
Infrared Technology and Applications XLVI
27 April 2020 | Online Only, California, United States
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