In this paper, we review selected imaging and related technology development programs in the Defense Advanced Research Projects Agency (DARPA) Microsystems Technologies Office (MTO). An overview is presented for the evolution of Joule-Thomson (J-T) micro-cryogenic cooler (MCC) technology. The initial design of a system on a chip method is shown for these micro-coolers to be used in conjunction with high operating temperature mid-wave infrared (MWIR) and long-wave infrared (LWIR) focal plane arrays. For the reflective visible band, results are shown for a gigapixel monocentric multi-scale camera design to solve the scaling issues for high pixel count and wide field of view. Lastly, we discuss two different approaches to multiband imaging and the potential advantages of this technology for the enhanced detection, recognition, and identification of targets.
In this paper, we review a few selected imaging technology development programs at the Defense Advanced Research Projects Agency (DARPA) in the reflective visible to the emissive/thermal long wave infrared (LWIR) spectral bands. For the reflective visible band, results are shown for two different imagers: a gigapixel monocentric multi-scale camera design that solves the scaling issues for a high pixel count, and a wide field of view and a single photon detection camera with a large dynamic range. Also, a camera with broadband capability covering both reflective and thermal bands (0.5 μm to 5.0 μm) with >80% quantum efficiency is discussed. In the emissive/thermal band, data is presented for both uncooled and cryogenically cooled LWIR detectors with pixel pitches approaching the fundamental detection limits. By developing wafer scale manufacturing processes and reducing the pixel size of uncooled thermal imagers, it is shown that an affordable camera on a chip, capable of seeing through obscurants in day or night, is feasible. Also, the fabrication and initial performance of the world’s first 5 μm pixel pitch LWIR camera is discussed. Lastly, we use an initial model to evaluate the signal to noise ratio and noise equivalent differential temperature as a function of well capacity to predict the performance for this thermal imager.
High-performance large-format detector arrays responsive to the 1-5μm wavelength range of the infrared spectrum
fabricated using large area HgCdTe layers grown on 6-inch diameter (211) silicon substrates are available for advanced
imaging applications. This paper reviews performance and capabilities of Raytheon Vision Systems (RVS) HgCdTe/Si
Focal Plane Arrays (FPA) and shows 2k x 2k format MWIR HgCdTe/Si FPA performance with NEdT operabilities
better than 99.9%. SWIR and MWIR detector performance for HgCdTe/Si is comparable to established performance of
HgCdTe/CdZnTe wafers. HgCdTe devices fabricated on both types of substrates have demonstrated very low dark
current, high quantum efficiency and full spectral band fill factor characteristic of HgCdTe. HgCdTe has the advantage
of being able to precisely tune the detector cutoff via adjustment of the Cd composition in the MBE growth. The
HgCdTe/Si detectors described in this paper are p-on-n mesa delineated architecture and fabricated using the same
mature etch, passivation, and metallization processes as our HgCdTe/CdZnTe line. Uniform device quality HgCdTe
epitaxial layers and application of detector fabrication processes across the full area of 6-inch wafers routinely produces
high performing detector pixels from edge to edge of the photolithographic limits across the wafer, offering 5 times the
printable area as costly 6×6cm CdZnTe substrates. This 6-inch HgCdTe detector wafer technology can provide
applications demanding very wide FOV high resolution coverage the capability to produce a very large single piece
infrared detector array, up to a continuous image plane 10×10 cm in size. Alternatively, significant detector cost
reduction through allowing more die of a given size to be printed on each wafer is possible, with further cost reduction
achieved through transition towards automated detector fabrication and photolithographic processes for both increased
yields and reduced touch labor costs. RVS continues to improve its FPA manufacturing line towards achieving low cost
infrared FPAs with the format, size, affordability, and performance required for current and future infrared applications.
Raytheon Vision Systems (RVS) is producing large format, high definition HgCdTe-based MWIR and SWIR focal plane
arrays (FPAs) with pitches of 15 μm and smaller for various applications. Infrared sensors fabricated from HgCdTe
have several advantages when compared to those fabricated from other materials -- such as a highly tunable bandgap,
high quantum efficiencies, and R0A approaching theoretical limits. It is desirable to operate infrared sensors at elevated
operating temperatures in order to increase the cooler life and reduce the required system power. However, the
sensitivity of many infrared sensors, including those made from HgCdTe, declines significantly above a certain
temperature due to the noise resulting from increasing detector dark current.
In this paper we provide performance data on a MWIR and a SWIR focal plane array operating at temperatures up to
160K and 170K, respectively. The FPAs used in the study were grown by molecular beam epitaxy (MBE) on silicon
substrates, processed into a 1536x1024 format with a 15 μm pixel pitch, and hybridized to a silicon readout integrated
circuit (ROIC) via indium bumps to form a sensor chip assembly (SCA).
This data shows that the noise equivalent delta temperature (NEDT) is background limited at f/3.4 in the SWIR SCA
(cutoff wavelength of 3.7 μm at 130K) up to 140K and in the MWIR SCA (cutoff wavelength of 4.8 μm at 115K) up to