Small Pixel High Definition (SPHD) IR Cameras continue to improve in performance, resolution, and yield. SPHD product adoption is helping drive important performance goals such as sensitivity, resolution and other features. We report on continued developments of high-resolution small pitch infrared camera system technology developed at Cyan Systems. We highlight demonstrated imaging capability from two recent, large format, infrared focal plane array architectures. Specifically, we present results from our full-high-definition (FHD) 5-micron pixel CS-3 camera now capable of broadband (~0.7 – 5.0 micron) wavelength sensitivity. We show more results from our newest digital readout integrated circuit (DROIC) small pixel mid-wave infrared camera with ultra-high-definition (3840 x 2160) format, and Cyans CS-3 full-high-definition (1920 x 1080) Broadband IR camera.
Cyan Systems has continued to mature our small pixel camera performance, including improvements in the packaging, optics, and electronics. The associated camera components demonstrate key resolution and enabling capabilities. We report on recent results from our new digital readout integrated circuit (DROIC) small pixel mid-wave infrared camera with an ultra-high-definition (3840 x 2160) format, in addition to demonstrations with Cyan’s CS-3 full-high-definition (1920 x 1080) camera. We address small pixel spatial sampling and modulation transfer function issues as the pixel size shrinks, and we examine the difference between the performance of present devices and the new generation of small pixel cameras.
Cyan Systems has developed and made multiple improvements on our small pixel camera performance including low noise and compact size, weight, and power. The associated camera components demonstrate key resolution and enabling capabilities. Performance data from compact our new small pixel broadband full high-definition (1920x1080) camera technology is presented. We also report on recent results from our new digital readout integrated circuit (DROIC) small pixel mid-wave infrared camera with an ultra high-defintion (3840x2160) format.
We discuss our recent work in development of 1280 x 1024/12μm pitch bulk InAsSb MWIR/MWIR twocolor focal planes with cutoff wavelengths of 4.2μm and 5.1μm in the two bands as well as SWIR/MWIR focal planes with cutoff wavelengths of 3.0μm and 4.9μm. Barrier detectors based on the InAsSb materials system have recently been developed to realize substantial improvements in the performance of MWIR detectors operating in a single MWIR wavelength band, enabling FPA performance at operating temperatures as high as 150K. We have extended this detector architecture to encompass two-color detectors operating in a sequential mode utilizing back-to-back barrier devices. These detectors utilize the ternary alloy InAsSb materials system grown by molecular-beam epitaxy on GaAs substrates as a pathway to cost-effective production of large-area focal-plane arrays. Based on extensive FPA characterization, NEDT values of 18.3mK (Band-1) and 14.2mK (Band-2) were measured under f/2.3 illumination at an array operating temperature of T = 120K, with high NEDT operabilities (2x median) of 99.93% and 99.7% in Band-1 and Band-2, respectively. No significant performance degradation was observed in epoxystabilized hybrids after 500 thermal cycles between 300K and 110K. Finally, we discuss the progress that has been made in SWIR/MWIR array development and present measurements of 1280 x 1024 FPA performance for SWIR/MWIR focal planes with cutoff wavelengths of 3.0μm and 4.9μm at T = 120K. NEDT values (f/2.3 illumination) of 18.5mK (SWIR) and 15.0mK (MWIR) and high operabilities of 99.96% (SWIR) and 99.3% (MWIR) for cutoff wavelengths of 3.0μm and 4.9μm were measured.
Barrier detectors based on III-V materials have recently been developed to realize substantial improvements in the performance of mid-wave infrared (MWIR) detectors, enabling FPA performance at high operating temperatures. The relative ease of processing the III-V materials into large-format, small-pitch FPAs offers a cost-effective solution for tactical imaging applications in the MWIR band as an attractive alternative to HgCdTe detectors. In addition, small pixel (5-10μm pitch) detector technology enables a reduction in size of the system components, from the detector and ROIC chips to the focal length of the optics and lens size, resulting in an overall compactness of the sensor package, cooling and associated electronics. To exploit the substantial cost advantages, scalability to larger format (2kx2k/10μm) and superior wafer quality of large-area GaAs substrates, we have fabricated antimony based III-V bulk detectors that were metamorphically grown by MBE on GaAs substrates. The electro-optical characterization of fabricated 2kx2k/10μm FPAs shows low median dark current (3 x 10-5 A/cm2 with λco = 5.11μm or 2.2 x 10-6 A/cm2 with λco = 4.6μm) at 150K, high NEdT operability (3x median value) >99.8% and >60% quantum efficiency (non-ARC). In addition, we report our initial result in developing small pixel (5μm pitch), high definition (HD) MWIR detector technology based on superlattice III-V absorbing layers grown by MBE on GaSb substrates. The FPA radiometric result is showing low median dark current (6.3 x 10-6 A/cm2 at 150K with λco = 5.0μm) with ~50% quantum efficiency (non-ARC), and low NEdT of 20mK (with averaging) at 150K. The detector and FPA test results that validate the viability of Sb-based bulk and superlattice high operating temperature MWIR FPA technology will be discussed during the presentation.
We describe our recent results in developing and maturing small pixel (5μm pitch), high definition (HD) mid-wave infrared (MWIR) detector technology as well as focal-plane-array (FPA) hybrids, and prototype 2.4 Megapixel camera development operating at high temperature with low dark current and high operability. Advances in detector performance over the last several years have enabled III-V high operating temperature (T≥150K), unipolar detectors to emerge as an attractive alternative to HgCdTe detectors. The relative ease of processing the materials into large-format, small-pitch FPAs offers a cost-effective solution for tactical imaging applications in the MWIR band. In addition, small pixel detector technology enables a reduction in size of the system components, from the detector and ROIC chips to the focal length of the optics and lens size, resulting in an overall compactness of the sensor package, cooling and associated electronics. An MBE system has been used to grow antimony-based detector structures with 5.1μm cutoff with low total thickness variation (TTV) across a 3” wafer, in order to realize high interconnect yield for small-pitch FPAs. A unique indium bump scheme is proposed to realize 5μm pitch arrays with high connectivity yield. Several 1kx2k /5μm hybrids have been fabricated using Cyan’s CS3 ROICs with proper backend processing and finally packaged into a portable Dewar camera. The FPA radiometric result is showing low median dark current of 2.3x10-5 A/cm2 with > 99.9% operability, and >60% QE (without AR coating).
InAsSb material with a cutoff wavelength in the 5 μm range has been grown on GaAs substrates. The MWIR InAsSb detector arrays were fabricated and hybridized to a ROIC to permit measurement of the electrical and optical properties of detectors. Detector arrays were fabricated in a 1024 x 1024 format on an 18 μm pitch. A fanout was utilized to directly acquire data from a set of selected detectors without an intervening read out integrating circuit (ROIC). Variable temperature Jdark vs Vd measurements have been made with the dark current density ~ 10-5 A/cm2 at 150 K. The external QE measured using a narrow band filter centered at ~ 4 μm had values in the 65 – 70 % range. Since the detectors were illuminated through a GaAs substrate, which has a reflectance of 29%, the internal QE is greater than 90%. A 1024 x 1024 ROIC on an 18 μm pitch was also designed and fabricated to interface with the barrier detectors. The ROIC operates at 30 Hz frame rate and has a well capacity of 20.7 M electrons. QE at 150 K for a 1024 x 1024 detector array hybridized to a ROIC had a median D* at 150 K under a flux of 1.07 x 1015 ph/(cm2/s) was 1.2 x 1011 cm Hz1/2 /W. The NEdT was 44 mK and imagery was obtained at 150 K using an f/2.3 MWIR lens.
InAsSb material with a cutoff wavelength in the 5 μm range has been grown on GaAs substrates. The MWIR
InAsSb detector arrays were fabricated and hybridized to fanouts and ROICs to permit measurement of the
electrical and optical properties of detectors. Detector arrays were fabricated in a 1024 x 1024 format on an 18
μm pitch. A fanout was utilized to directly acquire data from a set of selected detectors without an intervening
read out integrating circuit (ROIC). Variable temperature Jdark vs Vd measurements have been made with the
dark current density ~ 10-5 A/cm2 at 150 K. The external QE measured using a narrow band filter centered at ~ 4 μm had values in the 65 - 70 % range. Since the detectors were illuminated through a GaAs substrate
which has a reflectance of 29%, the internal QE is greater than 90 %.
A 1024 x 1024 ROIC on an 18 μm pitch was also designed and fabricated to interface with the barrier
detectors. The ROIC operates at 30 Hz frame rate and has a well capacity of 20.7 M electrons. QE at 150 K
for a 1024 x 1024 detector array hybridized to a ROIC had a median D* at 150 K under a flux of 1.07 x 1015
ph/(cm2/s was 1.2 x 1011 cm Hz1/2 /W. The NEdT was 44 mK and imagery was obtained at 150 K using an f/2.3 MWIR lens.
Mid-wavelength infrared (MWIR) InAsSb alloy barrier detectors grown on GaAs substrates were characterized as a function of temperature to evaluate their performance. Detector arrays were fabricated in a 1024 × 1024 format on an 18 μm pitch. A fanout was utilized to directly acquire data from a set of selected detectors without an intervening read out integrating circuit (ROIC). The detectors have a cutoff wavelength equal to ~ 4.9 μm at 150 K. The peak internal quantum efficiency (QE) required a reverse bias voltage of 1 V. The detectors were diffusion-limited at the bias required to attain peak QE. Multiple 18 μm × 18 μm detectors were tied together in parallel by connecting the indium bump of each detector to a single large metal pad on the fanout. The dark current density at -1 V bias for a set of 64 × 64 and 6 × 6 array of detectors, each of which were tied together in parallel was ~ 10-3 A/cm2 at 200 K and 5 × 10-6 A/cm2 at 150 K. The 4096 (64 × 64) and 36 (6 × 6) detectors, both have similar Jdark vs Vd characteristics, demonstrating high operability and uniformity of the detectors in the array. The external QE measured using a narrow band filter centered at ~ 4 μm had values in the 65 – 70 % range. Since the detectors were illuminated through a GaAs substrate which has a reflectance of 29%, the internal QE is greater than 90 %. A 1024 × 1024 ROIC on an 18 μm pitch was also designed and fabricated to interface with the barrier detectors. QE at 150 K for a 1024 × 1024 detector array hybridized to a ROIC matched the QE measured on detectors that were measured directly through a fanout chip. Median D* at 150 K under a flux of 1.07 × 1015 ph/(cm2/s was 1.0 x 1011 cm Hz1/2 /W.
We describe our recent efforts in developing visible to mid-wave (0.5 µm to 5.0 µm) broadband photon-trap InAsSb-based infrared detectors grown on GaAs substrates operating at high temperature (150-200K) with low dark current and high quantum efficiency. Utilizing an InAsSb absorber on GaAs substrates instead of an HgCdTe absorber will enable low-cost fabrication of large-format, high operating temperature focal plane arrays. We have utilized a novel detector design based-on pyramidal photon trapping InAsSb structures in conjunction with compound barrier-based device architecture to suppress both G-R dark current, as well as diffusion current through absorber volume reduction. Our optical simulation show that our engineered pyramid structures minimize the surface reflection compared to conventional diode structures acting as a broadband anti-reflective coating (AR). In addition, it exhibits > 70-80% absorption over the entire 0.5 µm to 5.0 µm spectral range while providing up to 3× reduction in absorber volume. Lattice-mismatched InAs0.82Sb0.18 with 5.25 µm cutoff at 200K was grown on GaAs substrates. 128×128/60μm and 1024×1024/18μm detector arrays that consist of bulk absorber as well as photon-trap pyramid structures were fabricated to compare the detector performance. The measured dark current density for the diodes with the pyramidal absorber was 3× lower that for the conventional diode with the bulk absorber, which is consistent with the volume reduction due to the creation of the pyramidal absorber topology. We have achieved high D* (< 1.0 x 1010 cm √Hz/W) and maintain very high (< 80 %) internal quantum efficiency over the entire band 0.5 to 5 µm spectral band at 200K.
In InAs1-xSbx material alloy composition was adjusted to achieve 200K cutoff wavelengths in the 5 μm
range. Reflectance was minimized and absorption in the InAs1-xSbx material maximized by the use of
pyramid shaped structures fabricated in the InAs1-xSbx material which function as an AR coating.
Compound-barrier (CB) detectors were fabricated and tested for optical response and dark current density
versus bias measurements were acquired as a function of temperature. For 5 μm cutoff detectors, QE is
high, ~ 75 % between 4.0 μm and 4.6 μm and > 80 % between 2.0 μand 4.0 μm, demonstrating the
efficacy of the pyramids as photon trap structures and as a replacement for multi-layer AR-coatings. Jdark
in the low 10-3 A/cm2 range at 200 K and low 10-5 A/cm2 range at 150 K was measured at the bias at
which the QE peaked.
The Photon-Trap Structures for Quantum Advanced Detectors (PT-SQUAD) program requires MWIR
detectors at 200 K. One of the ambitious requirements is to obtain high (> 80 %) quantum efficiency over
the visible to MWIR spectral range while maintaining high D* (> 1.0 x 1011 cm √Hz/W) in the MWIR. A
prime method to accomplish the goals is by reducing dark diffusion current in the detector via reducing
the volume fill ratio (VFR) of the detector while optimizing absorption. Electromagnetic simulations
show that an innovative architecture using pyramids as photon trapping structures provide a photon
trapping mechanism by refractive-index-matching at the tapered air/semiconductor interface, thus
minimizing the reflection and maximizing absorption to > 90 % over the entire visible to MWIR spectral
range. InAsSb with bandgap appropriate to obtaining a cutoff wavelength ~ 4.3 μm is chosen as the
absorber layer. An added benefit of reducing VFR using pyramids is that no AR-coating is required.
Compound-barrier (CB) detector test structures with alloy composition of the InAsSb absorber layer
adjusted to achieve 200 K cutoff wavelength of 4.3 μm (InAsSb lattice-matched to GaSb). Dark current
density at 200 K is in the low 10-4 A/cm2 at Vd = -1.0 V. External QE ~ 0.65 has been measured for
detectors with a Si carrier wafer attached. Since illumination is through the Si carrier wafer that has a
reflectance of ~ 30 %, this results in an internal QE > 0.9.
Recent efforts in developing InAs/GaSb strained-layer superlattices for LWIR detectors are
described. The structural properties of the devices grown by MBE at HRL were evaluated using
optical microscopy, x-ray diffraction, and atomic force microscopy. Epilayer roughness and surface
morphology are briefly described. Small format focal plane arrays were fabricated to serve as a
baseline for device study, and to determine the effects of underfill epoxy on detector performance. A
novel approach for epilayer transfer on silicon is also presented.
InAs/GaSb-based type II superlattices (T2SL) offer a manufacturable FPA technology
with FPA size, scalability and cost advantages over HgCdTe. Work at Jet Propulsion
Laboratory (JPL), Naval Research Laboratory (NRL), and Northwestern University
(NWU) has shown that the performance gap between HgCdTe and T2SL FPAs has
narrowed to within 5-10x over the last two years1,2,3. Due to the potential of T2SL
technology for fabrication of large format (> 1k x1k) and dual-band arrays, HRL has
recently resurrected efforts in this area4. We describe the progress on the FastFPA
program funded by the Army Night Vision Labs towards the development of detectors
and focal plane arrays (FPAs). Progress made in the areas of MBE growth, mesa diode
fabrication, dry etch processing, and FPA fabrication over the last one year is presented.
We have designed and evaluated (using computer simulations) several different 2D phased arrays with square elements for deep localized hyperthermia. These array include a 20x20 planar array, a 80x16 cylindrical-section array, and a 16x16 spherical-section array. Also, we have designed a new phased array with circular elements. We used single and multiple focus scanning methods with intensity gain maximization. We found that the array with circular elements is more effective in reducing grating lobes compared to the same array with square elements. The grating lobes were at least 30 dB smaller than the phased array with square elements and intensity gain was at least 1 dB greater. In addition, with equal intensity distribution patterns for rectangular and circular phased arrays, the number of elements in the circular phased array was smaller and its intensity gain was greater than the other arrays.
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