Raytheon Vision Systems (RVS) has developed an efficient method to measure MTF on Visible through MWIR small pixel FPAs. The measured data was obtained using an advanced but low cost test set with sub μm target projection on the FPA and real time display of the LSF as the slit is walked through focus. The test set is commercially procured, maintained and calibrated, provides target and filter holders and a light source. The analysis summary includes references from simplified MTF published analysis tools and a list of artifacts to be aware of when measuring MTF. The SWIR and MWIR detectors have a Mesa structure geometry for improved MTF performance and the Visible has state of the art crosstalk control to provide excellent MTF performance. The modeled data is compared to measured tilted slit MTF measured data and shows close agreement.
Raytheon has built hybrid focal planes based on Silicon P-I-N photo-sensors for the past three decades. The device has undergone a continuous improvement process during this period. The detector material has been improved and the thickness has been greatly reduced. Most recently, the readout integrated circuit (ROIC) and the hybridization process, have undergone significant advancements1,2,3. This paper presents recent advancements in the latest generation 8μm pixelpitch 1k2 format and 5k2 format visible Si PIN focal-planes. The current family of devices has very low read-noise ROICs, low detector dark current, operate with a 25 volt bias and deliver 50% mean response operability greater than 99.995%.
Wire used to connect focal plane electrical connections to external electrical circuitry can be modeled using the length, diameter and loop height to determine the resonant frequency. The design of the adjacent electric board and mounting platform can also be analyzed. The combined resonant frequency analysis can then be used to decouple the different component resonant frequencies to eliminate the potential for metal fatigue in the wires. It is important to note that the nominal maximum stress values that cause metal fatigue can be much less than the ultimate tensile stress limit or the yield stress limit and are degraded further at resonant frequencies. It is critical that tests be done to qualify designs that are not easily simulated due to material property variation and complex structures. Sine wave vibration testing is a critical component of qualification vibration and provides the highest accuracy in determining the resonant frequencies which can be reduced or uncorrelated improving the structural performance of the focal plane assembly by small changes in design damping or modern space material selection. Vibration flow down from higher levels of assembly needs consideration for intermediary hardware, which may amplify or attenuate the full up system vibration profile. A simple pass through of vibration requirements may result in over test or missing amplified resonant frequencies that can cause system failure. Examples are shown of metal wire fatigue such as discoloration and microscopic cracks which are visible at the submicron level by the use of a scanning electron microscope. While it is important to model and test resonant frequencies the Focal plane must also be constrained such that Coefficient of Thermal expansion mismatches are allowed to move and not overstress the FPA.
A multi-range focal plane was developed and delivered by Raytheon Vision Systems for a docking system that was demonstrated on STS-134. This required state of the art focal plane and electronics synchronization to capture nanosecond length laser pulses to determine ranges with an accuracy of less than 1 inch.
Raytheon Vision Systems (RVS) has developed scanning, high-speed (<3klps), all digital, with on-chip Analog-to-Digital Conversion (ADC), mid-wave infrared (MWIR 3-5mm) focal plane arrays (FPA) with excellent modulation transfer function (MTF) performance. Using secondary ion mass spectrometry (SIMS) data and detailed models of the mesa geometry, RVS modeled the predicted detector MTF performance of detectors. These detectors have a mesa structure and geometry for improved MTF performance compared to planar HgCdTe and InSb detector structures and other similar detector structures such as nBn. The modeled data is compared to measured MTF data obtained from edge spread measurements and shows good agreement, Figure 1. The measured data was obtained using a custom advanced test set with 1µm precision alignment and automatic data acquisition for report generation in less than five minutes per FPA. The measured MTF values of 83 unique parts, Figure 2, had a standard deviation of 0.0094 and a mean absolute deviation of 0.0066 at half Nyquist frequency, showing excellent process repeatability and a design that supports high MTF with good repeatability.
New foundry processes continue to produce smaller features and new designs. These new devices must be screened to
validate their usefulness for long lifetime use. The Failure-in-Time analysis in conjunction with foundry qualification
information can be used to evaluate foundry device lifetimes. This analysis is a helpful tool when zero failure life tests
are performed. The reliability of the device is estimated by applying the failure rate to the use conditions. JEDEC
publications.2,3,4 are the industry accepted methods.
Resolving the complexity of coastal and estuarine waters requires high spatial resolution, hyperspectral
imaging spectroradiometry. Hyperspectral measurements also provide capability for measuring bathymetry
and bottom types in optically shallow water and for detailed cross calibration with other instruments in
polar and geosynchronous orbit. This paper reports on recent design studies for a hyperspectral Coastal
Imager (CI - pronounced "sea") that measures key data products from sun synchronous orbit. These
products include water-leaving radiances in the near-ultraviolet, visible and near-infrared for separation of
absorbing and scattering coastal water constituents and for calculation of chlorophyll fluorescence. In
addition, CI measures spectral radiances in the near-infrared and shortwave infrared for atmospheric
corrections while also measuring cloud radiances without saturation to enable more accurate removal of
instrument stray light effects. CI provides contiguous spectral coverage from 380 to 2500 nm at 20 m
GIFOV at nadir across 5000+ km2 scenes with spectral sampling, radiometric sensitivity and calibration
performance needed to meet the demanding requirements of coastal imaging. This paper describes the CI
design, including concepts of operation for data collection, calibration (radiometric, spectral and spatial),
onboard processing and data transmission to Earth. Performance characteristics for the instrument and all
major subsystems including the optics, focal plane assemblies, onboard calibration, onboard processing and
thermal subsystem are presented along with performance predictions for instrument sensitivity and
calibration. Initial estimates of size, mass, power and data rate are presented.
Polarimetry sensor development has been in work for some time to determine the best use of polarimetry to differentiate
between manmade objects and objects made by nature. Both MWIR and LWIR and 2-color staring Focal Plane Arrays
(FPAs) and LWIR scanning FPAs have been built at Raytheon Vision Systems each with exceedingly higher
performance. This paper presents polarimetric performance comparisons between staring 2562 MWIR, 2562 LWIR, 5122
LWIR/LWIR staring FPAs and scanning LWIR FPAs.
LWIR polarimetry has the largest polarimetric signal level and a larger emissive polarimetric signature than MWIR
which makes LWIR less dependent on sun angles. Polished angled glass and metal objects are easily detected using
While single band 9-11 um LWIR polarimetry has advantages adding another band between 3 and 7 um improves the
capability of the sensor for polarization and spectral phenomenology. In addition the 3-7 um band has improved NEDT
over the 9-11 um band due to the shorter detector cutoff reducing the Noise Equivalent Degree of Linear Polarization.
To gain acceptance polarimetric sensors must provide intelligence signatures that are better than existing nonpolarimetric
Infrared sensors. This paper shows analysis indicating the importance of NEDOLP and Extinction ratios.
Advancements in finer geometry and technology advancements in circuit design now allow placement of digital
architecture on cryogenic focal planes while using less power than heritage analog designs. These advances in
technology reduce the size, weight, and power of modern focal planes. In addition, the interface to the focal plane is
significantly simplified and is more immune to Electromagnetic Interference (EMI). The cost of the customer's
instrument after integration with the digital scanning Focal Plane Array (FPA) has been significantly reduced by placing
digital architecture such as Analog to digital convertors and Low Voltage Differential Signaling (LVDS) Inputs and
Outputs (I/O) on the Read Out Integrated Circuit (ROIC).
Large format detector arrays are responsive uniformly over spectral 1-5μm wavelength
range and are available with RVS' high quality HgCdTe detector epitaxial layers on large
area 15 cm diameter wafers. Large wafers enable both low cost High Definition (HD)
staring FPAs, as well as the ability to approach giga-pixel format detector arrays with a
seamless 10cm ×10cm continuous image plane size possible. With a 15 cm diameter
detector substrate it is a straightforward growth path to a 5k×5k μm pitch 25 Mega-pixel
infrared focal plane array (FPA) with smaller pitches allowing even greater format along
the 10cm die length. This paper describes arrays 1.5 to 4 Mega-pixel infrared HgCdTe
developed by RVS for demanding higher performance applications. Performance data
for both the detector and ROIC for typical SWIR and MWIR FPAs operating at 85K will
be presented. This paper will provide FPA performance capability for small pitch large
format HgCdTe/Si detector arrays fabricated at RVS and manufacturing readiness low
cost Mega-pixel infrared FPAs for current and future wide FOV high-resolution systems.
Raytheon has been building silicon p-i-n (Si-PIN) detector arrays for the past twenty years for various remote sensing
instruments such as MODIS, EO-1, and Landsat now on orbit. See Figure 1. The Si-PIN technology at Raytheon has
matured in the past five years with the addition of a dedicated silicon wafer fab, improvements in hybrid technologies,
and the enhanced digital functionality of RVS custom read out integrated circuits (ROICs). This paper will discuss the
advantages that Raytheon Si-PIN arrays offer over conventional CCDs and monolithic CMOS imagers such as 100%
optical fill factor, high QE (visible - near IR), high MTF, and radiation hardness.
Polarimetry sensor development has been in work for some time to determine the best use of polarimetry to differentiate
between manmade objects and objects made by nature. Both MWIR and LWIR Focal Plane Arrays (FPAs) have been
built at Raytheon Vision Systems each with exceedingly higher extinction ratios. This paper compares field imagery
between MWIR and LWIR micro-grid polarimetric sensors independently and during simultaneous image collects.
LWIR polarimetry has the largest polarimetric signal level and an emissive polarimetric signature which allows
detection at thermal crossover and is less dependent on sun angles. Polished angled glass and metal objects are easily
detected using LWIR polarimetry. While LWIR
polarimetry has many advantages its resolution is not as
good as MWIR.
MWIR polarimetry has higher resolution than LWIR. With
good sun angles plastic drums, and wet surfaces provide
good polarization signatures. With poor sun angles
detection can be challenging.
To gain acceptance polarimetric sensors must provide
intelligence signatures that are better than existing nonpolarimetric
Infrared sensors. This paper shows several
examples of images without polarimetric processing and
identical images with MWIR and/or LWIR polarimetric
fusion onto the non-polarized images to show the
improvement of detection using polarimetric sensors. It is
the author's belief that the fastest way to gain acceptance of
polarimetric remote sensing is through field demonstration
as shown in Figure 1.