A high-resolution midwave infrared panoramic periscope sensor system has been developed. The sensor includes an f/2.5 catadioptric optical system that provides a field of view with 360-deg horizontal azimuth and -10- to +30-deg elevation without requiring moving components (e.g., rotating mirrors). The focal plane is a 2048×2048, 15-µm-pitch InSb detector operating at 80 K. An onboard thermoelectric reference source allows for real-time nonuniformity correction using the two-point correction method. The entire system (detector-Dewar assembly, cooler, electronics, and optics) is packaged to fit in an 8-in.-high, 6.5-in.-diameter volume. This work describes both the system optics and the electronics and presents sample imagery. We model both the sensor's radiometric performance, quantified by the noise-equivalent temperature difference, and its resolution performance. Model predictions are then compared with estimates obtained from experimental data. The ability of the system to resolve targets as a function of imaged spatial frequency is also presented.
A high-resolution mid-wave infrared panoramic periscope sensor system has been developed. The sensor includes a catadioptric optical system that provides a 360° horizontal azimuth by -10° to +30° elevation field of view without requiring moving components (e.g. rotating mirrors). The focal plane is a 2048 x 2048, 15μm pitch InSb detector operating at 80K. An on-board thermo-electric reference source allows for real-time nonuniformity
correction using the two-point correction method. The entire system (detector-dewar assembly, cooler, electronics and optics) is packaged to fit in an 8" high, 6.5" diameter volume. This work describes both the system optics and electronics and presents sample imagery. We also discuss the sensor's radiometric performance, quantified by the NEDT, as a function of key system parameters. The ability of the system to resolve targets as a function of imaged spatial frequency is also presented.
We are developing corrugated quantum well infrared photodetector (C-QWIP) technology for long wavelength
applications. A number of large format 1024 × 1024 C-QWIP focal plane arrays (FPAs) have been demonstrated. The
measured quantum efficiency η is ranging from 15 - 37%, depending on the detector type, doping density and number
of quantum wells in the detector material. The photoconductive gain is between 0.07 and 0.19, while the spectral width
is between 1.5 and 3.5 microns. Despite the large integrated η of the C-QWIPs, the number of collected photoelectrons
can be limited in shorter cutoff, small pixel FPAs under high speed operation. In this case, the read noise will have a
large impact on the system sensitivity. In this paper, we will discuss the detector model, the measured pixel
characteristics, and the effects of read noise on the FPA performance. Our analysis shows that the tolerable read noise
improves with the cutoff wavelength. For example, to achieve a sensitivity of 20 mK at 2 msec integration time, the
respective read noise will be 1000, 2000, 3000, and 4000 e¯ at λc = 8.8, 9.4, 10.7 and 11.7 μm. This analysis will help
to determine the read noise requirement for the C-QWIP FPAs.
ARL and L3-CE have been developing corrugated quantum well infrared photodetector (C-QWIP) technology for long
wavelength applications. Several large format 1024 × 1024 C-QWIP focal plane arrays (FPAs) have been demonstrated.
In this paper, we provide a detailed analysis on the FPA performance in terms of quantum efficiency η and compare it
with a detector model. We found excellent agreement between theory and experiment when both the material
parameters and the pixel geometry are taken into account. For C-QWIPs with the bound-to-quasi-bound structure, a η of
37% is observed, albeit at a large voltage of -11V. Since this voltage is outside the operating regime of the existing
readout electronics, we investigated several more compatible structures and achieved η in the range of 15 - 26%. This
range of η, although lower than the original value, is still approximately three times higher than that of the grating
coupled QWIPs, and the coupling bandwidth is also three times wider. The C-QWIP approach thus holds significant
performance advantages over the grating approach. Combined with its economical processing steps and flexible
wavelength coverage, the C-QWIP technology has proven its advantages in infrared detection.
Simultaneous detection of intensity and polarization at the pixel-level has many important applications in the mid-infrared
region. In this work a large-format aluminum wire grid micro polarizer array has been fabricated and tested on
silicon substrates. The arrays were made on 150mm silicon wafers using a 193nm deep-UV stepper, with each array
spanning over 1-million pixels. A unique multilayer design and a large-area nanoscale projection lithography combined
with high-aspect ratio wire-grid structures were utilized to achieve optimum extinction coefficient and transmission.
Measured extinction coefficients on test samples exceeded 30-dB, with maximum transmission around 90%. These
arrays could be designed to match the focal-plane array geometry for integration with mid-IR imagers.
Past work with polarimetry in the mid-wave infrared (MWIR) has yielded mixed results. In order to better characterize
polarimetric content in the MWIR and short-wave infrared (SWIR) atmospheric windows, we are developing focal
plane array (FPA) technology that will address shortcomings in earlier devices. In particular, our efforts are focusing on
placing micro-polarizing grids in very close proximity to the P-N junction of the detector. By placing these micropolarizers
very close to the photodetector junction, the opportunity for polarimetric cross talk between pixels is
minimized. CE's unique process for fabricating FPAs is well suited for implementing this approach. Since a
polarimetric FPA consisting of a standard FPA and micro-wire grid polarizers reduces the effective FPA format by a
factor of two in both dimensions, the ability to produce extremely large format FPAs are critical to obtain high
resolution polarimetric imagery. CE's FPA fabrication process is also highly scalable and has successfully fabricated
FPAs as large as 2k by 2k. This paper describes the progress we've made towards developing these unique polarimetric
The corrugated quantum well infrared detector (C-QWIP) offers improvements to quantum efficiency and spectral
bandwidth compared to current commercial QWIPs. In addition to improved performance, the C-QWIP also uses
manufacturing processes that are mature and low cost. Thus, very large format focal plane arrays (FPAs) can be
fabricated with high yield. There are two applications where the C-QWIP can provide cost effective solutions. The first
is very large format long-wave infrared (LWIR) sensors. Most very large format FPAs operate in the mid-wave infrared
(MWIR). The MWIR band has significantly lower flux than LWIR, therefore in situations where the backgrounds are
cold or there is potential motion blur, the LWIR C-QWIP offers better performance. The second application is two-color
registered high-resolution wide area imagery. ARL and CE have been developing both C-QWIP detectors and
read-out integrated circuits to support these needs. This paper describes the progress we've made in developing high
conversion efficiency LWIR C-QWIP FPAs and MWIR/LWIR two-color FPAs and our path forward to multimegapixel
C-QWIP FPAs and sensors.
In the rapid development of GaAs Quantum Well Infrared Photodetectors (QWIPs) we have fabricated a 1,024 x 1,024 (1K x 1K), 8-12 μm infrared focal plane array (FPA). This focal plane array is a hybrid using an L3 Cincinnati Electronics silicon readout integrated circuit (ROIC) bump bonded to the 1 megapixel GaAs QWIP. This effort was a collaboration of engineers at the Goddard Space Flight Center (GSFC), the Army Research Laboratory (ARL) and L3 Cincinnati Electronics (L3). We have integrated this focal plane into an SE-IR based imaging camera system and performed tests over the 55K-77K temperature range. As in previous developments the ease of fabrication of the GaAs array continues to be a valuable asset. The overall focal plane development costs are currently dominated by the costs associated with the silicon readout/hybridization. The GaAs array fabrication is based on a high yield, well-established GaAs processing capability. The broadband long wavelength response of this array combined with markedly improved quantum efficiency is of particular value in science applications where spectroscopy is required. One of the features of GaAs QWIP technology is the ability to precisely design and fabricate arrays responsive to a particular IR spectral region but the spectral response is typically only a few tenths of a micrometer wide limiting the spectral information content. By broadening the spectral response of this device the applications for imaging and spectroscopy are substantially increased. In this paper we will present the latest results of our corrugated 1K x 1K, 8-12 μm infrared focal plane array development including fabrication methodology, test data and experiments.
Recently, large format and high quantum efficiency corrugated quantum well infrared photodetector (C-QWIP) FPAs
have been demonstrated. Since the detector light coupling scheme does not alter the intrinsic absorption spectrum of the
material, the QWIPs can now be designed with different bandwidths and lineshapes to suit various applications.
Meanwhile, the internal optical field distribution of the C-QWIPs is different from that of a grating coupled detector, the
material structure thus should be designed and optimized differently with respect to quantum efficiency, conversion
efficiency and operating temperature. In this paper, we will provide a framework for the material design. Specifically,
we will present a theoretical detector performance model and discuss two specific examples, namely with 9.2 and 10.2
μm cutoff wavelengths. We found that for both λc, the photocurrent to dark current ratio is maximized at an electron
doping density ND of 0.28 × 1018 cm-3. The dark current limited detectivity meanwhile reaches a maximum at a higher
ND of 0.45 × 1018 cm-3. But the lowest noise equivalent noise temperature difference is actually obtained at an even
higher ND of 1.0 × 1018 cm-3 due to the larger quantum efficiency, if there are no limitations on the readout charge
capacity. These predictions are compared with the data of a 1024 × 1024 C-QWIP FPA hybridized to a fan-out circuit,
and the results are consistent.
Large format corrugated quantum well infrared photodetector (C-QWIP) focal plane arrays (FPAs) have been
developed over the past two years. The results of this development have demonstrated the potential for this technology
to satisfy requirements for very large format high performance long-wave infrared (LWIR) imaging systems. One
particular C-QWIP design has focused on developing an FPA that operates in the 8 to 10 &mgr;m spectrum with integration
times in the millisecond regime when used against warm backgrounds. This FPA is very suitable for many LWIR
applications and has been integrated into a camera system. The specifications of that camera are described in this paper.
The characterization of this camera system includes standard electro-optical tests and compares the results of those tests
to theoretical models for the FPA. This paper concludes by describing the ongoing effort to tailor the system
specifically for the C-QWIP. This includes design features of the read-out integrated circuit (ROIC), dewar-cooler
design and interfacing electronics, and video processing. This thorough characterization of the camera has
demonstrated the utility of the C-QWIP FPA for LWIR imaging and has established a path forward to further improve
the performance of imaging systems implementing this technology.
We report on the fabrication and characterization of microcantilever based uncooled focal plane array (FPA) for infrared imaging. By combining a streamlined design of microcantilever thermal transducers with a highly efficient optical readout, we minimized the fabrication complexity while achieving a competitive level of imaging performance. The microcantilever FPAs were fabricated using a straightforward fabrication process that involved only three photolithographic steps (i.e. three masks). A designed and constructed prototype of an IR imager employed a simple optical readout based on a noncoherent low-power light source. The main figures of merit of the IR imager were found to be comparable to those of uncooled MEMS infrared detectors with substantially higher degree of fabrication complexity. In particular, the NETD and the response time of the implemented MEMS IR detector were measured to be
as low as 0.5K and 6 ms, respectively. The potential of the implemented designs can also be concluded from the fact that the constructed prototype enabled IR imaging of close to room temperature objects without the use of any advanced data processing. The most unique and practically valuable feature of the implemented FPAs, however, is their scalability to high resolution formats, such as 2000x2000, without progressively growing device complexity and cost.
Previously, we demonstrated a large format 1024 x 1024 corrugated quantum well infrared photodetector focal plane array (C-QWIP FPA). The FPA has a cutoff at 8.6 μm and is BLIP at 76 K with f/1.8 optics. The pixel had a shallow trapezoidal geometry that simplified processing but limited the quantum efficiency QE. In this paper, we will present two approaches to achieve a larger QE for the C-QWIPs. The first approach increases the size of the corrugations for more active volume and adopts a nearly triangular pixel geometry for larger light reflecting surfaces. With these improvements, QE is predicted to be about 35% for a pair of inclined sidewalls, which is more than twice the previous value. The second approach is to use Fabry-Perot resonant oscillations inside the corrugated cavities to enhance the vertical electric field strength. With this approach, a larger QE of 50% can be achieved within certain spectral regions without using either very thick active layers or anti-reflection coatings. The former approach has been adopted to produce a series single color FPAs, and the experimental results will be discussed in a companion paper. In this paper, we also describe using voltage tunable detector materials to achieve multi-color capability for these FPAs.
Current generation QWIP detectors, although very cost effective, have relatively narrow spectral range and low quantum efficiencies. Tactical operation is generally limited to a single spectral band. These limitations arise from the design approach and restrict
applications to those that can tolerate these performance limitations.
Using recent device design improvements, a novel material, and special processing approaches, High Quantum Efficiency Dual Band C-QWIP detectors are currently being developed. These are expected to overcome traditional limitations in the QWIP design approach and deliver extremely high performance.
In the first phase of the program, single color LWIR and VLWIR C-QWIP FPAs in large (1024x1024) format will be demonstrated with targeted peak quantum efficiency of 35%, and correspondingly high BLIP operating temperatures. In the next phase of the program, the team will continue to improve QE towards 50% with conversion efficiency of 75%, and demonstrate dual band MW/LW FPAs. The detector gain will be optimized for operation in either low background or high background applications. These goals will
be accomplished using highly producible/low cost materials and processes. System considerations include ROIC well capacity, noise performance, as optics configuration and other concerns will be addressed. A robust design for high performance in a variety
of applications will be shown.
This work is being performed by the Army Research Laboratory (ARL) and L-3 Cincinnati Electronics (CE), with funding provided by the Missile Defense Agency.
The evolution of InSb Focal Plane Arrays (FPAs) at L-3 Communications Cincinnati Electronics (L-3 CE) has resulted in large format, high reliability, and high yields for 256x256, 640x512, 1Kx1K and even 2Kx2K formats using our patented front-side illuminated, reticulated pixel design. Baseline processes matured at 30um pitch and gradually were made producible at 25um pitch. Recent progress in process technology, specifically dry etch plasma processes and photolithography tools, has created a new set of processes/design capabilities which enable 15um pixel pitch FPAs, thus allowing us to develop a 15um pitch FPA with 4 times as many pixels, in the same foot print as the previous 30um pitch designs. We have developed a new 15um pitch, reticulated pixel design, implemented on a 512x512 format, which can then be sized into larger arrays, similar to the evolution that occurred on 30um pitch FPAs. As unit cell dimensions shrink by a factor of two, both the feature size and the alignment tolerances begin to limit optical fill factor. Addition of a novel micro-optic design, which optimizes signal collection to near 100% efficiency while maintaining near theoretical pixel MTF, will be presented.
Perimeter security is of increasing importance, both for Homeland security and a variety of related applications. Infrared (IR) imaging systems in a variety of configurations can provide a compact, cost effective solution for day/night long-range visual site perimeter surveillance. Over the past year, L-3 Communications Cincinnati Electronics (L-3 CE) has fielded currently available electro-optic/IR imaging systems with several configurations of optics and focal plane array (FPA) detector format to collect digital data on man and vehicle targets. The purpose of these deployments was to assess compatibility with existing sites and determine identification ranges. Of key interest to L-3 CE were the comparison of predicted night vision performance to field data at ranges up to ten kilometers, comparison of daytime and nighttime operation, and the population of an image database for future in-camera image enhancement algorithms. This paper provides information on the configuration of the imager, pan/tilt head, and data control/collection system, environmental conditions, and range performances achieved for the various test sites. It includes a summary of the data collected with sample imagery from the collection activities. This paper concludes with the results of data analysis, plans for future data collections, and implementation into ground based sites.
CMC Electronics Cincinnati (CMC) is now in production on 1Kx1K InSb focal plane arrays (FPAs), and continuing efforts on a third production run of 2Kx2K large format IR FPAs. These FPAs are based on our unique reticulated InSb architecture that has been shown to be inherently scalable across format size while maintaining performance properties. Performance in the 10mk to 15mk NETD range will be shown. The design and fabrication of these advanced FPAs has challenged the state of the art in fabrication processing, testing, and qualification of both InSb detectors and silicon ROICs. Program sponsored manufacturing improvement activities, as well as CMC internal R&D, continue to improve both the yields and the performance characteristics of these large arrays. The latest yield, operability, and performance data will be shown. Data will be drawn from a population of approximately 30 2Kx2K FPAs and 50 1Kx1K FPAs. A novel approach to rapid thermal cycling FPAs will we described and recent developments that enable the fabrication of reticulated, smaller pixel pitch devices and practical Ultra Large Format FPAs with additional capability and features will be discussed.
CMC Electronics Cincinnati (CMC) is now in production on 1Kx1K InSb focal plane arrays (FPAs), and continuing efforts on a third production run of 2Kx2K large format IR FPAs. These FPAs are based on our unique reticulated InSb architecture which has been shown to be inherently scalable across format size without losing performance properties. Current offerings range from 256x256 to 2Kx2K formats ranging in between 30um and 20um pixel pitch, with 15um pixel pitch FPAs in development. Performance in the 10mk to 15mk NETD range will be shown. The design and fabrication of these advanced FPAs has challenged the state of the art in fabrication processing of both InSb detectors and silicon ROICs. Improvements made to enable large format fabrication have improved the yields and lowered the cost of smaller format FPAs as well. Program sponsored manufacturing improvement activities, as well as CMC internal R&D, continue to improve both the yields and the performance characteristics of these large arrays. This has resulted in breakthroughs in FPA size, performance, reliability and yeilds. The latest yield, operability, and performance data will be shown. Data will be drawn from a population of approximately 30 2K FPAs and 50 1K FPAs. Recent developments in smaller pixel pitch and other R&D areas will be discussed.
Last year, CMC reported performance data on the first article large format Indium Antimonide (InSb) Focal Plane Arrays (FPAs) produced at CMC Electronics Cincinnati (CMCEC). CMCEC's FPA design contains novel, thermally matched elements, which allow scaling from 256 x 256 pixel FPAs up to and including 1Kx1K and 2Kx2K FPAs as shown in Figure 1. Since a common process and wafer size is used to fabricate 256 x 256 640 x 512, 1Kx1K and 2Kx2K FPAs, the main issue in providing 2Kx2K FPAs is one of yeild improvement, not invention. Approximately 30 of these large format 1Kx1K and 2Kx2K FPAs have been built and 18 have been integrated into deliverable systems over the last year.