DRS is the inventor and a leading developer of Blocked Impurity Band detector technology for ground, airborne and
space-based observing applications and the sole developer of antimony doped silicon (Si:Sb) blocked impurity band
(BIB) FPAs. Arsenic doped silicon (Si:As) and Si:Sb arrays in 1282 pixel formats were developed by DRS for use on the Spitzer Space telescope. In the subsequent years these arrays were extended in both format and capability. 10242 pixel format, low flux Si:As arrays were developed for the NASA WISE mission, and Si:As and Si:Sb arrays were developed for higher flux applications such as JPL’s MegaMIR camera and Cornell’s FORCAST instrument for SOFIA, in both 2562 and 10242 pixel array formats. Si:Sb arrays have advanced to offer similar responsivity, response uniformity, high operability and low dark currents long associated with Si:As BIB arrays but with high quantum efficiency that extends to 40 μm, compared to only 28 μm for Si:As. Recently, Si:Sb detector material has been further developed for low flux astronomy applications. Specifically, Si:Sb material has been grown to satisfy exceptionally low dark current requirements (such as < 0.5 e-/s/pixel at 5 K) for large format focal plane arrays for future infrared telescopes. This paper will focus on the characterization of this low flux Si:Sb detector material
Visible light photon counters (VLPCs) are solid-state devices providing high quantum efficiency (QE) photon
detection (>88%) with photon number resolving capability and low timing jitter (~250 ps). VLPC features high
QE in the 0.4-1.0μm wavelength range, as the main photon absorption mechanism is provided by electron-hole
pair generation across the silicon bandgap. In this paper, we will discuss the optical and electrical operating
principles of VLPCs, and propose a range of device optimization paths that improves various aspects of VLPC
for advanced quantum optics and quantum information processing experiments, both in the UV and the telecom
DRS Sensors & Targeting Systems, under contract to the Space Dynamics Laboratory of Utah State University, provided
the focal plane detector system for NASA's Wide-field Infrared Survey Explorer (WISE). The focal plane detector
system consists of two mercury cadmium telluride (MCT) focal plane module assemblies (FPMAs), two arsenic doped
silicon (Si:As) Blocked Impurity Band (BIB) FPMAs, electronics to drive the FPMAs and report digital data from them,
and the cryogenic and ambient temperature cabling that connect the FPMAs and electronics. The WISE Satellite was
launched in late 2009 and has been a very rewarding success. In light of the recent success on orbit, there were many
challenges and hurdles the DRS team had to overcome in order to guarantee the ultimate success of the instrument. This
report highlights a few of the challenges that the team overcame in hopes that the information can be made available to
the astronomy community for future use.
The Blocked Impurity Band (BIB) detector technology team at DRS Sensors and Targeting Systems specializes in
providing the highest performance, broadest application range of BIB detector products. These include detectors, Focal
Plane Arrays (FPA), and sensor assemblies for ground, airborne and space applications. We offer flight proven low flux
Si:As and Si:Sb FPAs in square formats up to 1024x1024. We also offer high-flux FPA systems for ground-based
telescopes and airborne applications in several square and rectangular formats, such as 160×640 sensors for push-broom
spatial-spectral imaging. NASA's Wide-field Infrared Survey Explorer mission selected DRS 1024×1024 arrays for its
the 12 and 24 micron wavelength bands. The Spitzer Space Telescope utilizes DRS 128×128 Si:As and Si:Sb FPAs, and
1024×1024 Si:Sb arrays are being fabricated by DRS for an upgrade to the SOFIA FORCAST instrument. DRS is
unique in providing detectors and FPAs in alternate detector materials such as Si:Sb, Si:Ga, and Si:P to optimize
wavelength range vs operating temperature. Sensor assemblies include detectors or FPAs packaged with cryogenic
cabling and electronics and ambient temperature drive and data acquisition electronics--fully tested, and environmentally
qualified. DRS is also unique in extending its conventional BIB detector product line to include novel detector
architectures for a variety of applications. Si:As detectors with avalanche gain (~40,000X) function as number-mode
photon counters at visible or mid-infrared wavelengths. A recent DRS innovation is the extension of Si:As BIB detectors
designs to achieve wavelength extension into the far-infrared (low THz) wavelength region. Wavelength extension to
~50 microns (6 THz) has been demonstrated, with further extension to at least ~100 microns (3 THz) in progress.
DRS Sensors & Targeting Systems with silicon materials partner Lawrence Semiconductor Research Laboratory and
development partner NASA Langley Research Center Earth Science Directorate are developing improved far-infrared
detectors for Earth energy balance observations from orbit. Our team has succeeded in demonstrating the feasibility of
extending the wavelength range of conventional arsenic-doped-silicon Blocked Impurity Band (BIB) detectors (cut-off
~28 μm) into the far infrared. The new far-IR member of the BIB detector family operates at temperatures accessible to
existing space-qualified cryocoolers, while retaining the very high values of sensitivity, stability, linearity, and
bandwidth typical of the broader class of silicon BIB detectors. The new detector should merit serious consideration for
the Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission defined by the recent National
Research Council's Decadal Survey for Earth Science. Proposed further development of this detector technology
includes wavelength extension to a goal of at least 100 μm, improvements in detector design, and implementation of
light-trapping packaging. These are developments that will enable increased radiometric accuracy, reduced spatial
smearing, and simpler calibration approaches for CLARREO.
Our group has developed the first 1024×1024 high background Si:As detector array, the Megapixel Mid-Infrared array
(MegaMIR). MegaMIR is designed to meet the thermal imaging and spectroscopic needs of the ground-based and airborne
astronomical communities. MegaMIR was designed with switchable capacitance and windowing capability to
allow maximum flexibility. We report initial test results for the new array.
The Wide-field Infrared Survey Explorer is a NASA Midex mission launching in late 2009 that will survey the entire
sky at 3.3, 4.7, 12, and 23 microns (PI: Ned Wright, UCLA). Its primary scientific goals are to find the nearest stars
(actually most likely to be brown dwarfs) and the most luminous galaxies in the universe. WISE uses three dichroic
beamsplitters to take simultaneous images in all four bands using four 1024×1024 detector arrays. The 3.3 and 4.7
micron channels use HgCdTe arrays, and the 12 and 23 micron bands employ Si:As arrays. In order to make a
1024×1024 Si:As array, a new multiplexer had to be designed and produced. The HgCdTe arrays were developed by
Teledyne Imaging Systems, and the Si:As array were made by DRS.
All four flight arrays have been delivered to the WISE payload contractor, Space Dynamics Laboratory. We present
initial ground-based characterization results for the WISE arrays, including measurements of read noise, dark current,
flat field and latent image performance, etc. These characterization data will be useful in producing the final WISE data
product, an all-sky image atlas and source catalog.
DRS Sensors & Targeting Systems, supported by detector materials supplier Lawrence Semiconductor Research
Laboratory, is developing far-infrared detectors jointly with NASA Langley under the Far-IR Detector Technology
Advancement Partnership (FIDTAP). The detectors are intended for spectral characterization of the Earth's energy
budget from space. During the first year of this effort we have designed, fabricated, and evaluated pilot Blocked
Impurity Band (BIB) detectors in both silicon and germanium, utilizing pre-existing customized detector materials and
photolithographic masks. A second-year effort has prepared improved silicon materials, fabricated custom
photolithographic masks for detector process, and begun detector processing. We report the characterization results from
the pilot detectors and other progress.
DRS Sensors & Targeting Systems, under contract to the Space Dynamics Laboratory of Utah State University, is
providing the focal plane detector system for NASA's Wide-field Infrared Survey Explorer (WISE). The focal plane
detector system consists of two mercury cadmium telluride (MCT) focal plane module assemblies (FPMAs), two arsenic
doped silicon (Si:As) Blocked Impurity Band (BIB) FPMAs, electronics to drive the FPMAs and report digital data from
them, and the cryogenic and ambient temperature cabling that connect the FPMAs and electronics. The MCT and Si:As
BIB focal plane arrays (FPAs) utilized in the WISE FPMAs are both megapixel class indium-bump hybridized devices
fabricated by Teledyne Imaging Systems and DRS Sensors & Targeting Systems, respectively. This paper reports
performance of the WISE Si:As BIB FPAs that are used for the WISE 12- and 23-μm wavelength bands.
We present a description of a new 1024×1024 Si:As array designed for ground-based use from 5 - 28 microns. With a maximum well depth of 5e6 electrons, this device brings large-format array technology to bear on ground-based mid-infrared programs, allowing entry to the megapixel realm previously only accessible to the near IR. The multiplexer design features switchable gain, a 256×256 windowing mode for extremely bright sources, and it is two-edge buttable. The device is currently in its final design phase at DRS in Cypress, CA. We anticipate completion of the foundry run in October 2005. This new array will enable wide field, high angular resolution ground-based follow up of targets found by space-based missions such as the Spitzer Space Telescope and the Widefield Infrared Survey Explorer (WISE).
Photon detectors and focal plane arrays (FPAs) are fabricated from silicon in many varieties. With appropriate choices for detector architecture, dopants, and operating temperature, silicon can cover the spectral range from ultraviolet to the very-long-wavelength infrared (VLWIR), exhibit high internal gain to allow photon counting over this broad spectral range, and can be made in large array formats for imaging. DRS makes silicon detectors and FPAs with unique architectures for a variety of applications. Large-format, VLWIR FPAs based on doped-silicon Blocked-Impurity-Band (BIB) detectors have been developed. These FPAs comprise an array of BIB detectors interfaced via indium column interconnects to a matching read-out integrated circuit (ROIC). Arsenic-doped silicon (Si:As) BIB detector arrays with useful photon response out to about 28 μm are the most fully developed embodiment of this technology. FPAs with Si:As BIB arrays have been made in a variety of pixel formats (to 10242) and have been optimized for low, moderate, and high infrared backgrounds. Antimony-doped silicon (Si:Sb) BIB arrays having response to wavelengths 40 μm have also been demonstrated. Avalanche processes in Si:As at low temperatures (~ 8 K) have led to two unique solid-state photon-counting detectors adapted to infrared and visible wavelengths. The infrared device is the solid-state photomultiplier (SSPM). To our knowledge, it is the only detector capable of counting VLWIR photons (formula available in paper) with high quantum efficiency. A related device optimized for the visible spectral region is the visible-light photon counter (VLPC). The VLPC is a nearly ideal device for detection of small bunches of photons with excellent time resolution. VLPCs coupled to scintillating fibers have demonstrated new capabilities for energetic charged particle tracking in high-energy physics. A fiber tracking system that utilizes VLPCs is currently in operation in the D0 detector at Fermilab's Tevatron. VLPCs may also be useful for quantum cryptography and quantum computation. Finally, DRS makes imaging arrays of pin-diodes utilizing the intrinsic silicon photoresponse to provide high performance over the 0.4 - 1.0 μm spectral range operating near room temperature. pin-diode arrays are particularly attractive as an alternative to charge-coupled devices (CCDs) for space applications where radiation hardening is needed.
The Blocked Impurity Band (BIB) detector was invented in the early 1980's and subsequently developed by our team. The original arsenic-doped silicon (Si:As) detectors addressed the need for low-noise, radiation-tolerant, mid-IR detectors for defense surveillance from space. We have since developed large-format BIB focal plane arrays to address high-background requirements of ground-based telescopes and missile interceptors, low-background requirements of the Space Infrared Telescope Facility (SIRTF), and very low background requirements of the mid-IR instruments for the Next Generation Space Telescope (NGST) and Terrestrial Planet Finder. Most of these applications employ Si:As BIB detectors, but antimony-doped silicon (Si:Sb) BIB detectors are used for some SIRTF bands. Other demonstrated types including phosphorus (Si:P) and gallium-doped (Si:Ga) BIB detectors may have application niches. We have proposed development of a BIB detector type utilizing both Si:As and Si:P layers to optimize dark current vs. wavelength performance. Wavelength response for silicon BIB detectors extend to a maximum of ~40 microns (Si:Sb), but we have also demonstrated germanium BIB detectors for wavelengths extending to several hundred microns. We are currently developing germanium BIB detector arrays for astrophysics applications, including space telescopes beyond NGST.
This paper addresses the use of Visible Light Photon Counters (VLPCs) for detection of light induced in light arrays of small scintillating crystals for gamma ray imaging. The use of plastic step-index-of-refraction fibers for collecting the scintillation light for detection by a VLPC is examined and data obtained in initial exploratory experiments are discussed. The results are compared with the number of detectable scintillation photons predicted by a model that in essence treats the crystal as an integrating cavity with highly efficient diffuse reflecting surfaces.