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.
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 1024<sup>2</sup>) 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 <i>pin</i>-diodes utilizing the intrinsic silicon photoresponse to provide high performance over the 0.4 - 1.0 μm spectral range operating near room temperature. <i>pin</i>-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.
Multicolor focal plane arrays are of interest for a variety of applications. We report on a method to create a multicolor detector array of high-performance arsenic-doped silicon Blocked-Impurity-Band (BIB) detectors by using diffractive microlenses. Advantage is taken of the strong chromatic aberration characteristic of diffractive lenses to direct light within a pixel to either a central detector or to second detector concentrically disposed around the first. A theoretical calculation of the efficacy of this approach for spectral separation is presented. Fabrication of diffractive microlenses on the backside (illuminated-side) of thinned specially-designed BIB detector arrays is described. Finally, early initial results and further development plans are discussed.