Orthogonal Transfer Arrays An Overview

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Orthogonal Transfer ArraysAn Overview

• A collaborative effort between
• MIT Lincoln Laboratory (Burke)
• Semiconductor Technology Associates (Bredthauer)
• University of Hawaii / PanSTARRS (Tonry, Luppino)
• WIYN Observatory (Jacoby)
• University of Arizona / Imaging Technology
  Laboratory (Lesser)

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Orthogonal Transfer Array (OTA)
OTCCD pixel structure
OTA 8x8 array of OTCCDs
Basic OTCCD cell
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Summary of OTA Properties

• 64 independent 500 x 500 CCDs
• Individual addressing of CCDs
• 1 arcmin field of view
• Bad columns confined to cells
• Point defects are tolerated
• A 4K x 4K imager
• Cells with bright stars ? guiders, read at 10-50
  Hz
• 8 channels / OTA 2s readout
• Intercell gaps (0.1-0.3 mm 1-3) and dead cells
  on OTA are dithered away
• Inter-OTA spacings 2 mm (20)

5cm
12 um pixels 0.11 at WIYN
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OPTIC The OTAs Ancestor

• Planet transit
• 0.3s samples binned to 60s
• Relative accuracy of 6E-4 mag
• Approaching HST (1E-4)

• CCD Format
• 2 2Kx4K OT CCDs
• 4 high-speed read zones
• 4 science zones

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Nominal OTA-CCD Configuration
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Target OTA CCD Performance
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CCD Amplifier Configuration

• 2-Stage source follower output
• Standard Configuration can operate at gt 10Mhz
• Used on a variety of devices
• KEPLER
• FAME

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Pinout Configuration
Right side
Left side
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CCD Array Configuration
49.48 mm

• 8x8 Array of elements
• 480x494 Subcells allow for increased bussing area
  
• 336?m x 132?m streets to allow for bussing
  (exactly 28 x 11 pixels)

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Wafer Configuration

• 3 OTAs
• 1 2.6K x 4K 12?m (standard imager)
• 2 1K x 2K for USNO (special imager)
• 1 800 x 1200 (standard imager)
• Numerous small test devices

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Quantum Efficiency

• Target 30?m thick epi layer (500 ohm-cm) silicon
  provides good red QE
• High resistivity also allows for deep depletion
  at nominal voltages
• AR Coatings can be tuned by ITL/Lesser for blue
  vs red

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CCD Spatial Response

• MTF maintained by high resistivity epi-material
• Can achieve adequate depletion with 10V bias
• Deep depletion improves blue MTF for backside
  illumination

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Fabrication Status

• Dividing wafer run into 3 silicon groups guards
  against silicon flaws
• 8 wafers of 40 ohm-cm material
• 8 wafers of 150 ohm-cm material
• 8 wafers of 500 ohm-cm material
• Production just beginning 10 week fabrication
  time ? first wafers in early February
• Wafer level testing in February (STA) and March
  (ITL)
• Package (ITL) 1 thin and 1 thick OTA in April for
  lab and on-sky testing at WIYN.

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ITL Backside CCD Processing

• Select via cold wafer tests
• Mechanically lap
• Dice
• Hybridize
• Wax protection of edges
• Selective etch
• Epitaxial etch

• Oxidize
• Chemisorption charge
• Antireflection coat
• Package
• Characterize

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WIYN Science Interests

• Solar neighborhood populations parallaxes,
  proper motions, planets
• Open and Globular cluster populations white
  dwarfs, variable stars, planets
• Local Group tidal streams, variable stars,
  stellar populations
• Galaxies irregular and dwarf spheroidals, star
  formation rates
• Cosmology SN Ia, High-z Ly? sources