Near Infrared System for SNAP

1
Near Infrared System for SNAP

• Vic Scarpine
• FNAL SNAP Electronics Meeting
• Feb. 11, 2003
• Much material obtained from Tarle and Bebek
  SNAP DOE talks

2
NIR System Concept

• 150 NIR Megapixels
• 36 (2k ? 2k) 18 mm HgCdTe detectors (0.34 sq.
  deg)
• 3 special bandpass filters covering 1.0 1.7 mm
  in NIR
• T 140?K (to limit dark current)

HgCdTe
3
NIR System Performance Goals





4
State of HgCdTe NIR Detectors

• Hg(1-x)CdxTe ?c determined by x this
  determines operating temperature.
• Rockwell Science Center (RSC) is the principal,
  recognized source for Mercury Cadmium Telluride
  (HgCdTe) infrared focal plane arrays (FPAs).
• RSC has developed devices (NICMOS 256 x 256
  FPAs, WFC3 1024 x 1024) for the IR channel on
  HST. Also U Hawaii, ESO, Subaru, NGST

5
Ongoing HgCdTe Characterization Efforts

• Detector Characterization Lab (DCL) at Goddard
  Space Flight Center (PI Ed Cheng)
• The DCL currently supports the characterization
  of HgCdTe detectors for the Hubble Space
  Telescope Wide Field Camera 3 instrument.
• NASA has funded four laboratories to develop and
  assess the quality of NGST prototype detectors
• The University of Hawaii Laboratory (PI Donald
  Hall) will develop and characterize HgCdTe
  detectors manufactured by Rockwell Scientific.
• The University of Rochester Laboratory (PI
  William Forrest) will develop and characterize
  InSb detectors made by Raytheon Infrared
  Operations.
• The Independent Detector Testing Laboratory (PI
  Don Figer) at Space Telescope Science Institute
  and the Johns Hopkins University will
  characterize both HgCdTe and InSb detectors in a
  comparative hardware setup.
• The Laboratory at NASA Ames Research Center (PI
  Craig McCreight) is developing and characterizing
  SiAs mid-infrared detectors.

6
Technical Challenges

• Establish read-out strategy within time
  constraints with manageable readout noise (can we
  achieve 5 e- with a Fowler-4 read?), power and
  data volume (see NIR breakout talk).
• Obtain 1 relative systematic photometric
  accuracy in under-sampled regime.
• Develop plan for testing and characterization of
  large numbers of HgCdTe detectors.
• Demonstrate that a prototype NIR detector can
  meet all SNAP NIR science driven requirements.

7
SNAP NIR Detector Specifications

• The Rockwell HgCdTe devices are SNAP baseline
  choice for the NIR system.
• WFC3 MBE material with 1.7 mm cutoff in the NGST
  2k x 2k format (under development) is a very good
  match for SNAP.
• Performance Goals
• Read Noise 5 electrons
• Dark Current 0.1 e-/sec/pixel
• Quantum Efficiency gt 60

8
SNAP NIR Issues

• SNAP requires dark currents below 0.1 e-/s/pix at
  140?K
• Appears to be met
• SNAP requires quantum efficiency above 60
• Appears to be met
• SNAP requires read noise to be below 5 e-
• Not meet yet
• Intra-pixel variation
• Simulations show this is controlled by 2x2 ½
  pixel dithering

9
NIR System Main RD Activities

• Establish facility for testing and characterizing
  NIR FPAs.
• Study read noise and ability to reduce it with
  multiple reads.
• Study intra-pixel variations and establish impact
  on accurate photometry.
• Develop mechanical and thermal concept for NIR
  imager in an integrated focal plane in concert
  with LBL thermal and mechanical engineering
  group.
• Develop plan for testing and qualifying large
  number of HgCdTe devices.
• Produce all deliverables.
• Realistic cost and schedule estimate for CDR.

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NIR Detectors Summary

• RD Phase NIR detectors
• Obtain and characterize a science grade HgCdTe
  detector.
• Assume that problem with anomalous read noise
  will be solved by WFC3 and a solution compatible
  with SNAP requirements will be found by the start
  of SNAP RD. If not, then will need to find a
  solution. This may require additional HgCdTe
  production lot runs or a modified readout
  strategy.
• Noise reduction through multiple reads needs to
  be verified.
• Intrapixel variations will be studied.
• Demonstration that 2?2 dithering will produce
  adequate photometry precision.
• Perform detector modeling.
• Establish science driven requirements.
• Establish SNAP science grade specifications.
• Obtain and characterize a SNAP science grade
  HgCdTe detector (optional 2nd detector).
• Prepare for large scale FPA qualification.
• Demonstrate all SNAP NIR requirements can be met
  with a SNAP science grade device.
• Incorporate developments at RSC, WFC3 and NGST.

11
Filters

• Activity
• Univ. of Indiana is working with a vendor to
  deposit filters on silicon sensors.
• LBNL will take a quick look at the issues for
  suspending discrete filters.
• Effort
• Concept for mechanical mounting discrete filters.
• Several cycles of direct deposition of filters on
  silicon wafers and CCDs.
• If successful, move on to HgCdTe deposition.
• Linkages
• CCD group
• HgCdTe group
• Imager mechanics
• Deliverables
• Demonstration of functioning CCDs with deposited
  filter.
• Mechanical mount conceptual design.
• Cost and schedule.

4 silicon wafer with B-band filter
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NIR System RD Schedule
13
SNAP NIR Players

• Greg Tarle, Univ of Michigan NIR coordinator
• Univ of Michigan - have begun to set up HgCdTe
  evaluation facility
• Number of professors, research scientists,
  post-docs
• Univ of Indiana working on filters and quantum
  efficiency measurements
• LBL development of readout electronics
• Don Figer Infrared detectors at Space Telescope
  Science Institute
• Rockwell HgCdTe FPA supplier. Possible readout
  chip.
• Ratheyon developing HgCdTe FPA

14
Issues for FNAL

• Tarle feels NIR effort undermanned and would
  welcome venture with FNAL
• Read noise major issue FNAL may be able to help
• Preparation for large scale FPA qualification
• FNAL could be FPA qualification site
• No one looking at HgCdTe linearity
• Readout electronics use of 14th floor
• Questions
• Were alternatives to HgCdTe investigated such as
  InGaAs?
• Should FNAL venture down this road? (Northwestern
  Center for Quantum Devices)
• How well is HgCdTe pixel uniformity controlled?