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Near Infrared System for SNAP*. Vic Scarpine FNAL SNAP Electronics Meeting Feb. 11, 2003 * Much material obtained from Tarle and Bebek SNAP DOE talks. State-of-the-art 2k x 2k HgCdTe detector with 1.7 m m cutoff under development by RSC. NIR System Concept. 150 NIR Megapixels:

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Near Infrared System for SNAP*

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near infrared system for snap

Near Infrared System for SNAP*

Vic Scarpine

FNAL SNAP Electronics Meeting

Feb. 11, 2003

* Much material obtained from Tarle and Bebek SNAP DOE talks

nir system concept

State-of-the-art 2k x 2k HgCdTe detector with 1.7 mm cutoff under development by RSC

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)



State of HgCdTe NIR Detectors

Hg(1-x)CdxTe – cdetermined 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…

ongoing hgcdte characterization efforts
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 Si:As mid-infrared detectors.
technical challenges
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.
snap nir detector specifications
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 > 60%

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

NIR System Main R&D 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.
nir detectors summary
NIR Detectors Summary
  • R&D 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 R&D. 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.


  • 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

snap nir players
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
issues for fnal
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?