16 January 2003STScI TIPS1 JWST's Near-Infrared Detectors: Ultra-Low Background Operation and Testing Bernie Rauscher, Don Figer, Mike Regan, Sito Balleza, Robert Barkhouser, Eddie Bergeron, Gretchen Greene, Ernie Morse, Steve McCandliss, Russ Pelton & Tom Reeves And coming soon!

16 January 2003STScI TIPS2 Outline What is a Near-Infrared Array Detector? JWST Science Drivers Detector Requirements Detector testing at STScI/JHU Optimal Use Summary

16 January 2003STScI TIPS3 JWST’s IR Arrays are “Hybrid” Sensors PN junctions are “bump bonded” to a silicon readout multiplexer (MUX). Silicon technology is more advanced than other semiconductor electronics technology. The “bump bonds” are made of indium.

16 January 2003STScI TIPS4 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E Wavelength [  m] Signal [e-/sec/pix] Zodiacal Light Sunshield JWST requirement JWST goal R=5 R=1000 JWST Needs Very Good Near Infrared Detectors! Completing the JWST Design Reference Mission “on time” requires background limited near- infrared (NIR) broadband imaging Zodiacal light is the dominant background component in the NIR The total NIR detector noise requirement is therefore =10 e- rms in a t=1000 seconds exposure. NIRSpec will probably be detector noise limited. The total noise goal is =3 e- rms per 1000 seconds exposure

16 January 2003STScI TIPS5 JWST Near Infrared (NIR) Detector Requirements

16 January 2003STScI TIPS6 Detector Testing at STScI/JHU: Independent Detector Testing Laboratory

16 January 2003STScI TIPS7 Past and present personnel Eddie Bergeron Data Analyst Mike Telewicz Intern Gretchen Greene Mechanical Engineer Monica Rivera Intern Russ Pelton Technician Tom Reeves Lab Technician Bernie Rauscher Project Scientist Steve McCandliss JHU Lead Scott Fels Intern Sito Balleza Systems Engineer Robert Barkhouser Optical Engineer Utkarsh Sharma Graduate Student Ernie Morse Data Analyst Don Figer Director Mike Regan System Scientist

16 January 2003STScI TIPS8 IDTL Experiments Read noise Conversion Gain Dark current Linearity Electronic Gain Latent charge (persistence) Relative and Absolute Quantum efficiency (QE) Intra-pixel sensitivity

16 January 2003STScI TIPS9 Dark Current Lowest measured dark current is ~0.006 e  /s/pixel.

16 January 2003STScI TIPS10 Read noise is ~10 e  for Fowler-8. (system read noise is ~2.5 e  ) IDTL Measurements: Read Noise

16 January 2003STScI TIPS11 IDTL Measurements: Conversion Gain Per correlated double sample

16 January 2003STScI TIPS12 IDTL Test System Hawaii Detector Hawaii Shirt

16 January 2003STScI TIPS13 Then & Now November 2000 November 2002

16 January 2003STScI TIPS14 IDTL First Light Images Jan. ‘01 (MUX) Raytheon ALADDIN Feb. ‘02 (MUX)Apr. ‘02 (SCA) Rockwell HAWAII-1R Rockwell HAWAII-1RG Jun. ‘02 (MUX)Jul. ‘02 (SCA) Raytheon SB-304 Nov. ‘02 (MUX) Rockwell HAWAII-2RG Jan. ‘03 (MUX)

16 January 2003STScI TIPS15 IDTL Test System Leach II Controller Electronics Vacuum Hose He Lines Entrance Window Dewar

16 January 2003STScI TIPS16 Detector Readout System Unix Instrument Control Computer COTS Leach II IR Array Controller Warm Harness Cryogenic Harness Detector Customization Circuit JWST SCA T~293 K T=30-50 K

16 January 2003STScI TIPS17 An Adaptable Readout System The only hardware change required to run a different detector is swap-in a DCC. We have DCCs for the following detectors. –Raytheon SB-290 SB-304 –Rockwell HAWAII-1R HAWAII-1RG HAWAII-2RG Each DCC is a multi-layer PCB. Extensive use of surface mount technology. Includes flexible “neck” to simplify interfacing. Rockwell HAWAII-2RG Detector Customization Circuit (DCC)

16 January 2003STScI TIPS18 Close-up of Detector Customization Circuits (DCCs) Rockwell HAWAII-2RG Raytheon SB-290/SB-304

16 January 2003STScI TIPS19 Optimal Use JWST Detector Readout Strategies Use of Reference Pixels

16 January 2003STScI TIPS20 Detector Readout JWST science requires MULTIACCUM and SUBARRAY readout. Other readout “modes” can be implemented using parameters. –For example, Fowler-8 can be implemented as MULTIACCUM- 2x8. Cosmic rays may be rejected either on the ground or on-orbit. MULTIACCUM parameters: t expose = exposure time, t 1 = frame time, and t 2 = group time. The small overhead associated with finishing the last group of samples is not included in the exposure time. MULTIACCUM Detector Readout

16 January 2003STScI TIPS21 Reference Pixels Raytheon 2Kx2K NIR Module Rockwell 2Kx2K NIR Module All candidate JWST detectors have reference pixels Reference pixels are insensitive to light In all other ways, designed to mimic a regular light-sensitive pixel NIR detector testing at University of Rochester, University of Hawaii, and in the IDTL at STScI -> reference pixels work! Reference pixel subtraction is a standard part of IDTL data reduction pipeline Raytheon 1024x1024 MIR MUX

16 January 2003STScI TIPS22 Use of Reference Pixels We have begun to explore how reference pixels should be used. Approaches considered include the following. –Maximal averaging (average all reference pixels together and subtract the mean) –Spatial averaging –Temporal averaging Spatial averaging is now a standard part of IDTL calibration pipeline

16 January 2003STScI TIPS23 A Picture of IDTL System Noise Shorting resistor mounted at SCA location 1/f “tail” causes horizontal banding. Total noise is =7 e- rms per correlated double sample.

16 January 2003STScI TIPS24 Averaging small numbers of reference pixels adds noise Averaged the last 4 columns in each row and performed row- by-row subtraction Before After

16 January 2003STScI TIPS25 Spatial Averaging In spatial averaging, data from many (~64 rows) of reference pixels are used to calibrate each row in the image A Savitzky-Golay smoothing filter is used to fit a smooth and continuous reference column This reference column is subtracted from each column in the image Using this technique, we can remove some 1/f noise power within individual frames In practice, this technique works very well This is a standard part of the IDTL data calibration pipeline

16 January 2003STScI TIPS26 Spatial Averaging: Before & After Before After

16 January 2003STScI TIPS27 Spatial Averaging: Example using Rockwell HAWAII-1RG Detector Rockwell HAWAII-1RG Double Correlated Sampling image. Read noise is ~15 e- rms (=5.3 e- using Fowler-8 sampling). Fit to reference columns using Savitzky-Golay filtering to smooth averaged reference pixel data in each row..

16 January 2003STScI TIPS28 Spatial Averaging Works! IDTL dark ramp. Astrisks include reference pixel correction using the Spatial Averaging method. Pluses do not. Fitted slope is =0.006 ±.001 e-/s/pixel.

16 January 2003STScI TIPS29 Temporal Averaging Dwell on the reference pixel and sample many times before clocking next pixel Potentially removes most 1/f Not tried this in IDTL yet. U. Hawaii has reported some problems with reference pixels heating up

16 January 2003STScI TIPS30 Temporal Averaging: Before & After Before After

16 January 2003STScI TIPS31 Summary The Independent Detector Testing Laboratory (IDTL) at STScI/JHU is up and running Test results including dark current, read noise, conversion gain, and persistence are in good agreement with other JWST test labs Reference pixels work and are an invaluable part of the data calibration pipeline Spatial averaging works well and is robust