James Webb Space Telescope: University of Rochester Detector Testing on Raytheon SB-304 InSb SCAs

1
James Webb Space Telescope University of
Rochester Detector Testingon Raytheon SB-304
InSb SCAs

• 2 Sep 2003
• Craig McMurtry, William Forrest,
• Judith Pipher, Andrew Moore

2
Overview

• Introduction
• SB-304 operation
• Number of clocks, biases, output and other
• Calibration of InSb SB-304 SCAs
• Source Follower Gain
• Capacitance
• Well Depth
• Linearity
• Dark current
• Methods of measurement
• Results
• SCA 006
• Toptimum and Tmax
• Dark current versus inverse temperature
  (Arrhenius plot)
• SCA 008

3
Overview (continued)

• Noise
• Methods of measurement
• Results
• System Noise
• Read noise in 100 seconds integration
• SCA 006
• SCA 008
• Total noise in 1000 seconds integration
• SCA 006
• SCA 008
• Summary of noise

4
Overview (continued)

• Quantum Efficiency
• Methods of measurement
• UR dewar optics and calibration equipment
• Responsive Quantum Efficiency (RQE)
• Detective Quantum Efficiency (DQE)
• Results
• SCA 006
• SCA 008
• Comparison to AR coating
• Latent or Persistent Image Performance
• Methods of measurement
• Results
• Possible amelioration techniques

5
Overview (continued)

• Operability
• Definitions
• Results
• Basic operability
• Radiometric Stability
• Method of measurement
• Results

6
Overview (continued)

• MTF and Electrical Cross-talk
• Methods of measurement
• Cosmic Ray Pixel Upsets
• MTF using knife edge and circular apertures
• Results
• Summary of SB-304 InSb SCA performance

7
Introduction

• Raytheon Detectors Proposed for JWST NIRCam and
  NIRSpec
• InSb detector technology
• 0.5 5.3 mm photo-response
• Based on SB-304 Read Out Integrated Circuit
  (ROIC) or multiplexer
• 2048 x 2048 active pixels
• 2 columns of 2048 reference pixels multiplexed to
  four outputs
• Total readout format is 2056 x 2048
• University of Rochester provided detector array
  testing facilities for JWST level requirements
• Competition was/is with Rockwell Scientific and
  University of Hawaii
• HgCdTe detector technology
• 5 mm cutoff

8
JWST Requirements
Parameter Requirement (Goal)
SCA Format 2048 x 2048 pixels
Fill Factor /95 (100)
Bad Columns/Rows lt5 containing gt1000
Bad Pixel Clustering lt 20 cluster up to 20 pixels
Pixel Operability gt98
Total Noise 1000 s 9 e- (2.5 e-)
Read Noise for single read 15 e- (7 e-)
Dark current lt 0.01 e-/s
9
JWST Requirements
Parameter Requirement (Goal)
DQE 70 0.6 l 1.0 mm 80 1.0 l 5.0 mm (90 95)
Well Capacity gt 6x104e- (2x105e-)
Electrical Cross-talk lt5 (lt2)
Radiometric Stability 1 over 1000 s
Latent Image lt 0.1 after 2nd read following gt80 full well exposure
Frame Read Time 12 sec (lt12 sec)
Pixel read rate 100KHz 10 ms/pix
Sub-array read 0.2 s for 1282 pixels
10
SB-304 Operation

• Number of required connections
• 7 Clocks
• pC1, pC2, pR1, pR2, vRstG, pRstR, VrowOn
• 9 Biases
• Vp, VnRow, VnCol, VddOut, Islew, Vssuc, Vdduc,
  Vdetcom, VrowOff
• 4 Output
• 1 ground
• Additional connections
• 2(4) wires for temperature sensor
• 1 for diagnostic Tend
• 1 clock pScanCol for bi-directional control, fast
  guiding
• 1 external load current source for output (warm
  connection only)

11
Calibration

• Source Follower Gain
• SCA 006 SFGain0.777
• SCA 008 SFGain0.785
• Capacitance
• Noise2 vs Signal method
• SCA 006
• 66 fF
• 3.22 e-/ADU
• SCA 008
• 68 fF
• 3.32 e-/ADU

12
Calibration

• Linearity
• Plotted Signal Rate vs Signal (C0/C)
• Small flux over long integration times
• Well Depth (Capacity)
• _at_ 300 mV applied detector bias
• SCA 006 well depth 1.4 x 105 e-
• SCA 008 well depth 1.3 x 105 e-
• Larger well depths possible with little or no
  increase in dark current

13
Dark Current Test Methods

• Dark dewars are difficult to make and keep dark
• Using an opaque mask placed in contact with InSb
  surface, UR dewar light leak lt 0.006 e-/s
• 3 Methods of measurement
• Usually yield same values, although some
  discrepancies possible
• Dark Charge versus integration time
• With reference pixel correction, accurate for
  moderate dark currents
• Lengthy measurement

14
Dark Current Test Methods

• Noise2 versus integration time
• With reference pixel correction, accurate for
  small dark currents
• Also, lengthy measurement

15
Dark Current Test Methods

• SUTR Dark Charge vs. time
• With reference pixel correction, accurate for
  small dark currents
• Relatively short measurement (single 2200 sec
  integration)
• Addition of possible charge per read due to
  higher read rate
• Confuses dark current measurement
• No detectable added noise

16
Dark Current Results

• SCA 006
• Idark 0.012 e-/s _at_ T30.0K (Toptimum)
• Idark 0.024 e-/s _at_ T32.3K (Tmax)
• Charge per read of 0.09 e-/read
• Again, no detectable added noise
• No measurable amp glow or digital circuit glow

17
Dark Current Results
Dark Current Results

• SCA 008
• Idark 0.025 e-/s _at_ T30.0K
• Charge per read of 0.07 e-/read
• No digital circuit glow
• Slight glow from output amplifier
• 0.05 e-/s including dark current
• Covers small region (see operability section)
• Known multiplexer defects (shorts)
• Amp glow not seen on other multiplexers

18
System Noise

• System Noise
• Shorting resistor placed between signal (video)
  and signal reference lines (analog ground)
• T295K
• Connected and functioning detector in dewar to
  allow typical voltage/current paths which may
  cause cross talk (worst case)

19
Read Noise Results

• Read noise
• Measured at T30.0K
• All integration times are 100 s
• SCA 006 results
• Follows 1/sqrt(N) where N is the number of Fowler
  sample pairs

20
Read Noise Results

• SCA 008 results
• Follows 1/sqrt(N)

21
Total Noise Measurement Methods

• Methods of measurement
• Box average (often called spatial noise method)
  uses the standard deviation of mean/sqrt(2) of
  difference of two 1000 sec Fowler-8 images
• Full frame average (spatial) noise computed
  using difference of two 1000 sec Fowler-8 images,
  and plotting histogram of pixel values
• The width of the distribution corresponds to the
  average noise mean is DC offset
• Gaussian fit rejects cosmic ray
• SCA 006 at right

22
Noise Measurement Methods

• Methods of measurement (cont)
• Temporal noise measurement is computed by taking
  the standard deviation of the mean per pixel for
  a large number of 1000 sec Fowler-8 images (time
  series)
• Distribution is typically a Gaussian whose width
  depends on the number of images taken.
• Cosmic Ray hits removed from single images (4 s
  clipping).

23
Noise Results

• Total Noise Requirement lt 9 e- in 1000 sec using
  Fowler-8 sampling
• SCA 006
• 6.2 e- (Temporal method), 6.7 e- (Full frame
  spatial method) _at_ T30.0K
• Note on charge per read temporal noise data are
  Fowler-8 images that were re-constructed from 98
  samples of a SUTR series. From the dark current
  results, 0.09 e-/read was inferred. One would
  expect to see (98-16 read)(0.09e-/read) worth
  of noise power. However, the noise for the
  reconstructed Fowler-8 images of temporal method
  was LESS than the noise for standard Fowler-8
  spatial method, i.e. no detectable noise
  contribution.
• 6.4 e- (Full frame spatial method) _at_ Tmax 32.3K
• For 1000 sec Fowler-1, total noise is 12.0 e-
  (temporal method) _at_T30.0K
• SCA 008
• 7.9 e- (temporal method) _at_ T30.0K

24
Quantum Efficiency

• UR dewar cross section optical path
• AW is as simple as possible.
• All IR filters from OCLI or Barr
• Transmission traces taken at room temperature and
  77K
• Visible filter, KG-5
• Transmission trace at room temperature and 4.2K
• Still have some optical problems (large angles!),
  likely interference patterns and vignetting
• Central portion illuminated well

25
Quantum Efficiency

• Reconstructed psuedo-flat fields for SCA 008,
  cos4q corrected
• Most effects are caused by dewar optics, not
  detector corners are vignetted
• J band on left, L (3.81mm) on right

26
Quantum Efficiency

• Photon sources and calibration equipment
• For l gt 3.0 mm, photon source is room temperature
  black body surface monitored with a calibrated
  temperature sensor
• Subtract extra signal from image taken of
  liquid nitrogen cup
• For 1.0 mm lt l lt 3.0 mm, photon source is NIST
  calibrated black body (Omega BB-4A, 100 1000 C,
  e 0.99)
• For llt1.0 mm, photon source is stabilized visible
  light source feeding an integrating sphere with a
  NIST calibrated Si diode detector
• Responsive Quantum Efficiency -- can be gt
  100 due to gain
• RQE signal/(expected photons)
• Signal is averaged signal measurement, corrected
  for non-linearity
• Expected photons from NIST calibrated detector
  or spectral black body calculations
• Detective Quantum Efficiency -- is lt 100
• DQE (Signal/Noise)2/(expected photons)
• Noise obtained via standard deviation of
  difference of two measurements

27
Quantum Efficiency Results
RQE DQE 0.65mm RQE DQE 0.70mm RQE DQE 1.25mm RQE DQE 1.65mm RQE DQE 2.19mm RQE DQE 3.81mm RQE DQE 4.67mm RQE DQE 4.89mm
SCA 006 88 82 105 95 107 97 96.2 96.7 84.6 85.3 97.1 98.5 84.7 85.0 80.1 -
SCA 008 - - 114 97.1 - - - 86.8 - -
DQE closely matches expected value from AR
coating transmission (see Raytheon data on AR
curve). From this, we infer that the optical
fill factor is gt 98.
28
Latent Image Measurement Method

• Our test procedures are described here (since the
  result one gets depends critically on the exact
  procedure)
• a. Very dark control region on array provided by
  an opaque mask of black paper.
• b. Use nominal bias. The number of latent traps
  populated depends upon the applied bias and
  depletion width.
• c. Wait at least 15 minutes on cold dark slide
  (assures no prior latents).
• d. Take multiple dark exposures for use as
  background level.
• e. Move directly from cold dark slide to filter's
  edge (this is the source). No other filter is
  allowed to pass in front of optical path in this
  transition. Use of filter edge to illuminate
  array provides a gradient of fluxes across array
  to allow choice in flux/fluence levels during
  analysis. Should do tests at several
  wavelengths.
• f. Integrate for Source Exposure Time. The
  number of latent traps populated depends upon the
  applied bias and thus depletion width. If the
  depletion width decreases (as it does during
  integration under illumination), then more traps
  near the implant will be exposed and collect
  charge. See Benson et al. ("Spatial
  distributions hole traps and image latency in
  InSb focal plane arrays", Proc SPIE Vol. 4131, p.
  171-184, Infrared Spaceborne Remote Sensing VIII)
  specifically figures 6 and 7.
• g. Move back to cold dark slide (again, no other
  filters pass array).
• h. Delay time is time to move filter wheel plus
  reset time plus time to mid-point of pedestal
  (e.g. JWST minimum is 6s in Fowler-1). Propose
  30s delay expected JWST dither time. Any
  amelioration techniques allowed during this
  interval (e.g. autoflush in the STScI tests).
• i. Take "darks" at Latent Integration Time in a
  loop such that a pair of tests (1 and 2) or (4
  and 5) are completed for the same single source
  exposure. UR usually takes twice as many darks
  as required. Multiple sampling and/or multiple
  pixel average assumed.
• j. Reduction All statistics are done with 4
  sigma clipping to eliminate dead/hot pixels and
  cosmic rays. Use 4 column by 25 row box averages
  ( of columns chosen to keep fluence roughly
  constant over box - gradient from filter edge,
  while of rows chosen to reduce pixel to pixel
  variation).
• A. Remove background level due to any light
  leak or dark current using prior
• dark frames.
• B. Remove any frame-to-frame instability
  (using reference pixels or masked off
• region as reference level).

29
Latent Image Results
30
Operability

• Operability is affected by two types of defects
• Missing contact between InSb diode implant and
  multiplexer unit cell
• First InSb bump-bonding to mux had moderate
  outages.
• Significant strides made in very short time (see
  next slides).
• PEDs (Photo-emissive defects)
• Defect centers that glow (both IR and visible
  photons).
• Techniques in place which either eliminate or
  dramatically reduce glow region such that 20-40
  pixel diameter region fail operability.
• Future multiplexers will have additional
  circuitry to fully eliminate all PEDs.
• Foundry improvement to reduce/eliminate defects.

31
Operability

• SCA 006
• Basic Fail 13.5
• Large fraction failing are unconnected pixels

32
Operability

• SCA 008
• Basic Fail 1.94
• Slight amp glow in lower left

33
Radiometric Stability

• Method of measurement
• Using similar technique as RQE measurement at l
  3.50 mm, a room temperature black body source was
  the source of stable flux.
• A calibrated temperature sensor was used to
  monitor/calibrate variations in the temperature
  of the black body (radiation source).
• A series of integrations were then taken over a 9
  hour period.
• Most of the errors or inaccuracies in this
  measurement are a result of source calibration
  error or instabilities in our system electronics
  and not due to the SCA itself.
• Result
• SCA 006 exhibited instabilities lt 0.07 over 1000
  s and lt 0.19 over the total 32000 s.
• Further improvement by factor of 10 - 100 may be
  gained by using our NIST calibrated black body
  source.

34
MTF and Electrical Cross-Talk

• Methods of measurement
• MTF using knife edge and circular apertures
  placed in contact with InSb surface
• Cosmic ray hit pixel upset for electrical
  cross-talk

35
MTF and Electrical Cross-Talk

• MTF results
• Edge spread functions shown for two wavelengths
• Edge spread modeled by diffusion and rectangular
  pixel function which is the ratio of pixel
  pitch/ distance between photon absorption and the
  depletion region

36
MTF and Electrical Cross-Talk

• MTF results (cont.)
• From the best fit model parameter, z (frequency
  in cycles/thickness) can be determined, which in
  turn leads to MTF
• MTF 0.64 (2 e 2pz)/(1 e-4pz)
• If Nyquist frequency is taken as ½ z, then MTF
  0.45
• Similar measurement on SB-226 InSb SCA produced
  MTF0.52
• If Nyquist frequency is taken as ¼ z, as in
  Rauschers MTF document, then MTF 0.58
• Exceeds (existing) requirement of 0.53 in NASA
  JWST 641 document

37
MTF and Electrical Cross-Talk

• Cosmic ray hit pixel upsets used to quantify
  electrical cross-talk
• Used CRs which appear to be normal incidence with
  charge predominantly in one pixel and equal
  distribution to neighbors
• Histogram of 30K dark data difference showing
  peaks at 0.1 for next nearest neighbors and
  0.5-1.2 for nearest neighbors
• Cross talk is lt 2

38
MTF and Electrical Cross-Talk

• 4th pixel over electrical cross-talk
• 4 interleaved outputs next pixel on same output
  is 4 pixels away
• Deterministic, can be removed or corrected in
  software
• Below is a table of pixel values in percentage of
  a single cosmic ray event notice 4th pixel over
  is 2

39
Power Dissipation

• Power Dissipation per 2K x 2K InSb detector array
• Original requirement was lt 1 mW per 1K x 1K
  array.
• Measured by summing powers generated by voltages
  and currents see Wu, et al., Rev Sci Inst., 68,
  3566 (1997).
• Total power dissipation on ROICs with moderate
  shorts lt 0.37 mW
• Total power dissipation on ROICs with no shorts lt
  0.1 mW

40
Additional Tests

• NASA Ames conducted proton radiation testing at
  UC Davis
• Please see paper Radiation environment
  performance of JWST prototype FPAs McCreight, et
  al., SPIE Vol. 5167 (in publication)
• STScI IDT Lab conducted independent tests on both
  InSb detector arrays from Raytheon and HgCdTe
  detector arrays from Rockwell Scientific.
• Please see paper Independent testing of JWST
  detector prototypes Figer, et al., SPIE Vol.
  5167 (in publication)

41
Summary ofSB-304 InSb SCA Performance
Parameter Requirement (Goal) SB-304-006 Result SB-304-008 Result
SCA Format 2048 x 2048 pixels 2048 x 2048 active 2 reference columns 2048 x 2048 active 2 reference columns
Fill Factor /95 (100) /98 (100) /98 (100)
Bad Columns/Rows lt5 containing gt1000 No Yes
Bad Pixel Clustering lt 20 cluster up to 20 pixels No Yes
Pixel Operability gt98 86.5 basic 98.1 basic
Total Noise 1000 s 9 e- (2.5 e-) 6.2 e- 7.9 e-
Read Noise for single read 15 e- (7 e-) 12 e- (CDS) 14.5 e- (CDS)
Dark current lt 0.01 e-/s 0.012 e-/s 0.025 e-/s
42
Summary ofSB-304 InSb SCA Performance
Parameter Requirement (Goal) SB-304-006 Result SB-304-008 Result
DQE 70 0.6 l 1.0 mm 80 1.0 l 5.0 mm (90 95) 82 _at_ 0.65 mm 97 _at_ J,H,L - 97 _at_ J
Well Capacity gt 6x104e- (2x105e-) 1.4 x 105e- 1.3 x 105e-
Electrical Cross-talk lt5 (lt2) lt1.3 (nearest and next nearest pixel) lt1.3 (nearest and next nearest pixel)
Radiometric Stability 1 over 1000 s lt 0.07 over 1000s lt 0.07 over 1000s
Latent Image lt 0.1 after 2nd read following gt80 full well exposure 0.3 (no amelioration) 0.12
Frame Read Time 12 sec (lt12 sec) lt 11 sec lt 11 sec
Pixel read rate 100KHz 10 ms/pix 100KHz 10 ms/pix 100KHz 10 ms/pix
Sub-array read 0.2 s for 1282 pixels lt0.05 s for 1282 lt0.05 s for 1282
43
Conclusions

• Raytheon has produced a robust, mature InSb
  detector array technology.
• Both the InSb detector arrays from Raytheon and
  the HgCdTe detector arrays from Rockwell
  Scientific have demonstrated excellent
  performance.
• The University of Arizona has selected Rockwell
  Scientific to produce the NIRCam SCAs and FPAs.
• Congratulations to UH and RSC!