James Webb Space Telescope: James Webb Space Telescope: University of Rochester Detector Testing University of Rochester Detector Testing on Raytheon SB-304 InSb SCAs on Raytheon SB-304 InSb SCAs 2 Sep 2003 Craig McMurtry, William Forrest, Judith Pipher, Andrew Moore
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James Webb Space Telescope: University of Rochester Detector Testing on Raytheon SB-304 InSb SCAs 2 Sep 2003 Craig McMurtry, William Forrest, Judith Pipher,
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James Webb Space Telescope:James Webb Space Telescope: University of Rochester Detector Testing University of Rochester Detector Testing
on Raytheon SB-304 InSb SCAson Raytheon SB-304 InSb SCAs
2 Sep 2003
Craig McMurtry, William Forrest,
Judith Pipher, Andrew Moore
2
OverviewOverview
• 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)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)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)Overview (continued)
• Operability
– Definitions
– Results• Basic operability
• Radiometric Stability
– Method of measurement
– Results
6
Overview (continued)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
IntroductionIntroduction
• Raytheon Detectors Proposed for JWST NIRCam and NIRSpec
– InSb detector technology• 0.5 – 5.3 m 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 m cutoff
8
JWST RequirementsJWST Requirements
Parameter Requirement (Goal)
SCA Format 2048 x 2048 pixels
Fill Factor 95% (100%)
Bad Columns/Rows <5 containing >1000
Bad Pixel Clustering < 20 cluster up to 20 pixels
Pixel Operability >98%
Total Noise 1000 s 9 e- (2.5 e-)
Read Noise for single read 15 e- (7 e-)
Dark current < 0.01 e-/s
9
JWST RequirementsJWST Requirements
Parameter Requirement (Goal)
DQE 70% 0.61.0 m
80% 1.05.0 m
(90%; 95%)
Well Capacity > 6x104e- (2x105e-)
Electrical Cross-talk <5% (<2%)
Radiometric Stability 1% over 1000 s
Latent Image < 0.1% after 2nd read following >80% full well exposure
– 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 clipping).
23
Noise ResultsNoise Results
• Total Noise Requirement: < 9 e- in 1000 sec using Fowler-8 sampling
– 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.
• For 1000 sec Fowler-1, total noise is 12.0 e- (temporal method) @T=30.0K
– SCA 008• 7.9 e- (temporal method) @ T=30.0K
24
Quantum EfficiencyQuantum Efficiency
• UR dewar cross section optical path
• A 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 EfficiencyQuantum Efficiency
• Reconstructed psuedo-flat fields for SCA 008, cos4 corrected– Most effects are caused by dewar optics, not detector; corners are vignetted – J band on left, L’’ (3.m) on right
26
Quantum EfficiencyQuantum Efficiency
• Photon sources and calibration equipment– For > 3.0 m, 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 m < < 3.0 m, photon source is NIST calibrated black body (Omega BB-4A, 100 – 1000 C, =0.99)
– For <1.0 m, photon source is stabilized visible light source feeding an integrating sphere with a NIST calibrated Si diode detector
• Responsive Quantum Efficiency -- can be > 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
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> 98%.
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).
• 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
OperabilityOperability
• SCA 006
– Basic Fail = 13.5%
– Large fraction failing are unconnected pixels
32
OperabilityOperability
• SCA 008
– Basic Fail = 1.94%
– Slight amp glow in lower left
33
Radiometric StabilityRadiometric Stability
• Method of measurement
– Using similar technique as RQE measurement at = 3.50 m, 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 < 0.07% over 1000 s and < 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-TalkMTF 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-TalkMTF 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-TalkMTF and Electrical Cross-Talk
• MTF results (cont.)
– From the best fit model parameter, (frequency in cycles/thickness) can be determined, which in turn leads to MTF:
MTF = 0.64 (2 e –2)/(1 + e-4)
– If Nyquist frequency is taken as ½ , then MTF = 0.45• Similar measurement on SB-226 InSb SCA produced MTF=0.52
– If Nyquist frequency is taken as ¼ , as in Rauscher’s MTF document, then MTF = 0.58
• Exceeds (existing) requirement of 0.53 in NASA JWST 641 document
37
MTF and Electrical Cross-TalkMTF 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 < 2%
38
MTF and Electrical Cross-TalkMTF 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%