James Webb Space Telescope: University of Rochester Detector Testing on Raytheon SB-304 InSb SCAs 2 Sep 2003 Craig McMurtry, William Forrest, Judith Pipher, Andrew Moore

2Overview 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

7Introduction 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 Requirements ParameterRequirement (Goal) SCA Format2048 x 2048 pixels Fill Factor/95% (100%) Bad Columns/Rows 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 Requirements ParameterRequirement (Goal) DQE 70% 0.6[  [ 1.0  m 80% 1.0[  [ 5.0  m (90%; 95%) Well Capacity> 6x10 4 e- (2x10 5 e-) Electrical Cross-talk<5% (<2%) Radiometric Stability1% over 1000 s Latent Image 80% full well exposure Frame Read Time12 sec (<12 sec) Pixel read rate 100KHz; 10  s/pix Sub-array read0.2 s for 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)

11Calibration Source Follower Gain –SCA 006 SFGain=0.777 –SCA 008 SFGain=0.785 Capacitance –Noise 2 vs Signal method –SCA fF 3.22 e-/ADU –SCA fF 3.32 e-/ADU

12Calibration Linearity –Plotted Signal Rate vs Signal (C 0 /C) –Small flux over long integration times Well Depth (Capacity) 300 mV applied detector bias –SCA 006 well depth = 1.4 x 10 5 e- –SCA 008 well depth = 1.3 x 10 5 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 < 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 Noise 2 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 –I dark = T=30.0K (T optimum ) –I dark = T=32.3K (T max ) –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 SCA 008 –I dark = T=30.0K –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 –Shorting resistor placed between signal (video) and signal reference lines (analog ground) –T=295K –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 T=30.0K –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  clipping).

23 Noise Results Total Noise Requirement: < 9 e- in 1000 sec using Fowler-8 sampling –SCA e- (Temporal method), 6.7 e- (Full frame spatial T=30.0K –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 T max = 32.3K For 1000 sec Fowler-1, total noise is 12.0 e- (temporal –SCA e- (temporal T=30.0K

24 Quantum 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 Efficiency Reconstructed psuedo-flat fields for SCA 008, cos 4  corrected –Most effects are caused by dewar optics, not detector; corners are vignetted –J band on left, L’’ (3.  m) on right

26 Quantum 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 calculations Detective Quantum Efficiency -- is < 100% –DQE = (Signal/Noise) 2 /(expected #photons) Noise obtained via standard deviation of difference of two measurements

27 Quantum Efficiency Results RQE; DQE 0.65  m RQE; DQE 0.70  m RQE; DQE 1.25  m RQE; DQE 1.65  m RQE; DQE 2.19  m RQE; DQE 3.81  m RQE; DQE 4.67  m RQE; DQE 4.89  m SCA %; 82% 105%; 95% 107%; 97% 96.2%; 96.7% 84.6%; 85.3% 97.1%; 98.5% 84.7%; 85.0% 80.1%; - SCA %; 97.1% %; - - 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%.

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 , 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 Test # Srce Flux (e-/s) Source Exposure (s) Source Fluence (e-) Delay (s)* Latent Integr’n Time (s) Max. Desired Latent Fluence (e-: %) Meas’d (%) Latent Fluence SCA006 ; SCA , ; ; , ; ; ≤ , : ; , ; ; , ; ; ≤ ,00030, Noise level 71510,000150, Noise level

30Operability 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.

31Operability SCA 006 –Basic Fail = 13.5% –Large fraction failing are unconnected pixels

32Operability 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 = 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 s. –Further improvement by factor of 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,  (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-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 % for nearest neighbors –Cross talk is < 2%

38 MTF and Electrical Cross-Talk 4 th 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 4 th pixel over is 2%

39 Power Dissipation Power Dissipation per 2K x 2K InSb detector array –Original requirement was < 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 < 0.37 mW –Total power dissipation on ROICs with no shorts < 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 (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 (in publication)

41 Summary of SB-304 InSb SCA Performance ParameterRequirement (Goal)SB ResultSB Result SCA Format2048 x 2048 pixels2048 x 2048 active + 2 reference columns Fill Factor/95% (100%)/98% (100%) Bad Columns/Rows 1000NoYes Bad Pixel Clustering < 20 cluster up to 20 pixels NoYes Pixel Operability>98%86.5% basic98.1% 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< 0.01 e-/s0.012 e-/s0.025 e-/s

42 Summary of SB-304 InSb SCA Performance ParameterRequirement (Goal)SB ResultSB Result DQE 70% 0.6[  [ 1.0  m 80% 1.0[  [ 5.0  m (90%; 95%) 0.65  m J,H,L’’ - J Well Capacity> 6x10 4 e- (2x10 5 e-)1.4 x 10 5 e-1.3 x 10 5 e- Electrical Cross- talk <5% (<2%)<1.3% (nearest and next nearest pixel) Radiometric Stability 1% over 1000 s< 0.07% over 1000s Latent Image 80% full well exposure 0.3% (no amelioration) 0.12% Frame Read Time12 sec (<12 sec)< 11 sec Pixel read rate 100KHz; 10  s/pix Sub-array read0.2 s for pixels<0.05 s for 128 2

43Conclusions 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!