James Webb Space Telescope Characterization of Flight Candidate

James Webb Space Telescope : Characterization of Flight Candidate of Raytheon NIR In. Sb Arrays 5 Aug 2003 Craig Mc. Murtry, William Forrest, Andrew Moore, Judith Pipher

Overview • • Introduction Calibration of In. Sb SB-304 SCAs Dark current Noise QE Latent or Persistent Image Performance Operability Radiometric Stability 2

Introduction • Raytheon Detectors Proposed for JWST NIRCam and NIRSpec – In. Sb photo-diode 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 3

Calibration • Source Follower Gain – Gain through two SF FETs – SCA 006 SFGain=0. 777 – SCA 008 SFGain=0. 785 • Capacitance – Noise 2 vs Signal method – SCA 006 • 66 f. F • 3. 22 e-/ADU – SCA 008 • 68 f. F • 3. 32 e-/ADU 4

Calibration • Linearity – Plotted Signal Rate vs Signal (C 0/C) – Small flux over long integration times • Well Depth (Capacity) – @ 300 m. V 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 5

Dark Current Test Methods • Dark dewars are difficult to make and keep dark – Using an opaque mask placed in contact with In. Sb surface, UR dewar light leak < 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 6

Dark Current Test Methods • Noise 2 versus integration time – With reference pixel correction, accurate for small dark currents – Also, lengthy measurement 7

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 (e-/read) due to higher read rate • Confuses measured dark current • No detectable added noise from charge per read due to higher read rate! 8

Dark Current Results • SCA 006 – Idark = 0. 012 e-/s @ T=30. 0 K – Idark = 0. 024 e-/s @ T=32. 3 K – Charge per read of 0. 09 e-/read • Again, no detectable noise due to this charge – No measurable amp glow or digital circuit glow 9

Dark Current Results • SCA 008 – Idark = 0. 025 e-/s @ T=30. 0 K – Charge per read of 0. 07 e-/read – No digital circuit glow – Slight glow (0. 05 e-/s including dark current) from output amplifier • Covers small region (see operability section) • Known multiplexer defects (shorts) – Amp glow not seen on other multiplexers 10

System Noise • System Noise – Shorting resistor placed between signal (video) and signal reference lines (analog ground) – T=295 K – Connected and functioning detector in dewar to allow typical voltage/current paths which may cause cross talk (worst case) 11

Read Noise • Read noise versus Fowler Sampling – Measured at T=30. 0 K – All integration times are 100 s • SCA 006 read noise results – Follows 1/sqrt(N) where N is the number of Fowler sample pairs 12

Read Noise • SCA 008 read noise results – Follows 1/sqrt(N) 13

Noise Measurement Methods • Methods of measurement for total noise in 1000 seconds. – 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 reject Cosmic Ray • SCA 006 at right 14

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). 15

Total Noise Results • Total Noise Requirement: < 9 e- in 1000 sec using Fowler-8 sampling – SCA 006 • 6. 2 e- (Temporal method), 6. 7 e- (Full frame spatial method) @ T=30. 0 K • 6. 4 e- (Full frame spatial method) @ T = 32. 3 K • For 1000 sec Fowler-1, total noise is 12. 0 e- (temporal method) @T=30. 0 K – SCA 008 • 7. 9 e- (temporal method) @ T=30. 0 K 16

Quantum Efficiency • Photon sources and calibration equipment – For l > 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 < l < 3. 0 mm, photon source is NIST calibrated black body (Omega BB-4 A, 100 – 1000 C, e =0. 99) – For l<1. 0 mm, photon source is stabilized visible light source feeding an integrating sphere with a NIST calibrated Si diode detector – cos 4 q corrected • Responsive Quantum Efficiency – 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 – DQE = (Signal/Noise)2/(expected #photons) • Noise obtained via standard deviation of difference of two measurements 17

Quantum Efficiency Results RQE; DQE 0. 65 mm RQE; DQE 0. 70 mm RQE; DQE 1. 25 mm RQE; DQE 1. 65 mm RQE; DQE 2. 19 mm RQE; DQE 3. 81 mm RQE; DQE 4. 67 mm RQE; DQE 4. 89 mm 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 as provided by Raytheon. From this, we infer that the optical fill factor is > 98%. 18

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 SCA 006 ; SCA 008 1 300 100 30, 000 30 100 9 ; 0. 03 0. 3 ; 0. 12 2 300 100 30, 000 100 0. 9 ; 0. 003 0. 017 ; ≤ 0. 01 3 30 1000 30, 000 30 1000 4. 5 : 0. 015 ; 4 300 500 150, 000 30 100 90 ; 0. 06 0. 48 ; 0. 22 5 300 500 150, 000 100 9 ; 0. 006 0. 03 ; ≤ 0. 01 6 3 10, 000 30, 000 200 8000 Noise level 7 15 10, 000 150, 000 200 8000 Noise level 19

Operability • Operability is affected by two types of defects: – Missing contact between In. Sb diode implant and multiplexer unit cell • First In. Sb 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. 20

Operability • SCA 006 – Basic Fail = 13. 5% – Large fraction failing are unconnected pixels 21

Operability • SCA 008 – Basic Fail = 1. 94% – Slight amp glow in lower left 22

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 < 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. 23

MTF and Electrical Cross-Talk • MTF – Measured using knife edge and circular apertures placed in contact with In. Sb surface – 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} 24

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 – 2 pz)/(1 + e-4 pz) – If Nyquist frequency is taken as ½ z, then MTF = 0. 45 • Similar measurement on SB-226 In. Sb SCA produced MTF=0. 52 – If Nyquist frequency is taken as ¼ z, as in Rauscher’s MTF document, then MTF = 0. 58 • Exceeds (existing) requirement of 0. 53 in JWST NASA 641 document 25

MTF and Electrical Cross-Talk • Cosmic ray hit pixel upsets used to quantify electrical cross-talk – Histogram of 30 K dark data difference showing peaks at 0. 1% for next nearest neighbors and 0. 5 -1. 2% for nearest neighbors – Cross talk is < 2% 26

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% 0 0. 025 0. 012 -0. 025 0. 037 -0. 037 0. 012 0. 099 0 -0. 025 0. 074 0. 546 0. 099 0 0. 037 -0. 012 0. 025 -0. 062 0. 012 -0. 050 1. 142 100 0. 782 0. 137 -0. 248 2. 062 -0. 211 0. 012 0. 062 0. 012 0. 161 0. 733 0. 012 0. 062 -0. 074 0 -0. 050 0 0. 025 -0. 062 -0. 037 0. 012 0 0. 074 0. 025 0. 012 0. 001 27

Additional Tests • NASA Ames conducted proton radiation testing at UC Davis – Please see talk “Radiation environment performance of JWST prototype FPAs” 5167 -25 on Wednesday • STSc. I IDT Lab conducted independent tests on both In. Sb detector arrays from Raytheon and Hg. Cd. Te detector arrays from Rockwell Scientific. – Please see talk “Independent testing of JWST detector prototypes” 5167 -29 on Wednesday 28

Summary of SB-304 In. Sb 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 Fill Factor /95% (100%) /98% (100%) Bad Columns/Rows <5 containing >1000 No Yes Bad Pixel Clustering < 20 cluster up to 20 No pixels Yes Pixel Operability >98% 86. 5% basic, 82. 1% meet N+QE 98. 1% basic, 91. 5% meet N+QE 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-/s 0. 012 e-/s 0. 025 e-/s 29

Summary of SB-304 In. Sb SCA Performance Parameter Requirement (Goal) SB-304 -006 Result SB-304 -008 Result DQE 70% 0. 6[ l [ mm 80% 1. 0[ l [ mm (90%; 95%) 82% @ 0. 65 mm 97% @ J, H, L’’ 97% @ J 1. 0 5. 0 Well Capacity > 6 x 104 e- (2 x 105 e-) 1. 4 x 105 e- 1. 3 x 105 e- Electrical Crosstalk <5% (<2%) <1. 3% (nearest and next nearest pixel) Radiometric Stability 1% over 1000 s < 0. 07% over 1000 s Latent Image < 0. 1% after 2 nd read following >80% full well exposure 0. 3% (no amelioration) 0. 12% Frame Read Time 12 sec (<12 sec) < 11 sec Pixel read rate 100 KHz; 10 ms/pix Sub-array read 0. 2 s for 1282 pixels <0. 05 s for 1282 30

Conclusions • Raytheon has produced a robust, mature technology. • Both the In. Sb detector arrays from Raytheon and the Hg. Cd. Te 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! 31