James Webb Space Telescope : Characterization of Flight Candidate of Raytheon NIR InSb Arrays

James Webb Space Telescope :James Webb Space Telescope : Characterization of Flight Candidate Characterization of Flight Candidate

of Raytheon NIR InSb Arraysof Raytheon NIR InSb Arrays

5 Aug 2003

Craig McMurtry, William Forrest,

Andrew Moore, Judith Pipher

2

OverviewOverview

• Introduction

• Calibration of InSb SB-304 SCAs

• Dark current

• Noise

• QE

• Latent or Persistent Image Performance

• Operability

• Radiometric Stability

3

IntroductionIntroduction

• Raytheon Detectors Proposed for JWST NIRCam and NIRSpec

– InSb photo-diode 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

4

CalibrationCalibration

• Source Follower Gain– Gain through two SF FETs– SCA 006 SFGain=0.777– SCA 008 SFGain=0.785

• Capacitance– Noise2 vs Signal method– SCA 006

• 66 fF

• 3.22 e-/ADU

– SCA 008• 68 fF

• 3.32 e-/ADU

5

CalibrationCalibration

• Linearity– Plotted Signal Rate vs

Signal (C0/C)

– Small flux over long integration times

• Well Depth (Capacity)– @ 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

6

Dark Current Test MethodsDark 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 < 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

7

Dark Current Test MethodsDark Current Test Methods

• Noise2 versus integration time

– With reference pixel correction, accurate for small dark currents

– Also, lengthy measurement

8

Dark Current Test MethodsDark 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!

9

Dark Current ResultsDark Current Results

• SCA 006

– Idark = 0.012 e-/s @ T=30.0K

– Idark = 0.024 e-/s @ T=32.3K

– Charge per read of 0.09 e-/read

• Again, no detectable noise due to this charge

– No measurable amp glow or digital circuit glow

10

Dark Current ResultsDark Current Results

• SCA 008

– Idark = 0.025 e-/s @ T=30.0K

– 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

11

System NoiseSystem Noise

• 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)

12

Read NoiseRead Noise

• Read noise versus Fowler Sampling

– Measured at T=30.0K

– All integration times are 100 s

• SCA 006 read noise results

– Follows 1/sqrt(N) where N is the number of Fowler sample pairs

13

Read NoiseRead Noise

• SCA 008 read noise results

– Follows 1/sqrt(N)

14

Noise Measurement MethodsNoise 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

15

Noise Measurement MethodsNoise 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).

16

Total Noise ResultsTotal 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=30.0K• 6.4 e- (Full frame spatial method) @ T = 32.3K• 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

17

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

– cos4 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

18

Quantum Efficiency ResultsQuantum Efficiency Results

RQE;

DQE

0.65m

RQE;

DQE

0.70m

RQE;

DQE

1.25m

RQE;

DQE

1.65m

RQE;

DQE

2.19m

RQE;

DQE

3.81m

RQE;

DQE

4.67m

RQE;

DQE

4.89m

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%.

19

Latent Image ResultsLatent Image Results

Test #

SrceFlux(e-/s)

Source Exposure (s)

Source Fluence (e-)

Delay (s)*

Latent Integr’n Time (s)

Max. DesiredLatent Fluence (e-: %)

Meas’d (%)Latent Fluence SCA006 ; SCA008

1 300 100 30,000 30 100 9 ; 0.03 0.3 ; 0.12

2 300 100 30,000 1000 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 1000 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  

20

OperabilityOperability

• 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.

21

OperabilityOperability

• SCA 006

– Basic Fail = 13.5%

– Large fraction failing are unconnected pixels

22

OperabilityOperability

• SCA 008

– Basic Fail = 1.94%

– Slight amp glow in lower left

23

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.

24

MTF and Electrical Cross-TalkMTF and Electrical Cross-Talk

• MTF– Measured using knife

edge and circular apertures placed in contact with InSb 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}

25

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 JWST NASA 641 document

26

MTF and Electrical Cross-TalkMTF and Electrical Cross-Talk

• Cosmic ray hit pixel upsets used to quantify electrical cross-talk

– 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%

27

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%

0 0.025 0.012 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 0.012 0 0.074 0.025 0.012 0.001

28

Additional TestsAdditional Tests

• NASA Ames conducted proton radiation testing at UC Davis

– Please see talk “Radiation environment performance of JWST prototype FPAs” 5167-25 on Wednesday

• STScI IDT Lab conducted independent tests on both InSb detector arrays from Raytheon and HgCdTe detector arrays from Rockwell Scientific.

– Please see talk “Independent testing of JWST detector prototypes” 5167-29 on Wednesday

29

Summary ofSummary ofSB-304 InSb SCA PerformanceSB-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

<5 containing >1000 No Yes

Bad Pixel Clustering

< 20 cluster up to 20 pixels

No 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

30

Summary ofSummary ofSB-304 InSb SCA PerformanceSB-304 InSb SCA Performance

Parameter Requirement (Goal) SB-304-006 Result SB-304-008 Result

DQE 70% 0.61.0 m

80% 1.05.0 m

(90%; 95%)

82% @ 0.65 m

97% @ J,H,L’’

-

97% @ J

Well Capacity > 6x104e- (2x105e-) 1.4 x 105e- 1.3 x 105e-

Electrical Cross-talk

<5% (<2%) <1.3% (nearest and next nearest pixel)

<1.3% (nearest and next nearest pixel)

Radiometric Stability

1% over 1000 s < 0.07% over 1000s < 0.07% over 1000s

Latent Image < 0.1% after 2nd read following >80% full well exposure

0.3%

(no amelioration)

0.12%

Frame Read Time 12 sec (<12 sec) < 11 sec < 11 sec

Pixel read rate 100KHz; 10 s/pix 100KHz; 10 s/pix 100KHz; 10 s/pix

Sub-array read 0.2 s for 1282 pixels <0.05 s for 1282 <0.05 s for 1282

31

ConclusionsConclusions

• Raytheon has produced a robust, mature 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!