Ultra low background characterization of Rockwell Scientific MBE HgCdTe arrays

1

Ultra low background characterization of Rockwell

Scientific MBE HgCdTe arrays

Donald N. B. Hall, University of Hawaii, Institute for Astronomy,

Honolulu, Hawaii

2

OUTLINE

• CHARACTERIZATION OF DARK CURRENT AND TOTAL NOISE IN 2Kx2K HAWAII-2RG ARRAYS UNDER JWST CONDITIONS

• MERITS OF SPATIAL vs TEMPORAL AVERAGING

• DATA CUBE FOR TEMPORAL AVERAGING

• TEMPERATURE DRIFT COMPENSATION

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TEST CONDITIONS MATCHED TO JWST

• FOUR OUTPUTS READING OUT 512 x 2048 PIXEL “STRIPES”

• 100 Kpxl/sec SAMPLE RATE• 12 SECOND FRAME RATE• 3DB NOISE BANDWIDTH FILTERED AT 160 KHz• 10 TAU, > 14 BIT SETTLING• PIXEL BY PIXEL RESET AT 100 Kpxl/sec• OPERATING TEMPERATURE 37.000K +- <1mK• ARRAY ALWAYS BEING READ OUT OR RESET• DETBIAS 250 mV – Vreset 100 mV, DSUB 350 mV

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H2RG mounted to KSPEC detector

module

ASIC mounting socket

5

4Kx4K DETECTOR MOSAIC

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NOISE MEASURD BY SPATIAL AVERAGING

• UH TESTING REPORTED AT MUNICH 2000 SPIE • GENERATE FRAME PAIRS USING A STANDARD

PROCEDURE• SUBTRACT AND COMPUTE TOTAL NOISE

(VARIANCE) IN DIFFERENCE FRAME• TEST DATA SET CURRENTLY FIVE RAMPS,

EACH CONSISTING OF TWO PIXEL BY PIXEL RESETS FOLLOWED BY 145 FRAMES

• CORRESPONDING FRAMES IN AJACENT RAMPS ARE DIFFERENCED TO COMPUTE TOTAL NOISE

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FEATURES OF UH SPATIAL TEST PROCEDURE

• SIMPLE COMPUTATION OF STRIPE AVERAGED TOTAL NOISE

• THE DISADVANTAGE IS THAT THERE IS NO INFORMATION ABOUT TOTAL NOISE IN INDIVIDUAL PIXELS

• CORRECTION WITH THE HORIZONTAL ROWS OF REFERENCE PIXELS PROVIDES SENSITIVE MEASUREMENT OF DARK CURRENT FOR INDIVIDUAL PIXELS

• TOTAL NOISE IS DOMINATED BY READ NOISE – DARK CURRENT CONTRIBUTION NEGLIGIBLE

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UH 2.5um, UH 5.0um, and STScI 5.0um MeasurementsDark Current Logarithmic

0.001

0.010

0.100

1.000

10.000

25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135

Temperature (K)

SC

A A

vera

ge

Dar

k C

urr

ent

(e- /s

ec, p

ixel

)

UH 2.5um

UH 5.0um

STScI 5.0um

DARK CURRENT vs TEMPERATURE FOR 2.5 AND 5 UM MATERIAL

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Id0 = 0.0003Id1 = 0.0007Id2 = 0.0012Id3 = 0.0009Id4 = -0.0003

JWST- 002 at 37.00K Feb. 9, 2005 darkramp-145 x 12 sec

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Id = 0.00057

JWST- 002 at 37.00K Feb. 9, 2005 darkramp-145 x 12 sec

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TOTAL NOISE AND DARK CURRENT MEASURED BY TEMPORAL AVERAGING

• THE DATA SET CONSISTS OF 36 RAMPS, EACH A PAIR OF PIXEL BY PIXEL RESETS FOLLOWED BY 145 FRAMES AT 12 SECOND INTERVALS

• DATA CUBES 36 DEEP ARE GENERATED FOR FRAME TIME DIFFERENCES OF 384, 768 AND 1152 SECONDS AND AVERAGES OF 1, 2, 4, 8, 16 AND 32 FRAMES. ALSO RAUSCHER SLOPE FIT

• IN EACH OF THESE CUBES THE DC VALUES ARE USED TO DERIVE DARK CURRENT AND THE STANDARD DEVIATION OF TOTAL CHARGE TO DERIVE TOTAL NOISE FOR EVERY PIXEL

• COSMIC RAY CORRECTION BEING REFINED

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CDS TOTAL NOISE FOR 2.5 UM MATERIAL

Standard Deviation for JWST-002 at 384 sec, 768 sec, and 1152 sec

32 Avg

16 Avg

8 Avg

4 Avg

2 Avg

1 Avg

0

2

4

6

8

10

12

14

1 2 4 8 16 32

NAvg

en

384 seconds

768 seconds

1152 seconds

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CDS TOTAL NOISE FOR 2.5 UM MATERIAL

Standard Deviation for JWST-002 at 384 sec, 768 sec, and 1152 sec

8 Avg

4 Avg

2 Avg

1 Avg

32 Avg16 Avg

0

20

40

60

80

100

120

140

160

0 8 16 24 32 40 48 56

64/Navg

en

2

384 seconds

768 seconds

1152 seconds

64

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DARK CURRENT HISTOGRAMS for JWST-002 2.5 um 1-1 SCA at 768 seconds

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TOTAL NOISE HISTOGRAMS for JWST-002 2.5 um 1-1 SCA at 768 seconds

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1-1 CDS READ NOISE

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1-1 TOTAL NOISE for 786 seconds SIGNAL ARRAYS VERTICAL REFERENCE ARRAYS

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CONCLUSIONS FROM 1-1 CDS

• SPATIAL AND TEMPORAL AVERAGING METHODS SHOW GOOD AGREEMENT FOR ARRAY AVERAGES

• NOISE IN VERTICAL REFERENCE PIXELS AND ADJACENT SIGNAL COLUMNS IS ONLY SLIGHTLY REDUCED

• SHOT NOISE IN THE DARK CURRENT IS A NEGLIGIBLE COMPONENT OF TOTAL NOISE

• MEASUREMENTS OF SYSTEM NOISE SHOW IT TO BE A NEGLIGIBLE CONTRIBUTION

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DARK CURRENT HISTOGRAMS for JWST-002 2.5 um 8-8 SCA at 768 seconds

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TOTAL NOISE HISTOGRAMS for JWST-002 2.5 um 8-8 SCA at 768 seconds

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8-8 CDS READ NOISE

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8-8 TOTAL NOISE for 786 seconds SIGNAL ARRAYS VERTICAL REFERENCE ARRAYS

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8-8 AVERAGE MEASUREMENTS

• AT ~ 5.2 RMS e-, TOTAL 8–8 CDS OF MEETS NIRSPEC REQUIREMENT

• FOR BOTH DARK CURRENT AND TOTAL NOISE, SPATIAL AND TEMPORAL MEASUREMENTS ARE IN GOOD AGREEMENT

• TOTAL NOISE IN REFERENCE PIXELS AND AJACENT PIXELS IS ONLY SLIGHTLY LOWER THAN IN THE FULL BODY OF THE ARRAY

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DARK CURRENT HISTOGRAMS for JWST-002 2.5 um 32-32 SCA at 768 seconds

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TOTAL NOISE HISTOGRAMS for JWST-002 2.5 um 32-32 SCA at 768 seconds

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H2RG-NIRCam-002-BernieMean-1008sec

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H2RG-NIRCam-002-BernieSig-1008sec

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CONCLUSIONS REGARDING 32-32 AND SLOPE

• 32 – 32 AVERAGED CDS IS WELL MATCHED TO THE OPTIMUM 1/3 RAMP AVERAGING OVER A RAMP OF 88 SAMPLES

• EMPIRICALLY THE 32 – 32 CDS TECHNIQUE GIVES A SIGNIFICANT GAIN IN TOTAL NOISE ( 3.35 rms e- vs 4.87 rms e-) OVER SLOPE DETERMINATION

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HAWAII-2RG TEMPERATURE SENSITIVITY AT 37 K

• IN ALL UH TESTS, THE TEMPERATURE OF THE DETECTOR WAS HELD CONSTANT TO <+- 1 Mk

• NIRCAM NEEDS TO SPECIFY THE ACCURACY TO WHICH TEMPERATURE MUST BE HELD (+- 50 Mk GOAL)TO MEET REQUIREMENTS

• THE REF PIXELS FULLY COMPENSATE SUPPLY AND SIGNAL CHAIN VOLTAGE CHANGES

• dV/dT IS LARGE (800 e-/K), THE REF PIXEL dV/Dt IS DIFFERENT TO THAT OF THE SIGNAL PIXELS AND VARIES MARKEDLY ACROSS THE ARRAY

• THE COEFFICIENT IS LINEAR FOR EACH PIXEL

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KSPEC Temperature Stability

36.970

36.975

36.980

36.985

36.990

36.995

37.000

37.005

37.010

0 500 1000 1500 2000 2500 3000

Time (minutes)

Tem

pera

ture

(K

)

KSPEC Control KSPEC Monitor

Radiation shield still cooling.

At 0 minutes, the control temperature reaches 37K.

KPEC Temperature Stability

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ULBcam Temperature Stability

36.990

36.995

37.000

37.005

37.010

37.015

37.020

37.025

37.030

0 500 1000 1500 2000 2500 3000

Time (minutes)

Tem

per

atu

re (

K)

ULB Control ULB Monitor

At 0 minutes, the control temperature reaches 37K.

ULBcam starts observing run.

ULBcam Temperature Stability

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Temperature Stability of 36 Ramp Data Cube

36.960

36.965

36.970

36.975

36.980

36.985

36.990

36.995

37.000

37.005

0 200 400 600 800 1000 1200

Time (minutes)

Tem

per

atu

re (

K)

Heating Control Detector Monitor

18:00 21:19 0:39 7:19 10:39 13:59

Temperature Stability of 36 Ramp Data Cube

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THERMAL PROFILE of TEMPERATURE DRIFT TEST

5up-5down dT=+/-50mK

36.900

36.920

36.940

36.960

36.980

37.000

37.020

37.040

37.060

0 50 100 150 200 250 300 350 400

Time (minutes)

Tem

pera

ture

(K

)

Control Monitor

Stabilization ramp

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100mK UP RAMP (36.95K to 37.05K)

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100mK UP RAMP (36.95K to 37.05K)

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CDS of 100mK UP RAMP (36.95K to 37.05K)

Logarithmic

Linear

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100mK DOWN RAMP (37.05K to 36.95K)

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100mK DOWN RAMP (37.05K to 36.95K)

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CDS of 100mK DOWN RAMP (37.05K to 36.95K)

Logarithmic

Linear

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TEMPERATURE DRIFT CORRECTION (TDC) TEMPLATE

• CREATE A TEMPLATE BY FORMING 128 CDS FRAMES BY SUBTRACTING FRAMES AT 36.4K FROM CORRESPONDING FRAMES AT 37.6K

• REF PIXEL CORRECT EACH AND CO-ADD TO FORM THE TDC TEMPLATE.

• MEASURE THE TEMPERATURE OF EACH FRAME IN AN OBSERVATION

• SCALE THE TEMPLATE TO THE ΔT FROM 37K AND SUBTRACT FROM THE REF PIXEL CORRECTED OBSERVED FRAME

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THERMAL PROFILE of TEMPERATURE DRIFT CORRECTION

2up-2dow n dT=+/-600mK

36.200

36.400

36.600

36.800

37.000

37.200

37.400

37.600

37.800

0 200 400 600 800 1000 1200

Time (minutes)

Tem

pera

ture

(K

)

Control Monitor

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H2RG-NIRCam4-UP-Template

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H2RG-NIRCam4-DOWN-Template

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H2RG-NIRCam4-UP T36.95 to 37.05K-corrected-Template

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H2RG-NIRCam4-UP T36.95 to T37.05K -Template corrected

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CDS of 100mK UP RAMP (36.95K to 37.05K)

Logarithmic

Linear

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CDS of 100mK UP RAMP (36.95K to 37.05K)Temperature Drift Compensated

Logarithmic

Linear

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H2RG-NIRCam4-DOWNT37.05 toT36.95K-Template-corrected

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H2RG-NIRCam4-DOWN T37.05 to T36.95K template corrected

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CDS of 100mK DOWN RAMP (37.05K to 36.95K)

Logarithmic

Linear

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CDS of 100mK DOWN RAMP (37.05K to 36.95K)Temperature Drift Compensated

Logarithmic

Linear

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CONCLUSIONS

• SPATIAL AND TEMPORAL AVERAGING ARE IN GOOD AGREEMENT REGARDING PIXEL DARK CURRENT AND FRAME AVERAGED TOTAL NOISE

• TEMPORAL AVERAGING DATA CUBE ALLOWS DETERMINATION OF TOTAL NOISE PER PIXEL

• TOTAL 8 – 8 NOISE OF <6 RMS e- MEETS SPEC• AT ~ 0.001 e-/sec, DARK CURRENT IS

NEGLIGIBLE NOISE SOURCE• TEMPLATE APPROACH CORRECTS 90%

THERMAL DRIFT – 0.8 e-/Mk TO 0.08 e-/mK