52
1 Ultra low background characterization of Rockwell Scientific MBE HgCdTe arrays Donald N. B. Hall, University of Hawaii, Institute for Astronomy, Honolulu, Hawaii
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
3
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
4
H2RG mounted to KSPEC detector
module
ASIC mounting socket
5
4Kx4K DETECTOR MOSAIC
6
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
7
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
8
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
9
Id0 = 0.0003Id1 = 0.0007Id2 = 0.0012Id3 = 0.0009Id4 = -0.0003
JWST- 002 at 37.00K Feb. 9, 2005 darkramp-145 x 12 sec
10
Id = 0.00057
JWST- 002 at 37.00K Feb. 9, 2005 darkramp-145 x 12 sec
11
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
12
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
13
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
14
DARK CURRENT HISTOGRAMS for JWST-002 2.5 um 1-1 SCA at 768 seconds
15
TOTAL NOISE HISTOGRAMS for JWST-002 2.5 um 1-1 SCA at 768 seconds
16
1-1 CDS READ NOISE
17
1-1 TOTAL NOISE for 786 seconds SIGNAL ARRAYS VERTICAL REFERENCE ARRAYS
18
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
19
DARK CURRENT HISTOGRAMS for JWST-002 2.5 um 8-8 SCA at 768 seconds
20
TOTAL NOISE HISTOGRAMS for JWST-002 2.5 um 8-8 SCA at 768 seconds
21
8-8 CDS READ NOISE
22
8-8 TOTAL NOISE for 786 seconds SIGNAL ARRAYS VERTICAL REFERENCE ARRAYS
23
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
24
DARK CURRENT HISTOGRAMS for JWST-002 2.5 um 32-32 SCA at 768 seconds
25
TOTAL NOISE HISTOGRAMS for JWST-002 2.5 um 32-32 SCA at 768 seconds
26
H2RG-NIRCam-002-BernieMean-1008sec
27
H2RG-NIRCam-002-BernieSig-1008sec
28
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
29
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
30
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
31
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
32
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
33
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
34
100mK UP RAMP (36.95K to 37.05K)
35
100mK UP RAMP (36.95K to 37.05K)
36
CDS of 100mK UP RAMP (36.95K to 37.05K)
Logarithmic
Linear
37
100mK DOWN RAMP (37.05K to 36.95K)
38
100mK DOWN RAMP (37.05K to 36.95K)
39
CDS of 100mK DOWN RAMP (37.05K to 36.95K)
Logarithmic
Linear
40
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
41
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
42
H2RG-NIRCam4-UP-Template
43
H2RG-NIRCam4-DOWN-Template
44
H2RG-NIRCam4-UP T36.95 to 37.05K-corrected-Template
45
H2RG-NIRCam4-UP T36.95 to T37.05K -Template corrected
46
CDS of 100mK UP RAMP (36.95K to 37.05K)
Logarithmic
Linear
47
CDS of 100mK UP RAMP (36.95K to 37.05K)Temperature Drift Compensated
Logarithmic
Linear
48
H2RG-NIRCam4-DOWNT37.05 toT36.95K-Template-corrected
49
H2RG-NIRCam4-DOWN T37.05 to T36.95K template corrected
50
CDS of 100mK DOWN RAMP (37.05K to 36.95K)
Logarithmic
Linear
51
CDS of 100mK DOWN RAMP (37.05K to 36.95K)Temperature Drift Compensated
Logarithmic
Linear
52
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
