IR Detectors for WFC3
on the Hubble Space Telescope
M. Robberto1, S. Baggett1, C. Hanley1, B. Hilbert1, J. MacKenty1,
E. S. Cheng2, R. J. Hill2, S. D. Johnson2, E. M. Malumuth2, E. Polidan2, A. Waczynski2, Y. Wen2,
A. Haas3, J. T. Montroy3, E. Piquette3, K. Vural3, and D. N. B. Hall4
1Space
Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218
2NASA/Goddard Space Flight Center, Greenbelt, MD 20771
3Rockwell Scientific Company, 5212 Verdugo Way, Camarillo, CA 93012
4University of Hawaii, Institute for Astronomy, 640 N. Aohoku Place, Hilo
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
1
WFC3 layout
UVIS Corrector Mech.
IR M1
Mirror
IR Detector
Cold Enclosure
RCP/
Cold Stop
UVIS Detector
IR Filter Wheel
Mechanism
IR Corrector Mech.
CSM
IR Fold
Mirror
Shutter Mechanism
Baffles
SOFA Mechanism
Optical Bench (In Phantom)
UVIS Optical Path (Blue)
IR Optical Path (Red)
Calibration
Subsystem
UVIS M2
Mirror
POM
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
2
WFC3 IR channel
The zodiacal scattering and the HST temperature create a
minimum of background at ~ 1.6 mm.
A detector with cut-off at ~ 1.7 mm can be operated at ~150K.
No need for liquid nitrogen. Extended lifetime.
WFC3-1R FPA
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
3
WFC3-1R FPA
• Producer:
• Type:
Rockwell Scientific Company
HgCdTe with 1.72mm cutoff
- MBE grown on ZnCdTe substrate
- Hawaii-1R MUX
• Operating T:
• Pixel size:
• Format:
150K
18 mm
1024  1024 pixels
- 1014  1014 active pixels
- 5 outer rows/column with reference pixels
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
4
P-on-N design of WFC3-1R
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
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Hawaii-1R MUX design
Quadrant 2
512x512
Quadrant 4
512x512
(507x507 photoactive)
(507x507 photoactive)
Hawaii-1R MUX ses reference pixels
Quadrant 1
512x512
Quadrant 3
512x512
(507x507 photoactive)
(507x507 photoactive)
1014  1014
active pixels
1014  5 reference pixels
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
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Hawaii-1R Unit Cell
Vrst
Vrst
Vcelldrain
Frst
Frst
pn
Vrst Vcelldrain
Vcelldrain
Frst
Cref
Vsub Freadbus
Active pixels
Vsub Freadbus
Inboard reference
pixels
Cref
bus
Fread
Vsub
Offboard reference
pixels
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
7
WFC3-1R specs
SPEC
Minimum Baseline
Read-out noise
Performance
units
17-20
15-17
<15
e/pix/read @ 100KHz
Dark current
0.3-0.4
0.2-0.3
<0.2
e/s/pix @ 150K
Operability
94-96
96-98
>98
% of active pixels
Quantum Efficiency
– Range and absolute value
– Stability
see viewgraph
0.5 %/hr p-p; 1.0 %/month
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
8
WFC3-1R specs
• Amplifier glow
• Linearity
• Full well capacity
• Pixel-to pixel response
<10 e/pix/read at the center
<400 e/pix/read at the border (<5%)
>95%, correctable to >99.7%
100,000 e/pix (150,000 goal)
– uniformity
better than 2%; 1% @ 1000-1800nm
(0.5% goal)
– stability
<0.2 % over 1 hr ; <1% over 2 months
• Radiation hardness
– Absolute sensitivity
<1,000 e/event
– Stability (SAA)
<0.1/e/s/pix after 5min
> 90%
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
9
QE specs
CEI S pec: HgCdTe Det QE
RSC Spec: HgCdTe Det QE
100
90
goal
80
% Efficiency
% Efficiency
70
60
50
40
min
30
20
10
0
700
900
1100
1300
1500
Wave le ngth (nm)
1700
1900
100
90
80
goal
70
60
base
50
40
30
min
20
10
0
700
900
1100
1300
1500
Wave le ngth (nm)
1700
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
10
1900
Program status
•
Original Rockwell Scientific WFC3 flight detector
contract started almost 2 years ago
– 4 Lots of FPAs completed by the end of November 2001
– 2 Lots of detectors completed by the end of June 2002
•
•
•
•
52 FPA have been hybridized
24 FPAs have been delivered to NASA/GSFC for test
Flight candidates selected
Lot 7 started July 2002
– First FPAs in early test phase at RSC
– Complete delivery by November 2002
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
11
Quantum efficiency
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
12
Quantum efficiency
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
13
QE at cutoff
1.0
Q1
0.9
Q2
QE - transmission
0.8
Q4
Q3
0.7
F160W
0.6
F160W-short
0.5
F160W-long
`
0.4
0.3
0.2
0.1
0.0
1600
1620
1640
1660
1680
1700
1720
1740
1760
1780
1800
wavelength (nm)
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
14
Cutoff Spatial Uniformity
FPA #15
1720 nm
1400 nm
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
15
QE summary
• Early detectors (before lot 6) exhibit
– long wavelength QE better than specification
– low QE at short wavelengths
• With Lot 6/process B detectors low wavelength QE has
been restored
• Lot 6/process A detectors show excellent QE at all
wavelengths.
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
16
Dark Current
FPA 43
60min dark
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
17
FPA#32
25000
1m
1m
1m 60m
60m
1m
1m
1m 90m
90m 1m
1m 120m
120m 1m
1m 150m
150m 1m
1m 180m
180m 1m
1m
24600
24400
24200
24000
23800
218
211
204
197
190
183
176
169
162
155
148
141
134
127
120
113
106
99
92
85
78
71
64
57
50
43
36
29
22
15
8
23600
1
Mean Signal (DN/pix)
24800
30m
30m
Read Number
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
18
FPA#32
6080
1m
1m
1m 60m
60m
1m
1m
1m 90m
90m 1m
1m 120m
120m 1m
1m 150m
150m 1m
1m 180m
180m 1m
1m
5680
5480
5280
5080
4880
218
211
204
197
190
183
176
169
162
155
148
141
134
127
120
113
106
99
92
85
78
71
64
57
50
43
36
29
22
15
8
4680
1
Mean Signal (DN/pix)
5880
30m
30m
Read Number
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
19
Dark Current rates
FPA#34 Dark current at 150K (8hours)
FPA#32 dark current at 150K (16 hours)
0
-0.08
Dark rate, ADU/second
Dark rate, ADU/second
-0.002
-0.085
-0.09
-0.095
-0.004
-0.006
-0.008
-0.01
-0.012
-0.014
-0.016
-0.018
-0.1
0
10000
20000
30000
40000
50000
-0.02
60000
0
5000
Tim e, second
20000
25000
30000
FPA#51 Dark current at 150K (12hours)
0
0
-0.01
-0.05
-0.02
Dark rate, ADU/second
Dark rate, ADU/second
15000
tim e, second
FPA#45 Dark current at 150K (8 hours)
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
-0.1
-0.15
-0.2
-0.25
-0.3
-0.35
-0.09
-0.1
10000
10000
15000
20000
25000
30000
-0.4
20000
25000
30000
35000
40000
45000
Tim e, second
Tim e, second
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
20
Optical Instability
FPA#34 Optical Interrupt
0.2
0.1
0.1
0.08
Dark rate, ADU/second
Dark rate, ADU/second
FPA#32 Optical Instability
0
-0.1
-0.2
-0.3
0.06
0.04
0.02
0
-0.02
-0.04
-0.4
0
2000
4000
6000
0
8000
500
1000
2000
2500
3000
3500
4000
Tim e, second
Time , second
FPA#51 Optical Interrupt
FPA#45 Optical Instability
8
0
7
-0.2
6
-0.4
Dark rate, ADU/second
Dark rate, ADU/second
1500
5
4
3
2
1
0
-0.6
-0.8
-1
-1.2
-1.4
-1.6
-1.8
-1
-2
-2
0
200
400
600
800
1000
0
500
1000
1500
2000
2500
Tim e, second
Tim e , second
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
21
FPA 32/50 Stability
Comparison
“Settled” dark
current level.
Data taken
immediately after 3/4
full-well flat field.
“Reset anomaly” peaks follow a trend line.
Time (hours)
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
22
Dark Current Summary
• Dark current specification is less than 0.2 e-/pixel/sec.
• Dark current levels as low as 0.02 e-/pixel/sec have been
achieved
• In Lot 3 and Lot 6 devices the dark current is not be stable
after power cycling, bias change, or exposure to light.
– Settling times range from a few minutes for some devices, to 10’s
of hours for most of the high-QE devices.
– Precludes simple on-orbit calibration (remembers the last
exposure).
– Powering down the detector on-orbit will be an efficiency impact
(long delays before data taking can resume).
• Lot 4 devices show both low and stable dark current
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
23
Readout Noise
Active pixels
Reference pixels
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
24
RON table
Double Correlated Sampling
FPA#
Stack
ADU e-
mV
Spatial
ADU
e-
mV
Note
31
22.6 38.5 133.3
24.7
42.0
145.7
g=1.7e/adu
32
18.4 27.6 108.6
20.2
30.3
119.2
g=1.5e/adu , narrow bandwith
33
28.8 51.8 169.9
26.9
48.5
158.7
g=1.8e/adu
21.7 32.5 128.0
24.5
36.7
144.6
g=1.5e/adu
20.1 30.1 118.6
24.6
36.9
145.1
g=1.5e/adu, 1st ramp rejected
21.7 34.7 128.0
25.2
40.4
148.7
g=1.6e/adu
19.2 30.8 113.3
25.2
40.3
237.8
g=1.6e/adu, 1st ramp rejected
20.2 32.4 119.2
20.7
33.1
195.3
g=1.6e/adu, narrow bandwith
19.2 30.7 113.3
20.2
32.4
119.2
g=1.6e/adu, T=140K
25.1 42.7 148.1
28.1
47.7
165.8
g=1.7e/adu
34
43
50
Gain = 5.9mV/adu measured on FPA#43 and #50
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
25
Readout Noise summary
• Best noise performance is ~30e-/DCS
• Noise higher in the detector pixels than in the reference pixels.
– Source in the detector material rather than in the mux
• Evidence of some 1/f low-frequency drift (below ~10 KHz)
– typical of surface state trapping
• White-spectrum excess noise reduces with temperature
roughly as the square-root of temperature
– suggests Johnson noise from a resistive element
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
26
Key Lots are 4 and 6
• Lot 3 and 4
–
–
–
–
–
–
Part of the original flight detector contract.
Cutoff demonstrated
Good dark current
Good stability (only lot 4)
Acceptable noise (only lot 4)
Poor QE
• Lot 5 and 6
–
–
–
–
First iteration.
Exceptionally good QE (lot 6)
Poor stability
Higher readout noise.
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
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Lot 7 goals
In priority order:
• Maintain QE enhancement process steps used for the Lot 6
devices.
• Improve or remove the dark current instability (like what
was achieved in the Lot 4 devices).
• Reduce the readout noise.
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
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Lot 7 Processing
Status and Schedule
• Split processing of two, 4-wafer batches for processing
risk mitigation
– 4 devices per wafer
• All 8 wafers have been grown
• First 4 wafers have been processed
– Polishing done
– A/R Coating done
– Dicing done
• Performance Evaluation Chip (PEC) under test
• First FPAs are being hybridized and tested at RSC
• The second batch processing will follow.
"Data contained herein is exempt from ITAR regulations under CFR 125.4(13) -- data approved for public disclosure."
August 27, 2002
SPIE 2002
29