© The Aerospace Corporation 2015
A LINEAR MODE PHOTON-COUNTING (LMPC) DETECTOR ARRAY IN A CUBESAT TO ENABLE EARTH SCIENCE LIDAR MEASUREMENTS
Renny Fields1, Xiaoli Sun2, James B. Abshire2, Jeff Beck3, Richard M. Rawlings3, William Sullivan III3, David Hinkley1 1The Aerospace Corporation, El Segundo, CA 90245 2NASA Goddard Space Flight Center, Greenbelt, MD 20771 3DRS Technologies, C4ISR Group, Dallas, TX 78712
Effort funded under the NASA Earth Science Technology Office InVEST 12 open solitication
1
AC9 LMPC
2 © The Aerospace Corporation 2015
UNCLASSIFIED
UNCLASSIFIED
HgCdTe electron initiated avalanche photodiode (e-APD) array • Developed by DRS Technologies in Dallas TX • 2x8 pixels with built in read-out integrated circuit (ROIC), 20 µm
diameter active area, 64 µm pitch, with µ-lens array F/7 optical path, 7 mm diameter entrance aperture
• 90% quantum efficiency • >1000 APD gain, more than sufficient to override ROIC noise • Linear mode photon counting (LMPC) detectors from visible to
mid-wave infrared (VIS/MWIR) wavelength range.
AR Coating
5-7 µm P-TypeMCT
N-TypeRegion
<1 µm
0.5 mm
Thic
knes
s
CdTePassivation
ROIC
epoxy epoxy
Unit Cell Cross Section
Pre-amp input pad
AR Coating
5-7 µm P-TypeMCT
N-TypeRegionN-TypeRegion
<1 µm
0.5 mm
Thic
knes
s
CdTePassivation
ROIC
epoxy epoxy
Unit Cell Cross Section
Pre-amp input pad
Diode Side View
Readout Integrated Circuit (ROIC)
Top View
LMPC CubeSat – Aerospace AeroCube-9 (AC-9)
+X -Z -
Y -X
-Z +Y
1 & 4
5
2
6
3
Optical Path Optical Path BUS 1. Dewar 2. Stirling cycle cooler 3. IDCA controller 4. FPA conditioning circuits 5. Radiator structure 6. Warm filter and objective lens
• HgCdTe responds from 0.4 to 4 microns to single photons (1000 electrons per photon)
• AC9 will use narrowband filters to pass 1.06, 1.55 and 2.06 microns for daylight operation
• Launch Nov 2016 (delivery Aug 2016)
• Filter wheel with 5 settings • 3 Bandpass filters • 1 blank (opaque) • 1 open
AC9 LMPC
3 © The Aerospace Corporation 2015
UNCLASSIFIED
UNCLASSIFIED
Why Fly a Linear Mode Photon Counting Detector?
Tier 1 Tier 2 Tier 3 Decadel Survey Missions
ICE
Sat
-II
CLA
RR
EO
SM
AP
DE
SD
ynl
Hys
pIR
I
AS
CE
ND
S
SW
OT
GE
O=C
AP
E
AC
E
LIS
T
PATH
GR
AC
E=I
I
SC
LP
GA
CM
3D=W
inds
LMPC Impact 0
0
0 0 0
At least three Tier 1 missions are strongly driven in science capability by photon detection sensitivity • LIST which is strongly related to ICESat & DESDynl will not reach
threshold goals without single photon response matched to high power efficient transmitters that respond to 1 micron
• While threshold science can be achieved with photomultipliers for CO2 at 1.5 and 2 microns, single photon response will significantly extend the science
• The potential for high sensitivity passive arrays across the 0.4-4 micron HgCdTe response shows potential for many other missions as this technology and its support elements mature
AC9 LMPC
4 © The Aerospace Corporation 2015
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UNCLASSIFIED
Packing Density View
IDCA PAYLOAD • Located centrally inside satellite • Radiator/payload hard mount to body by
solid brackets that are mechanically fixed but made from thermally isolating material.
ACS COMPONENTS • All ACS components hard mount
to body around primary payload
RADIATION DETECTOR • Commercially available Teledyne
Dosimeter • Uses AC8 Derived daughter PCB • Co-Located with IDCA sensor
SINGLE STAGE LASER • Output of laser co-bore sighted
with IDCA sensor Sensor
AC9 LMPC
5 © The Aerospace Corporation 2015
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Enabling Technology: Linear Mode HgCdTe e-APD
• High, near noiseless, uniform, avalanche gain
• Gain normalized dark current as low as 100 e/s
• Broad spectral range: UV – MWIR
• High quantum efficiency • High intrinsic bandwidth (~ 10
GHz) • Large dynamic range • Demonstrated photon counting
sensitivity • Continuous operation with no
dead time or after-pulsing – Minimum time between
events MBE < ~ 10 ns (limited by current ROIC bandwidth)
Excess Noise Factor vs. Gain
0
1
2
3
4
5
0 200 400 600 800 1000 1200Gain
F(M)
6,56,05,43,02,7k=0k=0.02k=0.001
'
Si
Measured data
Theory for Ideal k = 0 (McIntyre History-Independent)
1
10
100
1000
10000
0 5 10 15
Bias (V)G
ain
APD Gain vs. Bias
53 Pixels M = 1270 @13.1 V s/mean = 4.5 %
Beck, et al. 2006 JEM
0
0.05
0.1
0
0.05
0.1
Ampl
itude
(V)
0 50 100 150 200 250
0
0.05
0.1
Time (µs)
Gain = 254
Gain = 514
Gain = 1100
High SNR Single Photon Sensitivity
0 10 20 30 40 50 60-0.01
-0.005
0
0.005
0.01
0.015
0.02
0.025
0.03
Time (ns)
Volta
ge (V
)
8 ns
8 ns pulse separation (ROIC BW limited) Broad Spectral Response
AC9 LMPC
6 © The Aerospace Corporation 2015
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Blocking Noise from ROIC Glow
10/27/14 Sun et al., ESTF 2014, Paper B4P5
Si ROIC
1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,80
200
400
600
800
1000
1200
1400
1600
1800
2000
Pixel
FER
(kH
z)
No mirror blocking metalWith mirror blocking metal
FER ≤ 200 kHz for every pixel with blocking metal layer, a 1/5 reduction. Multiple metal layers are expected to decrease FER to diode limit (< 20 kHz).
“Tab” metal shield
Si ROIC
HgCdTe Array HgCdTe Array
16-Pixel-Mean PDE vs. FER Pixel-by-Pixel FER Comparison
All pixels: >50% PDE
ROIC Glow Photons
No metal shield With Metal shield
103 104 105 106 1070
0.2
0.4
0.6
0.8
1
False Event Rate (Hz)
PDE
A8327-14-2 (No metal shield)A8327-14-1 (With metal shield)
AC9 LMPC
7 © The Aerospace Corporation 2015
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Parameter GSFC ACT Program Specification Oct. 2014 Status Notes
Size and form factor 2x8 pixel array, 20 µm dia, 64 µm pitch Demonstrated Form factor can be changed if
funds available for a new ROIC
Photon Detection Efficiency 0.9 to 4.2 µm
> 40% (> 50% goal)
> 50% (> 65% demonstrated)
From optical input to the analog outputs
Dark count rate < 500 kHz (<100 kHz goal)
< 200 kHz demonstrated
Including detector dark current, ROIC and system noise
Pulse pair separation < 10 ns (< 6 ns goal) 9 ns demonstrated Stray capacitance limiting bandwidth
Timing jitter < 1.0 ns rms (< 0.5 ns rms goal)
~1.6 ns rms (< 1 ns rms in 2011 FPA)
Improvement with smaller pitch APDs pixel designs expected.
Excess Noise Factor < 1.4 Demonstrated 1.2-1.25 Decreased diode junction width
Outputs Analog and Digital (optional) Demonstrated Linear mode multi-photon
resolution with analog outputs
Housing LN2 Dewar (80K) with window, f/1.5 to f/4.9 Demonstrated May be housed in an existing
long lifetime space cryo-cooler
Simultaneity of Specifications
All specifications met at the same time
Demonstrated with exception of jitter
All spec’s met, except jitter, at the same time on the same device at the same threshold.
LMPC HgCdTe e-APD Performance Summary
AC9 LMPC
8 © The Aerospace Corporation 2015
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Physical Dimensions of the Cooler and Cold Filter Performance
Basic Dimensions of the Integrated Detector Cooler Assembly
4.214”
Ø1.529”
8.373”
0.602”
3.131”
1.887”
The background count rate was calculated using: • Materion’s measured cold filter
transmission • QE from previous LMPC APD array (analysis uses 300 K blackbody temperature, dual stacked cold filters, f/7, and a (64 µm)2 detector.)
Stacked filter transmission is very good (>90%) at 1064 nm, 1572 nm, and 2060 nm
The total expected background count rate
is 103 kHz
0 1 2 3 4 5 6
105
1010
1015
1020
1025
1030
Wavelength (µm)
Spec
tral r
adia
nce
(ph
/ (s
* m2 *
sr *
m))
LMPC QE, CubeSat Coldfilter - Incident Background Count Rate: 102.45 kHz at f/7.0
0 1 2 3 4 5 60
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Filte
r Tra
nsm
issi
on &
QE
2.25 µm cutoff
Cold filter transmission Spectral Radiance APD QE
AC9 LMPC
9 © The Aerospace Corporation 2015
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Overall System Block Diagram
Analog Power Supplies
FPGA LPDDR2
ARM LPDDR2
Flash (QSPI, µSD,
Atmel)
Photon Counters
Linear Capture
High-speed Capture & MUX
Capacitive Isolators
Pre-Filter
Mai
n Ve
hicl
e B
us
(Pow
er, G
PS
Tim
e, T
x2/R
x2, T
x1/R
x1)
DR
S S
enso
r Con
nect
or
(Pow
er, a
nalo
g ou
tput
s, s
tatu
s)
Zynq 7020 SoC (ARM + FPGA)
Control and Status
Digital Power Supplies
Analog board Digital board
AC9 LMPC
10 © The Aerospace Corporation 2015
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High-speed (Single Channel)
Linear-mode (16 Channel)
Photon Counters (16 Channel)
Three Data-Capture Subsystems
Zynq-7020
AD9249 (65MSPSx16)
AD9286 (500MSPS×1)
ARM
2 GB LPDDR2
(667 MT/s)
1 GB LPDDR2
(667 MT/s)
16x Analog Signals from DRS HgCdTe detector
MU
X
Main Bus
(Isolated)
8 GB µSD Card
Low-pass Filter e.g. LFCN-105 (F3db=180 MHz)
2×LTC2605 (16-bit DAC×16)
Comparators (ADCMP605)
Thresholds
Low-pass (F3db= 7 MHz) FPGA
16
16
16
16
16
16
16
1 1
Note: I2C/SPI control signals omitted for clarity
16+ MB Boot Flash
16:1 MUX (ADG782)
8 MB Backup Flash
AC9 LMPC
11 © The Aerospace Corporation 2015
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Remote Access
RW Interface
Solar H
arne
ss
Payload Solar Cells(8W sunlit)
EPS (bus)•Maturity: TRL8FGA
•Maturity: TRL8
1.0, 1.57, 2.05 micron light sources•COTS LEDs•Maturity: TRL5
Motorized Filter wheel•Aerospace Design•Maturity: TRL4
BUS Batteries•Molicel 18650H •Maturity: TRL9
FGA (GPSRADIO #1FLIGHT COMPUTER)
Radio 1 915 MHz
GPS1.57 GHz
Software
AC9 LED PCB
Temp Ha
rness (6)
Camera controller•Maturity: TRL6
Dosimeter• Teledyne•Maturity: TRL9
IDCA controller•Aerospace design•Maturity: TRL4
EPS
Software
Solar H
arne
ss
Avionics Solar Cells(2W orbit avg)
CAMERA PCB
Software
1235
Legend40-‐pin backplane
Temperature sensor
Custom Kapton Harness
Kapton jumper
Patch antenna
RF coax cable
Wire harness
IDCA CONTROLLER (payload)•Maturity: New
Radio #2 (optional)•Software radio•Maturity: TRL6
ACSDR
Software
Radio 2 915 MHz
4
Reaction Wheels•Maturity: TRL7
Torque Rods•Aerospace Design•Maturity: TRL9
Butterfly Gyro• STIM210•Maturity: TRL8
Sun Sensor Assembly• Maturity: TRL9.
Sun /Earth Sensor Assembly• Maturity: TRL8
AC9 Mission Specific Hardware
DRS Hardware
3
17
18 1919
0W/0.5W@90min
PHOTON COUNTING(2x PCBs) CAPTURE AND PROCESSING ELECTRONICSSoftware
0W/5W@5min
Dewar Card PCB
9W constant
90% efficient
STAR Camera (x2)•CMOS (VGA)•Maturity: TRL6• 21 deg lens
10 MP Camera (x2) CMOS•Maturity: TRL6• (1) Nadir face, 180 deg
SensorPCB
Software
29
Camera baffle
Wing Latch
RAP, SW1, RBF, Charge port
Sun Sensor anti-‐Nadir Assembly•Maturity: TRL9.
EPS-‐H(IDCA 28V, 20W Max output!!)
Software
7
Solar Cells (14V, 0.5A string, 4 strings)• Spectrolab•Maturity: TRL6
Payload Batteries•Molicel IBR18650BC •Maturity: TRL6• Power: 90% efficient
Temp Set Point
Dewar card is only on for short periods of time
Actual Temp
28V, 8-‐12 watts to IDCA Controller
Cryo
Cooler Pow
er Detector (inside Dewar)
8
STD Bus
Dosimeter PCB(AC8 derived)Comm with AUX on FGA
Analog Data
Comm Laser•Aerospace Design• Single Stage, nominal 2W optical output
Laser Power
ACB•Maturity: TRL8
ACS PCB
Software
3
10W constant
2W constant
Dewar card is only on for short periods of time
5W constant
9V or 26V to Switch A
AUX PCB To ACB AUXconnector
System Architecture
AC9 LMPC
12 © The Aerospace Corporation 2015
UNCLASSIFIED
UNCLASSIFIED
• NASA CSLI Option 1
• 450 km x 820 km x 99 deg inclined
• Aug 2016 delivery to Integrator
• Nov 2016 launch
• NASA CSLI Option 2
• 600 km SSO 10:30 LTDN
• April 2016 delivery to Integrator
• July 2016 launch
AC9 Launch Options
AC9 LMPC
13 © The Aerospace Corporation 2015
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UNCLASSIFIED
L1 Requirements No. Requirement
1 The LMPC shall measure near and short wave IR sources with the 2X8 Mercury Cadmium Telluride (MCT) electron Avalanche Photo Diode (e-‐APD) focal plane array (FPA) for 1 year to support the component needs for future NASA missions
2 The LMPC shall detect laser light from a ground source
3 The LMPC shall perform a radiometry assessment by scanning the Earth's moon for response calibraMon
4 The LMPC shall conduct a variable radiometric response experiment by imaging the sunlit Earth and clouds (i.e. no laser source)
5 The vehicle shall conform to CubeSat standards
6 The LMPC shall measure the effects of space radiaMon on the dark current, APD gain and quantum efficiency of a 2x8 HgCdTe electron Avalanche Photo Diode (e-‐APD) focal plane array (FPA) in a relevant space environment
No. Goal
1 The LMPC shall be compaMble with an opMcal communicaMons link
2 Measure an atmospheric gas absorpMon line
AC9 LMPC
14 © The Aerospace Corporation 2015
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Summary • Demonstrate single photon detection in space compatible with dark current • Present status:
– Despite the relative early stage of the LMPC ACT-10 2 by 8 array, AC9 will have the ability to resolve a 13kcount or greater increase in dark current induced by the radiation exposure • Developments under other programs have significantly reduced systematic
background counts due to ROIC glow and pixel jitter to < 1 ns – The ideal coating performance of the Materion cold filters insures relevant
performance at the 3 principal earth science lines – Current performance of AC9 star trackers with potentially 0.01 degree open loop
pointing opens relevant optical communication demonstrations – Impact of cryo-cooler vibration on spacecraft
• Linear acceleration RMS = [ 0.0133 , 0.0141 , 0.0096 ] g • Angle (jitter) RMS = [ 0.06 , 0.36 , 0.15 ] milli-deg (nominal R_gyro) • Angle (jitter) RMS = [ 0.06 , 0.51 , 0.77 ] milli-deg (bounding case R_gyro)
Even the tight 0.1 degree pointing will not be affected by cryo-cooler vibration