A Zero Noise Detector for the Thirty
Meter Telescope
Status Update October 2012
Don Figer
Director, CfD
Professor, College of Science, RIT
1
Summary
• We have produced a working 256x256 optical
imager that detects single photons.
– dark current is low
– cross-talk is higher than we would like
– quantum efficiency is ~20%, but can be increased
• We are testing a 32x32 infrared imager that
detects single photons
• In the following year, we will fabricate an all-new
design for the optical imager to reduce cross-talk
and increase manufacturability.
First Light Image
First Light Image with 256x256 Single Photon Detector
3
256x256 Readout IC
256×256 CMOS ROIC. This integrated circuit provides the control
electronics for the detector. The light-sensitive area corresponds to the
grey square near the center of the device.
4
Pixel Architecture
(left) Cross section view of two neighboring low-fill-factor GM-APD
structures showing the avalanche and absorber regions. Photons enter
the GM-APD via backside illumination and are absorbed in the
“absorber” regions. Charge is multiplied in the “multiplier” regions.
(right) Cross section view of two neighboring high-fill-factor GM-APDs
in which photoelectrons generated between pixels will diffuse and drift
until they reach an absorber depletion region. The high-fill-factor
architecture provides greater capability for the device to count every
photon as an event.
5
pn Junction Geometries
Experiment results showing dark count rate versus time delay from
GM-APD rearm to subsequent firing (quench time) as measured by the
inverse of the mean time to first detection event. The blue curve is for
the LFF GM-APD with the truncated stepped boron implant, and the
red curve is for the HFF GM-APD. The bottom architecture is superior
for suppressing dark count.
6
Bump Bonding
The left Image is an optical photograph of the indium bump formations
on test structures and the right image is a scanning electron
micrograph picture of indium bumps on the GM-APDs. The bumps, one
per pixel, electrically connect the readout circuit to the light-sensitive
diode array.
7
External Circuitry
The left graphic shows the system diagram of the test electronics for
the phase one detector. The right picture shows a custom electronics
board fabricated to test the detector.
8
Raft Assembly
(left) Image of detector mount, as seen through the side port of the
dewar. There are four positions for detectors. The upper left position is
occupied by a mechanical dummy unit. The other three positions are
empty. (right) Mechanical raft assembly. The upper two positions are
occupied by mechanical dummy units.
9
System Diagram
System diagram of the cold electronics. The diagram only shows two
cables from the detectors to the fanout board. In operation, there will be
four cables, one for each detector.
10
Dark Current
Dark Count Rate for a high fill-factor GM-APD device measured at
varying cryogenic temperatures.
Imaging Analysis
Image of a watch taken with a GM-APD device in a cryogenic camera
system. The image was taken with the device cooled in the test system
and a Nikon lens mounted on the optical window. The image is formed
by the summation of single photon detections
Single photon detection
Real Data
Tgate= 
• Given a constant source, , if APD is sensitive to single photons,
the trigger probability should evolve as P = 1 - exp(-Tgate)
– If 2 photons are required to trigger the APD, then
exp(-Tgate) - Tgate exp(-Tgate)
P=1-
Crosstalk & Afterpulse
Crosstalk
Afterpulse
There is no strong
evidence of afterpulsing
• P (Neighboring Pixel Triggered |
Reference Pixel Triggered)
• 31 by 31 pixel region
Personnel
RIT personnel working on the Moore project (top to bottom, left to
right): Tom Montagliano, Brandon Hanold, Don Stauffer, Brian Ashe,
Donald Figer, Tom Praderio, Chris Maloney, John Frye, Max Bobrov.
16
Gordon Moore
Progress and Plans
Brian Aull
25 September 2012
Accomplishments
Recent
Dark count data collected from 256x256
passive imager, and successfully fit to
simple analytic model
Results show that crosstalk dominates
dark count rate, native thermal dark
count rate is low
Defined the major elements of new
trenching and hybridization processes
and have begun development
Long Term
Remarkable progress in understanding
APD design and performance issues,
fabrication and process integration
Passive Imaging
Demonstration
• Back illuminated 256×256 APD
arrays
– High-fill-factor with deep implant step
– 25-mm pixel pitch
• Hybridized to PCROIC readout
chip
• Packaged and incorporated into
camera for field demo
• Successfully deployed to collect
imagery
• Dark count data from these
devices collected and analyzed
Modeling Crosstalk
APD BIAS
T=-30C
-30.0V
Probablity that a
pixel has fired
-29.5V
-29.0V
Time after ARM (ms)
• Dots are experimental data; solid curves show prediction of simple rate equation model
 h is number of photoelectrons created by APD light emission, e is probability that such a
photoelectron will trigger an APD that has not yet fired
Amorphous Silicon for
Crosstalk Suppression
T, R
aSi
Si
-
-
 (nm)
High attenuation, low reflection
at wavelengths where crosstalk
is worst
Good match to silicon thermal
expansion coefficient
Process-compatible
Process development runs in
progress
Planned Work
• Implement a hybridization technique based
on Ziptronix Direct Bond Interconnect (DBI)
process (funded by other sponsor)
• Fabricate a lot of APDs on silicon-oninsulator (SOI) wafer and characterize (no
CMOS readout)
– SOI facilitates APD thickness customization
and uniform back illumination
• Fabricate and test 256×256 focal planes
based on DBI hybridization of SOI APDs to
the PCROIC readout chip (funded by other
sponsor)
• With further funding, do advanced trench
process development/characterization and
investigation of spectral quantum yield of
light emission by Geiger-mode APDs
DBI
interconnects
Gordon Moore
InGaAs APDs
Progress and Plans
Michael Grzesik
01 October 2012
Previous Work
CCS-0889-A
n+ -InGaAs contact
n+ -InP cap
n-InP absorber
53.5 nm
InP field stop
3 μm
n-InP avalanche
1 μm
p+ InP
p+ InP
2 μm
InP Substrate
10 nm
1 μm
1.5 μm
Si>2e18
Si>2e18
n<5e15
Si:3.3e17
nid
Zn:8e17
Zn:2e18
 Initial measurements were aimed at
measuring the Dark Count Rate (DCR) for
InGaAs devices
 Interarrival plots indicated afterpulsing
 A circuit allowing for long holdoff times was
designed for new measurements
 DCR was determined using the tail end of
the newly measured interarrival plots
Hold-off
600 ms
A1*e-λ1t + A2*e-λ2t
λ1=51.3 Hz
λ2=8.02 Hz
Previous Work
77 K Data
 Measured DCR was
much larger than expected
600 ms Hold-off
10
 Afterpulsing is believed
to still be present and
dominating interarrival time
data
7
-2
DCR per unit area (Hz/cm )
10
8
10
 Proposed work for 2012
included measuring the
DCR using devices
bonded to Read Out
Circuits
100 K
120 K
6
80 K
60 K
10
5
 The Read Out Circuits
will reduce charge flowing
through a device during
breakdown mitigating
afterpulsing.
Avalanche: 2.0 mm
10
10
17
-3
FS doping: 3.2x10 cm
FS thichness: 65 nm
FS thichness: 60 nm
4
3
-2
0
2
4
6
8
Overbias (Volts)
Data is ~ 2 orders of magnitude off from calculations
10
Present Modeling of Breakdown
Voltage
 Earlier breakdown voltage
measurements show a
discrepancy between measured
and calculated values at cryogenic
temperatures of ~5 V
 A low temperature model for the
electron and hole impact ionization
coefficients has been constructed
 The phonon mean free path and
phonon energy were adjusted in
the models to match low
temperature data and predict
breakdown
 The new impact ionization
coefficients allow for an accurate
prediction of breakdown voltage
allowing for accurate device
growth and design
Planned Work
Over Next 3 Months
 Over the past year, hardware and software issues have
hindered DCR measurements for APDs bonded to readout
circuits.
 It is believed the final software issue has been identified in
the test setup and the setup will be functional in the next
month.
 DCR data will be taken and analyzed and compared with
both the theoretical calculations and previous long holdoff time
measurements.
 Modeling work is focused on modifying the presently used
impact ionization coefficient values so that the are valid in the
77K – 300K temperature range.
A GLOBAL NETWORK FOR SPACE
SCIENCE, TECHNOLOGY & INNOVATION
A New Funding Model…
• GNSSTI seeks to disrupt the current paradigm of
space science and exploration to drive scientific
discovery at an accelerated pace, and address
questions that inspire us all
– Scientific exploration of space holds promise to address
some of humankind’s most compelling questions: Where
did we come from? What is the nature and fate of the
Universe? Are we alone?
– Answering these questions is mired in small, singleinvestigator-focused funding models and large, expensive,
government-managed space missions using old
technology.
– Answers are within our reach, if we use new approaches
that leverage truly interdisciplinary, international teams,
emerging technologies, and new spaceflight approaches.
Why now?
• NASA budget constraints will limit space science program
content during the next decade
– Federal discretionary spending will be capped
– Significant emphasis on applied research across Federal science
• Large ground-based telescopes with significant private
funding now cost as much as capable space missions
– We have the opportunity seize this moment in time by bringing the
creativity of the “New Space” community to space science and
exploration.
• For example, there’s a window this decade when NASA will
not launch any mission capable of exoplanet imaging or that
returns samples from Mars
– NASA Astrophysics will not start any new large mission until after
JWST launches (NET 2018), likely to be followed by WFIRST widefield infrared telescope
– NASA Planetary Science likely facing a near-term budget decrease
and is expected to consider alternatives to a sample return
mission/strategy for remaining Mars launches before 2020
Plan
• Permanently establish and maintain a worldclass worldwide research organization with the
resources, personnel, and facilities to drive rapid
progress in our understanding of the Universe
and life within it
• In the next decade, create and execute first-of-akind, opportunistic projects to advance
fundamental scientific knowledge of our
Universe and the life within it
Citizen Science & Outreach
• Disseminate frontier scientific discoveries to the
public through existing and experimental media,
including involving citizens in design and data
analysis opportunities where appropriate
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and engineers in team-based, interdisciplinary,
world-class research
– Create U.S. network of University, Institute and other nonprofit scientific partners
• Create a structurally entrepreneurial global network
to explore the Universe
– International interest is high, and possibly enabling
Principles
•
•
•
•
Commitment to creative excellence
Commitment to scientific truth
Flexible Perseverance
Openness and transparency