September 17, 2014 Design and Characterization of a High-Speed
Multi-frame Hybrid CMOS Camera J.L. Porter 1, L.D. Claus 1, L. Fang
1, R.R. Kay 1, M.W. Kimmel 1, A.T. Pomerene 2, G.A. Robertson 1,
M.O. Sanchez 1, J.W. Stahoviak 2, D.C. Trotter 3 1 Sandia National
Laboratories 2 Sandia Staffing Alliance 3 Doug Trotter
Consulting
Slide 2
We are developing a high-speed solid-state x-ray framing camera
for use on high-energy-density science facilities such as Sandias Z
machine 22 MJ peak stored energy 26 MA peak current 100 TW
electrical power 100-300 ns pulse length 50 Megagauss magnetic
field 100 Mbar magnetic pressure 2 MJ, 400 TW x-ray source 150
experiments/year typical
Slide 3
Desired imager characteristics from user community High spatial
resolution (25m or better) High speed (1ns or better) Many frames
(10 or more frames) High sensitivity to visible light, x-rays, or
particles (100% fill factor and sensitive to single keV x-ray
photons) Large dynamic range (1000 or better) Large sensor
(multi-cm scale size) High timing precision (50 ps or better) Low
trigger insertion delay (few 10s ns) Compact, rugged, and easy to
integrate into diagnostic systems and experiments Radiation
tolerant (can operate on large ICF facilities)
Slide 4
Design specifications for Furi prototype camera Spatial
resolution: 25m pixel size and pitch Time resolution: 1ns minimum
integration time, user selectable integration times up to 100s
Frames: 2 frames/pixel in architecture that scales to 32
frames/pixel Sensitivity: 100% photodiode fill factor, 50% QE for 6
keV x-rays Dynamic range: 1 1000 photons/pixel @ 6 keV x-ray energy
Pixels: 1024x448 (25x11 mm 2 ) Biggest design challenge is dealing
with the large photocurrents generated during short exposure times
with high flux: up to 250A/pixel and 100A for entire sensor
Slide 5
A hybrid CMOS sensor enables near 100% diode fill factor and
use of different diode arrays with the same ROIC Substrate Contact:
- 50V Pixel Electronics N+ pixel P+ channel stop Optical, x-ray or
particle Illumination Interconnect CMOS ROIC ~1m thick P+ Si diode
array 6 ROIC and diode wafers produced at Sandias 0.35 m SOI CMOS
fabrication facility Wafer hybridization performed at Ziptronix
using their proprietary Direct Bond Interconnect process
(oxide-to-oxide bond) Die sawing, packaging, and integration with
control electronics performed at Sandia 25m
Slide 6
There is a tradeoff between Si diode detection efficiency and
time response for x-rays with energies >5 keV 25m thick
diodes
Slide 7
The unit pixel is composed of 11 transistors and 2 analog
storage capacitors photodiode node reset control frame #1 write
control frame #2 write control frame #1 read buffer frame #2 read
buffer frame #1 read control frame #2 read control photodiode input
frame read output
Slide 8
The ROIC incorporates high-speed timing generation and
distribution, multi-frame image capture, and data readoff Bias Row
and Frame Decode Column Decode PIXEL ARRAY DETECTOR ARRAY Analog
Memory Analog Memory Analog Memory Analog Memory Buffer Rese t High
Speed Timing Generation :::: I/O Buffers I/O Buffers Bias Unit
Pixel Unit Diode :::: :::: frame timing setup READ OUT 12-Bit
Control 5-Bit Control trigger Input analog outputs multiplexer
30x19 mm 2 die, 25x11 mm 2 sensor area High speed timing generation
with user selectable gate time between 1ns and 100s Timing
distribution fed from 2 sides of ROIC to each of 1024 image columns
(timing skew limits row dimension with this timing distribution
approach) Furi prototype 2-frame sensor
Slide 9
Compact and modular electronics package can be readily
customized and integrated into a range of diagnostic systems
Inputs/Outputs -7V power -slow and fast triggers -Frame timing
monitors -serial communication computer interface
Slide 10
A pulsed laser-produced-plasma x-ray source is used to
uniformly illuminate the sensor x-ray reference photodiode Furi
sensor Laser wavelength: 532 nm (frequency doubled) Laser energy:
15 J (max. at 2 ) Pulse duration: 1 4 nsec (user selectable) X-ray
target material: Ti (4.7 keV x-rays) pulsed laser vacuum vessel Ti
foil x-ray filter focusing lens Example of x-ray time-history
Slide 11
An x-ray line-pair test pattern was used to measure the spatial
resolution with 20 LP/mm clearly resolved 20 line-pair/mm 32 x 32
pixels
Slide 12
The time response is determined by varying the timing between
the x-ray pulse and the frame gate times x-ray pulse FWHM = 2.5ns,
frame gate time = 4ns, 10ns frame separation x-ray pulse convolved
with 4ns gate time for comparison with measurements
Slide 13
A large-area reference Si diode is used to determine the
absolute x-ray sensitivity and gain of each pixel Each absorbed 6
keV photon creates 1,700 electron/hole pairs and generates a 1mV
voltage change on the 250 fF pixel capacitor Initial measurements
of transmission through an x-ray step wedge indicate a dynamic
range > 400 presently limited by the broad-band nature of our
laser- produced-plasma x-ray source.
Slide 14
Demonstration of image capture on a dynamic object:
Shadowgraphs of a laser generated blast wave Z-Beamlet laser
driver: 1 kJ in 1 ns pulse, 527nm, F/10 focusing lens Imaging and
relay optics Shadowgraph probe laser: 4 1ns 1mJ pulses at 532nm
spaced in time blast wave expanding into 10-90 Torr N 2 Foil target
location Target chamber Furi visible sensor
Slide 15
Example of blast wave shadowgraphs recorded with visible Furi
sensors on a single experiment t=10nst=70nst=90nst=150ns 1TW
Z-Beamlet laser focused onto 1m-thick Mylar foil Time-gating
enables each individual shadowgraph to be seen and eliminates the
bright plasma emission that occurs when Z-Beamlet strikes the thin
foil blast waves shadowgraph timing 16.8mm17.8mm21.5mm
Slide 16
Near term plans for cameras with more frames Hippogriff
modification/evolution of Furi architecture -Interlacing mode to
provide 2,4,6, or 8 frames with decreasing spatial resolution
-Fabrication and hybridization complete, in packaging available for
testing next month Icarus - next generation 0.35m ROIC targeting
lower energy x-rays 4 frames, 25m, 1024x512 pixels Sensitive down
to 100 eV x-rays, will use common cathode photodiodes 500 500k e -
full well capacity In fabrication, planned for initial testing to
begin in early 2015 Acca future ROIC fabricated in smaller CMOS
process 8 frames, 25m, 512x512 pixels H-tree timing distribution
3-side abuttable to enable tiling multiple sensors Being designed
for IBM 0.13m CMOS process Tape out planned for April 2015
Slide 17
Conclusion and Future Plans Demonstrated fast multi-frame x-ray
and visible imaging with a hybrid CMOS camera -Initial measurements
are very promising but more characterization required with pulsed
sources to determine if all performance goals were achieved
-Excellent success with Ziptronix DBI hybridization process Cameras
with more frames/pixel presently in fabrication and design
-Interlacing with 4 or 8 frames options (Hippogriff, in packaging)
-4-frame/pixel camera (Icarus, in fabrication) -8-frame/pixel
camera in design using 0.13m CMOS process (fabrication planned for
2015) -Goal to develop cameras with 32 frames/pixel in 6 years
