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

We are developing a high-speed solid-state x-ray framing camera for use on high-energy-density science facilities such as Sandia’s Z machine 22 MJ peak stored energy 26 MA peak current 100 TW electrical power ns pulse length 50 Megagauss magnetic field 100 Mbar magnetic pressure 2 MJ, 400 TW x-ray source 150 experiments/year typical

Desired imager characteristics from user community  High spatial resolution (25µm 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 10’s ns)  Compact, rugged, and easy to integrate into diagnostic systems and experiments  Radiation tolerant (can operate on large ICF facilities)

Design specifications for “Furi” prototype camera  Spatial resolution: 25µm pixel size and pitch  Time resolution: 1ns minimum integration time, user selectable integration times up to 100µs  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 – 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 250µA/pixel and 100A for entire sensor

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 ~1µm thick P+ Si diode array  6” ROIC and diode wafers produced at Sandia’s 0.35 µm 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 25µm

There is a tradeoff between Si diode detection efficiency and time response for x-rays with energies >5 keV 25µm thick diodes

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

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 100µs  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

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

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

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

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

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.

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 Torr N 2 Foil target location Target chamber Furi visible sensor

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 1µm-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

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 0.35µm ROIC targeting lower energy x-rays –4 frames, 25µm, 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, 25µm, 512x512 pixels –H-tree timing distribution –3-side abuttable to enable tiling multiple sensors –Being designed for IBM 0.13µm CMOS process –Tape out planned for April 2015

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 0.13µm CMOS process (fabrication planned for 2015) -Goal to develop cameras with 32 frames/pixel in 6 years