In order to support the high luminosity upgrades at ATLAS and CMS, thinned silicon sensors for hybrid pixel detectors are critical to improve radiation hardness, reduce detector mass, and address high occupancy rates. Because silicon wafer processing tools are not equipped to handle thin wafers, the thinning step cannot be performed until the after the majority of the processing steps are complete, requiring post-processing to create the doped region that constitutes the diode contact at the backside of the wafer. This is challenging, because the high temperature anneal required to activate the dopant after ion implantation would be damaging to the existing front side structures. Current techniques for solving this problem, such as using Silicon-on-insulators wafers, are very expensive. A new microwave annealing technology has been developed which can activate the backside implant at low temperature, without damaging the frontside structures. We have verified this approach on a prototype sensor that was bump-bonded to a readout ASIC and used successfully to measure an Fe-55 x-ray spectrum.
ePix10K is a hybrid pixel detector developed at SLAC for demanding free-electron laser (FEL) applications, providing an ultrahigh dynamic range (245 eV to 88 MeV) through gain auto-ranging. It has three gain modes (high, medium and low) and two auto-ranging modes (high-to-low and medium-to-low). The first ePix10K cameras are built around modules consisting of a sensor flip-chip bonded to 4 ASICs, resulting in 352 × 384 pixels of 100 µm x 100 µm each. We present results from extensive testing of three ePix10K cameras with FEL beams at LCLS, resulting in a measured noise floor of 245 eV rms, or 67 e− equivalent noise charge (ENC), and a range of 11 000 photons at 8 keV. We demonstrate the linearity of the response in various gain combinations: fixed high, fixed medium, fixed low, auto-ranging high to low, and auto-ranging medium-to-low, while maintaining a low noise (well within the counting statistics), a very low cross-talk, perfect saturation response at fluxes up to 900 times the maximum range, and acquisition rates of up to 480 Hz. Finally, we present examples of high dynamic range x-ray imaging spanning more than 4 orders of magnitude dynamic range (from a single photon to 11 000 photons/pixel/pulse at 8 keV). Achieving this high performance with only one auto-ranging switch leads to relatively simple calibration and reconstruction procedures. The low noise levels allow usage with long integration times at non-FEL sources. ePix10K cameras leverage the advantages of hybrid pixel detectors with high production yield and good availability, minimize development complexity through sharing the hardware, software and DAQ development with all other versions of ePix cameras, while providing an upgrade path to 5 kHz, 25 kHz and 100 kHz in three steps over the next few years, matching the LCLS-II requirements.
Since it began operations in 2009, the Linac Coherent Light Source (LCLS) has opened a new and dynamic frontier in terms of light sources and their associated science [1 John Arthur, Rev. Sci. Instrum. 73, 1393 (2002).[Crossref], [Web of Science ®] , [Google Scholar], 2 C. Pellegrini and J. Rosenzweig, NIMA 331(1–3), 223–227 (1993).[Crossref], [Web of Science ®] , [Google Scholar]]. An increase in brightness by a factor of a billion over pre-existing synchrotrons, in combination with ultra-brief pulses of coherent X-rays, is ushering in a new era in the photon sciences. Pulses with durations of 50 fs under standard conditions and below 10 fs with a reduced energy per bunch are possible. Over 1013 or 1012 X-rays per pulse can be generated at the upper and lower ends of the X-ray energy range of 285 eV to 9600 eV. One of the unique machine parameters is its strobe-like time structure, where single ultra-brief pulses are delivered at a repetition rate of 120 Hz. The above characteristics represent a singular environment in which to operate detectors and demand the development of a new class of high-frame-rate camera systems.
Free electron lasers, such as SLAC's LCLS-II, will provide unique scientific imaging opportunities. In order to fully utilize these facilities, we need to develop detectors with shallow entrance windows that will enable detection of soft x-rays from 250eV-1.5KeV. Achieving adequately shallow entrance windows is challenging because the high temperature anneal used to active the dopant for the diode termination also drives the dopant profile deeper, growing the region that is insensitive to soft x-rays. A new microwave annealing technology provides an efficient way to achieve shallow entrance windows in fully depleted high-resistivity silicon sensors. The new technique can activate dopants at low substrate temperature, with minimal dopant diffusion. We implanted test wafers with low energy (10KeV) Arsenic implant, followed by microwave annealing with the new technique. SRP and SIMS measurements were used to verify dopant activation with negligible dopant diffusion. We then applied the microwave anneal process to a planar sensor device wafer, using the new process to create the backside diode contact. Electrical test of the resulting sensors shows good reverse bias diode characteristics. The sensors have been bump-bonded to a read-out ASIC and used successfully to measure an Fe-55 x-ray spectrum.
A multi-channel PIN-diode-based detector is developed. The electrodes, in a linear array with pitch of 250 mum, detect the signals generated by the secondary electrons incident into the other side of the detector. Each detection area has a throughhole, which allows the primary beamlet to pass through. The characterizations are performed by using a primary beamlet of a conventional SEM instead of secondary electrons. The experimental results is consistent with the stimulated prediction.
New free electron lasers, such as SLAC’s LCLS-II, will provide unique scientific imaging opportunities. In order to fully utilize these facilities, we need to develop detectors with shallow entrance windows that will enable detection of soft x-rays from 250 eV to 1.5 KeV. Achieving adequately shallow entrance windows is challenging because the high temperature anneal needed to activate the dopant also drives the dopant profile deeper, growing the region that is insensitive to soft x-rays. A new microwave annealing technology provides an efficient way to achieve shallow entrance windows in fully depleted high-resistivity silicon sensors. The microwave anneal technique can activate dopants at low substrate temperature, with minimal dopant diffusion, and can be used to fabricate both n-type and p-type entrance windows. SRP and SIMS measurements were used to verify dopant activation with negligible dopant diffusion. We then applied the microwave anneal process to a planar sensor wafer, using the new process to create the backside diode contact. Electrical test of the resulting sensors shows good reverse bias characteristics. The sensors have been bump-bonded to a read-out ASIC and used successfully to measure an Fe-55 x-ray spectrum. Process and device simulations were performed to characterize the quantum efficiency of the entrance window for soft x-rays. This technique is useful for other sensor applications requiring a shallow entrance window, including detectors for UV photons, low energy ions and low energy electrons.
The SuperCDMS experiment in the Soudan Underground Laboratory searches for dark matter with a 9-kg array of cryogenic germanium detectors. Symmetric sensors on opposite sides measure both charge and phonons from each particle interaction, providing excellent discrimination between electron and nuclear recoils, and between surface and interior events. Surface event rejection capabilities were tested with two $^{210}$Pb sources producing $\sim$130 beta decays/hr. In $\sim$800 live hours, no events leaked into the 8--115 keV signal region, giving upper limit leakage fraction $1.7 \times 10^{-5}$ at 90% C.L., corresponding to $< 0.6$ surface event background in the future 200-kg SuperCDMS SNOLAB experiment.
Free Electron Lasers opened a new window on imaging the motion of atoms and molecules. At SLAC, FEL experiments are performed at LCLS using 120Hz pulses with 1012 - 1013 photons in 10 femtoseconds (billions of times brighter than the most powerful synchrotrons). This extreme detection environment raises unique challenges, from obvious to surprising. Radiation damage is a constant threat due to accidental exposure to insufficiently attenuated beam, focused beam and formation of ice crystals reflecting the beam onto the detector. Often high power optical lasers are also used (e.g., 25TW), increasing the risk of damage or impeding data acquisition through electromagnetic pulses (EMP). The sample can contaminate the detector surface or even produce shrapnel damage. Some experiments require ultra high vacuum (UHV) with strict design, surface contamination and cooling requirements - also for detectors. The setup is often changed between or during experiments with short turnaround times, risking mechanical and ESD damage, requiring work planning, training of operators and sometimes continuous participation of the LCLS Detector Group in the experiments. The detectors used most often at LCLS are CSPAD cameras for hard x-rays and pnCCDs for soft x-rays.
