[Show abstract][Hide abstract] ABSTRACT: This paper reports the last technological development on the Low Gain
Avalanche Detector (LGAD) and introduces a new architecture of these detectors
called inverse-LGAD (iLGAD). Both approaches are based on the standard
Avalanche Photo Diodes (APD) concept, commonly used in optical and X-ray
detection applications, including an internal multiplication of the charge
generated by radiation. The multiplication is inherent to the basic n++-p+-p
structure, where the doping profile of the p+ layer is optimized to achieve
high field and high impact ionization at the junction. The LGAD structures are
optimized for applications such as tracking or timing detectors for high energy
physics experiments or medical applications where time resolution lower than 30
ps is required. Detailed TCAD device simulations together with the electrical
and charge collection measurements are presented through this work.
[Show abstract][Hide abstract] ABSTRACT: Radiation therapy with protons and heavier ions is an attractive form of cancer treatment that could enhance local control and survival of cancers that are currently difficult to cure and lead to less side effects due to sparing of normal tissues. However, particle therapy faces a significant technical challenge because one cannot accurately predict the particle range in the patient using data provided by existing imaging technologies. Proton computed tomography (pCT) is an emerging imaging modality capable of improving the accuracy of range prediction. In this paper, we describe the successive pCT scanners designed and built by our group with the goal to support particle therapy treatment planning and image guidance by reconstructing an accurate 3D map of the stopping power relative to water in patient tissues. The pCT scanners we have built to date consist of silicon telescopes, which track the proton before and after the object to be reconstructed, and an energy or range detector, which measures the residual energy and/or range of the protons used to evaluate the water equivalent path length (WEPL) of each proton in the object. An overview of a decade-long evolution of the conceptual design of pCT scanners and their calibration is given. Results of scanner performance tests are presented, which demonstrate that the latest pCT scanner approaches readiness for clinical applications in hadron therapy.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 08/2015; DOI:10.1016/j.nima.2015.07.066 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A measurement of the Higgs boson mass is presented based on the combined data samples of the ATLAS and CMS experiments at the CERN LHC in the H→γγ and H→ZZ→4ℓ decay channels. The results are obtained from a simultaneous fit to the reconstructed invariant mass peaks in the two channels and for the two experiments. The measured masses from the individual channels and the two experiments are found to be consistent among themselves. The combined measured mass of the Higgs boson is m_H=125.09±0.21 (stat)±0.11 (syst) GeV.
[Show abstract][Hide abstract] ABSTRACT: We have developed a fast simulation program to study the performance of silicon and diamond detectors, Weightfield2. The program uses GEANT4 libraries to simulate the energy released by an incoming particle in silicon (or diamond), and Ramo's theorem to generate the induced signal current. A graphical interface allows the user to configure many input parameters such as the incident particle, sensor geometry, presence and value of internal gain, doping of silicon sensor and its operating conditions,the values of an external magnetic field, ambient temperature and thermal diffusion. A simplified electronics simulator is also implemented to include the response of an oscilloscope and front-end electronics. The program has been validated by comparing its predictions for minimum ionizing and α particles with measured signals and TCAD simulations, finding very good agreement in both cases.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 04/2015; DOI:10.1016/j.nima.2015.04.015 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Low-Gain Avalanche Diodes (LGAD) are silicon detectors with output signals that are about a factor of 10 larger than those of traditional sensors. In this paper we analyze how the design of LGAD can be optimized to exploit their increased output signal to reach optimum timing performances. Our simulations show that these sensors, the so called Ultra-Fast Silicon Detectors (UFSD), will be able to reach a time resolution a factor of 10 better than that of traditional silicon sensors.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 04/2015; DOI:10.1016/j.nima.2015.04.025 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have been developing a novel radiation tolerant n(+)-in-p silicon microstrip sensor for very high radiation environments, aiming for application in the high luminosity large hadron collider. The sensors are fabricated in 6 in., p-type, float zone wafers, where large area strip sensor designs are laid out together with a number of miniature sensors. Radiation tolerance has been studied with ATLAS07 sensors and with independent structures. The ATLAS07 design was developed into new ATLAS12 designs. The ATLAS12A large-area sensor is made towards an axial strip sensor and the ATLAS12M towards a stereo strip sensor. New features to the ATLAS12 sensors are two dicing lines: standard edge space of 910 pm and slim edge space of 450 pm, a gated punch-through protection structure, and connection of orphan strips in a triangular corner of stereo strips. We report the design of the ATLAS12 layouts and initial measurements of the leakage current after dicing and the resistivity of the wafers.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 11/2014; 765:80-90. DOI:10.1016/j.nima.2014.06.086 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We pursue scribe-cleave-passivate (SCP) technology for making "slim edge" sensors. The goal is to reduce the inactive region at the periphery of the devices while maintaining their performance. In this paper we report on two aspects of the current efforts. The first one involves fabrication options for mass production. We describe the automated cleaving tests and a simplified version of SCP post-processing of n-type devices. Another aspect is the radiation resistance of the passivation. We report on the radiation tests of n- and p-type devices with protons and neutrons.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 11/2014; 765:59-63. DOI:10.1016/j.nima.2014.05.032 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Transient current technique (TCT) measurements with focused laser light on miniature silicon strip detectors (n+-type strips on p-type bulk) with one inactive edge thinned to about 100 µm using the Scribe-Cleave-Passivate (SCP) method are presented. Pulses of focused IR (λ=1064 nm) laser light were directed to the surface of the detector and charge collection properties near the slim edge were investigated. Measurements before and after irradiation with reactor neutrons up to 1 MeV equivalent fluence of 1.5×1015 neq/cm2 showed that SCP thinning of detector edge does not influence its charge collection properties.
TCT measurements were done also with focused red laser beam (λ=640 nm) directed to the SCP processed side of the detector. The absorption length of red light in silicon is about 3 µm so with this measurement information about the electric field at the edge can be obtained. Observations of laser induced signals indicate that the electric field distribution along the depth of the detector at the detector edge is different than in the detector bulk: electric field is higher near the strip side and lower at the back side. This is a consequence of negative surface charge caused by passivation of the cleaved edge with Al2O3. The difference between bulk and edge electric field distributions gets smaller after irradiation.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 07/2014; 751:41–47. DOI:10.1016/j.nima.2014.03.026 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: AC-coupled silicon strip sensors can be damaged in case of a beam loss due to the possibility of a large charge accumulation in the bulk, developing very high voltages across the coupling capacitors which can destroy them. Punch-through structures are currently used to avoid this problem helping to evacuate the accumulated charge as large voltages are developing. Nevertheless, previous experiments, performed with laser pulses, have shown that these structures can become ineffective in relatively long strips. The large value of the implant resistance can effectively isolate the “far” end of the strip from the punch-through structure leading to large voltages. We present here our developments to fabricate low-resistance strip sensors to avoid this problem. The deposition of a conducting material in contact with the implants drastically reduces the strip resistance, assuring the effectiveness of the punch-through structures. First devices have been fabricated with this new technology. Initial results with laser tests show the expected reduction in peak voltages on the low resistivity implants. Other aspects of the sensor performance, including the signal formation, are not affected by the new technology.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 06/2014; DOI:10.1016/j.nima.2014.05.089 · 1.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Proton radiography has applications in patient alignment and verification procedures for proton beam radiation therapy. In this paper, we report an experiment which used 200 MeV protons to generate proton energy-loss and scattering radiographs of a hand phantom. The experiment used the first-generation proton computed tomography (CT) scanner prototype, which was installed on the research beam line of the clinical proton synchrotron at Loma Linda University Medical Center. It was found that while both radiographs displayed anatomical details of the hand phantom, the energy-loss radiograph had a noticeably higher resolution. Nonetheless, scattering radiography may yield more contrast between soft and bone tissue than energy-loss radiography, however, this requires further study. This study contributes to the optimization of the performance of the next-generation of clinical proton CT scanners. Furthermore, it demonstrates the potential of proton imaging (proton radiography and CT), which is now within reach of becoming available as a new, potentially low-dose medical imaging modality.
IEEE Transactions on Medical Imaging 04/2014; 33(4):875-881. DOI:10.1109/TMI.2013.2297278 · 3.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The development of Low-Gain Avalanche Diodes (LGADs) has made possible to manufacture silicon detectors with output signals that are about a factor of 10 larger than those of traditional sensors. This increased output brings many benefits such as the possibility of developing thin detectors with large enough signals, a good immunity towards low charge collection efficiency and it is key for excellent timing capabilities. In this paper, we report on the development of silicon sensors based on the LGAD design optimized to achieve excellent timing performance, the so-called Ultra-Fast Silicon Detectors (UFSDs). In particular, we demonstrate the possibility of obtaining ultra-fast silicon detectors with time resolution of less than 30 picosecond.
Workshop on Picosecond Photon Sensors for Physics and Medical Applications, Clermont-Ferrand, France; 03/2014
[Show abstract][Hide abstract] ABSTRACT: The ATLAS experiment is a general purpose detector aiming to fully exploit the discovery potential of the Large Hadron Collider (LHC) at CERN. It is foreseen that after several years of successful data-taking, the LHC physics programme will be extended in the so-called High-Luminosity LHC, where the instantaneous luminosity will be increased up to 5 x 10(34) cm(-2) s(-1). For ATLAS, an upgrade scenario will imply the complete replacement of its internal tracker, as the existing detector will not provide the required performance due to the cumulated radiation damage and the increase in the detector occupancy. The current baseline layout for the new ATLAS tracker is an all-silicon-based detector, with pixel sensors in the inner layers and silicon micro-strip detectors at intermediate and outer radii. The super-module is an integration concept proposed for the strip region of the future ATLAS tracker, where double-sided stereo silicon micro-strip modules are assembled into a low-mass local support structure. An electrical super-module prototype for eight double-sided strip modules has been constructed. The aim is to exercise the multi-module readout chain and to investigate the noise performance of such a system. In this paper, the main components of the current super-module prototype are described and its electrical performance is presented in detail.
Journal of Instrumentation 02/2014; 9(02):P02003-P02003. DOI:10.1088/1748-0221/9/02/P02003 · 1.40 Impact Factor