Forest Martinez-McKinney

Evaluation of the radiation tolerance of SiGe heterojunction bipolar transistors under 24 GeV proton exposure

For the potential use in future high luminosity applications in high energy physics (HEP) [e.g., the Large Hadron Collider (LHC) upgrade], we evaluated the radiation tolerance of a candidate technology for the front-end of the readout application-specific integrated circuit (ASIC) for silicon strip detectors. The devices investigated were first-generation silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs). The current gain as a function of collector current has been measured at several stages: before and after irradiation with 24-GeV protons up to fluences of 1016 p/cm2, and after annealing at elevated temperature. The analog section of an amplifier for silicon strip detectors typically has a special front transistor, chosen carefully to minimize noise and usually requiring a larger current than the other transistors, and a large number of additional transistors used in shaping sections and for signal-level discrimination. We discuss the behavior of both kinds of transistors, with a particular focus on issues of noise, power, and radiation limitations

Detector development for Proton Computed Tomography (pCT)

Proton Computed Tomography (pCT) is being developed in support of proton therapy and treatment planning. The aim of pCT, to reconstruct an accurate map of the stopping power (S.P.) in a phantom and, in the future, in patients, is being pursued with a diverse list of detector systems, using the entire arsenal of tracking and energy detectors developed for High Energy Physics (HEP). The first radiographs and 3D images are being reconstructed with prototype detectors, which will be described. Most of the existing systems are being upgraded to higher proton fluxes to reduce the scanning time.

Charge collection measurements on slim-edge microstrip detectors

We have generated slim edges on manufactured silicon strip detectors by cleaving the non-active edge material and passivating the very smooth edge with a thin coat of silicon oxide. We report a comparison of I-V measurements and charge collection and noise measurements on two identical sensors, one with and one without slim edge treatment. The current voltage measurements of the entire sensor and individual strips indicate that the large current increase due to the treatment is confined to the guard ring, while the strips show essentially no increase in leakage currents. The noise on all strips, including the one adjacent to the slim edge, is not changed by the cut. The signal from a beta source before and after cutting is the same within 4%.

The particle tracking silicon microscope PTSM

A novel position- and energy-sensitive particle detector for radiobiological application is described. The aim is to support research in radiation response of biological systems, for example in the induction of mutations in C elegans, where precise knowledge of location and intensity of the radiation is crucial to understand radiation sensitivity of individual cells. The Particle Silicon Tracking Microscope (PTSM) consists of a silicon strip detector in direct contact with radiobiological samples (e.g., C elegans), such that the location and intensity of particle radiation can be controlled at the 10 /spl mu/m scale. The readout is performed with low-noise readout electronics, which allows the determination of the particles position from the hit strip address and its energy from the specific energy loss. In our implementation, the energy loss is measured through the time-over-threshold (TOT). The noise rate at acceptable thresholds is so low that the single particles can be detected with 100% efficiency. The performance of the front-end ASIC is described, and the results of initial environmental tests are reported. These include placing biological samples and saline solutions in direct contact with the silicon detectors.

A double-sided, shield-less stave prototype for the ATLAS Upgrade strip tracker for the High Luminosity LHC

A detailed description of the integration structures for the barrel region of the silicon strips tracker of the ATLAS Phase-II upgrade for the upgrade of the Large Hadron Collider, the so-called High Luminosity LHC (HL-LHC), is presented. This paper focuses on one of the latest demonstrator prototypes recently assembled, with numerous unique features. It consists of a shortened, shield-less, and double sided stave, with two candidate power distributions implemented. Thermal and electrical performances of the prototype are presented, as well as a description of the assembly procedures and tools.

A double-sided silicon micro-strip Super-Module for the ATLAS Inner Detector upgrade in the High-Luminosity LHC

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 × 1034 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.

Lessons learned in high frequency data transmission design: ATLAS strips bus tape

Requirements of HEP experiments lead to highly integrated systems with many electrical, mechanical and thermal constraints. A complex performance optimisation is therefore required. High-speed data transmission lines are designed using copper-polyimide flexible bus tapes rather than cable harnesses to minimise radiation length. Methods to improve the signal integrity of point-to-point links and multi-drop configurations in an ultra-low-mass system are described. FEA calculations are an essential guide to the optimisation of a tape design which supports data rates of 640 Mbps for point-to-point links over a length of up to 1.4 m, as well as 160 Mbps for multi-drop configuration. The designs were validated using laboratory measurements of S-parameters and direct bit error ratio tests.

Source dependence and technology scaling effects on the radiation tolerance of SiGe HBTs at extreme dose and fluence levels

We investigate the response of SiGe HBTs exposed to high fluence and total dose levels of proton, neutron and gamma irradiation typically encountered in high energy physics experiments. The transistor radiation tolerance is evaluated via a comparison of excess base current, base current ideality, and current gain degradation. The results indicate that the observed device degradation may be dominated either by conventional SRH recombination or radiation-induced carrier tunneling, depending on the technology generation and radiation source.