A double junction model of irradiated silicon pixel sensors for LHC

In this paper we discuss the measurement of charge collection in irradiated silicon pixel sensors and the comparison with a detailed simulation. The simulation implements a model of radiation damage by including two defect levels with opposite charge states and trapping of charge carriers. The modeling proves that a doubly peaked electric field generated by the two defect levels is necessary to describe the data and excludes a description based on acceptor defects uniformly distributed across the sensor bulk. In addition, the dependence of trap concentrations upon fluence is established by comparing the measured and simulated profiles at several fluences and bias voltages.Comment: Talk presented at the 10th European Symposium on Semiconductor Detectors, June 12-16 2005, Wildbad Kreuth, Germany. 9 pages, 4 figure

Fluence Dependence of Charge Collection of irradiated Pixel Sensors

The barrel region of the CMS pixel detector will be equipped with ``n-in-n'' type silicon sensors. They are processed on DOFZ material, use the moderated p-spray technique and feature a bias grid. The latter leads to a small fraction of the pixel area to be less sensitive to particles. In order to quantify this inefficiency prototype pixel sensors irradiated to particle fluences between $4.7\times 10^{13}$ and 2.6\times 10^{15} \Neq have been bump bonded to un-irradiated readout chips and tested using high energy pions at the H2 beam line of the CERN SPS. The readout chip allows a non zero suppressed analogue readout and is therefore well suited to measure the charge collection properties of the sensors. In this paper we discuss the fluence dependence of the collected signal and the particle detection efficiency. Further the position dependence of the efficiency is investigated.Comment: 11 Pages, Presented at the 5th Int. Conf. on Radiation Effects on Semiconductor Materials Detectors and Devices, October 10-13, 2004 in Florence, Italy, v3: more typos corrected, minor changes required by the refere

Metaphase and Interphase Cytogenetics with Alu-PCR-amplified Yeast Artificial Chromosome Clones Containing the BCR Gene and the Protooncogenes c-raf-1, c-fms, and c-erbB-21

A human yeast artificial chromosome (YAC) library was screened by polymerase chain reaction with oligonucleotide primers defined for DNA sequences of the BCR gene and the protooncogenes c-raf-1, c-fms, and c-erB-2. Alu-PCR-generated human DNA sequences were obtained from the respective YAC clones and used for fluorescence in situ hybridization experiments under suppression conditions. After chromosomal in situ suppression hybridization to GTG-banded human prometaphase chromosomes, seven of nine initially isolated YAC clones yielded strong signals exclusively in the chromosome bands containing the respective genes. Two clones yielded additional signals on other chromosomes and were excluded from further tests. The band-specific YACs were successfully applied to visualize specific structural chromosome aberrations in peripheral blood cells from patients with myelodysplasia exhibiting del(5)(q13q34), chronic myeloid leukemia and acute lymphocytic leukemia with t(9;22)(q34;q11), acute promyelocytic leukemia (M3) with t(15;17)(q22;q21), and in a cell line established from a proband with the constitutional translocation t(3;8)(p14.2;q24). In addition to the analysis of metaphase spreads, we demonstrate the particular usefulness of these YAC clones in combination with whole chromosome painting to analyze specific chromosome aberrations directly in the interphase nucleus

Position Dependence of Charge Collection in Prototype Sensors for the CMS Pixel Detector

This paper reports on the sensor R&D activity for the CMS pixel detector. Devices featuring several design and technology options have been irradiated up to a proton fluencec of 1E15 n_eq/cm**2 at the CERN PS. Afterward they were bump bonded to unirradiated readout chips and tested using high energy pions in the H2 beam line of the CERN SPS. The readout chip allows a non zero suppressed full analogue readout and therefore a good characterization of the sensors in terms of noise and charge collection properties. The position dependence of signal is presented and the differences between the two sensor options are discussed.Comment: Contribution to the IEEE-NSS Oct. 2003, Portland, OR, USA, submitted to IEEE-TNS 7 pages, 8 figures, 1 table. Revised, title change

Simulation of Heavily Irradiated Silicon Pixel Detectors

We show that doubly peaked electric fields are necessary to describe grazing-angle charge collection measurements of irradiated silicon pixel sensors. A model of irradiated silicon based upon two defect levels with opposite charge states and the trapping of charge carriers can be tuned to produce a good description of the measured charge collection profiles in the fluence range from 0.5x10^{14} Neq/cm^2 to 5.9x10^{14} Neq/cm^2. The model correctly predicts the variation in the profiles as the temperature is changed from -10C to -25C. The measured charge collection profiles are inconsistent with the linearly-varying electric fields predicted by the usual description based upon a uniform effective doping density. This observation calls into question the practice of using effective doping densities to characterize irradiated silicon. The model is now being used to calibrate pixel hit reconstruction algorithms for CMS.Comment: Invited talk at International Symposium on the Development of Detectors for Particle, AstroParticle and Synchrtron Radiation Experiments, Stanford Ca (SNIC06) 8 pages, LaTeX, 11 eps figure