273 research outputs found
Optimization of the Radiation Hardness of Silicon Pixel Sensors for High X-ray Doses using TCAD Simulations
The European X-ray Free Electron Laser (XFEL) will deliver 27000 fully
coherent, high brilliance X-ray pulses per second each with a duration below
100 fs. This will allow the recording of diffraction patterns of single
molecules and the study of ultra-fast processes. One of the detector systems
under development for the XFEL is the Adaptive Gain Integrating Pixel Detector
(AGIPD), which consists of a pixel array with readout ASICs bump-bonded to a
silicon sensor with pixels of 200 {\mu}m \times 200 {\mu}m. The particular
requirements for the detector are a high dynamic range (0, 1 up to 10E5 12 keV
photons/XFEL-pulse), a fast read-out and radiation tolerance up to doses of 1
GGy of 12 keV X-rays for 3 years of operation. At this X-ray energy no bulk
damage in silicon is expected. However fixed oxide charges in the SiO2 layer
and interface traps at the Si-SiO2 interface will build up. As function of the
12 keV X-ray dose the microscopic defects in test structures and the macro-
scopic electrical properties of segmented sensors have been investigated. From
the test structures the oxide charge density, the density of interface traps
and their properties as function of dose have been determined. It is found that
both saturate (and even decrease) for doses above a few MGy. For segmented
sensors surface damage introduced by the X-rays increases the full depletion
voltage, the surface leakage current and the inter-pixel capacitance. In
addition an electron accumulation layer forms at the Si-SiO2 interface which
increases with dose and decreases with applied voltage. Using TCAD simulations
with the dose dependent damage parameters obtained from the test struc- tures
the results of the measurements can be reproduced. This allows the optimization
of the sensor design for the XFEL requirements
Study of X-ray Radiation Damage in Silicon Sensors
The European X-ray Free Electron Laser (XFEL) will deliver 30,000 fully
coherent, high brilliance X-ray pulses per second each with a duration below
100 fs. This will allow the recording of diffraction patterns of single complex
molecules and the study of ultra-fast processes. Silicon pixel sensors will be
used to record the diffraction images. In 3 years of operation the sensors will
be exposed to doses of up to 1 GGy of 12 keV X-rays. At this X-ray energy no
bulk damage in silicon is expected. However fixed oxide charges in the
insulating layer covering the silicon and interface traps at the Si-SiO2
interface will be introduced by the irradiation and build up over time.
We have investigated the microscopic defects in test structures and the
macroscopic electrical properties of segmented detectors as a function of the
X-ray dose. From the test structures we determine the oxide charge density and
the densities of interface traps as a function of dose. We find that both
saturate (and even decrease) for doses between 10 and 100 MGy. For segmented
sensors the defects introduced by the X-rays increase the full depletion
voltage, the surface leakage current and the inter-pixel capacitance. We
observe that an electron accumulation layer forms at the Si-SiO2 interface. Its
width increases with dose and decreases with applied bias voltage. Using TCAD
simulations with the dose dependent parameters obtained from the test
structures, we are able to reproduce the observed results. This allows us to
optimize the sensor design for the XFEL requirements
Properties of a radiation-induced charge multiplication region in epitaxial silicon diodes
Charge multiplication (CM) in pn epitaxial silicon pad diodes of 75, 100
and 150 \upmum thickness at high voltages after proton irradiation with 1 MeV
neutron equivalent fluences in the order of cm was studied as
an option to overcome the strong trapping of charge carriers in the innermost
tracking region of future Super-LHC detectors. Charge collection efficiency
(CCE) measurements using the Transient Current Technique (TCT) with radiation
of different penetration (670, 830, 1060 nm laser light and -particles
with optional absorbers) were used to locate the CM region close to the
p-implantation. The dependence of CM on material, thickness of the
epitaxial layer, annealing and temperature was studied. The collected charge in
the CM regime was found to be proportional to the deposited charge, uniform
over the diode area and stable over a period of several days. Randomly
occurring micro discharges at high voltages turned out to be the largest
challenge for operation of the diodes in the CM regime. Although at high
voltages an increase of the TCT baseline noise was observed, the
signal-to-noise ratio was found to improve due to CM for laser light. Possible
effects on the charge spectra measured with laser light due to statistical
fluctuations in the CM process were not observed. In contrast, the relative
width of the spectra increased in the case of -particles, probably due
to varying charge deposited in the CM region.Comment: 11 pages, accepted by NIM
Design and Tests of the Silicon Sensors for the ZEUS Micro Vertex Detector
To fully exploit the HERA-II upgrade,the ZEUS experiment has installed a
Micro Vertex Detector (MVD) using n-type, single-sided, silicon micro-strip
sensors with capacitive charge division. The sensors have a readout pitch of
120 micrometers, with five intermediate strips (20 micrometer strip pitch). The
designs of the silicon sensors and of the test structures used to verify the
technological parameters, are presented. Results on the electrical measurements
are discussed. A total of 1123 sensors with three different geometries have
been produced by Hamamatsu Photonics K.K. Irradiation tests with reactor
neutrons and Co-60 photons have been performed for a small sample of sensors.
The results on neutron irradiation (with a fluence of 1 x 10^{13} 1 MeV
equivalent neutrons / cm^2) are well described by empirical formulae for bulk
damage. The Co-60 photons (with doses up to 2.9 kGy) show the presence of
generation currents in the SiO_2-Si interface, a large shift of the flatband
voltage and a decrease of the hole mobility.Comment: 33 pages, 25 figures, 3 tables, accepted for publication in NIM
Recommended from our members
Scanning transient current study of the I-V stabilization phenomena in silicon detectors irradiated by fast neutrons
Investigation of the I-V stabilization phenomena in neutron irradiated silicon detectors has been carried out using scanning transient current technique (STCT) on non-irradiated PP{sup +}-p-n{sup +} detectors. The PP{sup +}-p-n{sup +} detectors were used to simulate the PP{sup +}-n-n{sup +} detectors irradiated beyond the space charge sign inversion (SCSI). Two mechanisms partially responsible for the I- V stabilization have been identified
Pion-induced damage in silicon detectors
The damage induced by pions in silicon detectors is studied for positive and negative pions for fluence up to 10(14)cm-2 and 10(13) cm-2 respectively. Results on the energy dependence of the damage in the region of 65-330 MeV near to the resonance are presented. The change in detector characteristics such as leakage current, charge collection efficiency and effective impurity concentration including long-term annealing effects have been studied. Comparisons to neutron and proton-induced damage are presented and discussed
Bulk Damage Effects in Irradiated Silicon Detectors due to Clustered Divacancies
High resistivity silicon particle detectors will be used extensively in experiments at the future CERN Large Hadron Collider where the enormous particle fluences give rise to significant atomic displacement damage. A model has been developed to estimate the evolution of defect concentrations during irradiation and their electrical behaviour according to Shockley-Read-Hall (SRH) semiconductor statistics. The observed increases in leakage current and doping concentration changes can be described well after gamma irradiation but less well after fast neutron irradiation. A possible non-SRH mechanism is considered, based on the hypothesis of charge transfer between clustered divacancy defects in neutron damaged silicon detectors. This leads to a large enhancement over the SRH prediction for V2 acceptor state occupancy and carrier generation rate which may resolve the discrepancy
Investigation of nitrogen enriched silicon for particle detectors
This article explores the viability of nitrogen enriched silicon for particle physics application. For that purpose silicon diodes and strip sensors were produced using high resistivity float zone silicon, diffusion oxygenated float zone silicon, nitrogen enriched float zone silicon and magnetic Czochralski silicon. The article features comparative studies using secondary ion mass spectrometry, electrical characterization, edge transient current technique, source and thermally stimulated current spectroscopy measurements on sensors that were irradiated up to a fluence of 1015 neq/cm2. Irradiations were performed with 23 MeV protons at the facilities in Karlsruhe (KIT), with 24 GeV/c protons at CERN (PS-IRRAD) and neutrons at the research reactor in Ljubljana. Secondary ion mass spectrometry measurements give evidence for nitrogen loss after processing, which makes gaining from nitrogen enrichment difficult
A Search for Selectrons and Squarks at HERA
Data from electron-proton collisions at a center-of-mass energy of 300 GeV
are used for a search for selectrons and squarks within the framework of the
minimal supersymmetric model. The decays of selectrons and squarks into the
lightest supersymmetric particle lead to final states with an electron and
hadrons accompanied by large missing energy and transverse momentum. No signal
is found and new bounds on the existence of these particles are derived. At 95%
confidence level the excluded region extends to 65 GeV for selectron and squark
masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure
- …