Radiation tolerant sensors for the ATLAS pixel detector Wunstorf, R.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2001, Letnik:
466, Številka:
2
Journal Article
Recenzirano
The pixel detector in the ATLAS experiment at the LHC, Geneva, is an important detector component for high resolution tracking and vertex identification. For this demanding task the hybrid pixel ...detector with silicon sensors has to work in a very harsh radiation environment with up to 3.5×10
14
n
eq/cm
2 per year. On the basis of the known radiation effects a dual-track strategy was followed for the development of radiation tolerant silicon pixel sensors. The ATLAS pixel collaboration successfully developed the radiation hard sensor design which meets the challenging requirements for the ATLAS pixel detector. In parallel, the hardening of the silicon itself was followed within the ROSE collaboration, which developed the radiation tolerant DOFZ-silicon with oxygen enrichment by diffusion. Taking all the results together the radiation tolerant silicon sensors have been designed, produced and showed excellent performance before and after irradiation.
Silicon detectors are used or going to be used as tracking devices in many high energy physics experiments. Therefore they are located close to the interaction point, where the detectors are exposed ...to very high particle fluxes and ionization doses, especially in future experiments with very high energies and luminosities. Ongoing investigations concerning the radiation damage, started already several years ago, include bulk and surface damage related questions. The two main objectives of these studies are: (1) predict the radiation induced change in the detector parameters expected for any application, and (2) improve the radiation hardness of the detectors. A general overview of the current progress of the radiation hardness studies towards these goals is given here.
Silicon pad-detectors fabricated from oxygenated silicon were irradiated with 24-GeV/c protons with fluences between 2/spl middot/10/sup 13/ n/sub eq//cm/sup 2/ and 9/spl middot/10/sup 14/ n/sub ...eq//cm/sup 2/. The transient current technique was used to measure the trapping probability for holes and electrons. The measured trapping probabilities scale linearly with the fluence. Annealing, accelerated at 60/spl deg/C, leads to an increased trapping for holes while electron trapping decreases.
The Transient Current Technique (TCT) is used to measure pulse shapes of charge collection and to derive trapping times in irradiated silicon pad detectors in a fluence range up to
10
15
n
eq
cm
-
2
.... Simulations of electrical fields and charge collection mechanisms compared to the measurements of the TCT method allow to derive predictions of the charge collection efficiency. Independently, charge collection efficiencies have been determined in dedicated test beam data employing ATLAS pixel modules. Considering the geometry of pad and pixel structures the simulation for the tested fluence range can be verified and allows to extrapolate to larger fluences. This yields a useful input for the design of future silicon-based pixel detectors applicable in Super-LHC experiments.
Sensor design for the ATLAS-pixel detector Rohe, T.; Hügging, F.; Lutz, G. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/1998, Letnik:
409, Številka:
1-3
Journal Article
Recenzirano
The inner detector of the ATLAS experiment will contain three layers of pixel detectors. The first prototype of the sensor part will be an n+n-device in order to allow partial depleted operation ...after bulk inversion and a guard-ring scheme keeping the entire detector surface close to the electronic chip on ground potential. Further, a bias structure is introduced providing testability of the sensors before mounting them to the electronics. The design of the single pixel cell is the result of a detailed device simulation study.
Prototype performance and design of the ATLAS pixel sensors Hügging, F.; Gößling, C.; Klaiber-Lodewigs, J. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2001, Letnik:
465, Številka:
1
Journal Article
Recenzirano
Silicon pixel sensors for the ATLAS Pixel Detector have been successfully developed. The main attention for the design was given to survivability in the harsh radiation environment of LHC up to a ...fluence of 10
15n
eq/cm
2 during 10 years of operation. This leads to the need of long term operation at several hundreds of volts, partially depleted while maintaining good charge collection, small cell size and thin sensors reducing the multiple scattering. Additionally, a bias grid for testing the sensors before assembly under realistic bias conditions is implemented to allow a quality assurance.
The RD48 (ROSE) collaboration has succeeded to develop radiation hard silicon detectors, capable to withstand the harsh hadron fluences in the tracking areas of LHC experiments. In order to reach ...this objective, a defect engineering technique was employed resulting in the development of Oxygen enriched FZ silicon (DOFZ), ensuring the necessary O-enrichment of about 2×10
17 O/cm
3 in the normal detector processing. Systematic investigations have been carried out on various standard and oxygenated silicon diodes with neutron, proton and pion irradiation up to a fluence of 5×10
14
cm
−2 (1
MeV neutron equivalent). Major focus is on the changes of the effective doping concentration (depletion voltage). Other aspects (reverse current, charge collection) are covered too and the appreciable benefits obtained with DOFZ silicon in radiation tolerance for charged hadrons are outlined. The results are reliably described by the “Hamburg model”: its application to LHC experimental conditions is shown, demonstrating the superiority of the defect engineered silicon. Microscopic aspects of damage effects are also discussed, including differences due to charged and neutral hadron irradiation.
Studies of radiation damage of silicon detectors have shown that in most elementary particle physics applications, the major problem caused by non-ionizing interactions in silicon will be the change ...in the concentration of the electrically active impurity states. For many silicon applications in high radiation environments, the increase in the relative acceptor concentration during long term room temperature annealing is the limiting factor. The first step in developing radiation hardened silicon is to identify the defects which are responsible for this effect.
In earlier work, we developed a model which describes the experimentally observed fast neutron induced changes in the net electrically active impurity concentration and provides a method to determine the phosphorus and boron concentration of the starting material. Our previous work has been extended with experiments using silicon with different original boron/phosphorus ratios, larger neutron fluences and to long term room temperature annealing. The donor removal rate of phosphorus was measured and the acceptor removal rate of boron evaluated. Extending our model, we propose that slow restoration of the damage induced boron interstitial back to its original substitutional state is responsible for the acceptor increase observed during long term annealing.
This model, which involves only the behavior of the known shallow donors and acceptors present in the starting material, fits our data and the data of other experimenters without the need to invoke unidentified deep levels.
In future high-luminosity collider experiments, fine segmented silicon strip and pixel detectors will be used for tracking very close to the interaction point. Therefore the surface effects due to ...irradiation are very important for the long term performance of these devices. A good understanding of these effects is the basis for the development of less radiation sensitive detectors. An important tool for this understanding is device simulation. In the comparison of device simulations with measurements of ionisation-induced surface effects it became obvious that the electric field distribution in the passivation during the irradiation cuases a position dependent increase of interface charges. In order to achieve more realistic simulations this was taken into account by varying the oxide charge density according to results obtained from MOS-structures.
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