A. Greenall

First results on the charge collection properties of segmented detectors made with p-type bulk silicon

Radiation damage of n-type bulk detectors introduces stable defects acting as effective p-type doping and leads to the change of the conductivity type of the silicon substrate (type inversion) after a fluence of a few times 10 13 protons cm 2 . The diode junction after inversion migrates from the original side to the back plane of the detector. The migration of the junction can be prevented using silicon detectors with p-type substrates. Furthermore, the use of n-side readout gives higher charge collection efficiency for segmented devices operated below the full depletion voltage. Large area (E 6.4 6.4 cm 2 ) capacitively coupled 80mm pitch detectors using polysilicon bias resistors have been fabricated on p-type substrates (n-in-p diode structure). These detectors have been irradiated with 24 GeV/c protons to an integrated fluence of 3 10 14 cm 2 and kept for 7 days at 251C to reach the broad minimum of the annealing curve. Results are presented on the comparison of their charge collection properties with detectors using p-strip read-out after corresponding dose and annealing. r 2002 Elsevier Science B.V. All rights reserved.

The data acquisition and calibration system for the ATLAS Semiconductor Tracker

The SemiConductor Tracker (SCT) data acquisition (DAQ) system will calibrate, configure, and control the approximately six million front-end channels of the ATLAS silicon strip detector. It will provide a synchronized bunch-crossing clock to the front-end modules, communicate first-level triggers to the front-end chips, and transfer information about hit strips to the ATLAS high-level trigger system. The system has been used extensively for calibration and quality assurance during SCT barrel and endcap assembly and for performance confirmation tests after transport of the barrels and endcaps to CERN. Operating in data-taking mode, the DAQ has recorded nearly twenty million synchronously-triggered events during commissioning tests including almost a million cosmic ray triggered events. In this paper we describe the components of the data acquisition system, discuss its operation in calibration and data-taking modes and present some detector performance results from these tests

A model of charge collection for irradiated p+n detectors

Abstract The charge collection in irradiated p + n silicon detectors was studied as a function of the reverse bias voltage. Oxygenated and non-oxygenated devices were irradiated beyond type inversion with 24 GeV /c protons. The charge collection is successfully described with a model based on the hypothesis that the charge trapping depends on the carriers velocity. With this model, values for the full depletion voltage are extracted which show good agreement with those measured using the CV technique. The model allows a quantitative understanding of why although oxygenation of p + n devices improves substantially the full depletion voltage, much less improvement is observed in the charge collection efficiency.

Charge collection efficiency studies with irradiated silicon detectors

Abstract Small area (1×1 cm 2 ) microstrip detectors, made with a p+-n diode structure on FZ silicon substrates, both with and without oxygen enrichment, have been irradiated with 24 GeV /c protons to fluences of 1.9, 2.9 and 5.1×10 14 p/cm 2 . Their charge collection properties have been studied using a 106 Ru beta-source with a wide bandwidth current amplifier and compared with those for a non-irradiated device. The integrated charge collected at different times (10, 25, 40 and 80 ns ) has been used to estimate the effect of ballistic deficit. Predictions for the reduction in charge collection efficiency expected at fluences as high as 10 15 cm −2 are presented using a parameterization described in earlier work which also fits this data well.

Recent results from the ATLAS SCT irradiation programme

Abstract The irradiation facility at the CERN proton synchrotron, set up to irradiate full-size prototypes of silicon microstrip detectors for the ATLAS semiconductor tracker, is described and measurements of the detector currents during irradiation are reported. The detector dark currents can be described by bulk radiation damage models demonstrating the radiation hardness of the detector design and allowing the current damage factor α and the acceptor introduction term β to be determined. Results from testbeam studies of a module with an irradiated detector and binary readout in a magnetic field and with the beam incident over a range of angles are reported. The hit efficiency and spatial resolution satisfy the requirements for the SCT provided the detector is operated at the full charge collection voltage. The Lorentz angle was not found to be affected by the irradiation.

DC-DC converters with reduced mass for trackers at the HL-LHC

The development at CERN of low noise DC-DC converters for the powering of front-end systems enables the implementation of efficient powering schemes for the physics experiments at the HL-LHC. Recent tests made on the ATLAS short strip tracker modules confirm the full electromagnetic compatibility of the DC-DC converter prototypes with front-end detectors. The integration of the converters in the trackers front-ends needs to address also the material budget constraints. The impact of the DC-DC converters onto the material budget of the ATLAS tracker modules is discussed and mass reduction techniques are explored, leading to a compromise between electromagnetic compatibility and mass. Low mass shield implementations and Aluminum core inductors are proposed. Also, the impact on emitted noise due to a size reduction of critical components is discussed. Finally, material reduction techniques are discussed at the board layout and manufacturing levels.

A comparison of the performance of irradiated p-in-n and n-in-n silicon microstrip detectors read out with fast binary electronics

Abstract Both n-strip on n-bulk and p-strip on n-bulk silicon microstrip detectors have been irradiated at the CERN PS to a fluence of 3×10 14 p cm −2 and their post-irradiation performance compared using fast binary readout electronics. Results are presented for test beam measurements of the efficiency and resolution as a function of bias voltage made at the CERN SPS, and for noise measurements giving detector strip quality. The detectors come from four different manufacturers and were made as prototypes for the SemiConductor Tracker of the ATLAS experiment at the CERN LHC.

Annealing effects on irradiated n+n silicon detectors

The performance of ATLAS forward region full-sized n+n prototype silicon micro-strip detectors has been studied after irradiation with 2×1014 protons/cm2 and 52 days annealing at 20°C. The signal-to-noise ratio measured at −10°C with LHC speed read-out was found to be degraded primarily due to increased noise. The reduction in the reverse current and the changes in the voltage needed for maximum charge collection have both been studied as a function of annealing time. Above the depletion voltage, no effect on the charge collection efficiency has been observed during this annealing period.

Charge collection efficiency of irradiated n+n wedge silicon microstrip detectors for ATLAS

Abstract The charge collection efficiency of the n + n silicon microstrip detectors for the ATLAS forward tracking has been evaluated for detectors irradiated with 24 GeV/c protons. The charge collection efficiency is found to be 99±1% after a fluence of 2×10 14 protons/cm 2 and 81±2% after 4×10 14 protons/cm 2 . Furthermore, the charge collection efficiency of the detector irradiated with the lower dose does not show any dependence on the isothermal annealing up to 52 days at 20°C, as it remains constant through the whole annealing cycle.

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.