Novel Data Acquisition System for Silicon Tracking Detectors

We have developed a novel data acquisition system for measuring tracking parameters of a silicon detector in a particle beam. The system is based on a commercial Analog-to-Digital VME module and a PC Linux based Data Acquisition System. This DAQ is realized with C++ code using object-oriented techniques. Track parameters for the beam particles were reconstructed using off-line analysis code and automatic detector position alignment algorithm. The new DAQ was used to test novel Czochralski type silicon detectors. The important silicon detector parameters, including signal size distributions and signal to noise distributions, were successfully extracted from the detector under study. The efficiency of the detector was measured to be 95 %, the resolution about 10 micrometers, and the signal to noise ratio about 10.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics (CHEP03), La Jolla, Ca, USA, March 2003, 6 pages, LaTeX, 5 eps figures. PSN TUGP00

P-Type Silicon Strip Sensors for the new CMS Tracker at HL-LHC

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Employing infrared microscopy (IRM) in combination with a pre-trained neural network to visualise and analyse the defect distribution in Cadmium Telluride crystals

While Cadmium Telluride (CdTe) excels in terms of photon radiation absorption properties and outperforms silicon (Si) in this respect, the crystal growth, characterization and processing into a radiation detector is much more complicated. Additionally, large concentrations of extended crystallographic defects, such as grain boundaries, twins, and tellurium (Te) inclusions, vary from crystal to crystal and can reduce the spectroscopic performance of the processed detector. A quality assessment of the material prior to the complex fabrication process is therefore crucial. To locate the Te-defects, we scan the crystals with infrared microscopy (IRM) in different layers, obtaining a 3D view of the defect distribution. This provides us with important information on the defect density and locations of Te inclusions, and thus a handle to assess the quality of the material. For the classification of defects in the large amount of IRM image data, a convolutional neural network is employed. From the post-processed and analysed IRM data, 3D defect maps of the CdTe crystals are created, which make different patterns of defect agglomerations inside the crystals visible. In total, more than 100 crystals were scanned with the current IRM setup. In this paper, we compare two crystal batches, each consisting of 12 samples. We find significant differences in the defect distributions of the crystals.Peer reviewe

Processing and Interconnections of Finely Segmented Semiconductor Pixel Detectors for Applications in Particle Physics and Photon Detection

Radiation hardness is in the focus of the development of particle tracking and photon imaging detector installations. Semiconductor detectors, widely used in particle physics experiments, have turned into capacitive-coupled (AC-coupled) detectors from the originally developed conductively coupled (DC-coupled) detectors. This is due to the superior isolation of radiation-induced leakage current in AC-coupled detectors. However, some modern detector systems, such as the tracking detectors in the CERN LHC CMS or ATLAS experiments, are still DC-coupled. This originates from the difficulty of implementing AC coupling on very small pixel detector areas. In this report, we describe our advances in the detector processing technology. The first topic is the applications of the atomic layer deposition processing technology, which enables the very high densities of capacitance and resistance that are needed when the dimensions of the physical segmentation of pixel detectors need to be scaled down. The second topic is the flip-chip/bump-bonding interconnection technology, which is necessary in order to manufacture pixel detector modules on a large scale with a more than 99% yield of noise-free and faultless pixels and detector channels.Peer reviewe

Comparative evaluation of analogue front-end designs for the CMS Inner Tracker at the High Luminosity LHC

Publisher Copyright: © 2021 CERN for the benefit of the CMS collaboration..The CMS Inner Tracker, made of silicon pixel modules, will be entirely replaced prior to the start of the High Luminosity LHC period. One of the crucial components of the new Inner Tracker system is the readout chip, being developed by the RD53 Collaboration, and in particular its analogue front-end, which receives the signal from the sensor and digitizes it. Three different analogue front-ends (Synchronous, Linear, and Differential) were designed and implemented in the RD53A demonstrator chip. A dedicated evaluation program was carried out to select the most suitable design to build a radiation tolerant pixel detector able to sustain high particle rates with high efficiency and a small fraction of spurious pixel hits. The test results showed that all three analogue front-ends presented strong points, but also limitations. The Differential front-end demonstrated very low noise, but the threshold tuning became problematic after irradiation. Moreover, a saturation in the preamplifier feedback loop affected the return of the signal to baseline and thus increased the dead time. The Synchronous front-end showed very good timing performance, but also higher noise. For the Linear front-end all of the parameters were within specification, although this design had the largest time walk. This limitation was addressed and mitigated in an improved design. The analysis of the advantages and disadvantages of the three front-ends in the context of the CMS Inner Tracker operation requirements led to the selection of the improved design Linear front-end for integration in the final CMS readout chip.Peer reviewe

Selection of the silicon sensor thickness for the Phase-2 upgrade of the CMS Outer Tracker

Publisher Copyright: © 2021 CERN.During the operation of the CMS experiment at the High-Luminosity LHC the silicon sensors of the Phase-2 Outer Tracker will be exposed to radiation levels that could potentially deteriorate their performance. Previous studies had determined that planar float zone silicon with n-doped strips on a p-doped substrate was preferred over p-doped strips on an n-doped substrate. The last step in evaluating the optimal design for the mass production of about 200 m2 of silicon sensors was to compare sensors of baseline thickness (about 300 μm) to thinned sensors (about 240 μm), which promised several benefits at high radiation levels because of the higher electric fields at the same bias voltage. This study provides a direct comparison of these two thicknesses in terms of sensor characteristics as well as charge collection and hit efficiency for fluences up to 1.5 × 1015 neq/cm2. The measurement results demonstrate that sensors with about 300 μm thickness will ensure excellent tracking performance even at the highest considered fluence levels expected for the Phase-2 Outer Tracker.Peer reviewe

Finnish CMS-TOB cosmic rack

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Modeling the impact of defects on the charge collection efficiency of a Cadmium Telluride detector

Cadmium telluride is a favorable material for X-ray detection as it has an outstanding characteristic for room temperature operation. It is a high-Z material with excellent photon radiation absorption properties. However, CdTe single crystals may include a large number of extended crystallographic defects, such as grain boundaries, twins, and tellurium (Te) inclusions, which can have an impact on detector performance. A Technology Computer Aided Design (TCAD) local defect model has been developed to investigate the effects of local defects on charge collection efficiency (CCE). We studied a 1 mm thick Schottky-type CdTe radiation detector with transient current technique by using a red laser at room temperature. By raster scanning the detector surface we were able to study signal shaping within the bulk, and to locate surface defects by observing their impact on the CCE. In this paper we present our TCAD model with localized defect, and compare the simulation results to TCT measurements. In the model an inclusion with a diameter of 10 mu m was assumed. The center of the defect was positioned at 6 mu m distance from the surface. We show that the defect has a notable effect on current transients, which in turn affect the CCE of the CdTe detector. The simulated charge collection at the position of the defect decreases by 80 % in comparison to the defect-free case. The simulations show that the defects give a characteristic shape to TCT signal. This can further be used to detect defects in CdTe detectors and to estimate the overall defect density in the material.Peer reviewe

Beam test performance of a prototype module with Short Strip ASICs for the CMS HL-LHC tracker upgrade

The Short Strip ASIC (SSA) is one of the four front-end chips designed for the upgrade of the CMS Outer Tracker for the High Luminosity LHC. Together with the Macro-Pixel ASIC (MPA) it will instrument modules containing a strip and a macro-pixel sensor stacked on top of each other. The SSA provides both full readout of the strip hit information when triggered, and, together with the MPA, correlated clusters called stubs from the two sensors for use by the CMS Level-1 (L1) trigger system. Results from the first prototype module consisting of a sensor and two SSA chips are presented. The prototype module has been characterized at the Fermilab Test Beam Facility using a 120 GeV proton beam.Peer reviewe