Double-sided Silicon Microstrip Sensors Research Articles

The high count-rate self-triggering Silicon Tracking System of the CBM experiment at FAIR: Design, series assembly, upgrade options

The Compressed Baryonic Matter (CBM) experiment is a stationary target spectrometer with hadron and lepton identification. It is under construction at the Facility for Antiproton and Ion Research (FAIR) that is being realized next to the GSI grounds in Darmstadt, Germany. CBM will investigate QCD matter at highest, up to supernova core-collaps baryonic densities (Ablyazimov et al., 2017). This will be done in collisions of nuclear beams with targets at center of mass energies sNN=2.9–4.9 GeV. Because of the long beam extraction technique employed at FAIR’s SIS100 synchrotron, CBM’s data collection can be based on streaming time-stamped detector data into a compute farm. Event determination and physics analysis are performed there online, allowing for collision rates up to 10 MHz. CBM’s core tracking detector is the Silicon Tracking System, operating 8 tracking stations based on double-sided silicon microstrip sensors and self-triggering front-end electronics in a 1 Tm dipole magnetic field (Heuser et al., 2013).

The Silicon Tracking System of the CBM Experiment at FAIR

The Compressed Baryonic Matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR) aims to study the properties of nuclear matter at high net-baryon densities and moderate temperatures.The Silicon Tracking System (STS) is the key detector to reconstruct with a high efficiency up to 1000 charged particle trajectories created in heavy-ion collisions at interaction rates of up to 10 MHz. It will determine the momentum of the particles with a momentum resolution Δp/p ≈ 1-2% which requires ultra-low detector material budget of 0.3-1% X0 per layer. The detector comprise eight layers of double-sided silicon micro-strip sensors and will be placed inside the 1 Tm superconducting magnet which limits the space available, which in turn requires advanced cooling approaches and mechanical design with precise tracking layers alignment. The micro-strip sensors have to be radiation hard and checked for their quality optically and electrically before the assembly.This contribution gives an overview of the STS and presents the status of its component quality control and assembly procedures.

The Silicon Tracking System of the CBM Experiment at FAIR

The Compressed Baryonic Matter (CBM) experiment at FAIR (Darmstadt, Germany) is designed to study the dense nuclear matter in a fixed target configuration with heavy ion beams up to kinetic energies of 11 AGeV for Au+Au collision. The charged particle tracking with below 2% momentum resolution will be performed by the Silicon Tracking System (STS) located in the aperture of a dipole magnet. The detector will be able to reconstruct secondary decay vertices of rare probes, e.g., multistrange hyperons, with 50 мm spatial resolution in the heavy-ion collision environment with up to 1000 charged particle per inelastic interaction at the 10 MHz collision rate. This task requires a highly granular fast detector with radiation tolerance enough to withstand a particle fluence of up to 1014 neq/cm2 1-MeV equivalent accumulated over several years of operation. The system comprises 8 tracking stations based on double-sided silicon microstrip sensors with 58 мm pitch and strips oriented at 7.5∘ stereo angle. The analog signals are read out via stacked microcables (up to 50 cm long) by the front-end electronics based on the STS-XYTER ASIC with self-triggering architecture. Detector modules with this structure will have a material budget between 0.3% and 1.5% radiation length increasing towards the periphery. First detector modules and ladders built from pre-final components have been operated in the demonstrator experiment mCBM at GSI-SIS18 (FAIR Phase-0) providing a test stand for the performance evaluation and system integration. The results of mSTS detector commissioning and the performance in the beam will be presented.

Investigation into the charge collection efficiency of prototype microstrip sensors for the CBM Silicon Tracking System

Double-sided silicon microstrip sensors are known to be sensitive to the radiation dose received during operation. The lifetime fluence for the Silicon Tracking System of the CBM experiment is estimated as 1014 1 MeV neq cm−2. In order to maintain the signal-to-noise ratio sufficiently high during all the time of operation we study the newest sensor prototypes irradiated to the single and double lifetime doses. The results of the tests are addressed in this paper.

The Silicon Tracking System of the CBM experiment at FAIR

The Silicon Tracking System (STS) is the central detector in the Compressed Baryonic Matter (CBM) experiment at FAIR. Operating in the 1Tm dipole magnetic field, the STS will enable pile-up free detection and momentum measurement of the charged particles originating from beam-target nuclear interactions at rates up to 10 MHz. The STS consists of 8 tracking stations based on double-sided silicon micro-strip sensors equipped with fast, self-triggering read-out electronics. With about two million read-out channels, the STS will deliver a high-rate stream of time-stamped data that is transferred to a computing farm for on-line event determination and analysis. The functional building block is a detector module consisting of a sensor, micro-cables and two front-end electronics boards. In this contribution, the development status of the STS components and the system integration is discussed and an outlook on the detector construction is given.

A precision device needs precise simulation: Software description of the CBM Silicon Tracking System

Precise modelling of detectors in simulations is the key to the understanding of their performance, which, in turn, is a prerequisite for the proper design choice and, later, for the achievement of valid physics results. In this report, we describe the implementation of the Silicon Tracking System (STS), the main tracking device of the CBM experiment, in the CBM software environment. The STS makes uses of double-sided silicon micro-strip sensors with double metal layers. We present a description of transport and detector response simulation, including all relevant physical effects like charge creation and drift, charge collection, cross-talk and digitization. Of particular importance and novelty is the description of the time behaviour of the detector, since its readout will not be externally triggered but continuous. We also cover some aspects of local reconstruction, which in the CBM case has to be performed in real-time and thus requires high-speed algorithms.

Belle II Silicon Vertex Detector

The Belle II experiment at the SuperKEKB asymmetric energy e+e− collider in KEK, Japan will operate at an instantaneous luminosity 40 times larger than that of its predecessor, Belle. It is built with an aim of collecting a huge amount of data (50 ab−1 by 2025) for precise CP violation measurements and new physics search. Thus, we need an accurate vertex determination and reconstruction of low momentum tracks which will be achieved with the help of vertex detector (VXD). The Belle II VXD consists of two layers of DEPFET pixels (`Pixel Detector') and four layers of double-sided silicon microstrip sensors (`Silicon Vertex Detector'), assembled over carbon fibre ribs. In this paper, we discuss about the Belle II Silicon Vertex Detector, especially its design and key features; we also present its module (`ladder') assembly and testing procedures.

A Custom Probe Station for Microstrip Detector Quality Assurance of the CBM Experiment

The double-sided silicon microstrip sensors with 58µm pitch are the main building blocks of the Silicon Tracking System (STS) — the central detector of the Compressed Baryonic Matter (CBM) Experiment. The STS will employ about 1200 such sensors arranged on eight traking stations. Electrical characterization of the sensors is necessary to ensure their compliance with the specifications. For this purpuse a custom probe station is being developed at Tuebingen University. One of the main requirements is a high accuracy and a repeatability better than 1 µm to allow an automatic, succesive positioning on all 1024 pads of a sensor, as well as a positioning range in accordance with the size of STS sensors. The probe station is controlled via dedicated software developed at Tuebingen University. It allows to inspect the required ~10% of the sensors on the series production stage with characterization time 4-5 hours per one double-sided sensor. The construction of the probe station and first measurements are discussed in this paper.

Strip defect recognition in electrical tests of silicon microstrip sensors

This contribution describes the measurement procedure and data analysis of AC-coupled double-sided silicon microstrip sensors with polysilicon resistor biasing.The most thorough test of a strip sensor is an electrical measurement of all strips of the sensor; the measured observables include e.g. the strip's current and the coupling capacitance. These measurements are performed to find defective strips, e.g. broken capacitors (pinholes) or implant shorts between two adjacent strips.When a strip has a defect, its observables will show a deviation from the “typical value”. To recognize and quantify certain defects, it is necessary to determine these typical values, i.e. the values the observables would have without the defect.As a novel approach, local least-median-of-squares linear fits are applied to determine these “would-be” values of the observables. A least-median-of-squares fit is robust against outliers, i.e. it ignores the observable values of defective strips. Knowing the typical values allows to recognize, distinguish and quantify a whole range of strip defects.This contribution explains how the various defects appear in the data and in which order the defects can be recognized. The method has been used to find strip defects on 30 double-sided trapezoidal microstrip sensors for the Belle II Silicon Vertex Detector, which have been measured at the Institute of High Energy Physics, Vienna (Austria).

Radiation tolerance studies of silicon microstrip sensors for the CBM Silicon Tracking System

Double-sided silicon microstrip sensors will be used in the Silicon Tracking System of the CBM experiment. During experimental run they will be exposed to a radiation field of up to 1x1014 1 MeV neq cm-2. Radiation tolerance studies were made on prototypes from two different vendors. Results from these prototype detectors before and after irradiation to twice that neutron fluence are discussed.

Automated quality assurance for silicon microstrip sensors of the CBM Silicon Tracking System

The Silicon Tracking System (STS) is the main tracking detector of the upcoming fixed-target Compressed Baryonic Matter (CBM) experiment which aims to explore the phase diagram of the strongly interacting matter in a region of high net baryonic densities and moderate temperatures. The STS will be used for the reconstruction of tracks of charged particles and determination of their momenta. The system comprises 8 tracking stations located 30 cm downstream the target and will be mounted with 300 μm thick double-sided silicon microstrip sensors in three different sizes. In this paper, the Quality Assurance (QA) procedures for the STS sensors are overviewed highlighting the automated QA testing procedure for a single strip defect identification.

Characterization of silicon micro-strip sensors with a pulsed infra-red laser system for the CBM experiment at FAIR

The Compressed Baryonic Matter (CBM) experiment at FAIR is composed of 8 tracking stations consisting of 1292 double sided silicon micro-strip sensors. For the quality assurance of produced prototype sensors a laser test system (LTS) has been developed. The aim of the LTS is to scan sensors with a pulsed infra-red laser driven by step motor to determine the charge sharing in-between strips and to measure qualitative uniformity of the sensor response over the whole active area. The prototype sensors which are tested with the LTS so far have 256 strips with a pitch of 50 μm on each side. They are read-out using a self-triggering prototype read-out electronic ASIC called n-XYTER. The LTS is designed to measure sensor response in an automatized procedure at several thousand positions across the sensor with focused infra-red laser light (spot size ≈ 12 μm , wavelength = 1060 nm). The pulse with duration (≈ 10 ns) and power (≈ 5 mW) of the laser pulses is selected such, that the absorption of the laser light in the 300 μm thick silicon sensors produces a number of about 24000 electrons, which is similar to the charge created by minimum ionizing particles (MIP) in these sensors. Laser scans different prototype sensors is reported.

Track measurement in the high multiplicity environment at the CBM Experiment

In the Compressed Baryonic Matter (CBM) Experiment at FAIR, the Silicon Tracking System (STS) will perform track reconstruction and momentum determination of the charged particles created in interactions of heavy-ion beams with nuclear targets. The STS will consist of 8 tracking layers located at distances between 30 cm and 100 cm downstream of the target inside the 1 Tm magnetic dipole field. An ultra-low material budget is required to achieve momentum resolution of the order of Δp/p = 1%. Therefore, the front-end electronics is placed outside the physics aperture. The active volume of the STS is built from 300 μm thick double-sided silicon microstrip sensors mounted onto lightweight carbon fiber support ladders. The sensors will be read out through ultra-thin micro-cables with fast self-triggering electronics at the periphery of the stations where also other infrastructure such as cooling can be placed. In this paper, the development status of the detector system, highlighting the overview of the STS layout, tracking algorithm and performance simulations are presented.

Fabrication of AC-coupled double-sided silicon strip sensor

The AC-coupled double-sided silicon microstrip sensors are designed and 14 masks are used to produce prototype strip sensors. The biasing resistors are made of p-doped polysilicons and the coupling capacitors are built by separating implanted strips and readout strips by a thin oxide layer. The p-stops in the atoll patterns are introduced to disrupt an electron accumulation layer at the Si–SiO2 interface on the ohmic side. The junction side has a double metal structure using two metal layers separated from each other by a thick insulator layer. The strip sensors are fabricated on a 5-in., high resistivity, 〈100〉-orientation, and 380μm thick n-type double-sided polished silicon wafer. The prototype sensor with an area of 2.8×2.8cm2 consists of 256(512) readout channels with a strip pitch of 100(50)μm. The leakage currents and the bulk capacitances as a function of the reverse bias voltage are measured to understand the fabrication process of the prototype sensors. The signal to noise ratios are measured by using a 90Sr radioactive source in order to evaluate performance of the sensors. The design of the AC-coupled double-sided silicon strip sensor and its various components are described, and measurements of the electric characteristics and the signal to noise ratio are presented.

The AMS-02 silicon tracker: Recent results and current status

The AMS-02 tracker consists of eight layers of double-sided silicon microstrip sensors which are used to measure the particle rigidity in the 0.8 T field of a cylindrical superconducting magnet. The magnetic spectrometer is designed to operate on the International Space Station (ISS) to provide an unprecedented high precision measurement of the cosmic-ray spectra in the energy range between 1 GeV and several TeV, for particle charge up to Z = 26 .

The AMS silicon tracker: Construction and performance

Eight layers of double sided silicon microstrip sensors immersed in a 0.8 T magnetic field constitute the core of the AMS-02 apparatus. In each layer, simultaneous measurements of position and energy loss in silicon are performed along the particle trajectory. With its high spatial resolution, the silicon tracker will determine the rigidity ( R) and the charge sign of particles up to several TVs, with a relative resolution 2.5% at R < 100 GV . The low noise and wide dynamic range of the silicon readout electronics allow to exploit the energy loss measurements to determine the particle absolute charge for nuclei up to Fe. The AMS tracker construction has been completed and it will be integrated into the AMS experiment during the 2007. The performances of the silicon detectors observed under various beam tests are presented focusing on the spatial resolution and on the charge separation capability.

Qualification of a large number of double-sided silicon microstrip sensors for the ALICE Inner Tracking System

Delivery of more than 2000 AC-coupled double-sided silicon microstrip sensors, designed to equip the two outermost layers of the ALICE Inner Tracking System, has been recently completed by three manufactures. This represents the largest production of this type of sensors undertaken so far. Sensor testing and quality control has been performed at INFN Trieste. A careful optimization of the testing procedures has allowed performing a thorough qualification of the large number of sensors without making use of automated device-handling equipment. The paper presents an overview of the test procedures and results.

Operation aspects of CDF tracking and vertexing detectors

The CDF Run II tracking and vertexing detectors consist of a large cylindrical drift chamber (COT) and a combination of three silicon detector components. An unexpected wire aging problem was found in the COT in late 2003 which resulted in substantial gain drop in the inner layers. Hydrocarbon growth was found to be the cause of aging, and the performance of the COT was fully recovered by adding 100 ppm oxygen to the standard chamber gas. The silicon detector contains eight layers of double-sided silicon microstrip sensors. Our experiences with commissioning and operating this complex device and the performance of the detector are reviewed. As the luminosity delivered by the Tevatron has increased, measurable effects of radiation damage have been observed. Recent studies of the change of full depletion voltage versus integrated luminosities are presented.

Status and radiation hardness of the CDF RunII silicon detector

The Collider Detector of Fermilab RunII (CDFII) silicon detector consists of 8 layers of double-sided silicon micro-strip sensors and a total of 722,432 readout channels, making it one of the largest silicon detector currently in use by a HEP experiment. The detector has been commissioned since 2002, and now we are consistently taking good data with 85% of the detector. By 2009, we expect to accumulate 4– 8 fb - 1 of luminosity. With no upgrade planned, studies of lifetime and radiation hardness of the detectors are discussed. As the luminosity delivered by the Tevatron has increased, measurable effects of radiation damage have been observed. Studies of charge collection and noise versus applied bias voltage at several different integrated luminosities are shown. These results and their impact on the lifetime of the detector are discussed.

Operational experience and performance of the CDFII silicon detector

The CDFII silicon detector consists of 8 layers of double-sided silicon micro-strip sensors totaling 722,432 readout channels, making it one of the largest silicon detectors in present use by an HEP experiment. After nearly 2 years of data taking, we report on our experience operating the complex device. The performance of the CDFII silicon detector is presented and its effect on physics analyses is discussed. The CDFII silicon detector has begun to show measurable effects of radiation damage. These results and their impact on the expected lifetime of the detector are briefly reviewed.