Silicon Microstrip Detectors Research Articles

Production of ALICE microstrip detectors at ITC-irst

We report on the results from the production of 600 double-sided silicon microstrip detectors for the ALICE experiment. We present the fabrication process and some selected results from the electrical characterization of detectors and test structures. The large amount of experimental data allowed a statistically relevant analysis to be performed. The main technological aspects related to production yield optimization will also be addressed.

Noise characterisation of MOS transistors in a 0.35 μm CMOS technology of geometries dedicated to front-end circuits for strip detectors

Measurement results and analysis of noise in MOSFETs manufactured in a 0.35 μm CMOS process are presented in the paper. Noise sources and noise models in submicron MOSFETs are reviewed briefly. The test transistors are designed keeping in mind applications in low noise front-end circuit for neutron detectors based on silicon microstrip detectors and microstrip gas chambers. The measurement method and measurement set-up are described. The measured noise spectra for a family of P-channel and N-channel transistors with different gate lengths and for different bias currents are presented and discussed with respect to short channel effects.

Cryogenic detector modules and edgeless silicon sensors

We are studying the operation of silicon microstrip detector with readout electronics in the temperature range from 90 to 130 K. The sensor can be operated in the current-injection mode which significantly improves its radiation hardness. A first module prototype has been built, with APV25 readout chips and an embedded microtube, providing efficient low-mass cooling of the whole module with a two-phase flow of N 2 or Ar. First pedestal and pulse shape temperature dependencies are presented for this module. We have also built an edgeless test module with two pairs of laser cut sensors, with both angular and parallel cuts with respect to the strips (at 120 μ m pitch). We are studying the efficiency of the microstrip sensors very close ( < 200 μ m ) to the physical border of the cut silicon crystal and present here some electrical characteristics.

Near detector at a neutrino factory

A near detector at a neutrino factory is essential for the measurement of neutrino oscillations, by performing the ratio of neutrino interactions between the near and far detectors. The near detector needs to establish the neutrino flux, beam angle, divergence, and energy of the neutrino beam, as well as determining the polarization of the muons that produce the neutrinos. Cross-section measurements and other physics such as measurements of parton distribution functions and charm physics can also be carried out at a near detector.There are many technological choices for a near detector at a neutrino factory, but a detector comprising an active silicon target inside a magnetic field for precise vertex reconstruction, followed by muon and electron identification is capable of carrying out these goals. A prototype silicon detector consisting of four passive layers of boron carbide and five layers of silicon microstrip detectors (NOMAD-STAR) was implemented within the NOMAD neutrino oscillation experiment. Impact parameter and double vertex resolutions were measured for this detector and a sample of charm decays was reconstructed for the first time using silicon detectors inside a neutrino beam. Consequences and lessons learnt from this prototype shall be applied to the case of a near detector at a neutrino factory.

Status of the CDF silicon detector

The CDF Run II silicon micro-strip detector is an essential part of the heavy flavor tagging and forward tracking capabilities of the experiment. Since the commissioning period ended in 2002, about 85% of the 730 k readout channels have been consistently providing good data. A summary of the recent improvements in the DAQ system as well as experience maintaining and operating such a large, complex detector are presented.

Performance of irradiated [formula omitted]-on- [formula omitted] silicon microstrip sensors

The silicon microstrip detector type with n + readout fabricated on p bulk, n + -on- p , is a candidate to be operational in radiation environments much severer than in LHC. We characterized n + -on- p detectors which were irradiated up to 1.1 × 10 14 protons / cm 2 10 years ago. The noise level and charge collection were evaluated using the ATLAS SCT readout electronics system. Radiation-induced increase in the noise and loss in the charge collection are not significant. The charge collection is not degraded in any particular point in the inter-strip region when the detector is operated under partial depletion.

Requirements for the Silicon Tracking System of CBM at FAIR

The Compressed Baryonic Matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt will systematically study dense baryonic matter created in collisions of intense heavy-ion beams with nuclear targets. The research addresses current questions of strong-interaction physics as confinement in normal nuclear matter, chiral symmetry restoration in deconfined matter at high temperatures and densities, and the search for the critical end-point of the phase boundary. With beams of ions as heavy as Au and U, energies up to 45 GeV/nucleon and intensities up to 10 12 ions per pulse, FAIR will enable CBM to probe the phase diagram of quantum chromo dynamics (QCD) in a region poorly known, while being complementary to current and future research programmes at RHIC and LHC. The CBM experiment is planned as a fixed-target spectrometer optimized for the detection of rare probes. Among these are open charm and low-mass vector mesons, important observables for the initial energetic and dense phase of the collisions. The experimental concept and challenge is to accomplish charged particle tracking in the high-multiplicity, high-radiation collision environment. This will be realized exclusively with a silicon tracking detector system installed in a strong magnetic dipole field directly behind the target. Key to the physics of CBM and benchmark for the tracking is the reconstruction of short-lived charmed mesons that puts high demands on the silicon detectors. The article presents a conceptual design of the CBM experiment with emphasis on the silicon tracking system. Requirements for silicon microstrip and pixel detectors and their arrangement in the tracker are discussed in relation to important physics observables addressed by CBM.

Effects of accelerated annealing on p-type silicon micro-strip detectors after very high doses of proton irradiation

Miniature (1 cm length) strip detectors have been produced with n-side read-out on p-type substrates to exploit the advantages, after exposure to large fluxes of hadrons, of reading out segmented devices from the n-side. These p-type prototypes have been irradiated with 24 GeV/ c protons to three fluences compatible with the expected doses (at different radii) for the inner tracker at the upgraded LHC (sLHC), namely 1.1, 3.5 and 7.5×10 15 cm −2. We have previously shown that those devices exhibit a signal to noise greater than 8:1 with LHC speed electronics even after the highest dose. The measurements were performed at the minimum of the curve of the annealing of the full depletion voltage after irradiation before the reverse annealing sets in. We have now studied the charge collection performance after accelerated annealing at 80 °C. At this temperature, the effects of the annealing are accelerated by a factor of about 7400 compared to room temperature, and our study spans an equivalent annealing time of several years at room temperature. The results, in terms of charge collection efficiency, are in sharp contrast with the evolution of the full depletion voltage as measured with the capacitance-voltage technique and suggest that these heavily irradiated detectors can be kept at room temperature for long periods without degrading their performance (e.g., during maintenance time). It is also apparent that the description of these heavily irradiated devices in terms of their full depletion voltage is no longer appropriate for the prediction of their charge collection properties.

Fast readout of the COMPASS RICH CsI-MWPC photon chambers

A new readout system for CsI-coated MWPCs, used in the COMPASS RICH detector, has been proposed and tested in nominal high-rate conditions. It is based on the APV25-S1 analog sampling chip, and will replace the Gassiplex chip readout used up to now. The APV chip, originally designed for silicon microstrip detectors, is shown to perform well even with “slow” signals from a MWPC, keeping a signal-to-noise ratio of 9. For every trigger the system reads three consecutive in-time samples, thus allowing to extract information on the signal shape and its timing. The effective time window is reduced from ∼3 μs for the Gassiplex to below 400 ns for the APV25-S1 chip, reducing pile-up events at high particle rate. A significant improvement of the signal-to-background ratio by a factor 5–6 with respect to the original readout has been measured in the central region of the RICH detector. Due to its pipelined architecture, the new readout system also considerably reduces the dead time per event, allowing efficient data taking at higher trigger rate.

Device simulations of isolation techniques for silicon microstrip detectors made on p-type substrates

Recent studies have shown that silicon particle detectors made on p-type substrates feature an improved radiation hardness compared to more conventional single-side n-type devices. In particular, they show an increased charge collection efficiency at very high irradiation levels. At present few devices have been fabricated on these substrates and there are still many doubts regarding the best type of isolation structure to be employed for the interruption of the inversion electron layer present between the n/sup +/ electrodes. In this paper, a description of the behavior of microstrip detectors featuring three isolation solution (p-spray, p-stop and a combination between the previous two) is presented. The analysis is based on device simulations and covers the breakdown and interstrip capacitance issues.

The LHCb VELO: status and upgrade developments

The VErtex LOcator (VELO) is the silicon microstrip vertexing and triggering sub-detector of the LHCb experiment. It consists of a series of forward disks with the active region extending to just 8 mm from the LHC beams. The current status of the VELO is presented. Due to the high radiation environment, the VELO may have to be replaced after some years, possibly with new materials. A candidate material is Czochralski silicon. We present here promising new results on the first test beam of a large, high resistivity Czochralski microstrip silicon detector read out with LHC speed electronics. The performance was studied before and after irradiation with high energy protons. A signal to noise of over 20:1 was obtained from the detector and significant charge collection efficiencies were measured at relatively modest voltages after a fluence of 4.3/spl times/10/sup 14/ 1 MeV neutron equivalents (n/sub eq/) per cm/sup 2/. Studies using the Transient Current Technique probed the electric field within MCz test detectors and proved that MCz silicon does not type invert up until a radiation level of at least 5/spl times/10/sup 14/ 24GeV/c p/cm/sup 2/. This would mean the VELO could possibly replace, in a potential upgrade, n/sup +/-on-n DOFZ sensors and the complicated processing involved, for standard p/sup +/-on-n processing with MCz.

The thermal failure analysis of microstrip silicon detectors

The paper is aimed at investigating the thermal failure analysis of microstrip silicon detectors caused by the radiation environment in large collider experiments. Damages in the bulk of the silicon wafer and as well at its surface generated by irradiation lead to an increase of the leakage current and hence the power dissipation in the detector. Cooling of the silicon detector together with readout chips and other electronic components has to be investigated in order to avoid the thermal runaway [H.-J. Ziock et al., Nucl. Instr. and Meth. A 342 (1994) 96; W.O. Miller, C. Haber, A. Seiden, Thermal runaway in silicon strip detectors, CERN/ATLAS Internal Note, INDET-NO-102, April 1995; T. Kohriki, T. Kondo, H. Iwasaki, S. Terada, Y. Unno, T. Ohsugi, IEEE Trans. Nucl. Sci. NS-43(3) (1996)]. This effect would cause the failure of the detector. In simulations which have been carried out we made use of the finite element method (FEM). three-dimensional (3D) thermal–electric elements from the ANSYS package [ANSYS, Engineering Analysis Systems, Swanson Analysis System Inc., Houston, PA 15342, USA] have been used for analyzing the thermal behavior of the silicon sensors after 10 yr of operation in the radiation environment.

The use of capacitive charge division in silicon microstrip detectors

The structure of silicon microstrip detectors with a great number of passive strips located between the readout (active) strips is described. Owing to the use of capacitive charge division among the passive and active strips, it is possible to essentially increase the readout pitch and to reduce the number of electronic readout channels by five to ten times. Since the cost of the front-end electronics exceeds significantly that of the detectors themselves, this method allows the cost of the entire detector-electronics system to be decreased severalfold without substantial deterioration of the position resolution.

Determining the position of an ionizing particle in a system of silicon microstrip detectors

Essentially all aspects of determining the particle hit position by a combination of signals in adjacent readout channels are considered. Different methods for finding a cluster and discriminating between real clusters produced by incident particles and false clusters due to noise fluctuations are analyzed. The main algorithms for finding the particle position inside a cluster at different angles of incidence are described. A new algorithm that involves the angle of incidence, measured by the external tracking system or determined from the internal structure of a cluster, is proposed. By optimizing the methods for finding a cluster and the algorithms of its analysis, it is possible to improve the spatial resolution of the detector by 20–40%.

A silicon microstrip detector in a magnetic spectrometer for high-resolution electron scattering experiments at the S-DALINAC

A silicon microstrip detector was developed as focal plane detector of the 169.7 ° magic angle double-focussing spectrometer at the superconducting Darmstadt electron linear accelerator (S-DALINAC). It allows experiments with minimum ionizing electrons at data rates up to 100 kHz, utilizing the maximum resolution of the spectrometer achievable in dispersion-matching mode.

EndCap module production of the ATLAS Semiconductor Tracker

ATLAS is one of the four experiments at the Large Hadron Collider at CERN. The ATLAS Semiconductor Tracker (SCT) forms a central part of the tracking system of the inner detector of the ATLAS experiment. It consists of 4 cylindrical barrel layers and 18 end-cap disks of 4088 modules in total made of single-sided p-on-n silicon microstrip detectors with about 6 million read-out channels. Most of the modules consist of 4 single-sided silicon sensors glued back to back with a 40 mrad stereo angle on a support structure, and read-out by custom made ASICs based on radiation hard DMILL technology. The mass production of about 2000 SCT end-cap modules began in mid-2003 at various production sites around the world.

Status and performance of the CDF Run 2 silicon detectors

In 2001, an upgraded silicon detector system was installed in the CDF II experiment on the Tevatron at Fermilab. The complete system consists of three silicon micro-strip detectors: SVX II with five layers for precision tracking, Layer 00 with one beampipe-mounted layer for vertexing, and two Intermediate Silicon Layers located between SVX II and the main CDF II tracking chamber. Currently all detectors in the system are operating at or near design levels. The performance of the combined silicon system is excellent in the context of CDF tracking algorithms, and the first useful physics results from the innermost Layer 00 detector have been recently documented. Operational and monitoring efforts have also been strengthened to maintain silicon efficiency through the end of Run 2 at the Tevatron.

The compact muon solenoid silicon tracker: testing of hybrids, modules and substructures at operating temperature

The Compact Muon Solenoid (CMS) is one of two general purpose detectors which are foreseen to operate at the Large Hadron Collider (LHC), which is presently being built at the European laboratory for particle physics (CERN) in Switzerland. The Central Tracker of CMS consists of a Pixel System, which is located close to the interaction point and a Silicon Strip Tracker (SST) which instruments the intermediate and outer region. The SST is composed of 15148 Silicon Microstrip Detector Modules which contain the readout electronics (hybrids) and sensors. These modules will be assembled into substructures with control electronics and optics for transmitting data. The substructures will be integrated into the subsystems of the SST. The SST will be operated for up to ten years in the harsh radiation environment of the LHC. The lifetime of the SST will be extended by operating the detector at lowered temperature. The sensors, which are very delicate with respect to radiation damage, will be operated at a maximum temperature of -10/spl deg/C. Since the assembly of the modules as well as the mounting on substructures is done at room temperature, tests in a CMS-like environment are necessary to prove the mechanical and electrical stability.

The CDF Run IIb Silicon Detector: Design, preproduction, and performance

A new silicon microstrip detector was designed by the CDF collaboration for the proposed high-luminosity operation of the Tevatron p p ¯ collider (Run IIb). The detector is radiation-tolerant and will still be functional after exposure to particle fluences of 10 14 1 - MeV equivalent neutrons / cm 2 and radiation doses of 20 MRad. The detector will maintain or exceed the performance of the current CDF silicon detector throughout Run IIb. It is based on an innovative silicon “supermodule” design. Critical detector components like the custom radiation-hard SVX4 readout chip, the beryllia hybrids and mini-port (repeater) cards, and the silicon sensors fulfill their specifications and were produced with high yields. The design goals and solutions of the CDF Run IIb silicon detector are described, and the performance of preproduction modules is presented in detail. Results relevant for the development of future silicon systems are emphasized.

Spatial resolution of double-sided silicon microstrip detectors for the PAMELA apparatus

The PAMELA apparatus has been assembled and it is ready to be launched in a satellite mission to study mainly the antiparticle component of cosmic rays. In this paper, the performances obtained for the silicon microstrip detectors used in the magnetic spectrometer are presented. This subdetector reconstructs the curvature of a charged particle in the magnetic field produced by a permanent magnet and consequently determines momentum and charge sign, thanks to a very good accuracy in the position measurements (better than 3 μ m in the bending coordinate). A complete simulation of the silicon microstrip detectors has been developed in order to investigate in great detail the sensor's characteristics. Simulated events have been then compared with data gathered from minimum ionizing particle (MIP) beams during the last years in order to tune free parameters of the simulation. Finally some either widely used or original position finding algorithms, designed for such kind of detectors, have been applied to events with different incidence angles. As a result of the analysis, a method of impact point reconstruction can be chosen, depending on both the particle's incidence angle and the cluster multiplicity, so as to maximize the capability of the spectrometer in antiparticle tagging.