S Meroli

Energy loss measurement for charged particles in very thin silicon layers

The energy loss distribution f(D) of highly relativistic charged particles has been measured for thin silicon layers with thickness ranging from 5.6 to 120 mm. In this work, using an innovative method, the dependence of the energy loss distribution from the thickness of the silicon absorber has been investigated in great detail with reference to CMOS Active Pixel Sensors. The measured energy loss distributions are well-reproduced by calculations also when the target electrons binding energy is taken into account. Finally the results obtained with this method are compared with existing experimental results and theoretical data.

A combined approach to the simulation of ionizing radiation effects in silicon devices

Silicon devices (both pixels and microstrips) have been widely used in the past years in High Energy Physics experiments and also in other applications involving the detection of ionizing radiation such as medical imaging and dosimetry. The simulation of the silicon devices response to ionizing radiation is an important step needed to understand the performances in terms of signal, noise, spatial and energy resolution as a function of several technology parameters like doping profile, geometrical dimensions, bias voltage. These simulations are routinely carried out using two separate approaches (and tools): radiation interaction with a geometrically segmented silicon material (GEANT4, FLUKA, PENELOPE) taking into account the physical processes and giving as output the deposited energy; transport of generated electron/hole pairs through the device with electronic signal formation (SENTAURUS-TCAD). In this work we propose a new combined approach using both methods, applied to the case of CMOS pixel sensor, to obtain a better understanding of the behavior of the devices.

A 5 Gb/s Radiation Tolerant Laser Driver

A laser driver for data transmission at 5 Gb/s has been developed as a part of the Giga Bit Transceiver (GBT) project. The Giga Bit Laser Driver (GBLD) targets High Energy Physics (HEP) applications for which radiation tolerance is mandatory. The GBLD ASIC can drive both VCSELs and some types of edge emitting lasers. It is essentially composed of two drivers capable of sinking up to 12 mA each from the load at a maximum data rate of 5 Gb/s, and of a current sink for the laser bias current. The laser driver include also pre-emphasis and duty cycle control capabilities.

3D monolithically stacked CMOS active pixel sensor detectors for particle tracking applications

In this work we propose an innovative approach to particle tracking based on CMOS Active Pixel Sensors layers, monolithically integrated in an all-in-one chip featuring multiple, stacked, fully functional detector layers capable to provide momentum measurement (particle impact point and direction) within a single detector. This will results in a very low material detector, thus dramatically reducing multiple scattering issues. To this purpose, we rely on the capabilities of the CMOS vertical scale integration (3D IC) technology. A first chip prototype has been fabricated within a multi-project run using a 130 nm CMOS Chartered/Tezzaron technology, featuring two layers bonded face-to-face. Tests have been carried out on full 3D structures, providing the functionalities of both tiers. To this purpose, laser scans have been carried out using highly focussed spot size obtaining coincidence responses of the two layers. Tests have been made as well with X-ray sources in order to calibrate the response of the sensor. Encouraging results have been found, fostering the suitability of both the adopted 3D-IC vertical scale fabrication technology and the proposed approach for particle tracking applications.

Tilted CMOS active pixel sensors for particle track reconstruction

In this work, we propose an innovative approach to characterize CMOS Active Pixel Sensors to be used for particle track reconstruction. The main idea is to use three pixel layers in the conventional way (e.g. orthogonally disposed with respect to the particle trajectory), whereas a fourth layer can be tilted with respect to the others up to 90 degrees. This would potentially allow for a better track reconstruction, thanks to the big number of reconstruction points. In order to check the suitability of the approach a dedicated tracking system featuring four sensors of 256×256 pixels has been assembled and tested at the INFN BTF, Frascati (Italy). Test results demonstrate the suitability of the approach, e.g. the system sensitivity to tilted trajectories.

The management of large cabling campaigns during the Long Shutdown 1 of LHC

The Large Hadron Collider at CERN entered into its first 18 month-long shutdown period in February 2013. During this period the entire CERN accelerator complex will undergo major consolidation and upgrade works, preparing the machines for LHC operation at nominal energy (7 TeV/beam). One of the most challenging activities concerns the cabling infrastructure (copper and optical fibre cables) serving the CERN data acquisition, networking and control systems. About 1000 kilometres of cables, distributed in different machine areas, will be installed, representing an investment of about 15 MCHF. This implies an extraordinary challenge in terms of project management, including resource and activity planning, work execution and quality control. The preparation phase of this project started well before its implementation, by defining technical solutions and setting financial plans for staff recruitment and material supply. Enhanced task coordination was further implemented by deploying selected competences to form a central support team.

Measurement of charge collection efficiency profiles of CMOS active pixel sensors

Recently, CMOS Active Pixels Sensors (APS) have become strong candidates as pixel detectors to be used in high energy physics experiments. A very good resolution and an excellent detection efficiency could be obtained with these detectors. In this paper we have experimentally studied, by means of charged particle beams at a grazing angle, for four different CMOS APS the diffusion properties of electron/hole pairs formed by ionizing particles interacting within the sensitive silicon layer beneath the sensor surface. By averaging many events originating at the same distance from the surface of the device, we extracted with great accuracy the charge collection efficiency (CCE) profiles of the four sensors under test. Basic transport parameters (minority carrier diffusion length, minority carrier lifetime, width of the region at maximum CCE) have been extracted using a mathematical procedure based on the extended Ramos theorem.

Measurement of submicrometric intrinsic spatial resolution for active pixel sensors

To measure the intrinsic spatial resolution of silicon pixel sensor is usually a non-trivial task, particularly for small pixel sizes where the multiple scattering may be the limiting factor. In this work, we present a new measurement technique to obtain the intrinsic spatial resolution of silicon active pixel sensors. The method relies on the capability of the device to record the passage of a charged particle, incoming at a grazing angle, over several tens or hundreds of pixels, acting as a solid state ionization chamber and thus defining a track. The track will then be fitted by a line and the intrinsic spatial resolution will be obtained using two methods: i) extracted by the σ of the fit; ii) defining a telescope-on-chip configuration to find a residual distribution. Comparison with a more traditional measurement (telescope configuration) and a discussion on the limit of this technique, when the pixel size shrinks, will also be presented.

Analysis of the performance of CMOS APS imagers after proton damage

In this work we have irradiated a standard commercial CMOS imager with a 24 MeV proton beam at INFN Laboratori Nazionali del Sud, Catania (Italy) up to a nominal fluence of 1014 [protons/cm?2]. The device under test was a standard VGA detector, fabricated with a 130 nm technology without radiation hardening. During the irradiation the detector was operated to monitor the progressive damaging of the sensor and the associated on-pixel electronics. After 18 months from the irradiation damage session, with the detector stored at room temperature, a study on the detection efficiency and charge collection capability has been carried out using fluorescent X-ray photons, emitted from copper target. We found that the detector is still working at 1013 protons/cm2, with a moderate increase of the noise and a slightly decrease of the detection capabilities.

Vertically integrated CMOS active pixel sensors for tracking applications in HEP experiments

In this work we propose an innovative approach to particle tracking based on CMOS Active Pixel Sensors layers, monolithically integrated in an all-in-one chip featuring multiple, stacked, fully functional detector layers capable to provide momentum measurements (particle impact point and direction) within a single detector. This will results in a very low material detector, thus dramatically reducing multiple scattering issues. A first chip prototype has been fabricated within a multi-project run using a 130nm CMOS 3D Chartered/Tezzaron technology, featuring two layers bonded face-to-face. Tests have been carried out on full 3D structures, providing the functionalities of both tiers and their inter-communications. Actually, laser scans have been carried out using highly focussed spot size, obtaining coincidence responses of the two layers. X-rays sources have been used as well for sensor calibration purposes. Beam tests with 3MeV protons have been carried out at the INFN LABEC laboratories in Florence (Italy) to assess the suitability of the proposed approach for Minimum Ionizing Particle detection.