[en] The LHC is expected to reach luminosities up to 3000 fb"−"1 and the innermost layer of the ATLAS upgrade plans to cope with higher occupancy and to decrease the pixel size. 3D-Si sensors are a good candidate for the innermost layer of the ATLAS pixel upgrade since they exhibit good performance under high fluences and the new designs will have smaller pixel size to fulfill the electronics expectations. This paper reports TCAD simulations of the 3D-Si sensors designed at IMB-CNM with non-passing-through columns that are being fabricated for the next innermost layer of the ATLAS pixel upgrade. It shows the charge collection response before and after irradiation, and the response of 3D-Si sensors located at large η angles.

[en] During neutron irradiation of boron carbide, helium bubbles nucleate, inducing cracks and then reducing lifetime of control rods. The role of helium bubbles has been clearly identified by transmission electron microscopy (TEM) photographs. X-ray diffraction may be a complement to TEM studies of B₄C microstructure evolution under irradiation. In this article, we show that X-ray profiles may be used to calculate a mean bubble density and a local strain value as a function of neutron irradiation. Both the data are useful to present a quantitative analysis of the mechanism responsible for the damage of irradiated B₄C material. To observe an eventual solubility of helium atoms in the B₄C matrix, we have performed different isochronal annealing on irradiated B₄C samples. Results of X-ray diffraction experiments on both irradiated and annealed samples permit to confirm previous works on B₄C behaviour under neutron irradiation and to present a quantitative analysis of irradiated B₄C samples. The study of strain η and coherent diffracting domains (CDD) as a function of N(α), number of neutronic capture per unit volume, exhibits a saturation of η near 1% and a constant increase of CDD up to 4 x 10¹⁶ CDD/cm³. This η and CDD evolution can be explained by helium bubble growth up to a 'characteristic' size in the material during irradiation. Moreover, no second phase has been observed during both irradiation and annealing of B₄C irradiated samples. (orig.)

[en] Low Gain Avalanche Detectors (LGAD) represent a remarkable advance in high energy particle detection, since they provide a moderate increase (gain ~10) of the collected charge, thus leading to a notable improvement of the signal-to-noise ratio, which largely extends the possible application of Silicon detectors beyond their present working field. The optimum detection performance requires a careful implementation of the multiplication junction, in order to obtain the desired gain on the read out signal, but also a proper design of the edge termination and the peripheral region, which prevents the LGAD detectors from premature breakdown and large leakage current. This work deals with the critical technological aspects required to optimize the LGAD structure. The impact of several design strategies for the device periphery is evaluated with the aid of TCAD simulations, and compared with the experimental results obtained from the first LGAD prototypes fabricated at the IMB-CNM clean room. Solutions for the peripheral region improvement are also provided.

[en] A new vertical JFET transistor has been recently developed at the IMB-CNM, taking advantage of a deep-trenched 3D technology to achieve vertical conduction and low switch-off voltage. The silicon V-JFET transistors were mainly conceived to work as rad-hard protection switches for the renewed HV powering scheme (HV-MUX) of the ATLAS upgraded tracker. This work presents the features of the first batch of V-JFETs produced at the IMB-CNM clean room, together with the results of a full pre-irradiation characterization of the fabricated prototypes. Details of the technological process are provided and the outcome quality is also evaluated with the aid of reverse engineering techniques. Concerning the electrical performance of the prototypes, promising results were obtained, already meeting most of the HV-MUX specifications, both at room and below-zerotemperatures.

[en] A new vertical JFET technology, based on a 3D trenched design, has been developed at the IMB-CNM. These transistors are conceived to work as rad-hard protection switches in the renewed High Voltage powering scheme for the Upgrade ATLAS ITk strip detectors. The first fabricated wafers have been fully characterized and the V-JFET performance is very close to the required specifications, showing excellent agreement with simulations. In this work the performance of the fabricated prototypes is tested under harsh ionizing radiation conditions. The variation of the main figures of merit is evaluated as a function of the Total Ionising Dose (TID) and the impact of different design parameters and fabrication strategies are compared. A final study, performed with the aid of TCAD simulations, is also included to understand the effects of the ionization damage observed on the V-JFET performance.

[en] This work presents a new silicon vertical JFET (V-JFET) device, based on the trenched 3D-detector technology developed at IMB-CNM, to be used as a switch for the High-Voltage powering scheme of the ATLAS upgrade Inner Tracker. The optimization of the device characteristics is performed by 2D and 3D TCAD simulations. Special attention has been paid to the on-resistance and the switch-off and breakdown voltages to meet the specific requirements of the system. In addition, a set of parameter values has been extracted from the simulated curves to implement a SPICE model of the proposed V-JFET transistor. As these devices are expected to operate under very high radiation conditions during the whole experiment life-time, a study of the radiation damage effects and the expected degradation of the device performance is also presented at the end of the paper

[en] The Large Hadron Collider (LHC) recorded its first collisions during the last months of 2009. By 2020 a two-stage upgrade of the accelerator complex, the High Luminosity LHC (HL-LHC), will increase the instantaneous luminosities up to a factor of ten compared to the current design. The particle fluxes at ATLAS will increment substantially with special impact on the inner tracking detector which will be subjected to large occupancies and radiation damage. In order to cope with the higher instantaneous luminosities ATLAS will upgrade its current Inner Detector (ID) in two phases, first by introducing a new pixel layer (IBL) mounted directly on the beam pipe, and later by completely replacing the current ID with several layers of semiconductor detectors (pixels and strips). The upgrades to the ATLAS ID require the development of new silicon technologies, since the current planar pixel sensors are not suitable for the expected radiation doses at small radii. For these inner detector layers, the most promising technology is the so-called 3D sensor, while improved planar sensors are considered for the external layers. Silicon detectors with cylindrical electrodes offer advantages over standard planar sensors mainly because they are more radiation hard. 3D detectors with the double sided geometry have been fabricated at IMB-CNM clean room facilities. The layouts fits the new pixelated readout chip FE-I4 developed by the ATLAS collaboration.

[en] Purpose: A new design of a solid-state-microdetector based on silicon 3D microfabrication and its performance to characterise Lineal energy, Specific Energy, dose, LET and other microdosimetric variables required for modelling particle relative biological effectiveness (RBE) is presented. Methods: A microdosimeter formed by a matrix of independent sensors with well-defined micrometric cylindrical shape and with a volume similar to those of cellular dimensions is used to measure microdosimetric variables. Each sensor measures the radiation deposited energy which, divided by the mean cord length of the sensors, provides us with the Linear Energy (y) of the radiation as well as its energy distribution, and frequencymean. Starting from the these distributions in different points of a proton beam, we generate biophysical data (e.g. Linear Energy Transfer (LET), Specific Energy (z), etc…) needed for relative biological effectiveness (RBE) calculations radiation effect models used in particle radiotherapy treatment planning. In addition, a Tissue Equivalent Proportional Counter (TEPC) will be used as baseline to calibrate the “y” magnitude of the microdosimeter unit-cells. Results: The experimental measurements will soon be carried out at the Perelman Center for Advanced Medicine (University of Pennsylvania), which provides proton beam for clinical research proposals. The results of distributions measured of the microdosimetric variables from the first tests developed in the proton facility will be presented and compared with Monte Carlo simulations using the Geant4 code. Conclusion: The use of 3D microdosimeters such as the one presented here will enhance the accuracy of RBE calculations normally affected by the inherent uncertainty of monte carlo simulations due to the approximation of material composition and energy dependent physical laws involved in such calculations. The effect of such approximations will be quatified by comparison with absolute measurement of radiation quality parameters

[en] We present a novel neutron detector based on an ultra-thin 3D silicon sensor with a sensitive volume only 10 μm thick. This ultra-thin active volume allows a high gamma-ray rejection, a key requirement in order to discriminate the signal coming from the neutrons in a mixed neutron-gamma ray environment. The device upper-side is covered with a novel boron-based compound that detects neutrons by means of the ¹⁰B(n,α)⁷Li nuclear reaction. The performance of test devices has been investigated first with a gamma-ray source to evaluate the gamma-ray rejection factor, and then with an ²⁴¹AmBe neutron source to assess the neutron-gamma ray discrimination properties.

[en] We used Geant4 and MCNPX codes to evaluate the detection efficiency of planar silicon detectors coupled to different Boron-based converters with varied compositions and thicknesses that detect thermal neutrons via the ¹⁰B(n,α)⁷Li nuclear reaction. Few studies about the thermal neutron transport in Geant4 have been reported so far and it is becoming increasingly difficult to ignore its discrepancies with MCNPX in this neutron energy range. In the thermal energy range, Geant4 shows high discrepancies with MCNPX giving a maximum efficiency of about 3.3% in the ¹⁰B case whereas that obtained with MCNPX was 5%. Disagreements obtained between both codes in this energy range are analyzed and discussed.