The Phase-2 upgrade of the Large Hadron Collider (LHC) to High-Luminosity LHC (HL-LHC) allows an increase in the operational luminosity value by a factor of 5–7 that will result in delivering ...3000 fb−1 or more integrated luminosity. Due to high luminosity, the number of interactions per bunch crossings (pileup) will increase up to a value of 140–200. To cope with high pileup rates, a precision minimum ionising particles (MIPs) timing detector (MTD) with a time resolution of ∼30–40 ps and hermetic coverage up to a pseudo-rapidity of |η|=3 is proposed by the Compact Muon Solenoid (CMS) experiment. An endcap part (1.6<|η|<3) of the MTD, called the endcap timing layer, will be based on low-gain avalanche detector (LGAD) technology. LGADs provide a good timing resolution due to a combination of a fast signal rise time and high signal-to-noise ratio. The performance of the ETL depends on optimising the crucial features of the sensors, namely; gain, signal homogeneity, fill factor, leakage current, uniformity of multiple-pad sensors and long term stability. The paper mainly focuses on the study of the fill factor of LGADs with varying temperature and irradiation at varying proton fluences as these sensors will be operated at low temperatures and are subjected to a high radiation environment.
The 3.1 production of LGADs from Hamamatsu Photonics K.K. (HPK) includes 2x2 sensors with different structures, in particular, different values of narrower inactive region widths between the pads, called the no-gain region. In this paper, the term interpad-gap is used instead of no-gain region in order to follow the conventional terminology. These sensors have been designed to study their fill factor, which is the ratio of the area within the active region (gain region) to the total sensor area. A comparative study on the dependence of breakdown voltage with the interpad-gap width for the sensors has been carried out. Using infrared light (as the electron–hole pair creation by IR laser mimics closely to the traversing of MIPs) from the Scanning-Transient Current Technique (Scanning-TCT) set-up shows that the fill factor does not vary significantly with a variation in temperature and irradiation at high proton fluences.
Light collection in scintillators ZnSe(X), where X is an isovalent dopant, was studied using Monte Carlo calculations. Optimum design was determined for detectors of “scintillator—Si-photodiode” ...type, which can involve either one scintillation element or scintillation layers of large area made of small-crystalline grains. The calculations were carried out both for determination of the optimum scintillator shape and for design optimization of light guides, on the surface of which the layer of small-crystalline grains is formed.
Abstract
Aluminium oxide (Al
2
O
3
) has been proposed as an alternative to thermal silicon dioxide (SiO
2
) as field insulator and surface passivation for silicon detectors, where it could ...substitute p-stop/p-spray insulation implants between pixels due to its negative oxide charge, and enable capacitive coupling of segments by means of its higher dielectric constant.
Al
2
O
3
is commonly grown by atomic layer deposition (ALD), which allows the deposition of thin layers with excellent precision.
In this work, we report the electrical characterization of single pad detectors (diodes) and MOS capacitors fabricated on magnetic Czochralski silicon substrates and using Al
2
O
3
as field insulator. Devices are studied by capacitance-voltage, current-voltage, and transient current technique measurements. We evaluate the influence of the oxygen precursors in the ALD process, as well as the effect of gamma irradiation, on the properties of these devices. We observe that leakage currents in diodes before the onset of breakdown are low for all studied ALD processes. Charge collection as measured by transient current technique (TCT) is also independent of the choice of oxygen precursor. The Al
2
O
3
films deposited with O
3
possess a higher negative oxide charge than films deposited by H
2
O, However, in diodes a higher oxide charge is linked to earlier breakdown, as has been predicted by simulation studies. A combination of H
2
and O
3
precursors results in a good compromise between the beneficial properties provided by the respective individual precursors.
We report on the fabrication of capacitively (AC) coupled n+-in-p pixel detectors on magnetic Czochralski silicon substrates. In our devices, we employ a layer of aluminium oxide (Al2O3) grown by ...atomic layer deposition (ALD) as dielectric and field insulator, instead of the commonly used silicon dioxide (SiO2). As shown in earlier research, Al2O3 thin films exhibit high negative oxide charge, and can thus serve as a substitute for p-stop/p-spray insulation implants between pixels. In addition, they provide far higher capacitance densities than SiO2 due to their high dielectric constant, permitting more efficient capacitive coupling of pixels. Furthermore, metallic titanium nitride (TiN) bias resistors are presented as an alternative to punch-through or poly-Si resistors.
Devices obtained by the above mentioned process are characterized by capacitance–voltage and current–voltage measurements, and by 2 MeV proton microprobe. Results show the expected high negative charge of the Al2O3 dielectric, uniform charge collection efficiency over large areas of pixels, and acceptable leakage current densities.
Abstract
The upgrade of the ALICE TPC will allow the experiment to cope with the high interaction rates foreseen for the forthcoming Run 3 and Run 4 at the CERN LHC. In this article, we describe the ...design of new readout chambers and front-end electronics, which are driven by the goals of the experiment. Gas Electron Multiplier (GEM) detectors arranged in stacks containing four GEMs each, and continuous readout electronics based on the SAMPA chip, an ALICE development, are replacing the previous elements. The construction of these new elements, together with their associated quality control procedures, is explained in detail. Finally, the readout chamber and front-end electronics cards replacement, together with the commissioning of the detector prior to installation in the experimental cavern, are presented. After a nine-year period of R&D, construction, and assembly, the upgrade of the TPC was completed in 2020.
The results of tests of an experimental prototype of a two-energy scintillation detector, which is based on a two-layer composite system of fine-crystalline ZnSe(Al) and LGSO(Ce) scintillators, are ...presented and its properties are determined. The X-rays spectra for each element of the detector were obtained. The analysis of these spectra allowed determination of the energy efficiency of the X-ray absorption for each element of the detector in an energy range of 30–70 keV. The dependences of proper signals from photodetectors under the action of X rays (the tube voltage varied from 40 to 90 kV) were restored. The corresponding X-ray spectra are presented as well. The dependences of scintillation signals from disperse ZnSe(Al) and LGSO(Ce) scintillators on the X-ray tube voltage are presented (the voltage varied from 40 to 70 keV). Due to the high registration efficiency of relatively low-energy X rays (up to 70 keV), this detector can be used not only in engineering introscopy (customs baggage control, mail, cargo-container, and vehicle checks, etc.), but also in various fields of medical radiology.
We present the current status of our project of developing a photon counting detector for medical imaging. An example motivation lays in producing a monitoring and dosimetry device for boron neutron ...capture therapy, currently not commercially available. Our approach combines in-house developed detectors based on cadmium telluride or thick silicon with readout chip technology developed for particle physics experiments at CERN. Here we describe the manufacturing process of our sensors as well as the processing steps for the assembly of first prototypes. The prototypes use currently the PSI46digV2.1-r readout chip. The accompanying readout electronics chain that was used for first measurements will also be discussed. Finally we present an advanced algorithm developed by us for image reconstruction using such photon counting detectors with focus on boron neutron capture therapy. This work is conducted within a consortium of Finnish research groups from Helsinki Institute of Physics, Aalto University, Lappeenranta-Lahti University of Technology LUT and Radiation and Nuclear Safety Authority (STUK) under the RADDESS program of Academy of Finland. Keywords: Solid state detectors, X-ray detectors, Gamma detectors, Neutron detectors, Instrumentation for hadron therapy, Medical-image reconstruction methods and algorithms.
The upgrade of the ALICE TPC will allow the experiment to cope with the high interaction rates foreseen for the forthcoming Run 3 and Run 4 at the CERN LHC. In this article, we describe the design of ...new readout chambers and front-end electronics, which are driven by the goals of the experiment. Gas Electron Multiplier (GEM) detectors arranged in stacks containing four GEMs each, and continuous readout electronics based on the SAMPA chip, an ALICE development, are replacing the previous elements. The construction of these new elements, together with their associated quality control procedures, is explained in detail. Finally, the readout chamber and front-end electronics cards replacement, together with the commissioning of the detector prior to installation in the experimental cavern, are presented. After a nine-year period of R&D, construction, and assembly, the upgrade of the TPC was completed in 2020.
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