3D Silicon Detectors Research Articles

3D silicon detectors for neutron imaging applications

Neutron detection is of great importance in many fields spanning from scientific research, to nuclear science, and to medical application. The development of silicon-based neutron detectors with enhanced neutron detection efficiency can offer several advantages such as spatial resolution, enhanced dynamic range and background discrimination. In this work, increased detection efficiency is pursued by fabricating high aspect ratio 3D micro-structures filled with neutron converting materials (B4C) on planar silicon detectors. An in-depth feasibility study was carried out in all aspects of the sensor fabrication technology. Passivation of the etched structures was studied in detail, to ensure good electrical performance. The conformal deposition of B4C with a newly developed process showed excellent results. Preliminary electrical characterisation of the completed devices is promising, and detectors have been mounted on dedicated boards in view of the upcoming tests with neutrons.

Silicon Detectors for the LHC Phase-II Upgrade and Beyond – RD50 Status Report

A large R&D program has been underway to develop silicon sensors with sufficient radiation tolerance for LHC-Phase-II trackers and the next generation of collision experiments. Key areas of recent RD50 research include new technologies such as CMOS and Low Gain Avalanche Detectors (LGADs), where a dedicated multiplication layer to create a high field region is built into the sensor. We also seek for a deeper understanding of the connection between macroscopic sensor properties such as radiation-induced increase of leakage current, effective doping concentration and trapping, and the microscopic properties at the defect level. Another strong activity is the development of advanced sensor types, like 3D silicon detectors. We will present the state of the art in silicon detectors at radiation levels corresponding to LHC-Phase-II fluences and beyond. Based on our results, we will give an outlook towards the silicon detectors to be used for particle detectors at future colliders like the FCC.

Optimal Design of Multiple Floating Rings for 3D Large-Area Trench Electrode Silicon Detector.

The 3D electrode silicon detector eliminates the limit of chip thickness, so it can reduce the electrode spacing (small area) and effectively improve the radiation hardness. In order to expand the application range of the 3D electrode detector, we first propose a 3D large-area silicon detector with a large sensitive volume, and realize multiple floating rings on the upper and lower surfaces of the detector. Due to the influence of different charge states and energy levels in the Si-SiO2 interface system, the top and bottom of the 3D P+ electrode are more prone to avalanche breakdown in the 3D large-area detector before the detector is completely depleted or the carrier saturation drift velocity is reached. Moreover, the electric field distribution becomes very uneven under the influence of the oxide charge, resulting in non-equilibrium carriers that cannot drift in the optimal path parallel to the detector surface. In this paper, the effect of floating rings on the performance of a 3D large-area silicon detector is studied by TCAD simulation. It can increase avalanche breakdown voltage by 14 times in a non-irradiated environment, and can work safely in a moderate irradiated environment. The charge collection efficiency can be effectively improved by optimizing the drift path.

Manufacturability and Stress Issues in 3D Silicon Detector Technology at IMB-CNM.

This paper provides an overview of 3D detectors fabrication technology developed in the clean room of the Microelectronics Institute of Barcelona (IMB-CNM). Emphasis is put on manufacturability, especially on stress and bow issues. Some of the technological solutions proposed at IMB-CNM to improve manufacturability are presented. Results and solutions from other research institutes are also mentioned. Analogy with through-silicon-via technology is drawn. This article aims at giving hints of the technology improvements implemented to upgrade from a R&D process to a mature technology.

Timing performance of small cell 3D silicon detectors

A silicon 3D detector with a single cell of 50 × 50 μm2 was produced and evaluated for timing applications. The measurements of time resolution were performed for 90Sr electrons with dedicated electronics used also for determining time resolution of Low Gain Avalanche Detectors (LGADs). The measurements were compared to those with LGADs and also simulations. The studies showed that the dominant contribution to the timing resolution comes from the time walk originating from different induced current shapes for hits over the cell area. This contribution decreases with higher bias voltages, lower temperatures and smaller cell sizes. It is around 30 ps for a 3D detector of 50 × 50 μm2 cell at 150 V and −20 °C, which is comparable to the time walk due to Landau fluctuations in LGADs. It even improves for inclined tracks and larger pads composed of multiple cells. A good agreement between measurements and simulations was obtained, thus validating the simulation results.

Efficiency of depleted UO2 based semiconductor neutron detectors in direct and indirect configuration—A GEANT4 simulation study

In the present work, Monte Carlo simulations using GEANT4 are carried out to estimate the efficiency of semiconductor neutron detectors with depleted UO2 (DUO2) as converter material, in both planar (direct and indirect) and 3D geometry (cylindrical perforation and trenches structure) configurations. The simulations were conducted for neutrons of variable energy viz., thermal (25 meV) and fast (1 to 10 MeV) that were incident on varying thicknesses (0.25 μm to 1000 μm), diameters (1 μm to 9 μm) and widths (1 μm to 9 μm) along with depths (50 μm to 275 μm) of DUO2 for planar, cylindrical perforated and trench structures, respectively. In the case of direct planar detectors, efficiency was found to increase with the thickness of DUO2 and the rate at which efficiency increased was found to follow the macroscopic fission cross section at the corresponding neutron energy. In the case of indirect planar detector, efficiency was lower as compared to direct configuration and was found to saturate beyond a thickness of ∼3 μm. This saturation is explained on the basis of mean free path of neutrons in the DUO2 material. For the 3D perforated silicon detectors of cylindrical (trench) geometry, backfilled with DUO2, the efficiency for detection of thermal neutrons ∼25 meV and fast neutrons ∼ typical energy of 10 MeV was found to be ∼0.0159% (∼0.0177%) and ∼0.0088% (0.0098%), respectively. These efficiency values were two (one) order values higher than planar indirect detector for thermal (fast) neutrons. Histogram plots were also obtained from the GEANT4 simulations to monitor the energy distribution of fission products in planar (direct and indirect) and 3D geometry (cylindrical and trench) configurations. These plots revealed that, for all the detector configurations, the energy deposited by the fission products are higher as compared to the typical gamma ray background. Thus, for detectors with DUO2 as converter material, higher values of low level discriminator (LLD) can be set, so as to achieve good background discrimination.

3D detectors with high space and time resolution

For future high luminosity LHC experiments it will be important to develop new detector systems with increased space and time resolution and also better radiation hardness in order to operate in high luminosity environment. A possible technology which could give such performances is 3D silicon detectors. This work explores the possibility of a pixel geometry by designing and simulating different solutions, using Sentaurus Tecnology Computer Aided Design (TCAD) as design and simulation tool, and analysing their performances. A key factor during the selection was the generated electric field and the carrier velocity inside the active area of the pixel.

Radiation Hard Silicon Particle Detectors for Phase-II LHC Trackers

The major LHC upgrade is planned after ten years of accelerator operation. It is foreseen to significantly increase the luminosity of the current machine up to 1035 cm−2s−1 and operate as the upcoming High Luminosity LHC (HL-LHC) . The major detectors upgrade, called the Phase-II Upgrade, is also planned, a main reason being the aging processes caused by severe particle radiation. Within the RD50 Collaboration, a large Research and Development program has been underway to develop silicon sensors with sufficient radiation tolerance for HL-LHC trackers. In this summary, several results obtained during the testing of the devices after irradiation to HL-LHC levels are presented. Among the studied structures, one can find advanced sensors types like 3D silicon detectors, High-Voltage CMOS technologies, or sensors with intrinsic gain (LGAD). Based on these results, the RD50 Collaboration gives recommendation for the silicon detectors to be used in the detector upgrade.

3D Simulation and Modeling of Ultra-fast 3D Silicon Detectors

3D detectors with very small electrode spacing can provide ultra-fast detection due to their extremely small charge collection time. Since the detector full depletion voltage and charge collection time are independent to the detector thickness, ultra-fast 3D detectors can be made relatively thick (or not too thin, ~200 μm) to ensure a large signal. The results of the 3D simulations and modeling of 3D silicon detectors with very small electrode spacing and relatively large thickness will be shown in this paper. The column spacing LP is in the range of 5 μm to 10 μm. At a bias voltage of only a few volts, the electric field in the detector can be large enough to ensure the carrier saturation drift velocity in most volume of the detector, and the detector charge collection time there can be as short as 10’s of ps. In this paper, we will analysis the simulated electrical characteristics of this detector structure through systematic 3D simulations using the Silvaco’s TCAD tool. Profiles of detector electric potential and electric field will be presented. We will investigate the region of low electric field (the “slow region”) in the detector. We will also exam whether the detector reach the breakdown condition at operation voltages suggested in this work.

A combined surface and bulk TCAD damage model for the analysis of radiation detectors operating at HL-LHC fluences

In this work we present the development and the application of a new TCAD modelling scheme to simulate the effects of radiation damage on silicon radiation detectors at the very high fluence levels expected at High Luminosity LHC (up to 2 × 1016 1MeV n/cm2). In particular, we propose a combined approach for the analysis of the surface effects (oxide charge build-up and interface trap states introduction) as well as bulk effects (deep level traps and/or recombination centers introduction). Experimental measurements have been carried out aiming at: i) extraction from simple test structures of relevant parameters to be included within the TCAD model and ii) validation of the new modelling scheme through comparison with measurements of different test structures (e.g. different technologies) before and after irradiation. The good agreements between experimental measurements and simulation findings foster the suitability of the TCAD modelling approach as a predictive tool for investigating the radiation detector behavior at different fluences and operating conditions. This would allow the design and optimization of innovative 3D and planar silicon detectors for future HL-LHC High Energy Physics experiments.

Initial results from new 3D neutron detectors

In this paper we report the initial results from our second generation of 3D silicon detectors for neutrons. The devices are briefly described and the first functional characterization tests carried out in laboratory before coupling to neutron converter material are reported. Particular emphasis is given to the read-out system used for the suppression of signals induced by γ-rays, that is one of the main issues in neutron detection. Experimental results are discussed with the aid of TCAD simulations.

SPACE DOSIMETRY MEASUREMENTS IN THE STRATOSPHERE USING DIFFERENT ACTIVE AND PASSIVE DOSIMETRY SYSTEMS.

Several measurements have been performed on the cosmic radiation field from the surface of the Earth up to the maximum altitudes of research aeroplanes. However, there is only limited information about that between 15 and 30 km altitudes. In order to study the radiation environment in the stratosphere, an experiment was built by students from Hungarian universities that flew on board the BEXUS (Balloon Experiments for University Students) stratospheric balloon in Northern Sweden, from the ESRANGE Space Center. The main technical goals of the experiment were to test at the first time the TRITEL 3D silicon detector telescope system in close to space conditions and to develop a balloon technology platform for advanced cosmic radiation and dosimetric measurements. The main scientific goals were to give an assessment of the cosmic radiation field at the altitude of the BEXUS balloons, to use the TRITEL system to determine dosimetric and radiation quantities during the balloon flight and to intercompare the TRITEL and Pille results to provide a correction factor for the Pille measurements. To fulfil the scientific and technological objectives, several different dosimeter systems were included in the experiment: an advanced version of the TRITEL silicon detector telescope, Geiger-Müller (GM) counters and Pille thermoluminescent dosimeters. The float altitude of the BEXUS balloon was ∼28.6 km; the total flight time was ∼4 h. Measurement data from the active instruments were received in real time by the ground team during the mission. There were no failures in the operation of the system; everything worked as expected. This article presents the scientific goals and results in detail. From the TRITEL measurements, the linear energy transfer spectra, the average quality factor of the cosmic radiation as well as the absorbed dose and the dose equivalent were determined. Estimations for the uncertainty in the TRITEL measurements were given. The deposited energy spectra measured with the TRITEL instrument were compared with the count rates measured with the GM counters. The experiences and results gained in the frame of the project will be used in the evaluation of TRITEL data from measurements on board the International Space Station. As an outlook a short overview is given of the planned rocket radiation experiments based on the system used in the BEXUS programme.

Preliminary microdosimetric measurements with ultra-thin 3D silicon detectors of a 62 MeV proton beam

In this paper we present the first direct microdosimetric measurements of 62 MeV proton beams using ultra-thin 3D silicon detectors at different depths in a solid-water phantom. The detectors have 3D columnar electrodes that penetrate a 10 μm thick silicon membrane, resulting in a micrometric scale sensitive volume. The 62 MeV proton beam was generated in a cyclotron CYCLONE-110 at Centre de Recherches du Cyclotron (CRC) at Louvain-la-Neuve. The proton beam average energy was modulated with stacked tissue-equivalent solid water layers. The energy loss profile was studied through the Bragg curve and pulse height spectra. The experimental silicon microdosimetric spectra showed the lineal energy dependence along the Bragg curve. This work demonstrates the potential capability of the ultra-thin 3D silicon detectors as 3D detector technology-based microdosimeters.

3D Radiation Detectors: Charge Collection Characterisation and Applicability of Technology for Microdosimetry

A study of charge collection in SINTEF 3D active edge silicon detectors was carried out at ANSTO using Ion Beam Induced Charge (IBIC) technique. An IBIC study has shown that several different geometries of 3D detectors have full depletion under low applied bias. The effect of fast neutron and gamma radiation on their charge collection efficiency was also investigated. A 3D active edge silicon detector technology has demonstrated extremely promising performance for application of the 3D Sensitive Volumes (SVs) fabrication methods to SOI microdosimetry.

72: First investigations of Ultra-Thin 3D silicon detectors as microdosimeters

IMB-CNM (CSIC) has developed a new type of threedimensional diode on ultrathin SOI silicon wafers with 3D columnar structures with P-N junctions fabricated with micromachining techniques for plasma diagnostic applications or neutron detection in demanding environments [1, 2]. The three-dimensional electrodes are columns etched through the silicon instead of being deposited on the surface like in the standard planar diodes. The sensitive volume is a silicon membrane only 10 microns thick (fig.1). The ultra-thin sensors have shown to be insensitive to the gamma radiation background, their membrane structure avoids the backscattering contributions from the supporting silicon wafer and the confinement of the electric field given by the columnar electrodes reduces charge sharing. All these characteristics make the ultra-thin 3D devices the perfect candidates for microdosimetry. Recently, IMB-CNM have carried out the first tests of these devices with beams of 62MeV protons and 95MeV/u C ions. The results of these first experiments show that, although they were not specifically designed for microdosimetric applications, the detectors with ultra-thin 3D structure are able to characterize the therapeutic hadron beams. Results from these proof-of-concept tests will be presented and compared with Monte Carlo simulations using MCNPX and Geant4 codes.

Testbeam and laboratory test results of irradiated 3D CMS pixel detectors

The CMS silicon pixel detector is the tracking device closest to the LHC p–p collisions, which precisely reconstructs the charged particle trajectories. The planar technology used in the current innermost layer of the pixel detector will reach the design limit for radiation hardness at the end of Phase I upgrade and will need to be replaced before the Phase II upgrade in 2020. Due to its unprecedented performance in harsh radiation environments, 3D silicon technology is under consideration as a possible replacement of planar technology for the High Luminosity-LHC or HL-LHC. 3D silicon detectors are fabricated by the Deep Reactive-Ion-Etching (DRIE) technique which allows p- and n-type electrodes to be processed through the silicon substrate as opposed to being implanted through the silicon surface. The 3D CMS pixel devices presented in this paper were processed at FBK. They were bump bonded to the current CMS pixel readout chip, tested in the laboratory, and testbeams carried out at FNAL with the proton beam of 120GeV/c. In this paper we present the laboratory and beam test results for the irradiated 3D CMS pixel devices.

Silicon sensors for HL-LHC tracking detectors

It is foreseen to significantly increase the luminosity of the LHC by upgrading towards the HL-LHC (High Luminosity LHC) in 2021 in order to harvest the maximum physics potential. After the upgrade, unprecedented levels of radiation will require the experiments to upgrade their tracking detectors to withstand hadron fluences equivalent to over 1016 1MeV neutrons per cm2. Within the RD50 Collaboration, a massive R&D program is underway to develop silicon sensors with sufficient radiation tolerance. Recent defect characterization and Edge-TCT measurement results improved the understanding of irradiated detector performance. RD50 results show that sensors with n-side readout, easiest made with p-type silicon, have a superior radiation hardness due to the high overlap of electric and weighting field after irradiation, larger contribution of electrons to the total signal and finally due to charge multiplication which may enhance the collected charge at high bias voltages in this type of detector. A further area of activity is the development of advanced sensor types like 3D silicon and thin pixel detectors designed for the extreme radiation levels expected for the inner layers.

Performance of CMS 3D silicon pixel detectors before and after irradiation

Three-dimensional (3D) silicon detectors are emerging as one of the most promising technologies for the innermost layers of tracking devices for the foreseen upgrades of the LHC. 3D sensors compatible with the CMS readout, fabricated at FBK (Trento, Italy), were tested in the laboratory and with a 120GeV/c proton beam at the FNAL test beam facility, before and after irradiation up to a fluence of 3.5×1015neq/cm2. Preliminary results of the data analysis are presented.

Simulation and laboratory test results of 3D CMS pixel detectors for HL-LHC

The CMS pixel detector is the innermost tracking device at the LHC, reconstructing interaction vertices and charged particle trajectories. The current planar sensors located in the innermost layer of the pixel detector will be exposed to very high fluences which will degrade their performances. As a possible replacement for planar pixel sensors in the High Luminosity-LHC (HL-LHC), 3D silicon technology is under consideration due to its expected good performance in harsh radiation environments. Studies are also in progress for using 3D silicon pixel detectors in near-beam proton spectrometers at the LHC. Deep Reactive Ion Etching (DRIE) plays a key role in fabricating 3D silicon detectors in which readout and ohmic electrodes are processed through the silicon substrate instead of being implanted on the silicon surface. 3D pixel devices considered in this study were processed at FBK (Trento, Italy), bump bonded to the CMS pixel readout chip, and characterized in the laboratory. Numerical simulations were also carried out. We report on selected results from laboratory measurements and TCAD simulations.

Simulation and characterization of a dual-type 3-dimensional silicon detector

A three-dimensional (3D) silicon detector is an alternative semiconductor detector for high radiation environments. The 3D detector has several advantages such as radiation hardness so it can be used for a longer period of time in a high radiation environment without replacement. A dual-type 3D silicon detector is simulated, and the full depletion voltage, capacitance, response time and charge collection efficiency are measured.