arXiv subjects

G. Kramberger

Publications and source records attributed to G. Kramberger.

At least 19 recordsLinked to original sources

arXiv2026

Tracking and timing measurements on irradiated TI-LGADs

Trench-isolated (TI) LGADs, developed at FBK, are pixelated LGAD implementations where pads are separated by physical trenches etched within the silicon substrate and filled with a dielectric material. Developed as a solution to the LGAD fill factor problem, this technology provides a path towards 4D tracking with reduced inefficiencies in the interpad regions. Through a dedicated 120 GeV SPS pion test beam campaign, the time resolution, efficiency, and inter-pad distance of carbon infused irradiated TI-LGADs is presented. Fluences up to 2.5$~$x$~$$10^{15}$$~$n$_{\text{eq}}$$~$cm$^{-2}$ are evaluated, for single trench implementations with varied trench width at a temperature of -25 $^o$C. The results show an interpad distance degradation with the irradiation of the detector and an optimal time resolution between 35 ps and 45 ps for all studied devices.

physics.ins-det↗

arXiv2025

Beam-test evaluation of pre-production Low Gain Avalanche Detectors for the ATLAS High Granularity Timing Detector

The High Granularity Timing Detector (HGTD) will be installed in the ATLAS experiment as part of the Phase-II upgrade for the High Luminosity-Large Hadron Collider (HL-LHC). It will mitigate pile-up effects in the forward region, and measure per bunch luminosity. The design of HGTD is based on Low Gain Avalanche Detector (LGAD) sensors. This paper presents the results of beam-test campaigns conducted at CERN and DESY in 2023 and 2024 on single LGADs from HGTD pre-production test structures, before and after neutron irradiation up to fluences of $2.5 \times 10^{15}~\mathrm{n_{eq}/cm^2}$. The tested LGADs can meet HGTD requirements in terms of charge collection, time resolution, and hit efficiency, even under HL-LHC end-of-life conditions, supporting their deployment in the final detector.

physics.ins-det↗

arXiv2025

Thermal Cycling Reliability of Hybrid Pixel Sensor Modules for The ATLAS High Granularity Timing Detector

The reliability of bump connection structures has become a critical aspect of future silicon detectors for particle physics. The High Granularity Timing Detector (HGTD) for the ATLAS experiment at the High-Luminosity Large Hadron Collider will require 8032 hybrid pixel sensor modules, composed of two Low Gain Avalanche Diode sensors bump-bonded to two readout ASICs and glued to a passive PCB. The detector will operate at low temperature (-30 degrees Celsius) to mitigate the impact of irradiation. The thermomechanical reliability of flip-chip bump connections in HGTD modules is a critical concern, particularly due to their characteristically lower bump density (pixel pitch dimensions of 1.3 mm by 1.3 mm). This paper elaborates on the challenges arising from this design characteristic. Finite element analysis and experimental testing were employed to investigate failure modes in the flip-chip bump structures under thermal cycling from -45 degrees Celsius to 40 degrees Celsius and to guide the module redesign. The optimized design demonstrates significantly enhanced robustness and is projected to fulfill the full lifetime requirements of the HGTD.

physics.ins-det↗

arXiv2025

Performance of neutron and proton irradiated AC-LGAD sensors

Characterization of strip and pixel AC-LGAD devices with both laser TCT and probe station (IV/CV) will be shown on AC-LGADs irradiated with 1 MeV reactor neutrons at JSI/Ljubljana and with 400~MeV protons at FNAL ITA to fluences from 1e13~$n_{eq}/cm^2$ to a few times 1e15~$n_{eq}/cm^2$. This study was conducted within the scope of the ePIC detector time of flight (TOF) layer R\&D program at the EIC, which will feature AC-LGADs with strip and pixel geometry. Sensors in the TOF layer will receive up to 1e13~$n_{eq}/cm^2$ fluence over the lifetime of the experiment.

physics.ins-det↗

arXiv2024

Measurements of time resolution of the RD50-MPW2 DMAPS prototype using TCT and $^{90}\mathrm{Sr}$

Results in this paper present an in-depth study of time resolution for active pixels of the RD50-MPW2 prototype CMOS particle detector. Measurement techniques employed include Backside- and Edge-TCT configurations, in addition to electrons from a $^{90}\mathrm{Sr}$ source. A sample irradiated to $5\cdot 10^{14}\,\mathrm{n}_\mathrm{eq}/\mathrm{cm}^2$ was used to study the effect of radiation damage. Timing performance was evaluated for the entire pixel matrix and with positional sensitivity within individual pixels as a function of the deposited charge. Time resolution obtained with TCT is seen to be uniform throughout the pixel's central region with approx. $220\,\mathrm{ps}$ at $12\,\mathrm{ke}^-$ of deposited charge, degrading at the edges and lower values of deposited charge. $^{90}\mathrm{Sr}$ measurements show a slightly worse time resolution as a result of delayed events coming from the peripheral areas of the pixel.

physics.ins-det↗

arXiv2023

Destructive breakdown studies of irradiated LGADs at beam tests for the ATLAS HGTD

In the past years, it has been observed at several beam test campaigns that irradiated LGAD sensors break with a typical star shaped burn mark when operated at voltages much lower than those at which they were safely operated during laboratory tests. The study presented in this paper was designed to determine the safe operating voltage that these sensors can withstand. Many irradiated sensors from various producers were tested in two test beam facilities, DESY (Hamburg) and CERN-SPS (Geneva), as part of ATLAS High Granularity Timing Detector (HGTD) beam tests. The samples were placed in the beam and kept under bias over a long period of time in order to reach a high number of particles crossing each sensor. Both beam tests lead to a similar conclusion, that these destructive events begin to occur when the average electric field in the sensor becomes larger than 12 Volts per micrometre.

physics.ins-det↗

arXiv2023

Gain Recovery in Heavily Irradiated Low Gain Avalanche Detectors by High Temperature Annealing

Studies of annealing at temperatures up to 450$^\circ$C with LGADs irradiated with neutrons are described. It was found that the performance of LGADs irradiated with 1.5e15 n/cm$^2$ was already improved at 5 minutes of annealing at 250$^\circ$C. Isochronal annealing for 30 minutes in 50$^\circ$C steps between 300$^\circ$C and 450$^\circ$C showed that the largest beneficial effect of annealing is at around 350$^\circ$C. Another set of devices was annealed for 60 minutes at 350$^\circ$C and this annealing significantly increased V$_{\mathrm{gl}}$. The effect is equivalent to reducing the effective acceptor removal constant by a factor of $\sim$ 4. Increase of V$_{\mathrm{gl}}$ is the consequence of increased effective space charge in the gain layer caused by formation of electrically active defects or re-activation of interstitial Boron atoms.

physics.ins-det↗

arXiv2023

Performance in beam tests of Carbon-enriched irradiated Low Gain Avalanche Detectors for the ATLAS High Granularity Timing Detector

The High Granularity Timing Detector (HGTD) will be installed in the ATLAS experiment to mitigate pile-up effects during the High Luminosity (HL) phase of the Large Hadron Collider (LHC) at CERN. Low Gain Avalanche Detectors (LGADs) will provide high-precision measurements of the time of arrival of particles at the HGTD, improving the particle-vertex assignment. To cope with the high-radiation environment, LGADs have been optimized by adding carbon in the gain layer, thus reducing the acceptor removal rate after irradiation. Performances of several carbon-enriched LGAD sensors from different vendors, and irradiated with high fluences of 1.5 and 2.5 x 10^15 neq/cm2, have been measured in beam test campaigns during the years 2021 and 2022 at CERN SPS and DESY. This paper presents the results obtained with data recorded by an oscilloscope synchronized with a beam telescope which provides particle position information within a resolution of a few um. Collected charge, time resolution and hit efficiency measurements are presented. In addition, the efficiency uniformity is also studied as a function of the position of the incident particle inside the sensor pad.

physics.ins-det↗

arXiv2022

Study of neutron irradiation effects in Depleted CMOS detector structures

In this paper results of Edge-TCT and I-V measurements with passive test structures made in LFoundry 150 nm HV-CMOS process on p-type substrates with different initial resistivities ranging from 0.5 to 3 k$Ω$cm are presented. Samples were irradiated with reactor neutrons up to a fluence of 2$\cdot$10$^{15}$ n$_{\mathrm{eq}}$/cm$^2$. Depletion depth was measured with Edge-TCT. Effective space charge concentration $N_{\mathrm{eff}}$ was estimated from the dependence of depletion depth on bias voltage and studied as a function of neutron fluence. Dependence of $N_{\mathrm{eff}}$ on fluence changes with initial acceptor concentration in agreement with other measurements with p-type silicon. Long term accelerated annealing study of $N_{\mathrm{eff}}$ and detector current up to 1280 minutes at 60$^\circ$C was made. It was found that $N_{\mathrm{eff}}$ and current in reverse biased detector behaves as expected for irradiated silicon.

physics.ins-det↗

arXiv2022

Tuning of gain layer doping concentration and Carbon implantation effect on deep gain layer

Next generation Low Gain Avalanche Diodes (LGAD) produced by Hamamatsu photonics (HPK) and Fondazione Bruno Kessler (FBK) were tested before and after irradiation with ~1MeV neutrons at the JSI facility in Ljubljana. Sensors were irradiated to a maximum 1-MeV equivalent fluence of 2.5E15 Neq/cm2. The sensors analysed in this paper are an improvement after the lessons learned from previous FBK and HPK productions that were already reported in precedent papers. The gain layer of HPK sensors was fine-tuned to optimize the performance before and after irradiation. FBK sensors instead combined the benefit of Carbon infusion and deep gain layer to further the radiation hardness of the sensors and reduced the bulk thickness to enhance the timing resolution. The sensor performance was measured in charge collection studies using \b{eta}-particles from a 90Sr source and in capacitance-voltage scans (C-V) to determine the bias to deplete the gain layer. The collected charge and the timing resolution were measured as a function of bias voltage at -30C. Finally a correlation is shown between the bias voltage to deplete the gain layer and the bias voltage needed to reach a certain amount of gain in the sensor. HPK sensors showed a better performance before irradiation while maintaining the radiation hardness of the previous production. FBK sensors showed exceptional radiation hardness allowing a collected charge up to 10 fC and a time resolution of 40 ps at the maximum fluence.

physics.ins-det↗

arXiv2021

Characterisation of analogue front end and time walk in CMOS active pixel sensor

In this work we investigated a method to determine time walk in an active silicon pixel sensor prototype using Edge-TCT with infrared laser charge injection. Samples were investigated before and after neutron irradiation to 5e14 neq/cm2. Threshold, noise and calibration of the analogue front end were determined with external charge injection. A spatially sensitive measurement of collected charge and time walk was carried out with Edge-TCT, showing a uniform charge collection and output delay in pixel centre. On pixel edges charge sharing was observed due to finite beam width resulting in smaller signals and larger output delay. Time walk below 25 ns was observed for charge above 2000 electrons at a threshold above the noise level. Time walk measurement with external charge injection yielded identical results.

physics.ins-det↗

arXiv2021

Bistability of the BiOi complex and its implications on evaluating the acceptor removal

The dependencies of the B$_{i}$O$_{i}$ defect concentration on doping, irradiation fluence and particle type in p-type silicon diodes have been investigated. We evidenced that large data scattering occurs for fluences above $10^{12}$ 1 MeV neutrons/cm$^2$, becoming significant larger for higher fluences. We show that the B$_{i}$O$_{i}$ defect is metastable, with two configurations A and B, of which only A is detected by Deep Level Transient Spectroscopy and Thermally Stimulated Currents techniques. The defect's electrical activity is influenced by the inherent variations in ambient and procedural experimental conditions, resulting not only in a large scattering of the results coming from the same type of measurement but making any correlation between different types of experiments difficult. It is evidenced that the variations in [B$_{i}$O$_{i}^\mathrm{A}$] are triggered by subjecting the samples to an excess of carriers, by either heating or an inherent short exposure to ambient light when manipulating the samples prior to experiments. It causes $\approx$7h variations in both, the [B$_{i}$O$_{i}^\mathrm{A}$] and in the effective space charge. The analyses of structural damage in a diode irradiated with 10$^{19}$ 1 MeV neutrons/cm$^2$ revealed that the Si structure remains crystalline and vacancies and interstitials organize in parallel tracks normal to the Si-SiO$_{2}$ interface.

cond-mat.mtrl-sci↗

arXiv2020

Experimental Study of Acceptor Removal in UFSD

The performance of the Ultra-Fast Silicon Detectors (UFSD) after irradiation with neutrons and protons is compromised by the removal of acceptors in the thin layer below the junction responsible for the gain. This effect is tested both with C-V measurements of the doping concentration and with measurements of charge collection using charged particles. We find a perfect linear correlation between the bias voltage to deplete the gain layer determined with C-V and the bias voltage to collect a defined charge, measured with charge collection. An example for the usefulness of this correlation is presented.

physics.ins-det↗

arXiv2020

Measurements with silicon detectors at extreme neutron fluences

Thin pad detectors made from 75 $μ$m thick epitaxial silicon on low resistivity substrate were irradiated with reactor neutrons to fluences from 2.5$\times 10^{16}$ n/cm$^2$ to 1$\times 10^{17}$ n/cm$^2$. Edge-TCT measurements showed that the active detector thickness is limited to the epitaxial layer and does not extend into the low resistivity substrate even after the highest fluence. Detector current was measured under reverse and forward bias. The forward current was higher than the reverse at the same voltage but the difference gets smaller with increasing fluence. Rapid increase of current (breakdown) above ~ 700 V under reverse bias was observed. An annealing study at 60$^\circ$C was made to 1200 minutes of accumulated annealing time. It showed that the reverse current anneals with similar time constants as measured at lower fluences. A small increase of forward current due to annealing was seen. Collected charge was measured with electrons from $^{90}$Sr source in forward and reverse bias configurations. Under reverse bias the collected charge increased linearly with bias voltage up to 6000 electrons at 2.5$\times 10^{16}$ n/cm$^2$ and 3000 electrons at 1$\times 10^{17}$ n/cm$^2$. Rapid increase of noise was measured above $\sim$ 700 V reverse bias due to breakdown resulting in worse S/N ratio. At low bias voltages slightly more charge is measured under forward bias compared to reverse. However better S/N is achieved under reverse bias. Effective trapping times were estimated from charge collection measurements under forward bias showing that at high fluences they are much longer than values extrapolated from low fluence measurements - at 1$\times 10^{17}$ n/cm$^2$ a factor of 6 larger value was measured.

physics.ins-det↗

arXiv2020

Effect of deep gain layer and Carbon infusion on LGAD radiation hardness

The properties of 50 um thick Low Gain Avalanche Diode (LGAD) detectors manufactured by Hamamatsu photonics (HPK) and Fondazione Bruno Kessler (FBK) were tested before and after irradiation with 1 MeV neutrons. Their performance were measured in charge collection studies using b-particles from a 90Sr source and in capacitance-voltage scans (C-V) to determine the bias to deplete the gain layer. Carbon infusion to the gain layer of the sensors was tested by FBK in the UFSD3 production. HPK instead produced LGADs with a very thin, highly doped and deep multiplication layer. The sensors were exposed to a neutron fluence from 4e14 neq/cm2 to 4e15 neq/cm2. The collected charge and the timing resolution were measured as a function of bias voltage at -30C, furthermore the profile of the capacitance over voltage of the sensors was measured.

physics.ins-det↗

arXiv2020

Beam test results of IHEP-NDL Low Gain Avalanche Detectors(LGAD)

To meet the timing resolution requirement of up-coming High Luminosity LHC (HL-LHC), a new detector based on the Low-Gain Avalanche Detector(LGAD), High-Granularity Timing Detector (HGTD), is under intensive research in ATLAS. Two types of IHEP-NDL LGADs(BV60 and BV170) for this update is being developed by Institute of High Energy Physics (IHEP) of Chinese Academic of Sciences (CAS) cooperated with Novel Device Laboratory (NDL) of Beijing Normal University and they are now under detailed study. These detectors are tested with $5GeV$ electron beam at DESY. A SiPM detector is chosen as a reference detector to get the timing resolution of LGADs. The fluctuation of time difference between LGAD and SiPM is extracted by fitting with a Gaussian function. Constant fraction discriminator (CFD) method is used to mitigate the effect of time walk. The timing resolution of $41 \pm 1 ps$ and $63 \pm 1 ps$ are obtained for BV60 and BV170 respectively.

physics.ins-det↗

arXiv2020

Radiation Campaign of HPK Prototype LGAD sensors for the High-Granularity Timing Detector (HGTD)

We report on the results of a radiation campaign with neutrons and protons of Low Gain Avalanche Detectors (LGAD) produced by Hamamatsu (HPK) as prototypes for the High-Granularity Timing Detector (HGTD) in ATLAS. Sensors with an active thickness of 50~$μ$m were irradiated in steps of roughly 2$\times$ up to a fluence of $3\times10^{15}~\mathrm{n_{eq}cm^{-2}}$. As a function of the fluence, the collected charge and time resolution of the irradiated sensors will be reported for operation at $-30^{\circ}$.

physics.ins-det↗

arXiv2020

Properties of HPK UFSD after neutron irradiation up to 6e15 n/cm2

In this paper we report results from a neutron irradiation campaign of Ultra-Fast Silicon Detectors (UFSD) with fluences of 1e14, 3e14, 6e14, 1e15, 3e15, 6e15 n/cm2. The UFSD used in this study are circular 50 micro-meter thick Low-Gain Avalanche Detectors (LGAD), with a 1.0 mm diameter active area. They have been produced by Hamamatsu Photonics (HPK), Japan, with pre-radiation internal gain in the range 10-100 depending on the bias voltage. The sensors were tested pre-irradiation and post-irradiation with minimum ionizing particle (MIPs) from a 90Sr based \b{eta}-source. The leakage current, internal gain and the timing resolution were measured as a function of bias voltage at -20C and -30C. The timing resolution was extracted from the time difference with a second calibrated UFSD in coincidence, using the constant fraction method for both. The dependence of the gain upon the irradiation fluence is consistent with the concept of acceptor removal and the gain decreases from about 80 pre-irradiation to 7 after a fluence of 6e15 n/cm2. Consequently, the timing resolution was found to deteriorate from 20 ps to 50 ps. The results indicate that the most accurate time resolution is obtained at a value of the constant fraction discriminator (CFD) threshold used to determine the time of arrival varying with fluence, from 10% pre-radiation to 60% at the highest fluence. Key changes to the pulse shape induced by irradiation, i.e. (i) a reduce sensitivity of the pulse shape on the initial non-uniform charge deposition, (ii) the shortening of the rise time and (iii) the reduced pulse height, were compared with the WF2 simulation program and found to be in agreement.

physics.ins-det↗