Low Gain Avalanche Detectors Research Articles

Laboratory and beam-test performance study of a 55 µm pitch iLGAD sensor bonded to a Timepix3 readout chip

This contribution reports on characterisation results of a large-area (2 cm2) small pitch (55 µm) inverse Low-Gain Avalanche Detector (iLGAD), bonded to a Timepix3 readout chip. The ilGAD sensors were produced by Micron Semiconductor Ltd with the goal to obtain good gain uniformity and maximise the fill-factor — an issue present with standard small-pitch LGAD designs. We have conducted detailed performance evaluations using both X-ray calibrations and beam tests. An X-ray fluorescence setup has been used to obtain energy calibration and to identify the optimal operating settings of the new devices, whereas the extensive beam tests allowed for a detailed evaluation of the detector performance. The beam-tests were performed at the CERN SPS North Area H6 beamline, using a 120 GeV/c pion beam. The reference tracking and time-stamping is achieved by a Timepix3-based beam telescope setup.The results show a gain of around 5 with very good uniformity, measured across the whole gain area, as well as a hit time resolution down to 1.3 ns without correcting for the time-walk effects. Furthermore, it is shown that the gain opens the possibility of a good X-ray energy resolution down to 4.5 keV.

R&D of a timing measurement ASIC for possible HL-LHC upgrade

The Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) at CERN will undergo a major upgrade for the High Luminosity phase of the LHC (HL-LHC), which is expected to start in 2029 [1]. In addition to improving the detector rate capabilities and performance at increased higher luminosity, precision timing measurements are added to mitigate pile-up effects. The timing detector currently under construction covers pseudo-rapidity up to η=3[2] . A possible pathway for further improvements is the extension of timing capabilities to cover the full tracker acceptance up to η=4. Low Gain Avalanche Detectors (LGAD) pixels have been shown to be a suitable candidate for replacing a part of the pixel detector end-caps during a future Long Shutdown or Year-End Technical Stop of the LHC. Here, we present preliminary results of our design efforts towards a readout Application-specific integrated circuit (ASIC) capable of operating with LGAD pixel sensors [3]. The first results of the modeling of a part of the ASIC are demonstrated.

Spectroscopic performance of Low-Gain Avalanche Diodes for different types of radiation

LGADs (Low-Gain Avalanche Diodes or Detectors) are a type of silicon Avalanche Photo-Diodes originally developed for the fast detection of minimum ionizing particles in high-energy physics experiments. Thanks to their fast timing performance, the LGAD paradigm enables detectors to accurately measure minimum ionizing particles with a timing resolution of a few tens of picoseconds. Such a performance is due to a thin substrate and the presence of a moderate signal gain. This internal gain of a few tens is enough to compensate for the reduced charge deposition in the thinner substrate and the noise of fast read-out systems. While LGADs are optimized for the detection of minimum ionizing particles for high-energy particle detectors, it is critical to study their performance for the detection of different types of particle, such as X-rays, gamma-rays, or alphas. In this paper, we evaluate the gain of three types of LGADs: two devices with different geometries and doping profiles fabricated by Brookhaven National Laboratory, and one fabricated by Hamamatsu Photonics with a different process.Since the gain in LGADs depends on the bias voltage applied to the sensor, pulse-height spectra have been acquired for bias voltages spanning from the depletion voltage up to the breakdown voltage. The signal-to-noise ratio of the generated signals and the shape of their spectra allow us to probe the underlying physics of the multiplication process.

Low gain avalanche detectors for precision timing in the CMS MTD endcap timing layer

The MIP Timing Detector (MTD) of the Compact Muon Solenoid (CMS) is designed to provide precision timing information (with resolution of ∼40 ps per layer) for charged particles, with hermetic coverage up to a pseudo-rapidity of |η| = 3. This upgrade will reduce the effects of pile-up expected under the High-Luminosity LHC running conditions and brings new and unique capabilities to the CMS detector. The time information assigned to each track will enable the use of 4D reconstruction algorithms and will further discriminate in the time domain interaction vertices within the same bunch crossing to recover the track purity of vertices in current LHC conditions. The endcap region of the MTD, called the Endcap Timing Layer (ETL) will be instrumented with silicon-based low gain avalanche detectors (LGADs), covering the high radiation pseudo-rapidity region between |η| = 1.6 and 3.0. Each endcap will be instrumented with a two-disk system of LGADs, read out by Endcap Timing Readout Chips (ETROCs), being designed for precision timing measurements. We will present an overview of the MTD ETL design, which is detailed in the MTD technical design report. We will also present the R&D and test beam studies that were instrumental for achieving the ETL design, characterization of the LGAD sensors, as well as recent progress on the development of the ETROC readout electronics.

Correlation between charge and current gain in LGADs treated with IR lasers

This study investigates the correlation between the gain, defined as the increase of measured charge generated from the absorption of incident radiation, and the gain measured as the increase of sensor leakage current in Low Gain Avalanche Detectors (LGAD) before and after neutron irradiations. LGADs exhibit high signal-to-noise ratios for minimum ionizing particles and will be used in high-energy physics experiments, mainly related to timing applications. Transient Current Technique (TCT) measurements were conducted with LGADs and PIN diodes. The electric field screening effect, caused by free and trapped carriers, is identified as the main reason for the differences measured in gain determined from the increase in leakage current and collected charge. These effects are more significant in irradiated LGAD sensors. The experimental results confirm expectations, demonstrating a growing spread between the two measured gains with fluence. The study enables the prediction of charge gain from the leakage current measurements, which are easier to conduct.

Investigation of low gain avalanche detectors exposed to proton fluences beyond 1015 n eq cm-2

Low gain avalanche detectors (LGADs) deliver excellent timing resolution, which can mitigate mis-assignment of vertices associated with pileup at the High Luminosity LHC and other future hadron colliders. The most highly irradiated LGADs will be subject to 2.5 × 1015 n eq cm-2 of hadronic fluence during HL-LHC operation; their performance must tolerate this. Hamamatsu Photonics K.K. and Fondazione Bruno Kessler LGADs have been irradiated with 400 and 500 MeV protons respectively in several steps up to 1.5 × 1015 n eq cm-2. Measurements of the acceptor removal constants of the gain layers, evolution of the timing resolution and charge collection with damage, and inter-channel isolation characteristics, for a variety of design options, are presented here.

Overview of the ATLAS High-Granularity Timing Detector: project status and results

The increase of the particle flux (pile-up) at the high-luminosity phase of the Large Hadron Collider (LHC) with an instantaneous luminosity up to L ≈ 7.5 × 1034 cm-2 s-1 will have a severe impact on the ATLAS detector reconstruction and trigger performance. A High Granularity Timing Detector (HGTD) will be installed in the forward region for pile-up mitigation and luminosity measurement. This detector, based on Low Gain Avalanche Detectors and custom ASICs, will provide a time resolution of 30 ps per track at the beginning of HL-LHC and 50 ps at the end. This proceeding paper will summarise the overall specifications of the HGTD as well as the project status.

A high granularity timing detector for the ATLAS Phase-II upgrade: Project overview and status

A High Granularity Timing Detector (HGTD) has been proposed for the ATLAS Phase-II upgrade to mitigate the pile-up effects at the High-Luminosity Large Hadron Collider (HL-LHC). The HGTD is based on silicon devices, Low Gain Avalanche Detectors (LGAD), aiming to provide 30–50 ps time resolution per track. Significant progress has been made in the development of various detector components, particularly the radiation-resistant sensor and readout chip. This proceeding concisely summarizes the project overview and current status of the HGTD project.

Low Gain Avalanche Detectors for the ATLAS High Granularity Timing Detector: Laboratory and test beam campaigns

The High Granularity Timing Detector (HGTD) is designed for the mitigation of pile-up effects in the ATLAS forward region and for bunch per bunch luminosity measurements. HGTD, based on Low Gain Avalanche Detector (LGAD) technology and covering the pseudorapidity region between 2.4 and 4.0, will provide high precision timing information to distinguish between collisions occurring close in space but well-separated in time. Apart from being radiation resistant, LGAD sensors should deliver 30 ps time resolution per track for a minimum-ionizing particle (35 ps per hit) at the start of lifetime, increasing to 50 ps per track (70 ps per hit) at the end of HL-LHC operation. Each readout cell has a transverse size of 1.3×1.3 mm2 leading to a highly granular detector with about 3 millions of readout electronics channels. A dedicated ASIC for the HGTD detector, ALTIROC, is being developed in several phases producing prototype versions of 2×2, 5×5 and 15×15 channels. HGTD modules are hybrids of the LGAD and ALTIROC connected through flip-chip bump bonding process. Several test beam campaigns have been conducted at DESY and CERN SPS between 2021 and 2022. A summary of the results from LGAD-alone and hybrids will be presented.

Radiation tolerance of the MUX64 for the High Granularity Timing Detector of ATLAS

The MUX64 ASIC is a 64-to-1 analog multiplexer to accommodate 64 inputs, with one addressed to output for ADC readout. It is developed for monitoring of the Low-Gain Avalanche Detectors (LGAD) detector modules in the High Granularity Timing Detector (HGTD) of the ATLAS Phase-II upgrade. The MUX64 chips will be used in the radiation field of high-luminosity pp collisions at LHC to an integrated luminosity of 4000 fb-1. This work presents the radiation tolerance study for the MUX64 being tested with 80 MeV protons and X-ray exposures for damages caused by Non-Ionizing Energy Loss (NIEL) and Total Ionizing Dose (TID), respectively. The irradiated samples demonstrated tolerance to the NIEL to a fluence of 3.21 × 1015 (Si, 1 MeV) neq/cm2, and the TID of 7.46 × 105 Gy (Si).

Characterization of Ultra-Fast Silicon Detectors (UFSD) for high energy physics applications

Ultra-fast silicon detectors (UFSD) are a specialized type of radiation detectors based on Low Gain Avalanche Detectors (LGADs) that are designed to have extremely fast response times. This work presents detailed results on the study of 50μm thin-LGADs with different doping concentrations produced by Micron Semiconductors Ltd. A temperature dependent study of electrical characteristics and infrared laser measurements are presented in this work.

Design and development of Low Gain Avalanche Detectors using Teledyne e2v process

The Low Gain Avalanche Detectors (LGAD) has become the preferred technological choice for fast track timing detectors in High Energy Physics applications. Additional uses of such sensors are currently being investigated, ranging from Light Detection and Ranging (LIDAR) to Low Let particle dosimetry in medical and space applications. This paper describes the development and test of LGAD devices, fabricated using a commercial process from Teledyne e2v silicon foundry. Motivation behind the project, and details of the TCAD simulations of the manufacturing process and of the electrical performances of the devices will be provided. Test results on gain and time resolution using laser injection will also be shown.

Design and performance of the Fermilab Constant Fraction Discriminator ASIC

We present the design and performance characterization results of the novel Fermilab Constant Fraction Discriminator ASIC (FCFD) developed to readout low gain avalanche detector (LGAD) signals by directly using a constant fraction discriminator (CFD) to measure signal arrival time. Silicon detectors with time resolutions less than 30ps will play a critical role in future collider experiments, and LGADs have been demonstrated to provide the required time resolution and radiation tolerance for many such applications. The FCFD has a specially designed discriminator that is robust against amplitude variations of the signal from the LGAD that normally requires an additional correction step when using a traditional leading edge discriminator. The application of the CFD directly in the ASIC promises to be more reliable and reduces the complication of evolving time-walk corrections throughout the operational lifetime of the detector system. We will present a summary of the measured performance of the FCFD for input signals generated by internal charge injection, LGAD signals from an infrared laser, and LGAD signals from minimum-ionizing particles. The mean time response for LGAD signals with charge ranging between 5 and 26 fC has been measured to vary no more than 10ps, orders of magnitude more stable than an uncorrected leading edge discriminator based measurement, and effectively removes the need for any additional time-walk correction. The measured contribution to the time resolution from the FCFD ASIC is found to be 10ps for signals with charge above 20fC.

Gain recovery in heavily Irradiated Low Gain Avalanche Detectors by high temperature annealing

Studies of annealing at temperatures up to 450 °C with Low Gain Avalanche Detectors (LGAD) irradiated with neutrons are described. It was found that the performance of LGADs irradiated with 1.5e15 n/cm2 was already improved at 5 min of annealing at 250 °C. Isochronal annealing for 30 min in 50 °C steps between 300 °C and 450 °C showed that the largest beneficial effect of annealing is at around 350 °C. Another set of devices was annealed for 60 min at 350 °C and this annealing significantly increased depletion voltage of the gain layer (Vgl). The effect is equivalent to reducing the effective acceptor removal constant by a factor of ∼ 4. Increase of Vgl 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.

Gain measurements on NLGAD detectors

In the last few years, Low Gain Avalanche Detectors (LGAD) have demonstrated their outstanding performance when detecting high-energy charged particles. However, due to the difference in the multiplication mechanism for holes and electrons, the detection performance for low penetrating particles (e.g low-energy protons or soft x-rays) is significantly reduced. A novel design of an LGAD detector, the NLGAD, was designed and fabricated at CNM to overcome this drawback. A qualitative description of the NLGAD concept is presented in this work, along with gain response measurements of the first prototypes under visible light of 660 nm and 15 keV x-rays. Additionally, a review of the gain response under visible light of 404 nm and IR light of 1064 nm, previously studied, is also evaluated in this work. The results demonstrate that the NLGAD concept has the potential to detect low penetrating particles.

Characterization of the response of IHEP-IME LGAD with shallow carbon to Gamma Irradiation

Low Gain Avalanche Detectors (LGAD) for the High-Granularity Timing Detector (HGTD) are crucial in reducing pileups in the High-Luminosity Large Hadron Collider. Numerous studies have been conducted on the bulk irradiation damage of LGADs. However, few studies have been carried out on the surface irradiation damage of LGAD sensors with shallow carbon implantation. In this paper, the IHEP-IME LGADs with shallow carbon implantation were irradiated up to 2 MGy using gamma irradiation to investigate surface damage. Important characteristic parameters, including leakage currents, breakdown voltage (BV), inter-pad resistances, and capacitances, were tested before and after irradiation. The results showed that the leakage current and BV increased after irradiation, whereas overall inter-pad resistance exhibited minimal change and remained above 109 Ω before and after irradiation. Capacitance was found to be less than 4.5 pF with a slight decrease in the gain layer depletion voltage (V gl ) after irradiation. No parameter affected by the inter-pad separation was observed before and after irradiation. All characteristic parameters meet the requirements of HGTD, and this design can be used to further optimization.

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 × 1015 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 μm. 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.

One-Dimensional Position-Sensitive LGAD With a DC Coupled and Resistive Charge Division Mechanism

Low-gain avalanche detectors (LGADs) are promising candidates for four-dimensional (4D) tracking detectors in future high-energy physics (HEP) experiments, offering high position and time resolution. However, conventional pixel array LGADs suffer from large dead areas between pixels and require a large number of readout channels, resulting in a poor spatial resolution and high cost. In this paper, we present a one-dimensional position-sensitive LGAD (1D PS-LGAD) based on DC coupling and a resistive charge division mechanism. The 1D PS-LGAD features two cathodes and one anode, with two-dimensional position coordinates obtained by cross-placing two 1D PS-LGADs. With an active thickness of 50 μm and an active area of 2.7 mm × 2.7 mm, a 1D PS-LGAD demonstrated an average position measurement error (PME) of 32.2 ±35.4 μm, accounting for 1.2% of the side length of the active area with a 100% fill factor. The coincidence time resolution and position resolution were 8.8 ps and 22.5 μm, respectively, at the center of the device for incident 532 nm light with a spot diameter of approximately 25 μm and a mean photoelectron number (MPEN) of 6000 when the reverse voltage was 620 V.

New insight into gain suppression and single event Burnout effects in LGAD

Low Gain Avalanche Detectors (LGADs) will be employed in the CMS MTD and ATLAS HGTD upgrades to mitigate the high levels of pile-up events expected in the High Luminosity phase of the LHC. Over the last several years, much attention has been focused on designing radiation-tolerant gain implants to ensure that these sensors survive the expected fluence (>1015 neq/cm2). This work reports several effects observed during our previous studies on two relevant phenomena Single Event Burnout (SEB) and carrier density-induced Gain Suppression (GS). Influence of irradiation level, pad configuration and gain layer depth on SEB are discussed. In this paper, we also extend GS study with a new insight into the spatio-temporal dynamics of charge transport in LGAD, probed with a focused ion beam.

Novel ion imaging concept based on time-of-flight measurements with low gain avalanche detectors

Treatment planning in ion beam therapy requires accurate knowledge of the relative stopping power (RSP) distribution within the patient. Currently, RSP maps are obtained via conventional x-ray computed tomography (CT) by converting the measured attenuation coefficients of photons into RSP values for ions. Alternatively, to avoid conversion errors that are inherent to this method, ion computed tomography (iCT) can be used since it allows determining the RSP directly. In typical iCT systems, which usually consist of a tracking system and a separate residual energy detector, the RSP is obtained by measuring the particle trajectory and the corresponding water equivalent path length (WEPL) of single ions travelling through the patient. In this work, we explore a novel iCT approach which does not require a residual energy detector. Instead, the WEPL is estimated indirectly by determining the change in time of flight (TOF) due to the energy loss along the ion’s path. For this purpose, we have created a Geant4 model of a TOF-iCT system based on low gain avalanche detectors (LGADs), which are fast 4D-tracking detectors that can measure the time of arrival and position of individual particles with high spatial and time precision. To assess the performance of this TOF-iCT concept, we determined the RSP resolution and accuracy for different system settings using the Catphan® CTP404 sensitometry phantom. Within the set of investigated system parameters, the lower limit of the RSP accuracy was found at 0.91%, demonstrating the proof-of-principle of this novel TOF-iCT concept. The main advantage of using this approach is that it could potentially facilitate clinical integration due to its compact design, which, however, requires experimental verification and an improvement of the current WEPL calibration procedure.