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

Abstract

The High Granularity Timing Detector (HGTD) will be installed in the ATLAS detector to mitigate pile-up effects during the High Luminosity (HL) upgrade of the Large Hadron Collider (LHC) at CERN. The design of the HGTD is based on the use of Low Gain Avalanche Detectors (LGADs), with an active thickness of 50 μm, that allow to measure with high-precision the time of arrival of particles. The HGTD will improve the particle-vertex assignment by measuring the track time with a resolution ranging from approximately 30 ps at the beginning of the HL-LHC operations to 50 ps at the end. Performances of several unirradiated, as well as neutron- and proton-irradiated, LGAD sensors from different vendors have been measured in beam test campaigns during the years 2018 and 2019 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 are presented. In addition to these properties, the charge uniformity is also studied as a function of the position of the incident particle inside the sensor pad.

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

“…At DESY, a silicon photomultiplier (SiPM) combined with a quartz bar provided a time reference that was acquired by the DAQ together with two DUTs. The measured time resolution from this device was found to be 62.6±0.6 ps for an operating voltage of 27 V. This time resolution was degraded compared to the previous measurements [11] due to ageing and irradiation effects.…”

“…In beam tests [11] as well as in laboratory measurements [12], it was observed that the addition of carbon in the gain layer helps reducing the operating voltage needed to collect the same charge by a reduction of the acceptor removal rate after irradiation, hence improving the radiation hardness [13] of the sensors. This is extremely important at higher fluences where standard LGADs need a rather high voltage to maintain their performance (gain, time resolution) after irradiations.…”

“…The beam profile size was about 2 × 2 cm 2 in both cases. The set-up used at DESY was identical to the set-up described in detail in [11].…”

“…Many previous beam test campaigns were devoted to quantifying LGAD performances before [8,9] and after [10,11] irradiation. A variety of pad structures, such as single-pad diodes and segmented -1 -…”

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

“…annealing time would have any impact on the occurrence of mortality. The performance of these type-3.1 and 3.2 sensors were tested at HGTD beam tests in 2018 and 2019 [17]. HPK-P1 sensors of type-1.1 and 1.2 were chosen to give a clearer picture if mortality was impacted by the sensor active material thickness, as they are thinner than the more recently produced LGADs at 35 µm versus the more typical ∼50 µm.…”