LGAD-Based Silicon Sensors for 4D Detectors

Abstract

Low-Gain Avalanche Diodes (LGAD) are a class of silicon sensors developed for the fast detection of Minimum Ionizing Particles (MIPs). The development was motivated by the need of resolving piled-up tracks of charged particles emerging from several vertexes originating from the same bunch-crossing in High-Energy Physics (HEP) collider experiments, which, however, are separated not only in space but also in time by a few tens of picoseconds. Built on thin silicon substrates and featuring an internal moderate gain, they provide fast signals for excellent timing performance, which are therefore useful to distinguish the different tracks. Unfortunately, this comes at the price of poor spatial resolution. To overcome this limitation, other families of LGAD-based silicon sensors which can deliver in the same substrate both excellent timing and spatial information are under development. Such devices are, to name a few, capacitively coupled LGADs (AC-LGAD), deep-junction LGADs (DJ-LGAD) and trench-isolated LGADs (TI-LGADs). These devices can be fabricated by even small-scale research-focused clean rooms for faster development within the scientific community. However, to scale up production, efforts towards integrating these sensor concepts in CMOS substrates, with the obvious advantage of the possibility of integrating part of the read-out electronics in the same substrate, have begun.

First experimental time-of-flight-based proton radiography using low gain avalanche diodes

“…LGADs have been mainly used for high energy physics experiments with MIP-like particles, the corresponding intrinsic time resolutions are also usually measured for MIPs (Giacomini 2023). However, as shown in figure 8(b), protons with clinical energies (<300 MeV) typically result in more than three times larger signals than MIPs, while even larger signals can be expected for heavier ions, e.g.…”

Single-photon counting detectors for diffraction-limited light sources

“…However, the requirements for photon science require additional developments, including small pixels ≲ 100 μm and full sensitivity at the entrance window, in contrast to HEP detectors, with large pads and a thin sensitive layer on a thick substrate. Various LGAD fabrication technologies are described in detail in [83]. A few feasibility studies have been dedicated to X-ray detection [84; 85; 51], aimed at reducing the effective noise, thanks to the multiplication gain, while maximizing the fill factor, which is limited in most LGAD technologies due to the presence of regions without multiplication between the pixels.…”

Neural network methods for radiation detectors and imaging

“…Another family of image sensor is called the low-gain avalanche detector (LGAD), a silicon sensor fabricated on thin substrates to deliver fast signal pulses to achieve enhanced time resolution [28], as well as to increase the X-ray signal amplitudes and the signal-to-noise ratio to achieve single photon resolution [29]. As a result, LGADs are popularly used in experiments that require fast time resolution and good spatial resolution such as 4D tracking [30] and for soft X-ray applications in low energy diffraction, spectro-microscopy and imaging experiments such as the resonant inelastic X-ray scattering experiments [29]. In summary, radiation pixel detectors aim to capture incident photons and convert the accumulated charges in the pixel into an output image.…”