Fabrication of Silicon Sensors Based on Low-Gain Avalanche Diodes

Abstract

Low-Gain Avalanche Diodes are a recently-developed class of silicon sensors. Characterized by an internal moderate gain that enhances the signal amplitude and if built on thin silicon substrates of a few tens of microns, they feature fast signals and exhibit excellent timing performance. Thanks to their fast timing they are planned to be exploited in timing detectors in High-Energy Physics experiments, for example for the upgrades of the ATLAS and CMS detectors at the High Luminosity Large Hadron Collider (HL-LHC) at CERN. However, to achieve a spatially uniform multiplication a large pixel pitch is needed, preventing a fine spatial resolution. To overcome this limitation, the AC-coupled LGAD approach was introduced. In this type of device, metal electrodes are placed over an insulator at a fine pitch, and signals are capacitively induced on these electrodes. The fabrication technology is similar for the two LGAD families, although a fine tuning of a few process parameters needs to be carefully studied. Other R&D efforts towards detectors that can simultaneously provide good time and spatial resolution, based on the LGAD concept, are under way. These efforts aim also to mitigate the loss of performance at high irradiation fluences due to the acceptor removal within the gain layer. In this paper we describe the main points in the fabrication of LGADs and AC-LGADs in a clean-room. We also discuss novel efforts carried on related topics.

Ion Microbeam Studies of Charge Transport in Semiconductor Radiation Detectors With Three-Dimensional Structures: An Example of LGAD

“…It has to be noted however, that there are other segmentation strategies that can be applied to decrease the interpad distance, one being the most promising is the Trench-Isolated-TI-LGAD [18]. More details about the different aspects of the LGAD structure, characteristics, radiation hardness and application areas can be found in the literature [5].…”

“…The increased demand for position-sensitive radiation sensing with enhanced radiation hardness and very good time resolution has paved the way for new solutions and new technologies of semiconductor detector manufacturing, often resulting in a complex 3D (three dimensional) structure of the final device [1,2]. Good examples of such detectors are monolithic silicon pixel detectors [3,4], multipixel silicon LGAD detectors [5][6][7][8], detectors with 3D electrodes (silicon and diamond) [9,10], etc. Studying the charge transport in such structures is most frequently accomplished today by different variations of the TCT (transient current technique) technique, which uses laser light to create charge carriers in certain detector regions, generally through the small openings in electrodes that enable passage of light [11,12].…”

4D-tracking in the 10-ps range: A technological perspective

“…Sensors based on the internal gain by doping (LGAD [1]) can satisfy R2. Both the space and time resolutions must be accompanied by a high detection efficiency (ε), typically required to be above 99%.…”

Monolithic arrays of silicon sensors

“…In Figure 6, we see the results of a few 2-dimensional TCAD simulations of the capacitance of the cell depicted in Figure 2 for different substrate thickness with and without n-spray. As it can be seen, capacitance towards the backside scales inversely with the thickness [14]. However, we must also consider the capacitance towards the neighbouring pixels, which can in fact be dominant with respect to the parallel plate value.…”