Design,fabrication and characterization of 8x9 n-type silicon pad array for sampling calorimetry

TL;DR

This paper details the design, fabrication, and testing of an 8x9 n-type silicon pad array detector for calorimetry in high-energy physics, including simulations, electrical characterization, and radiation hardness assessments.

Contribution

It presents a comprehensive development process for silicon pad arrays tailored for the Forward Calorimeter upgrade at CERN, including novel fabrication and testing methods.

Findings

90% of pads had leakage current below 10 nA at full depletion

Stable operation up to 500 V without breakdown confirmed

Full depletion voltage around 50 V with 35 pF capacitance

Abstract

This paper reports the development and testing of n-type silicon pad array detectors targeted for the Forward Calorimeter (FoCal) detector, which is an upgrade of the ALICE detector at CERN, scheduled for data taking in Run~4~(2029-2034). The FoCal detector includes hadronic and electromagnetic calorimeters, with the latter made of tungsten absorber layers and granular silicon pad arrays read out using the High Granularity Calorimeter Readout Chip~(HGCROC). This paper covers the Technology Computer-Aided Design (TCAD) simulations, the fabrication process, current versus voltage (IV) and capacitance versus voltage (CV) measurements, test results with a blue LED and $^{90}$Sr beta source, and neutron radiation hardness tests. IV measurements for the detector showed that 90\% of the pads had leakage current below 10~nA at full depletion voltage. Simulations predicted a breakdown voltage of 1000~V and practical tests confirmed stable operation up to 500~V without breakdown. CV measurements in the data and the simulations gave a full depletion voltage of around 50~V at a capacitance of 35~pF. LED tests verified that all detector pads responded correctly. Additionally, the 1$\times$1 cm$^2$ pads were also tested with the neutron radiations at a fluence of $5\times10^{13}$ 1~MeV~n$_{eq}$/cm$^2$.