Silicon sensors for the CMS HGCAL upgrade: challenges, sensor design & electrical characterization

E Brondolin

doi:10.1088/1748-0221/15/05/c05068

Abstract

The CMS detector will undergo significant improvements to face the 10-fold increase in integrated luminosity of LHC, the so-called High-Luminosity LHC, scheduled to start in 2027. This will include a completely new calorimeter in the CMS endcap regions, which should be able to withstand fluences of up to 1016 neq/cm2. The new High Granularity Calorimeter (HGCAL) will have unprecedented transverse and longitudinal readout and trigger segmentation that will facilitate the particle-flow approach to reconstruct electromagnetic and hadronic particle showers and their energies. In regions of low radiation, HGCAL will be equipped with small plastic scintillator tiles as active material coupled to on-tile silicon photomultipliers. In the higher radiation zone, silicon has been chosen due to its intrinsic radiation hardness. The silicon sensors will be of hexagonal shape, with three nominal thicknesses of 120 μm, 200 μm and 300 μm, optimized for regions of different radiation levels. They will be segmented into several hundred cells with hexagonal shape of 0.5 to 1.1 cm2 in size, each of which is read out individually. A comprehensive campaign is in progress to converge on optimal sensor design choices and parameters, such as bulk doping, layouts and production methods. Results from full electrical sensor characterization are presented for different sensors, together with first results from an irradiation campaign of large-area silicon sensors.

Highlights

An example of single cell leakage current for a Low-density sensors (LD) 6” p-type sensor with common p-stop is shown at 1000 V, while in figure 4 the total leakage current in a High-density sensors (HD) 6” p-type sensor with atoll p-stop is shown as a function of different bias voltages
The inter-pad capacitance measured for all 8” prototypes tested varies from 3 to 5.5 pF depending on the active thickness of the specific sensor under-test
In 2019 first Hamamatsu Photonics K.K. (HPK) 8” sensors prototypes were received and electrical characterisation tests were performed to assess the quality of the production process

Summary

Introduction

Current sensor layout of hexagonal 8” silicon wafers with single pad size of 1.18 cm2 (left) and of 0.52 cm2 (right). In figure 4 (left) an example of single cell leakage current for a LD 6” p-type sensor with common p-stop is shown at 1000 V, while in figure 4 (right) the total leakage current in a HD 6” p-type sensor with atoll p-stop is shown as a function of different bias voltages.

Results

Conclusion