Abstract

At an instantaneous luminosity of 5 × 1034 cm−2s−1, the high-luminosity phase of the Large Hadron Collider (HL-LHC) is expected to deliver a total of 3000 fb−1 of collisions, hereby increasing the discovery potential of the LHC experiments significantly. However, the radiation environment of the tracking system will be severe, requiring new radiation hard sensors for the CMS tracker. The CMS tracker collaboration has almost completed a large material investigation and irradiation campaign to identify the silicon material and design that fulfills all requirements of a new tracking detector at HL-LHC. Focusing on the upgrade of the outer tracker region, pad diodes as well as fully functional strip sensors have been implemented on silicon wafers with different material properties and thicknesses. The samples were irradiated with a mixture of neutrons and protons corresponding to fluences as expected for various positions in the future tracker. The measurements performed on the structures include electrical sensor characterization, measurements of the collected charge and bulk defect characterization. In this paper, the performance and limitations of the different materials are presented.

Highlights

  • At an instantaneous luminosity of 5 × 1034cm−2s−1, the high-luminosity phase of the Large Hadron Collider (HL-LHC) is expected to deliver a total of 3000 f b−1 of collisions, hereby increasing the discovery potential of the LHC experiments significantly

  • The CMS tracker collaboration has almost completed a large material investigation and irradiation campaign to identify the silicon material and design that fulfills all requirements of a new tracking detector at HL-LHC

  • Focusing on the upgrade of the outer tracker region, pad diodes as well as fully functional strip sensors have been implemented on silicon wafers with different material properties and thicknesses

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Summary

The wafer and materials

The common wafer layout has been designed with a variety of structures. Each wafer contains many test structures used for different purposes (Fig. 2), some important parts of which are introduced below [3]. For the interstrip capacitance measurement, the bias ring is connected to the strips with a polysilicon resistor This structure is labelled with CAP AC. These strixel sensors contain segmented strips with a larger area compared to the pixel detectors This layout with different active thicknesses has been processed by different technologies for the substrate production. It has been shown that silicon substrates with a high oxygen content show a higher degree of radiation tolerance This campaign features materials with different oxygen concentrations:. Labels for the materials for this paper are composed of silicon type (FZ: float zone with physical thickness of 320 μm and deep diffusion; MCZ: magnetic Czochralski; FTH: thinned float zone), nominal active thickness (320, 200 μm) and doping type (N: n-bulk; P: p-bulk with p-stop; Y: p-bulk with p-spray)

Irradiation
Measurement setup and results
Charge collection
Device simulation
Findings
Summary and outlook
Full Text
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