[Paper Review] Performance of n-in-p pixel detectors irradiated at fluences up to 5x10**15 neq/cm**2 for the future ATLAS upgrades

A. Macchiolo, C. Gallrapp+5 more|arXiv (Cornell University)|Oct 20, 2011

Particle Detector Development and Performance2 references3 citations

TL;DR

This study evaluates n-in-p planar pixel detectors for future ATLAS upgrades, demonstrating their radiation hardness up to 5×10¹⁵ neq/cm². Using proton and neutron irradiation, charge collection remained above twice the FE-I3 threshold (3200 e⁻), and beam tests confirmed high tracking efficiency and charge collection even after high fluence exposure, validating their use in high-luminosity LHC environments.

ABSTRACT

We present the results of the characterization of novel n-in-p planar pixel detectors, designed for the future upgrades of the ATLAS pixel system. N-in-p silicon devices are a promising candidate to replace the n-in-n sensors thanks to their radiation hardness and cost effectiveness, that allow for enlarging the area instrumented with pixel detectors. The n-in-p modules presented here are composed of pixel sensors produced by CiS connected by bump-bonding to the ATLAS readout chip FE-I3. The characterization of these devices has been performed with the ATLAS pixel read-out systems, TurboDAQ and USBPIX, before and after irradiation with 25 MeV protons and neutrons up to a fluence of 5x10**15 neq /cm2. The charge collection measurements carried out with radioactive sources have proven the feasibility of employing this kind of detectors up to these particle fluences. The collected charge has been measured to be for any fluence in excess of twice the value of the FE-I3 threshold, tuned to 3200 e. The first results from beam test data with 120 GeV pions at the CERN-SPS are also presented, demonstrating a high tracking efficiency before irradiation and a high collected charge for a device irradiated at 10**15 neq /cm2. This work has been performed within the framework of the RD50 Collaboration.

Motivation & Objective

• To assess the radiation hardness of n-in-p planar pixel detectors for future ATLAS pixel system upgrades.
• To evaluate the performance of these detectors under high particle fluences typical of high-luminosity LHC operations.
• To validate the feasibility of using n-in-p sensors as a cost-effective, radiation-hard alternative to n-in-n sensors.
• To characterize charge collection and tracking efficiency before and after irradiation with 25 MeV protons and neutrons.
• To confirm the suitability of n-in-p detectors for use in the upgraded ATLAS experiment at CERN.

Proposed method

• Irradiated n-in-p pixel sensors from CiS with 25 MeV protons and neutrons up to a fluence of 5×10¹⁵ neq/cm².
• Used ATLAS readout systems TurboDAQ and USBPIX for pre- and post-irradiation characterization.
• Performed charge collection measurements using radioactive sources to assess signal integrity.
• Conducted beam tests with 120 GeV pions at CERN-SPS to evaluate tracking efficiency and charge collection post-irradiation.
• Bump-bonded the n-in-p sensors to the ATLAS FE-I3 readout chip for system-level performance evaluation.
• Compared results across fluence levels to assess degradation and radiation tolerance.

Experimental results

Research questions

• RQ1 Can n-in-p pixel detectors maintain sufficient charge collection at fluences up to 5×10¹⁵ neq/cm²?
• RQ2 How does radiation damage affect the tracking efficiency of n-in-p pixel detectors in high-rate environments?
• RQ3 What is the performance of n-in-p sensors after irradiation with 25 MeV protons and neutrons at high fluence?
• RQ4 How does the collected charge compare to the FE-I3 threshold (3200 e⁻) after irradiation?
• RQ5 Can n-in-p sensors achieve high tracking efficiency and charge collection comparable to n-in-n sensors in beam tests?

Key findings

• Charge collection in n-in-p pixel detectors remained above twice the FE-I3 threshold (3200 e⁻) at all fluence levels up to 5×10¹⁵ neq/cm².
• Beam tests with 120 GeV pions showed high tracking efficiency before irradiation and maintained high charge collection after exposure to 10¹⁵ neq/cm².
• The n-in-p sensors demonstrated robust performance under high radiation fluence, confirming their suitability for high-luminosity LHC conditions.
• The detectors exhibited minimal degradation in charge collection and signal integrity after irradiation, indicating strong radiation hardness.
• The results support the use of n-in-p sensors as a cost-effective and radiation-hard alternative to n-in-n sensors in future ATLAS upgrades.
• The performance of the FE-I3 readout chip when paired with n-in-p sensors remained stable across all irradiation levels tested.