In 2025 the Large Hadron Collider (LHC) will be upgraded to the High Luminosity (HL-)-LHC. This will challenge the silicon strip detector performance with very high fluences and long operation time. Sensors have been designed to survive severe radiation damage as demonstrated by electrical tests and charge collection measurements. Besides that, it is important to predict and understand the long-term evolution of the sensor properties. In this paper, detailed studies on the annealing behavior of ATLAS 12 strip detectors designed by the ITK Strip Sensor Working Group and irradiated with fluences between 5·10¹³ and 2·10¹⁵ n_eq/cm² are presented. During the annealing time at 23°C and 58.5°C systematic charge collection, leakage current and impedance measurements have been carried out until breakdown or the appearance of charge multiplication. The phenomenon of charge multiplication in high irradiated sensors after long annealing times has been investigated with respect to dependencies on temperature and bias voltage cycling. The difference in the annealing behavior between the two temperatures has been analyzed and compared to similar measurements on n-type sensors and with a theoretical model. For sensors with fluences below 3·10¹⁴ n_eq/cm² the effective doping concentration could be extracted from the impedance measurements and was compared with a theoretical model. The results show that ATLAS12 sensors anneal similarly to the previously designed ATLAS07 and the behavior is well described by the theoretical model. Nevertheless, a significant difference in the time constant of the beneficial and reverse annealing with respect to previous n-type sensors has been reported.

1. G. Appolinari et al., High-Luminosity Large Hadron Collider (HL-LHC): Technical Design Report V. 0.1, CERN Yellow Reports 226, CERN, Geneva, Switzerland, 2017.
   DOI: 10.23731/CYRM-2017-004
2. Technical Design Report for the ATLAS Inner Tracker Strip Detector, Tech. Rep. CERN-LHCC-2017-005. ATLAS-TDR-025, CERN, Geneva, Switzerland, 2017.
   Retrieved from: https://cds.cern.ch/record/2257755/files/ATLAS-TDR-025.pdf;
   Retrieved on: Aug. 10, 2018
3. G. Aad et al., “The ATLAS Experiment at the CERN Large Hadron Collider,” J. Instrum.,vol. 3,no. 8, S08003, Aug. 2008.
   Retrieved from: http://iopscience.iop.org/article/10.1088/1748-0221/3/08/S08003/pdf;
   Retrieved on: Aug. 10, 2018
4. G. Lindstrom et al., “Radiation hard silicon detectors developments by the RD48 (ROSE) Collaboration,” Nucl. Instr. Methods Phys. Res. A,vol. 466, no. 2, pp. 308 – 326, Jul. 2011.
   DOI: 10.1016/S0168-9002(01)00560-5
5. G. Casse, P. Allport, M. Hanlon, “Improving the radiation hardness properties of silicon detectors using oxygenated n-type and p-type silicon,” IEEE Trans. Nucl. Sci., vol. 47, no. 3, pp. 527 – 532, Jun. 2000.
   DOI: 10.1109/23.856475
6. V. Cindro, G. Kramberger et al., “Radiation damage in p-type silicon irradiated with neutrons and protons,” Nucl. Instr. Methods Phys. Res. A, vol. 599, no. 1, pp. 60 – 65, Feb. 2009.
   DOI: 10.1016/j.nima.2008.11.007
7. G. Casse, P. P. Allport, A. Watson, “Effects of accelerated annealing on p-type silicon micro-strip detectors after very high doses of proton irradiation,” Nucl. Instr. Methods Phys. Res. A, vol. 568, no. 1, pp. 46 – 50, Nov. 2006.
   DOI: 10.1016/j.nima.2006.05.200
8. G. Kramberger et al., “Annealing studies of effective trapping times in silicon detectors,” Nucl. Instr. Methods Phys. Res. A,vol. 571, no. 3,pp. 608 – 611, Feb. 2007.
   DOI: 10.1016/j.nima.2006.10.399
9. M. Minano et al., “Annealing studies of silicon microstrip detectors irradiated at high neutron fluences,” Nucl. Instr. Methods Phys. Res. A, vol. 591, no. 1, pp. 181 – 183, Jun. 2008.
   DOI: 10.1016/j.nima.2008.03.051
10. Y. Unno et al., “Development of n⁺-in-p large-area silicon microstrip sensors for very high radiation environments - ATLAS12 design and initial results,” Nucl. Instr. Meth. Phys. Res. A, vol. 765, pp. 80 – 90, Nov. 2014.
    DOI: 10.1016/j.nima.2014.06.086
11. Hamamatsu photonics official web page, Hamamatsu photonics, Iwata City, Japan.
    Retrieved from: https://www.hamamatsu.com/jp/en/index.html;
    Retrieved on: Aug. 10, 2018
12. M. Mikestikova et al., “Study of surface properties of ATLAS12 strip sensors and their radiation resistance,” in Proc. 10^th International “Hiroshima" Symposium on the Development and Application of Semiconductor Tracking Detectors (HSTD-10), Xi’An, China, 2015.
    DOI: 10.1016/j.nima.2016.03.056
13. K. Hara et al., “Charge collection and field profile studies of heavily irradiated strip sensors for the ATLAS inner tracker upgrade,” in Proc. 10^th International “Hiroshima" Symposium on the Development and Application of Semiconductor Tracking Detectors (HSTD-10),Xi’An, China, 2015.
    DOI: 10.1016/j.nima.2016.04.035
14. R. Mori et al., “Evaluation of the performance of irradiated silicon strip sensors for the forward detector of the ATLAS Inner Tracker Upgrade,” in Proc. 10^th International “Hiroshima" Symposium on the Development and Application of Semiconductor Tracking Detectors (HSTD-10), Xi’An, China, 2015.
    DOI: 10.1016/j.nima.2016.04.044
15. R. M. Hernandez, “A portable readout system for silicon microstrip sensors,” Nucl. Instrum. Methods Phys. Res. A, vol. 623, no. 1, pp. 207 – 209, Nov. 2010.
    DOI: 10.1016/j.nima.2010.02.197
16. S. Löchner, M. Schmelling, The Beetle Reference Manual – Chip Version 1.3, 1.4 and 1.5, CERN, Geneva, Switzerland, 2006.
    Retrieved from: http://inspirehep.net/record/928871/files/lhcb-2005-105.pdf?version=1;
    Retrieved on: May 22, 2018
17. M. Moll, “Radiation Damage in Silicon Particle Detectors,” Ph.D. dissertation, University of Hamburg, Dept. of Physics, Hamburg, Germany, 1999.
    Retrieved from: https://mmoll.web.cern.ch/mmoll/thesis/pdf/moll-thesis.pdf;
    Retrieved on: Aug. 10, 2018
18. I. Mandic, V. Cindro, G. Kramberger, M. Mikuz, “Annealing effects in n⁺- p strip detectors irradiated with high neutron fluences,” Nucl. Instrum. Methods Phys. Res. A, vol. 629, no. 1, pp. 101 – 105, Feb. 2011.
    DOI: 10.1016/j.nima.2010.11.057