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Radiation hardness of the Avalanche Photodiodes for ECAL CMS detector at CERN

Radiation hardness of the Avalanche Photodiodes for ECAL CMS detector at CERN. A. Singovski The University of Minnesota. APD’s in the CMS detector. PbWO 4 crystal. Radiation doses are in red, 10 4 Gy. Neutron fluence in green 10 13 neutrons/cm 2 with E > 100 keV.

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Radiation hardness of the Avalanche Photodiodes for ECAL CMS detector at CERN

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  1. Radiation hardness of the Avalanche Photodiodes for ECAL CMS detector at CERN A. Singovski The University of Minnesota

  2. APD’s in the CMS detector PbWO4 crystal

  3. Radiation doses are in red, 104 Gy. Neutron fluence in green 1013 neutrons/cm 2 with E > 100 keV. Levels outside of the detector are down by a factor of 100 or more. Radiation level after 10 years Crystal calorimeter 100

  4. APD’s for CMS • Manufacturer: • Hamamatsu Photonics, Japan. • Quantity: • Two APD’s per crystal– 124,000 APD’s with spares. • Accessibility during operation: • None. • Radiation levels: • Maximum expected dose 200 kGy and 2 1013 neutrons/cm2.

  5. Basic APD Structure: Junction Si2N4 AR coating 5 ´ 5 mm2 active area Groove to minimize surface leakage current. APD is grown epitaxially on an n++ wafer.

  6. APD radiation damage • Radiation damage of APD can influence ECAL performance by essentially two effects: • rise of the bulk current  increase APD noise contribution to the energy resolution • early breakdown  breakdown happens before APD can reach operation point at Gain=50

  7. APD contribution to the ECAL resolution • Resolution: • where, a :due to intrinsic shower fluctuations & photo statistics • b : related to stability and reproducibility • c : noise contributions • CMS design goal : a ~3%, b~0.5%, c~200 MeV • APD contributions: • a - photo statistics (area, QE) & excess noise factor • b - gain variation with bias voltage and temperature • c - capacitance as series noise and dark current as parallel noise

  8. Irradiation Tests. • Irradiation with protons: • 70 MeV protons beam at PSI – Switzerland. • 11013 hadrons/cm2 in ~ 2 hours. • Irradiation with gammas. • All irradiation with 60C0 source. • Irradiation with neutrons. • Californium source (252Cf) for irradiation at the University of Minnesota. • 2 1013 neutrons/cm2 in ~ 2 days.

  9. Device failure Irradiation in a 70 MeV proton beam.

  10. Neutron irradiation facility • Use old tandem laboratory facility in Minneapolis to store and operate two 7 mg sources for irradiation samples. • High and low flux areas 1013 and 1011 n/cm2 in 2 – 4 days. • Must provide biases to components during irradiation. • Return sources after 4 years of operation. Draws for irradiation

  11. Neutron irradiation results

  12. Durk current 70 MeV protons 1 MeV neutrons from 252Cf

  13. Neutron irradiation summary • All APD tested so far survived -> no significant shift in breakdown voltage. • The mean bulk current after 2x1013 neutrons/cm2 is Id280nA (non-amplified value). • It corresponds to 14A at Gain=50 and ~ 80MeV noise contribution (no-recovery case, CMS TDR). • Acceptable for CMS ECAL detector

  14. Gamma irradiation 60Co irradiation facility at PSI APDs 32 wires containing 60Co surround the probe and give a very uniform irradiation field. Present activity is 2.5 kGy/h

  15. Gamma irradiation results

  16. Gamma irradiation results 2 APD with a significant shift of Vb after 60Co irradiation (vs. good one) Id/Gain Noise

  17. Screening Method: - irradiate 100% of APD`s (0.5 Mrad) with Co-60 gamma source (at PSI); - measure VB and Id(V) of all irradiated APD`s 1 day after irradiation (at PSI); - measure noise at M=1, 50, 150, 300 before annealing (at CERN APD Lab) - anneal all APD`s in the oven (for 4 weeks at T=80C, at CERN APD Lab); - measure VB, Id(V) after annealing/ageing (at CERN APD Lab); • reject potentially non-reliable APD`s: ones showing • Shift of Vb more than 5V • high Id • high noise

  18. APD rejection High dark current High noise

  19. Screening efficiency 225 APD`s which passed 1st irradiation and annealing were irradiated the 2nd time. No change of VB>2V was found for all APD`s !!!

  20. Gamma irradiation summary • APDs are sensitive to the gamma irradiation. • Several percents “die” after irradiation -> get a breakdown close to the operation point. • Screening, applied to 100% of APDs make them 99.9% rad. Hard.

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