There are two types of radiation-induced damage in silicon, generated by ionizing and non-ionizing energy loss (NIEL). By displacement of atoms, NIEL induces various types of bulk defect, which change the properties of the silicon. The consequences are a change in the effective doping concentration, the trapping of drifting charge carriers and a higher generation rate of free charge carries. The results presented here relate to the change in the effective doping concentration, which leads to a change of a silicon detectors full depletion voltage and the higher carrier generation, which leads to an increase in the amount of leakage current. The leakage current and the full depletion voltage are important quantities for the operation of a silicon detector and therefore subject to continuous monitoring.

In addition to the monitoring of these quantities, established models are used to make predictions on the development of the detector properties. The "alpha" model describes the relation between the change in leakage current per volume as a function of the neutron equivalent fluence and depends on the temperature history since the irradiation due to annealing effects. The Hamburg model describes the change of the effective doping concentration as a function of the neutron equivalent fluence and is subject to annealing effects as well.

Previously approved results: https://twiki.cern.ch/twiki/bin/view/CMSPublic/CMSPixelOperationPlots2019

Figure in png format other formats Description
.pdf The expected leakage current in each of the forward pixel disks is calculated based on the full temperature and irradiation history using the empirical radiation damage model I(Φ,t,T)=I0+α(t,T)∙Φ∙V. Radiation-induced increase of leakage current depends on fluence Φ, time t, temperature T, volume V. The α-parameter set for the radiation damage model used comes from M. Moll, Radiation Damage in Silicon Particle Detectors, Universitšt Hamburg, DESY-THESIS-1999-040, 1999, https://mmoll.web.cern.ch/mmoll/thesis/.

For the simulation, a FLUKA fluence simulation (v3.23.1.0) was used with high granular resolution and detector geometry as input. Actual temperature history is taken from the database where on-module temperature sensor measurements for each readout group (ROG) are stored: only one module temperature per ROG is read out and the temperature of the other modules belonging to the same ROG is assumed to be the same. The low luminosity periods at the start of the data taking 2017 and 2018 have a large difference between prediction and measurements. This is probably due to temperature effects that are not fully taken into account yet. No rescaling factors are applied. The integrated luminosity for 2017 is 50 fb-1 and for 2018 is 70 fb-1.

The leakage current data is from the CMS forward pixel detector, averaged over all the modules in the ROG, and rescaled to T=0℃.

.pdf The expected leakage current in each of the forward pixel disks is calculated based on the full temperature and irradiation history using the empirical radiation damage model I(Φ,t,T)=I0+α(t,T)∙Φ∙V. Radiation-induced increase of leakage current depends on fluence Φ, time t, temperature T, volume V. The α-parameter set for the radiation damage model used comes from M. Moll, Radiation Damage in Silicon Particle Detectors, Universitšt Hamburg, DESY-THESIS-1999-040, 1999, https://mmoll.web.cern.ch/mmoll/thesis/.

For the simulation, a FLUKA fluence simulation (v3.23.1.0) was used with high granular resolution and detector geometry as input. Actual temperature history is taken from the database where on-module temperature sensor measurements for each readout group (ROG) are stored: only one module temperature per ROG is read out and the temperature of the other modules belonging to the same ROG is assumed to be the same. The low luminosity periods at the start of the data taking 2017 and 2018 have a large difference between prediction and measurements. This is probably due to temperature effects that are not fully taken into account yet. No rescaling factors are applied. The integrated luminosity for 2017 is 50 fb-1 and for 2018 is 70 fb-1.

The leakage current data is from the CMS forward pixel detector, averaged over all the modules in the ROG, and rescaled to T=0℃.

.pdf The expected leakage current in each of the forward pixel disks is calculated based on the full temperature and irradiation history using the empirical radiation damage model I(Φ,t,T)=I0+α(t,T)∙Φ∙V. Radiation-induced increase of leakage current depends on fluence Φ, time t, temperature T, volume V. The α-parameter set for the radiation damage model used comes from M. Moll, Radiation Damage in Silicon Particle Detectors, Universitšt Hamburg, DESY-THESIS-1999-040, 1999, https://mmoll.web.cern.ch/mmoll/thesis/.

For the simulation, a FLUKA fluence simulation (v3.23.1.0) was used with high granular resolution and detector geometry as input. Actual temperature history is taken from the database where on-module temperature sensor measurements for each readout group (ROG) are stored: only one module temperature per ROG is read out and the temperature of the other modules belonging to the same ROG is assumed to be the same. The low luminosity periods at the start of the data taking 2017 and 2018 have a large difference between prediction and measurements. This is probably due to temperature effects that are not fully taken into account yet. No rescaling factors are applied. The integrated luminosity for 2017 is 50 fb-1 and for 2018 is 70 fb-1.

The leakage current data is from the CMS forward pixel detector, averaged over all the modules in the ROG, and rescaled to T=0℃.

.pdf The expected leakage current in each of the forward pixel disks is calculated based on the full temperature and irradiation history using the empirical radiation damage model I(Φ,t,T)=I0+α(t,T)∙Φ∙V. Radiation-induced increase of leakage current depends on fluence Φ, time t, temperature T, volume V. The α-parameter set for the radiation damage model used comes from M. Moll, Radiation Damage in Silicon Particle Detectors, Universitšt Hamburg, DESY-THESIS-1999-040, 1999, https://mmoll.web.cern.ch/mmoll/thesis/.

For the simulation, a FLUKA fluence simulation (v3.23.1.0) was used with high granular resolution and detector geometry as input. Actual temperature history is taken from the database where on-module temperature sensor measurements for each readout group (ROG) are stored: only one module temperature per ROG is read out and the temperature of the other modules belonging to the same ROG is assumed to be the same. The low luminosity periods at the start of the data taking 2017 and 2018 have a large difference between prediction and measurements. This is probably due to temperature effects that are not fully taken into account yet. No rescaling factors are applied. The integrated luminosity for 2017 is 50 fb-1 and for 2018 is 70 fb-1.

The leakage current data is from the CMS forward pixel detector, averaged over all the modules in the ROG, and rescaled to T=0℃.

.pdf The expected leakage current in each of the forward pixel disks is calculated based on the full temperature and irradiation history using the empirical radiation damage model I(Φ,t,T)=I0+α(t,T)∙Φ∙V. Radiation-induced increase of leakage current depends on fluence Φ, time t, temperature T, volume V. The α-parameter set for the radiation damage model used comes from M. Moll, Radiation Damage in Silicon Particle Detectors, Universitšt Hamburg, DESY-THESIS-1999-040, 1999, https://mmoll.web.cern.ch/mmoll/thesis/.

For the simulation, a FLUKA fluence simulation (v3.23.1.0) was used with high granular resolution and detector geometry as input. Actual temperature history is taken from the database where on-module temperature sensor measurements for each readout group (ROG) are stored: only one module temperature per ROG is read out and the temperature of the other modules belonging to the same ROG is assumed to be the same. The low luminosity periods at the start of the data taking 2017 and 2018 have a large difference between prediction and measurements. This is probably due to temperature effects that are not fully taken into account yet. No rescaling factors are applied. The integrated luminosity for 2017 is 50 fb-1 and for 2018 is 70 fb-1.

The leakage current data is from the CMS forward pixel detector, averaged over all the modules in the ROG, and rescaled to T=0℃.

.pdf The expected leakage current in each of the forward pixel disks is calculated based on the full temperature and irradiation history using the empirical radiation damage model I(Φ,t,T)=I0+α(t,T)∙Φ∙V. Radiation-induced increase of leakage current depends on fluence Φ, time t, temperature T, volume V. The α-parameter set for the radiation damage model used comes from M. Moll, Radiation Damage in Silicon Particle Detectors, Universitšt Hamburg, DESY-THESIS-1999-040, 1999, https://mmoll.web.cern.ch/mmoll/thesis/.

For the simulation, a FLUKA fluence simulation (v3.23.1.0) was used with high granular resolution and detector geometry as input. Actual temperature history is taken from the database where on-module temperature sensor measurements for each readout group (ROG) are stored: only one module temperature per ROG is read out and the temperature of the other modules belonging to the same ROG is assumed to be the same. The low luminosity periods at the start of the data taking 2017 and 2018 have a large difference between prediction and measurements. This is probably due to temperature effects that are not fully taken into account yet. No rescaling factors are applied. The integrated luminosity for 2017 is 50 fb-1 and for 2018 is 70 fb-1.

The leakage current data is from the CMS forward pixel detector, averaged over all the modules in the ROG, and rescaled to T=0℃.

Figure in png format other formats Description
.pdf Based on the full temperature and irradiation history the expected full depletion voltages of the forward pixel tracker disks are simulated using the Hamburg model (M. Moll, Radiation Damage in Silicon Particle Detectors, Universitšt Hamburg, DESY-THESIS-1999-040, 1999) for radiation damage. Warm periods during various technical stops lead to a change of depletion voltage due to annealing. Simulation input: FLUKA fluence simulation (v3.23.1.0) with high granular resolution and detector geometry where the different impact of charged and neutral particles on oxygenated silicon are taken into account. The Hamburg model is fitted to 2018 data leaving the gC parameter as a free parameter. The gY parameter is fixed to 7×10-2 cm-1†and gA to 1.4×10-2 cm-1. The resulting prediction is compared to the Hamburg model using two sets of Hamburg parameters for oxygenated Si (DOFZ): CB-oxy and RD48-oxy. Actual temperature history is taken from the database where on-module temperature sensor measurements for each readout group (ROG) are stored: only one module temperature per ROG is read out and the temperature of the other modules belonging to the same ROG is assumed to be the same.† Data points are taken from bias voltage scans and are defined to be the point of saturation of the charge collection. The integrated luminosity for 2017 is 50 fb-1 and for 2018 is 70 fb-1.
.pdf Comparison of the fit to the data following the Hamburg model, with a linear dependence of the effective doping concentration† on the received fluence in the stable damage term, with an alternative empirical formulation where the stable damage term has a logarithmic dependence on the fluence.
.pdf Based on the full temperature and irradiation history the expected full depletion voltages of the forward pixel tracker disks are simulated using the Hamburg model (M. Moll, Radiation Damage in Silicon Particle Detectors, Universitšt Hamburg, DESY-THESIS-1999-040, 1999) for radiation damage. Warm periods during various technical stops lead to a change of depletion voltage due to annealing. Simulation input: FLUKA fluence simulation (v3.23.1.0) with high granular resolution and detector geometry where the different impact of charged and neutral particles on oxygenated silicon are taken into account. The Hamburg model is fitted to 2018 data leaving the gC parameter as a free parameter. The gY parameter is fixed to 7×10-2 cm-1†and gA to 1.4×10-2 cm-1. The resulting prediction is compared to the Hamburg model using two sets of Hamburg parameters for oxygenated Si (DOFZ): CB-oxy and RD48-oxy. Actual temperature history is taken from the database where on-module temperature sensor measurements for each readout group (ROG) are stored: only one module temperature per ROG is read out and the temperature of the other modules belonging to the same ROG is assumed to be the same.† Data points are taken from bias voltage scans and are defined to be the point of saturation of the charge collection. The integrated luminosity for 2017 is 50 fb-1 and for 2018 is 70 fb-1.
.pdf Comparison of the fit to the data following the Hamburg model, with a linear dependence of the effective doping concentration† on the received fluence in the stable damage term, with an alternative empirical formulation where the stable damage term has a logarithmic dependence on the fluence.

-- JorineMirjamSonneveld - 2020-02-17

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