Total Ionizing Dose measurements for electronics: A comparison of RadFET and Floating Gate dosimeter PhD student: Salvatore Danzeca EN/STI/ECE Supervisor: Doct. Giovanni Spiezia (CERN) Prof. Laurent Dusseau (UM2)

Contents Definitions RadMON Basic of radiation effect on MOSFET RadFET – dose sensor Calibration results Floating gate dosimeter Outlooks and conclusions

Definitions of dosimetry and dose Generally, dosimetry is the study of how ionizing radiation imparts energy to matter. More specifically, dosimetry is the measurement of absorbed dose in matter Absorbed dose (Also often called Dose or Total Dose): the mean energy absorbed per unit mass of irradiated material The SI unit of dose is the (Gy): 1 Gy = 1 J/kg Another unit of dose used in the space world is the (rad) 1 rad = 100 ergs/g (1 Gy = 100 rad) The standard definition for the TID effect is a `circuit degradation or failure resulting from radiation-induced charge trapped in insulating layers (usually oxides)’

The RadMon Characterization of sensors and research of new ones RadMon = Radiation Monitoring for the LHC EFFECTS SEE DD TID Memory Measure the Total Ionizing Dose , the Displacement Damage and the High Energy Hadron Fluence in order to: Monitor the Radiation Level in the LHC tunnel Anticipate the electronics degradation Investigate the cause of failures PIN Diode RadFet Continous effort to know the response of the sensors: The system is COTS based: when we buy a new batch of sensors, we need to characterize them Continous effort to search for new sensors: New sensors with better sensitivity

Basic mechanism of ionizing radiation passing through a MOS structure MOS Capacitor SiO2 The creation of the e/h pairs (they can recombine in a very short time window ~ps ) The holes undergoes to a hopping transport through the oxide The holes can be trapped in the SiO2. The term `trap’ is generally used to name a neutral defect in the oxide that can capture holes and retain them for a certain amount of time. holes and hydrogen-containing defects or dopant complexes can also lead to the formation of a second type of ionization defect: the interface trap. The oxide trapped charges can be annealed by tunnelling of the electrons from the substrate and from thermal excitation

Total Ionizing Dose Effects PRE-IRRADIATION POST-IRRADIATION Main effects on MOSFET: Oxide charge trapping = holes trapped in SiO2 induces Vth shift Creation of interface states at SiO2-Si interface due to chemical bonding changes at interface induces Vth shift, and carrier mobility degradation ∆Vth = ∆Vot + ∆Vit

RadFET tox The RadFET is a p-type MOSFET with a very thick gate oxide The sensitivity increases with the square of the oxide thickness The sensitivity changes applying different bias (Fi) The RadFETs characterized for the RadMon V6 have two oxide thicknesses : 100nm and 400nm ∆Vot(F i, En ) = (q/ϵox)· g0 · fy (Fi, En ) · ft(F i ) · (tox)2 · D

Calibration 60Co RadFET 100 nm RadFET 400 nm +5V BIASING GND BIASING

Floating Gate Dosimeter: FGDOS Operation principle: The sensor is a capacitor that uses the field oxide as dielectric, connected to the electrically “floating” gate of a nMOSFET. Charges can be placed on the floating capacitor prior to the irradiation through an injector. Ionizing radiation generates electron- hole pairs in the field oxide, gradually discharging the capacitor. The capacitor can be charged back to the initial value, giving the possibility to reuse it several times. In the case of the FGDOS the sensitivity can be chosen according with the expected dose rate. Two configurations: High Sensitivity and Low Sensitivity RadFet + + - - S D gate ox. + + + + N+ N+ p Silicon + + + - - - Floating Gate + + + + + + + + + + S + + + + D Field oxide gate ox. - - - - - - - - - - - - - - N+ N+ p Silicon B In collaboration with IC-Malaga

Floating gate Model work accepted in the IEEE TNS journal: Danzeca et al. ‘Characterization and Modelling of a Floating Gate Dosimeter with gamma and protons at various energies’

Working Principle - Output Raw Output Processed Output

First test in mixed radiation field – H4IRRAD External Zone

60Co gamma and Proton results   RadMon V5 RadMon V6 Floating Gate Ratio ADC 12 bit 16 bit High Sensitivity Radfet/FGDOS ADC Resolution 2.4 mV 150 uV 100nm GND Resolution [Gy] 1.304348 8.15E-02 3.00E-04 272 100nm 5V Resolution [Gy] 0.429338 2.68E-02 89 400nm GND Resolution [Gy] 0.062827 3.93E-03 13 400nm 5V Resolution [Gy] 0.01875 1.17E-03 4 60Co irradiation done in USC Santiago de Campostela Proton Test at Paul Schrerrer Institute TID EFFECTS D p Silicon gate ox. S Floating Gate B + + + + + + + + + + - - - - - - - - - - + + + + - - - - Field oxide N+ + + + - - - + + + + + + work accepted in the IEEE TNS journal: Danzeca et al. ‘Characterization and Modelling of a Floating Gate Dosimeter with gamma and protons at various energies’

Outlooks and conclusions RadFET Basic mechanism of ionizing radiation on MOSFET MOSFET dosimetry Calibration Results Floating Gate Device Working principles of the Floating Gate dosimetry Floating gate model Mixed radiation field results 60Co and proton tests – TID effects Dose rate effects still to be studied in details Floating gate in the space http://moon.luxspace.lu/radiation-experiment/

Thank You!

Backup slides

Backup Slide

RadFet Resolution – RadMon V5 and V6

The RadFet readout circuit Circuit a) and b) are the two biasing configuration Circuit c) is the ‘read’ circuit

MOSFET Devices - Simple switch model | VGS | Gate MOS Capacitor SiO2 Source (of carriers) Drain (of carriers) Open (off) (Gate = ‘0’) Closed (on) (Gate = ‘1’) Ron | VGS | < | VTH | | VGS | > | VTH | VTH is called the threshold voltage and it defines the ‘state’ of the MOSFET