Silicon MOSFETs have been sensitive to Total Ionizing Dose (TID) since the early days of radiation studies on electronic devices, and that is still the case after more than 40 years and 20 generations (nodes) of CMOS technologies. Silicon dioxide (SiO2), the insulator that has been a blessing for the semiconductor industry because of its compatibility with Si, has instead been a curse for the application of CMOS circuits in radiation environments. Defects in SiO2 and at its interface with the Si channel of MOS transistors have determined the TID response of CMOS circuits built in micrometer bulk planar technologies of the 1980s as well as in today’s nanometer-scale FinFETs.

In this course, prepared in collaboration with Dr. Giulio Borghello (CERN), and Dr. Stefano Bonaldo (DEI, University of Padova), Dr. Federico Faccio (CERN) will illustrate the basic mechanisms of TID in SiO2: charge yield, charge and hydrogen transport, charge trapping and de-trapping, interface state activation and annealing. The course will show how very similar mechanisms have differently affected the performance of MOSFETs in time. While in older technologies the gate oxide was the weak point and determined failure at krad TID levels, with the down-scaling of CMOS in the 100 nm range and below, the radiation response became dominated by auxiliary oxides like Shallow Trench Isolation (STI) or spacers.

The last part of the course will thus focus on the consequences of ionization in these insulators: the leakage currents that often represent the prevalent limitation to radiation tolerance in recent technologies, the dose-rate effects observable at high TID levels, and the transistor size dependencies including RINCE, RISCE (Radiation-Induced Narrow or Short Channel Effects) and halo implant effects. The manufacturing of these auxiliary oxides is less controlled and less uniform across nodes and fabrication plants than for the thermally grown gate oxide, leading to a wide variability in radiation response. This will be illustrated by a comparison between manufacturers, plants of the same manufacturer and manufacturing lots. In conclusion the course will show how, with or even without costly dedicated design techniques, TID tolerance to ultra- high levels (>100Mrad) is not a dream anymore.