Radiation effects on CMOS LC oscillators

Oscillators are the main buildingblocks for frequency generation and are widely used in communication systems, FPGAs and time-accurate systems. In application such as spacecrafts and satellites, high-energy physics experiments like those installed on the HL-LHC(High-Luminosity Large Hadron Collider) and Future Circular Collider (FCC) and nuclear instrumentation such as in the ITER (International Thermonuclear Experimental Reactor) fusion reactor, large amounts of ionizing radiation can cause sudden phase and frequency errors in the oscillator due to chargesdeposited by the particles. Fortunately, advancements have been made in the reliability of PLLs over the past 30 years and major improvements were achieved when migrating towards All-Digital PLLs (ADPLL) in which the feedback loop is implemented entirely digitally by replacing sensitive analog blocks (such as charge pumps) with redundant digital filters. Henceforth, the critical circuit remains the oscillator which still operates in analog mode.

Single Event Effects (SEEs) have usually been considered a result of charge collection in the source/drain junctions of a MOS transistor giving rise to Single-Event Phase Transients in the oscillator. Recently, we have made a ground breaking discovery of a secondary and furthermore dominant mechanism LC oscillators which is caused by electron and hole pairs generated in the oxides (SiO2)surrounding the spiral inductor that cause Single-Event Frequency Transients(SEFT). Although inductors are passive structures, their electromagnetic behavior (parasitic capacitance) can be impacted by free charges inside and around its geometry. The main goal of the project is to understand this mechanism and develop techniques to reduce the impact on LC oscillators.

Throughout your research, you will have the opportunity to develop and test several chips to prove your developments in practice.