Single-event effects in on-chip planar inductors

Oscillators are the main building blocks for frequency generation and are widely used in wireless RF communication systems (Up/Downlink), serial communication (Spacewire/Fibre), FPGAs and specific time-accurate systems (like time-to-Digital Converters for ranging or detection).  In space, large amount of ionizing radiation can cause sudden phase and frequency errors in the oscillator, so called Single-Event Effects (SEEs), leading to erroneuous communication or failures.  As system requirements increase, less phase/frequency errors can be tolerated.  Single-Event Effects have usually been considered a result of charge collection in the source/drain junctions of a MOS transistor.  Recently our group made the ground-breaking discovery that on-chip inductors show an extreme sensitivity to ionizing radiation in terms of singel-event effects, that has the radiation-effects community puzzled.  It was discovered while irradiation an LC-oscillator using heavy-ions revealing remarkable frequency transients upon particle strikes in the sprial inductor, as shown on the main picture.  Until now, passive devices like unductors were considered insensitive to radiation.  We believe that radiation-induced free charges in the SiO2 dielectric temporarily aflter the electromagnetic properties of the inductor and modifiy its 'complex) impedance, leading to frequency errors in the oscillator.  Free electron hole pairs have a considerably longer lifetime in SiO2 (compared to Si) ranging up to several microseconds, sufficiently long to accumulate large phase errors.  Such effect has never been reported earlier and is the motiviational drive for this research.  With increasing performance demands of space-deployed systems, these radiation effects will pose a severe limitation in the upcoming years and might also impact other passives operation at RF/mm-wave frequencies.  The project aims to develop the necessary knowledge and technology to overcome these novel radiation effects.