A nanowatt oscillator powered only by 68 MeV proton irradiation of a crystalline silicon photodiode pair

It is shown, that an ultra-low-power voltage controlled oscillator, realized with conventional NAND gates in ring-oscillator configuration, can be operated by a series connected pair of commercial Silicon pin solar cells, only irradiated by a high energy proton beam as power supply. However a very fast degradation of the solar cells is observed, leading to a stop of the oscillator operation after a very short time. By monitoring the oscillator frequency changes when the stack of photodiodes, in this case illuminated with weak ambient light, is not directly exposed to the proton beam but positioned in different positions close to the proton beam, an evaluation of the off-beam-axis irradiation damage could be done. A detailed electrical analysis of the photodiode properties before and after the direct proton irradiation has been added. • CMOS based voltage-controlled oscillator operates with nano-Watt electrical power. • Silicon photodiodes irradiated with MeV protons generate electrical power for VCO. • Silicon degrades extremely fast under MeV proton irradiation. • Degradation is measurable by monitoring the VCO frequency during irradiation. • Spurious irradiation in out-of-proton-beam region is clearly revealed.