Ionising Radiation Induced Changes in the Electromagnetic Emission of Integrated Circuits

In this work, we explore changes in the electromagnetic emission (EME) of an integrated circuit (IC) induced by ionising radiation. For this, we use a custom IC consisting of several ring oscillator arrays fabricated in a TSMC 40 nm CMOS process. We utilise the 150-Ohm method according to IEC 61967-4 to measure the conducted electromagnetic emission of our test IC at one of the oscillator output pins. Between the EME measurements, we irradiate the IC with ionizing radiation produced by a high luminosity X-ray radiation source. Therefore we obtain EME spectra for the unirradiated IC and for doses up to 100 Mrad. In this paper we show the measurement results demonstrating an impact of ionising radiation on the conducted electromagnetic emission of our device under test (DUT). Contrary to previous assumptions, the frequency of the ring oscillators does not decrease steadily with increasing dose, but increases again between certain dose steps. We can justify our observations by taking into account transistor-level measurements which are provided by literature where an increased performance of NMOS devices at moderate doses compared to unirradiated devices is presented.