RADECS 2026 · Paper · accepted
Total Ionizing Dose Influence on Trapping Activities in Nanoscale CMOS
Yurii Chubenko, Semih Ramazanoglu, Alicja Michałowska-Forsyth · Institute of Electronics, TU Graz
Radiation and its Effects on Components and Systems · Prague
Most radiation studies measure a transistor before and after exposure, which quietly skips the part I find most interesting — what the device does while it is actually being hit. So I set out to watch a single minimum-size 40 nm NMOS device with the X-rays still on: kept biased and read continuously, at high bandwidth, through the whole stress and the annealing that follows.
Approach
The measurement runs on a custom, low-noise platform I built from off-the-shelf instruments. It records the source-terminal current of two minimum-size transistors in 40 nm bulk CMOS under X-ray irradiation at a constant dose rate — up to 100 Mrad over 42 hours — followed by 24 hours of annealing at 100 °C, sampled almost without gaps at 2.5 µs.
Instead of stopping to take I–V curves at logarithmically spaced dose steps, the way these campaigns are usually run, I leave the device biased and never interrupt it. Fine changes in the current, and the discrete trapping steps themselves, show up in time and stay lined up with the bias, temperature and dose records.
What we found
The continuous recording shows detectable discrete charge-trapping and detrapping events tied to the radiation dose, and a clear rise in low-frequency noise — it turns up as soon as the X-ray shutter opens, and again during high-temperature annealing. We looked at the effect in both the time and the frequency domain; it is strongest in the smallest devices, and most likely comes from slow-switching traps.
Experiment at a glance
- 40 nm bulk CMOS
- Technology
- 2 × min-size n-MOSFET
- Devices
- 100 Mrad over 42 h
- Total dose
- 24 h @ 100 °C
- Annealing
- 2.5 µs, continuous
- Sampling
As far as we can tell this effect has been underreported, and it matters wherever nanoscale transistors have to stay quiet under heavy radiation — high-energy-physics setups such as the CERN High-Luminosity LHC, but also medical imaging and space electronics.