Total Ionizing Dose Influence on Trapping Activities in Nanoscale CMOS

What radiation does inside

The transistor has a conducting channel a few hundred atoms wide, covered by a thin insulating layer. Defects in that layer can trap electrical charge. In a device this small, a single trapped charge can measurably change the current.

Radiation can create more defects in the insulator, as illustrated in the 3D model above. When a defect traps or releases charge, the current changes. Charge can also escape and some defects can recover, so the response changes over time.

Why we measure continuously

Measurements taken between irradiation steps show how the device changes at selected dose levels. They can miss short-lived events that occur during exposure or settle before the next measurement.

We kept the device powered and recorded its current throughout the experiment. The comparison below shows how continuous recording captures changes that measurements at intervals can miss.

What we saw

The current changes in sharp steps as individual defects trap or release charge, rather than rising or falling smoothly with the dose.

This switching produces low-frequency noise during irradiation. We also observed it during heated annealing, while the device was quiet at room temperature after irradiation stopped. The paper reports these observations.

Experiment at a glance

40 nm bulk CMOS

Technology

min-size n-MOSFET

Devices

~42 h, continuous

Under the beam

100 deg C, ~1 day

Then annealed

almost gap-free, µs-scale

Sampling