Channel-length impact on radiation-induced threshold-voltage shift in N-MOSFET devices at low gamma ray radiation doses

SiO₂ gate dielectric and Si/SiO₂ interface are two important components, which will shape the future of the MOSFETs and integrated circuits (ICs) technologies for ionizing radiation environment applications. This study discusses their size effect on irradiated NMOS device response. N-channel MOSFETs of different gate sizes were first irradiated with ⁶⁰Co gamma rays source at several total doses (low doses). Then, they were characterized by using both voltage- and frequency-charge pumping (CP) techniques. On one hand, all transistors reveal two radiation-induced oxide-trap formation mechanisms, caused by low radiation total doses. Initially, there is a positive charge build-up in the oxide layer, followed latter by diminution of net positive charge (turn around effect). The interface traps exhibit a linear increase with radiation dose. On the other hand, the response of irradiated transistors is shown to depend on their gate lengths