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

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