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

SiO/sub 2/ gate dielectric and Si/SiO/sub 2/ 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 /sup 60/Co 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.

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