Degradation of NMOSFETs during high-field injection with reverse biased voltage at source and drain junctions

Degradation to threshold voltage V_t and transconductance g_m of n-channel MOSFETs due to reverse biased potential at source and drain junctions during high-field electron injection were studied. Both gate injection and substrate injection modes were used to estimate initial oxide traps and breakdown characteristics. During gate injection, stress induced V_t and g_m shifts show minimal dependence on the reverse biased floating voltage whereas during substrate injection V_t shifts linearly depend on the floating reverse biased voltage and g_m shifts show minimal dependence. An asymmetry in the distribution of electron traps at the gate-oxide and substrate-oxide interfaces was observed. For gate injection the oxide field at breakdown is higher than substrate injection and these field values are independent of reverse biased voltage. Charge to breakdown decreases with reverse biased voltage for gate injection and increases for substrate injection. Moreover, charge to breakdown values for gate injections are smaller than substrate injection