Abstract: Breakdown voltage (V_bd) and charge to breakdown (Q_bd) are two parameters often used to evaluate gate oxide reliability.In this paper,we investigate the effects of measurement methods on V_bd and Q_bd of the gate oxide of a 0.18μm dual gate CMOS process.Voltage ramps (V-ramp) and current ramps (J-ramp) are used to evaluate gate oxide reliability.The thin and thick gate oxides are all evaluated in the accumulation condition.Our experimental results show that the measurement methods affect V_bd only slightly but affect Q_bd seriously,as do the measurement conditions.This affects the I-t curves obtained with the J-ramp and V-ramp methods.From the I-t curve,it can be seen that Q_bd obtained using a J-ramp is much bigger than that with a V-ramp.At the same time,the Weibull slopes of Q_bd are definitely smaller than those of V_bd.This means that V_bd is more reliable than Q_bd.Thus we should be careful to use Q_bd to evaluate the reliability of 0.18μm or beyond CMOS process gate oxide.

Key words: gate oxide reliability,  voltage to breakdown,  charge to breakdown,  voltage ramp,  current ramp