We have performed TDDB measurement at temperature lower than 125°C in electric field (EOX) range 7 - 13.5 MV/cm and evaluated the intrinsic lifetime in a wide electric field range, using both area and temperature dependences of oxide lifetime. For positive gate bias, log(tBD) of 7.1 and 9.6 nm oxides is not proportional to the electric field but proportional to 1/EOX. This suggests that the breakdown mechanism of 9.6 nm oxide is the same as that of 7.1 nm oxide and adheres to the anode hole injection model. However, the breakdown mechanism of 4.0 nm is not the same as that of 7.1 and 9.6 nm oxides. The slope of log(tBD) versus 1/EOX plot in 4.0 nm oxide increases with decrease in oxide field. The intrinsic lifetime in the positive gate bias decreases with increasing oxide thickness, while the lifetime in the negative gate bias increases with increasing oxide thickness in the range of electric fields employed in this present experiment.