Polarity dependent of gate oxide breakdown from measurements

In this work, polarity dependent of gate oxide breakdown is investigated for both NMOS and PMOS in a large range of oxide thicknesses, 27Å, 170Å and 850Å. All the devices are measured using constant voltage stress (CVS) method. From the measurements, It is found that for thick gate oxide, lifetime (T_BD) under negative gate bias is always shorter regardless of the types of the MOSFETs. However, when the oxide thickness scaled down, the accumulation case gets shorter lifetime than the inversion case for both NMOS and PMOS. In addition, the gate current changes over the stress time for different oxide thicknesses are also exhibited which imply different breakdown processes.