Gate Metal and Cap Layer Effects on Ge nMOSFETs Low-Frequency Noise Behavior

Low-frequency noise is used to estimate the quality of the gate stack for planar Ge nMOSFETs with different effective work function metals and cap layers. It is shown that replacing TiN by a TiAl-based metal gate will induce a significant decline of the threshold voltage ${V}_{T}$ and noise power spectral density, indicating the introduction of Al will induce an advantageous effect on the trap density in the underlying HfO2. Meanwhile, the application of a LaO x cap tends to reduce ${V}_{T}$ and the trap density in the gate oxide, which could attribute to the La in-diffusion in the gate stack. The 1/f noise analysis shows that the noise could mainly be associated with number fluctuations and correlated mobility fluctuations.