1/F noise performance of nMOSFETS with Hf-based gate dielectrics

The low frequency noise performance of n-channel MOSFETs with different Hf-based gate oxides, deposited by MOCVD and using polysilicon as a gate material has been investigated. Independent of the used gate oxide, the LF noise spectra of nMOSFETs are predominantly of the 1/f ^γ type, with the frequency exponent γ close to 1. The noise spectral density of HfO ₂ devices are two orders of magnitude higher than for SiON and Hf _xSi _1-xON, due to charge trapping in the oxide layer, while no significant differences are noticed among the various Hf _xSi _1-xON compositions, where 0 < x < 100. The volume and the surface trap densities extracted from the noise are significantly higher for pure HfO ₂ than for the Hf _xSi _1-xON devices. In the latter case, trap densities are comparable with the ones extracted for SiON reference devices. The surface trap density calculated from N _t varies from the highest for HfO ₂ (∼3×10 ¹³ cm ^-2) to ∼5×10 ¹¹ cm ^-2 for the Hf _xSi _1-xON gate dielectrics, irrespective of the SiO ₂/HfO ₂ ratio x and has a comparable value for the SiON reference devices (∼8×10 ¹¹ cm ^-2). Hooge's parameter α _H, as an alternative figure of merit, shows that the devices with MOCVD HfO ₂ gate dielectric have the noisiest performance, while Hf _xSi _1-xON devices yield the lowest an, even better than for SiON.