Low-frequency noise in submicrometer MOSFETs with HfO2, HfO2/Al2O3 and HfAlOx gate stacks

Low-frequency noise measurements were performed on p- and n-channel MOSFETs with HfO₂, HfAlO_x and HfO₂/Al₂O₃ as the gate dielectric materials. The gate length varied from 0.135 to 0.36 μm with 10.02 μm gate width. The equivalent oxide thicknesses were: HfO₂ 23 Å, HfAlO_x 28.5 Å and HfO₂/Al₂O₃ 33 Å. In addition to the core structures with only about 10 Å of oxide between the high-κ dielectric and silicon substrate, there were "double-gate oxide" structures where an interfacial oxide layer of 40 Å was grown between the high-κ dielectric and Si. DC analysis showed low gate leakage currents in the order of 10^-12A(2-5×10^-5 A/cm²) for the devices and, in general, yielded higher threshold voltages and lower mobility values when compared to the corresponding SiO₂ devices. The unified number-mobility fluctuation model was used to account for the observed 1/f noise and to extract the oxide trap density, which ranged from 1.8×10¹⁷ cm^-3eV^-1 to 1.3×10¹⁹ cm^-3eV^-1, somewhat higher compared to conventional SiO₂ MOSFETs with the similar device dimensions. There was no evidence of single electron switching events or random telegraph signals. The aim of this paper is to present a general discussion on low-frequency noise characteristics of the three different high-κ/gate stacks, relative comparison among them and to the Si--SiO₂ system.