Universal Relationship between Low-Field Mobility and High-Field Carrier Velocity in High-K and SiO₂ Gate Dielectric MOSFETs

The relationships between velocity, v, and mobility, μ, are investigated to clarify the effectiveness of μ enhancement to increase v in short channel FETs with SiO₂ as well as high-K gate dielectric. The v-μ relationships were extracted on the basis of accurate understanding of v-μ dependence of μ; v_sub dependences of μ in high-K, high N_sub, and short-channel FETs were carefully studied and the deviations from the standard V_sub dependence were found in each case. It was found that v-μ relationship is universal, namely independent of gate dielectrics, in Si nFETs with L_eff of down to 80 nm. Due to lower μ and resultant weaker v saturation in high-K FETs, μ booster technologies more significantly contribute to v and I_on enhancements in short-channel high-K FETs than in SiO₂ FETs