Mobility and threshold-voltage comparison between (110)- and (100)-oriented ultrathin-body silicon MOSFETs

Mobility and threshold-voltage (V-th) behavior in (110) and (100) ultrathin body (UTB) n- and p-MOSFETs are experimentally examined, and performance is compared between (110) and (100) UTB CMOSFETs based on the estimated propagation delay time. Out-of-plane effective mass (m(z)) is the key parameter that causes the difference in mobility and Vth behavior between (110) and (100). Large V-th increase and monotonic mobility degradation, as a decrease of the silicon-on-insulator (SOI) thickness, are observed in (110) UTB nMOSFETs due to a smaller m. than (100). Mobility enhancement in (100) UTB double-gate (DG) pMOSFETs is demonstrated, which may be attributable to volume inversion. Propagation delay time is estimated based on the measured mobility, and delay is improved by 30% in (110) UTB DG CMOSFETs compared to conventional bulk CMOSFETs.