Impacts of uniaxial mechanical stress on high frequency performance of MOSFETs

The effects of uniaxial mechanical stress on the radio frequency (RF) performance of n- and p-metal-oxide-semiconductor field effect transistors (MOSFETs) fabricated on (100) Si wafer are investigated up to 10 GHz. Uniaxial mechanical stress is applied to the MOSFETs parallel to the direction of drain current flow using a four-point bending fixture. Under tensile stress, the gate transconductance (gm) increases in the n-MOSFETs while it decreases in the p-MOSFETs, whereas the results were vice versa for compressive stress. These tendencies are same to the effects of uniaxial mechanical stress on direct current (DC) transconductance of the MOSFETs, therefore, it is considered that the gm with RF is dependent on stress-induced sub-band splitting of Si. The total gate capacitance (C_G) extracted from scattering parameters increases (decreases) under tensile (compressive) stress for both n- and p-MOSFETs, which is explained by the variation of the effective mass perpendicular to the Si/SiO₂ interface. The cut-off frequencies (f_T) estimated from the gm and the C_G varies in inverse proportion to the gate capacitance variation.