Mechanically Strained Strained-Si NMOSFETs

The drain-current enhancement of the mechanically strained strained-Si NMOSFET device is investigated for the first time. The improvements of the drain current are found to be ∼3.4% and ∼6.5% for the strained-Si and control Si devices, respectively, with the channel length of 25 μm at the external biaxial tensile strain of 0.037%, while the drain-current enhancements are ∼2.0% and ∼4.5% for strained-Si and control Si devices, respectively, with the channel length of 0.6 μm. Beside the strain caused by lattice mismatch, the mechanical strain can further enhance the current drive of the strained-Si NMOSFET. The strain distribution due to the mechanical stress has different effect on the current enhancement depending on the strain magnitude and channel direction. The smaller current enhancement for strained-Si device as compared to the control device can be explained by the saturation of mobility enhancement at large strain.