Analysis of drivability enhancement factors in nanograting metal-oxide-semiconductor field-effect transistors

The enhancement factors of a new structure called the nanograting metal-oxide-semiconductor field-effect transistor (MOSFET), which was proposed to achieve higher current drivability, were analyzed. From the measurement of the transconductance, the drivability enhancements of both n- and p-type MOSFETs were confirmed. This was mainly ascribed to the increased effective channel width. However, the enhancement ratios in nMOS and pMOS were different. In the nanograting MOSFETs, the existence of the current flowing in the (110) direction on the (110) surface caused the effective electron mobility to be lower and the effective hole mobility to be higher than that in the conventional devices on the (100) surface. The stress from the polycrystalline silicon (poly-Si) gate also resulted in the change of the mobility. Because of the reasons above, the mobility difference between the nanograting nMOSFET and pMOSFET became slighter, thus, the area balance of the nanograting complementary MOS (CMOS) circuit could be improved. Combining this with the increased drivability could give the area advantage of the nanograting CMOSFETs.