Suppression of the floating-body effect using SiGe layers in vertical surrounding-gate MOSFETs

The use of silicon germanium (SiGe) heterostructures in vertical surrounding-gate MOSFETs provides an additional means for tailoring current-voltage (I-V) characteristics by controlling physical effects inside the device. Incorporation of an SiGe layer in the vertical MOSFET source can delay the floating-body effect by changing the back injection efficiency and current gain of the parasitic bipolar junction transistor (BJT). Structures with abrupt and ramped SiGe source layers showed up to 2 V and 6 V increases in breakdown voltage at low gate voltages with suppression of the floating-body effect kink. Comparison of simulation to experiment displayed the difficulties of accurately predicting device parameters, but demonstrated the usefulness of simulation to qualitatively predict device behavior.