Band-to-Band-Tunneling Leakage Suppression for Ultra-Thin-Body GeOI MOSFETs Using Transistor Stacking

This letter indicates that the ultra-thin-body (UTB) germanium-on-insulator (GeOI) MOSFETs preserve the leakage reduction property of stacking devices, while the band-to-band-tunneling leakage of bulk Ge-channel devices cannot be reduced by stacking transistors. The seemingly contradictory behavior of the stack-effect factors is explained by the difference in the flows of band-to-band-tunneling hole fluxes for UTB GeOI and bulk Ge-channel devices and validated by TCAD mixed-mode simulations. At 300 K, the stack-effect factors of UTB GeOI MOSFETs range from 6.8 to 40 (N = 2) and from 12 to 142 (N = 3) at Vdd = 0.5-1 V. As the temperature increases or Vdd decreases, the stack-effect factor for UTB GeOI devices decreases, while the stack-effect factor for bulk Ge-channel MOSFETs increases, because the subthreshold leakage current becomes more significant at higher temperature or lower voltage with respect to the band-to-band-tunneling leakage current.