Fastest Ge p-MOSFET: Germanium (Ge) is of interest as a potential material for the channels of future ultrafast CMOS devices because it offers high hole mobility that enables fast switching. However, because Ge is unstable in the air, it is typically covered, or passivated, with a silicon layer. Unfortunately, that increases the effective oxide thickness (EOT) on the Ge layer – a limiting factor for future devices which must be extremely dense with ultra-thin oxide layer. A research team led by the University of Tokyo will describe how they eliminated the Si passivation layer, and instead used a plasma post-oxidation technique to process a Ge channel’s surface and to optimize its interface properties with NiGeSi source/drains and high-k HfO2/Al2O3/GeOx and Ta gate stacks. They also discovered that the electron mobility in the Ge channel can be enhanced to the highest value ever achieved by asymmetrically straining it along its <110> crystal facet. They used these techniques to build the fastest Ge p-MOSFET ever reported, with record peak hole mobility of 763 cm2/Vs, at a thin EOT of just 0.82nm.
- The image at left above shows the fabrication process and device structure of s-Ge p-MOSFETs with self-aligned NiGeSi metal source/drains.
- The middle image is a TEM electron microscope cross-section of the interfacial layer.
- The image at right is a graph showing the effective mobility of the s-Ge -pMOSFETs.
(Paper #26.1, “High Mobility Strained-Ge pMOSFETs with 0.7-nm Ultrathin EOT using Plasma Post Oxidation HfO2/Al2O3/GeOx Gate Stacks and Strain Modulation,” R. Zhang et al, Univ. Tokyo)