The big picture is that planar semiconductor transistors don’t really work below 20nm. The reason is that the gate does a poor job of controlling the channel since too much channel is too far from the gate and so there is a lot of leakage even when the transistor is nominally off. So the channel needs to be made thinner. One way to do this is to make it into a thin fin and wrap the gate around it. That is what Intel, IBM and TSMC have all done and I reported on their papers at IEDM last month.
The other alternative is to build the channel as a thin layer on an insulating wafer (SOI). This is the approach that has been pioneered by ST Microelectronics and its partners. They also presented at IEDM in a paper entitled FDSOI CMOS Devices Featuring Dual Strained Channel and Thin BOX Extendable to the 10um Node. The paper has a long list of authors from ST, CEA-LETI, IBM, Soitec, and Albany Nano Tech.
Planar fully depleted silicon-on-insulator (FDSOI) technology represents an important device architecture for continued CMOS scaling. Its advantages include excellent short-channel electrostatics, un-doped channels and effective back bias for performance boost and leakage lowering. Moreover, FDSOI is fabricated using a more conventional, lower-cost process than more complex FinFET architectures. Researchers from STMicroelectronics and the IBM Technology Development Alliance discussed the successful implementation of strained FDSOI devices with gate lengths, spacers & buried oxide (BOX) dimensions compatible with design rules of the 10nm technology node.
Two additional enabling elements for scaling FDSOI devices to the 10nm node were reported: advanced strain techniques for performance improvement, and reduced BOX thickness for better SCE & higher body factor. The researchers also will report the first demonstration of strain reversal in strained SOI by the incorporation of SiGe in a short-channel PFET device. With regard to performance, at 0.75V the devices achieved a competitive effective drive current of 340 μA/μm for NFET at Ioff=1 nA/um, and with a fully compressively strained 30% SiGe-on-insulator (SGOI) channel on a thin (20nm) BOX substrate, PFET effective drive current was 260 μA/μm at Ioff=1 nA/um.