The FD-SOI innovation
Fully Depleted Silicon On Insulator, or FD-SOI, is a planar process technology that relies on two primary innovations. First, an ultra-thin layer of insulator, called the buried oxide, is positioned on top of the base silicon.
Then, a very thin silicon film implements the transistor channel. Thanks to its thinness, there is no need to dope the channel, thus making the transistor Fully Depleted.
The combination of these two innovations is called “ultra-thin body and buried oxide Fully Depleted SOI” or UTBB-FD-SOI.
By construction, FD-SOI enables much better transistor electrostatic characteristics versus conventional bulk technology. The buried oxide layer lowers the parasitic capacitance between the source and the drain. It also efficiently confines the electrons flowing from the source to the drain, dramatically reducing performance-degrading leakage currents.
FD-SOI allows efficient transistor control
FD-SOI technology enables control of the behavior of transistors not only through the gate, but also by polarizing the substrate underneath the device, similarly to the body bias available in Bulk technology
In bulk technology, body biasing is very limited, due to parasitic current leakage and inefficiency at reduced transistor geometry.
Thanks to the transistor construction in FD-SOI and its ultra-thin insulator layer, biasing is much more efficient. Also, the presence of the buried oxide allows the application of higher biasing voltages, resulting in breakthrough dynamic control of the transistor
The FBB advantage
When polarization of the substrate is positive-- “Forward Body Biasing” or FBB-- the transistor can be switched faster.
This provides an extremely powerful technique to optimize performance and power consumption. Easy to implement, FBB can be modulated dynamically during the transistor operation, bringing a great flexibility for designers and letting them design their circuits to be faster when required and more energy efficient when performance isn’t as critical.