FD-SOI: Is It Really a Thing?

By Cadence

April 27, 2016

Apparently, asking if something is really a thing is really a thing. So, recently, the SOI consortium organized one of their regular symposia and the thing most people in the audience wanted to know is whether FD-SOI is really a thing.

The SOI consortium deals with all things silicon-on-insulator (SOI) and organizes several symposia in different parts of the world each year. For the last few years the focus has been completely on FD-SOI (or sometimes called UTBB-FDSOI). This stands for ultra-thin-body-and-box-fully-depleted-silicon-on-insulator. You can see where the name comes from by looking at the starting wafer-blank and how a transistor is built on top of it. There is an ultra-thin buried oxide (box) on top of the silicon that makes the bulk of the wafer (I guess that counts as a semiconductor play-on-words), and on top of that there is another ultra-thin layer of silicon (the body). The buried oxide is an insulator and the body forms the transistor channels after manufacture. Since the channel area is backed by an insulator, there are no leakage paths that are not well-controlled by the gate, as there are in bulk planar CMOS. FinFET achieves even better control of the channel by having the gate on both sides of it (in fact, the top, too), but it is a lot more expensive to manufacture.

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