FDSOI

Fully Depleted Silicon-On-Insulator (FDSOI) is a semiconductor fabrication technology that builds transistors on a very thin silicon device layer separated from the bulk substrate by a buried oxide (BOX). The silicon film is thin enough and lightly doped so that the transistor channel is fully depleted of carriers when off, providing strong electrostatic control over the channel and mitigating short-channel effects.

The typical FDSOI stack consists of a thin silicon layer on BOX, with conventional CMOS transistor structures and metal gates. Because the top silicon is electrically isolated from the substrate, a back-gate bias can be applied through the handle wafer to tune the threshold voltage and other device characteristics without changing the lithography. This back-bias capability enables dynamic voltage scaling, improved performance, and better analog/RF behavior, while maintaining low leakage at small geometries.

FD-SOI nodes have been commercialized by multiple foundries, notably STMicroelectronics with 28FDSOI and GlobalFoundries with 22FDX, among others. The technology is positioned as a low-power, high-performance option for mobile, embedded, Internet of Things, automotive, and radio-frequency applications where energy efficiency and chip area are important.

Compared with conventional bulk CMOS, FDSOI offers reduced leakage, a steeper subthreshold slope from the fully depleted body, and improved drive current at low supply voltages. The ability to tune threshold with body bias helps address process variability and enable operation across wide voltage ranges. Challenges include fabrication cost, the need for specialized SOI substrates, and thermal management considerations due to the insulating BOX.

FD-SOI gained momentum in the 2010s as design tools and manufacturing readiness improved and remains a competitive option for applications requiring a balance of performance, power, and area. See also silicon-on-insulator and related transistor architectures.