The news comes the same day NXP announced it will use FD-SOI for multiple future processors. So far, a total of just 10,000 FD-SOI wafers/month are shipping from all fabs including Globalfoundries and STMicroelectronics, said Sam Wang, a chip analyst for Gartner.
I take this to mean all FD-SOI wafers worldwide coming out of Soitec including the GloFo 22.
TSMC made the point that you can easier migrate a 28nm design to 22ULP than to FD SOI.
Imagine that you have a design that uses power gating or clock gating to manage power consumption. Moving that to FD SOI and changing the power management to use back biasing, requires a complete re-design of the SoC.
It's also a niche area. NXP are using it for ultra low power micro controllers. I doubt anyone is going to use it for GPUs or smartphone SoCs.
The near futur will tell us whether TSMC is making the big mistake not to go to FD-SOI.
Of course , comparing the number of 28 nm bulk wafers with 28nm FD-SOI has no value since Samsung and ST are the only companies producing 28nm FD-SOI. The good reason why NXP is not ordering its FD-SOI 28nm wafers to GlobalFoundries is simply because GlobalFoundries started FD-SOI with 22 nm.
FS-SOI has this valuable feature for a back-bias for low consumption and a foward bias for high performance dynamically on the same chip that Bulk Si is missing