One last comment:
you need to differentiate between SiON and HKMG - the problem related to HKMG.
Many customers QCOM?) selected the more conservative approach: SiON
therefore TSMC probably experienced a combination of HKMG yield issues as well as capacity shortage.
The vast majority of TSMC 28nm wafers in 2012 were SiON
"Compared to 65nm"
kind of a low bar....kind of embarrassing 10% within one year time frame. No?
Bottom line acccording to DD time (couple weeks ago) Mediatek still can't secure sufficient number of 28nm wafers - and new smart phone launch delayed by several months
and regards yields - keep in mind I keep a very close ear what vendors like LRCX, NVLS and KLAC were saying about this...
It looks like the ramps are about the same IF you consider revenue. There was probably less demand for 65nm and 40nm than their was for 28nm. TSMC could charge higher prices relatively for the 28nm. 28nm is 100% on 300mm which should increase the volume of 28nm die.