Forget about 20nm.
GlobalFoundries only have 28nm HP process for GPUs, which AMD will use in 2015. So both Nvidia and AMD will use 28nm process throughout 2015 and won`t switch to newer nodes until 2016.
AMD = 28nm SHP Global Foundries
Nvidia = 28nm HPM TSMC
AMD will use 28nm for their GPUs in 2015
GlobalFoundries only have 28nm HP process for GPUs, which AMD will use in 2015. So both Nvidia and AMD will use 28nm process throughout 2015 and won`t switch to newer nodes until 2016.
AMD = 28nm SHP Global Foundries
Nvidia = 28nm HPM TSMC