TSMC is the largest foundry in the world, and it's usually the main company that Nvidia, Qualcomm and others turn to when they want their chips manufactured. As an IP vendor, ARM has to work close with TSMC, much earlier than their IP clients, so they can prepare everything for the transition to the new chip architectures and the new process technologies.
While we're currently only on 28nm/32 nm, ARM has been working with TSMC and others for the next-gen 20nm/22nm process, and also for the 14nm/15nm process, which are still many years away. As chip makers create smaller and smaller processes, it becomes ever harder to shrink the chips, while maintaining or improving performance and power consumption.
This is why ARM need to use a technology called FinFET, which is much like Intel's tri-gate transistor technology that they're using in Ivy Bridge. Although ARM and their partners won't be using FinFET until they get to the 14nm/15nm process, they have already started working on transitioning to FinFET for their 64 bit ARMv8 architecture:
“By working closely with TSMC, we are able to leverage TSMC’s ability to quickly ramp volume production of highly integrated SoCs in advanced silicon process technology,” said Simon Segars, executive vice president and general manager, processor and physical IP divisions, ARM. “The ongoing deep collaboration with TSMC provides customers earlier access to FinFET technology to bring high-performance, power-efficient products to market.”
“This collaboration brings two industry leaders together earlier than ever before to optimize our FinFET process with ARM’s 64-bit processors and physical IP,” said Cliff Hou, vice president, TSMC Research & Development. “We can successfully achieve targets for high speed, low voltage and low leakage, thereby satisfying the requirements of our mutual customers and meeting their time-to-market goals.”
The 64-bit architecture is supposed to be “finished” next year, although we won't see a 64-bit CPU based on it until 2014 (the CPU coming next after Cortex A15). We're going to wait even more for the FinFET chips, as 20nm chips are only expected to come in late 2013/early 2014, so I don't think we'll see the 14nm/15nm FinFET ones until 2015-2016.