“There’s no real difference between PCs and mobile phones today,” said Matti Floman from Nokia who gave the first keynote speech at last week’s JEDEC Mobile Forum. There is no difference in the types of applications run; there’s no difference in performance; there’s no difference in connectivity. Because smartphones now offer the sort of universal, run-any-app abilities of PCs, they are rapidly moving down the phone hierarchy, penetrating the broad mobile phone subscriber market and pushing out phones with lesser abilities such as feature phones.
Although user expectations are not different between PCs and phones, there’s certainly a difference in terms of hardware design. It’s not easy to make powerful memory that doesn’t consume lots of power, said Floman. In addition, phones need to fit more and more memory capacity into smaller and smaller volumes to make room for more battery in the phone—to accommodate users’ desire for more time between battery charges. Smartphone form factors are also evolving, said Floman. The favored form factor these days is a thin phone with a large display.
Semiconductor memory requirements to accommodate these design characteristics include:
- Scalability (in terms of capacity, performance, and functionality), because no one can see five years ahead
- More bandwidth
- New packages (to accommodate 3D IC assembly and thermal issues)
- Lower power consumption
- Scalable modules
Then Floman focused on what’s really important now: power. “Power is the focus of the future,” he said. Power consumption is limited by battery capacity and the heat tolerance of stacked packages, because whether or not the mobile phone makers are using 3D IC assembly, they are already stacking die. Here’s an image Floman used to show the evolution of 3D stacking in smartphone design.
Floman noted that the maximum operating temperature for NAND Flash devices is 85° C and that DRAMs are limited to 105° C. Die stacking compounds the problem of heat dissipation.
One of the most interesting slides that Floman presented at the JEDEC Mobile Forum, in my opinion, was an image that showed three processor/memory architectures for mobile phones. The graphic looked like this:
The two architectures on the left are execute-in-place (XIP) architectures. The leftmost architecture employs pseudo-static RAM and NOR Flash as memory and executes operating-system code directly from the NOR Flash memory. The middle architecture replaces the pseudo-static RAM and NOR Flash memory with LPDDR2 SDRAM and LPDDR2-N Non-Volatile Flash memory. It’s still an execute-in-place architecture but the memory components are newer and deliver more performance with better capacity.
The architecture on the right is a shadowing architecture where the OS code is stored in a mass-storage device (NAND Flash memory) and the code is first transferred to DRAM and then executed. High-end smartphones use this architecture.
These architectural designs will hold unless a new type of memory with both fast read/write times and non-volatile storage become commercially available in the required capacities and the required cost per bit. If that happens, the smartphone will only need one memory type—perhaps that might be magnetic RAM (MRAM) or Memristor-based memory. But that’s not the situation today.
The best possible performance, said Floman, will come from Wide I/O DRAM while the UFS (Universal Flash Storage) standard appears to be poised to become the next commonly used storage medium for smartphone design. UFS “will be the next generation mass memory” for smartphones, said Floman.
All of this evolution has but a single purpose. “You will not buy your next phone from the same manufacturer unless it provides new functions,” Floman said as he concluded his keynote speech.