Personal computers and servers are on the brink of a conversion from DDR3 to DDR4. The electronics industry awaits that interval when it would migrate from interfaces to something faster with lower power requirements. Currently, the most proposed solutions point to changes to DRAM packaging technology.

A number of such alternatives are under development. Wide-IO promises to provide a wider, faster bus for communication between a cell phone base band chip and a single DRAM, while reducing interface power consumption to a fraction of today's level. This standard uses a DRAM stacked atop the processor chip communicating across through-silicon vias (TSVs) either directly or through an interposer. These signals don't have to drive an external package pin or a trace on a circuit board, and they don't require electrostatic discharge (ESD) protection, all of which is highly capacitive, and this significantly reduces signalling power requirements. In a cell phone, that translates to longer battery life.

The Hybrid Memory Cube (HMC) and a competing technology called High-Bandwidth Memory (HBM) are aimed at computing and networking applications. These approaches stack multiple DRAM chips atop a logic chip. All bus interface functions are the responsibility of the logic chip, and the DRAMs communicate with it through thousands of TSVs. As with Wide-IO, that means very fast signalling with low power dissipation.

Of these three technologies, the hybrid memory cube is furthest along and has been demonstrated at tradeshows in working systems, but the other technologies are not far behind.

All three technologies are aimed at point-to-point DRAM-processor interfaces without the standard upgradeability that today's DIMMs provide. Since the industry is likely to stop upgrading systems by adding DRAM and move towards upgrading on-board NAND flash (or its successor) instead, a point-to-point interface is a very acceptable change to computer design.

The HMC or HBM approach will see initial use in supercomputers in the near future, but it is unlikely to reach widespread use until DDR4 reaches its end of life, and that could be five years from now. I would expect to see serious conversion to one or both of these technologies in the coming decade.

It appears that it may be a couple of years before Wide-IO is adopted in portable electronics, but once that occurs, the industry would be likely to undergo a very sudden conversion to that standard. I am not holding my breath for its acceptance, though. Back in the early 1990s there was a big wave behind the multi-chip module (MCM). This technology never took off because low-priced SRAMs were forcing manufacturers to scrap processor chips priced an order of magnitude higher. With Wide-IO we have a similar problem: A $1 DRAM will be bonded to a $35 base band chip. This may prevent the technology from being adopted at all, and we may instead see some ingenious developments to allow less exotic approaches to achieve the speed and power requirements of tomorrow's cell phones.

By: DocMemory
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