Feeds

3D processor-memory mashups take center stage

'I have seen the future, and it is stacked'

Boost IT visibility and business value

ISSCC A trio of devices that stack layers of compute units and memory in a single chip to boost interconnect bandwidth were presented at this week's International Solid-State Circuits Conference in San Francisco.

Sharing the stage at the ISSCC's High Performance Digital session were three technologies; one prototype developed by IBM that places cache memory layers on top of a "processor proxy" layer, and two working chips – one developed at the University of Michigan, and another by the Georgia Institute of Technology working with KAIST and Amkor Technology, both in South Korea.

Note that these parts aren't merely RAM-stacked-on-top-of-a-processor packages such as, for example, Apple's A5. These are single parts with processor and memory closely coupled, married together in a single slab.

The ISSCC presentations each were titled in impressive boffin-speak – so impressive that we'll quote the title of each paper before we dig into a few of its details.

IBM's "3D system prototype of an eDRAM cache stacked over processor-like logic using through-silicon vias": Like the other two chips, the IBM prototype routes data, clock, and power signals through its layers – what IBM calls "strata" – by means of through-silicon vias (TSVs).

TSVs are essentaily just what they sound like: signal paths that are etched through a silicon layer and filled with a conductor. In IBM's prototype, the TSVs are copper-filled, and are about 20 micrometers (0.0008 inches) in diameter.

A 3D System Prototype of an eDRAM Cache Stacked Over Processor-Like Logic Using Through-Silicon Vias

IBM's TSVs are connected layer-by-layer with tiny conductive balls. (click to enlarge)

The prototype that IBM presented at ISSCC was a two-strata affair, but the design is intended to be extendable to more cache-memory strata. The design of those cache strata borrows heavily from the Power7's integrated L3 cache, including its embedded DRAM (eDRAM), IP library, logic macros, and design and test flow.

IBM didn't use a true processor for the base of its stack, but instead a proxy for test purposes only, which included circuits to exercise the memory and emulates the noise and power of a true processor up to 350 watts per square centimenter.

Slide from IBM's ISSCC paper, 'A 3D System Prototype of an eDRAM Cache Stacked Over Processor-Like Logic Using Through-Silicon Vias'

Unlike the two other larger-process 3D chips presented, IBM's is built at a snug 45nm

That high power level would be needed in the target four-strata design, seeing as how IBM says that the design's clock skew is estimated to be less than 13 picoseconds in a four-strata design, which would allow a "worst-case" L3 clock frequency of 2GHz, resulting in a data bandwidth of 450 gigabits per second.

The essential guide to IT transformation

Next page: How low can you go?

More from The Register

next story
The Return of BSOD: Does ANYONE trust Microsoft patches?
Sysadmins, you're either fighting fires or seen as incompetents now
Microsoft: Azure isn't ready for biz-critical apps … yet
Microsoft will move its own IT to the cloud to avoid $200m server bill
Oracle reveals 32-core, 10 BEEELLION-transistor SPARC M7
New chip scales to 1024 cores, 8192 threads 64 TB RAM, at speeds over 3.6GHz
Docker kicks KVM's butt in IBM tests
Big Blue finds containers are speedy, but may not have much room to improve
US regulators OK sale of IBM's x86 server biz to Lenovo
Now all that remains is for gov't offices to ban the boxes
Gartner's Special Report: Should you believe the hype?
Enough hot air to carry a balloon to the Moon
Flash could be CHEAPER than SAS DISK? Come off it, NetApp
Stats analysis reckons we'll hit that point in just three years
Dell The Man shrieks: 'We've got a Bitcoin order, we've got a Bitcoin order'
$50k of PowerEdge servers? That'll be 85 coins in digi-dosh
prev story

Whitepapers

5 things you didn’t know about cloud backup
IT departments are embracing cloud backup, but there’s a lot you need to know before choosing a service provider. Learn all the critical things you need to know.
Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Build a business case: developing custom apps
Learn how to maximize the value of custom applications by accelerating and simplifying their development.
Rethinking backup and recovery in the modern data center
Combining intelligence, operational analytics, and automation to enable efficient, data-driven IT organizations using the HP ABR approach.
Next gen security for virtualised datacentres
Legacy security solutions are inefficient due to the architectural differences between physical and virtual environments.