QCT is Developing Multi-Layer 3D Chips, as Well as Smaller Device Features

In its never-ending quest to provide customers with higher-performance, more cost-effective products, Qualcomm CDMA Technologies (QCT) is pushing the semiconductor technology envelope in at least two directions. The first follows the familiar "Moore's Law" path observed more than 40 years ago by industry pioneer Gordon Moore, who noted that the number of transistors that can be squeezed onto a silicon chip tends to double roughly every 18 months.

Jim Clifford, QCT senior vice president and general manager of operations, says the company has a well-defined plan for fabricating the next several generations of chips with even smaller features. QCT is currently ramping 45 nanometer (nm) chips to volume production, while looking ahead to its first devices for the 28nm technology node and, eventually, 22nm.

"We know how to get to 28 nanometers, and we know how to get to 22 nanometers," says Clifford. Beyond that, a variety of technology approaches are still being considered. Nonetheless, he says, "I think most of us believe there is still ‘More Moore' to come."

More than Moore
Meanwhile, Qualcomm is pursuing another next-generation technology strategy for stacking multiple silicon chips, or dies, along with novel methods of interconnecting them. Clifford describes this three-dimensional integration approach as "More than Moore," because it has the potential to significantly increase chip performance and lower production costs without shrinking the actual circuitry printed on individual chips.

The technique, called through-silicon-via (TSV), allows chip makers to stack multiple layers of chips atop each other and connect them electrically through precisely etched vertical holes, also known as vias. Once TSV technology has been scaled up to mass-production levels, chip makers should be able to combine a half-dozen or more chips at a time into high-performance monolithic devices.

Blending technologies
The TSV approach has the potential to solve numerous design challenges by allowing chip architects to blend the best qualities of multiple process technologies into a single multi-layer device.

Radio-frequency chips, for instance, are often manufactured using expensive silicon-germanium technology that provides extremely high chip speeds, but not the extremely fine chip features of other leading-edge processes. Memory chips, on the other hand, tend to use processes optimized for building the smallest possible features in order to pack as much storage capacity as possible into a single chip.

Architectural innovation
Clifford envisions TSV technology allowing Qualcomm engineers in the not-too-distant future to achieve performance that is currently only a dream by combining modem, power-management and radio-frequency chips with just the right amounts of memory.

As cellphone chipsets incorporate memory-hungry functions such as 1080p high-definition encode and decode, for instance, TSV technology should allow high-bandwidth memory chips to be stacked directly above them and linked with hundreds or even thousands of direct via connections. That multitude of interconnections should allow enormous amounts of data to be transferred rapidly between the chips even at relatively low clock speeds, which in turn should significantly reduce power dissipation.

"TSV offers us huge architectural innovation," says Clifford. "You have the ability to put the circuitry anywhere you want it, in precisely the right technology."

IMEC collaboration
To accelerate its 3D integration efforts, Qualcomm recently joined in a collaborative effort led by Leuven, Belgium-based IMEC, Europe's leading independent nanoelectronics research institute, to develop innovative, cost-effective 3D interconnect methodologies.

Qualcomm was the first fabless semiconductor design company to join IMEC's 3D integration program in 2007. Other partners in the initiative include foundries, integrated chip companies, packaging and assembly companies and manufacturing equipment suppliers.

QCT's next-generation semiconductor initiatives reflect Qualcomm's company wide commitment to research and development. That commitment allows Qualcomm to continually advance the boundaries of wireless technology – one of the fastest growing industries in the world today.