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Qualcomm: Scaling down is not cost-economic anymore – so we are looking at true monolithic 3D

By Zvi Or-Bach, President and CEO of MonolithIC 3D Inc.

Over the course of three major industry conferences (VLSI 2013, IEDM 2013 and DAC 2014), executives of Qualcomm voiced a call for monolithic 3D “to extend the semiconductor roadmap way beyond the 2D scaling” as part of their keynote presentations.

Karim Arabi, Qualcomm VP of Engineering, voiced the strongest support and provided many details of monolithic 3D’s role, in his keynote at this year’s DAC. A good summary was posted at the Tech Design Forums site under the title “3D and EDA need to make up for Moore’s Law, says Qualcomm.” In this blog, I’ll highlight some of the very interesting quotes from Arabi’s keynote: “Qualcomm is looking to monolithic 3D and smart circuit architectures to make up for the loss of traditional 2D process scaling as wafer costs for advanced nodes continue to increase. One of the biggest problems is cost. We are very cost sensitive. Moore’s Law has been great. Now, although we are still scaling down, it’s not cost-economic anymore”

Qualcomm is not the only fabless company voicing its concern with cost. Early in 2013 Nvidia said it is “deeply unhappy” and executives of Broadcom followed suite. The following chart, presented by ARM, illustrates it nicely.

But it seems that the problem is even more severe than that. In our blog Moore’s Law has stopped at 28nm we examined the expected increase of SoC cost due to poor scaling of embedded SRAM (eSRAM). We should note that the chart above, like many others, is about the cost per transistor associated with dimensional scaling. Escalating lithography cost causes escalating wafer cost, which neutralizes the 2X transistor density increases.

Yet eSRAM scales far less than 2X and, accordingly, for most SOCs, scaling would be even more costly. This issue has been confirmed again with the recent VLSI 2014 paper “10-nm Platform Technology Featuring FinFET on Bulk and SOI” by Samsung, IBM, STMicroelectronics, GLOBALFOUNDRIES and UMC. They presented that the size of their 10nm bitcell is 0.053 µm², which is only 25 percent smaller than the 0.07 µm² reported for 14nm bitcell size. One should expect that an additional area penalty would occur for effective use in large memory blocks, as reported even for 14nm, which could bring the effective SRAM scaling to only about 15 percent, a long way from the 50 percent required to neutralize the escalating wafer costs.

However, cost is not the only issue that forced Qualcomm to consider monolithic 3D. Quoting Arabi:

“Interconnect RC is inching up as we go to deeper technology. That is a major problem because designs are becoming interconnect-dominated. Something has to be done about interconnect. What needs to be done is monolithic three-dimensional ICs. Through-silicon vias and micro bumps are useful where you need I/Os … But they are not really solving the interconnect issue I’m talking about … So we are looking at true monolithic 3D. You have normal vias between different stacks. Then interconnect lengths will be smaller than with 2D. If we can connect between layers the delay becomes smaller.”

The interconnect issue was also addressed at IEDM 2013 by Geoffrey Yeap, Qualcomm VP of Technology, in his invited talk:

“As performance mismatch between transistors and interconnects continue to increase, designs have become interconnect-limited. Monolithic 3D (M3D) is an emerging integration technology poised to reduce the gap significantly between transistors and interconnect delays to extend the semiconductor roadmap way beyond the 2D scaling trajectory predicted by Moore’s Law.”

Yeap provided the following chart for the growing gap between transistor delay and interconnect delay:

Arabi DAC 2014 keynote was also reported on Cadence’s website, which provides our final Arabi quote for this blog: Qualcomm is looking at “monolithic” 3D-ICs that use normal vias between stacked dies. This can provide a one-process-node advantage along with a 30 percent power savings, 40 percent performance gain, and 5-10 percent cost savings.

Clearly, monolithic 3D integration has a very important role in the future of the semiconductor industry. It is therefore fitting that the traditional IEEE conference on SOI has extended its scope and now calls itself S3S: SOI technology, 3D Integration, and Subthreshold Microelectronics. The 2014 S3S conference is scheduled for October 6-9, 2014 at the Westin San Francisco Airport. This would be a great opportunity to learn more about monolithic 3D technology, with five invited presentations covering topics from design tools to monolithic 3D NAND and other 3D memories. CEA Leti will present their work on CMOS monolithic 3DIC, and researchers from MIT and Stanford will present manufacturing monolithic 3D devices with materials other than silicon.

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2 Responses to “Qualcomm: Scaling down is not cost-economic anymore – so we are looking at true monolithic 3D”

  1. Rodney Green Says:

    I have been thinking about interconnect for some time with regard to 3D integrated silicon. I am by no means a wafer level expert, but I do have a possible solution which may be helpful in an entirely different way. I have had the thought that multi-layer IC s could be done with the Mulpin packaging system. This has the promise that silicon could be interconnected in layers separate from the die itself, and this would enable different systems to be designed and simply stacked in any required combination and order. Shielding (RF) would also be a feature between layers. Thus an I.C may consist of many layers and the pins will emerge from the I.C on many PCB layers and connected there on the PCB. This could be a solution in some cases where the interconnections are mot too many. I just think that if costs are of major concern, there could be ways of reducing this with ICs consisting of sub systems each on a separate layer. the stack of ICs could be pre-assembled at the factory or delivered to the client to be assembled on the PCB (in layers and consequently buried as a classical Mulpin structure. I hope this could be of some use, even if it simply gets others thinking outside the box so to speak.

  2. Brian Cronquist Says:

    These are exciting times for monolithic 3D. It looks like there will be a fab/foundry with monolithic 3D capability. Just today, Qualcomm and SMIC announced that “they will work together to bring new 28nm design-ins and products for the growing mobile communication industry.” What is most exciting is the next statement in the release: “Going forward, SMIC will also extend its technology offerings on 3DIC and RF front-end wafer manufacturing in support of Qualcomm Technologies as its Snapdragon product portfolio continues to expand.” As pointed out above in the blog, Qualcomm has been talking monolithic 3D for about 2 years. Now we see another part of their strategy…sign up a wafer fab/foundry to do monolithic 3D, and at the most cost effective advanced node of 28nm. Smart!
    http://www.marketwatch.com/story/smic-and-qualcomm-collaborate-on-28nm-wafer-production-in-china-2014-07-03

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