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The Rise of the Monolithic 3-D Chip

Researchers aim to ease miniaturization pressure with dense 3-D circuitry instead of stacked chips

4 min read
The Rise of the Monolithic 3-D Chip
Two-story Circuit: Multistory circuits could let chipmakers increase the density of devices on a chip without having to shrink transistors.
Image: CEA-Leti

Ever since the integrated circuit made its debut, semiconductors have been “single-story” affairs. But chipmakers are now considering ways to build additional transistor-packed layers right on top of the first. The approach—dubbed monolithic, or sequential, fabrication—could boost the density, efficiency, and performance of logic chips without necessitating a move to smaller transistors. And that could be a boon for an industry that is seriously contemplating the end of miniaturization.

The concept of 3-D circuitry is nothing new. Chips are routinely packaged one on top of another. Nowadays, this packaging is increasingly done using large copper pillars—called through-silicon vias, or TSVs—to vertically connect already-completed chips.

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3 Ways 3D Chip Tech Is Upending Computing

AMD, Graphcore, and Intel show why the industry’s leading edge is going vertical

8 min read
Vertical
A stack of 3 images.  One of a chip, another is a group of chips and a single grey chip.
Intel; Graphcore; AMD
DarkBlue1

A crop of high-performance processors is showing that the new direction for continuing Moore’s Law is all about up. Each generation of processor needs to perform better than the last, and, at its most basic, that means integrating more logic onto the silicon. But there are two problems: One is that our ability to shrink transistors and the logic and memory blocks they make up is slowing down. The other is that chips have reached their size limits. Photolithography tools can pattern only an area of about 850 square millimeters, which is about the size of a top-of-the-line Nvidia GPU.

For a few years now, developers of systems-on-chips have begun to break up their ever-larger designs into smaller chiplets and link them together inside the same package to effectively increase the silicon area, among other advantages. In CPUs, these links have mostly been so-called 2.5D, where the chiplets are set beside each other and connected using short, dense interconnects. Momentum for this type of integration will likely only grow now that most of the major manufacturers have agreed on a 2.5D chiplet-to-chiplet communications standard.

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