| Summary: | As the traditional 2-D scaling is approaching its physical limit, there is a great motivation to explore the third dimension for future integrated circuit design. The memory industry has already adopted monolithic 3-D integration (e.g., in 176-layer 3-D NAND Flash), while the 3-D vertical integration structure of logic transistors (e.g., 3-D stacked nanosheets, NMOS on top of PMOS) is emerging for sub-3-nm logic nodes. The other trend is to stack the embedded nonvolatile memories [e.g., resistive random access memory (RRAM), phase change memory (PCM), magnetic random access memory (MRAM), and ferroelectric field-effect-transistor (FeFET)] on top of CMOS using the back-end-of-line (BEOL) processing. Taking one step further, the integration of multiple tiers of active transistors with embedded memories is expected to offer significant improvements in the throughput and energy efficiency thanks to the massive connectivity between logic and memories. Besides the technological breakthroughs, circuit design automation methodologies have become key enablers to optimize the tier partitioning in monolithic 3-D architectures. In addition, heat dissipation should be taken care of by accurate thermal modeling in these monolithic 3-D architectures. New heat spreading materials and advanced embedded cooling techniques are also important.
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