What are the advantages of 3D stacked SRAM structure?

1. What is 3D stacked SRAM?

3-D stacked SRAM is to stack SRAM memory cells directly vertically above the computing chip, instead of tiling beside it like traditional 2-D layout. The most direct benefit of this is that the data transmission path is compressed to the extreme. You can think of it as a kind of cache "attached to the top of the computing unit", which not only has the access speed of SRAM in nanosecond level, but also approaches the level of HBM in capacity expansion.

 

2.Advantages of 3D stacked SRAM structure

SRAM itself is much faster than DRAM, and 3D stack architecture further lowers the transmission delay to almost the same as on-chip cache. Compared with HBM, the bandwidth density has increased by several orders of magnitude-it is no longer a theoretical value that the bandwidth of a single chip exceeds 100 TB/s. For frequent small-grained random access in AI training and reasoning, this "on-demand" response speed can make the computing core no longer idle waiting for data.
 

Although HBM has a high bandwidth, it comes at the cost of high power consumption and relies on expensive CoWoS packaging. 3D stacked SRAM is integrated by wafer-level bonding technology, which avoids the high cost of high-end packaging. More importantly, the energy consumption of data handling per bit has dropped significantly. In the large-scale deployment scenario such as AI reasoning, the saved electricity and packaging costs add up to a considerable improvement in operating costs.
 

Traditional 2D memory expansion is limited by chip area, while 3D stacked SRAM supports flexible integration at wafer level, Tile level or die level. When designing an AI accelerator, you can freely combine SRAM layers with different capacities according to the computing power requirements, and are no longer bound by physical pins and traces. This degree of freedom leaves ample room for imagination for the next generation of in-memory computing and near-memory computing architecture.