Logic-based eDRAM: Origins and rationale for use

The IBM logic-based eDRAM (embedded DRAM) technology integrates a trench DRAM (dynamic random access memory) storage-cell technology into a logic-circuit technology, merging the two previously separate technologies. Since its introduction in the 1970s, the DRAM technology has been driven by cost while the logic technology has been driven by speed, leading to an ever-widening gap between slower memory and faster logic devices. That has led to the need for increasingly complex levels of memory hierarchies, resulting in considerable degradation of system performance despite many design and architecture compromises. DRAM can provide six to eight times as much memory as SRAM (static random access memory) in the same area, but has been too slow to be used at any cache level. Our studies, highlighted in this paper, indicated that the use of logic-based DRAM could resolve that difficulty--and was necessary for integrating systems on a chip. This has led to the inclusion of logic-based eDRAM as a memory option in the IBM ASICs (application-specific integrated circuits) product.