Embedded Memories: Progress and a Look into the Future

Memories are categorized as embedded memories (e-memories) and stand-alone memories. E-memories favor high speed rather than low cost. In addition, they must maintain compatibility with the logic process, because they must be cofabricated on the same chip as the logic. In contrast, standalone memories give the first priority to low cost and thus high density rather than high speed. There are two types of e-memories: RAMs and ROMs (or "almost ROMs" such as flash memories). RAMs ensure an unlimited number of read and write cycles, and at present, RAMs come in two types: SRAMs, and DRAMs that necessitate refresh operations to retain the data stored at cell capacitors. ROMs ensure nonvolatility of stored data, exemplified by flash memories and ferroelectric RAMs (FeRAMs).