eFlash (embedded Flash) is a type of non-volatile memory commonly used in microcontrollers and SoCs for code storage. It’s typically implemented at mature nodes (e.g. 40nm, 65nm) where process constraints still allow it.
eFlash relies on floating gate cells and is a FEOL (front-end-of-line) technology, requiring modifications to the core CMOS process — such as special oxides, high-voltage transistors, and dual-gate stacks. These additions increase mask count, fab complexity, and wafer cost. Moreover, floating gate technology does not scale well below 28nm due to these requirements, making it incompatible with advanced nodes.
In contrast, ReRAM (RRAM) is CMOS-compatible, integrates in the BEOL (back-end-of-line), and scales more easily to advanced geometries. It also supports lower-power, faster operation, and can reduce cost in embedded applications.