Nonvolatile Memories: NOR vs. NAND Architectures

Flash memories are nonvolatile memories, i.e., they are able to retain information even if the power supply is switched off. These memories are characterized by the fact that the erase operation (the writing of logic “1”) has to be performed at the same time on a group of cells called a sector or block; on the other hand, the program operation (the writing of logic “0”) is a selective operation during which a single cell is programmed. The fact that the erase can be executed only on an entire sector allows one to design the matrix in a compact shape and therefore in a very competitive size, from an economic point of view. Depending on how the cells are organized in the matrix, it is possible to distinguish between NAND Flash memories and NOR Flash memories. The main electric characteristics are reported below.