Flash EEprom system with cell by cell programming verification

摘要

A system of Flash EEprom memory chips with controlling circuits serves as non-volatile memory such as that provided by magnetic disk drives. Improvements include selective multiple sector erase, in which any combinations of Flash sectors may be erased together. Selective sectors among the selected combination may also be de-selected during the erase operation. Another improvement is the ability to remap and replace defective cells with substitute cells. The remapping is performed automatically as soon as a defective cell is detected. When the number of defects in a Flash sector becomes large, the whole sector is remapped. Yet another improvement individually verifies the states of a plurality of cells that are being programmed in parallel in order to terminate the programming, as a result of the verification, on a cell-by-cell basis as the cells reach their programmed states.