Device and method in a semiconductor memory for erasing/programming memory cells using erase/program speeds stored for each cell

摘要

In a flash memory, flash cells are paired off so each pair includes a memory cell for storing data and a query cell for storing a characteristic analog value representative of the erase or programming speed of the memory cell. To erase a memory cell, the value stored in the query cell with which it is associated is retrieved, the current state of the memory cell is read, and an erase pulse having a pulse width (or amplitude) that is a function of the value retrieved from the query cell and the current state of the memory cell is then sent to the memory cell to erase it. To program a data bit into a memory cell, the value stored in the query cell with which it is associated is retrieved, and a programming pulse having a pulse width that is a function of the data bit and the value retrieved from the query cell is then to the memory cell to program it. Because the value stored in each query cell is characteristic of the particular memory cell with which the query cell is associated, the erase or programming pulse sent to the memory cell is highly accurate and, hence, is unlikely to over-erase or over-program the memory cell. As a result, the time-consuming verification steps required by most conventional flash memories are eliminated.