Batch erasable nonvolatile memory device and erasing method

摘要

A batch erasable nonvolatile memory device and an apparatus using the same provided with memory cells which are adapted to execute an erase operation by a ejecting an electric charge accumulated at floating gates by program operation (including a pre-write operation), carries out, in sequence, a first operation for reading memory cells of an erase unit and carrying out a pre-write operation on those nonvolatile memory cells at the floating gates of which electric charge is not stored, a second operation for carrying out a batch erase operation at a high speed for the nonvolatile memory cells of said erase unit with a relatively large energy under a relatively large erase reference voltage, a third operation for carrying out a read operation of said all erased nonvolatile memory cells and a write operation on those nonvolatile memory cells which are adapted to have a relatively low threshold voltage, and a fourth operation for carrying out a batch erase operation at a low speed for the nonvolatile memory cells of said erase unit with a relatively small energy under a relatively small erase reference voltage, or is provided with an automatic erasing circuit for executing these operations.