Methods and system for erasing data stored in nonvolatile memory in low power applications

摘要

The erasing of data stored in a nonvolatile memory is performed using multiple partial erase operations. Each partial erase operation has a time duration that is shorter than the minimum time duration of an erase operation that is needed to reliably erase the data stored in the storage location. However, the sum of the time durations of the multiple partial erase operations is sufficient to reliably erase the data in the storage location. In one example, during a partial erase operation, a voltage is applied to a memory storage transistor to remove some, but not necessarily all, of the charge stored on a charge storage layer of the transistor. Following multiple partial erase operations, sufficient charge is removed from the charge storage layer to ensure reliable data erasure.

主权项

1. A method for erasing data stored in a nonvolatile memory, the method comprising:
writing a number M of words of data in a first storage location of plurality of storage locations in a first page of the nonvolatile memory; in association with the writing to the first storage location, performing during a first time period a first erase operation on a second page of the nonvolatile memory; writing M words of data in each of at least one second storage location of the plurality of storage locations in the first page of the nonvolatile memory; in association with the writing to the at least one second storage location, performing during at least one second time period a second erase operation on the second page of the nonvolatile memory, wherein the first time period and the at least one second time period are non adjoining time periods, wherein a duration of the first erase operation is shorter than a time duration needed to reliably erase the data stored in the second page, wherein the sum of the durations of the first time period and the at least one second time period is equal to or longer than the time duration needed to erase the data stored in the second page, and wherein an erase operation is performed on the second page every time M words of data are written to a storage location of the plurality of storage locations of the first page, the data stored in the second page is reliably erased in a number N of erase operations that is equal to or less than a ratio of the number P of words of storage space in the first page to the number M of words of data written in each writing operation such that the second page of the nonvolatile memory is determined to be reliably erased when the P words of storage space in the first page have been written to.