US Patent 7345925 Soft erasing methods for nonvolatile memory cells

Erasure methods for a nonvolatile memory cell that includes a gate electrode on a substrate, source and drain regions in the substrate at respective sides of the gate electrode, and a charge storage layer interposed between the gate electrode and the substrate. A nonzero first voltage is applied to the source region starting at a first time. While continuing to apply the first nonzero voltage to the source region, a second voltage having an opposite polarity to the first voltage is applied to the gate electrode starting at a second time later than the first time. The second voltage may increase in magnitude, e.g., stepwise, linearly and/or along a curve, after the second time.