US Patent 7876610 Memory cell array with specific placement of field stoppers

A plurality of first transistors formed on a substrate share a gate electrode. Isolation regions isolate the plurality of first transistors from one another. In the region where the plurality of first transistors, an impurity region is formed in such a manner that it includes the source and drain regions of the plurality of first transistors and that the depth of the impurity region is greater than the depth of the source and drain regions. The impurity region sets the threshold voltage of the first transistors.