US Patent 7358558 Flash memory device

A floating gate of a flash memory device is formed in a moat formed in an isolation film. Therefore, an electric field applied between a control gate and a channel region upon cycling can be precluded or mitigated. A distance between the control gate and the channel region is set greater than a predetermined value. Therefore, an electric field applied between the control gate and the channel region upon cycling can be mitigated. As a result, a data retention characteristic and an endurance characteristic can be improved.