 When source and drain are reversed, the opposite side's charge determines the transistor's threshold.This way two different charge levels at either end of the charge trapping cell will cause two different currents to flow through the cell, depending on the direction of the current flow.Samsung Electronics in 2006 disclosed its research into the use of Charge Trapping Flash to allow continued scaling of NAND technology using cell structures similar to the planar structures in use at that time.