 Since vertical features cannot be etched sideways, a charge trapping layer becomes a very interesting way to build a vertical NAND flash string.Toshiba and Samsung Electronics have disclosed prototypes for vertical charge trapping NAND structures.Toshiba in 2007 and Samsung in 2009 announced the development of 3D V-NAND, a means of building a standard NAND flash bit string vertically rather than horizontally to increase the number of bits in a given area of silicon.