 Both floating gate flash and charge trapping flash use a stacked gate structure in which a floating gate or charge trapping layer lies immediately above the channel, and below a control gate.The floating gate or charge trapping layer is insulated from the channel by a tunnel oxide layer and from the control gate by a gate oxide layer.Materials for all of these layers are the same with the exception of the storage layer, which is conductive polysilicon for the floating gate structure and is typically silicon nitride for the charge trap.