A method for locating a fault in a communications network includes modifying the time-to-live value in an Internet Protocol header of a data packet and transmitting the data packet through the communications network. The device may include a semiconductor substrate including a peripheral region and a cell array region, wherein the substrate in the cell array region may be recessed lower than the peripheral region, a plurality of cell transistor layers stacked in the cell array region, and a plurality of peripheral circuit transistors formed in the peripheral region. The cover and the core have a difference in Shore D hardness therebetween such that 525.