<p>SSDs  mainly depend on flash memory chips to store data. &nbsp;The name \"flash\"  was suggested because the process of erasing the memory contents  reminded him of the flash of a camera. Flash memory chips store data in a  large array of floating gate metal&ndash;oxide&ndash;semiconductor (MOS)  transistors. Silicon wafers are manufactured with microscopic transistor  dimension, now approaching 40 nanometers. In this flash memory thin  insulating glass layers are necessary for proper operation of the memory  cells. These layers are subjected to stressful temperatures and  voltages, and their insulating properties deteriorate over time. Quite  simply, flash memory can wear out.<strong></strong>A  floating gate memory cell is a type of metal-oxide-semiconductor  field-effect transistor (MOSFET). Silicon forms the base layer, or  substrate, of the transistor array. Areas of the silicon are masked off  and infused with different types of impurities in a process called  doping. Impurities are carefully added to adjust the electrical  properties of the silicon. Some impurities, for example phosphorous,  create an excess of electrons in the silicon lattice. Other impurities,  for example boron, create an absence of electrons in the lattice. The  impurity levels and the proximity of the doped regions are set out in a  lithographic manufacturing process. In addition to doped silicon  regions, layers of insulating silicon dioxide glass (SiO2) and  conducting layers of polycrystalline silicon and aluminum are deposited  to complete the MOSFET structure.</p>