SONOS, short for "silicon–oxide–nitride–oxide–silicon", more precisely, "polycrystalline silicon"—"silicon dioxide"—"silicon nitride"—"silicon dioxide"—"silicon",is a cross sectional structure of MOSFET (metal-oxide-semiconductor field-effect transistor), realized by P.C.Y. Chen of Fairchild Camera and Instrument in 1977. This structure is often used for non-volatile memories, such as EEPROM and flash memories. It is sometimes used for TFT LCD displays.It is one of CTF (charge trap flash) variants. It is distinguished from traditional non-volatile memory structures by the use of silicon nitride (Si3N4 or Si9N10) instead of "polysilicon-based FG (floating-gate)" for the charge storage material.A further variant is "SHINOS" ("silicon"—"hi-k"—"nitride"—"oxide"—"silicon"), which is substituted