Floating-gate MOSFET

The floating-gate MOSFET (FGMOS), also known as a floating-gate MOS transistor or floating-gate transistor, is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) where the gate is electrically isolated, creating a floating node in direct current, and a number of secondary gates or inputs are deposited above the floating gate (FG) and are electrically isolated from it. These inputs are only capacitively connected to the FG. Since the FG is surrounded by highly resistive material, the charge contained in it remains unchanged for long periods of time, nowadays typically longer than 10 years. Usually Fowler-Nordheim tunneling and hot-carrier injection mechanisms are used to modify the amount of charge stored in the FG. The FGMOS is commonly used as a floating-gate memory cell, the digital storage element in EPROM, EEPROM and flash memory technologies. Other uses of the FGMOS include a neuronal computational element in neural networks, analog storage element, digital potentiometers and single-transistor DACs. The first MOSFET was invented by Mohamed Atalla and Dawon Kahng at Bell Labs in 1959, and presented in 1960. The first report of a FGMOS was later made by Dawon Kahng and Simon Min Sze at Bell Labs, and dates from 1967. The earliest practical application of FGMOS was floating-gate memory cells, which Kahng and Sze proposed could be used to produce reprogrammable ROM (read-only memory). Initial applications of FGMOS was digital semiconductor memory, to store nonvolatile data in EPROM, EEPROM and flash memory. In 1989, Intel employed the FGMOS as an analog nonvolatile memory element in its electrically trainable artificial neural network (ETANN) chip, demonstrating the potential of using FGMOS devices for applications other than digital memory. Three research accomplishments laid the groundwork for much of the current FGMOS circuit development: Thomsen and Brooke's demonstration and use of electron tunneling in a standard CMOS double-poly process allowed many researchers to investigate FGMOS circuits concepts without requiring access to specialized fabrication processes.