floatinggate

Floatinggate refers to a type of non-volatile memory that uses a floating-gate transistor to store electrical charge. The floating gate is a conductor embedded in a MOS structure and is electrically isolated by insulating layers from the surrounding circuitry. Data are stored by charging or discharging the floating gate, which shifts the transistor’s threshold voltage and thus its ability to conduct at a given gate voltage. This change in threshold is read as a binary state, enabling data storage without continuous power.

Construction and operation: A typical floating-gate cell comprises a substrate with source and drain regions and a channel between them. A thin tunneling oxide separates the floating gate from the substrate, while a thicker intergate dielectric separates the floating gate from the control gate above it. Programming inserts or removes electrons on the floating gate through methods such as hot-electron injection or Fowler-Nordheim tunneling, typically by applying voltages to the control gate (and sometimes the drain). Erasing removes charge via tunneling back off the floating gate. The stored charge modulates the transistor’s threshold voltage, and read operations determine data by applying a gate voltage and sensing current.

History and variants: Floating-gate memory evolved from earlier EEPROM concepts and became the foundation of most flash memory technologies. Variants include charge-trap memories that replace the floating gate with a trapping layer (for example, nitride-based schemes), which can offer different endurance, scaling, and programming characteristics.

Applications and characteristics: Floating-gate memory is widely used in flash memory devices such as USB drives, solid-state drives, memory cards, and embedded microcontrollers. It provides non-volatile storage with relatively high density, but faces limitations in program/erase endurance, retention, and high-voltage requirements, which drive ongoing innovations in device design and wear management.