EEPROM (redirected from EEPROMs)

(Electrically Erasable Programmable ROM) A rewritable memory chip that holds its content without power. Although EEPROMs spawned flash memory, EEPROMs are byte addressable at the write level, whereas flash chips must erase a block of bytes before rewriting.

A Floating Gate Holds the Charge
EEPROMs use a transistor with a floating gate underneath a control gate. To program the bit, a voltage is applied to the control gate. This causes electrons to tunnel through the insulating oxide layer into the floating gate, which impedes subsequent operation of the control gate. The 0 or 1 is determined by whether the voltage on the control gate is blocked or not.

EEPROMs have a lifespan of between 10K and 100K write cycles, which is considerably greater than the EPROMs (single "E") that preceded them. See EPROM, SEEPROM, memory types and flash memory.

EEPROM Floating Gate

The storage part of an EEPROM cell acts like a permanently-open or closed transistor. Charging is accomplished by grounding the source and drain terminals and placing a voltage on the control gate. When the "floating gate" is charged, it impedes the flow of electrons from the control gate to the silicon, and the 0 or 1 is determined by whether the voltage on the control gate is blocked or not. A reverse voltage from another transistor causes the charge to dissipate into the substrate.

EEPROM Cell

A single EEPROM bit is made up of two transistors: the MOS transistor for erasure and the floating gate transistor for storage. (Image courtesy of TechBites Interactive Inc, www.techbites.com.)

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EEPROM - Electrically Erasable Programmable Read-Only Memory See also EAPROM.