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flash memory

Flash memory is a memory technology developed by Intel for fast, non-volatile memory that permanently stores data after the power supply is switched off. Flash memory technology was developed from the technology for Electrically Erasable PROMs( EEPROM) and uses the quantum mechanical effect in semiconductors.

The memory cells of a flash memory work with MOSFETs, which are equipped with a special electrode, the floating gate. The floating gate forms a charge trap in which the electrical charge is stored. It is located in an oxide layer below the control gate and normally prevents the charge from flowing to the N and P layers. The charge on the floating gate forms a conductive channel between drain and source as an electric field, through which the charge is read out. The charge is erased block by block. By applying a negative erase voltage, the charge carriers are driven out of the floating gate.

As an alternative to floating gate technology, a technology called charge-trap flash( CTF) is increasingly being used in flash memories, which enables higher storage densities to be achieved.

Flash memory architectures

Structure of a flash memory cell with floating gate

Structure of a flash memory cell with floating gate

Flash memories come in two architectures, as NAND gates and as NOR gates, both as single-cell flash memory cells, Single Level Cell( SLC), but also as multi-cells in which two or three digital states can be stored, the Multi Level Cell ( MLC), the Triple Level Cell( TLC) and the Quadruple Level Cell ( QLC). Since NAND flash es can store two states in each memory cell, this design is given preference over NOR flashes.

Flash memories are characterized by low energy consumption, are addressable byte by byte, and are writeable and erasable block by block. The number of save and erase operations is around 100,000. The access times are around 0.1 ns and are heavily dependent on the SSD controller(solid state disk), while the read speed is well above 100 MB/s. With this data rate, videos can be transferred in HDTV and in the 4k standard.

Classification of flash memory cells

Classification of flash memory cells

In flash memory technology, the individual chips, which have several gigabytes of storage capacity, can be combined into chip stacks with large storage capacity. Flash memories are used in hybrid hard disks or solid-state drives (SSD), but also in memory cards for workstations or in fast intermediate memories of mainframes; beyond that, however, primarily in single inline memory modules( SIMM), PC cards and PCMCIA cards, in digital cameras and MP3 players, USB sticks, camcorders and printers, tablet PCs, notebooks and handhelds.

There are special flash modules for notebooks, laptops, PDAs, printers and other peripherals such as digital cameras. The various designs have a proprietary name and notation: Examples include the Compact Flash Card( CF), SmartMedia Card, MemoryStick, Multimedia Card( MMC), the SD card, and others with storage capacities of up to one hundred gigabytes( GB) and above. Reading flash memories can be performed in special card readers, but also in the card slots of PCs, printers and notebooks or via PC card adapters.

Englisch: flash memory
Updated at: 07.09.2017
#Words: 500
Links: memory, non-volatile memory (NVM), data, power supply (PS), electrically erasable PROM (EEPROM)
Translations: DE

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