RAM cells need constant refreshing, however NAND FLASH cells can retain data for years together. What makes this possible ?
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5\$\begingroup\$ Not all RAM cells need constant refreshing. \$\endgroup\$ – Ignacio Vazquez-Abrams Apr 28 '14 at 9:49
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What makes NAND memories non-volatile is that the logic state is retained in a physical state that doesn't depend on the supply voltage.
For EEPROM memories in general (including Flash), this is a charge trapped in a floating gate.
answered Apr 28 '14 at 9:52
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As clabacchio pointed out, NAND flash memories can stores information in an array of memory cells made from Floating-gate MOSFET. Also some newer flash memory(included NAND memories) has a new technology. it's Multi-level cell.
I think these links will be very helpful and useful:
Note: I know that they have spoken about Flash memory in these links but the technology that they have spoken about it is NAND type.
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Also note that data retention is usually guaranteed for a period, e.g. 10 years. Also note that bit flipping can occur. SD cards for example usually have ECC built in to correct this, to some extent.
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1\$\begingroup\$ While true this doesn't really answer the question of how they work, as opposed to the implications of using FLASH memory. \$\endgroup\$ – PeterJ Jun 4 '14 at 1:39
