NAND flash layout Transistors are strung together in a series Similar to the

Nand flash layout transistors are strung together in

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NAND flash layout Transistors are strung together in a series Similar to the transistors in an NAND gate 66 Output F = 0 only when both a & b = 1 I.e., F will be grounded only when both a and b conduct
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NAND reading 67 Apply V on to all others so that they all conduct, no mater they are charged or not. Bit line
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NAND flash 68
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Write and erase Write: 1 => 0 Apply high POSITVE voltage (>> voltage for read) to the control gate Attract electrons from channel to floating gate (through quantum tunneling) Erase: 0 => 1 Need to apply much higher NEGATIVE voltage Get rid of electrons from floating gate May stress surrounding cells So dangerous to do on individual pages 69
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Read/write units Page is the smallest unit for read and write (write is also called program, 1->0) Block is the smallest unit for erase (0->1) i.e., make cells "empty" (i.e., no electrons) 70
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Example 71
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Latencies: read, write, and erase 72
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P/E cycle P: program/write; E: erase Every write & erase damages oxide layer surrounding the floating-gate to some extent P/E cycle: Data are written to cells (P): cell value from 1 -> 0 Then erased (E): 0 -> 1 73
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Multi-level cell (MLC) 74 - state-drive-primer-2-slc-mlc-and-tlc-nand-flash Note different levels of electrons
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MLC reading 2 bits, 3 intermediate voltages 75 00 10 01 11 V2 V3 V1 Current vs voltage
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SLC compared with MLC SLC: Less complex Faster More reliable Less storage More costly 76
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Read more Solid-state revolution: in-depth on how SSDs really work How do SSDs work? - extremetech-explains-how-do-ssds-work 77
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References How Flash Memory Works Floating Gate Basics ash.html Friend of Flash hive/2008/86/040-041_logfs/article.html 78
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References Understanding Flash: Floating Gates and Wear - flash-floating-gates-and-wear/ From Transistors to Functions ansistors2Gates/ 79
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References Solid State Drive Primer - tech.com/resources/blog/details/solid-state-drive- primer-1-the-basic-nand-flash-cell How Does a Transistor Work? &feature=youtu.be 80
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References How Flash Memory Works 81
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  • Fall '14
  • Flash memory, Hard disk drive, Solid-state drive, Seek time

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