A phone remembers by breaking a rule
Flash memory stores bits by letting electrons tunnel onto an isolated conductor. They should not be able to cross the insulator. A thin enough insulator is not a veto.
Established2 min read
Kahng and Sze proposed the floating-gate transistor in 1967. A conductive island is wrapped in oxide. A strong pulse lets electrons tunnel through the oxide onto the island, or off it. With the pulse gone, the barrier is thick enough, in probability, that the charge sits for years. The bit is a trapped surplus.
Every USB stick, SD card, and phone vault is this trick at industrial scale. Quantum mechanics is not confined to the physics department. It is the reason the picture is still there in the morning.
Caveats
- Charge does leak, slowly. Flash is not an archive for centuries.
- Other memories — magnetic disks, SRAM — do not use tunnelling. Flash does.
Sources
- 1Kahng D., Sze S. M.. A Floating Gate and Its Application to Memory Devices. Bell System Technical Journal 46, 1967.