Flash memory lifetimes are limited by use, because repeated program/erase (P/E) cycles degrade the tunnel oxide which insulates flash memory cells. In principle, heating the oxide will repair the damage but thermal annealing has been impractical because flash memories can’t tolerate the high temperatures and long baking times required.
At the upcoming International Electron Devices Meeting, Macronix researchers will describe how they built flash memories that could heal themselves by means of tiny onboard heaters that provide thermal annealing just at the spots where it is needed. They modified the wordline from a single-ended to a double-ended structure, which enabled current to be passed through the gate to generate Joule heating. High temperatures (>800° C) thus were generated only in immediate proximity to the gate. The devices demonstrated record-setting endurance of >100 million P/E cycles with excellent data retention. Interestingly, the researchers also saw that the heating enabled faster erasing, which is thought to be temperature-independent.
The schematic image above shows the structure of the diode-strapped wordline. A PN diode can be formed directly on top of the wordline, and local interconnect can be used to connect to the metal heat plates.
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