Phase change memory lets a single bit act as different logic gates

Columbia University

Phase change materials can switch between two forms depending on how quickly they're cooled. Cool them quickly and you get an amorphous form, which provides significant resistance to the flow of electrons. Cool them slowly and they will allow electrons to flow more readily. Once cooled, these two forms remain stable, locking the differences in conduction in place.

This difference has been exploited to create a type of storage called phase change memory that's as fast as standard RAM but retains its contents between power cycles. So far, phase change memory hasn't been a commercial success. But some researchers are now experimenting with the idea of building processors out of the technology.

The efforts started out with a simple arrangement of resistors and phase change bits that operated like a logic gate, allowing AND, OR, and NOT operations. But a new paper shows that by carefully controlling how the phase change bits are set in the first place, it's possible to have a single bit perform different logic operations, acting as a NOT, NOR, or NAND gate. Regardless of the operation's output, it's stored even if power is shut down.