IBM Reveals 8-Bit Analog Chip With Phase-Change Memory
Today at the IEEE International Electron Devices Meeting in San Francisco, IBM reported a new 8-bit analog chip. But the true development was less about analog chips catching up to their digital peers and more a radical rethink of chip architecture. This chip is the first to perform 8-bit calculations right where information is stored.
IBM’s new analog chip is based on phase-change memory. The key ingredient is a material that can undergo phase changes in response to electrical current. Typically, these are alloys of germanium, tellurium, and antimony.
In one phase, which is conductive, the atoms are lined up nicely. In the other phase, which doesn’t conduct electricity, the atoms move around, heated locally by current, and become jumbled. A phase-change material held between two electrodes doesn’t switch completely between ordered and jumbled arrangements like ones and zeros.
Instead, at any point in time, there is a mix of both: The overall resistance of the material is determined by the size of the regions where atoms are jumbled. But these resistances suffer from drift and fluctuation. Because current passes through the phase-change material when information is read, the jumbled regions change a little bit every time—which has limited the precision and practicality of such devices.
To circumvent this problem, the IBM researchers introduced a so-called projection segmentto the phase-change memory device. First proposed in 2015 by the same team, the projection segment is a conducting layer of metal nitride that wraps around a phase-change material core and runs parallel to it between electrodes. The projection segment separates the information writing and reading processes.