  Stateful logic is a digital processing-in-memory technique that could address
von Neumann memory bottleneck challenges while maintaining backward
compatibility with standard von Neumann architectures. In stateful logic,
memory cells are used to perform the logic operations without reading or moving
any data outside the memory array. Stateful logic has been previously
demonstrated using several resistive memory types, mostly by resistive RAM
(RRAM). Here we present a new method to design stateful logic using a different
resistive memory - phase change memory (PCM). We propose and experimentally
demonstrate four logic gate types (NOR, IMPLY, OR, NIMP) using commonly used
PCM materials. Our stateful logic circuits are different than previously
proposed circuits due to the different switching mechanism and functionality of
PCM compared to RRAM. Since the proposed stateful logic form a functionally
complete set, these gates enable sequential execution of any logic function
within the memory, paving the way to PCM-based digital processing-in-memory
systems.

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