Testing Algorithms for Hard to Detect Thermal Crosstalk Induced Write Disturb Faults in Phase Change Memories

Phase change memory (PCM) is a promising non-volatile memory technology, to serve as storage class memory in modern systems. However, during write operations on PCM cells, high temperatures are locally generated for the heating of the used phase change material. The heat diffusion may influence adjacent cells (thermal crosstalk), leading to the generation of write disturb faults and the appearance of errors in the data stored in the memory array. Moreover, as technology scaling increases proximity among cells, the probability of thermal crosstalk influence is also increased. Thermal crosstalk is a key reliability challenge in PCMs. Although various techniques have been proposed to alleviate its influence, it may affect the memory operation under special conditions that maximize the heat in the neighborhood of a cell. Due to these special conditions, the corresponding write disturb faults are hard to detect. Existing testing solutions in literature are not capable of producing such conditions and may fail to cover those hard to detect faults. In this paper, we propose effective testing algorithms, capable of generating proper conditions for the activation and detection of hard to detect thermal induced write disturb faults, at a cost-efficient manner. The algorithms' complexity varies from 3MxN to 10MxN (where M and N are the number of memory array rows and columns respectively).