Investigation of coupling characteristics of series-connected phase-change memory cells varied in programmable volume

The coupling characteristics of two externally series-connected mushroom-type phase-change memory (PCM) cells varied in diameter of heater plug were investigated to assess the feasibility of the stacked PCM structure. The results indicated that the pair of the series-connected cells can accomplish triple-level storage with favorable features of direct overwrite capability and large programming margin. The mushroom-type cell was also demonstrated to be suitable for the concept of the stacked PCM structure due to its great tolerance to over-programming. The stacked PCM structure is considered as a potential approach for accomplishing the multilevel storage of PCM.