Correlative transmission electron microscopy and electrical properties study of switchable phase-change random access memory line cells

Abstract

Phase-change memory line cells, where the active material has a thickness of 15 nm, were prepared for transmission electron microscopy (TEM) observation such that they still could be switched and characterized electrically after the preparation. The result of these observations in comparison with detailed electrical characterization showed (i) normal behavior for relatively long amorphous marks, resulting in a hyperbolic dependence between SET resistance and SET current, indicating a switching mechanism based on initially long and thin nanoscale crystalline filaments which thicken gradually, and (ii) anomalous behavior, which holds for relatively short amorphous marks, where initially directly a massive crystalline filament is formed that consumes most of the width of the amorphous mark only leaving minor residual amorphous regions at its edges. The present results demonstrate that even in (purposely) thick TEM samples, the TEM sample preparation hampers the probability to observe normal behavior and it can be debated whether it is possible to produce electrically switchable TEM specimen in which the memory cells behave the same as in their original bulk embedded state. V

High speed, high temperature electrical characterization of phase change materials: metastable phases, crystallization dynamics, and resistance drift

“…2). 9,[25][26][27][30][31][32][33] The sinusoidal segments used before and after the pulse reveal the initial crystalline state (hexagonal) resistance and the metastable amorphous state resistance along with the first 2 ms of the crystallization process (Fig. 2a).…”