In mobile systems, the demand for the energy saving continues to require a low power memory sub-system. During the last decade, the floating-gate flash memory has been an indispensable low power memory solution. However, NOR flash memory has begun to show difficulties in scaling due to the device's reliability and yield issues. Over the past few years, phase-change random access memory (PRAM) has emerged as an alternative non-volatile memory (NVM) owing to its promising scalability and low cost process [1,2]. In this paper, a PRAM, implemented in a 58nm PRAM process with a low power double-data-rate nonvolatile memory (LPDDR2-N) interface, is presented [3].

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The diffusion of Ge in Ge-rich layer (GRL) and the factors affecting on it during the oxidation of strained Si1−xGex layers were examined. Strained Si1−xGex layers, having different initial Ge concentrations (x=0.15 and 0.3), were oxidized at 800 and 900°C in a dry O2 ambient for different oxidation times. The diffusion of Ge into the underlying Si1−xGex layer having an initial constant composition and the resulting transformation to GRL were both enhanced with an increase in oxidation temperature. After complete transformation to GRL, GeO2 started to become incorporated into the resulting oxide layer. The formation of GeO2 was initiated by the Ge saturation of the GRL layer with Ge and by the differences in diffusivity of Ge atoms in Si1−xGex and Si substrate. The relaxation occurred when the Ge concentration in the GRL reached a critical value and was not affected by either oxidation time or temperature.

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