Noncontact SThM Thermal Conductivity Measurements of GeSbTe Thin Films Sputtered on Silicon and Glass Substrates

Abstract

Chalcogenide materials based on germanium–antimony–tellurium (GST) are typically used in phase change memory (PCM) applications. The thermal conductivity of GST films is an important factor in predicting the temperature evolution and the structural alterations of the material in response to rapid thermal transitions inherent in memory operations. While several techniques have been used to determine the thin film thermal conductivity of GSTs, they require fabricating electrical connections for metal heaters or thermometers on test samples. In this paper, we report using a noncontact scanning thermal microscopy (SThM) technique to measure the thermal conductivity of GST thin films while circumventing the need for sample preparation. A Wollaston wire probe of a 5-μm diameter was used as a Joule-heated thermometer to measure the probe thermal resistance in air far away and at 100 nm away from the sample surface. Detailed heat transfer modeling between the probe, sample, and ambient, which considers the nonclassical heat transfer across the gap between the SThM probe and sample surface, was used to determine the thermal resistance of several GST films sputtered with different powers on glass and silicon substrates. The thermal conductivity of GST thin film shows a reducing trend from 0.7 to 0.2 W m−1 K−1 when the thickness reduces from 159 nm to 24 nm. The reasons for thermal conductivity reduction are elucidated based on analytical thermal conductivity modeling.