Thermoelectric phenomena strongly influence the behavior of chalcogenide materials in nanoelectronic devices including phase-change memory cells. This work uses a novel silicon-on-insulator experimental structure to measure the phase and temperature-dependent Seebeck and Thomson coefficients of Ge2Sb2Te5 films including the first data for films of thickness down to 25 nm. The Ge2Sb2Te5 films annealed at different temperatures contain varying fractions of the amorphous and crystalline phases which strongly influence the thermoelectric properties. The Seebeck coefficient reduces from 371 μV/K to 206 μV/K as the crystalline fraction increases by a factor of four as quantified using x-ray diffraction. The data are consistent with modeling based on effective medium theory and suggest that careful consideration of phase purity is needed to account for thermoelectric transport in phase change memory.

Phase purity and the thermoelectric properties of Ge2Sb2Te5 films down to 25 nm thickness

For low-dimensional materials, size effect of a physical property is usually expected to occur when one (or more) of the dimension sizes decreases to that comparable to or smaller than one of the intrinsic characteristic lengths, e.g., the mean free path. We report here an unexpected size effect, that in centimeter-long stripes of 100-nm-thick metallic thin films, a reduction of the absolute value of thermopower occurs when the stripe width is in the order of 30-50 μm, which is 100–1000 times larger than the intrinsic mean free path of the material. When the stripe width is reduced to 1.5 μm, a relative reduction of thermopower up to 35% is measured in some metals. We suggest that the sidewall scattering due to rough edges of these stripes may be the origin of this unexpected phenomenon. The results may be applied to construct novel thermoelectric devices, such as thermocouples made from a single metal film.

Unexpected size effect in the thermopower of thin-film stripes

Description of electronic transport properties of monocrystalline films by a statistical model

Recent experimental measurements reported on the electrical resistivity, temperature coefficient of resistance and thermoelectric power of nineteen transition metal films have been reviewed. All the theoretical models proposed so far to analyse these experimental results have been briefly summarized. Some suggestions for further experimental study on transition metal films are outlined.

C.R. Tellier

Papers

Thermoelectric power of metallic films in the Mayadas-Shatzkes model