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

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.

[1]  Simone Raoux,et al.  Crystallization properties of ultrathin phase change films , 2008 .

[2]  D. Emin,et al.  Hall mobility of amorphous Ge2Sb2Te5 , 2006 .

[3]  D. Suh,et al.  Thermoelectric heating of Ge2Sb2Te5 in phase change memory devices , 2010 .

[4]  A. T. Burkov,et al.  Experimental set-up for thermopower and resistivity measurements at 100-1300 K , 2001 .

[5]  Keiji Tanaka,et al.  Electronic Properties of Amorphous and Crystalline Ge2Sb2Te5 Films , 2005 .

[6]  John Ziman,et al.  Electrons and Phonons: The Theory of Transport Phenomena in Solids , 2001 .

[7]  T Uruga,et al.  Toward the ultimate limit of phase change in Ge(2)Sb(2)Te(5). , 2010, Nano letters.

[8]  Thermoelectric power of metallic films in the Mayadas-Shatzkes model , 1977 .

[9]  M. Asheghi,et al.  Thermoelectric Characterization and Power Generation Using a Silicon-on-Insulator Substrate , 2012, Journal of Microelectromechanical Systems.

[10]  A. J. Tosser,et al.  Thermoelectric power of thin polycrystalline metal films in an effective mean free path model , 1980 .

[11]  Thickness dependence of the amorphous-cubic and cubic-hexagonal phase transition temperatures of GeSbTe thin films on silicon nitride , 2012 .

[12]  M. Kitao,et al.  Thermoelectric Power of Glassy As40Se60−xTex , 1985 .

[13]  H. Wong,et al.  Microthermal Stage for Electrothermal Characterization of Phase-Change Memory , 2011, IEEE Electron Device Letters.

[14]  L. E. Shelimova,et al.  Thermoelectric Properties of nGeTe · mSb2Te3Layered Compounds , 2001 .

[15]  Mehdi Asheghi,et al.  Impact of thermoelectric phenomena on phase-change memory performance metrics and scaling , 2012, Nanotechnology.

[16]  Eric Pop,et al.  Nanoscale Joule heating, Peltier cooling and current crowding at graphene–metal contacts , 2011, Nature Nanotechnology.

[17]  William A. Goddard,et al.  Silicon nanowires as efficient thermoelectric materials , 2008, Nature.

[18]  Oliver Paul,et al.  Test structures to measure the Seebeck coefficient of CMOS IC polysilicon , 1997 .

[19]  Li Shi,et al.  Measuring Thermal and Thermoelectric Properties of One-Dimensional Nanostructures Using a Microfabricated Device , 2003 .

[21]  Kenneth E. Goodson,et al.  PHONON-BOUNDARY SCATTERING IN THIN SILICON LAYERS , 1997 .

[22]  S. Dong,et al.  Microstructures and thermoelectric properties of GeSbTe based layered compounds , 2007 .

[23]  Christofer Hierold,et al.  Electrothermal effects at the microscale and their consequences on system design , 2006 .

[24]  Electrical characterization of sputtered Ge:Sb:Te films using impedance measurements , 2002 .

[25]  Sang Chul Lee,et al.  Thermal conductivity anisotropy and grain structure in Ge2Sb2Te5 films , 2011 .

[26]  Ian G. Brown,et al.  Thermoelectric effect in very thin film Pt/Au thermocouples , 2006 .

[27]  Joachim Sonntag,et al.  Disordered electronic systems. III. Thermoelectric power in alloys with phase separation , 2006 .

[28]  Helena Silva,et al.  Self-heating of silicon microwires: Crystallization and thermoelectric effects , 2011 .