HT2005-72679 THERMAL CHARACTERIZATION OF DIELECTRIC AND PHASE CHANGE MATERIALS FOR THE OPTICAL RECORDING APPLICATIONS

Abstract Advances in the phase change optical recording technology strongly depend on the optical and thermal optimizations of the metal/ZnS-SiO 2 /phase change multilayer structure, which requires accurate modeling and thermal characterization of PC media structure. In the present work, the thermal conductivities of the amorphous and crystalline Ge 4 Sb 1 Te 5 (GST) phase change; and ZnS-SiO 2 dielectric layers of thickness in the range of 50 nm to 300 nm have been measured using the transient thermoreflectance technique. The data are between a factor of 2-4 different from the previously measured values for thin film and bulk samples. The thermal boundary resistance at metal/ZnS-SiO 2 interface is found to be around 7×10 -8 m 2 W -l . This might have serious implications for the future phase change recording application which attempts to achieve the high writing speeds by decreasing the thickness of ZnS-SiO 2 dielectric layer

Temperature-Dependent Thermal Conductivity of Undoped Polycrystalline Silicon Layers

Polycrystalline silicon is used in microelectronic and microelectromechanical devices for which thermal design is important. This work measures the in-plane thermal conductivities of free-standing undoped polycrystalline layers between 20 and 300 K. The layers have a thickness of 1 μm, and the measurements are performed using steady-state Joule heating and electrical-resistance thermometry in patterned aluminum microbridges. The layer thermal conductivities are found to depend strongly on the details of the deposition process through the grain size distribution, which is investigated using atomic force microscopy and transmission electron microscopy. The room-temperature thermal conductivity of as-grown polycrystalline silicon is found to be 13.8 W·m -1 ·K -1 and that of amorphous recrystallized polycrystalline silicon is 22 W·m -1 ·K -1 , which is almost an order of magnitude less than that of single-crystal silicon. The maximum thermal conductivities of both samples occur at higher temperatures than in pure single-crystalline silicon layers of the same thickness. The data are interpreted using the approximate solution to the Boltzmann transport equation in the relaxation time approximation together with Matthiessen's rule. These measurements contribute to the understanding of the relative importance of phonon scattering on grain and layer boundaries in polysilicon films and provide data relevant for the design of micromachined structures.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44568/1/10765_2004_Article_297892.pd

Simulation of dimensionality effects in thermal transport

The discovery of nanostructures and the development of growth and fabrication techniques of one- and two-dimensional materials provide the possibility to probe experimentally heat transport in low-dimensional systems. Nevertheless measuring the thermal conductivity of these systems is extremely challenging and subject to large uncertainties, thus hindering the chance for a direct comparison between experiments and statistical physics models. Atomistic simulations of realistic nanostructures provide the ideal bridge between abstract models and experiments. After briefly introducing the state of the art of heat transport measurement in nanostructures, and numerical techniques to simulate realistic systems at atomistic level, we review the contribution of lattice dynamics and molecular dynamics simulation to understanding nanoscale thermal transport in systems with reduced dimensionality. We focus on the effect of dimensionality in determining the phononic properties of carbon and semiconducting nanostructures, specifically considering the cases of carbon nanotubes, graphene and of silicon nanowires and ultra-thin membranes, underlying analogies and differences with abstract lattice models.Comment: 30 pages, 21 figures. Review paper, to appear in the Springer Lecture Notes in Physics volume "Thermal transport in low dimensions: from statistical physics to nanoscale heat transfer" (S. Lepri ed.

Thermal Transport in Micro- and Nanoscale Systems

Small-scale (micro-/nanoscale) heat transfer has broad and exciting range of applications. Heat transfer at small scale quite naturally is influenced – sometimes dramatically – with high surface area-to-volume ratios. This in effect means that heat transfer in small-scale devices and systems is influenced by surface treatment and surface morphology. Importantly, interfacial dynamic effects are at least non-negligible, and there is a strong potential to engineer the performance of such devices using the progress in micro- and nanomanufacturing technologies. With this motivation, the emphasis here is on heat conduction and convection. The chapter starts with a broad introduction to Boltzmann transport equation which captures the physics of small-scale heat transport, while also outlining the differences between small-scale transport and classical macroscale heat transport. Among applications, examples are thermoelectric and thermal interface materials where micro- and nanofabrication have led to impressive figure of merits and thermal management performance. Basic of phonon transport and its manipulation through nanostructuring materials are discussed in detail. Small-scale single-phase convection and the crucial role it has played in developing the thermal management solutions for the next generation of electronics and energy-harvesting devices are discussed as the next topic. Features of microcooling platforms and physics of optimized thermal transport using microchannel manifold heat sinks are discussed in detail along with a discussion of how such systems also facilitate use of low-grade, waste heat from data centers and photovoltaic modules. Phase change process and their control using surface micro-/nanostructure are discussed next. Among the feature considered, the first are microscale heat pipes where capillary effects play an important role. Next the role of nanostructures in controlling nucleation and mobility of the discrete phase in two-phase processes, such as boiling, condensation, and icing is explained in great detail. Special emphasis is placed on the limitations of current surface and device manufacture technologies while also outlining the potential ways to overcome them. Lastly, the chapter is concluded with a summary and perspective on future trends and, more importantly, the opportunities for new research and applications in this exciting field

Thermal characterization of Cu/CoFe multilayer for giant magnetoresistive head applications

Abstract Giant Magnetoresistance (GMR) head technology is one of the latest advancement in hard disk drive (HDD) storage industry. The GMR head superlattice structure consists of alternating layers of extremely thin metallic ferromagnet and paramagnet films. A large decrease in the resistivity from antiparallel to parallel alignment of the film magnetizations can be observed, known as giant magnetoresistance (GMR) effect. The present work characterizes the in-plane electrical and thermal conductivities of Cu/CoFe GMR multilayer structure in the temperature range of 50 K to 340 K using Joule-heating and electrical resistance thermometry in suspended bridges. The thermal conductivity of the GMR layer monotonously increased from 25 Wm -1 K -1 (at 55 K) to nearly 50 Wm -1 K -1 (at room temperature). We also report the GMR ratio of 17% and a large negative magnetothermal resistance effect (GMTR) of 33% in Cu/CoFe superlattice structure. The Boltzmann transport equation (BTE) is used to estimate the GMR ratio, and to investigate the effect of repeats, as well as the spin-dependent interface and boundary scatting on the transport properties of the GMR structure. Aside from the interesting underlying physics, these data can be used in the predictions of the Electrostatic Discharge (ESD) failure and self-heating in GMR heads