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Information Sciences

Phonon Transport in Semiconductor Nanostructures  

     Nanoscale energy transport in crystalline semiconductors has become a subject of great practical as well as fundamental interest. The minimum feature size of commercially available semiconductor devices has entered the sub-100 nm regime. Electron transport and reliability in these nanscale transistors are expected to be strongly affected by highly localized heating. Thermal transport properties of semiconductor wires of diameters well below 100 nm are of great interest for potential thermoelectric applications.
    Continuum models for energy transport fail when the mean free path of heat carriers is comparable to or greater than the characteristic dimensions of a system under consideration. Despite previous research efforts, however, fundamental understanding of sub-continuum energy transport in silicon, GaAs, and other related semiconductors remains incomplete. This is due in part to the lack of experimental tools to directly probe propagation and scattering of short-wavelength phonons that dominate heat transport near room temperature and above.
    e are conducting an experimental and theoretical study of the thermal conductivity of silicon nanostructures. Scattering of phonons at the boundaries of ultra-thin films and nanowires results in reduction of the thermal conductivity from bulk values. By analyzing the magnitude and temperature dependence of the thermal conductivity of such well-defined nanostructures, we gain useful insight into the characteristics of phonons that dominate heat conduction.

Micro- and Nano-scale Thermal Phenomena in Magnetic Data Storage Device  

     As the magnetic information storage industry strives to maintain continued growth in areal density and data transfer rate, they face a number of technical challenges. Among the most serious challenges is the degradation in performance and reliability of recording heads due to self-heating. Self-heating is a growing concern because efficient removal of heat generated in recording heads becomes more difficult with continued miniaturization. To successfully meet the thermal management challenges of future magnetic recording technology, one must have a thorough fundamental understanding of micro- and nano-scale heat transfer in recording heads.

    We are conducting fundamental studies of micro- and nanoscale heat transfer in thin film magnetic recording heads. We are especially interested in thermal phenomena in current-perpendicular-to-plane (CPP) tunneling magnetoresistance (TMR) and giant magnetoresistance (GMR) sensors. TMR sensors consist of ultra-thin (> 2 nm) dielectric tunnel barrier layers sandwiched between two magnetic electrodes. We experimentally determine the thermal resistance of tunnel barriers as thin as 1.5 nm, which is a remarkable feat. We are also conducting studies of heat generation and transport during writing operations of recording heads, which so far have received little attention despite their significance in head-media interface reliability.

UCLA Department of Mechanical and Aerospace Engineering, Last update: January 31st, 2008