Heat Conduction in Novel Electronic Films

Abstract

Heat conduction in novel electronic films influences the performance and reliability of micromachined transistors, lasers, sensors, and actuators. This article reviews experimental and theoretical research on heat conduction in single-crystal semiconducting and superconducting films and superlattices, polycrystalline diamond films, and highly disordered organic and oxide films. The thermal properties of these films can differ dramatically from those of bulk samples owing to the dependence of the material structure and purity on film processing conditions and to the scattering of heat carriers at material boundaries. Predictions and data show that phonon scattering and transmission at boundaries strongly influence the thermal conductivities of single-crystal films and superlattices, although more work is needed to resolve the importance of strain-induced lattice defects. For polycrystalline films, phonon scattering on grain boundaries and associated defects causes the thermal conductivity to be strongly anisotropic and nonhomogeneous. For highly disordered films, preliminary studies have illustrated the influences of impurities on the volumetric heat capacity and, for the case of organic films, molecular orientation on the conductivity anisotropy. More work on disordered films needs to resolve the interplay among atomic-scale disorder, porosity, partial crystallinity, and molecular orientation.

Thermal transport in phononic crystals and the observation of coherent phonon scattering at room temperature

“…In this formulation, assuming a sufficiently large sample thickness [23][24][25][26] and feature sizes 13 , if coherent boundary scattering were absent, the Si phonon dispersion would remain basically unaltered before and after the PnC patterning and fixing L c would lead to a constant incoherent boundary scattering limit (Supplementary Table 1). We thus set out to realize an experiment where the geometry of the PnC lattice is varied, while L c is kept constant.…”

Thermal conductivity of amorphous carbon thin films

“…6,7 But we also anticipate that these new data will provide valuable insights on the high and low conductivities that can be produced in thin film a-C for applications in the thermal engineering of microdevices. 8,9 The concept of a ''minimum thermal conductivity'' ⌳ min is based on a theory of heat transport originally proposed by Einstein: 10 the atomic vibrations are assumed to be incoherent and therefore heat diffuses between the Einstein oscillators on a time scale of 1/2 the period of vibration. Einstein's theory could not explain the large thermal conductivities of most crystalline dielectrics but his and related models 4,5,11 are useful for understanding the thermal conductivity of amorphous materials and crystals with certain types of strong disorder.…”

Nanoscale heat conduction across tunnel junctions

“…[4][5][6] In the present work, we employ electrical techniques that use a lithographically patterned metal stripe as a heater and electrical resistance thermometer. 7,8 We apply either dc or harmonic current to the heater and monitor resulting changes in its electrical resistance, which can be precisely calibrated as a function of temperature.…”