Two Carrier Heat Transfer Modeling for Heat Assisted Magnetic Recording

In this work we show the structure and application of a two carrier thermal model applied to a near field transducer, representative of that used in Heat Assisted Magnetic Recording (HAMR). As part of the HAMR device operation, high energy non-thermalized electrons are initially excited by laser incidence on a gold nanostructure. The high energy electrons can travel in a ballistic fashion over longer distances than the optical thickness of gold, resulting in a spreading of the local heat. During their travel the hot electrons collide with lower-energy electrons, thermalizing the hot electrons via inelastic scattering. The thermalized electrons then transfer energy to the lattice due to electron-phonon coupling, as captured in the two carrier model. Starting with an electromagnetic solution for local heating in a sub-micron-scale microfabricated gold structure, the chosen modeling technique applies physical effects of unique interest at the nanometer scale, including brief ballistic transport of hot electrons, experimentally-verified interface thermal resistance, and electron-phonon temperature mismatch. By design, the model is built to use far-field boundary conditions from conventional one-carrier FEMs as well as lubrication-flow computational fluid dynamics. The fundamental governing equations of the two carrier model are two versions of Poisson’s Equation for heat diffusion, coupled by empirically determined terms. These equations are combined with equations for interfacial discontinuities in the temperature fields, yielding a third degree of freedom. The continuous fields are discretized using the finite difference method, and solved using algorithms developed for linear algebra, such as Gaussian Elimination, or non-direct iterative methods. Through use of the model we explore effects of ballistic electron transport length, electron-phonon coupling, as well as interfacial thermal resistance between gold and neighboring ceramics. The model results show the relative impact of the nanoscale heat transfer phenomena in a nanometer scale metal-ceramic structure, allowing us to identify the relative importance of design features and compare candidate designs.