Modeling and simulation of nanometer-scale thermomechanical data bit formation

In thermomechanical data storage, pulse-heated atomic force microscope (AFM) cantilever scans over a thin polymer substrate. As heat flows along the AFM cantilever tip into the polymer, the polymer softens and is locally displaced by the tip, creating indentations of radius near 30 run. As a scanning cantilever follows the contour of previously written data bits, a measurable change in the temperature signal of the cantilever allows thermal data reading. Heat conduction governs the ultimate limits of thermomechanical data storage density and writing rate. The size and formation time of single data bit depend upon heat transfer in the AFM cantilever, along the cantilever tip, and in the polymer data layer. The temperature of the tip-polymer interface, which governs bit formation time, is lower than the value predicted from continuum theory due to phonon-boundary scattering in the silicon cantilever tip. While a higher cantilever tip temperature will reduce the polymer mechanical modulus during bit formation, increased temperature or longer heating times will increase heat spread in the polymer data layer. An increase in the polymer melted region dimensions will limit the spatial periodicity of data bits, as overlap melting from adjacent bits could lead to bit erasing. The present work analyses heat conduction in the cantilever tip and in the polymer data layer during thermomechanical data writing and reading, and addresses sub-continuum heat conduction in the cantilever tip as well as thermal conductivity anisotropy in the polymer data layer.