Thermomechanical formation and thermal sensing of nanometer-scale indentations in PMMA thin films for parallel and dense AFM data storage

Thermomechanical writing occurs as Joule-heated, cantilevered tips imprint nanometer-scale indentations (bits) in a 50-nm-thick polymer (PMMA) film. Thermal data reading incorporates the same cantilevers operated in a mode to detect a temperature change when a tip follows the contour of a previously written bit. Binnig et al. [1] demonstrated single-cantilever writing and reading density at 400 Gbit/in². A micromachined 32×32 cantilever array has been fabricated [2] and has demonstrated parallel read/write operation at 150 Gbit/in² [3]. Although much progress has been made to develop a thermomechanical data storage device [4], the fundamental process of thermomechanical bit formation is not well understood. Furthermore, macroscopic polymer rheological parameters are unlikely to apply as the bit size approaches the polymer molecule radius of gyration. We have performed detailed investigations of the thermomechanical storage processes by applying atomic force microscope (AFM)-based force detection during thermal operation. We examine the thermomechanics of polymer indentation with respect to time and temperature of interaction. This work impacts the operation of AFM cantilevers for combined thermal writing and reading and understanding of fundamental polymer mesoscopic transport.