TEM/STEM Investigations of Phase Change Materials for Non-volatile Memory Applications

Phase change materials are very interesting for future information technology because of their possibility to encode information in the readable difference of physical properties between the crystalline and the amorphous phase. Phase change materials are the dominant non-volatile memory material used in rewritable optical memory. This includes the current state of the art Blue-ray disc. Mobile computer platforms like smart mobile phones, tablets and netbooks are in need of energy and space efficient memory. Optical or magnetic recording media do not meet these needs anymore. Phase change materials used as non-volatile electronic memories are promising candidates as competition for flash memory. Flash memory is the current state of the art electronic non-volatile memory. In addition, non-volatile electronic applications as competition to Dynamic Random Access Memory (DRAM) are possible because of the high switching speeds of phase change materials. The key to the successful application of phase change materials as electronic non-volatile memory is the understanding of their physical properties and especially their switching kinetics. In the present work, transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) were used in a systematic manner to investigate the properties of a variety of phase change materials. The crystal growth velocities of grains growing in 30 nm thick amorphous layers of the phase change materials Ag$_{4}$In$_{3}$Sb$_{67}$Te$_{26}$ (AIST) and GeTe were measured directly by TEM bright field imaging. Grains of the measured materials were grown in a matrix of the amorphous phase by ex situ heating. This is done for sputtered as deposited material and material molten by laser which is quenched to room temperature. Furthermore we investigated lamellas of as deposited and melt quenched AIST and GeTe by fluctuation electron microscopy (FEM). The comparison of growth velocity and FEM data reveals that increasing medium range order (MRO) leads to a decrease in growth velocity. This is also related to different glassy states of the phase change materials. [...