Fabrication and phase transition of long-range-ordered, high-density GST nanoparticle arrays

We use a monolayer of self-assembled polystyrene (PS) spheres (220 nm in diameter) as a reactive ion etching (RIE) mask to fabricate large-scale (more than 1 cm(2)), long-range-ordered, high-density Ge(1)Sb(2)Te(4) (GST) phase-change material nanoparticle arrays. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) images show that periodic and isolated GST nanoparticle arrays 30-80 nm high and 150-200 nm bottom diameter were formed. Phase transitions of the GST films and nanoparticle arrays were studied by subjecting the samples to high-resolution transmission electron microscopy (HRTEM) electron-beam radiation. Nanocrystals between 2 and 5 nm in diameter were observed for GST nanoparticle arrays due to the large surface-to-volume ratio. The density of the GST arrays can reach as high as 10(9) cm(-2), which can lead to the realization of future high-density phase-change random access memory (PCRAM).