We present a novel scalable and stackable nonvolatile solid state memory. Each cell consists of a storage element, based on phase change memory (PCM) element, and an integrated selector, using an Ovonic threshold switch (OTS). The cell is implemented to enable a true cross-point array. The main device characteristics and behaviors, corresponding physical processes in different operation modes, and key material properties are discussed.

This work presents an analytical model of crystalline phase formation in nanoglasses of phase change memory. We describe a data loss mechanism when the cell resistance changes significantly at elevated temperatures over long periods of time with no electrical bias applied. Unlike the standard approach, which relates crystalline shunt formation to aggregates of crystalline particles forming the percolation cluster, we look at the rare events of almost rectilinear path formation in very thin structures. They can occur at crystalline volume fractions considerably lower than the critical volume fraction required for percolation. We find the characteristic parameters which can describe statistics of these rare events.

We discuss possible mechanisms for Poole-Frenkel type of non-ohmic conduction in chalcogenide glasses in the range of room temperatures. Overall, we list 8 such mechanisms, only one of which (Schottky emission) can be ruled out as inconsistent with the observations. Seven others can give more or less satisfactory fits of the observed non-linear IV curves. Our analysis calls upon indicative facts that would enable one to discriminate between the various alternative models.

A summary is presented of our theoretical and experimental work over more than two years related to switching in chalcogenide glass phase change memory. As a significant addition to the well known experiments, we have studied switching under considerably lower voltages and elevated temperatures, as well as the statistics of switching events and relaxation oscillations. Our analytical theory, based on field induced crystal nucleation, predicts all of our observed features and their dependencies on material parameters.

New technique to separate bulk and interface electrical properties of polycrystalline and glassy Ge2Sb2Te5 (GST) in phase-change memory (PCM) devices is proposed. PCM with different GST thicknesses are measured. The average activation energies for bulk conductivity are 0.37 eV and 0.09 eV as well as bulk resistivities are about μOhm*cm2 and 20 μOhm*cm. The contact barriers is 0.07eV and specific contact resistance is about 0.3 μOhm*cm2 in studied PCM devices.

It is discovered that bulk resistivities for both SET and RESET states in PCM obey Meyer-Neldel rule with almost identical isokinetic temperatures 335K − 340K. This information is discussed in terms of GST structure.