Electronics > Nanoscale semiconductor non-volatile memories based on phase-change

Project abstract

The project investigates the phase-change non-volatile memories, which rely on the ability of a chalcogenide material (Ge2Sb2Te5) to change its phase from crystalline to amorphous and vice versa as a result of electrical pulses. This technology has emerged in the past five years as a promising alternative to conventional non-volatile memories, namely the Flash cell. The goal of the project is to study the ultimate limits of scalability and reliability of this technology with rigorous scientific method based on structural modeling of active material in its various phases and electrothermal modeling of the memory cell. This effort is motivated by the urgent need to describe the various memory alternatives according to their ability to meet the requirements of scaling for different technological generations, in order to justify the huge industrial investment of research and development.
This project is divided into two Workpackages (WP): WP1-Structural modeling of phase-change material and WP2- Electrothermal modeling of phase change memory cell. The CNR-ISTM, with expertise in the field of numerical modeling of the structure of solid materials and their transport properties, will lead the WP1, while WP2 will be conducted by Polimi-DEI, with a recognized expertise in the electrical and quantum modeling of nanoscale non-volatile memories.
The project is being reported.

Electro-thermal simulation of programming in a phase-change memory array. The increase of temperature around the programmed bit is evaluated to predict possible disturb phenomena in adjacent cells.

Project results

First the structural modeling activity will clarify the geometric structure and the GST bands, in its stable and metastable crystalline phase. As for the amorphous phase, various structural and local assumptions and the geometric and energy evolution along the phase transition from metastable crystalline structure to that amorphous and vice versa will be studied. We develop an electrothermal model that will be applied to the cell structure in order to clarify the physical scaling laws of programming currents and the minimum distance between first-neighbor cells in the memory array. Finally, a statistical study of the reliability in retention of change phase cells will be conducted, to clarify the real margins of the technology reliability.