PhD Alumni

Boniardi Mattia

Present position: Device Engineer at Micron Technology

Thesis title:  Time Dependent Phaenomena in Chalcogenide Materials for Phase Change Memories
Advisor:  Andrea L. Lacaita
Research area:  Microelectronics and Emerging Technologies
Thesis abstract:  
In the overall Non-Volatile Memory (NVM) panorama, the current mainstream Flash memory technology is expected to reach fundamental physical standstill. Therefore several solid-state emerging technologies have been proposed, aiming to maintain the current scaling trends for the NVM devices. Among them the Phase Change Memory (PCM) shows several interesting features such as fast read/write operation, low voltage operation, superior endurance properties and great scaling potential. Mattia’s Ph.D. work is focused on certain time dependent phaenomena involved in the amorphous phase of the material employed in the PCM operation, the alloy Ge2Sb2Te5 (GST). The PCM operation relies on the ability of GST to reversibly change its phase between two states, namely the crystalline, low resistive state, associated to the logic 1 bit and the amorphous, high resistive state, associated to the logic 0. The amorphous phase is metastable and gets involved with two subsequent phaenomena: the structural relaxation (SR) and the crystallization mechanisms. They are modeled together for the first time into a unified framework, providing a microscopic common interpretation based on multi-phonon interactions, in the physical framework of the Meyer-Neldel rule. He has also been focused upon the array characterization and modeling. A SR variability study on chip is reported, allowing reliability predictions on the stability of the amorphous state evolution with time at the retention time specs, on a large population of cells. A Monte-Carlo modeling of discrete defect distribution within the amorphous material will be the way to the statistic description of SR. Finally one of the most recent trend in the PCM research and development is the new material investigation. Indeed it is recognized that the reliability and performance of such technology strongly depend on the particular phase change compound material. So his work is also dedicated to the Ge-Sb-Te compound system investigation, aiming to provide on one hand some physics-based guidelines for phase-change material choice and on the other hand to investigate and potentially enlarge the possible application spectrum for the PCM technology.