For the first time, we evaluate the electrical behavior of boron doped GeTe Phase-Change Memories (PCM). Our results demonstrate 25% RESET current reduction and excellent resistance contrast between SET and RESET states with B doping. A further benefit of controlled SET dynamics makes it favorable for MLC applications. Finally, we demonstrate that boron doped GeTe phase change materials maintain good device endurance reliability.

This paper investigates Carbon-doped GeTe (GeTeC) as novel material for Phase-Change Memories (PCM). In the first part of the manuscript, a study of GeTeC blanket layers is presented. Focus is on GeTeC amorphous phase stability, which has been studied by means of optical reflectivity and electrical resistivity measurements, and on GeTeC structure and composition, analyzed by XRD and Raman spectroscopy. Then, electrical characterization of GeTeC-based PCM devices is reported: resistance drift, data retention performances, RESET current and power, and SET time have been investigated. Very good data retention properties and reduction of RESET current make GeTeC suitable for both embedded and stand-alone PCM applications, thus suggesting GeTeC as promising candidate to address some of the major issues of today’s PCM technology.

In situ transmission electron microscopy (TEM) observations were performed for a better understanding of the “melt quenched” GeTe crystallization mechanism. The evolution of the crystallite morphology observed during annealing shows a growth-dominated crystallization behavior. Scanning transmission electron microscopy—electron dispersive x-ray spectroscopy and high resolution electron microscopy experiments were also performed on cycled GeTe devices, showing that void formation is responsible for the cell failure after 107 cycles.

GeSb4 is a promising material for phase change random ac cess memories. In this work, X-Ray synchrotron radiation diffraction, time resolved reflectivity m easurement and Transmission Electronic Microscopy a re used to study crystallization behaviour of amorphou s films of GeSb4. Films with thickness as low as 10 nm are studied. When temperature increases, Sb and Ge phas s sequentially crystallize. It’s shown that bo th the crystallization temperature and microstructure evol uti n are strongly dependent on the film thickness.

The commercialization of Phase-Change Memories (PCM), based on the well-known GST compound, have been recently started, tailored for consumer applications. Despite other excellent performances (i.e. low-power, scalability,...), data retention is assured up to 85°C, still limited for the automotive market segment. Alternative active material able to comply with the stringent requirements of automotive applications should possibly exhibit higher crystallization temperature (T C ) as well as higher Activation Energy (E A ) with respect to GST. Recent literature shows that GeTe provides better retention, while several works put in evidence how data retention is enhanced by inclusions in pure host alloys.

The characteristics of Ge2Sb2Te5 (GST), GeTe and nitrogen-doped GeTe thin films deposited on W/SiO2 substrates were investigated by reflectometer, static tester and atomic force microscopy (AFM). Differential Scanning Calorimetry measurements and Differential Thermal analyses were carried out on these materials to determine their crystallization and melting temperatures. It was found that the amorphization and crystallization behaviors of these materials were different, especially that the nitrogendoped GeTe materials show a growth-dominated crystallization behavior although GST and GeTe shows a nucleation-dominated crystallization behavior. Characteristic temperatures of these materials were determinate to estimate amorphous phase stability and reset power required to melt-quenched the materials.