GeTe sequences in superlattice phase change memories and their electrical characteristics

Abstract

We studied GeTe structures in superlattice phase change memories (superlattice PCMs) with a [GeTe/Sb2Te3] stacked structure by X-ray diffraction (XRD) analysis. We examined the electrical characteristics of superlattice PCMs with films deposited at different temperatures. It was found that XRD spectra differed between the films deposited at 200 °C and 240 °C; the differences corresponded to the differences in the GeTe sequences in the films. We applied first-principles calculations to calculate the total energy of three different GeTe sequences. The results showed the Ge-Te-Ge-Te sequence had the lowest total energy of the three and it was found that with this sequence the superlattice PCMs did not run.

The Crystal Orbital Hamilton Population (COHP) Method as a Tool to Visualize and Analyze Chemical Bonding in Intermetallic Compounds

“…In that connection, chalcogenide superlattices (CSL) [123,124] and nanocrystals [125,126] were investigated for their capabilities to serve in such systems. In particular, interfacial phase-change materials (iPCMs) [127][128][129], in which the transformations do not occur between an amorphous and a crystalline phase, but between two crystalline phases, are of great interest as candidate systems. The more recent determinations of the crystal structure for the ternary Ge 4 Se 3 Te [31] (Figure 7) indicated that the type of structure observed for that chalcogenide may serve as an archetype for future PCMs.…”

Fabrication of topological-switching RAM (TRAM)

“…The TEM views showed that the [GeTe = 1 nm/ Sb 2 Te 3 =1 nm] periodic unit had a rough surface but that the [GeTe = 1 nm/ Sb 2 Te 3 = 4 nm] one was uniform. The results of synchrotron radiation Xray diffraction (XRD) measurements suggested that the crystal structure of the GeTe films in the [GeTe = 1 nm/ Sb 2 Te 3 = 4 nm] periodic unit was not cubic but rather was aligned to the caxis of the hexagonal Sb 2 Te 3 layer [9].…”

First principles investigation of the unipolar resistive switching mechanism in an interfacial phase change memory based on a GeTe/Sb2Te3superlattice

“…The superlattice structure is designed such that the change in the Ge-Te bonding state does not require an amorphouscrystalline phase transition. Figure 1(b) shows the atomic structure of the GeTe=Sb 2 Te 3 superlattice [20][21][22] given by Tominaga and coworkers. Each of the Ferro, Petrov, and Inverted Petrov structures consists of nine atomic layers of -Te-Sb-Te-Te-Ge-Te-Ge-Te-Sb-, -Te-Sb-Te-Ge-TeTe-Ge-Te-Sb-, and -Te-Sb-Te-Te-Ge-Ge-Te-Te-Sb-, respectively.…”

“…That is, the atomic structures of the HRS and LRS remain unclear and the resistive switching mechanism has yet to be clarified. 22,23,[26][27][28][29][30][31] In this study, we propose a mechanism for unipolar resistive switching and describe the new LRS and HRS structures based on the results of first-principles molecular dynamics (MD) simulation. Basically, unipolar switching is current-driven.…”