Change in Structure of Amorphous Sb–Te Phase‐Change Materials as a Function of Stoichiometry

Abstract

The concept of phase-change memory using chalcogenide glasses dates back to the 1960s, as pioneered by Ovshinsky. [1] Starting from late 1980s, Ge-Sb-Te alloys along the GeTe-Sb 2 Te 3 pseudo-binary line (Group I), such as Ge 2 Sb 2 Te 5 , Ge 1 Sb 2 Te 4 and Ge 8 Sb 2 Te 11 , [2][3][4][5] doped Sb 2þx -Te alloys (Group II), such as Ag-, In-doped Sb 2þx Te (AIST), and alloyed Sb (Group III), [6][7][8][9][10] such as Ge 15 Sb 85 , were identified as suitable PCMs. These alloys were initially used for the rewritable optical data storage industry. [11] More recently, the Ge 1 Sb 2 Te 4 (GST) alloy has been used as the core material for electronic non-volatile memories, [12][13][14][15][16][17][18][19] e.g., 3D Xpoint. Moreover, PCMs can be used for neuro-inspired computing and in-memory computing, [20][21][22][23][24][25][26][27] and could also enable various nonvolatile photonic applications, including memory and computing devices, switches, and displays. [28][29][30][31][32][33][34][35][36] PCMs utilize the significant contrast in electrical resistivity or optical reflectivity between their crystalline and amorphous phase to encode data. [11] The switching between the two logic states is achieved by rapid and reversible phase transitions, namely, SET (crystallization) and RESET (melt-quenched amorphization). In addition to binary storage, multiple resistivity or reflectivity states can be obtained within a PCM cell via partial amorphization (iterative RESET) and crystallization (accumulative SET), enabling multilevel storage [37,38] and neuro-inspired computing applications. [39,40]

Bonding Nature and Optical Properties of As2Te3 Phase‐Change Material

“…These peak positions are significantly shorter than those in amorphous Sb 2 Te 3 , where the first peak of Sb−Sb and Sb−Te contacts is found between 2.9 and 3.0 Å. [ 59–62 ] By multiplying RDF with bond population B AB at given interatomic distances, the bond‐weighted distribution function (BWDF) is obtained, which provides a clear cutoff to distinguish chemical bonds with strong covalent interactions in the amorphous phase. [ 63–67 ] The B AB refers to the integration of projected COOP (pCOOP) onto a specific pair of atoms, A and B, over energy up to the Fermi level ( E F ).…”

Glassy and liquid Sb2S3: insight into the structure and dynamics of a promising functional material

“…The metavalent bonding 33 seems to be missing in Sb 2 S 3 ; and the four-fold coordinated antimony sites, present in GST and a -Sb 2 Te 3 , 34,35 were not observed in vitreous Sb 2 S 3 , 27–29 even though there is a controversy in amorphous tellurides related to the antimony local order. 36,37…”

“…The metavalent bonding 33 seems to be missing in Sb 2 S 3 ; and the four-fold coordinated antimony sites, present in GST and a-Sb 2 Te 3 , 34,35 were not observed in vitreous Sb 2 S 3 , [27][28][29] even though there is a controversy in amorphous tellurides related to the antimony local order. 36,37 Using high-energy X-ray diffraction and Raman spectroscopy supported by first-principles simulations, we will unravel a detailed structural organization of bulk glassy and liquid Sb 2 S 3 over an extended temperature range, 298 r T r 1143 K. Thermal properties and electrical conductivity measurements will also be provided showing a remarkable contrast in electronic properties between amorphous, crystalline and liquid states. Finally, the diffusion coefficients and viscosity of liquid Sb 2 S 3 will be computed and compared with known experimental data, which reveal a significant fragility of molten antimony sesquisulfide in comparison with canonical dielectric As 2 S 3 .…”

Metavalent Bonding in Layered Phase‐Change Memory Materials

“…Chalcogenide phase-change memory materials (PCMs), [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] in particular, Ge-Sb-Te (GST) alloys along the GeTe-Sb 2 Te 3 DOI: 10.1002/advs.202300901 pseudo-binary line, [1] have enabled a wide range of electronic and photonic applications. The GST-based 3D Xpoint memory is commercially available and serves as a critical component to bridge the performance gap between memory and storage units for data-centric applications.…”