Fifty years after its discovery, the ovonic threshold switching (OTS) phenomenon, a unique nonlinear conductivity behavior observed in some chalcogenide glasses, has been recently the source of a real technological breakthrough in the field of data storage memories. This breakthrough was achieved because of the successful 3D integration of so-called OTS selector devices with innovative phase-change memories, both based on chalcogenide materials. This paves the way for storage class memories as well as neuromorphic circuits. We elucidate the mechanism behind OTS switching by new state-of-the-art materials using electrical, optical, and x-ray absorption experiments, as well as ab initio molecular dynamics simulations. The model explaining the switching mechanism occurring in amorphous OTS materials under electric field involves the metastable formation of newly introduced metavalent bonds. This model opens the way for design of improved OTS materials and for future types of applications such as brain-inspired computing.
Fifty years after its discovery, the ovonic threshold switching (OTS) phenomenon, a unique nonlinear conductivity behavior observed in some chalcogenide glasses, has been recently the source of a real technological breakthrough in the field of data storage memories. This breakthrough was achieved because of the successful 3D integration of so-called OTS selector devices with innovative phase-change memories, both based on chalcogenide materials. This paves the way for storage class memories as well as neuromorphic circuits. We elucidate the mechanism behind OTS switching by new state-of-the-art materials using electrical, optical, and x-ray absorption experiments, as well as ab initio molecular dynamics simulations. The model explaining the switching mechanism occurring in amorphous OTS materials under electric field involves the metastable formation of newly introduced metavalent bonds. This model opens the way for design of improved OTS materials and for future types of applications such as brain-inspired computing.
“…Ge-GeTe 3 tetrahedra and GeTe defective octahedral motifs present in a-GeTe phase 43 , 44 are expected also in Ge 52 Te 48 -rich [Ge 30 Se 70 ] 1-x [Ge 52 Te 48 ] x films. The structure of our [Ge 30 Se 70 ] 1-x [Ge 52 Te 48 ] x thin films obtained by co-sputtering can be depicted as GeSe 4-n Te n tetrahedral motifs with n = {0, 1, 2, 3, 4} forming a disordered network connected, for small x values, by means of the chalcogen elements and, for higher x values, coexisting with a non-negligible amount of Ge–Ge homopolar bonds and possibly some Te–Te bonds as well as Se–Te bonds as proposed in a previous work 22 . Figure 4 FTIR and Raman spectra of ( a ) [Ge 30 Se 70 ] 1-x [Ge 52 Te 48 ] x , ( b ) [Ge 30 Se 70 ] 1-x–y [Ge 52 Te 48 ] x Sb y and ( c ) [Ge 1-2x Se x Te x ] 1-y Sb y thin films.…”
Section: Resultsmentioning
confidence: 64%
“…We must note that during SiN x deposition the temperature of the chalcogenide thin film samples can reach up to 180 °C due to thermal heating resulting from RF sputtering of the Si target. We note that since this temperature is below the glass transition temperature of our chalcogenide samples, it is expected to have no detrimental impact on the films, as already studied for similar chalcogenide bulk glasses and thin films 4 , 22 – 27 .…”
Thanks to their unique optical properties Ge–Sb–S–Se–Te amorphous chalcogenide materials and compounds offer tremendous opportunities of applications, in particular in near and mid-infrared range. This spectral range is for instance of high interest for photonics or optical sensors. Using co-sputtering technique of chalcogenide compound targets in a 200 mm industrial deposition tool, we show how by modifying the amorphous structure of GeSb
w
S
x
Se
y
Te
z
chalcogenide thin films one can significantly tailor their linear and nonlinear optical properties. Modelling of spectroscopic ellipsometry data collected on the as-deposited chalcogenide thin films is used to evaluate their linear and nonlinear properties. Moreover, Raman and Fourier-transform infrared spectroscopies permitted to get a description of their amorphous structure. For the purpose of applications, their thermal stability upon annealing is also evaluated. We demonstrate that depending on the GeSb
w
S
x
Se
y
Te
z
film composition a trade-off between a high transparency in near- or mid-infrared ranges, strong nonlinearity and good thermal stability can be found in order to use such materials for applications compatible with the standard CMOS integration processes of microelectronics and photonics.
“…The relationship however is not always simple as the density of localized states plays an important role 33 as well as the method through which a bang gap value is obtained 18 . The (optical) band gap was not determined in this paper but previous studies have reported a band gap for GeSe 2 thin films in the range of 2.02-2.2 eV 31,34,35 . Sb doping has been shown to lower this bandgap value to 1.75-1.4 eV 31,35,36 for comparative doping levels.…”
Raman spectroscopy and electrical measurements are performed on sputtered GexSe1−x thin films to identify and link bond presence to electrical behaviour.
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