Effect of the Thermal Conductivity on Resistive Switching in GeTe and Ge₂Sb₂Te₅ Nanowires

Abstract

The thermal conduction characteristics of GeTe and Ge2Sb2Te5(GST) nanowires were investigated using an optical method to determine the local temperature by Raman spectroscopy. Since the localization of surface charge in a single-crystalline nanostructure can enhance charge-phonon scattering, the thermal conductivity value (κ) of single crystalline GeTe and GST nanowires was decreased significantly to 1.44 Wm(-1) K(-1) for GeTe and 1.13 Wm(-1) K(-1) for GST, compared to reported values for polycrystalline structures. The SET-to-RESET state in single-crystalline GeTe and GST nanowires are characteristic of a memory device. Unlike previous reports using GeTe and GST nanowires, the SET-to-RESET characteristics showed a bipolar switching shape and no unipolar switching. In addition, after multiple cycles of operation, a significant change in morphology and composition was observed without any structural phase transition, indicating that atoms migrate toward the cathode or anode, depending on their electronegativities. This change caused by a field effect indicates that the structural phase transition does not occur in the case of GeTe and GST nanowires with a significantly lowered thermal conductivity and stable crystalline structure. Finally, the formation of voids and hillocks as the result of the electromigration critically degrades device reliability.

Pressure-Induced Phase Transitions in Germanium Telluride: Raman Signatures of Anharmonicity and Oxidation

“…In the intermediate pressure range with a vanishing Raman signal, the cubic unit cell (NaCl) with no Raman active modes is the only compatible structure (Fig.4(a)). At the transition from rhombohedral to cubic we detect a strong mode with a shoulder around 50 cm −1 , over a small pressure range (3)(4)(5)(6). By inspection of Fig.4(b) this probably corresponds to the low energy mode of the distorted cubic structure.…”

“…Since a metastable cubic NaCl phase is also found in ambient conditions and the transition between this phase and an amorphous phase is technologically relevant, investigating pressure induced phase transitions assumes importance. GeTe is also used in prototype devices, in the form of nanoparticles or nanowires [3,4] and in this form it is particularly sensitive to oxidation which alters its properties. In this work we establish the pressure phase diagram of GeTe by high pressure Raman scattering and ab initio calculations.…”

High‐Speed Bipolar Switching of Sputtered Ge–Te/Sb–Te Superlattice iPCM with Enhanced Cyclability

“…While very common in resistive switching memory oxide‐based and similar devices, bipolar switching in PCRAM has rarely been reported. There are many reasons for this, for example, the switching may not have been reproducible, might exhibit low switching speeds or relatively poor endurance or reliability . These negative aspects reflect the character of the underlying bipolar switching mechanism which is generally associated with either void or filament formation resulting from ionic flow within the active area of a device .…”

“…There are many reasons for this, for example, the switching may not have been reproducible, might exhibit low switching speeds or relatively poor endurance or reliability . These negative aspects reflect the character of the underlying bipolar switching mechanism which is generally associated with either void or filament formation resulting from ionic flow within the active area of a device . In principle, such switching tends to be much slower than the conventional unipolar melt‐quench switching in PCRAM and also unavoidably leads to additional stress in the device, hastening eventual switching failure.…”

Reconfigurable, graphene-coated, chalcogenide nanowires with a sub-10-nm enantioselective sorting capability

“…In particular, the rapid and reversible phase transition of GST between amorphous and crystalline 48,49 makes the material ideal for rapidly tunable photonic devices 50–52 . The GST nanowire has proved to be promising and useful for high-density memory devices since it has a low-power consumption and writing currents 53–58 . Our research extends the above knowledge into the field of chiral recognition, i.e., enantioselective optical separation.…”