Ultra-low Energy Phase Change Memory with Improved Thermal Stability by Tailoring the Local Structure through Ag Doping

Significant Power Consumption Reduction and Speed Boosting in Phase Change Memory with Nanocurrent Channels

The excessive power consumption is challenging for phase change memory (PCM) on its way to becoming universal memory in complex hierarchies of memory systems. Here, from the perspective of device structure, by adding a nanocurrent-channel (NCC) layer between the electrode layer and phase change layer, a RESET power consumption reduction by more than 95% and 10 times faster SET speed were realized simultaneously. Through the first principle calculations, Au and SiO2 were screened as the metal and insulating matrix material of NCC layer, respectively. Our PCM device with a Au-SiO2 NCC layer shows an ultralow RESET power consumption, down to 381 fJ, and an ultrafast SET speed (8 ns). Much higher current density near NCC in the phase change layer and thermal barrier effect of insulating matrix material were confirmed by finite element analysis (FEA), and the role of Au nanochannels was revealed by transmission electron microscopy (TEM). Our NCC layer structure provides a simple and practicable method to significantly decrease PCM power consumption.

Ultrahigh Stability and Operation Performance in Bi-doped GeTe/Sb2Te3 Superlattices Achieved by Tailoring Bonding and Structural Properties

Changes in bond types and the reversible switching process between metavalent and covalent bonds are related to the operating mechanism of the phase-change (PC) behavior. Thus, controlling the bonding characteristics is the key to improving the PC memory performance. In this study, we have controlled the bonding characteristics of GeTe/Sb2Te3 superlattices (SLs) via bismuth (Bi) doping. The incorporation of Bi into the GeTe sublayers tailors the metavalent bond. We observed significant improvement in device reliability, set speed, and power consumption induced upon increasing Bi incorporation. The introduction of Bi was found to suppress the change in density between the SET and RESET states, resulting in a significant increase in device reliability. The reduction in Peierls distortion, leading to a more octahedral-like atomic arrangement, intensifies electron-phonon coupling with increased bond polarizability, which are responsible for the fast set speed and low power consumption. This study demonstrates how the structural and thermodynamic changes in phase change materials alter phase change characteristics due to systematic changes of bonding and provides an important methodology for the development of PC devices.

Resolving length-scale-dependent transient disorder through an ultrafast phase transition

Material functionality can be strongly determined by structure extending only over nanoscale distances. The pair distribution function presents an opportunity for structural studies beyond idealized crystal models and to investigate structure over varying length scales. Applying this method with ultrafast time resolution has the potential to similarly disrupt the study of structural dynamics and phase transitions. Here we demonstrate such a measurement of CuIr2S4 optically pumped from its low-temperature Ir-dimerized phase. Dimers are optically suppressed without spatial correlation, generating a structure whose level of disorder strongly depends on the length scale. The redevelopment of structural ordering over tens of picoseconds is directly tracked over both space and time as a transient state is approached. This measurement demonstrates the crucial role of local structure and disorder in non-equilibrium processes as well as the feasibility of accessing this information with state-of-the-art XFEL facilities.

Phase Change Heterostructure Memory with Oxygen-Doped Sb2Te3 Layers for Improved Durability and Reliability through Nano crystalline Island Formation

Phase-change random access memory represents a notable advancement in nonvolatile memory technology; however, it faces challenges in terms of thermal stability and reliability, hindering its broader application. To mitigate these issues, doping and structural modification techniques such as phase-change heterostructures (PCH) are widely studied. Although doping typically enhances thermal stability, it can adversely affect the switching speed. Structural modifications such as PCH have struggled to sustain stable performance under high atmospheric conditions. In this study, these challenges are addressed by synergizing oxygen-doped Sb2Te3 (OST) with PCH technology. This study presents a novel approach in which OST significantly improves the crystallization temperature, power efficiency, and cyclability. Subsequently, the integration of the PCH technology bolsters the switching speed and further amplifies the device's reliability and endurance by refining the grain size (≈7 nm). The resultant OST-PCH devices exhibit exceptional performance metrics, including a drift coefficient of 0.003 in the RESET state, endurance of ≈4 × 108 cycles, an switching speed of 300 ns, and 67.6 pJ of RESET energy. These findings suggest that the OST-PCH devices show promise for integration into embedded systems, such as those found in automotive applications and Internet of Things devices.

Ultra-Stable, Endurable, and Flexible Sb2TexSe3-x Phase Change Devices for Memory Application and Wearable Electronics

Flexible memory and wearable electronics represent an emerging technology, thanks to their reliability, compatibility, and superior performance. Here, an Sb₂Te_xSe_3-x (STSe) phase change material was grown on flexible mica, which not only exhibited superior nature in thermal stability for phase change memory application but also revealed novel function performance in wearable electronics, thanks to its excellent mechanical reliability and endurance. The thermal stability of Sb₂Te₃ was improved obviously with the crystallization temperature elevated 60 K after Se doping, for the enhanced charge localization and stronger bonding energy, which was validated by the Vienna ab initio simulation package calculations. Based on the ultra-stability of STSe, the STSe-based phase change memory shows 65 000 reversible phase change ability. Moreover, the assembled flexible device can show real-time monitoring and recoverability response in sensing human activities in different parts of the body, which proves its effective reusability and potential as wearable electronics. Most importantly, the STSe device presents remarkable working reliability, reflected by excellent endurance over 100 s and long retention over 100 h. These results paved a novel way to utilize STSe phase change materials for flexible memory and wearable electronics with extreme thermal and mechanical stability and brilliant performance.

Enabling Active Nanotechnologies by Phase Transition: From Electronics, Photonics to Thermotics

Phase transitions can occur in certain materials such as transition metal oxides (TMOs) and chalcogenides when there is a change in external conditions such as temperature and pressure. Along with phase transitions in these phase change materials (PCMs) come dramatic contrasts in various physical properties, which can be engineered to manipulate electrons, photons, polaritons, and phonons at the nanoscale, offering new opportunities for reconfigurable, active nanodevices. In this review, we particularly discuss phase-transition-enabled active nanotechnologies in nonvolatile electrical memory, tunable metamaterials, and metasurfaces for manipulation of both free-space photons and in-plane polaritons, and multifunctional emissivity control in the infrared (IR) spectrum. The fundamentals of PCMs are first introduced to explain the origins and principles of phase transitions. Thereafter, we discuss multiphysical nanodevices for electronic, photonic, and thermal management, attesting to the broad applications and exciting promises of PCMs. Emerging trends and valuable applications in all-optical neuromorphic devices, thermal data storage, and encryption are outlined in the end.

Pt Modified Sb2Te3 Alloy Ensuring High-Performance Phase Change Memory

Phase change memory (PCM), due to the advantages in capacity and endurance, has the opportunity to become the next generation of general−purpose memory. However, operation speed and data retention are still bottlenecks for PCM development. The most direct way to solve this problem is to find a material with high speed and good thermal stability. In this paper, platinum doping is proposed to improve performance. The 10-year data retention temperature of the doped material is up to 104 °C; the device achieves an operation speed of 6 ns and more than 3 × 10⁵ operation cycles. An excellent performance was derived from the reduced grain size (10 nm) and the smaller density change rate (4.76%), which are less than those of Ge₂Sb₂Te₅ (GST) and Sb₂Te₃. Hence, platinum doping is an effective approach to improve the performance of PCM and provide both good thermal stability and high operation speed.