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This paper presents a comprehensive investigation into the thermal stability of superlattice-like (SLL) thin films fabricated by varying the sputtering sequences of the SLL [Ge8Sb92(25nm)/GeTe(25nm)]1 and SLL [GeTe(25nm)/Ge8Sb92(25nm)]1 configurations. Our results reveal significantly enhanced ten-year data retention (Tten) for both thin films measured at 124.3 °C and 151.9 °C, respectively. These values surpass the Tten of Ge2Sb2Te5 (85 °C), clearly demonstrating the superior thermal stability of the studied SLL configurations. Interestingly, we also observe a distinct difference in the thermal stability between the two SLL configurations. The superior thermal stability of SLL [GeTe(25nm)/Ge8Sb92(25nm)]1 is attributed to the diffusion of the Sb precipitated phase from Ge8Sb92 to GeTe. This diffusion process effectively reduces the impact of the Sb phase on the thermal stability of the thin film. In contrast, in the case of SLL [Ge8Sb92(25nm)/GeTe(25nm)]1, the presence of the Sb precipitated phase in Ge8Sb92 facilitates the crystallization of GeTe, leading to reduced thermal stability. These findings underscore the significant influence of the sputtering sequence on the atomic behavior and thermal properties of superlattice-like phase change materials. Such insights provide a robust foundation for the design and exploration of novel phase change materials with improved thermal performance. [ABSTRACT FROM AUTHOR]

The interplay between impurities (i.e., C and N) and the twin boundary (TB) in GeTe was systematically investigated by first principles calculations. The strong segregation propensity of C and N at TBs was demonstrated. Moreover, TBs were shown to restrain impurity diffusion, exerting a trapping effect on impurities. With the presence of impurities, the mechanical strength of TB was significantly enhanced. Such a strengthening effect arises from the strong covalent bonding between the impurity (C and N) and host atoms at TB. The present work provides atomic-scale understanding underlying impurity-induced TB strengthening and offers new insights based on the synergy between grain boundary engineering and impurity doping into designing more robust and stable phase-change material devices. [ABSTRACT FROM AUTHOR]

The single layer Zn 44 Sb 39 Se 17 thin film, being fabricated by Sb 70 Se 30 and Zn using co-sputtering method, exhibits double phase change transition. The double phase change processes are mainly attributed to the crystallization of the Sb and ZnSb phases. The potential operating temperature for ten years of two phase change processes are 64 °C and 179 °C, of which the good stability of the second phase change can be sufficient for the autoelectronic applications. Meanwhile we also discovered the Zn 44 Sb 39 Se 17 thin film presents apparent low power consumption in comparison with Ge 2 Sb 2 Te 5 and other reported Sb-Se based phase change materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • A large number of low angle bonds are formed in amorphous Al-rich Al–Sb system. • Excessive Al atoms restrict the bond transition from low angle to high angle. • The difficult bond angle transition explains the good stability of Al–Sb system. • The weak Al–Sb bond in the low angle accounts for the fast phase change speed. Abstract In this work, ab-initio molecular dynamics simulations were performed for Al–Sb system with and without excessive Al. Our results demonstrated the population of low angle bond is apparently increased due to the addition of excessive Al. The necessary bond transition from low angle to high angle in crystallization process was significantly retarded, which might be the origin of enhanced thermal stability of AlSb with excessive Al. The weak Al–Sb bond in the low Al–Sb–Al bond angle accounts for the fast phase change speed of Al–Sb system. Our work clarified the physical origin of the superior properties of Al–Sb system at the atomic scale and provided some new insights toward PCMs design. [ABSTRACT FROM AUTHOR]

• Sn 22 Sb 76 Sc 2 thin films were prepared by SnSb 4 and Sc co-sputtering. • The thermal stability of Sn 22 Sb 76 Sc 2 can meet the need of electric vehicle. • The reversible SET/RESET operations based on Sn 22 Sb 76 Sc 2 is realized at 20ns. • The thermal stability of Sn 22 Sb 76 Sc 2 derives from the formation of Sc-Sn bond. • The phase change speed is not deteriorated with the enhancement of thermal stability. To address the challenge of reconciling the trade-off between phase change speed and thermal stability in phase change materials, we synthesized Sc-doped SnSb 4 thin films with a composition of Sn 22 Sb 76 Sc 2 and investigated their phase change properties. Our findings demonstrate that the Sn 22 Sb 76 Sc 2 thin film exhibits enhanced thermal stability and faster phase change speed than Ge 2 Sb 2 Te 5. The Sc-Sn bond formed during crystallization contributes to an improved data retention capability of up to 166 °C. Notably, the phase change speed of the Sn 22 Sb 76 Sc 2 thin film on the basis of device test can reach up to 20 ns. Additionally, the power consumption of the Sn 22 Sb 76 Sc 2 thin film (1.1 × 10−11 J) is nearly two orders of magnitude lower than that of Ge 2 Sb 2 Te 5 (9.7 × 10−10 J). These results provide compelling evidence that the Sn 22 Sb 76 Sc 2 thin film can overcome the "inverted relation" between high thermal stability and fast phase change speed, achieving a balanced performance. [ABSTRACT FROM AUTHOR]

• The Sb 54 Zn 46 thin film is fabricated by antimony and zinc targets co-sputtering. • The thermal stability of Sb 54 Zn 46 can satisfy the electro-mobile application. • The strong Sb-Zn bond stretching mode accounts for the high thermal stability. • The phase change speed of Sb 54 Zn 46 (10 ns) is much faster than that of Ge 2 Sb 2 Te 5. • Growth-dominant crystallization mechanism explains the fast phase change speed. In this work, we fabricate the Sb 54 Zn 46 thin film by pure antimony and zinc targets co-sputtering and analyze its phase change properties. The ten-years data retention of Sb 54 Zn 46 thin film, being a good reflection of thermal stability, is improved to 119 °C from 24 °C of pristine antimony thin film, which is much higher than that of the traditional phase change material Ge 2 Sb 2 Te 5 (85 °C). The increased thermal stability of Sb 54 Zn 46 thin film mainly derives from the formation of the strong Sb-Zn bond stretching mode during crystallization. In addition, the phase change speed of Sb 54 Zn 46 thin film measured in device test increases to 10 ns, which is also much faster than that of the traditional phase change material Ge 2 Sb 2 Te 5 (100 ns). These results illustrate that the fast phase change speed of Sb 54 Zn 46 thin film is mainly ascribed to the Sb-rich atomic environment and the growth-dominant crystallization mechanism. Our work substantiates the co-sputtering Sb 54 Zn 46 thin film can ensure fast phase change speed while effectively increasing its thermal stability. [ABSTRACT FROM AUTHOR]

• Y-doped Sb 7 Se 3 thin film was successfully fabricated for the first time. • Y-doped Sb 7 Se 3 thin film shows good thermal stability, enhanced phase change speed. • Y-doped Sb 7 Se 3 thin film shows relatively low power of consumption. • Theoretical calculations suggested strong Y-Se bond can be formed. • The band structure and band gap can be also tuned by Y dopant in Sb-Se system. By combining experiments and first-principles calculations, Y-doped Sb 7 Se 3 thin films were successfully fabricated and investigated. Our results suggest that Y is one promising dopant for simultaneously enhancing thermal stability, increasing phase change speed and reducing power of consumption. In particular, the temperature of ten year data retention for Y-doped Sb 7 Se 3 thin film increases to 118.5 °C. The fast phase change speed (10 ns) can be realized for Y-doped Sb 7 Se 3 thin film, which is fairly competitive with that of traditional GST (100 ns). Theoretical calculations suggest the electrical conductivity can be reduced by Y doping, which might be one underlying reason for low power consumption. Furthermore, it is found that Y also shows an advantageous role in tuning the band structure and triggering the indirect to direct band gap transition in Sb-Se system, which is of great importance for the design of optoelectronic devices. Thus, our work indicates the important role of Y dopant in Sb-Se system for both phase change memory and other semiconductor devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • The stacked films enabling up to four resistive states by adjusting the thickness. • Resistance variation is caused by the crystallization of each layer. • Interfaces can affect the crystallization behavior of MnTe films layer. • The reversible switch between three resistance states can be achieved with a 50 ns electrical pulse in MnTe/GeTe -based PCM cells. With substantial data storage requirements, enhancing the storage density of emerging non-volatile memories is a common challenge for achieving commercial applications. Phase change memory is capable of multi-level data storage in a storage cell, which can be applied in neural-inspired and all-photonic memory computing. In this study, we propose a MnTe/GeTe stacked thin film structure suitable for multi-level phase change memories and systematically study on the correlation between structure and performance. As the temperature rises, the stacked thin film sequentially crystallizes into form MnTe 2 , GeTe and Te phases, resulting in three changes in resistance. By utilizing different resistance states, the phase change memory cell based on the MnTe (15 nm)/GeTe (35 nm) stacked thin film can achieve multi-level storage with a 50 ns electrical pulse. The results show that the amorphous thermal stability of the stacked thin films is improved and that the minimal thickness variation before and after crystallization enhances its reliability. Therefore, the MnTe/GeTe stacked thin film is a phase change memory material with favorable structural properties and potential for multi-level storage applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three resistance states with clear distinction are obtained in indium selenide phase-change thin films. • Amorphous indium selenide thin films crystallize at two different temperatures to form two crystalline phases. • Reversible switch between three resistance states as fast as 60 ns is implemented in In 2 Se 3 -based PCM cells. • Successive crystallization in indium selenide thin films is applicable to multi-level phase-change memory. Increasing the storage density of phase-change memory is a challenging subject towards the universal memory commercialization. Multi-level data storage can be implemented in phase-change memory cells by designing multiple stages of crystallization of phase-change materials, which is favorable to push forward the application of phase-change memory in storage-class memory and the emerging in-memory computing. Here, the structure and properties of In 2 Se 3 phase-change thin films with multi-level phase transitions are investigated. The In 2 Se 3 thin films changes resistance states twice upon heating with high crystallization temperature and good thermal stability. The amorphous In 2 Se 3 thin films undergo partial crystallization of the Se phase followed by crystallization of the γ-In 2 Se 3 phase, with successive stages of crystallization accounting for the three distinct levels of resistivity. The phase-change memory cell based on In 2 Se 3 thin films shows a continuous switching process of high resistance state, intermediate resistance state and low resistance state with low drift coefficient in SET-RESET operations at a speed as fast as 60 ns, and the RESET power is as low as 311 pJ, indicating that the In 2 Se 3 thin films have good performance of three-state storage property and can effectively improve the memory density. [ABSTRACT FROM AUTHOR]

[Display omitted] • The coordination number of Ca2+ is 7–8 in liquid Ca(NO 3) 2 ·4H 2 O. • An NO 3 − links two Ca2+ in monodentate to form a long chain or a short ring structure. • Edge-sharing mono-oxygen bridge bonds between NO 3 − and two Ca2+. • An underlying mechanism of deep supercooling of liquid Ca(NO 3) 2 ·4H 2 O is revealed. Calcium nitrate tetrahydrate, Ca(NO 3) 2 ·4H 2 O, has the potential prospects as a room temperature phase change material due to appropriate melting point and high enthalpy. However, the supercooling problem prevents its widespread use in an energy storage field. In this work, the microscopic structure of liquid Ca(NO 3) 2 ·4H 2 O at different temperatures are studied by X-ray diffraction and Raman spectroscopy and compared with that of Ca(NO 3) 2 ·4H 2 O crystal. The first coordination layer of a calcium ion contains 3 water molecules and 4–5 nitrate ions. A nitrate ion acts as a dioxygen bridge to link two calcium ions in a monodentate fashion and form a longer chain or a shorter ring structure in the liquid state. In the crystalline state, two oxygen atoms of a nitrate ion bind with a calcium ion in a bidentate manner. The structure and stability of [Ca2+ m (NO 3 −) n (H 2 O) q ] clusters are examined by DFT calculations to confirm the results obtained by X-ray diffraction and Raman spectroscopy. The key factor of severe supercooling problem would be the conversion from edge-sharing mono-oxygen bridge bonds of Ca-NO 3 (Ca-O(NO)O-Ca) in liquid to corner-sharing dioxygen bridge bonds of Ca-NO 3 (Ca-O(NO 2)-Ca) in solid. This work provides a theoretical basis for solving the supercooling problem. [ABSTRACT FROM AUTHOR]

• The property of Ta-doped Ge 5 Sb 95 thin film is investigated systematically. • An ultrafast programing operation (~20 ns) is achieved for Ta 0.16 (Ge 5 Sb 95) 0.84. • The RESET power consumption is as low as picojoule level for Ta 0.16 (Ge 5 Sb 95) 0.84. • The thin film shows high thermal stability, high speed, and low power consumption. In the field of phase change memory (PCM), the contradiction between operation speed and thermal stability is one of the critical factors restricting its development, including realizing the framework of storage class memory. Ta-doped Ge 5 Sb 95 has been proposed as a potential material, which displays better thermal stability and higher phase transition speed than classic Ge 2 Sb 2 Te 5. Ta incorporation can improve the crystallization temperature and data retention ability, while increasing the electrical resistance, which reveals a significant enhancement in amorphous thermal stability and a reduction in programming power consumption, with almost no sacrifice in phase transition speed. For the PCM cells based on the optimized composition Ta 0.16 (Ge 5 Sb 95) 0.84 , reversible phase transitions are successfully realized by using 20 ns electric pulse and RESET power consumption is as low as picojoule level with a resistance ratio up to 10000 times, showing high thermal stability, fast speed, and low power consumption application potential in PCM. [ABSTRACT FROM AUTHOR]