[en] Highlights: • ZnSb-doping can effectively enhance thermal stability of Sb_2Te_3 films. • Sb-rich changes crystal phase but their grain size is refined with Zn addition. • The Sb-rich increases the speed while maintaining enhancing crystallization temperature. • High Sb/Te ratio reveals the improvement in cycle ability. - Abstract: Crystallization process and amorphous state stability of pseudobinary ZnSb-Sb_2Te_3 materials have been studied for application in phase change memory. The effects of Zn concentration and Sb content on crystalline resistance, crystallization temperature, crystallization activation energy and amorphous state stability of films have been studied. The microstructures of Sb-rich Zn-Sb-Te films were analyzed through X-ray diffraction. Different crystalline phases have been observed in annealed Sb-rich Zn-Sb-Te films. Low Zn-doping concentration Zn-Sb-Te films crystallized into rhombohedral Sb_2Te_3 phase while high Zn-doping concentration Zn-Sb-Te films crystallized into rhombohedral Sb phase. The crystallization activation energy (E_a) of Zn_1_._1Sb_4_5_._7Te_5_3_._2 and Zn_5_._2Sb_4_6_._3Te_4_8_._5 films were confirmed to be 2.0 and 2.93 eV, while E_a of Zn_1_6_._0Sb_4_7_._3Te_3_6_._7 film increased to 3.2 eV and further reached to 3.3 eV for Zn_1_9_._7Sb_4_8_._1Te_3_2_._2 film. Zn addition increased the crystallization temperature and crystalline resistance of Zn-Sb-Te films largely, and enhanced the amorphous thermal stability and data retention ability of the films, while high Sb/Te ratio reveals the improvement in crystallization speed and good cycle ability. Therefore, Sb-rich Zn-Sb-Te film seems to be a good way to solve the contradiction between thermal stability and fast crystallization speed

[en] The Zn-doped Sb_2Te_3 films have been investigated systematically during the phase transformation process. It was found that, the increase of crystallization temperature in the Zn-doped Sb_2Te_3 films leads to its enhanced amorphous stability, and Zn incorporation can increase electrical resistance, widen optical band gap and refine crystalline grain size. The crystallization mechanism can be tuned into nucleation-dominated from growth-dominated type. Moreover, Sb_2Te_3 film with high Zn-doping concentration such as Zn_3_8_._8(Sb_2Te_3)_6_1_._2 film was found to exhibit a higher crystallization temperature (233 °C), better data retention ability (keeping the amorphous state at 146.5 °C for ten years), and wider band gap (0.839 eV). A lower threshold of crystallization (~ 25 ns) can be realized in the Zn_3_8_._8(Sb_2Te_3)_6_1_._2 film irradiated at the laser power of 70 mW in comparison with that in the conventional Ge_2Sb_2Te_5 film. We confirm that the Zn doping is responsible for a fast switching and the Zn_3_8_._8(Sb_2Te_3)_6_1_._2 compound is stable against segregation with cycling. - Highlights: • Zn-doping can effectively enhance thermal stability of Sb_2Te_3 films. • Zn-doping can effectively refine their grain size. • A short crystallization time (~ 25 ns) can be realized in the Zn_3_8_._8(Sb_2Te_3)_6_1_._2 film. • A reversible phase change process can be realized in Zn_3_8_._8(Sb_2Te_3)_6_1_._2 film

[en] Highlights: • The thermal stability of the Sb film increases with increasing Si₃N₄ concentration and the crystallization rate maintains a high speed. • The crystallization mode of homogeneous Sb ch changes from an explosive crystallization mode to nucleation-dominate mode by Si₃N₄ doping. • The bottleneck of the trade-off between thermal stability and crystallization of phase change material can be broken through by the addition of Si₃N₄. -- Abstract: Phase change materials (PCMs) are of great importance for universal storage to transform the existing Von-Neumann computing system architecture and artificial intelligence neuron system. The pure Sb film has attracted great attention among PCMs due to its lower melting point and faster crystallization speed. The unstable nature in amorphous state severely limits its application in nonvolatile universal storage. Here we combine Sb with Si₃N₄ to tune its crystallization mode and consequently improve its thermal stability. It is found that stable Si₃N₄ can degrade the long-range order and suppress the nano-size growth of grain Sb. With the addition of Si₃N₄, the nano-growth spacing of Sb crystallite is compressed, and Si₃N₄ encapsulates the Sb in a physically wrapped morphology. The tunable crystallization mode induced by such unique loculated microstructure contributes to the obvious improvement of thermal stability of Sb film. These results pave the way to explore novel PCMs, as well as to engineer traditional PCMs such as Ge-Sb-Te for building high-stability universal storage.

[en] The thermal stability and optical bandgap of the amorphous Sb₄Te film can be improved significantly by combining with VO₂, which leads to a high crystallization temperature (around 220 °C), good data retention (ten-year data retention above 130 °C), and high amorphous resistance. The crystallization mechanism of Sb₄Te changes from growth-dominated mode into nucleation-dominate one, which is confirmed by in situ microstructure observation experimentally and crystallization kinetics index theoretically, due to the long-range orders of Sb–Te and Sb–Sb bonds disorganized by the introduction of VO₂ nano-grid framework. The Sb₄Te crystallites can be refined and confined in the VO₂ nano-grid framework. VO₂–Sb₄Te films with less than 15 at.% of VO₂ maintain the high crystallization speed. The nano-grid framework of VO₂ enables an efficient way to invade the long-order bonds of Sb₄Te, which improves the rigid trade-off between thermal stability and crystallization speed. It provides a novel clue for optimizing other phase-change materials. (paper)

[en] Ag-doped Sb–Te films were deposited by magnetron co-sputtering and the structure, electrical, optical and thermal properties were analyzed. The results show that Ag-doping restrains crystal grain size, and changes a preferred orientation of the crystalline phase. The crystallization temperature is increased due to the Ag addition. Both amorphous resistance and crystalline resistance are enhanced and the resistance ratio reaches ∼10⁴. Compared with Ge₂Sb₂Te₅, Ag_26.82(Sb₃Te)_73.18 film exhibits a better amorphous thermal stability, a higher crystallization temperature (∼166 °C), a wider optical band gap (0.515 eV), a larger crystallization activation energy (3.17 eV) as well as a better 10 years data retention at 92 °C. (paper)

[en] The phase-change characteristics of Ge₂Te₃ films for phase-change random access memory applications were investigated by doping with TiO₂ using magnetron cosputtering. The first and the second phase transitions, which corresponded to the crystallizations of GeTe and Te, occurred at around 210 ⁰C and 225 ⁰C for the Ge₂Te₃ film, respectively. The incorporation of TiO₂ suppressed the crystallization of GeTe and held back the phase transition induced by the Te. The precipitation of aggregated GeTe from Ge₂Te₃-TiO₂ was observed at the annealing temperature of 400 ⁰C. The resistance ratio between RESET and SET states exceeded two orders of magnitude. Compared with Ge₂Sb₂Te₅-based cell device, the Ge₂Te₃-TiO₂ film-based ones had a lower power consumption. The reversible phase change could be accomplished by the electric pulse duration of 50 ns for Ge₂Te₃-TiO₂ with 15 at% TiO₂-based cell device.

[en] Highlights: • Composition dependence of phase change properties of Sb-Se films is investigated. • The crystallization temperature increase with increasing Se content. • Both Hall mobility and carrier concentration decrease with increasing Se content. • Sb-Se films are favorable for the optical storage in spectral region 1.7–25 μm. Composition dependence of structural, electrical and optical properties of binary Selenium-Antimony films was investigated for electrical and optical nonvolatile memories with low power and high speed. For preferred Sb₅₁Se₄₉ and Sb₄₇Se₅₃ films, the temperature for 10-year data retention can be up to 125.9 and 141.8 °C. Both amorphous and crystalline resistivities increase with Se content. The resistance ratio between two states maintain almost 3 orders of magnitude. Hall mobility and carrier concentration increases with the decrease in Se content. The microstructure of annealed Sb-Se films exhibits uniform distribution of crystallized phases with orthorhombic Sb₂Se₃ and hexagonal Sb. The high ON/OFF ratios of both refractive index (n) and extinction coefficient (k) between the amorphous and crystalline states alloys Sb-Se film to be favorable for the optical storage in spectral region 1.7–25 μm.

[en] Cu-doped Sb₂Te is extensively used for phase change optical storage. The phase change dynamics in Cu-doped Sb₂Te thin films by Picoseconds laser pulses were studied. The crystallization threshold and the reflectivity contrast of the Cu-Sb₂Te alloy increased with the Cu content, the reflectivity contrast of about 28% was obtained on Cu-doped Sb₂Te film with the Cu content of 27at.%, and the reversible phase change realized due to the ps laser pulses irradiation in strong-weak cycles. (paper)

[en] The crystallization characteristic, electrical, and optical properties of ZnSb-doped Sb₃Te thin films have been systematically investigated. The results show that the crystalline phase, grain size, and the preferred orientation are influenced by ZnSb addition. Meanwhile, ZnSb doping can effectively increase the thermal stability of Sb₃Te films such as crystallization temperature and crystallization activation energy, and maintain fast crystallization speed. Among ZnSb-doped Sb₃Te films, Zn_5.3Sb_72.7Te_22.0 film exhibits both shorter complete crystallization time (135 ns at 70 mW) and appropriate thermal stability (keeping the amorphous state at 107.2 C for 10 years). (orig.)

[en] The effect of HfO₂ on phase change characteristics of Sb₂Te₃ films for phase change memory (PCM) applications was investigated by in situ temperature dependence of electrical resistance measurement, X-ray diffraction, field emission scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. It is shown that HfO₂ inhibited the crystallization of the amorphous Sb₂Te₃ films, which improved the long-term stability of metastable amorphous phase. Memory devices based on Sb₂Te₃-HfO₂ composite films with HfO₂ concentrations of 10 at.% and 15 at.% were successfully fabricated and characterized. The 15 at.% HfO₂-based memory device exhibited lower reset voltage and power consumption compared with the 10 at.% HfO₂- and Ge₂Sb₂Te₅-based ones. The endurances exceeded 1.6 x 10⁵ and 2.2 x 10⁵ SET-RESET cycles for 10 at.% and 15 at.% HfO₂-based memory devices, respectively, and the resistance ratio between RESET and SET states achieved two orders of magnitude for both memory devices. The Sb₂Te₃-HfO₂ composite films, especially with HfO₂ concentration of 15 at.%, could be one of the most promising materials for application in PCM devices. (orig.)