Crystal orientation dependence of the out-of-plane dielectric properties for barium stannate titanate thin films

The orientation-dependent out-of-plane dielectric properties of barium stannate titanate (Ba(Sn_0.15Ti_0.85)O₃ (BTS)) thin films prepared by sol–gel method were investigated. Films with (1 0 0), (1 1 0), and (1 1 1) orientation were grown on LaNiO₃-buffered (1 0 0), (1 1 0), and (1 1 1) LaAlO₃ (LAO) single-crystal substrates, respectively. The different temperature of the dielectric constant maximum (T_m) of the BTS thin films with different orientation was believed to be attributing to stress inside the films. Films with the (1 1 1) orientation had higher relative dielectric constant and tunability than (1 0 0)- and (1 1 0)-oriented films. This difference in dielectric properties in these three kinds of oriented BTS films may be attributed to change in the direction and magnitude of electric polarization in orientation engineered BTS films and stress in the films.     

High speed and low power consumption of superlattice-like Ge/Sb<Subscript>70</Subscript>Se<Subscript>30</Subscript> thin films for phase change memory application

In comparison to Ge₂Sb₂Te₅ (GST) and pure Sb₇₀Se₃₀ (SbSe) thin films, superlattice-like (SLL) Ge/Sb₇₀Se₃₀ (Ge/SbSe) has a higher crystallization temperature, larger crystallization activation energy, better data retention and lower power consumption. SLL Ge/SbSe thin films with different thickness of Ge and SbSe layers were prepared by magnetron sputtering system. The amorphous-to-crystalline transitions of SLL Ge/SbSe thin films were investigated through in situ film resistance measurement. The crystallization activation energy of SLL Ge/SbSe thin films was calculated from a Kissinger plot. The data retention time was estimated through isothermal time-dependent resistance measurement by Arrhenius equation. The phase structure of the thin films annealed at different temperatures was investigated by using X-ray diffraction. Phase change memory cells based on the SLL [Ge(8 nm)/SbSe(5 nm)]₄ thin films were fabricated to test and evaluate the switching speed and operation consumption.     

N-doped Zn15Sb85 phase-change materials for higher thermal stability and lower power consumption

Comparing to un-doped Zn₁₅Sb₈₅ material, N-doped Zn₁₅Sb₈₅ material had higher crystallization temperature, lower conductivity and better data retention. The optical band gap was derived from the transmittance spectra and a significant increase was observed with increasing nitrogen doping concentration. The measurement of atomic force microscopy indicated that the crystallization was inhibited and the surface of thin films became smoother after N doping. Phase change memory devices based on N-doped Zn₁₅Sb₈₅ thin film were fabricated to test and verify their electrical properties.     

The“gene”of reversible phase transformation of phase change materials:Octahedral motif

Nonvolatile phase change random access memory(PCRAM)is regarded as one of promising candidates for next-generation memory in the era of Big Data.The phase transition mechanism of phase change materials is the key scientific issue to be addressed for phase change memory.Moreover,obtaining homogeneous phase change materials with high speed,low power consumption,long life and good thermal stability is still the ultimate challenge for high-density three-dimensional(3D)PCRAM.In this paper,starting from the octahedral structure motifs(octahedrons)which are considered as the"gene"of phase change materials,a new view on the phase transition mechanism is proposed.Based on this mechanism,a homogeneous phase change material is developed by constructing three matched octahedrons,which achieved an overall improvement in performance,showing 180℃ten-year data retention,6 ns SET speed,one order of magnitude longer life time and 75%reduced power consumption compared with traditional Ge₂Sb₂Te₅(GST)devices.It is of great significance to use it in 3D PCRAM chip and multi-level brain-inspired computing chip in the future.     

Anomalous dielectric properties of Ba1−xCaxTiO3 thin films near the solubility limit

Barium calcium titanium Ba_1?xCa_xTiO₃ (BCTx) is an important ferroelectric and antiferroelectric material. The BCTx (x = 0, 0.1, 0.21, 0.3) thin films were prepared on (100)-oriented LaNiO₃/Si substrates by a sol–gel process. X-ray diffraction showed that all the BCTx thin films exhibited a single perovskite phase with (100)-preferred orientation. The temperature dependent dielectric properties showed that the BCT0.21 film which is near the solubility limit of CaTiO₃ (CT) in BaTiO₃ (BT) had a large dielectric constant and the lowest temperature coefficient. Although the dielectric loss for BCT0.21 film is slightly higher than the others, the BCT0.21 thin film is still a promising candidate for the devices which demand high and stable memory capability in temperature changeable environment.     

Sb2Te3-Ta2O5 nano-composite films for low-power phase-change memory application

Sb₂Te₃-Ta₂O₅ nano-composite films were deposited by the cosputtering of Sb₂Te₃ and Ta₂O₅ targets using radio frequency magnetron sputtering system at room temperature. A phase-change random access memory (PCRAM) device based on the Sb₂Te₃-Ta₂O₅ films was successfully fabricated. Compared to a pure Ge₂Sb₂Te₅ based PCRAM cell, the reset voltage of the Sb₂Te₃-Ta₂O₅ based cell was obviously reduced, which was attributed to the reduced thermal conductivity and lower melting point of the Sb₂Te₃-Ta₂O₅ films. In addition, the device with the Sb₂Te₃-Ta₂O₅ layer could work with much shorter pulse widths for both SET and RESET, suggesting that the Sb₂Te₃-Ta₂O₅ based compounds are promising candidates for low-power and fast-speed PCRAM application.     

Ge2Sb2Te5 and PbZr0.30Ti0.70O3 composite films for application in phase change random access memory

The improvement in the phase change characteristics of Ge₂Sb₂Te₅ (GST) films for phase change random access memory (PCM) applications was investigated by doping the GST films with PbZr_0.30Ti_0.70O₃ (PZT) using cosputtering at room temperature. The doped films showed a retarded crystallization to a higher temperature and higher resistivity in the crystalline state compared to pure GST films. Phase separation has been observed in annealed GST-PZT films and the segregated domains exhibited relatively uniform size. The reduced reset voltage of GST-PZT based cell was due to the reduced programming volume by incorporating PZT into GST. This work clearly reveals the highly promising potential of GST-PZT composite films for application in PCM.     

The etching process and mechanism analysis of Ta-Sb2Te3 film based on inductively coupled plasma

Compared to the conventional phase change materials, the new phase change material Ta-Sb₂Te₃ has the advantages of excellent data retention and good material stability. In this letter, the etching characteristics of Ta-Sb₂Te₃ were studied by using CF₄/Ar. The results showed that when CF₄/Ar = 25/25, the etching power was 600 W and the etching pressure was 2.5 Pa, the etching speed was up to 61 nm/min. The etching pattern of Ta-Sb₂Te₃ film had a smooth side wall and good perpendicularity (close to 90°), smooth surface of the etching (RMS was 0.51nm), and the etching uniformity was fine. Furthermore, the mechanism of this etching process was analyzed by X-ray photoelectron spectroscopy (XPS). The main damage mechanism of ICP etching in CF4/Ar was studied by X-ray diffraction (XRD).