Phase-change behavior in Si/Sb80Te20 nanocomposite multilayer films

Phase-change behavior in Si/Sb₈₀Te₂₀ nanocomposite multilayer films were investigated by utilizing in situ resistance measurements. It was found that the crystallization temperature increased firstly with increasing Si layer thickness within the multilayer films, and then remained almost unchanged at 170°C. The multilayer films have the merits of both good thermal stability and fast phase-change speed. An increase in crystallization temperature by around 95°C was observed for the multilayer films when the Sb₈₀Te₂₀ layer thickness was reduced to 3 nm. Cross-sectional transmission electron microscopy (TEM) observations revealed that Si/Sb₈₀Te₂₀ nanocomposite multilayer films had layered structures with clear interfaces. The reversible phase change between set and reset states was verified in phase-change random access memory (PCRAM) cell based on [Si (1 nm)/Sb₈₀Te₂₀ (5 nm)]₁₇ multilayer film.     

Characterization of Cr‐doped Sb2Te3 films and their application to phase‐change memory

Phase‐change memory (PCM) is regarded as one of the most promising candidates for the next‐generation nonvolatile memory. Its storage medium, phase‐change material, has attracted continuous exploration. Along the traditional GeTe–Sb₂Te₃ tie line, the binary compound Sb₂Te₃ is a high‐speed phase‐change material matrix. However, the low crystallization temperature prevents its practical application in PCM. Here, Cr is doped into Sb₂Te₃, called Cr–Sb₂Te₃ (CST), to improve the thermal stability. We find that, with increase of the Cr concentration, grains are obviously refined. However, all the CST films exhibit a single hexagonal phase as Sb₂Te₃ without phase separation. Also, the Cr helps to inhibit oxidation of Sb atoms. For the selected film CST_10.5, the resistance ratio between amorphous and crystalline states is more than two orders of magnitude; the temperature for 10‐year data retention is 120.8 °C, which indicates better thermal stability than GST and pure Sb₂Te₃. PCM cells based on CST_10.5 present small threshold current/voltage (4 μA/0.67 V). In addition, the cell can be operated by a low SET/RESET voltage pulse (1.1 V/2.4 V) with 50 ns width. Thus, Cr–Sb₂Te₃ with suitable composition is a promising novel phase‐change material used for PCM with high speed and good thermal stability performances. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Performance improvement of phase-change memory cell with Ge2Sb2Te5-HfO2 composite films

The phase-change characteristics of Ge₂Sb₂Te₅ (GST) films for phase-change random access memory (PCM) devices were improved by incorporating HfO₂ into GST film using cosputtering at room temperature. Phase separation (GST-rich nanocrystals were surrounded by HfO₂-rich amorphous phase) has been observed in annealed GST-HfO₂ composite films and the segregated domains exhibited a relatively uniform size. The reduced reset voltage of GST-HfO₂ based cell was due to the reduced programming volume by incorporating HfO₂ into GST. This work clearly reveals the highly promising potential of GST-HfO₂ composite films for application in PCM.     

Textured PLCT Thin Films Prepared on Pt/Ti/SiO2/Si Substrate by Metal-Organic Decomposition

Textured calcium modified (Pb,La)TiO₃ (PLCT) films were deposited on Pt/Ti/SiO₂/Si substrates by using a metal-organic decomposition (MOD) process. The PLCT films exhibit good ferroelectric properties, a very low leakage current and a sharp PLCT/Pt interface. The (100) texture of the PLCT film is growth-controlled; the (100) oriented grains grow preferentially so as to minimize the surface energy. Particularly, the (100) preferred orientation is easy to form in the PLCT film with a layered structure for which the substrate almost does not affect the nucleation and growth of the film.     

Planarization machining of sapphire wafers with boron carbide and colloidal silica as abrasives

The as-cutted sapphire wafers are planarized by the grinding and polishing two-step machining processes with micrometer B₄C and nanometer silica as abrasives, respectively. The material removal rates (MRRs) of two processes are measured. During the polishing process, the MRR increases with the down-pressure increased, whereas the rotational speeds have less effect on the MRR. The alkaline colloidal silica is more favorable than the acidic to polish sapphire wafer. The ground and polished surfaces of the substrate are compared by scanning electron microscopy, atomic force microscopy, and X-ray rocking curves. Our results show that B₄C abrasives are effective in elimination of the ununiformity in thickness within a wafer. The colloidal silica can achieve a nanoscale flatness of wafer, but the lasting polishing time seems unfavorable. The polishing process is also analyzed in terms of chemical mechanical polishing mechanism.     

Material and device properties of ZnO-based film bulk acoustic resonator for mass sensing applications

Zinc oxide based film bulk acoustic resonator as mass sensor was fabricated by multi-target magnetron sputtering under optimized deposition condition. Each layer of the device was well crystallized and highly textural observed by transmission electron microscopy and X-ray diffraction measurement. Through piezoelectric test, the device vibrated with significant distance. The influence of top electrode on resonant frequency and the bio-specimen of mass loading effect were investigated. Data show that the device has qualified properties as mass biosensor, with a resonant frequency of 3-4 GHz and a high sensitivity of 8-10 kHz cm²/ng.     

Ceria concentration effect on chemical mechanical polishing of optical glass

It was found material removal rate (MRR) sharply increased from 250 to 675 nm/min as the concentration decreased from 1 to 0.25 wt% in optical glass chemical mechanical polishing (CMP) using ceria slurries. Scanning electron microscopy was employed to characterize the ceria abrasive used in the slurry. Atomic force microscopy results showed good surface had been got after CMP. Schematic diagrams of the CMP process were shown. Furthermore, the absorption spectra indicated a sudden change from Ce⁴⁺ to Ce³⁺ of the ceria surface when the concentration decreased, which revealed a quantum origin of the phenomenon.     

AROMATIC AND HETEROCYCLIC DINITRILES AND THEIR POLYMERS ⅪⅤ. STUDY ON THE CATALYSTS OF THE POLYMERIZATION OF AROMATIC NITRILES*

Various catalysts for the polymerization ot aromatic nitriles were investigated. It was found that Lewis acid-metal is a preferable catalyst system for the polymerization of aromatic nitriles, and the polymerization rate is about 10 times faster than Lewis acid alone. The polymerization rate of benzonitrile catalyzed by Lewis acid and different metals was measured, and the activity of metals was in the following decreasing order ,magnesium, zinc, sodium, calcium. Furthermore, the polymerization of benzonitrile catalyzed by different Lewis acid and zinc was also investigated.     

THE POLYMERIZATION OF AROMATIC AND HETEROCYCLIC DINITRILES

This review is a concise survey about the works in our laboratory on the polymerization of aromatic and heterocyclic dinitriles, including the polymerization kinetics and mechanism, synthesis of heterocyclic dinitriles, the structure of polymers, and the correlation between the structures of dinitriles and polymerization rates and thermal performances of Polymers.