Influence of Thomson effect on amorphization in phase-change memory: dimensional analysis based on Buckingham’s П theorem for Ge2Sb2Te5

To evaluate the Thomson effect on the temperature increase in Ge _2 Sb _2 Te _5 (GST)-based phase-change random access memory (PCRAM), we created new dimensionless numbers based on Buckingham’s П theorem. The influence of the Thomson effect on the temperature increase depends on the dominant factor of electrical resistance in a PCRAM cell. When the effect is dominated by the volumetric resistance of the phase-change material $\left(C=\tfrac{{\rho }_{c}}{{\rm{\Delta }}x/\sigma }\ll O(1)\right),$ the dimensionless evaluation number is $B=\tfrac{{\mu }_{T}\sigma {\rm{\Delta }}\phi }{k},$ where ρ _c is the contact resistance, Δ x is the thickness of PCM, σ and k are the electrical and thermal conductivities, μ _T is the Thomson coefficient, and Δ ϕ is the voltage. When the contact resistance cannot be ignored, the evaluation number is B /(1 +  C ). The characteristics of hexagonal-type crystalline GST in a PCRAM cell were numerically investigated using the defined dimensionless parameters. Although the contact resistance of GST exceeded the volumetric resistance across the temperature range, the ratio of contact resistance to the whole resistance reduced with increasing temperature. Moreover, increasing the temperature of GST enhanced the influence of the Thomson effect on the temperature distribution. At high temperatures, the Thomson effect suppressed the temperature increase by approximately 10%–20%

Effect of Nb Content on Martensitic Transformation Temperatures and Mechanical Properties of Ti-Ni-Nb Shape Memory Alloys for Pipe Joint Applications

Several Ti-Ni-Nb shape memory alloys (SMAs) with various Nb contents (0$15 mol$1:1) were tested to investigate the martensitic transformation temperatures and mechanical properties. The martensitic transformation temperatures (M s , M f , A s and A f ) of the solution-treated Ti-Ni-Nb alloys at 1173 K for 300 seconds with Ni/Ti ratio of 1.0 decrease with increasing the Nb content. These transformation temperatures also depend on the Ni/Ti ratio, heat treatment condition and cold working rate. Furthermore, in the alloy with Nb content of 6 mol% and Ni/Ti atomic ratio being less than 1.05, the fracture stress and fracture strain reached about 1,000 MPa and over 20%, respectively. Based on the obtained results, several processing conditions such as the chemical composition, fabrication process and heat treatment are optimized for the Ti-Ni-Nb SMAs to develop SMA pipe joints

Crystallization processes of Sb100−xZnx (0 ≤ x ≤ 70) amorphous films for use as phase change memory materials

The phase change processes of as-deposited Sb-Zn films were investigated. The as-deposited amorphous SbZn film showed an unusual increase in resistance during heating, which was attributed to crystallization of the metastable SbZn phase. Further heating up to more than 300oC resulted in a structural transformation into the stable SbZn phase accompanied by a drop in resistance as in conventional phase change materials. Even though off-stoichiometric Sb-rich films exhibited crystallization into the metastable phase as well, the precipitation of Sb crystalline grains caused an undesirable drop in resistance at temperatures lower than that of the SbZn film. A memory device using an SbZn film showed typical switching behavior and successfully switched from the amorphous to crystal state and vice versa by the application of an electric pulse. These results revealed that stoichiometric SbZn film is a promising novel phase change material for phase change memory with high thermal stability