R&D: Three Articles on Phase Change Memories

R&D: Dual Mechanism Synergistic Optimization of Thermal Stability and Power Consumption of Sb₃Te Phase-change Random Access Memory

In this study, C and Re co-doped Sb₃Te films were prepared by magnetron sputtering.

Journal of Applied Physics has published an article written by Ningning Rong, Peng Xu, Shiwei Gao, College of Physics, Donghua University, Shanghai 201620, China, Liangcai Wu, College of Physics, Donghua University, Shanghai 201620, China, and National Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Micro-system and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China, Yuan Xue, Zhitang Song, and Sannian Song, National Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Micro-system and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China.

Abstract: “With the rapid development of data storage technology, the research on phase-change memory materials has attracted much attention. In this study, C and Re co-doped Sb₃Te films were prepared by magnetron sputtering. The effects of different C contents in co-doping on the properties of Sb₃Te films were systematically explored, and the results showed that co-doping increased the crystallization temperature to 231 °C, and the 10-year data retention temperature reached 151.8 °C. The film thickness (∼1.73%) and the surface roughness changed little before and after crystallization. The Re dopant enters the crystal lattice and forms a stable Re–Te bond with Te, which effectively stabilizes the precursor structure and promotes rapid crystallization. The introduction of element C tends to form clusters at the grain boundaries, which improves the thermal stability and inhibits grain growth. The performance of memory device based on C_15WRST has significantly improved, including a reversible phase transition with a pulse width of 6 ns, a SET/RESET voltage of only 1.1/1.6 V, a resistance drift coefficient reduced to 0.0072, and a power consumption of only 5 pJ. Thus, the C and Re co-doping strategy improves the thermal stability and reliability, while reducing the resistance drift and RESET power consumption of the devices.“

R&D: Experimental Investigation and Thermodynamic Optimization of Sb-Si-Te Phase-Change Memory Material

Set of self-consistent thermodynamic parameters of the Sb-Si-Te system are obtained, which facilitate the design of phase-change materials.

SSRN has published an article written by Yongji Wang, University of Science and Technology Beijing, China, Changrong Li, University of Science and Technology Beijing – School of Materials Science and Engineering, China, Cuiping Guo, and Zhenmin Du, University of Science and Technology Beijing, China

Abstract: “To design alloy materials capable of periodic transitions between high-resistance amorphous and low-resistance polycrystalline states, and to determine the controllable composition range and temperature interval, the thermodynamic database is strongly necessary. According to the solidification microstructure of as-cast alloys and the phase constituents of annealed samples, the liquidus surface projection and the phase equilibrium relationships at 500 °C for the Sb-Si-Te system have been constructed. For the isothermal section at 500 °C over the entire composition range, there are 10 two-phase regions, and 7 three-phase regions. The maximum solubilities of Si in the intermetallic phases δ with P-3m1 and γ with R-3m space groups are about 3.1 and 4.1 at.%, respectively. In the liquidus surface projection, there are 10 primary solidification regions and 9 invariant reactions. The Sb-Te binary system is reoptimized based on the available literature to ensure compatibility with the thermodynamic database of multi-component systems. On the basis of experimental data, the thermodynamic parameters of all the phases in the Sb-Si-Te system are optimized by CALculation of PHAse Diagram (CALPHAD) method. The liquid phase is described as the solution phase with the associated model (Sb, Sb2Te3, Si, Si2Te3, Te). The phases δ and γ are modeled as (Sb, Si)0.4(Sb, Te, Si)0.6. Sb2Si2Te6 is described as (Sb)0.2(Si)0.2(Te)0.6 by a three-sublattice model. A set of self-consistent thermodynamic parameters of the Sb-Si-Te system are obtained, which facilitate the design of phase-change materials.“

R&D: Flexible Memory Application of Nanoscale Ti–Ge–Te Thin Film as Information Storage Medium With Excellent Thermal Stability, Low Resistance Drift and Superior Bending Characteristic

Impact of titanium dopant and mechanical bending on the thermal stability, electrical resistance, surface morphology, microstructure, and crystallization mechanism of GeTe thin film are investigated systematically.

Advanced Science has published an article written by Han Gu, School of Mathematics and Physics, Jiangsu University of Technology, Changzhou, 213001 China, Weihua Wu, School of Mathematics and Physics, Jiangsu University of Technology, Changzhou, 213001 China, and National Laboratory of Solid State Microstructures, Nanjing University, Nanjing, 210093 China, Xiaochen Zhou, Pei Zhang, Bowen Fu, School of Mathematics and Physics, Jiangsu University of Technology, Changzhou, 213001 China, Jiwei Zhai, Shanghai Key Laboratory for R&D and Application of Metallic Functional Materials, School of Materials Science & Engineering, Tongji University, Shanghai, 201804 China, Sannian Song, and Zhitang Song, State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, 200050 China.

Abstract: “The flexible Ti–Ge–Te phase change material was proposed and fabricated by magnetron cosputtering method. The impact of titanium dopant and mechanical bending on the thermal stability, electrical resistance, surface morphology, microstructure, and crystallization mechanism of GeTe thin film are investigated systematically. With the incorporation of appropriate titanium dopant, the crystallization process and grain size of GeTe material can be hindered. Meanwhile, the thermal stability, surface morphology, and crystal structure have not been changed obviously when the bending times reaching 10⁶, demonstrating the distinguished mechanical bending performance. The phase change memory devices with Ti-doped GeTe were prepared based on flexible polyimide substrates, and the electronical properties are evaluated. The consequences show that the phase change memory can still exhibit the negative resistance phenomenon and complete the erase/write operation after bending 10⁶ cycles. The density functional theory calculations of band structure illustrate that titanium dopant can convert the indirect band gap of GeTe material to the direct type. The formation energy and charge density difference indicate the massive electron cloud agglomerate between the Ti and Te atoms, deducing that the foreign Ti may occupy the position of Ge and form the covalent bonds with Te.“