Co-reporter:Keyuan Ding, Feng Rao, Mengjiao Xia, Zhitang Song, Liangcai Wu, Songlin Feng
Journal of Alloys and Compounds 2016 Volume 688(Part B) pp:22-26
Publication Date(Web):15 December 2016
DOI:10.1016/j.jallcom.2016.07.186
•W0.08(Sb2Te3)0.92 shows 10 ns operation speed, 6 ns Set operation speed.•The W atoms are suggested to locate in the Sb positions.•The grain size of W0.08(Sb2Te3)0.92 is about 5 nm.•The stronger WTe bonds induces the small grain size of W0.08(Sb2Te3)0.92.W doping is proposed to reduce the grain size of Sb2Te3. The grain size of W0.08(Sb2Te3)0.92 is about 5 nm, which is smaller than that of Sb2Te3 (∼80 nm) under the same annealing condition. The phase change memory based on W0.08(Sb2Te3)0.92 material shows 10 ns operation speed, 6 ns Set operation speed, and 1.3 × 105 reversible phase change ability. Through experimental and theoretical investigation, the W atoms are suggested to be located at the Sb positions, and bind with the Te atoms. The stronger WTe bonds induce the small grain size of W0.08(Sb2Te3)0.92, leading to high speed phase change ability.
Co-reporter:Xilin Zhou, Mengjiao Xia, Feng Rao, Liangcai Wu, Xianbin Li, Zhitang Song, Songlin Feng, and Hongbo Sun
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 16) pp:14207
Publication Date(Web):August 4, 2014
DOI:10.1021/am503502q
Phase-change materials are highly promising for next-generation nonvolatile data storage technology. The pronounced effects of C doping on structural and electrical phase-change behaviors of Ge2Sb2Te5 material are investigated at the atomic level by combining experiments and ab initio molecular dynamics. C dopants are found to fundamentally affect the amorphous structure of Ge2Sb2Te5 by altering the local environments of Ge–Te tetrahedral units with stable C–C chains. The incorporated C increases the amorphous stability due to the enhanced covalent nature of the material with larger tetrahedral Ge sites. The four-membered rings with alternating atoms are reduced greatly with carbon addition, leading to sluggish phase transition and confined crystal grains. The lower RESET power is presented in the PCM cells with carbon-doped material, benefiting from its high resistivity and low thermal conductivity.Keywords: C doping; finite-element modeling; Ge2Sb2Te5; microstructure; molecular dynamic simulations; phase-change material
Co-reporter:Cheng Peng, Feng Rao, Liangcai Wu, Zhitang Song, Yifeng Gu, Dong Zhou, Hongjia Song, Pingxiong Yang, Junhao Chu
Acta Materialia 2014 Volume 74() pp:49-57
Publication Date(Web):1 August 2014
DOI:10.1016/j.actamat.2014.03.069
Abstract
Homogeneous phase W–Ge–Te material has been proposed and investigated for phase-change memory (PCM) applications. The crystallization temperature of GeTe is markedly improved by introducing W atoms. In the W–Ge–Te material, W atoms bonding to Ge and Te atoms serve as substitutional impurities. During the crystallization process, the diffusion of Ge and Te atoms is restricted by W atoms that have larger atomic mass, which further leads to more uniform crystallization of the material. W atoms serve as nucleation centers and attract the surrounding Ge and Te atoms, quickly building crystal grains. W0.1(GeTe)0.9 film has a 10-year data retention temperature of 225 °C and an ultrafast crystallization time of 3 ns. Specifically, W0.1(GeTe)0.9 film can withstand the Pb-free solder reflow temperature (260 °C) for 4.6 × 104 s. A voltage pulse of as little of 10 ns long can realize reversible operations for W0.1(GeTe)0.9-based PCM devices. In addition, good endurance (5 × 105 cycles) has also been obtained for the cell.
Co-reporter:Keyuan Ding, Kun Ren, Feng Rao, Zhitang Song, Liangcai Wu, Bo Liu, Songlin Feng
Materials Letters 2014 Volume 125() pp:143-146
Publication Date(Web):15 June 2014
DOI:10.1016/j.matlet.2014.03.180
•Crystallization temperature of the Ge2Sb2Te5 films increases remarkably.•The Ea of Cu-doped Ge2Sb2Te5 films increases.•The best 10-years lifetime at temperature up to 134 °C is found in Cu0.10(Ge2Sb2Te5)0.90 films.•The power consumption of PCRAM test cell based on Cu0.10(Ge2Sb2Te5)0.90 film is low.Cu0.10(Ge2Sb2Te5)0.90 is proposed for low power consumption phase change memory (PCM). The thermal stability of Ge2Sb2Te5 is increased by 10 at% Cu doping, with the crystallization temperature and data retention increased from 163 °C to 202 °C and from 87 °C to 134 °C, respectively. The electric operation results have proved the low power consumption and good cycling ability (>104), which may result from the low melting point (486 °C) and the negligible phase separation in Cu0.10(Ge2Sb2Te5)0.90. The good thermal stability, low Tm and good cycling phase change ability have made Cu0.10(Ge2Sb2Te5)0.90 a promising candidate for the low power consumption PCM application.
Co-reporter:Xilin Zhou, Liangcai Wu, Zhitang Song, Yan Cheng, Feng Rao, Kun Ren, Sannian Song, Bo Liu, Songlin Feng
Acta Materialia 2013 Volume 61(Issue 19) pp:7324-7333
Publication Date(Web):November 2013
DOI:10.1016/j.actamat.2013.08.038
Abstract
The effects of nitrogen doping on the phase-change performance of Sb-rich Si–Sb–Te materials are systemically investigated, focusing on the chemical state and the role of nitrogen upon crystallization. The tendency of N atoms to bond with Si (SiNx) in the crystalline film is analyzed by X-ray photoelectron spectroscopy. The microstructures of the materials mixed with Sb2Te crystal grains and amorphous Si/SiNx regions are elucidated via in situ transmission electron microscopy, from which a percolation behavior is demonstrated to possibly describe the random crystallization feature in the nucleation-dominated nanocomposite material. The phase-change memory cells based on N-doped Sb-rich Si–Sb–Te materials display more stable and reliable electrical performance than the nitrogen-free ones. An endurance characteristic in the magnitude of 107 cycles of the phase-change memory cells is realized with moderate nitrogen addition, meaning that the nitrogen incorporation into Si–Sb–Te material is a suitable method to achieve high-performance phase-change memory for commercial applications.
Co-reporter:Feng Rao, Zhitang Song, Yan Cheng, Mengjiao Xia, Kun Ren, Liangcai Wu, Bo Liu, Songlin Feng
Acta Materialia 2012 Volume 60(Issue 1) pp:323-328
Publication Date(Web):January 2012
DOI:10.1016/j.actamat.2011.09.015
Abstract
Upon phase transition, the resistivity changes of Ge2Sb2Te5 (GST) and Si3.5Sb2Te3 (SST) are proved to be closely related to the variations of band gap and density of localized states. Amorphous SST has a slightly more localized state than amorphous GST; however, the larger band gap of SST material causes relatively difficult phase transition processes. Therefore, the phase change memory (PCM) cell based on the SST film shows larger threshold voltages for both set and reset operations than that of the GST-based PCM cell. The formation of amorphous Si-rich segregated areas in the SST film during phase transitions increases the randomness of the whole film microstructure, which leads to a different Urbach tail absorption result to that of the GST film.
Co-reporter:Feng Rao, Kun Ren, Yifeng Gu, Zhitang Song, Liangcai Wu, Xilin Zhou, Bo Liu, Songlin Feng, Bomy Chen
Thin Solid Films 2011 Volume 519(Issue 16) pp:5684-5688
Publication Date(Web):1 June 2011
DOI:10.1016/j.tsf.2011.03.015
Growth-dominant Sb2Te material with large crystal grain is converted to the nano composite material after Si doping. The increase of Si content in SixSb2Te material helps to further diminish the grain size, form more uniform grain distribution, and enhance the thermal stability of the amorphous phase. Si2Sb2Te crystallizes into a nano composite structure [amorphous Si + crystalline Sb2Te (< 20 nm grain size)] without any Te or Sb phase segregation, which ensures better operation stability for the application in T-shaped phase change memory device. Comparing to Ge2Sb2Te5 film, Si2Sb2Te film shows better data retention ability (10 years at 397 K). Meanwhile, electrical measurements prove that phase change memory cell based on Si2Sb2Te film also has low power consumption than that of the Ge2Sb2Te5 film based cell.
Co-reporter:Feng Rao, Zhitang Song, Liangcai Wu, Yuefeng Gong, Songlin Feng, Bomy Chen
Solid-State Electronics 2009 Volume 53(Issue 3) pp:276-278
Publication Date(Web):March 2009
DOI:10.1016/j.sse.2008.12.003
Four nm thick TiN film was inserted between Sb2Te3 and Ge2Sb2Te5 films in conventional doublelayer phase change memory cell. The novel sandwich-structure phase change memory cell was still able to show triple level data storage ability. Interdiffusion between Sb2Te3 and Ge2Sb2Te5 films is suppressed by this TiN layer. Compared with conventional doublelayer phase change memory cell, smooth resistance stages with more consistent resistance magnitudes and better data endurance characteristics of all resistance states have been achieved on the sandwich-structure phase change memory cell.
