Co-reporter:Guangyu Liu, Liangcai Wu, Min Zhu, Zhitang Song, Feng Rao, Sannian Song, Yan Cheng
Solid-State Electronics 2017 Volume 135(Volume 135) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.sse.2017.06.004
•Sb2Te film properties (Resistance-temperature, data retention and film thickness change characteristics) and XRD.•Microscopic structure (Crystalline grains size, grain boundary, HRTEM and SAED images).•Device characteristics (Resistance-voltage, endurance and resistance drift characteristics).Chalcogenide alloys are paid much attention in the study of nonvolatile phase-change memory (PCM). A comprehensive research is investigated on Sb2Te (ST), a base material, from properties to performances in this paper. For the characteristics of ST films, the sheet resistance is extremely stable during cooling process in resistance-temperature measurement and the thickness change of ST film is 5.7%. However, low 10-year data retention temperature (∼55 °C) and large crystal grain are the demerits for ST. In addition, the structure characteristics show stable hexagonal phase and large grain of several hundred nanometers at crystalline state after annealing. As for electrical properties, although the ST-based PCM devices are characterized by fast operation speed of ∼20 ns, only about 8 × 103 times of stable operation cycles can be obtained. After that, the endurance performance deteriorates gradually due to the growth of grains. About resistance drift, the drift coefficients are very small both in crystalline state and in amorphous state.
Co-reporter:Yun Meng, Liangcai Wu, Zhitang Song, Shuai Wen, Minghui Jiang, Jingsong Wei, Yang Wang
Materials Letters 2017 Volume 201(Volume 201) pp:
Publication Date(Web):15 August 2017
DOI:10.1016/j.matlet.2017.05.003
•SET/RESET speed of 10 ns was obtained with large sensing margin.•The reflectivity ratio of Sb2Te3-SiC is large enough for application.•The role of SiC in suppressing crystallization was proved by XRD, and TEM results.In this study, doping of Sb2Te3 with silicon carbide has been proposed to enhance the optical and electrical properties of Sb2Te3. The silicon carbide-doped Sb2Te3 (Sb2Te3-SiC)-based phase change memory cell can be triggered by a 10 ns electric pulse, indicating its excellent electrical properties. Furthermore, femtosecond pulses are used to study the reversible phase transition processes. The large reflectivity ratio of Sb2Te3-SiC is beneficial for achieving distinguishable logical states in optical applications. X-ray diffraction and transmission electron microscopy results show the SiC doping plays an important role in refining the grain size of Sb2Te3, producing smaller grain.
Co-reporter:Yun Meng, Qiuming She, Liangliang Cao, Yan Chen, Peigao Han, Zhitang Song, Bo Liu, Liangcai Wu, Lianke Song
Journal of Alloys and Compounds 2016 Volume 664() pp:591-594
Publication Date(Web):15 April 2016
DOI:10.1016/j.jallcom.2016.01.036
•The oxidation of Sb and Te elements can be avoided.•The thermal stability of Sb2Te is improved obviously through SiC doping.•XRD and TEM show the Sb2Te-SiC nanomaterial is very uniform and no phase separation occurred.•SET/RESET operation of 7 ns is realized with large sensing margin.Sb–Te alloy is widely considered as one of the important materials for phase change memory (PCM) with fast operation speed. However, the poor amorphous phase stability limits its wide application. In this work, silicon carbide (SiC) doped Sb2Te (Sb2Te-SiC) nanomaterial was proposed to improve the thermal stability of Sb2Te. It was found that the crystallization temperature of Sb2Te was remarkably improved from 149 °C to 251 °C. Accordingly, the temperature for 10-year data retention increases from 56.5 °C to 156.4 °C. X-ray diffraction and transmission electron microscope results indicate that the grain size of Sb2Te-SiC film was largely reduced with SiC doping. Besides, experimental results show the Sb2Te-SiC nanomaterial is very uniform and no phase separation was observed even after 300 °C annealing. Furthermore, the Sb2Te-SiC nanomaterial based PCM cells show fast operation speed of 7 ns and good endurance ability of 2.1 × 104 cycles.
Co-reporter:Yun Meng, Xilin Zhou, Peigao Han, Zhitang Song, Liangcai Wu, Chengqiu Zhu, Wenjing Guo, Ling Xu, Zhongyuan Ma, Lianke Song
Applied Surface Science 2015 Volume 355() pp:667-671
Publication Date(Web):15 November 2015
DOI:10.1016/j.apsusc.2015.07.069
Highlights
- •
Thermal stability of Sb3Te film was significantly increased through W doping.
- •
SET/RESET speed of 10 ns was obtained with large sensing margin.
- •
The role of W in suppressing crystallization was proved by XRD, TEM and Raman scattering.
Co-reporter:Xinglong Ji, Liangcai Wu, Min Zhu, Feng Rao, Zhitang Song, Zhigao Hu, Shuang Guo, Ling Xu, Xilin Zhou and Songlin Feng
RSC Advances 2015 vol. 5(Issue 32) pp:24966-24974
Publication Date(Web):18 Feb 2015
DOI:10.1039/C4RA11504J
Phase change materials rule the basic scientific issues in the research of phase change memory. As an important member in the phase change material system, GeTe is competitive for both technological applications and fundamental studies. However, its relatively poor thermal stability in the amorphous state and serious grain clustering need to be overcome for the application of GeTe. Here we propose Ge–Te–Ti (GTT) as a novel phase change material. For GTT, just with a small Ti fraction, the temperature for 10 year's data retention reaches 175 °C, and its grain size decreases one order of magnitude. Results of Raman scatting measurements indicate that the basic structure unit distribution of GTT deviates from the normal distribution to the Ge-rich direction with the Ti fraction increasing. The Ti-induced amorphous structure adjustment in GTT is the physical origin for the thermal stability enhancement, which makes GTT more extensively applicable in high temperature fields through the appropriate disordering adjustment.
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:Xinglong Ji, Liangcai Wu, Shilong Lv, Feng Rao, Min Zhu, Zhitang Song, Xilin Zhou, Songlin Feng
Acta Materialia 2014 Volume 73() pp:48-55
Publication Date(Web):July 2014
DOI:10.1016/j.actamat.2014.03.067
Abstract
Investigation of atomic migration behavior in nanoscale phase-change material is very valuable for phase-change memory applications. In this work, Ti0.5Sb2Te3-based phase-change nanobridges were fabricated and mass transport by atomic migration was studied. A 3-D finite-element simulation on the electrothermal field was introduced to describe the electrothermal environment in the phase-change region. During the nanosecond operation, an obvious compositional distribution resulting from atomic migration was observed in the Ti0.5Sb2Te3 phase-change nanobridge. Based on the mass continuity equation, a physical model for mass transport is proposed to illustrate that the density variation during the amorphous-to-crystalline structural transformation is the main reason for the atomic migration in nanoscale Ti0.5Sb2Te3 phase-change material.
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:Dongning Yao, Xilin Zhou, Liangcai Wu, Zhitang Song, Limin Cheng, Feng Rao, Bo Liu, Songlin Feng
Solid-State Electronics 2013 Volume 79() pp:138-141
Publication Date(Web):January 2013
DOI:10.1016/j.sse.2012.07.020
Nitrogen-doped Ge2Sb2Te5 thin film is proposed to present the feasibility for electrical phase-change memory application. The effect of nitrogen doping on the structure is studied by in situ sheet resistance measurement and X-ray diffraction method. The temperature upon crystallization from amorphous to cubic structure is increased by nitrogen addition, while the phase transformation to hexagonal phase occurs at a lower temperature compared with the nitrogen-free Ge2Sb2Te5 material. The X-ray diffraction test reveals that the grain size has been refined significantly by the incorporation of nitrogen atoms in the film. Phase-change memory device based on nitrogen incorporated Ge2Sb2Te5 material is fabricated using complementary metal oxide semiconductor technology. A complete crystallization of the phase-change cell is realized in the current–voltage sweeping process. Nitrogen-doped Ge2Sb2Te5 with higher sheet resistance in the crystalline state is favored for phase-change memory application due to the decreased reset voltage and promoted resistance ratio of the reset and set states.Highlights► The structure is studied by in situ Rs measurement and X-ray diffraction method. ► The grain size has been refined significantly by the doping of nitrogen atoms. ► A complete crystallization of the device is realized in the I–V sweeping process.
Co-reporter:Limin Cheng,, Liangcai Wu, Zhitang Song, Feng Rao, Cheng Peng, Dongning Yao, Bo Liu
Materials Letters 2012 Volume 71() pp:98-100
Publication Date(Web):15 March 2012
DOI:10.1016/j.matlet.2011.12.039
The thermal and electrical-property changes of 2.02 at.% nitrogen-doped Ge-rich Ge3Sb2Te5 (NGST) were investigated. The crystallization temperature was 180 °C. The corresponding activation energy was 2.96 eV. The maximum temperature for a 10 year data lifetime was estimated to be 97 °C. NGST films showed retarded crystallization to a higher temperature, and higher resistivity in the crystalline state, compared to pure Ge2Sb2Te5 (GST) films. An NGST-based cell showed relatively low power consumption and better contrast resistance than obtained with GST. The addition of N and Ge to the Ge2Sb2Te5 film improves both the thermal stability and electrical properties. This work demonstrated the great promise of NGST composite films for application in phase-change memory (PCM).Highlights► Nitrogen-doped Ge3Sb2Te5(NGST) was fabricated to improve the properties for PCM. ► The activation energy (Ea ) was found to be 2.96eV. ► The maximum temperature for a 10 year data lifetime was estimated to be 97 °C. ► Electrical properties were also improved by NGST.
Co-reporter:Cheng Peng, Liangcai Wu, Zhitang Song, Feng Rao, Min Zhu, Xuelai Li, Bo Liu, Limin Cheng, Songlin Feng, Pingxiong Yang, Junhao Chu
Applied Surface Science 2011 Volume 257(Issue 24) pp:10667-10670
Publication Date(Web):1 October 2011
DOI:10.1016/j.apsusc.2011.07.072
Abstract
Al doped Sb2Te3 material was proposed to improve the performance of phase-change memory. Crystallization temperature, activation energy, and electrical resistance of the Al doped Sb2Te3 films increase markedly with the increasing of Al concentration. The additional Al–Sb and Al–Te bonds enhance the amorphous thermal stability of the material. Al0.69Sb2Te3 material has a better data retention (10 years at 110 °C) than that of Ge2Sb2Te5 material (10 years at 87 °C). With a 100 ns width voltage pulse, SET and RESET voltages of 1.3 and 3.3 V are achieved for the Al0.69Sb2Te3 based device.
Co-reporter:Xilin Zhou, Liangcai Wu, Zhitang Song, Feng Rao, Kun Ren, Cheng Peng, Bo Liu, Dongning Yao, Songlin Feng, Bomy Chen
Thin Solid Films 2011 Volume 520(Issue 3) pp:1155-1159
Publication Date(Web):30 November 2011
DOI:10.1016/j.tsf.2011.08.111
The phase transformation properties of the nitrogen-doped Sb-rich Si–Sb–Te films were investigated in detail. It was found that the addition of N atoms into the Si–Sb–Te films increases the temperature for phase transition from the amorphous phase to a stable hexagonal structure and enhances the sheet resistance of the films following grain refinement. The surface topography of the crystalline films was improved by doping nitrogen atoms. The activation energy for crystallization of the films was increased from 1.84 to 2.89 eV with the increased nitrogen content from 0 to 21 at.%, which promises an improved thermal stability. A prolonged data lifetime up to 10 years at 149.4 °C was realized. From the device performance point of view, the N-doped Si–Sb–Te film with a moderate nitrogen content was preferable for the phase-change memory applications due to its advantage of higher reliability.
Co-reporter:Liangcai Wu, Zhitang Song, Bo Liu, Ting Zhang, Feng Rao, Jie Shen, Feng Wang, Songlin Feng
Journal of Non-Crystalline Solids 2007 Volume 353(44–46) pp:4043-4047
Publication Date(Web):15 November 2007
DOI:10.1016/j.jnoncrysol.2007.06.039
A Ge2Sb2Te5 based phase change memory (PCM) cell was fabricated by a standard 0.18 μm complementary metal–oxide-semiconductor technology, combined with subsequent special lift-off process. Through current–voltage measurements, the phase change from the amorphous state (high resistance state) to the face-centered cubic crystalline state and the hexagonal close-packed crystalline state (two kinds of different low resistance states) was observed. In addition to the typical phase-transition, where the PCM cell changes from initial amorphous state directly into final crystalline state, intermediate resistance states were observed during the phase changes from the high resistance state to the low resistance state.
