Investigation on Phase Change Behaviors of Si-Sb-Te Alloy: The Effect of Tellurium Segregation
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Investigation on Phase Change Behaviors of Si-Sb-Te Alloy: The Effect of Tellurium Segregation Xilin Zhou1, 2, Liangcai Wu1, Zhitang Song1, Feng Rao1, Kun Ren1, 2, Yan Cheng1, Bo Liu1, Dongning Yao1, Songlin Feng1, and Bomy Chen3 1 State Key Laboratory of Functional Materials for Informatics, Laboratory of Nanotechnology, Shanghai Institute of Micro-system and Information Technology (SIMIT), Chinese Academy of Sciences (CAS), Shanghai 200050, P. R. China 2 Graduate University of the Chinese Academy of Sciences, Beijing, 100049, P. R. China 3 Silicon Storage Technology, Inc., 1171 Sonora Court, Sunnyvale, CA 94086, U.S.A. ABSTRACT In this study, novel Si2Sb2Te6 phase change material is investigated in detail for the phase change memory application using transmission electron microscopy and X-ray photoelectron spectroscopy. The phenomenon that Te diffuses to the film surface during phase switching and successively evaporates out has been confirmed. The phase change memory cells employing Si2Sb2Te6 and Si3Sb2Te3 materials are fabricated and programmed. For the Si2Sb2Te6-based cell a data endurance of 5×105 cycles is achieved with a failure mode resembling reset stuck, which can be attributed to the migration of Tellurium during the operation cycles. It means that a thermally stable material system of SixSb2Te3 is preferred for the PCM applications. INTRODUCTION Nowadays advanced applications from digital cameras to smart phones are driving the demand for novel nonvolatile memory (NVM) technology capabilities. Phase change memory (PCM) technology directly addresses the needs of current electronic systems with innovative key technology features, such as nonvolatility, high scalability, low power consumption, and good data retention [1]. Conventional phase change materials used in PCM are chalcogenide materials, especially the Te-based alloys. These alloys possess notable difference in electrical properties between the amorphous (reset state with high resistivity) and crystalline (set state with low resistivity) phases, which can be employed as bistable states of PCM in nonvolatile electronic storage. Over the past few years, various material families have been found qualified for PCM application. Among these, Si-Sb-Te (SST) materials have been reported with low energy cost and good data detention due to its higher resistance and enhanced thermal stability compared with Ge-Sb-Te (GST) alloys [2−4]. Similar to the Ge2Sb2Te5 (GeTe-Sb2Te3) system, the imitator Si2Sb2Te6 pseudobinay alloy has been proposed along the Si2Te3-Sb2Te3 tie line [3]. The phenomenon of Te phase separation, however, is still observed in the Te-rich Si-Sb-Te materials (Si2Sb2Te5−6) [3, 5], since Te in GST is confirmed to be diffused towards grain boundaries and interfaces at high annealing temperature [6, 7].Te segregation, which mainly ascribes to its low melting temperature and high vapor pressure, will lead stoichiometric deviation and deteriorate the reproducibility of the phase change cycles. In this study the phase separation evidence of a phase
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