Characteristics of N-doped Sb 2 Te 3 Films by X-ray Diffraction and Resistance Measurement for Phase-change Memory
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Characteristics of N-doped Sb2Te3 Films by X-ray Diffraction and Resistance Measurement for Phase-change Memory You Yin1, Naoya Higano1, Kazuhiro Ohta2, Akihira Miyachi1, Masahiro Asai1, Daisuke Niida1, Hayato Sone1, and Sumio Hosaka1 1 Department of Nano-Material Systems, Gunma University, 1-5-1 Tenjin, Kiryu, Gunma, 3768515, Japan 2 Department of Electronic Engineering, Gunma University, 1-5-1 Tenjin, Kiryu, Gunma, 3768515, Japan
ABSTRACT In this paper, characterizations of sputtered undoped and nitrogen-doped Sb2Te3 (ST and STN) films by X-ray diffraction (XRD) and resistance measurements are described and their application of lateral phase-change memory (PCM) is presented. Nitrogen concentration of the films was controlled by changing the flow rate ratio of N2/Ar during sputtering. Resitivity of STN films drops by 3-4 orders of magnitude due to crystallization. Resistivity increase of the STN film (N2/Ar=0.15) at above 270oC results from phase precipitation of SbN. Experimental results reveal that the temperature of crystallization to face-centered cubic (fcc) significantly increases from below 100oC to 160-220oC with increasing the ratio of N2/Ar (in the range of 00.15) and crystal structure further transforms from fcc to hexagonal. At high flow rate ratio of N2/Ar (>0.15), hexagonal Te phase firstly appears at 160oC and then orthorhombic SbN appears at 290oC. INTRODUCTION Chalcogenides in phase change memory (PCM) are characterized by the fast reversible switching between amorphous and crystalline phases, accompanying large difference in electrical properties [1, 2]. By applying a short but high electrical pulse, chalcognide in PCM can be amorphized via melting and quick quenching so the PCM enters a highly resistive state. On the other hand, by applying a long but low electrical pulse, it can be poly-crystallized and PCM correspondingly enters a lowly resistive state. PCM attracted much attention as an emerging nonvolatile memory due to its almost perfect properties such as excellent endurance, nondestructive read, direct overwrite, low programming energy, huge read dynamic range, fast speed, high performance, multi-state storage capability [3-8]. Compared with widely researched Ge2Sb2Te5 (GST) chalocogenide, Sb2Te3 material for phase-change memory could have some advantages such as low reset current resulting from its low melting point [4, 9]. However, a short retention time is possible for Sb2Te3 material owing to its low crystallization temperature. In order to increase its crystallization temperature and finally extend the retention time, a series of N-doped Sb2Te3 (ST-N) films were investigated by X-ray diffraction (XRD) and resistivity measurement as a function of annealing temperature.
EXPERIMENTAL A series of 200-nm-thick ST and STN film samples with a SiO2 capping layer on glass substrates were prepared by changing the flow rate ratio of N2/Ar during sputtering as given in Table I using a radio frequency sputtering equipment (MNS-3000-RF, ULVAC, Inc.) at a background pressure below 5◊
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