Electrical Resistance Change with Crystallization in Si-Te Amorphous Thin Films
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1251-H06-07
Electrical Resistance Change with Crystallization in Si-Te Amorphous Thin Films Yuta Saito, Yuji Sutou and Junichi Koike Department of Materials Science, Tohoku University 6-6-11-1016 Aoba-yama, Sendai 980-8579, Japan ABSTRACT The electrical resistance change of amorphous SixTe100-x (x: 10-23) films during heating was investigated by a two-point probe method. The SixTe100-x films showed two-stage crystallization processes. The film was firstly crystallized to Te and subsequently crystallized to Si2Te3 with an electrical resistance drop. The first crystallization temperature Tx1st slightly increased with increasing Si content, while the second crystallization temperature Tx2nd was independent on the composition and was a constant temperature of 310 ºC. In all films, the electrical resistance once increased in the temperature range from 250 to 295 ºC before the crystallization of the Si2Te3. This temporal resistance increase could be explained by considering a formation of high-resistivity Si-rich amorphous phase. INTRODUCTION Recently, phase change random access memory (PCRAM) has been attracting considerable attention due to high scalability, fast access time and good retention time. In the PCRAM, the data recording is accompanied by the reversible phase transition of a phase change material between amorphous and crystalline phases caused by Joule heating. Ge2Sb2Te5 (GST) phase change material is used for an optical disc and has been widely studied for the PCRAM. However, a high reset current which causes high power consumption is required due to its high melting point (~630 ºC). Thus, many attempts have been made to reduce the power consumption, for example, scaling down of a contact size between a heater and a phase change material [1, 2] and nitrogen doping to increase the electrical resistivity of a crystalline state of GST [3]. Using a material with a low melting point is also one of the effective approaches for reducing the power consumption. Therefore, eutectic binary alloys such as Ge-Sb [4], Sb-Se [5] and Sb-Te [6] have been studied as phase change materials due to their low melting point. Si-Te binary system possesses a eutectic composition at the Te content of 85 at.%. Its eutectic melting point of 407 ºC is lower by more than 200 ºC than the melting point of GST. C. Murthy et al. have reported electrical memory switching phenomena in bulk Si-Te glasses [7]. Furthermore, the crystallization kinetics was investigated by Zhang et al. in Si15Te85 and Si20Te80
bulk glasses using DSC [8]. However, there is no report of the electrical resistance change during heating process for the eutectic Si-Te thin film, which is one of the key properties for PCRAM application. In this study, the crystallization process and the corresponding electrical resistance change were investigated in the Si-Te thin films, including the eutectic composition of Si15Te85.
EXPERIMENT Si-Te films with 250 nm thickness were deposited on SiO2 (20 nm)/Si substrates by co-sputtering of Si and Te targets. In-situ electrical res
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