Effects of Oxygen-doping on Crystallization and Physical Properties of Ge2Sb2Te5 Films
- PDF / 156,558 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 12 Downloads / 233 Views
1072-G03-13
Effects of Oxygen-doping on Crystallization and Physical Properties of Ge2Sb2Te5 Films YU-HSUNG PERNG1, YING-TAI HSU1,2, and LIH-HSIN CHOU1 1 Nartional Tsing Hua University, Hsinchu, 30013, Taiwan 2 Chi Mei Light Technology Co., Tainan, 744, Taiwan ABSTRACT Oxygen-doped Ge2Sb2Te5 films (denoted as Ge2Sb2Te5-O) with oxygen concentration in between 0 and 10.3 at. % were prepared by direct current magnetron reactive sputtering with Ge2Sb2Te5 target. Both the crystallization temperature and activation energy of Ge2Sb2Te5-O films increased, while the crystalline grain size refined with oxygen concentration. For both amorphous and crystalline phases, optical band gap Egopt increases with oxygen concentration – a similar trend as observed in resistivity measurements. X-ray diffraction results showed that the face center cubic (fcc) structure maintained even after 400 anneal with oxygen addition in between 7.5 – 8.3 at.% - a different phenomenon from undoped Ge2Sb2Te5 film, but with crystallinity diminished gradually with oxygen concentration. Only Sb2Te3 diffraction peak was observed in the 10.3 at.% O film after 400 anneal. In conjunction with the bonding information obtained from X-ray photoelectron spectroscopy (XPS), effects of oxygen on the microstructures, thermal properties, resistivity and stability of fcc structure are examined and the embedded mechanisms are discussed in this study.
℃
℃
INTRODUCTION Phase change materials having rapid and reversible amorphous-to-crystalline phase transformation, first reported in the late 1960s by Ovshinsky [1], can be used to fabricate PhaseChange random access memory (PCRAM), which was a technology for nonvolatile memory. The Ge2Sb2Te5-O films have been studied [2] due to their advantaged application in PCRAM which have enhanced resistivity and thus can reduce the device reset current. Two methods: reactive sputtering and ion implantation were employed to obtain the oxygen doped samples. The reported studies [3-6] gave different experimental data from our observations for the physical properties change due to oxygen doping. Some literatures [3-5] reported that the crystal grain size was enlarged with increasing oxygen content, opposite to ours. Bo Liu et al.’s ion implantation work [6] supposed that the resistivity of oxygen-doped films with crystalline fcc phase was lower than that of undoped fcc crystalline films. Our results showed the opposite. In this study, reactive sputtering method was applied in order to get uniform distribution of oxygen atoms in higher (> 5 at.%) concentration. In conjunction with the bonding information obtained from XPS, effects of oxygen on the microstructures, thermal properties, and resistivity are examined and the embedded mechanisms are discussed and a mechanism describes the crystallization behavior in our samples is proposed. This study also explains why the fcc structure is stabilized up to at least 400 with suppression of the HCP phase with an oxygen concentration around 8 at.%.
℃
EXPERIMENT The oxygen-doped Ge2Sb2Te5 (d
Data Loading...
