Effects of Oxygen on the Microstructures, Crystallization, Thermal and Electrical Properties of Tellurium Doped GeSb9 Fi
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1072-G03-07
Effects of Oxygen on the Microstructures, Crystallization, Thermal and Electrical Properties of Tellurium Doped GeSb9 Films Hsiang-Wen Shih, Yu-Hsung Perng, and Lih-Hsin Chou Materials Sciecnce & Engineering, National Tsing Hua University, 101, Sec. 2, Kuang Fu Road, Hsinchu, 30013, Taiwan ABSTRACT Tellurium and oxygen co-doped GeSb9 films (denoted as GeSb9-Te/O) with fixed Te concentration for phase change random access memory (PRAM) are investigated. The crystallization temperatures increased from 169 to 201 and the crystallization activation energy decreased from 5.53 eV to 2.89 eV as the oxygen concentration increased from 0 at.% to 17.3 at.%.The structures of crystalline GeSb9-Te/O films annealed at 250 are identified as Sb rhombohedral structure with oxygen concentration less than 18 at.%, and the lattice parameter increased from 4.48 Å to 4.52 Å as the oxygen concentration increased from 0 at.% to 17.3 at.%. The grain size became smaller after oxygen doping. For films with oxygen concentration below 6 at.% and annealed at 250 , only some of Ge form germanium suboxide GeOx, others remain metallic state. In films with oxygen concentration 28.1 at.% and annealed at 250 , the GeO2 bond and Sb2O3 bond co-existed. The resistivity of amorphous phase (or crystalline phase) increases from 5.17 Ω-cm to 24.81 Ω-cm (or 1.12×10-4 Ω-cm to 1.05×10-3 Ω-cm), about 4.8 times (or about 9.4 times) as oxygen concentration increases from 0 at.% to 17.3 at.%. The film properties show beneficial in PRAM application.
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INTRODUCTION Ge2Sb2Te5 alloy has been widely used in PRAM devices. It takes approximately 50 ns for write/read and is 30-times faster than conventional flash memory, but is considerably slower than SRAM and MRAM [1]. J. Siegel et al. [2] found that Sb-rich GeSb (Ge0.07Sb0.93) film has the shortest transformation time; i.e. as low as about 400 ps, ever reported for phase change materials. For GeSb alloys, the higher Sb-content films were found to exhibit the shortest crystallization time [3]. L. van Pieterson et al. [4] further reported that as Sb concentration higher than stoichiometric concentration 85 at.%, the crystallization time will be reduced since Sb crystallized easily and a growth-dominated crystallization was observed. However, one of the biggest problems encountered is that PRAM devices require a large programming current. N. Matsuzaki et al. [5] found that oxygen-doped Ge2Sb2Te5 film can operate at lower current than that of undoped. It was reported that tellurium addition to GeSb9 films increase the resistivity of GeSb9 films and don’t affect the incubation time [6]. Therefore, in this study, we use co-doping in order to combine the influence of both tellurium and oxygen on films properties, then investigate effects of oxygen on the microstructures, bonding, electrical properties, and thermal properties of GeSb9 films with fixed Te concentration and examine its feasibility in PRAM application.
EXPERIMENT The GeSb9-Te/O films were prepared by DC reactive magnetron co-sputtering
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