Giant dielectric constant in Al 2 O 3 /TiO 2 multilayer films synthesized by atomic layer deposition
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.90
Giant dielectric constant in Al2O3/TiO2 multilayer films synthesized by atomic layer deposition Takuji Tsujita 1, 2, Yukihiro Morita 1, 2, Mikihiko Nishitani 2 1
Advanced Research Division, Panasonic Corporation, Kadoma, Osaka, Japan
2 Panasonic Science Research Alliance Laboratory, Graduate School of Engineering, Osaka University, Suita, Osaka, Japan
ABSTRACT
Multilayer films formed from Al2O3 and TiO2 by atomic layer deposition were systematically studied. The relationship between the electrical characteristics of the films and the type of oxidizer used for the Al2O3 layers was investigated. The results indicated that oxygen defects in TiO2 layer and a highly insulating Al2O3 layer are necessary for realizing a giant dielectric constant and a low dielectric loss. A high electrical resistance of 1.7108 Ω / diameter of 1 mm and a dielectric constant of 1140 were achieved at 100 Hz by suitable choice of oxidizer for the Al2O3 layer.
INTRODUCTION High-permittivity materials have become the subject of vigorous development in recent years with the promise of applications in memory devices and capacitors, and research on multilayer high-permittivity films has become a focus of strong interest. Films formed from Al2O3 and TiO2 have been attracting attention as high-k materials. Not only AlxTiyOz monolayer films but also Al2O3/TiO2 films have been investigated by several research institutions [1-3]. Li et al. reported a high-permittivity material composed of Al2O3 and TiO2 layers, which exhibited a giant dielectric constant of about 1000 due to Maxwell-Wagner relaxation [4]. Using the same material, Lee et al. reported a device structure that exhibited both a giant dielectric constant and low dielectric loss [5]. In the present study, we focused on Al2O3/TiO2 multilayer films and assessed the viability of device fabrication using atomic layer deposition (ALD). The electrical characteristics of the films were measured to determine the mechanism by which both giant permittivity and low dielectric loss could be obtained. It was found that the leakage current was larger when H2O was used as the oxidizer for both the Al2O3 and TiO2 layers in the same way as Li et al. reported. Therefore, unique stronger oxidizer was tried such as O3 and H2O mixture. The films were also characterized using scanning transmission electron microscopy (STEM), Energy dispersive X-ray spectrometry (EDX) and electron energy loss spectroscopy (EELS).
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EXPERIMENTAL DETAILS An ALD system (Picosun, SNALE-R) was used to fabricate the Al2O3/TiO2 multilayer films. Trimethylaluminum (TMA) and TiCl4 were selected as precursors, and H2O and O3 were used as oxidizers for the f 1mm precursor. Figure 1 shows a schematic diagram of Pt electrode Al2O3 the device st
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