Hrtem Investigation of Effect of Various Rare Earth Oxide Dopants on Epitaxial Zirconia High-K Gate Dielectrics
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HRTEM INVESTIGATION OF EFFECT OF VARIOUS RARE EARTH OXIDE DOPANTS ON EPITAXIAL ZIRCONIA HIGH-K GATE DIELECTRICS Takanori Kiguchi1, Naoki Wakiya2, Kazuo Shinozaki2 and Nobuyasu Mizutani1,2 1 Center for Advanced Materials Analysis, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8550, Japan 2 Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8552, Japan ABSTRACT The effects of several rare earth oxide on the capacitance-voltage (C-V) characteristics and the SiO2 interlayer growth of ZrO2 based gate dielectrics were examined. The width of the hysteresis window of La2O3 stabilized ZrO2 (LaSZ) gate dielectric was only 0.2V, on the other hands, that of Sc2O3 stabilized ZrO2 (ScSZ) gate dielectric was 1.4V. HRTEM analysis indicated that the growth of SiO2 interlayer of RSZ (R=Sm,Nd,La) gate dielectric was about 1nm, which was less than half of the ScSZ one. These results indicate the advantage of the ZrO2 gate dielectric doped with rare earth oxide composed of larger ionic radius cation. INTRODUCTION Yttria stabilized zirconia (YSZ) is famous material as a gate dielectric and/or a buffer layer for MIS-type Si devices such as ferroelectric gate transistor using PZT, and so on [1-4]. It is several important characteristics, as follows; 1.relatively high dielectric constant (~25, so called high-K material), 2.barrier for Pb-Si inter diffusion, 3.low leakage current, 4.transmission of epitaxy from Si substrate into ferroelectric layer (PZT), and so on. These buffer layers for Si devices are claimed to satisfy the conditions of so-caled high-K gate dielectrics. It is, however, pointed out that there are some problems for YSZ as follows; 1.Capacitance-voltage (C-V) character with hysteresis makes FeRAM action unstable. The hysteresis is said to be ascribed to mobile ions such as oxygen ions [2,5]. 2. Oxygen ions can easiry diffuse in YSZ layer due to its high oxygen conductivity at high temperature and low dielectric SiO2 layer grow at the YSZ/Si interface[3-5]. This increases the working voltage of FeRAM. These problems result in the high mobility of oxygen ions and/or oxygen vacancy. The mobility of oxygen ions decrease with increasing the size of dopant cations of rare earth oxide [6]. Then the larger cations are effective for above the problems of YSZ gate dielectrics. The purpouse of this work is to inhibit the SiO2 interface layer growth and to decrease the C-V hysteresis, by doped with the cation of different size.
EXPERIMENT Stabilized zirconia thin films were deposited on (001) p-Si substrates with SiOx (x
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