The size effect of the polarization of SrBi 2 Ta 2-x Nb x O 9 Capacitor
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The size effect of the polarization of SrBi2Ta2-xNbxO9 Capacitor
Keisuke Tanaka 1,2, Masamichi Azuma, Yasuhiro Shimada, Tatsuo Otsuki 2 and Carlos A. Paz de Araujo 3 1 Panasonic Semiconductor Development Company, Colorado Springs, CO USA 2 Semiconductor Company, Matsushita Electric Industrial Co., Ltd., Takatsuki, Osaka Japan 3 Symetrix Corporation, Colorado Springs, CO USA
ABSTRACT It is known that the ferroelectric characteristic drastically changes between the bulk crystal state and the thin film state, fabricated for the high density FeRAM. Therefore, the theoretical clarification of the high density FeRAM characteristic has become very important to realize the next generation FeRAM devices on time. The size dependence of the polarization of SrBi2Ta2-xNbxO9 (SBTN) ferroelectric capacitor was calculated in the two-dimensional capacitor system considered with two different mechanisms, the depolarization effect and the surface effect due to the change of the long-range interaction between the polarization in the vicinity of the surface and interface. The free energy expression of the polarization is described as a function of position of polarization using the Landau phenomenological theory. The simulations of the size effect of the polarization were performed. The simulated result shows that the polarization is stable down to capacitor size of 0.01um2 which can be applied for next generation FeRAM devices.
INTRODUCTION In recent years, the FeRAM integration technology has matured for manufacturing FeRAM commercial products using the design rule from 0.8um to 0.5um. [1] The FeRAM technology has improved towards realizing the next generation high density FeRAM using sub-micron design rules with sub-micron square ferroelectric capacitor. However, it is known that the ferroelectric characteristic drastically changes with its size between the bulk crystal state and the thin film state. There are experimental and theoretical studies about fine size region using PbTiO3 and PZT ceramic fine particles. [2-5] O9.6.1
On the other hand, it is still not clear about ferroelectric characteristics of SrBi2Ta2-xNbxO9 (SBTN) in the sub-micron square region in the capacitor shape. There is much difficulty to clear the ferroelectric characteristics in the finite size region using try and error experimental method. Therefore, the theoretical clarification of the high density FeRAM characteristic has become very important to realize the next generation FeRAM device on time. The purpose of this work is to clear the size effect of the polarization of SBTN capacitor using theoretical method.
MODEL OF FERROELECTRIC CAPACITOR The size dependence of the polarization of SBTN ferroelectric capacitor was calculated in the two-dimensional capacitor system. The two-dimensional ferroelectric capacitor was consider as a thin ferroelectric film between two metallic electrodes with the polarization normal to the electrodes in closed circuit condition. Two different mechanisms, the depolarization effect and the surface effect due to the change o
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