Ferroelectric Films and Multilayers with Ultrahigh Dielectric Constants
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Ferroelectric Films and Multilayers with Ultrahigh Dielectric Constants Kewen Li, Kevin Zou, Yanyun Wang, and Hua Jiang Boston Applied Technologies, Incorporated, Woburn, MA 01801, USA Xuesheng Chen Department of Physics and Astronomy, Wheaton College, Norton, MA 02766, USA ABSTRACT This work presents a systematic study of ferroelectric films and multilayers made by a metal-organic chemical liquid deposition method. BaxSr1-xTiO3, Pb(Mg1/3Nb2/3)O3-PbTiO3, and Pb(Zn1/3Nb2/3)O3-PbTiO3 films, as well as multilayers incorporated with these materials have been grown at different conditions. Ultrahigh dielectric constant (~6700) has been achieved in the PMN/PZN-PT multilayers when the sublayer thickness approached to nanometer scale, where interfaces become dominant. When the sublayer materials with desired Curie temperatures were properly chosen, the temperature dependent dielectric constant of the multilayer structure could be greatly reduced. These nanostructured multilayers may find very important applications where temperature variation is a key concern. Pb doping in BaxSr1-xTiO3 was found very efficient in increasing the dielectric constant and reducing the loss. It is believed that the addition of Pb improved the film density and reduced the grain boundary defects. INTRODUCTION Ferroelectric films have shown great potential for microwave, electro-optic, integrated circuit, MEMS, capacitors and energy storage applications.1-3 In some applications, such as integrated capacitors and energy storage capacitors, however, two major issues related to the ferroelectric materials hampered the further advancement of the technology; i.e. the dielectric constant drops significantly (almost an order of magnitude) in a ferroelectric thin film from the value of its bulk counterpart . Another drawback of ferroelectric films is their large temperature dependency of dielectric constant, especially near the Curie temperature of the material. A solution to these two issues becomes critical and very important. Nanotechnology is the science of creating functional materials, devices and systems through control of matter and the exploitation of novel phenomena and properties on the atomic scale.4 Recent advances in nanostructure technology present the opportunity for ferroelectric films/multilayers with ultrahigh dielectric constant and flat temperature response. Using MetalOrganic Chemical Liquid Deposition (MOCLD) method,5 we deposited and studied several ferroelectric films and multilayers, including BaxSr1-xTiO3 (BST), Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT), and Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT). BST is an excellent ferroelectric material for capacitor applications since it has high dielectric constant, low loss, and adjustable Curie temperature through the choice of chemical composition.6 For example, the Curie temperature of bulk BST ranges from 30 K to 400 K for Ba concentrations ranging from x = 0 to 1, respectively. PMN-PT and PZN-PT are the materials found have the highest dielectric constant to date, in both bulk and thin film f
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