Fabrication and Characteristics of Ferroelectric/Fluorescent Oxide Structures for Ferroelectrically Controlled Emission
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Fabrication and Characteristics of Ferroelectric/Fluorescent Oxide Structures for Ferroelectrically Controlled Emission Devices Koji Aizawa, Naoya Hashimoto, Hiroyuki Inagaki, Hironori Oshiro, Hideo Horibe, and Yoshiaki Tokunaga Kanazawa Institute of Technology 7-1 Ohgigaoka, Nonoichi, Ishikawa 921-8501, Japan ABSTRACT The crystallinity, electrical, and optical properties of the ferroelectric/fluorescent oxide structures using sol-gel-derived (Ba0.6Sr0.4)TiO3 (BST) and (Sr0.8Eu0.2)Bi2.2Ta2O9 (Eu-SBT) grown on STO(110) single crystal substrates were introduced for the first time. In the present structures, the SBT films partly included a (116)-oriented Eu-SBT crystallite. The polarization vs. voltage characteristics of the BST/Eu-SBT structures showed the hysteresis loop caused by spontaneous polarization reversal, and then several emission peaks from Eu3+ ion were observed in a photoluminescence spectrum of a present BST/Eu-SBT structure. INTRODUCTION Ferroelectric materials have attracted much attention for advanced microelectronics applications such as non-volatile memories, sensors, actuators, and electro-optic devices. Additionally, electroluminescent (EL) cells connected to ferroelectric capacitors in series have been developed for a novel application to ferroelectrically controlled optical transducer over the past fifty years [1, 2]. Ferroelectrically controlled emission devices using ferroelectric/fluorescent structure The luminance (L) of EL cell is proportional to the product of frequency (f) and transferred charge density (ΔQ) as a following equation [3].
L = k × f × ΔQ Where, the coefficient k depends on the properties of active layer. When double-bipolar pulses as an operating signal is applied to an EL cell with a ferroelectric capacitor, ΔQ values are changed by the difference of charge density with (Qsw) and without (Qnsw) polarization reversal of ferroelectric capacitor. Therefore, it is expected that luminance of EL cell associated with ferroelectric capacitor is controlled and retained by spontaneous polarization of ferroelectric material. Particularly, these configurations introduced by Ref. [1, 2] are electrically equivalent to a ferroelectric/phosphor structure. Up to now, electrical and luminescent properties of ferroelectric/ fluorescent oxide structures using Sr0.8Bi2.2Ta2O9 (SBT)/Y2O3:Eu structures formed on a Pt-coated substrate were investigated by authors [4]. SBT is known as ferroelectric material in the family of bismuthlayered perovskite compounds with general formula of (Bi2O2)2+(SrTa2O7)2-, and its film has been widely used for a non-volatile memory application because of its fatigue-free property [5]. Y2O3:Eu has been used as red emitting phosphors in fluorescence lamps for a long time [6]. In the fabricated SBT/Y2O3:Eu/Pt structures, we have showed ferroelectric properties with a
remanent polarization value of approximately 1 μC/cm2 and EL spectra with an emissive peaks associated with the 5D0-7F transition of Eu3+ ions. On the other hand, we have also clarified that a high oper
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