Ferroelectric and Electrical Properties of BaZrO3 Doped Sr0.8Bi2.2Ta2O9 Thin Films
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1071-F03-09
Ferroelectric and Electrical Properties of BaZrO3 Doped Sr0.8Bi2.2Ta2O9 Thin Films Mehmet S. Bozgeyik1,2, J. S. Cross3, H. Ishiwara4, and K. Shinozaki1 1 Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1 S7 Ookayama, Meguro-ku, Tokyo, 152-8550, Japan 2 Physics Dept., Kahramanmaras Sutcu Imam Univ., Faculty of Science and Literature, Kahramanmaras, 46100, Turkey 3 Fujitsu Laboratories, Ltd., 10-1 Morinosato-wakakiya, Atsugi, Kanagawa, 243-0197, Japan 4 Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan ABSTRACT For the first time, BaZrO3 (BZO) doped Sr0.8Bi2.2Ta2O9 (SBT) thin films were prepared and related ferroelectric and electrical properties were evaluated. Sol-gel thin films of SBT doped with two different BZO mol% ratios were fabricated by spin coating technique on Pt(100nm)/Ti(50nm)/Si(100) substrates. The films were well crystallized at 750 0C in oxygen gas by RTA for 30 min. From the XRD analysis the crystalline orientation pattern showed that the dominant orientation is (115) for both doped and pure SBT. The films with 5 and 7 mol% BZO ratios showed ferroelectric hysteresis loops at a frequency of 10 kHz. The remanent polarization (2Pr) was significantly reduced to ~5.7 µC/cm2 and 1.9 µC/cm2 by 5 and 7 mol % doping, respectively. Such a low remanent polarization of 7 mol% BZO doped SBT is suitable for 1T (One Transistor) –FET (Field Effect Transistor) type FeRAMs. The dielectric constant decreased to ~135 by 7 mol% doping compare to that of 205 of SBT. Doping leads to an increase in leakage current to 10-7 A/cm2 level at electric field at 300 kV/cm. KEYWORDS: Ferroelectric Properties, Sr0.8Bi2.2Ta2O9, SBT, BaZrO3, Thin Film, FeFET INTRODUCTION Ferroelectric Field Effect Transistor (FeFET) 1T-type FeRAM is a particular application in which the stored data can be read out nondestructively and with high device packing density by scaling down. For a FeFET it is desirable to choose a ferroelectric film with a small remanent polarization as well as low dielectric constant, so that the supplied voltage is effectively applied to the ferroelectric film at saturated polarization condition. For ordinary MFIS (MetalFerroelectric-Insulator-Si) of FeFETs the charge induced by polarization of ferroelectric film is much larger than the maximum induced charge of a buffer layer at a breakdown voltage; the insulator buffer layer breaks down before the polarization of the ferroelectric film is saturated [1]. Therefore, ferroelectric gate material needs to have low enough remanent polarization to match the charge (~1 µC/cm2) required to control the channel conductivity of FET for memory operation. Also, it is a fact that the dielectric constant of typical ferroelectric material is much higher than that of buffer layers, so most of the external voltage is applied to the buffer layer. So, lowering the dielectric constant of ferroelectric material leads to increase the applied voltage in ferroelectric-g
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