Effective Orientation Control of Pb(Zr 0.4 Ti 0.6 )O 3 Thin Films Using A New Ti/Pb(Zr 0.4 Ti 0.6 )O 3 Seeding Layer
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C7.5.1
Effective Orientation Control of Pb(Zr0.4Ti0.6)O3 Thin Films Using A New Ti/Pb(Zr0.4Ti0.6)O3 Seeding Layer B. K. Moona), *, O. Arisumib), K. Hornika), R. Bruchhausa), H. Itokawab), A. Hilligera), H. Zhuanga), U. Eggera), K. Nakazawab), S. Yamazakib), T. Ozaki b), N. Nagela), I. Kunishimab), K. Yamakawab) and G. Beitela) a), b)
Infineon-Toshiba FeRAM Development Alliance (FDA)
a)
Infineon Technologies AG, Memory Products Div., Balanstr. 73, 81609 Munich, Germany,
b)
Toshiba Corp. Semiconductor Company, Toshiba Yokohama Complex, Shinsugita-cho,
Isogo-ku, Yokohama, 235-8522, Japan, * Current address: Infineon Technologies North America Corp., 1983 Route 52, Suite 1, Hopewell Junction, NY 12533, USA (e-mail: [email protected]) ABSTRACT The effect of thin Ti/PbZr0.4Ti0.6O3 seed layers on the properties of PbZr0.4Ti0.6O3 (PZT) capacitors has been investigated. The seed layer is based on a bi-layer of thin Ti and thin PZT with a total thickness ranging from 10 to 25 nm, which was deposited on Ir/Pt or Ir/IrO2/Pt by sputtering. After crystallization of the seed layers the main 130-nm-thick PZT film was deposited and crystallized. As a result, a highly preferred (111)-orientation of the PZT was obtained on a 10-nm-thick seed layer, where the peak intensity ratios of (111)/{100} and (111)/{110} are about 100 and 20, respectively. The 10-nm-thick seed forms a pyrochlore phase with a very smooth surface, where the formation of the pyrochlore phase is attributed to Pb diffusion, resulting in a Pb deficient stoichiometry. The seed layer transformed to the perovskite phase during the main PZT crystallization. It is shown that an IrO2 layer beneath the Pt can prevent Pt layer degradation related to the volume expansion due to the oxidation of Ir during the main PZT crystallization. Capacitors with the 10-nm-thick seed layer fabricated on the Ir/Pt and Ir/IrO2/Pt substrates showed typical 2 Pr values of 44.0 µC/cm2 and 41.2 µC/cm2, respectively. The voltage found for 90%-polarization saturation is about 3.0 V, and the capacitors are fatigue-free at least up to 1010 switching cycles.
C7.5.2
INTRODUCTION There is considerable interest in ferroelectric random access memories (FeRAMs), because they combine non-volatility with a fast access time and low operation voltage [1, 2]. Among many ferroelectric materials, three oxides with perovskite structure have been extensively studied. The oxides are lead zirconate titanate (Pb(Zr,Ti)O3: PZT) [3, 4], strontium bismuth tantalate (SrBi2Ta2O9: SBT) [5, 6] and lanthanum-modified bismuth titanate (BLT) [7]. For the application to the storage capacitor of FeRAMs, all materials need further optimization with respect to the control of crystallographic orientation to result in high performance and reliable devices. The most promising material for future FeRAMs devices is PZT. PZT has a higher polarization than SBT and BLT and the thermal budget for crystallization appears to be lower than SBT. For perovskite type ferroelectric oxides, the control of the crystallographic orien
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