Formation and characteristics of highly c -axis-oriented Bi 3.25 La 0.75 Ti 3 O 12 thin films on SiO 2 /Si(100) and Pt/T
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Highly c-axis-oriented Bi3.25La0.75Ti3O12 (BLT) films with a homogeneous in-plane orientation were successfully grown on SiO2/Si(100) and Pt/Ti/SiO2/Si(100) substrates by a sol-coating route. The substitution of lanthanum ions for bismuth ions in the layered perovskite suppressed the formation of pyrochlore phase and enhanced the c-axis-oriented growth. The c-axis-oriented BLT film fabricated on a Pt/Ti/SiO2/Si(100) substrate showed fatigue-free characteristics with a large remanent polarization of 26–28 C/cm2 and the coercive field of 50–75 kV/cm. These features significantly enhance the potential value of the BLT film for the applications to high-density ferroelectric random-access memories devices. In addition, the c-axis-oriented BLT film, with a homogeneous in-plane orientation on an amorphous surface, can be used as a suitable template material for applications to various electro-magneto-optic devices.
I. INTRODUCTION
Thin-film Bi3.25La0.75Ti3O12 (BLT), prepared by pulsed laser deposition (PLD), was recently proposed as a promising alternative to ferroelectric thin films having polarization fatigue.1 Thin-film BLT showed wellsaturated polarization-electric field (P-E) switching curves and fatigue-free behavior after being subjected to 3 × 1010 read/write cycles at a frequency of 1 MHz. However, as Kingon pointed out, such films are characterized by a mixed orientation of grains with a possibility of increased bit-to-bit variability in a capacitor for highdensity ferroelectric random-access memory (FRAM) devices.2 In addition, PLD-grown films generally exhibit highly nonuniform film profiles. These are problematic for device applications because large-scale processing in the integrated circuit industry requires a uniform and homogeneous film over a large area of Si substrate for the reproducibility of devices. The sol-coating route employed in the present study is a useful method for the fabrication of various electronic and electro-optic thin films and has definite advantages over other commonly
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Address all correspondence to this author. e-mail: [email protected] Also affiliated with Research Institute of Industrial Science and Technology (RIST), P.O. Box 135, Pohang 790-330, Republic of Korea
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J. Mater. Res., Vol. 16, No. 11, Nov 2001 Downloaded: 18 Mar 2015
used techniques. The advantages include (i) the ability to produce a uniform film over a large area, (ii) a relatively lower cost, (iii) easy control of composition and thickness, (iv) good chemical homogeneity, and (v) low processing temperature. Park and co-workers1 reported that lanthanum-modified Bi4Ti3O12 (BT) sustained the layered perovskite structure of BT phase. They proposed that lanthanum ions substituted for bismuth ions located near the Ti–O octahedron layer and thereby enhanced the stability of oxygen ions in the lattice. Accepting this proposition, one can expect that BLT also has a layered perovskite structure and thus possesses a high affinity for the c-axisoriented preferential growth by vi
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