Synthesis of thin films of polycrystalline ferroelectric BiNbO 4 on Si by pulsed laser ablation
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Synthesis of thin films of polycrystalline ferroelectric BiNbO4 on Si by pulsed laser ablation Soma Chattopadhyay, Pushan Ayyub, R. Pinto, and M. S. Multani Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India (Received 19 March 1997; accepted 23 June 1997)
The stibiotantalite (ABO4 ) family includes a number of ferroelectrics and antiferroelectrics with excellent potential for applications. We report the deposition of phase-pure, polycrystalline thin films of BiNbO4 on Si(100) substrates using pulsed laser ablation. The deposition conditions were optimized with respect to substrate temperature, laser parameters, and the ambient oxygen pressure. The films were characterized by x-ray diffraction, energy dispersive x-ray analysis, and Raman spectroscopy, while their microstructure was studied by atomic force microscopy and scanning electron microscopy. Dielectric hysteresis studies indicated that films with a thickness below ø250 nm are ferroelectric, while thicker ones are antiferroelectric.
In recent years ferroelectric thin films have been extensively investigated1 because of their current and potential applications in signal-processing, electro-optics, and data storage (as nonvolatile random access memories). Applications are also envisaged in devices such as thin film capacitors, microdisplacement transducers and actuators, charge storage, phase switching, IR vidicons, and solid-state displays. Thin films of antiferroelectric materials (such as PbZrO3 ) have also been studied2–5 as they too can be used in some of the above devices. The growth of ferro- or antiferro-electric films on Si is particularly attractive from the point of view of integrated devices. Laser ablation is known to produce high quality single and polycrystalline films of various metal oxides such as PbTiO3 .6,7 The ABO4 family of compounds (A Bi31 or 31 Sb , and B Nb51 , Ta51 , or Sb51 ) includes both ferroelectrics and antiferroelectrics with the stibiotantalite structure which typically consists of layers of vertexsharing, distorted BO6 octahedra parallel to the (001) plane of the orthorhombic unit cell. They are known to exhibit multiple structural and dielectric phase transitions and possess excellent ferroelectric, piezoelectric, pyroelectric, and electro-optic properties at room temperature.8 In spite of these interesting properties, we do not find any report of the successful growth of these systems in thin film form. Monocrystalline BiNbO4 is antiferroelectric at room temperature and up to 360 ±C, ferroelectric between 360 ±C and 570 ±C, and paraelectric above 570 ±C.8 BiNbO4 is orthorhombic at room temperature (a 0.498 nm, b 1.170 nm, c 0.5675 nm) and transforms irreversibly to a triclinic (b) form above 1020 ±C.9 Here we report the in situ growth of single phase polycrystalline BiNbO4 films on Si(100) by pulsed laser deposition (PLD), and a study of its dielectric properties. J. Mater. Res., Vol. 13, No. 5, May 1998
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