FATIGUE-FREE SRBI2(TAXNB1-X)(2)O-9 FERROELECTRIC THIN-FILMS

Fatigue free ferroelectric thin films of layer-structured SrBi2(TaxNb1-x)(2)O-9 (0 < x < 1) (SBTN) have been processed, for the first time, using the metallorganic decomposition (MOD) technique. The precursors for the MOD process were synthesized by using Sr(C7H15COO)(2), Bi(C7H15COO)(3), Ta(OC2H5)(5), Nb(OC2H5)(5), and (C7H15COOH) as starting materials. Films of various compositions were spin coated onto Si-SiO2-Ti-Pt and sapphire substrates. The films were pyrolyzed at different temperatures and characterized for their phase, composition, microstructure and ferroelectric properties. The deposited films were of high quality and found to exhibit excellent ferroelectric properties; typically, at an applied voltage of 5 V, SET films showed 2P(r) values greater than 20 mu C cm(-2), dielectric constant around 300 and a coercive held E(c) less than 60 kV cm(-1). The films showed a very low fatigue rate up to 10(9) cycles and a leakage current density of less than 2 x 10(-8) A cm(-2) at 167 kV cm(-1). These results compare well with earlier reports (S.B. Desu and D.P. Vijay, Mater. Sci. Eng. B, 32 (1995) 75) on the ferroelectric properties of laser ablated SBTN thin films. In addition, the P-r and E(c) values obtained on laser ablated and MOD derived SBTN thin films are similar. However, a significant difference can be noticed in the value of the measured leakage current densities; MOD derived films exhibit current densities at least an order of magnitude lower than the laser ablated films. Since the MOD technique is amenable to large scale production, the results of this study bear significant technological implication for the commercial development of fatigue free nonvolatile random access memories.