Optical and Electrical Properties of Sol-Gel Processed Gd Doped Ferroelectric PLZT Thin Films
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Optical and Electrical Properties of Sol-Gel Processed Gd Doped Ferroelectric PLZT Thin Films Reji Thomas, Shoichi Mochizuki, Toshiyuki Mihara and Tadashi Ishida AIST Kansai National Institute of Advanced Industrial Science and Technology, 1-8-31 Midorioka, Ikeda, Osaka 563 8577, Japan. ABSTRACT Gadolinium(Gd) doped ferroelectric lead lanthanum zirconate titanate ( PLGZT 6/2/65/35) thin films were prepared by sol-gel spin coating technique. Fused silica and platinized silicon were used as substrates. Two-step pre-annealing heat treatment was employed to prepare crack free films. Annealing temperature was optimized though the x-ray diffraction studies to prepare films in single perovskite phase. Effects of Pb concentration and the seeding layer on the crystallization were studied. Optical transmission spectra were recorded and from this, refractive index, extinction coefficient and thickness were calculated for amorphous films on fused silica annealed at 400°C. In addition, the resultant films showed more than 60% transmission in the visible region. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) capacitors. Ferroelectric properties of crystalline films were studied by plotting the P-E hysteresis loop. INTRODUCTION Perovskite PZT based materials depending on the chemical composition exhibit various properties; pyroelectric, piezo electric, ferroelectric, elasto-optic effect, linear and quadratic electro-optic effect and hence used in wide range of applications; piezoelectric resonators, pyroelectric detectors, electro-optic modulators, and so forth [1]. At Zr/Ti =65/35, PZT is in the ferroelectric rhombohedral phase with slim hysteresis loop and hence characterized by a low coercive field, make it suitable for low voltage application. The off-valent donor La3+ replacing Pb2+ increase the electrical resistivity and are characterized by square hysteresis loop, low coercive field, high remanent polarization, high dielectric constant, high coupling factors, high mechanical compliance and reduced aging and hence widely studied [1]. In the thin film form, PLZT are promising for optical waveguide modulators, displays, thin film capacitors and ferroelectric random access memories. The most utilized deposition methods, in terms of films with device quality characteristics, include sputter deposition, laser ablation, MOCVD and solgel [2]. Sol-gel processing is the widely used processing method for PLZT thin films because of its control over stoichiometry and microstructure [3]. Here we present preparation of Pb (La0.06 Gd0.02)(Z0.65 T0.35) O3 (PLGZT 6/2/65/35) thin film by sol-gel process and its structural, electrical and optical properties. EXPERIMETAL DETAILS Lead (II) acetate trihydrate (99% Aldrich), lanthanum acetate hydrate (99.9% Aldrich), Gadolinium (III) acetate hydrate (99.9% Aldrich), zirconium (IV) n-propoxide (Aldrich) and Titanium (IV) iso-propoxide (97% Aldrich) were used as precursors. 2-methoxyethnol (99.8%, Aldrich) was used as a solvent to facilitate the dehydration by boiling
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