Low-Temperature Processing Using Triple Alkoxide Precursors for Layer-Structured Perovskite Thin Films: Preparation and
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*National Industrial Research Institute of Nagoya, 1 Hirate-cho, Kita-ku, Nagoya 462-8510, Japan, [email protected] "**FrontierCollaborative Research Center, Tokyo Institute of Technology, 4259 Nagatsuda-cho, Midori-ku, Yokohama 226-8503, Japan
ABSTRACT CaBi 2Ta2O9 and BaBi 2Ta2O 9 thin films were successfully prepared by using triple alkoxide precursors such as Ca[BiTa(OC 2H 5 )9] 2 and Ba[BiTa(OC 2H5 )9] 2, respectively. As-deposited films were amorphous and crystallized below 500'C by rapid thermal annealing in oxygen. The crystallinity improved with annealing temperature. The development of the crystal structure and surface topography of the thin films were investigated. Additionally, some electrical properties were evaluated. INTRODUCTION Ferroelectric memories with metal-ferroelectric-insulator-semiconductor field effect transistors (MFIS-FET) and metal-ferroelectric-metal-insulator-semiconductor (MFMIS) FET structures are expected to show high performance, such as high speed and high memory density [1, 2]. In the cell structures, low coercive electric field (E,), low dielectric constant (c) and low leakage current density are necessary for the ferroelectric thin film. Additionally, high dielectric constant and low leakage current density are necessary for the insulator thin film. CaBi 2Ta 2O 9 (CBT) and BaBi 2Ta 2O 9 (BBT) are layer-structured perovskite compounds that have similar crystal structures as SrBi 2Ta2O 9 (SBT), which is known as one of best candidates for ferroelecric memory applications [3]. For the development of the ferroelectric memories with MFIS and MFMIS structures using layer-structured ferroelectric thin films, it is important to investigate the low-temperature processing and clarify the fundamental characteristics of CBT and BBT thin films. In this work, the preparation of CBT and BBT thin films using triple alkoxides is presented. The structure development and some electrical properties of the thin films are reported. EXPERIMENT Preparation of Triple Alkoxide Solutions as Precursors Ca[BiTa(OC 2H5 )9] 2 and Ba[BiTa(OC 2H,) 9] 2 solutions are prepared by a similar method as a Sr[BiTa(OC 2H5 )9] 2 solution [4, 5]. The following procedure was conducted in a dry nitrogen atmosphere. Calcium, or barium, was dissolved in anhydrous ethanol by reaction at 78°C. Bismuth triethoxide (Bi(OC 2H5 ) 3, Kojundo Chemical Laboratory Co. Ltd.) was added to the 167 Mat. Res. Soc. Symp. Proc. Vol. 596 ©2000 Materials Research Society
calcium or barium alkoxide solutions in the molar ratio of 2:1 and then heated at 78 0 C for 2 h. Tantalum pentaethoxide (Ta(OC 2H5 )5, Kojundo Chemical Laboratory Co., Ltd.) in the molar ratio of 2:1 with respect to the calcium or barium alkoxide, was added to the calcium-bismuth or barium-bismuth double alkoxide solutions. Also, diethanolamine (NH(C2H4OH) 2) was added to the solutions. Then the solutions were heated at 78°C for 2 h. Next, deionized water, diluted in ethanol in the volume ratio of 1:9 (H20:C2H5OH), was added to the Ca[BiTa(OC 2H 5 ) 9] 2 or Ba[BiTa(OC 2
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