Platinum-Accelerated Phase Transition in Bismuth-Based Layer-Structured Ferroelectric Thin Films
- PDF / 237,064 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 20 Downloads / 162 Views
U12.13.1
Platinum-Accelerated Phase Transition in Bismuth-Based Layer-Structured Ferroelectric Thin Films Kazumi Kato1,2, Kazuyuki Suzuki1, Desheng Fu1, Kaori Nishizawa1, Takeshi Miki1 1 National Institute of Advanced Industrial Science and Technology, 2266-98 Anagahora, Shimoshidami, Moriyama-ku, Nagoya 463-8560, Japan 2 Frontier Collaborative Research Center, Tokyo Institute of Technology, 4259 Nagatsuda-cho, Midori-ku, Yokohama 226-8503, Japan ABSTRACT The phase transition of non ferroelectric pyrochlore to ferroelectric perovskite in CaBi4Ti4O15 thin films depended on matching of the atomic arrangements in platinum bottom electrodes to the Ca-Bi-Ti-O thin films. CaBi4Ti4O15 thin films crystallized on (200)-oriented platinum at 650ºC showed c-axis orientation. In contrast, thin films randomly crystallized on highly crystalline (111)-oriented platinum at the same temperature contained pyrochlore phase and showed P-V hysteresis loops. The ferroelectric properties improved with the degrees of (h00) orientation. INTRODUCTION Bismuth-based layer-structured ferroelectrics (BLSFs) are attractive materials because of their high potentials for application to ferroelectric random access memories (FeRAM) [1, 2], piezoelectric resonators and sensors [3, 4]. For most of the devices, the ferroelectrics are integrated as in shape of thin or thick film with electrodes and buffer materials into silicon semiconductors. As the ferroelectric films are usually deposited upon the bottom electrodes, the crystallinity and electrical properties of the ferroelectric films are often dominated by the underlayers. (111)-oriented Pt is normally used as the bottom electrode for the BLSFs film capacitors. Various heterostructures of the Pt and buffer layers such as Pt/Ti, Pt/TiO2, Pt/ZrO2 and Pt/Ta have been applied to the capacitors so far [5, 6]. It was reported that the crystallinity and surface roughness of the Pt affected the ferroelectric properties and leak current densities of SrBi2Ta2O9 (SBT) thin films when finally annealed at 800ºC [5]. Especially for the Pt/Ti heterostructure [5, 7], the diffusion and oxidation of Ti were confirmed to give damages to the ferroelectric capacitors when annealed at such a high temperature. Necessity of the high temperature for the synthesis of BLSFs is recognized as due to existence of intermediate phases such as fluorite and pyrochlore [8]. The intermediate phases are not ferroelectric and transit to BLSFs at the high temperature as 800ºC. Since the high temperature entirely proceeds undesirable diffusion and resultantly degrades silicon semiconductors, the processing temperature for the BLSFs thin films must be lowered enough. Therefore, external assistance rather than temperature to accelerate or control phase transition
U12.13.2
should be investigated. In the present work, we investigate the consistent phase, crystallographic orientation and surface morphology of CaBi4Ti4O15 (CBTi144) thin films crystallized on the differently textured Pt bottom electrodes at relatively low temperature as 650ºC
Data Loading...
