Registered Deposition of Nanoscale Ferroelectric Grains by Template‐Controlled Growth

Abstract

Nanostructured ferroelectric materials are of growing interest in international research because of their impact on the future development of non-volatile ferroelectric random access memory (FeRAM) [1] as well as on the potential utilization of scanning-probe-based ferroelectric mass-storage media.[2] For both memory concepts, the scaling of the ferroelectric properties needs to be understood in order to elucidate possible limitations to memory densities. Furthermore, the question arises as to how ferroelectric nanostructures can be generated with a predefined registration as a link to the process integration of devices. In addition to several theoretical and experimental approaches to calculate a size effect on phase transitions in fine ferroelectric particles, [3±5] various experimental studies have been carried out in order to investigate scaling effects of ferroelectric nanograins on different substrates.[6±10] A major drawback that the commonly used top±down approaches encounter is the difficulty in achieving ferroelectric structures with lateral sizes below 50 nm. In addition, erosive top±down approaches like focused ion beam (FIB) [6] technology or dryetching methods [8] inevitably induce severe lattice damage to the sidewalls of the fabricated capacitors. Hence, it becomes hard to distinguish between real intrinsic ferroelectric properties and the impact of processing artifacts. Alternative non-invasive approaches like nanosphere lithography [10] and electron-beam direct writing (EBDW) [7] have almost no influence on the intrinsic material properties. Still, the minimum structure sizes achieved are in the range of 160 nm for nanosphere lithography and about 100 nm for EBDW, as the gel film used in the latter method is not optimized for obtaining the smallest possible features by electron-beam exposure, in contrast with dedicated electron-beam resists. To overcome these drawbacks, our group introduced a ªbottom±upº method, growing separated PbTiO 3 and Pb(Zr x Ti 1±x )O 3 (PZT) grains on Si/SiO 2 /TiO 2 /Pt(111) substrates by a chemical solution deposition (CSD) technique. The as-deposited thin film broke up into single-crystalline islands after the crystallization process due to a very high precursor dilution, [11,12] which resulted in the microstructural instability of the thin films.[13] Within the scope of these studies, PbTiO 3 grains of sizes below 15 nm were fabricated, emerging at grain boundaries of the underlying platinum electrode. It was found that for grains smaller than approx. 20 nm, no piezoresponse could be observed by piezoresponse force microscopy (PFM) measurements at room temperature, whereas larger grains clearly showed ferroelectric behavior. [14] This vanishing of detectable piezoresponse for small grains is discussed elsewhere.[15]One major drawback still existed within these studies: the crystalline islands merely featured a low short-range ordering. In order to achieve a high registration, a prepatterned field becomes necessary. [16] In this communication, we report on the re...

Fine-structured ZnO patterns with sub-micrometer on the ceramic surface fabricated by a replication method

“…The replication method used is rather generic and we expect that a large number of different ceramics can be patterned by using this process. Journal of the Ceramic Society of Japan 118 [12] 1140-1143 2010…”

“…This may lead to severe problems such as sidewall redeposition, contamination, and structural damage. 12) Furthermore, nanoimprint lithography (NIL) using nanoscale molds, first reported by Chou, 13),14) is recognized as a promising candidate for nanolithography in the next generation. However, the disadvantage of this technique involves expensive and complex processes.…”

Morphology of water-based chemical solution deposition (CSD) lead titanate films on different substrates: Towards island formation

“…22 A combination of top-down and bottom-up can also result in well-defined organized nanostructures. Clemens et al for example used electron-beam lithography generated TiO 2 templates as seeds for the formation of PT nanostructures, 23 followed by the deposition of the ferroelectric material by chemical solution deposition, a powerful bottom-up technique. 15 During the last several years, our laboratory has gathered a considerable know-how on the synthesis of totally water-based precursor solutions for the preparation of numerous (multi)metal oxides as powders or as thin films.…”

Direct electrical characterization of embedded ferroelectric lead titanate nanoislands

“…1 Regarding technological issues, new fabrication routes were presented recently, demonstrating the production of large-area high density ferroelectric structure arrays in effective manners. [2][3][4][5][6] Appropriate characterization methods such as piezoresponse force microscopy 7 ͑PFM͒ were developed in parallel, capable of detecting piezoelectricity and domain structures with very high spatial resolution. Using PFM, ferroelectricity is detected indirectly in terms of piezoelectric hysteresis loops or piezoelectric phase switching.…”