The ferroelectric and electro-optical properties of LiNbO 3 make it an important material for current and future applications. It has also been suggested as a possible lead-free replacement for present PZTdevices. The atomic layer deposition (ALD) technique offers controlled deposition of films at an industrial scale and thus becomes an interesting tool for growth of LiNbO 3. We here report on ALD deposition of LiNbO 3 using lithium silylamide and niobium ethoxide as precursors, thereby providing good control of cation stoichiometry and films with low impurity levels of silicon. The deposited films are shown to be ferroelectric and their crystalline orientations can be guided by the choice of substrate. The films are polycrystalline on Si (100) as well as epitaxially oriented on substrates of Al 2 O 3 (012), Al 2 O 3 (001), and LaAlO 3 (012). The coercive field of samples deposited on Si (100) was found to be $220 kV cm À1 , with a remanent polarization of $0.4 mC cm À2. Deposition of lithium containing materials is traditionally challenging by ALD, and critical issues with such deposition are discussed.
Atomic layer deposition (ALD) is a thin film synthesis technique that can provide exquisite accuracy and precision in film thickness and composition even on complex, large area substrates. Based on self-limiting surface chemistry, ALD can be insensitive to process conditions and reactor designs, allowing an ALD process developed in one lab to be easily reproduced in other labs. In practice, however, ALD is sometimes difficult to reproduce or replicate, and the results can vary substantially between ALD reactors and between labs. This is exemplified by large deviations in reports on the growth of, e.g., Al2O3, FeOx, and TiO2 given the same precursors under similar conditions. Furthermore, the problem of irreproducibility seems to be growing as ALD is adopted by more researchers and integrated into new applications. In this article, the authors highlight some of the major sources of variations and errors and common misconceptions related to ALD. In particular, the authors focus on issues related to precursors, substrates, and deposition tools. The authors illustrate these problems through examples from the literature, and they present results from numerical simulations that describe how nonidealities would manifest in thickness profiles in a typical cross-flow reactor. They also describe how reproducibility in ALD is linked to consistent experimental practice and reporting between labs. The authors’ hope is that by educating newcomers to ALD and advocating for consistent reporting of deposition conditions, they can minimize irreproducibility and enable ALD practitioners to realize the full potential afforded by self-limiting surface chemistry.
properties in thin film complex oxides and their heterostructures is still in its infancy.Functional perovskite oxide thin films have traditionally been deposited by physical, high temperature techniques, such as molecular beam epitaxy (MBE) and pulsed laser deposition (PLD). While these methods can provide films of very high structural quality, they do not offer deposition of conformal film on complex structures while maintaining control of stoichiometry. Chemical deposition techniques were long thought unsuitable for deposition of complex systems with high structural quality. This has changed dramatically over the last two decades. One of the most important techniques to emerge in this area has been atomic layer deposition (ALD).In this short review we aim to summarize the perovskite and ABO 3 -oxides, down to the ilmenite structure, that have been deposited using the ALD technique. The review includes work done over the last 20 years, and covers all oxide perovskites with ferromagnetic, piezoelectric and ferroelectric functionality known to have been deposited by ALD ( Table 1). The origin of the properties in these specific structures is briefly discussed, followed by a complete listing of the known systems. Perovskite heterostructures with new properties and combinations of properties are brought up, before thoughts on possible future work in the field concludes the paper. Why Atomic Layer Deposition?The ALD technique was pioneered independently in both Russia and Finland during the 1960s and 70s, and its history was thoroughly described by Puurunen in 2014. [4] The technique has been comprehensively discussed in several review papers over the last years. The first commercial application was to deposit zinc sulfide, used for electroluminescent display panels. The number of materials with known deposition routes was very limited for the first 20 years, before it exploded in the 1990s and still continues to grow. At the time of the review written by Miikkulainen et al. in 2013, binary oxides of most of the natural elements had been reported, as well as many nitrides, sulfides and fluorides (Figure 2). [5] As the community has embraced the possibility of growing epitaxial films of high chemical and structural quality, systems that are even more complex have been deposited, including materials with ternary, quaternary and even quinary compositions.The advantages and drawbacks of ALD as a thin film deposition technique have been reviewed several times the The last 20 years have seen a massive increase in reports on complex oxides with functional properties synthesized by atomic layer deposition (ALD). Many of these compounds have perovskite or perovskite-related structures, and exhibit a range of electric and magnetic properties. This short review summarizes the current status of functional perovskites and ABO 3 compounds down to the ilmenite structure prepared by ALD, focusing on ferromagnetism and ferro-and piezoelectricity. All perovskite-related compounds known to have been deposited by ALD down to the ilmeni...
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