Abstract
Atomic layer deposition (ALD) is the fastest growing thin-film technology in microelectronics, but it is also recognized as a promising fabrication strategy for various alkali-metal-based thin films in emerging energy technologies, the spearhead application being the Li-ion battery. Since the pioneering work in 2009 for Li-containing thin films, the field has been rapidly growing and also widened from lithium to other alkali metals. Moreover, alkali-metal-based metal–organic thin films have been successfully grown by combining molecular layer deposition (MLD) cycles of the organic molecules with the ALD cycles of the alkali metal precursor. The current literature describes already around 100 ALD and ALD/MLD processes for alkali-metal-bearing materials. Interestingly, some of these materials cannot even be made by any other synthesis route. In this review, our intention is to present the current state of research in the field by (i) summarizing the ALD and ALD/MLD processes so far developed for the different alkali metals, (ii) highlighting the most intriguing thin-film materials obtained thereof, and (iii) addressing both the advantages and limitations of ALD and MLD in the application space of these materials. Finally, (iv) a brief outlook for the future perspectives and challenges of the field is given.
Highlights
Atomic layer deposition (ALD) is a state-of-the-art gas-phase fabrication technique for high-quality inorganic thin films, and owing to its many superior features, it has been the fastest growing thin-film technology in microelectronics already for decades.[1−7] The first developments of the ALD technique date back to the 1960s and 1970s,1,2 and the semiconductor industry adopted the technique for high-k dielectrics in the 2000s, but in recent years, it has been emerging in other application areas too, such as solar power, light-emitting diodes (LEDs), and optics
We present a comprehensive account of the current state of research in the field, comprising the entire literature on alkali-metal-based ALD processes and the new alkali-containing metal−organic materials realized through ALD/molecular layer deposition (MLD)
While alkali-metal-bearing processes do not yet form more than a niche among the research topics in the field of ALD technology, the interest in these processes is rapidly growing. This boost is driven by the role of the alkali metals in energy harvesting and storage technologies, the spearhead naturally being the lithium-ion battery technology
Summary
Atomic layer deposition (ALD) is a state-of-the-art gas-phase fabrication technique for high-quality inorganic thin films, and owing to its many superior features, it has been the fastest growing thin-film technology in microelectronics already for decades.[1−7] The first developments of the ALD technique date back to the 1960s and 1970s,1,2 and the semiconductor industry adopted the technique for high-k dielectrics in the 2000s, but in recent years, it has been emerging in other application areas too, such as solar power, light-emitting diodes (LEDs), and optics. Particular efforts are made to summarize and discuss the ALD (Sections 4 and 5) and ALD/MLD (Section 6) processes so far developed for alkali-metal-based inorganic and metal−organic thin films, respectively. After addressing these main issues, we devote a short section to the application potential of these thin-film materials (Section 7) and a brief outlook for the future perspectives and challenges in this scientifically exciting and industrially promising field (Section 8)
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