Optics and displays
Nanometer-scale thin, molecular-level tailored ALD films have numerous applications in optics, especially because with other thin film deposition methods such as PVD and CVD satisfactory uniform, conformal and defect- and pinhole-free film quality is seldom achieved. Protective films to lenses and other optical components, antireflection layers, functional nanolaminates and graded layer structures with exact refractive index control, optical filters, polarizing coatings, hot/cold mirrors and UV blocking layers are just a few examples of where ALD technique can be utilized in this field. With ALD films also the electrical properties or appearance, i.e. color, luster or reflectivity, of the coated surface can be modified and fine-tuned. Because in advanced optical applications even a couple of nanometers deviation from film uniformity or cracks, pinholes, defects or non-conformality in the film can render the whole component or device nonfunctional, ALD is the optimal if not, in some cases, the only method with which thin films that fulfill these strict quality requirements can be produced.
Generally classical optics is understood as 2D films, whereas the modern optics as 3D structures. The field of modern optics including diffractive and reflective devices is growing fast at the moment and new applications based on micro and nano optics are actively developed, where ALD's ability to produce uniform, conformal coatings also in 3D is again called for.
ALD metals can also be applied in optical applications, e.g., for focusing x-rays and in x-ray mirrors. The fabrication of lightweight and flexible x-ray mirrors is possible using ALD structures even on polymer substrates, and high reflectivity values can be reached.
Thanks to nanostructure trench filling capability, ALD opens a path for innovative nanostructured optical devices and integrated optical devices. For example, high performance optical phase retarders or wave plates, based on all dielectric immersion nanogratings, which can be key elements in many optical applications can be fabricated by the aid of ALD.
ALD can also be applied for shape engineering due to the conformal film growth onto a template. Lens arrays which are used in microdisplays, digital imaging, and telecommunication can be fabricated by ALD.
Electroluminescent displays were the first real industrial application of the ALD method, and ALD is still in use in certain display industries, especially for displays designed for extreme/harsh ambient conditions. On smaller scale, e.g. cell phone displays, ALD is an effective method for depositing protective coatings on them.