Antireflection Coating on PMMA Substrates by Atomic Layer Deposition

Abstract

Antireflection coatings (ARC) are essential for various optical components including such made of plastics for high volume applications. However, precision coatings on plastics are rather challenging due to typically low adhesion of the coating to the substrate. In this work, optimization of the atomic layer deposition (ALD) processes towards conformal optical thin films of Al2O3, TiO2 and SiO2 on poly(methyl methacrylate) (PMMA) has been carried out and a five-layer ARC is demonstrated. While the uncoated PMMA substrates have a reflectance of nearly 8% in the visible (VIS) spectral range, this is reduced below 1.2% for the spectral range of 420–670 nm by applying a double-side ARC. The total average reflectance is 0.7%. The optimized ALD coatings show a good adhesion to the PMMA substrates even after the climate test. Microscopic analysis on the cross-hatch areas on PMMA after the climate test indicates very good environmental stability of the ALD coatings. These results enable a possible route by ALD to deposit uniform, crack free, adhesive and environmentally durable thin film layers on sensitive thermoplastics like PMMA.

Is Poly(methyl methacrylate) (PMMA) a Suitable Substrate for ALD?: A Review

“…After finding the ideal conditions for ALD processes, the authors conclude that the best results were achieved when an Al 2 O 3 T-ALD layer is deposited on PMMA substrates to prevent surface cracking before the subsequent PE-ALD coatings. The plasma intensity played an important role in the film’s adhesion and refractive index towards the antireflection coating property [ 49 ]. For instance, the SiO 2 and TiO 2 films deposited using the ‘low’ plasma (100 W) conditions on pre-coated PMMA substrates with 40 nm Al 2 O 3 T-ALD show no significant delamination of the film after the cross-hatch test.…”

“…For instance, the SiO 2 and TiO 2 films deposited using the ‘low’ plasma (100 W) conditions on pre-coated PMMA substrates with 40 nm Al 2 O 3 T-ALD show no significant delamination of the film after the cross-hatch test. Figure 18 illustrates the investigated multilayered coatings on PMMA, where it is possible to discern the well-defined SiO 2 , TiO 2 , and Al 2 O 3 layers [ 49 ].…”

“…( a ) Optical microscopic images after cross-hatch tests and ( b ) after climate test of antireflection coatings double-sided coated PMMA. Focused ion beam scanning electron microscopy (FIB-SEM) cross-sectional image of multilayered antireflection coatings on PMMA ( c ) focused on a crack ( d ) focused on a crack-free region (from [ 49 ], this work by Pallabi Paul is licensed under a Creative Commons Attribution (CC BY 4.0)).…”

“…Depending on the ALD process, the deposition temperature ranges between room temperature (≈20 • C) and 400 • C. In this context, the deposition temperature should be below the T g of the PMMA to ensure that the polymer remains in the solid-state. For example, if the deposition temperature is too high, PMMA will start to decompose [40,[45][46][47][48][49][50][51]. Considering that the majority of ALD processes occur for temperatures >100 • C, the PMMA T g value plays a key factor in the selection of the ALD process.…”

SiO2 thin film growth through a pure atomic layer deposition technique at room temperature

“…40,58,59 It is possible to decrease the temperature below 50 C, and these SiO 2 lms are described as excellent candidates for thin lm encapsulation in organic devices or TFT gate insulators due to the absence of impurities and good electrical properties. [41][42][43]60 Currently, the use of amino ligands as precursors leads to promising results, even on large surfaces; however, a nal annealing step at 900-1000 C is required to decrease interface defects or carbon contamination. 44,45 Many efforts have been done, in terms of parameters and choice of precursors, in order to optimise ALD process, for the growth of SiO 2 coatings at high temperatures.…”