Predicting Moisture Transmission in Ultrathin Inorganic Barriers: A Finite Element Approach to Pinhole Defect Impact on Flexible Electronics

Flexible electronics are becoming increasingly popular especially for wearable health monitors, implantable devices, and foldable displays, basically in places where rigid electronics simply don’t work. These devices rely on delicate organic layers and incredibly thin films that allow them to bend and stretch without breaking. But there’s a big downside: they’re very vulnerable to moisture. When water vapor gets into these layers, it can quickly damage the material and drastically shorten the device’s life. To help protect them, ultra-thin coatings, often made from aluminum oxide (Al₂O₃), are used as barriers against moisture and oxygen. These coatings show a lot of promise for keeping moisture out, but they bring their own challenges — particularly with maintaining a flawless surface, which is tough to achieve on larger scales. One major problem is the presence of tiny pinholes that often appear in these thin coatings during production. These microscopic holes can act like open doors for water vapor, significantly reducing the effectiveness of the barrier. Even a few pinholes can make a big difference in how much moisture gets through, which can defeat the purpose of having a protective layer in the first place. So, it’s not just about minimizing pinholes; it’s about understanding how these tiny defects affect the moisture resistance of the coating under real-world conditions. Things like the size of the pinholes, how close they are to each other, and how many there are all play a role. Even with advanced coating techniques like atomic layer deposition, which is known for producing very uniform coatings at the nanoscale, getting rid of pinholes entirely is extremely difficult, especially across the larger surfaces that are needed for practical applications.

Recognizing these issues, Professor Kyungjin Kim’s team at the University of Connecticut took a closer look at how these pinhole defects impact moisture resistance in flexible electronics. In a study published in Applied Surface Science, they created a finite element (FE) framework to simulate how moisture moves through different configurations of pinholes in ultra-thin coatings. What’s unique about their approach is that it doesn’t just measure the effect of pinholes — it also provides insights into how adjustments in pinhole size, density, and clustering can minimize moisture transmission. The validity of this can be applied to films of any size of surface area. The team modeled the most broad sizes of a pinhole damage effect on diffusion behaviors that covers pinhole damages ranging from 2.2 mm down to 100nm. Their framework can guide manufacturers in designing coatings effectively by carefully managing these defect characteristics, potentially leading to flexible electronics that last longer and perform better in the real world.

The research team wanted to understand better how moisture affects the functional lifetime of flexible electronics, so they set up a series of simulations to see how water vapor moves through the pinholes in ultra-thin protective coatings. These pinholes, though small, can have a huge impact on how well the coating blocks moisture. And, in real-world applications, achieving a perfectly flawless coating over a large area is nearly impossible. By creating different sizes and densities of pinholes in their simulations, Dr. Cagan Diyaroglu et al. were able to see how moisture slipped through these tiny imperfections and determine how much each type of pinhole increased the rate of water vapor transmission (WVTR). Early in their experiments, the authors found that the size of individual pinholes made a big difference. Even tiny increases in the diameter of a pinhole led to a significant rise in WVTR. For example, pinhole damages from the diameter of 2.2 mm down to 100 nm for a fixed number of pinholes (n = 32) vary WVTR six orders of magnitude from 1 to 8 x 10^-6 g/m²/day. Larger pinholes, or even clusters of smaller ones, could weaken the coating’s ability to keep moisture out. This matched up with findings from previous thin-film studies and highlighted that just a few large or closely grouped defects can severely limit a barrier’s effectiveness. The team didn’t stop at individual pinholes — they also looked at what happened when pinholes were clustered together. By placing pinholes closer and closer, they saw an interference effect between pinholes where WVTR changes and eventually becomes same as the bare polymer substrate’s without barrier coatings. When they compared their results to real-world data from Al₂O₃ films, the findings held up, confirming that there is a critical distance between pinhole clusters that could lead to degradation rate changes in flexible electronics. This is key information for any industry aiming to make durable products that rely on these thin coatings to block moisture.

Dr. Cagan Diyaroglu et al. also took a close look at how the thickness of the polymer substrate coated by Al₂O₃ affected moisture resistance. Their simulations showed that while thicker substrates provided better protection, pinholes could still allow moisture to get through. However, for flexible electronics applications, the polymer substrate stays thin to be flexible. Therefore, the inorganic barriers like A₂O₃ are important to coat the polymer substrates. These findings suggested that simply applying the inorganic barrier film onto a substrate isn’t enough; it’s equally important to control the number and distribution of pinholes. Their research implies that the best approach might be finding the right balance between thickness and pinhole control, allowing for efficient and effective coatings.

To make their model easy to use for others, the researchers built an interactive, customized graphical user interface with ANSYS Parametric Design Language within ANSYS software. With this tool, users can adjust pinhole patterns, sizes, and spacing to explore different setups, making it a valuable resource for further studies and for manufacturers trying to improve product quality. By demonstrating how different pinhole configurations impact moisture resistance, this tool gives manufacturers a practical way to predict how long their coatings will last, ultimately helping them build better, more durable products. The new study brings a practical solution to a tough problem in the world of flexible electronics: keeping moisture out of delicate devices that need protection to stay reliable over time. Indeed, the tool allows engineers to predict exactly how different pinhole sizes and patterns affect the amount of moisture that seeps through the barrier. With flexible electronics becoming more common and demand rising, we believe the new study offers a timely approach for making these devices more durable and dependable.

In conclusion, a major benefit of Professor Kyungjin Kim and team research is that it helps manufacturers avoid the trial-and-error approach they often rely on when designing thin-film barriers. Traditionally, balancing the right thickness and pinhole management has been tricky, requiring extensive testing and adjustments. Now, with this simulation tool, engineers can experiment with different pinhole configurations in a virtual environment, gaining a clear picture of how changes in pinhole size or spacing impact the barrier’s performance. This can save companies both time and resources by letting them optimize the design before production begins, leading to better products that are more resilient to moisture damage. Another discovery from the research work of Professor Kyungjin Kim and her colleague is that, from computational experiments performed with different strategies, the WVTR equation is proposed for polymer substrates coated with ultrathin barrier films. They also provide analyses of pinhole distances to include the effect of interaction between neighboring pinholes on WVTR. This work is considered to be the most advanced and comprehensive data collection of pinhole damage distribution effect to date. This insight provides a new direction for quality control in production: instead of aiming for an impossible, defect-free coating over a large area, engineers can focus on limiting the size and clustering of pinholes to keep moisture resistance high. Understanding this allows for realistic improvements in both coating processes and inspection practices, helping manufacturers create more robust, longer-lasting protective layers. We think what’s exciting about the new model is that it isn’t limited to just aluminum oxide barriers. The framework is versatile enough to work with other types of coatings, including hybrid materials that combine organic and inorganic layers. This means the tool could be beneficial not only for flexible electronics but also for other industries needing moisture protection, like packaging, automotive electronics, and medical devices. By offering a practical, adaptable way to understand and control moisture issues, this study moves the field closer to creating high-performance materials that truly meet the demands of today’s flexible technology.