Thin Film Mechanics

Why Thermal Fatigue Matters

Space environments expose solar cells to some of the most severe temperature fluctuations experienced by electronic materials. During each orbit, spacecraft components repeatedly transition between intense solar irradiation and deep shadow, leading to rapid temperature swings that can exceed −100 °C to +100 °C, depending on the orbit and spacecraft design.

In Low Earth Orbit, satellites typically experience thermal cycling every ~90 minutes as they move in and out of sunlight. Other orbital regimes, such as Geostationary Orbit and deep-space missions, can impose different but equally demanding thermal stresses due to long-duration exposure to solar heating or extended periods of shadow.

These temperature variations generate thermomechanical stress in multilayer devices. Because each material layer has a different coefficient of thermal expansion, repeated cycling leads to strain accumulation. Over time this can cause:

• interfacial delamination

• crack formation along grain boundaries

• mechanical degradation of functional layers

Understanding and mitigating these failure mechanisms is critical for the reliability of thin-film technologies used in space.

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From Space to Earth Applications

While space provides a strong motivation, thermal fatigue is also highly relevant for terrestrial energy technologies. Thin-film devices used in outdoor environments experience daily and seasonal temperature fluctuations that can gradually degrade interfaces and encapsulation layers.

Our research therefore focuses on universal failure modes of thin-film interfaces under extreme thermal conditions. By identifying the mechanical limits of materials and interfaces, we aim to develop design strategies that improve device durability across a wide range of applications.

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Mechanical Testing and Experimental Platforms

To investigate these phenomena, we have established a universal thin-film mechanics testing platform that enables quantitative measurements of interfacial adhesion and fracture behavior.

Our laboratory performs a range of standardized mechanical tests, including:

• Pull-off adhesion tests

• 90° peel tests

• Lap shear tests

• Double cantilever beam (DCB) fracture tests

These methods allow us to extract key mechanical parameters such as adhesion energy, fracture toughness, and interfacial strength across different length scales.

Combined with controlled thermal cycling protocols and materials characterization, these measurements provide fundamental insights into how interfaces fail under extreme conditions—and how they can be engineered to remain stable.