Atomic layer deposition has become a cornerstone technology for advancing microelectromechanical and nanoelectromechanical systems due to its unique capabilities in conformal thin-film growth, precise thickness control, and low-temperature processing. The technique’s self-limiting surface reactions enable atomic-scale accuracy, making it indispensable for fabricating complex three-dimensional nanostructures and integrating functional materials into miniaturized devices.

One of the most critical aspects of ALD in MEMS/NEMS applications is the ability to engineer thin films with tailored mechanical stress. Residual stress in thin films can significantly impact device performance, leading to deformation, delamination, or reduced operational lifetime. Aluminum oxide and silicon nitride deposited via ALD demonstrate tunable stress profiles through process parameter adjustments. For instance, varying the deposition temperature between 100°C and 300°C can transition aluminum oxide films from tensile to compressive stress states. Similarly, adjusting precursor purge times and reactant exposures influences film density and stoichiometry, directly affecting mechanical properties. Stress-controlled ALD films are particularly valuable in freestanding MEMS structures such as cantilevers and membranes, where unbalanced stress can cause buckling or resonance frequency shifts.

Three-dimensional nanostructuring is another area where ALD excels. The technique’s conformality allows uniform coating of high-aspect-ratio features, including trenches, pores, and suspended architectures, which are challenging for traditional deposition methods. In inertial sensors, ALD-grown films enable the fabrication of precisely spaced capacitive gaps, improving sensitivity while maintaining mechanical robustness. Nanomechanical resonators benefit from ALD’s ability to deposit ultrathin, low-loss coatings that enhance quality factors without adding excessive mass. Furthermore, ALD facilitates the integration of multiple materials in 3D nanostructures, such as combining insulating, conductive, and piezoelectric layers for multifunctional NEMS devices.

Device integration relies on ALD’s compatibility with temperature-sensitive substrates and pre-patterned components. Unlike high-temperature processes that may degrade underlying materials, ALD can deposit high-quality films at or near room temperature, preserving the integrity of polymer-based or biological elements in hybrid systems. This capability is crucial for heterogeneous integration, where MEMS/NEMS devices must interface with CMOS electronics or flexible substrates. Encapsulation is another key application, with ALD providing pinhole-free barriers that protect sensitive components from moisture and environmental contaminants. Thin alumina or hafnia films as thin as 10 nm have been shown to effectively block water vapor permeation, extending device reliability.

Emerging trends include the use of ALD for strain engineering in 2D material-based NEMS, where sub-nanometer precision is required to modify electronic and mechanical properties without introducing defects. Additionally, ALD-enabled multi-material heterostructures are being explored for novel transduction mechanisms, such as magnetoelectric or optomechanical coupling. The technique’s scalability and reproducibility further support its adoption in industrial MEMS/NEMS manufacturing, where uniformity across large wafers is essential.

Despite its advantages, challenges remain in optimizing ALD processes for specific MEMS/NEMS applications. Precursor selection influences film properties, and some chemistries may introduce impurities or require long cycle times. Innovations in plasma-enhanced and spatial ALD aim to address these limitations, offering faster deposition rates and improved material quality. As device dimensions continue to shrink and performance demands increase, ALD will play an increasingly vital role in enabling next-generation micro- and nanosystems.

The intersection of ALD with MEMS/NEMS highlights a synergistic relationship where atomic-level control meets microscale and nanoscale engineering. From stress-optimized coatings to intricate 3D architectures and seamless integration, ALD provides the necessary tools to push the boundaries of what is achievable in miniaturized electromechanical devices. Continued advancements in process development and material innovation will further solidify its position as an enabling technology for future applications in sensing, actuation, and beyond.