The secret to DLC’s versatility lies in its structure. The term does not describe a single material but a broad family of metastable amorphous carbon coatings characterized by different ratios of sp2 and sp3 hybridized bonds, often containing hydrogen or additional dopants. Carbon atoms with sp3 hybridization form tetrahedral bonds similar to those in diamond, delivering high hardness, high elastic modulus, excellent wear resistance, and a wide electronic bandgap. In contrast, sp2 hybridization produces graphitic structures with delocalized pi electrons, leading to higher electrical conductivity at the expense of hardness. Because most DLC films contain mixtures of both bonding states, their functional properties can be tailored by controlling deposition parameters and film composition, allowing engineers to dial in hardness, friction coefficient, electrical conductivity, optical transparency, chemical inertness, and biocompatibility.

Hydrogen incorporation represents another fundamental lever. Hydrogenated DLC films generally exhibit lower residual stress, reduced friction coefficients, improved chemical stability, and smoother surfaces compared with hydrogen-free coatings, but excessive hydrogen may reduce hardness, thermal stability, and wear resistance. The article classifies DLC materials into hydrogen-free amorphous carbon, hydrogenated amorphous carbon, tetrahedral amorphous carbon, doped systems, and advanced engineered architectures such as nanocomposite, multilayer, and graded films. Silicon incorporation can improve oxidation resistance, thermal stability, and adhesion while reducing internal stress, nitrogen doping modifies electrical conductivity, fluorine reduces surface energy and enhances hydrophobicity, and metallic dopants including tungsten, titanium, chromium, and silver have been investigated to improve conductivity, tribological behavior, catalytic activity, or antibacterial performance.

Why does this matter now? The rapid evolution of microsystems is reshaping the requirements imposed on engineering materials. Wearable healthcare devices, autonomous sensors, implantable medical systems, intelligent manufacturing, space exploration, and distributed Internet of Things networks all demand materials capable of performing multiple functions beyond conventional structural support. At the microscale, where surface forces dominate over inertial forces, the low coefficient of friction exhibited by many DLC coatings plays a crucial role in minimizing stiction, reducing energy losses, and extending device lifetime in microelectromechanical systems. Equally important is the outstanding chemical stability of DLC, which provides effective protection against corrosion, oxidation, and surface degradation in biological fluids, high humidity, and extreme temperatures, ensuring stable operation over prolonged periods.

The article is careful to note that DLC should not be regarded as a universal replacement for other functional thin-film materials. Silicon carbide offers excellent thermal stability for harsh-environment MEMS, silicon nitride and alumina provide outstanding dielectric properties, titanium nitride is widely employed as a hard conductive coating, and graphene exhibits exceptional electrical conductivity and flexibility. Polymeric coatings such as parylene offer excellent conformality but lower hardness, while self-assembled monolayers provide molecular-scale functionalization but lack mechanical robustness. DLC occupies a unique position by simultaneously combining high hardness, low friction, chemical inertness, tunable electrical properties, optical transparency, and excellent biocompatibility within a single coating platform, although these advantages are often accompanied by challenges related to residual stress, adhesion, and process optimization.

On the manufacturing side, plasma-enhanced chemical vapor deposition remains the most widely adopted technique for DLC synthesis because of its relatively low processing temperature, good film uniformity, and compatibility with complex three-dimensional geometries. Physical vapor deposition methods, including magnetron sputtering and filtered cathodic vacuum arc, have also gained considerable attention, while high-power impulse magnetron sputtering offers enhanced plasma ionization and improved control over film density, adhesion, and microstructure. One of the most important challenges for future deposition technologies is achieving high-performance DLC coatings at temperatures compatible with complementary metal–oxide–semiconductor processing and flexible polymer substrates, which will be essential for integrating DLC with flexible electronics, wearable sensors, and heterogeneous microsystems without compromising existing electronic components.

Characterization is equally critical, since the properties of DLC are highly sensitive to bonding configuration, hydrogen content, residual stress, and defect density. Raman spectroscopy remains the most widely employed tool for evaluating structural organization, providing valuable information on disorder and sp2 clustering, but it alone cannot accurately quantify the sp3 fraction and should be interpreted together with other techniques. X-ray photoelectron spectroscopy enables investigation of surface chemistry and dopant incorporation, electron energy loss spectroscopy offers insights into carbon hybridization, Fourier transform infrared spectroscopy identifies hydrogen bonding configurations, and nanoindentation remains the standard technique for measuring hardness and elastic modulus. Depending on the intended application, additional methods such as scratch testing, ball-on-disk tribometry, and electrochemical impedance spectroscopy assess adhesion, tribological performance, and corrosion resistance.

The emerging applications are striking. In flexible and stretchable microsystems, careful control of deposition parameters, hydrogen content, film thickness, and doping enables DLC coatings with reduced residual stress and improved flexibility suitable for polymeric substrates, while structural engineering approaches such as island-bridge layouts, serpentine interconnects, and kirigami-inspired geometries accommodate large mechanical deformation. In BioMEMS and biomedical microdevices, properly engineered DLC surfaces can support cell adhesion while minimizing inflammatory responses, and surface functionalization enables highly selective biosensors capable of detecting biomarkers, pathogens, or metabolites. The article emphasizes that biological evaluation should rely on standardized testing protocols from the ISO 10993 series rather than isolated biocompatibility claims, since protein adsorption, hemocompatibility, and bacterial colonization depend strongly on surface chemistry, roughness, wettability, and elemental doping.

Looking further afield, DLC coatings could improve the durability and performance of microbatteries, microsupercapacitors, piezoelectric and triboelectric energy harvesters, and miniaturized power management devices. Hybrid structures combining DLC with two-dimensional materials or carbon nanostructures may lead to devices with enhanced sensing capabilities, improved charge transport, and superior mechanical performance, potentially enabling applications in photonic microsystems, quantum sensing, and high-performance environmental monitoring. Machine learning algorithms, high-throughput experimentation, and real-time process monitoring may accelerate the optimization of deposition parameters and material properties, and sustainability is likely to become an important driver, with low-temperature deposition processes and energy-efficient manufacturing routes reducing the environmental impact of thin-film fabrication.

Significant barriers remain before DLC’s full potential can be realized. Precise control of residual stress directly influences film adhesion, mechanical reliability, and long-term stability, and stress management continues to limit the deposition of thick, defect-free coatings and their integration with fragile microstructures. From an industrial perspective, reproducibility and scalability remain significant obstacles: achieving uniform coatings over large areas, ensuring consistent film properties across production batches, and establishing standardized characterization and qualification protocols are critical steps toward commercial implementation. The article outlines a phased outlook, with short-term efforts focused on deposition reproducibility and CMOS-compatible low-temperature processes, medium-term advances emphasizing multifunctional coatings and AI-assisted process optimization, and longer-term convergence with intelligent manufacturing and self-powered microsystems. The future impact of diamond-like carbon, the article concludes, will depend on the convergence of materials science, microfabrication, device engineering, and sustainable manufacturing, transforming DLC into a key enabling material for reliable, multifunctional, and highly integrated microsystems supporting advances in healthcare, environmental monitoring, smart manufacturing, and future microelectronic devices.

Subject of Research: Diamond-like carbon films as multifunctional platform materials for MEMS, flexible electronics, and biomedical microdevices

Article Title: Future directions for diamond-like carbon in microsystems and microdevices

Article References: Fraga, M. A. (2026). Future directions for diamond-like carbon in microsystems and microdevices. Frontiers in Carbon, 5, Article 1924248. https://doi.org/10.3389/frcrb.2026.1924248

Image Credits: AI Generated

DOI: 10.3389/frcrb.2026.1924248

Keywords: diamond-like carbon, DLC films, MEMS, microsystems, thin-film deposition, CMOS compatibility, biocompatibility, flexible electronics, residual stress, surface functionalization, tribology, BioMEMS