In the microscopic world of MEMS, a chip smaller than a fingernail can perform sensing, actuation and control functions. Behind this capability, thin-film deposition acts as a kind of “coating technique,” giving microstructures conductivity, insulation, wear resistance, corrosion resistance and other key properties.
MEMS coating deposits one or more thin-film layers on micrometer- or nanometer-scale substrates through physical or chemical methods. Compared with conventional coating, MEMS coating requires extremely high precision. Film thickness may range from several nanometers to several micrometers, uniformity errors must be tightly controlled, and the coating must conform to complex microstructures without pinholes or cracks.
Mainstream MEMS coating processes include PVD, CVD and ALD. PVD processes such as sputtering and evaporation are suitable for metal conductive films such as aluminum and copper and hard protective films such as titanium nitride. CVD generates films through chemical reactions and can deposit insulating films such as silicon dioxide and silicon nitride, covering deep holes and grooves more uniformly. ALD provides atomic-layer control and is especially useful for ultrathin, uniform high-k films in miniaturized MEMS sensors.
The function of these films defines the application boundary of MEMS devices. In consumer electronics, MEMS microphone diaphragms require ultrathin metal films to convert acoustic signals into electrical signals. In automotive electronics, MEMS pressure sensors need corrosion-resistant silicon nitride films to withstand high-temperature and high-pressure engine environments. In medical devices, implantable MEMS surfaces may require biocompatible films such as titanium oxide to avoid immune reactions.
As MEMS devices move toward smaller size, higher integration and harsher operating environments, coating technologies are also advancing. Sub-nanometer precision, green deposition processes and multifunctional composite films are supporting new applications in aerospace, deep-sea exploration and other extreme scenarios.
