What Is Micromachining?

Micromachining is a set of fabrication processes used to create mechanical structures, channels, cavities, and functional devices with dimensions measured in micrometers. It draws on techniques first developed for semiconductor manufacturing, extending them beyond the formation of electronic circuits to shape three-dimensional mechanical geometries in silicon, polymers, metals, and ceramics. The discipline forms the manufacturing foundation for micro-electromechanical systems (MEMS), microfluidic chips, optical sensors, and a broad range of miniaturized devices where conventional machining cannot achieve the required dimensional precision.

The field divides broadly into two families: processes that remove material from a bulk substrate (bulk micromachining) and processes that build structures up from deposited thin films (surface micromachining). Within those families, the specific mechanism of material removal varies widely, including wet chemical etching, dry plasma etching, focused-ion-beam milling, and electrochemical dissolution. Each process trades off resolution, achievable aspect ratio, compatible materials, and throughput differently, which means that most complex micromachined devices are made using sequences of several complementary techniques.

Etching

Etching is the most widely used material removal mechanism in micromachining. Wet etching immerses the substrate in a reactive chemical solution: isotropic wet etchants attack equally in all directions, producing rounded profiles, while anisotropic etchants such as potassium hydroxide (KOH) in water preferentially remove material along specific crystallographic planes of silicon, producing flat-walled pyramidal pits and membranes. Dry etching uses ionized gas plasmas to remove material without a liquid; deep reactive-ion etching (DRIE), also called the Bosch process, alternates between etching and passivation steps to cut nearly vertical sidewalls tens to hundreds of micrometers deep. The choice between wet and dry etching determines surface roughness, undercut behavior, and whether the process is compatible with on-chip electronics. A review of etching science and its role in semiconductor micromachining appears in a 2025 PMC article on etching in microfabrication.

Electrochemical Machining

Electrochemical micromachining (EMM) removes metal by anodic dissolution: the workpiece serves as the anode in an electrolyte bath, and material is selectively dissolved by applying a controlled voltage pulse between the workpiece and a shaped tool cathode. Because material removal is purely electrochemical rather than mechanical or thermal, EMM produces very smooth surfaces without introducing residual stress, cracking, or heat-affected zones. Key process parameters include pulse voltage, pulse duration, inter-electrode gap, and electrolyte composition. EMM is particularly suited to machining hard metals such as stainless steel, titanium, and nickel alloys that are difficult to shape by DRIE. High-aspect-ratio microfeatures produced by EMM appear in fuel injector nozzles, cardiac stents, and MEMS components where silicon is not the preferred structural material, as described in the ScienceDirect overview of electrochemical micromachining for MEMS and nanotechnology.

Polymer Micromachining and Embossing

Many microfluidic devices use polymer substrates rather than silicon because polymers are inexpensive, optically transparent, and biocompatible. Hot embossing presses a heated rigid mold into a thermoplastic sheet such as polymethyl methacrylate (PMMA) or polycarbonate, transferring the mold's microfeature pattern to the polymer surface. Micro-injection molding achieves similar geometry by forcing molten polymer into a precision-machined mold under high pressure, enabling high-volume replication of channel networks and reservoirs. Soft lithography uses an elastomeric mold made from polydimethylsiloxane (PDMS) to stamp or cast microstructures; the gentle room-temperature process is widely used in life sciences laboratories. A broad survey of these fabrication routes and their suitability for microfluidic devices is provided by a 2021 PMC review of fabrication methods for microfluidic devices.

Applications

Micromachining has applications in a wide range of industries, including:

• Microfluidics and lab-on-chip platforms for biological and chemical analysis
• Pressure sensors and inertial sensors in automotive and consumer electronics
• Optical MEMS devices such as micromirrors, tunable filters, and waveguide couplers
• Medical devices including neural probes, drug delivery micropumps, and cochlear implant components
• Inkjet printer nozzle arrays produced by bulk silicon etching