Microelectromechanical Systems III: Fabrication Fundamentals

Explore MEMS fabrication categories, tracing the shift from silicon-centric IC-derived processes to function-driven, multi-material methods, including polymers, metals, ceramics, and carbon materials, with yield and integration trade-offs.

Explore silicon's dominance in MEMS due to high Young's modulus, low creep, and CMOS compatibility, plus polymers, ceramics, and carbon MEMS for flexibility, piezoelectric applications, and advanced fabrication challenges.

Explore bulk and surface micromachining in MEMS, contrasting material removal with layer-by-layer construction and sacrificial supports to yield robust bulk structures and fine planar mechanisms.

Moms, or multi-user MEMS processes, provides a standardized shared MEMS fabrication service to lower prototyping costs. Designers adapt devices to the fixed process, gaining predictability and accessibility.

Photolithography defines wafer patterns by UV-exposing photoresist through a mask; positive resists dissolve on development, while negative resists cross-link to form thick, high-aspect-ratio features.

Explore how thin-film deposition builds MEMS structures layer by layer to form structural, sacrificial, and functional layers using chemical vapor deposition, physical vapor deposition, and electroplating, highlighting conformality and vacuum.

Study thermal oxidation of silicon to silicon dioxide, providing insulation, structural, and sacrificial layers, and masks in MEMS. Use the Diel-Grof model to predict oxide growth and emphasize thickness control.

Compare diffusion and ion implantation for silicon doping: diffusion yields isotropic gradient profiles with an oxide mask, while ion implantation provides anisotropic profiles and precise dopant concentration and junction depth.

Compare wet and dry etching in MEMS fabrication, noting isotropic wet etching with undercuts and rounded channels, anisotropic wet etching, and dry plasma etching for directional, high aspect ratio sidewalls.

Explore bulk micromachining techniques, including anisotropic wet etching with KOH or TMAH and dry etching, for shaping single-crystal silicon wafers at a 54.7-degree angle.

Master the surface micromachining flow by depositing sacrificial and structural layers, patterning with masks, and releasing the sacrificial layer to create tiny gaps and suspended MEMS structures.

Explore sacrificial layers and release methods to free MEMS moving parts, using silicon dioxide or polyimide supports, with HF-based selective etching and vapor phase options to reduce stiction.

Wafer bonding techniques enable multi-layer, sealed MEMS devices with cavities and reference chambers for heterogeneous integration, using bond rings, polymeric encapsulation, and methods like anodic, fusion, and adhesive bonding.

Explore LIGA, a microfabrication technology enabling high-aspect-ratio MEMS with x-ray lithography, vertical sidewalls, and micron-level precision, serving as masters for scalable replication across metals, polymers, and ceramics.

Explore x-ray lithography and electroforming in the LIGA process, using deep x-ray exposure to create a high-fidelity photoresist mold, then electroplate to produce precise nickel structures.

Use UB-LIGA with SU-8 and UV exposure to mimic LIGA on legacy equipment, accepting lower aspect ratios and sidewall taper for affordable MEMS prototyping.

Discover when high aspect ratio mems are required and how Leica enables tall, straight walls for microgears, micromotors, microfluidic channels, and precision molds.

Packaging dominates MEMS cost, often over 50% of total device cost, because packaging must protect fragile microstructures, interact with the physical world, and provide environment-controlled access to sensing variables.

Explore wafer-level packaging, performed before dicing. Compare it with dial-level packaging after dicing, noting hermetic wafer-scale sealing, improved alignment, and lower unit costs at scale.

Compare wire bonding and flip-chip interconnections for MEMS sensors, balancing cost. Wire bonding is cheap and mature but fragile; flip-chip offers shorter paths and greater robustness for high-performance MEMS.

Explore how MEMS devices are tested with calibrated pressure chambers, shaker tables, and flow checks to detect leakage, prevent clogging, and ensure quality.

Explore how MEMS device reliability is shaped by mechanical design, stiction, wear, and environmental exposure, and how process variability, packaging stress, drift, and contamination constrain high-volume yield.

Celebrate finishing the microelectromechanical systems III: fabrication fundamentals course, and commit to ongoing learning, feedback, and obtaining a signed certificate to showcase practical engineering knowledge.