Microelectromechanical Systems I: Fundamentals of MEMS

Mems are tiny integrated systems that combine mechanical structures with electrical components, often on a single chip. They enable accelerometers, pressure sensors, and micromirrors, actuated electrostatically and integrated with electronics.

Contrast MEMS with integrated circuits by highlighting moving, multiphysics devices that interact with pressure and fluids, unlike rigid, isolated ICs. Design must address mechanical stress and resonance in MEMS.

Trace MEMS history from 1950s silicon bulk micromachining to 2000s rapid commercialization, highlighting surface micromachining, silicon sensors, polysilicon structures, accelerometers, and microfluidic 2D printer printheads.

Explore MEMS inertial sensors that convert motion into electrical signals via capacitive plates and a suspended mass, and see optical micromirror switches and bioMEMS using electrokinetic forces.

Explore the MEMS market context: a high-volume, cost-sensitive industry with tight micron tolerances and strict cleanroom certification, where custom designs and variability create strong entry barriers.

Explore why semiconductors matter in MEMS, focusing on silicon, fabrication techniques like lithography, etching, doping and thin film deposition, and transduction via semiconductor effects enabling capacitive sensing and CMOS integration.

Explore silicon as a semiconductor material for mems, covering its electrical roles through doping, junctions, sensing, and isolation, and its mechanical behavior, including stiffness, fatigue, and strength-to-weight at micro scales.

Discover how doping silicon with impurities creates n-type and p-type semiconductors, introducing extra electrons and vacancies that enable conductivity via donor and acceptor interactions.

Explore p-n junctions and depletion regions, where p-type and n-type materials form a barrier that builds an internal electric field, depleting free carriers and blocking current.

Explore the mOSFET, a metal oxide semiconductor field effect transistor, with source, drain, and gate, and how a gate signal controls depletion layers to switch current.

Define CMOS, PNP/NPN, and CMOS compatibility, temperature limits, contamination rules, layer stacks, and readout constraints to interface MEMS signals with CMOS amplifiers and ADCs while avoiding unintended junctions.

Explore scaling laws for mEMS devices by examining how length, area, and volume scale with a size factor, revealing how mass and surface effects dominate at small scales.

Explore how surface forces dominate at micro scales, including electrostatic attraction, van der Waals forces, and surface tension, and contrast with gravity and inertia-based body forces.

The electrostatic force scaling acts as the mems actuation workhorse, driving micromirrors, with force proportional to overlapping area and voltage squared, divided by the square of the gap.

Electromagnetic actuation relies on current and Lorentz forces from magnetic fields; magnetic force scales with the fourth power of size, complicating miniaturization. MEMS favor electric forces for actuation and control.

Explore how scaling MEMS boosts strength-to-weight ratio and stiffness, yields high resonant frequencies, and enables fast sensing of vibrations and acceleration.

Shrink diffusion and heat time constants at small mEMS scales, so heat diffuses rapidly and mass transfer is very fast, enabling steady-state models and fast sensing despite thermal noise.

Explore the mechanics of mEMS structures, from mass-spring systems and diaphragms to accelerometers and resonators, and understand how small mass and stiffness govern performance and signal coupling.

Explore how stress, strain, and elastic deformation govern microscale mEMS sensing structures, using a cantilever probe and laser in an electron beam microscope to map surfaces.

Explore silicon anisotropy and crystal orientation, detailing how crystal planes affect Young's modulus and resonant frequency, wafer orientation, and etching profiles in MEMS with multi-physics simulations.

Explore how beams, plates, and anchors serve as mems primitives, using Kirchhoff plate theory and flexural rigidity to analyze deflection, stress, and boundary effects.

Learn electrostatic actuation fundamentals for MEMS. Voltage forms a field that polarizes electrodes, creating attractive forces to move a micromirror, with force rising as gaps shrink and current remains low.

Explore parallel plate electrostatic actuation in MEMS, where fixed and movable plates with a gap yield non-linear forces that overcome mechanical restoring forces, causing pull-in instability at one-third of gap.

Explore how thermal effects influence MEMS, including Joule heating, optical absorption, environmental temperature coupling, thermal expansion and actuation, drift, and thermal stresses.

Analyze steady state and transient thermal behavior on MEMS maps, showing when to use steady state for long-term operation and transient for fast heating, with millisecond time constants.

Analyze joule heating in MEMS, where current through a resistive heating element raises temperature via I^2R, and how thermal constraints control voltage and duty cycle to avoid drift.

Celebrate finishing MEMS fundamentals and embrace how MEMS behave, with scaling laws at the heart of the subject and basic algebra clarifying Kirchhoff's law.