MEMS (microelectromechanical systems)

MEMS are machines so small they are built the same way computer chips are — by etching tiny gears, beams, springs, and membranes out of a silicon wafer using the same lithography and chemical-etch steps that pattern transistors. Picture a playground swing, a tuning fork, or a trampoline membrane, but shrunk until the whole thing fits on a fleck of silicon the size of a grain of pepper, with moving parts measured in micrometres (a human hair is ~70 µm thick). The point is to give a chip a body: where ordinary electronics only push electrons around, a MEMS device can physically bend, vibrate, or deflect in response to the real world — and turn that motion into an electrical signal.

The magic is that the mechanical part and the electronics can be made in the same factory and often on the same chip, so a $1 part can sense motion, pressure, or sound. The dominant trick is to release a moving structure by etching away ("sacrificing") a layer beneath it, leaving a beam or proof mass free to move over a tiny gap. That gap usually forms a capacitor, so when the structure moves the capacitance changes by femtofarads — a vanishingly small change that on-chip amplifiers turn into a clean voltage. This single idea — a movable silicon part plus a capacitive read-out — underlies the accelerometer in your phone, the pressure sensor in a car tyre, and the microphone in your earbuds.