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MicroElectroMechanical Systems (MEMS)
(Released October 2001)

  by Salvatore A. Vittorio  


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Accelerometers: An instrument that measures acceleration or gravitational force capable of imparting acceleration. Accelerometers may also be used for detecting and measuring vibrations.

Actuators: Mechanisms for activating process control equipment by use of pneumatic, hydraulic, or electronic signals.

Anisotropic etching: Etching which involves different etch rates in different directions in the material.

Annealing: The process of heating and then cooling a metal, alloy, or glass, usually to remove internal stresses and to make the material less brittle. Also, cooling slowly, usually in a furnace.

Aspect ratio: A ratio of one dimension to another, such as the ratio of the span to mean chord of a wing, or the ratio of the height to the width of a doorway.

Baked: A term used to characterize films (such as paint) which have been heated to speed the evaporation of thinners (in the case of paint) and/or to promote the reaction of binder components so as to form a hard film.

Buffered: Pertaining to an acid or base solution to which a substance capable of neutralizing the acid or base has been added.

Capacitor: A device that consists of two conductors (such as parallel metal plates) insulated from each other by a dielectric. A capacitor introduces capacitance (i.e., the ratio of the charge on one of the conductors of a capacitor to the potential difference between the conductors) into a circuit, stores electrical energy, blocks the flow of direct current, and permits the flow of alternating current.

Chemical vapor deposited: Pertaining to the growth of thin solid films on a crystalline substrate as the result of thermochemical vapor-phase reactions. Chemical vapor deposition is normally abbreviated as CVD.

Closed-loop feedback: An automatic control system for an operation or process in which feedback in a closed path or group of paths acts to maintain output at a desired level.

CMOS: Complementary metal oxide semiconductor. A CMOS device is formed by the combination of a PMOS (p-type-channel metal oxide semiconductor device) with an NMOS (n-type-channel metal oxide semiconductor device. See planar devices for definitions of p- and n-type semiconductors.

Demultiplex: To separate a multiplex signal into its component parts. See multiplex.

Double-diffused devices: Devices (transistors) in which two pn junctions are formed in the semiconductor wafer by gaseous diffusion of both p-type and n-type impurities; see planar devices for definitions of p- and n-type semiconductors.

Electromechanical: Pertaining to a mechanical device, system, or process that is electrostatically or electromagnetically actuated or controlled.

Epitaxial: Pertaining to semiconductor layers having the same crystalline orientation as the substrates on which they are grown.

Etching: Removal of portions of a layer of conductive material from a usually insulating base through chemical or electrolytic means. In wet etching, the material is dissolved when immersed in a chemical solution. In dry etching, the material is sputtered or dissolved using reactive ions or a vapor phase etchant.

Inertial measurement units: In inertial navigators, platforms that maintain sensing instruments in a precise angular orientation in space. Inertial navigators, also known as inertial navigation systems, are self-contained systems that can automatically determine the position, velocity, and attitude of a moving vehicle by means of the double integration of the outputs of accelerometers that are either strapped to the vehicle or stabilized with respect to inertial space.

Inertial sensors: Accelerometers that detect a change in inertia (resistance to change in momentum) of the mass or body to which they are attached and convert that change into a useful input signal for an information-gathering system.

Integrated circuit: An interconnected array of active and passive elements integrated with a single semiconductor substrate or deposited on the substrate by a continuous series of compatible processes, and capable of performing at least one complete electronic circuit function. Also known as integrated semiconductor.

Internal stresses: Stress systems within solids that are not dependent on external forces. Also known as residual stresses.

Ion implantation: Introducing impurities into the near-surface regions of solids by directing a beam of ions at the solid.

Isotropic etching: Etching which takes place at the same rate in different directions of a material.

Junctions: Regions of transition between two different semiconducting regions in a semiconductor device (such as a pn junction), or between a metal and a semiconductor.

Micromachining: Machining (i.e., performing various cutting or grinding operations on a piece of work) for the purpose of fabricating memsmechanical parts.

Micrometer: A unit of length equal to one-millionth of a meter.

Monolithic: 1. Formed from a single crystal, such as a monolithic silicon chip. 2. Produced in or on a monolithic chip, as a monolithic circuit. A monolithic integrated circuit (MIC) is an IC having elements formed in place on or within a semiconductor substrate, with at least one element being formed within the substrate. See substrate and integrated circuit.

Multiplex: (adjective) Being or relating to a system of transmitting several messages, programs, or signals simultaneously on the same circuit or radio frequency channel. (transitive verb) To send (messages or signals) by a multiplex system. (intransitive verb) To multiplex messages or signals.

Nanosatellites: Very small lightweight [under 20 kg (44 lbs)] satellites containing memselectronic equipment, components, and payloads.

Passivation: The protection (as of a solid state device) against contamination by coating or surface treatment. Growth of an oxide layer on the surface of a semiconductor to provide electrical stability by isolating the transistor surface from electrical and chemical conditions in the environment.

Photons: Quanta (plural of quantum, i.e., very small increments or parcels of electromagnetic radiation (such as light).

Piezoelectric: Having the ability to generate a voltage when mechanical force is applied, or to produce a mechanical force when a voltage is applied, as in a piezoelectric crystal.

Piezoresistive effect: The change in the electrical resistivity of a metal or semiconductor that is produced by mechanical stress.

Piezoresistors: Resistors that undergo a change in resistivity when undergoing mechanical stress. See resistors.

Planar devices: Semiconductor devices having planar electrodes in parallel planes, made by alternate diffusion of p- and n-type impurities into a substrate. p-type semiconductors have electron hole densities exceeding the conduction electron densities. n-type semiconductors have conduction electron densities exceeding the hole densities.

Polycrystalline Si: Silicon (Si) which is composed of aggregates of individual Si crystals.

Polyimides: Polymeric compounds containing multiple imides, i.e., NH groups derived from ammonia (NH3) by replacement of two hydrogen atoms by metals or equivalents of acid groups.

Proof mass: A predetermined test mass in a measuring device or machine, such as in acceleration measurement equipment, which serves as the reference mass for the quantity to be measured.

Resistors: Devices designed to have definite amounts of electrical resistance; used in circuits to limit current flow or to provide voltage drops.

Semiconductors: Solid crystalline materials whose electrical conductivities are intermediate between that of conductors and insulators, and which are usually strongly temperature-dependent.

Sputtering: 1. The ejection of atoms or groups of atoms from the surface of the cathode (negative electrode) of a vacuum tube as the result of heavy-ion impact. 2. The use of this process to deposit a thin layer of metal on a glass, plastic, metal, or other surface in a vacuum.

Strain gauges: Instruments for measuring the strain, or response to stress, on a structure. The stress is essentially the load on the structure. The load may be dynamic (such as the impact load of a meteor crashing on the Earths surface) or static (such as the load a television set applies to the floor or stand it is constantly resting upon). In the case of the meteor crashing to the Earth, the strain may be the subsequent crater that is formed. In the case of the television set sitting upon a surface, the strain is the (invisible) pressure that the floor or stand is enduring.

Substrate: The material of which something is made and from which it derives its special qualities. In electronics, it is the physical material on which a memscircuit is fabricated; used primarily for mechanical support and insulating purposes, as with ceramic, plastic, and glass substrates; semiconductor and ferrite substrates may also provide useful electrical functions.

Tensile: Pertaining to the stress (i.e., tension) resulting from the elongation of an elastic body.

Thermal diffusion: A phenomenon in which a temperature gradient in a mixture of fluids gives rise to a flow of one constituent relative to the mixture as a whole. Also known as thermodiffusion.

Transducer: Any device or element which converts an input signal into an output signal of a different form; examples include the memsphone, phonograph pickup, loudspeaker, barometer, automobile horn, and doorbell.

Transistor: An active component of an electronic circuit consisting of a small block of semiconducting material to which at least three electrical contacts are made, usually two closely spaced rectifying (i.e., converting an alternating current (ac) to a unidirectional one) contacts and one ohmic (nonrectifying) contact; it may be used as an amplifier, detector, or switch.