{"id":"mosfet","level":"transistor","name":"Metal–oxide–semiconductor field-effect transistor","shortName":"MOSFET","role":"Uses a gate voltage to control current between source and drain.","description":"The MOSFET is the central controllable device of CMOS logic. An insulated gate changes the electric potential in the semiconductor channel, regulating current between source and drain. A body or substrate is also part of the device, even when a simplified circuit symbol emphasizes only three terminals. Real operation is continuous and analog: digital circuits choose voltage ranges that stand for zero and one. The atlas cross section separates gate, dielectric, channel, terminals, and body so each function can be inspected. Its dimensions are explanatory rather than a vendor cross section. Moving outward reveals how complementary devices form gates, then memory and arithmetic, through their wiring relationships.","specs":[{"label":"Electrical terminals","value":"Gate, source, drain, body","context":"Body may be implicit in simplified diagrams."},{"label":"Control variable","value":"Gate-to-source voltage","context":"Operating behavior also depends on other terminal voltages."},{"label":"Device behavior","value":"Continuous current–voltage relation","context":"Binary logic is a circuit-level abstraction."}],"interfaces":[{"name":"Gate","direction":"in","signal":"Control voltage and charging current"},{"name":"Source/drain path","direction":"out","signal":"Controlled conduction current"}],"tradeoff":"Stronger drive can reduce delay. Capacitance and leakage constrain the associated power benefit.","whyAI":"CMOS circuits combine these devices into digital machinery. No isolated transistor implements a neural-network concept by itself.","related":["gate-stack","channel","source-drain","finfet","gaa","inverter","crystal-lattice"],"sources":[{"title":"MIT 6.012 — MOSFET Cross Section and Operation","url":"https://ocw.mit.edu/courses/6-012-microelectronic-devices-and-circuits-fall-2005/5c5960f14ae37d0a65478c4f3f628d98_lec9.pdf"},{"title":"Purdue ECE 255 — MOSFET Models","url":"https://engineering.purdue.edu/wcchew/ece255s18/ece%20255%20s18%20latex%20pdf%20files/ece255Lecture_9_Feb6_MOSFETs.pdf"}],"scale":"Nanometer-scale active features; schematic cross section","kind":"mosfet","mechanism":["Apply a gate voltage relative to the other transistor terminals.","Use the gate field to change the mobile charge and potential in the channel.","Allow the resulting controlled source–drain current to charge or discharge a circuit node."],"misconception":"A MOSFET is an analog physical device; zero and one are voltage-range conventions established by the surrounding digital circuit.","check":{"question":"What primarily controls a MOSFET channel?","options":["The gate electric field","A mechanical gate that swings open","A software token stored in the silicon atom"],"answer":0,"explanation":"The insulated gate changes the channel’s electrostatics. Real current varies continuously with terminal voltages."},"branch":"Device physics","subbranch":"Field-effect electrostatics","science":[{"title":"Long-channel linear-region current","equation":"I_D ≈ μₙ C′_ox (W/L)[(V_GS − V_T)V_DS − V_DS²/2]","explanation":"Gate overdrive creates channel charge; drain bias drives it along the channel. Mobility, gate capacitance per area, and width-to-length ratio set the ideal current scale.","assumptions":"Long-channel nMOS, strong inversion, 0 ≤ V_DS < V_GS − V_T, constant mobility, gradual-channel approximation; not a predictive compact model for modern short-channel FinFETs or GAA devices."}],"history":[{"year":1960,"title":"Kahng files the insulated field-effect device patent","significance":"The patent records a controllable semiconductor device with an insulated electrode, an early foundational step toward MOS integrated circuits. The date is the filing year, not the 1963 grant year.","source":{"title":"Kahng — US3102230A","url":"https://patents.google.com/patent/US3102230A/en"}}],"learningObjective":"Connect gate voltage, channel charge and current to a switch.","engineeringExample":"In the long-channel expression, raising V_GS above V_T increases the overdrive term; velocity saturation and short-channel effects limit the extrapolation.","evidenceNotes":"The equation is a first-order regime model, not a modern node compact model.","visualFamily":"device-crosssection","prerequisites":["pn-junction","dielectric"],"labId":"switch","scope":"Vary gate and drain bias in the long-channel current model; geometry, doping and short-channel behavior are not adjustable here.","investigationId":"switching","labScope":"Vary gate and drain bias in the long-channel current model; geometry, doping and short-channel behavior are not adjustable here."}