2IntroductionIntegrated circuits: many transistors on one chip.Very Large Scale Integration(VLSI): billions!Complementary Metal Oxide Semiconductor–Fast, cheap, low power transistorsToday: How to build simple CMOS chips–CMOS transistors–Building logic gates from transistors–Transistor layout and fabricationRest of the course: How to build a good CMOS chip
3Silicon LatticeTransistors are built on a silicon substrateSilicon is a Group IV (tetravalent) materialForms crystal lattice with bonds to four neighborsSiSiSiSiSiSiSiSiSiFig1.7Ain textbook.
GaNIt’s not all silicon, although that still dominates baseband apps.More than two decades after the first demonstration, gallium nitride (GaN) wide bandgap (WBG) semiconductors are revolutionizing an increasing number of applications from power electronics, RF communications, to light-emitting diode (LED) lighting, photovoltaic solar cells, integrated nanophotonics, and more. 4
GaN5What is wrong w/ the picture on the left?This is from Panasonic marketing material
GaNGaN WBG power device technology is increasing energy efficiency and transforming the electric grid from a passive one to an actively controlled physical-cyber system. Economic (>$40G/yr. electricity savings) and environmental (equivalent of 300 coal fired power plants) benefitsCritical for new device concepts and system architectures which will radically change the way we generate, distribute, and consume electricity every day. 6
7DopantsSilicon is a semiconductorPure silicon has no free carriers and conducts poorlyAdding dopants increases the conductivityGroup V: extra electron (n-type) AsGroup III: missing electron, called hole (p-type) BAsSiSiSiSiSiSiSiSiBSiSiSiSiSiSiSiSi-++-P-type
9p-n Junctionsp-type and n-type semiconductor junction = diode.Current flows only in one directionhole flow: left to right in this picturep-typen-typeanodecathodeElectron mobility=2-3X of holes+ sideof batterygoes here for forward biasFig 1.8
10nMOS TransistorFour terminals: gate, source, drain, bodyGate – oxide – body stack looks like a capacitor–Gate and body = conductors– SiO2(oxide) = good insulator–Called metal – oxide – semiconductor (MOS) capacitor–(gate is often no longer metal*)* Metal gates are returning today!
11nMOS OperationBody is often tied to ground (0 V), particularly in an integrated circuit. (Exceptions include top NMOS in 2-input NAND.)Gate voltage < threshold:–P-type body is at low voltage–Source-body and drain-body diodes are OFF–No current flows, transistor is OFFno free electronsno channel