Saturation Regiononce pinch-off occurs, there is no further increase in drain current saturation ID triode VDS>VGS-VT increasing VGS VDSVT and VDS VT and VDS > VGS-VT ID = 1/2kn’(W/L)(VGS-VT)2 where kn’= (electron mobility)x(gate capacitance) = mn(eox/tox) …electron velocity = mnE and VT depends on the doping concentration and gate material used (…more details later) Gate G body B source S + drain D - VD>Vs +++ +++ +++ metal oxide p n+ n+ Saturation Regionoccurs at large VDS VGS - VDS VGS - VT VT Pinch-off occurs when VG - VD is less than VT. Gate G body B source S + drain D - VDS large +++ +++ +++ metal oxide p n+ n+ Saturation Regionoccurs at large VDS The saturation region is when the MOSFET experiences pinch-off. At some point, the difference is too small to maintain the channel near the drain  pinch-off

Gate G body B source S + drain D - VDS large +++ +++ +++ metal oxide p n+ n+ Saturation Regionoccurs at large VDS As the drain voltage increases, the difference in voltage between the drain and the gate becomes smaller. Increasing VGS decreases EB EB EF ~ EC y 0 Lī S D + - +++ VGS1>Vt +++ metal oxide p n+ - n+ Triode Region A voltage-controlled resistor VDS ID increasing VGS B S D - + +++ VGS2>VGS1 +++ +++ G metal oxide p n+ n+ - VDS cut-off B 0.1 v S D + - +++ VGS3>VGS2 +++ +++ Increasing VGS puts more charge in the channel, allowing more drain current to flow +++ metal oxide p n+ - n+ Gate G body B source S drain D + - n++ oxide p n+ n+ W L Flatbands! For this choice of materials, VGS VTn+-n-n+ structure  inversionĬhannel Charge (Qch) VGS>VT Depletion region charge (QB) is due to uncovered acceptor ions Qch

Gate: metal or heavily doped poly-Si G body B source S drain D metal oxide p n+ n+ W L Structure: n-channel MOSFET(NMOS) IG=0 (bulk or substrate) ID=IS y IS xĭ G B (IB=0, should be reverse biased) S Circuit Symbol (NMOS)enhancement-type: no channel at zero gate voltage ID= IS IG= 0 G-Gate D-Drain S-Source B-Substrate or Body ISĮnergy bands (“flat band” condition not equilibrium) (equilibrium)

HFET, MESFET, JFET, DRAM, CCD (Some in Sup.MOSFET Scaling and Current Topics (Literature + Sup.Introduction toMetal-Oxide-SemiconductorField Effect Transistors(MOSFETs)Chapter 7, Anderson and Anderson

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