The MOSFET is by far the most common transistor in digital circuits, as billions may be included in a memory chip or microprocessor. Similarly, 'oxide' in the name can also be a misnomer, as different dielectric materials are used with the aim of obtaining strong channels with smaller applied voltages. The 'metal' in the name MOSFET is sometimes a misnomer, because the gate material can be a layer of polysilicon (polycrystalline silicon). In depletion mode transistors, voltage applied at the gate reduces the conductivity. In an enhancement mode MOSFET, voltage applied to the gate terminal increases the conductivity of the device. The main advantage of a MOSFET is that it requires almost no input current to control the load current, when compared with bipolar transistors (bipolar junction transistors/BJTs). The basic principle of the field-effect transistor was first patented by Julius Edgar Lilienfeld in 1925. Operating as switches, each of these components can sustain a blocking voltage of 120 V in the off state, and can conduct a con ti nuous current of 30 A in the on state, dissipating up to about 100 W and controlling a load of over 2000 W. Type of field-effect transistor Two power MOSFETs in D2PAK surface-mount packages. vanchor>:target~.vanchor-textDMOS) Radiation-hardened-by-design (RHBD) Other types Dual-gate Depletion-mode Metal-insulator-semiconductor field-effect transistor (MISFET) NMOS logic Power MOSFET Double-diffused metal–oxide–semiconductor (.mw-parser-output.Scaling Higher subthreshold conduction Increased gate-oxide leakage Increased junction leakage Drain-induced barrier lowering and VT roll off Lower output resistance Lower transconductance Interconnect capacitance Heat production Process variations Modeling challenges.Construction Gate material Insulator Junction design.Applications MOS integrated circuits CMOS circuits Digital Analog Analog switches Single-type Dual-type (CMOS).Operation Metal–oxide–semiconductor structure MOS capacitors and band diagrams Structure and channel formation Modes of operation Cutoff, subthreshold, and weak-inversion mode Triode mode or linear region (also known as the ohmic mode) Saturation or active mode Body effect.Note that both decreasing VGS and increasing L would effect other parts of circuit performance but lets leave that alone since its not part of the question. lower VGS-Vt and higher L would give higher A. The current gain (gm) can be controlled by Ids and VGS. Therefore the voltage gain (A) can be controlled by L and VGS. So the gain of a single transistor becomes A= (2 x Ve x L)/ (VGS-Vt). we would rather use the parameter Ve which is constant in a technology (it is different for pmos and nmos in that technology), so we could use the relationship (lambda=1/(Ve x L)) and therefore rds becomes rds= (Ve x L)/ Ids. Note that lamda is dependent on the channel length and therefore we wouldnt like to use it in calculations (since it is not constant). One of the main effects of lamda is in calculating the gain of a transistor (A= gm x rds). As mentioned in the previous reply, as a result of channel length modulation the mosfets have a finite output resistance (rds= 1/ (lambda x Ids )) - as opposed to the ideal case inwhich they could operate as a perfect current source in saturation with rout = infinity.

Nmos transistor typical length