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Text of the page (random words):
e i povilonis who fabricated the device m o thurston l a d asaro and j r ligenza who developed the diffusion processes and h k gummel and r lindner who characterized the device 29 30 with its high scalability 31 and much lower power consumption and higher density than bjts 32 the mosfet made it possible to build high density integrated circuits 33 the mosfet is also capable of handling higher power than the jfet 34 the mosfet was the first truly compact transistor that could be miniaturised and mass produced for a wide range of uses 7 the mosfet thus became the most common type of transistor in computers electronics 35 and communications technology such as smartphones 36 the us patent and trademark office calls it a groundbreaking invention that transformed life and culture around the world 36 in 1948 bardeen and brattain patented the progenitor of mosfet an insulated gate fet igfet with an inversion layer their patent and the concept of an inversion layer forms the basis of cmos technology today 37 cmos complementary mos a semiconductor device fabrication process for mosfets was developed by chih tang sah and frank wanlass at fairchild semiconductor in 1963 38 39 the first report of a floating gate mosfet was made by dawon kahng and simon sze in 1967 40 the concept of a double gate thin film transistor tft was proposed by h r farrah bendix corporation and r f steinberg in 1967 41 a double gate mosfet was first demonstrated in 1984 by electrotechnical laboratory researchers toshihiro sekigawa and yutaka hayashi 42 43 finfet fin field effect transistor a type of 3d non planar multi gate mosfet originated from the research of digh hisamoto and his team at hitachi central research laboratory in 1989 44 45 basic information edit see also charge carrier majority and minority carriers fets can be majority charge carrier devices in which the current is carried predominantly by majority carriers or minority charge carrier devices in which the current is mainly due to a flow of minority carriers 46 the device consists of an active channel through which charge carriers electrons or holes flow from the source to the drain source and drain terminal conductors are connected to the semiconductor through ohmic contacts the conductivity of the channel is a function of the potential applied across the gate and source terminals the fet s three terminals are 47 source s through which the carriers enter the channel conventionally current entering the channel at s is designated by i s drain d through which the carriers leave the channel conventionally current leaving the channel at d is designated by i d drain to source voltage is v ds gate g the terminal that modulates the channel conductivity by applying voltage to g one can control i d more about terminals edit cross section of an n type mosfet all fets have source drain and gate terminals that correspond roughly to the emitter collector and base of bjts most fets have a fourth terminal called the body base bulk or substrate this fourth terminal serves to bias the transistor into operation it is rare to make non trivial use of the body terminal in circuit designs but its presence is important when setting up the physical layout of an integrated circuit the size of the gate length l in the diagram is the distance between source and drain the width is the extension of the transistor in the direction perpendicular to the cross section in the diagram i e into out of the screen typically the width is much larger than the length of the gate a gate length of 1 μm limits the upper frequency to about 5 ghz 0 2 μm to about 30 ghz the names of the terminals refer to their functions the gate terminal may be thought of as controlling the opening and closing of a physical gate this gate permits electrons to flow through or blocks their passage by creating or eliminating a channel between the source and drain electron flow from the source terminal towards the drain terminal is influenced by an applied voltage the body simply refers to the bulk of the semiconductor in which the gate source and drain lie usually the body terminal is connected to the highest or lowest voltage within the circuit depending on the type of the fet the body terminal and the source terminal are sometimes connected together since the source is often connected to the highest or lowest voltage within the circuit although there are several uses of fets which do not have such a configuration such as transmission gates and cascode circuits unlike bjts the vast majority of fets are electrically symmetrical the source and drain terminals can thus be interchanged in practical circuits with no change in operating characteristics or function this can be confusing when fet s appear to be connected backwards in schematic diagrams and circuits because the physical orientation of the fet was decided for other reasons such as printed circuit layout considerations effect of gate voltage on current edit i v characteristics and output plot of a jfet n channel transistor simulation result for right side formation of inversion channel electron density and left side current gate voltage curve transfer characteristics in an n channel nanowire mosfet note that the threshold voltage for this device lies around 0 45 v fet conventional symbol types the fet controls the flow of electrons or electron holes from the source to drain by affecting the size and shape of a conductive channel created and influenced by voltage or lack of voltage applied across the gate and source terminals for simplicity this discussion assumes that the body and source are connected this conductive channel is the stream through which electrons flow from source to drain n channel fet edit in an n channel depletion mode device a negative gate to source voltage causes a depletion region to expand in width and encroach on the channel from the sides narrowing the channel if the active region expands to completely close the channel the resistance of the channel from source to drain becomes large and the fet is effectively turned off like a switch see right figure when there is very small current this is called pinch off and the voltage at which it occurs is called the pinch off voltage conversely a positive gate to source voltage increases the channel size and allows electrons to flow easily see right figure when there is a conduction channel and current is large in an n channel enhancement mode device a conductive channel does not exist naturally within the transistor and a positive gate to source voltage is necessary to create one the positive voltage attracts free floating electrons within the body towards the gate forming a conductive channel but first enough electrons must be attracted near the gate to counter the dopant ions added to the body of the fet this forms a region with no mobile carriers called a depletion region and the voltage at which this occurs is referred to as the threshold voltage of the fet further gate to source voltage increase will attract even more electrons towards the gate which are able to create an active channel from source to drain this process is called inversion p channel fet edit in a p channel depletion mode device a positive voltage from gate to body widens the depletion layer by forcing electrons to the gate insulator semiconductor interface leaving exposed a carrier free region of immobile positively charged acceptor ions conversely in a p channel enhancement mode device a conductive region does not exist and negative voltage must be used to generate a conduction channel effect of drain to source voltage on channel edit for either enhancement or depletion mode devices at drain to source voltages much less than gate to source voltages changing the gate voltage will alter the channel resistance and drain current will be proportional to drain voltage referenced to source voltage in this mode the fet operates like a variable resistor and the fet is said to be operating in a linear mode or ohmic mode 48 49 if drain to source voltage is increased this creates a significant asymmetrical change in the shape of the channel due to a gradient of voltage potential from source to drain the shape of the inversion region becomes pinched off near the drain end of the channel if drain to source voltage is increased further the pinch off point of the channel begins to move away from the drain towards the source the fet is said to be in saturation mode 50 although some authors refer to it as active mode for a better analogy with bipolar transistor operating regions 51 52 the saturation mode or the region between ohmic and saturation is used when amplification is needed the in between region is sometimes considered to be part of the ohmic or linear region even where drain current is not approximately linear with drain voltage even though the conductive channel formed by gate to source voltage no longer connects source to drain during saturation mode carriers are not blocked from flowing considering again an n channel enhancement mode device a depletion region exists in the p type body surrounding the conductive channel and drain and source regions the electrons which comprise the channel are free to move out of the channel through the depletion region if attracted to the drain by drain to source voltage the depletion region is free of carriers and has a resistance similar to silicon any increase of the drain to source voltage will increase the distance from drain to the pinch off point increasing the resistance of the depletion region in proportion to the drain to source voltage applied this proportional change causes the drain to source current to remain relatively fixed independent of changes to the drain to source voltage quite unlike its ohmic behavior in the linear mode of operation thus in saturation mode the fet behaves as a constant current source rather than as a resistor and can effectively be used as a voltage amplifier in this case the gate to source voltage determines the level of constant current through the channel composition edit fets can be constructed from various semiconductors out of which silicon is by far the most common most fets are made by using conventional bulk semiconductor fabrication techniques using a single crystal semiconductor wafer as the active region or channel among the more unusual body materials are amorphous silicon polycrystalline silicon or other amorphous semiconductors in thin film transistors or organic field effect transistors ofets that are based on organic semiconductors often ofet gate insulators and electrodes are made of organic materials as well such fets are manufactured using a variety of materials such as silicon carbide sic gallium arsenide gaas gallium nitride gan and indium gallium arsenide ingaas in june 2011 ibm announced that it had successfully used graphene based fets in an integrated circuit 53 54 these transistors are capable of about 2 23 ghz cutoff frequency much higher than standard silicon fets 55 types edit depletion type fets under typical voltages jfet poly silicon mosfet double gate mosfet metal gate mosfet mesfet depletion electrons holes metal insulator top source bottom drain left gate right bulk voltages that lead to channel formation are not shown the channel of a fet is doped to produce either an n type semiconductor or a p type semiconductor the drain and source may be doped of opposite type to the channel in the case of enhancement mode fets or doped of similar type to the channel as in depletion mode fets field effect transistors are also distinguished by the method of insulation between channel and gate types of fets include the mosfet metal oxide semiconductor field effect transistor utilizes an insulator typically sio 2 between the gate and the body this is by far the most common type of fet the dgmosfet dual gate mosfet or dgmos a mosfet with two insulated gates the igbt insulated gate bipolar transistor is a device for power control it has a structure akin to a mosfet coupled with a bipolar like main conduction channel these are commonly used for the 200 3000 v drain to source voltage range of operation power mosfets are still the device of choice for drain to source voltages of 1 to 200 v the jlnt junctionless nanowire transistor is a type of field effect transistor fet which channel is one or multiple nanowires and does not present any junction the mnos metal nitride oxide semiconductor transistor utilizes a nitride oxide layer insulator between the gate and the body the isfet ion sensitive field effect transistor can be used to measure ion concentrations in a solution when the ion concentration such as h see ph electrode changes the current through the transistor will change accordingly the biofet biologically sensitive field effect transistor is a class of sensors biosensors based on isfet technology which are utilized to detect charged molecules when a charged molecule is present changes in the electrostatic field at the biofet surface result in a measurable change in current through the transistor these include enzyme modified fets enfets immunologically modified fets immunofets gene modified fets genfets dnafets cell based biofets cpfets beetle chip fets beetlefets and fets based on ion channels protein binding 56 the dnafet dna field effect transistor is a specialized fet that acts as a biosensor by using a gate made of single strand dna molecules to detect matching dna strands finfet including gaafet or gate all around fet used on high density processor chips the jfet junction field effect transistor uses a reverse biased p n junction to separate the gate from the body the static induction transistor sit is a type of jfet with a short channel the depfet is a fet formed in a fully depleted substrate and acts as a sensor amplifier and memory node at the same time it can be used as an image photon sensor the fredfet fast reverse or fast recovery epitaxial diode fet is a specialized fet designed to provide a very fast recovery turn off of the body diode making it convenient for driving inductive loads such as electric motors especially medium powered brushless dc motors the higfet heterostructure insulated gate field effect transistor is now used mainly in research 57 the modfet modulation doped field effect transistor is a high electron mobility transistor using a quantum well structure formed by graded doping of the active region the tfet tunnel field effect transistor is based on band to band tunneling 58 the tqfet topological quantum field effect transistor switches a 2d material from dissipationless topological insulator on state to conventional insulator off state using an applied electric field 59 the hemt high electron mobility transistor also called a hfet heterostructure fet can be made using bandgap engineering in a ternary semiconductor such as algaas the fully depleted wide band gap material forms the isolation between gate and body the mesfet metal s...
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