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orking fet bardeen and brattain instead invented the point contact transistor in 1947 which was followed by shockley s bipolar junction transistor bjt in 1948 3 4 the first fet device to be successfully built was the junction field effect transistor jfet 3 a jfet was first patented by heinrich welker in 1945 5 the static induction transistor sit a type of jfet with a short channel was invented by japanese engineers jun ichi nishizawa and y watanabe in 1950 following shockley s theoretical treatment on the jfet in 1952 a working practical jfet was built by george c dacey and ian m ross in 1953 6 however the jfet still had issues affecting junction transistors in general 7 junction transistors were relatively bulky devices that were difficult to manufacture on a mass production basis which limited them to a number of specialised applications the insulated gate field effect transistor igfet was theorized as a potential alternative to junction transistors but researchers were unable to build working igfets largely due to the troublesome surface state barrier that prevented the external electric field from penetrating into the material 7 by the mid 1950s researchers had largely given up on the fet concept and instead focused on bjt technology 8 the foundations of mosfet technology were laid down by the work of william shockley john bardeen and walter brattain shockley independently envisioned the fet concept in 1945 but he was unable to build a working device the next year bardeen explained his failure in terms of surface states bardeen applied the theory of surface states on semiconductors previous work on surface states was done by shockley in 1939 and igor tamm in 1932 and realized that the external field was blocked at the surface because of extra electrons which are drawn to the semiconductor surface electrons become trapped in those localized states forming an inversion layer bardeen s hypothesis marked the birth of surface physics bardeen then decided to make use of an inversion layer instead of the very thin layer of semiconductor which shockley had envisioned in his fet designs based on his theory in 1948 bardeen patented the progenitor of mosfet an insulated gate fet igfet with an inversion layer the inversion layer confines the flow of minority carriers increasing modulation and conductivity although its electron transport depends on the gate s insulator or quality of oxide if used as an insulator deposited above the inversion layer bardeen s patent as well as the concept of an inversion layer forms the basis of cmos technology today in 1976 shockley described bardeen s surface state hypothesis as one of the most significant research ideas in the semiconductor program 9 after bardeen s surface state theory the trio tried to overcome the effect of surface states in late 1947 robert gibney and brattain suggested the use of electrolyte placed between metal and semiconductor to overcome the effects of surface states their fet device worked but amplification was poor bardeen went further and suggested to rather focus on the conductivity of the inversion layer further experiments led them to replace electrolyte with a solid oxide layer in the hope of getting better results their goal was to penetrate the oxide layer and get to the inversion layer however bardeen suggested they switch from silicon to germanium and in the process their oxide got inadvertently washed off they stumbled upon a completely different transistor the point contact transistor lillian hoddeson argues that had brattain and bardeen been working with silicon instead of germanium they would have stumbled across a successful field effect transistor 9 10 11 12 13 by the end of the first half of the 1950s following theoretical and experimental work of bardeen brattain kingston morrison and others it became more clear that there were two types of surface states fast surface states were found to be associated with the bulk and a semiconductor oxide interface slow surface states were found to be associated with the oxide layer because of adsorption of atoms molecules and ions by the oxide from the ambient the latter were found to be much more numerous and to have much longer relaxation times at the time philo farnsworth and others came up with various methods of producing atomically clean semiconductor surfaces in 1955 carl frosch and lincoln derrick accidentally covered the surface of silicon wafer with a layer of silicon dioxide 14 they showed that oxide layer prevented certain dopants into the silicon wafer while allowing for others thus discovering the passivating effect of oxidation on the semiconductor surface their further work demonstrated how to etch small openings in the oxide layer to diffuse dopants into selected areas of the silicon wafer in 1957 they published a research paper and patented their technique summarizing their work the technique they developed is known as oxide diffusion masking which would later be used in the fabrication of mosfet devices 15 at bell labs the importance of frosch s technique was immediately realized results of their work circulated around bell labs in the form of btl memos before being published in 1957 at shockley semiconductor shockley had circulated the preprint of their article in december 1956 to all his senior staff including jean hoerni 7 16 17 in 1955 ian munro ross filed a patent for a fefet or mfsfet its structure was like that of a modern inversion channel mosfet but ferroelectric material was used as a dielectric insulator instead of oxide he envisioned it as a form of memory years before the floating gate mosfet in february 1957 john wallmark filed a patent for fet in which germanium monoxide was used as a gate dielectric but he didn t pursue the idea in his other patent filed the same year he described a double gate fet in march 1957 in his laboratory notebook ernesto labate a research scientist at bell labs conceived of a device similar to the later proposed mosfet although labate s device didn t explicitly use silicon dioxide as an insulator 18 19 20 21 in 1955 carl frosch and lincoln derrick accidentally grew a layer of silicon dioxide over the silicon wafer for which they observed surface passivation effects 22 14 by 1957 frosch and derrick using masking and predeposition were able to manufacture silicon dioxide transistors and showed that silicon dioxide insulated protected silicon wafers and prevented dopants from diffusing into the wafer 22 15 j r ligenza and w g spitzer studied the mechanism of thermally grown oxides and fabricated a high quality si sio 2 stack in 1960 23 24 25 metal oxide semiconductor fet mosfet edit main article mosfet following this research mohamed atalla and dawon kahng proposed a silicon mos transistor in 1959 26 and successfully demonstrated a working mos device with their bell labs team in 1960 27 28 their team included e e labate and 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 ...
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