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MOSFET Metal Oxide Semiconductor Field Effect TransistorThe most common field effect transistor in both digital and analog circuits Uses channel of n or p type semiconductor named NMOSFET and PMOSFET respectively Silicon is the main choice of semiconductor used however SiGe is used by some chip manufacturers Some other more common semiconductors such as GaAs are not useful in MOSFETs because they do not form.good gate oxides At the gate terminal is composed a of a layer of polysilicon with a thin layer of silicon dioxide which acts as aninsulator between the gate and the conducting channel When in operation a potential is applied between the source and gate generating an electric field through the oxidelayer creating an inversion channel in the conducting channel also known as a depletion region .The inversion channel is of the same type as the source and drain creating a channel in which current can passthrough In the case of n type as shown on the right the charge carriers will be holes By varying the potential between the gate and body this channel in which current flows can be altered to allowmore or less or current to flow through depending on its size BipolarFirstJunction.Transistorcreated in 1948 by BellSimilar to the MosfetReliable under severe conditions dominant in automobiles.NPN and PNPDigital logic circuits BooleanDownfalls of BJT Large base current ib is neededto turn transistor on Electrons and holes contribute to conduction which.slows down the switching speed Linear operation BJT needs to be biased around theQ point determined from a curve tracer Introduction to NEMSNano electromechanical systems NEMS are nanoscale machines computers sensors actuators devices.and systems with dimensions typically less than 100nm They represent a combination of semiconductor processing and mechanical engineering on an extremelysmall scale To understand what NEMS are one should first understand what an electromechanical device is One of the first known electromechanical systems was built in 1785 by Charles Augustine de Coulomb to.measure electrical charge Regardless of the scale of the device most electromechanical devices contain two principle components The mechanical element deflects or vibrates in response to an applied force There are two types ofresponses for the mechanical element 1 The element can simply deflect from an applied force. 2 The element vibrates naturally and a change in amplitude of oscillation occurs The transducer converts the mechanical energy to electrical energy or vice versa In some cases thetransducer just keeps the mechanical element vibrating steadily while its characteristics are monitored When the system is perturbed the signals are then measured to determine the size of the applied force Shrinking the electromechanical devices.More than 150 years after Coulombs first documented electromechanical device a young man namedWilliam McLellan pictured at bottom left won a public challenge by creating a motor that was1 64th of an inch in size He created it using tweezers and a microscope Since that time motors hundreds of times smaller than McLellan s have been created thanks tomicro electromechanical systems firmly established in the mid 80 s Devices on the scale of.micrometers in size see picture at bottom right were and still are used for many things to make ourlives more convenient including Digital projectors that contain millions of electrically driven micro mirrors Microscale motion detectors used for automobile airbag deployment Being used in all sorts of computers to create more technology in much less space .The latest challenge has now become creating nano electromechanical systems however there areproblems that must first be solved as the physics of nanoscale devices changes because of the tiny NEMS and its attributesThe process of creating NEMS involves much more than just scaling downNew physical phenomena associated with interfaces surfaces and atomic.scales must be conquered as we go even smaller into the nanoscale Some problems that people are dealing with today include Understanding of new physics at the nanoscale level Characterization of the length scale where continuum theories breakdown Communicating signals from the nano world to the macroscopic world etc .As time passes NEMS hold promise to revolutionize abilities to measuresmall displacements and forces at a molecular scale Some attributes include Fundamental frequencies in the 1 100GHz Mechanical qualitie factors in the range of 1000 to 10 000 Masses in the femtogram range. Force sensitivities at the attoNewton level Power consumption in attoWatts short response time etc Potential of NEMSNEMS is currently used for doing things for all different aspects of life including metrology andfundamental science detecting charges by mechanical methods thermal transport studies and as time.passes it has the possiblity for so much more NEMS has potential for enormous benefits in medicine and biotechnology includingSensing of individual cellsSensing of individual proteinsSensing of DNA. Design of low power switches Nanomechanical resonators for ultra sensitive detection of adsorbed mass Radio frequency devices for computing Nano tweezers Ultra high data storage and more . Mark CianchettiSilicon Nanopillars for ElectronShuttling TransistorA Background Information Mechanical resonators are able to.operate in the high frequency GHZ This device will operate at roomtemperature Vibrating arm is one thousand timesthinner than a human hair . Device is manufactured in a two step Nanolithography Dry EtchingB Device Structure The gold aligning the top of the device.serves as a mask and conductingmaterial for current transport Figure 1 Diagram of shuttling transistor It will be assumed that the current ismeasured coming out of the drain andthe bias voltage is applied at the. Mark CianchettiDevice ExcitationStimulating the device Excess charge present on the shuttle is necessary to start the device 2 Due to the interaction between the applied AC signal and the charge on the shuttle the.island will begin to resonant 3 Resonation occurs only if the AC signal frequency matches one of the mechanicaleigenmodes 4 The resonant frequencies can be varied by changing the width or length of the pillarsilicon pillar .5 The DC bias voltage does not have to applied in order to stimulate the device The DCbias serves to finely tune the current that travels through the device Figure 2 Transistor device and applied voltages Mark CianchettiIV Characteristics. The AC current that flows through thedevice is determined by the instantaneousvoltage when X t is maximum X t being maximum corresponds to theisland being right beside the drain . The instantaneous voltage at this point isFigure 3 Definition of X t defined by the frequency of the AC signal 1 If the AC signal frequency is equalto the resonating frequency Vsd isequal to 0 volts .2 If the AC frequency is greater thanthe resonating frequency Vsd is3 If the AC signal frequency is lessthan the resonating frequency Vsdis positive .Figure 4 X t versus Vsd t An applied DC voltage Image iii in Figure 4 serves toslightly increase or decrease the phase shift Mark CianchettiContinued IV Characteristics.A Current Voltage Characteristics 1 When the AC voltage applied at thesource has a frequency equal to theresonating frequency net current 0 Shown by label ii in Figure 3 .2 When the frequency of the AC signal isless than the resonating frequency netcurrent is negative Shown by label i in Figure 3 3 When the AC voltage applied at the.source has a frequency greater than theFigure 5 IV characteristics of transistors resonating frequency net current isoperating at different resonating positive Shown by label iii in Figure 3 frequencies . The electrons are able to be transported from the island to either the drain or source due to electrontunneling Co tunneling will not occur due to the large distance when X t is maximized or minimized It should be noted that the current is AC current When negative and positive current is describedabove this simply means the AC current signals are 180 degrees out of phase All Pictures and Information gathered from Silicon nanopillars for mechanical single electron transport .by Dominik Scheible and Robert Blick Advantages of using single electron transistorDue to its small size low energy consumption and very high sensitivity Single Electron Transistor has manyapplication in many areas the most exciting feature is the potential to fabricate them in large scale and use them inmodern computing as well as other complex electronic devices Single Electron Transistor due to their smaller size .could eventually lead to advances such as much tinier semiconductor chips more powerful and yet less powerhungry cell phones long lived remote sensors SET withstand radiation much better than traditional MOSFET or BJT and work purely through electronic means making it suitable for satellite electronics or other devices that are bombarded by high radiation levels SET also exhibit higher signal to noise ratios for signal processing operations unlike conventional transistors that.always allow small amount of current or electrons to leak through in off state this results in background signal InSET the tiny arm is inactive in off state and is non oscillating with absolute no contact with either electrode Thisproperty make it impossible for floe of background current impossible Sensitivity of SET is much better than the sensitivity of MOSFET making SET an ideal component to be used inextremely precise solid state electrometers a device used to measure chrge Also the gate of SET can be coupled.with some molecules which enhances its application in chemical signal transduction process for measuring chemicalproperties SET transistors are already used in MESOSCOPIC physics experiments that have required extremecharge sensitivity SET can be used as memory cells since the state of Coulomb island can be changed by existence of single electron This can make SET the best candidate for producing memory of greater capacity The read write of the memory.fabricated using SET is about 20ns and retention time of such memory can be days to weeks Properties of memoryusing SET are far more advantageous than that of a CMOS Memory made with SET SET incorporated into silicon can store a terabit of data in a square centimeter of standard silicon a data density of about 100 times greater than thememory made with conventional transistors A single electron transistor incorporated in silicon circuitry is immune to interference SET fabricated in this way.could result in ultra fast single electron processor and is compatible with standard semiconductor fabrication proces enabling manufacturers to push beyond conventional microchip technology without abandoning their multibilliondollar investment in production capacity The fact that SET have a periodic transfer function it can be used in multi valued logic and in analog to digitalconverters for example flash ADCs with fewer circuit elements .SET can solve one of the greatest problem being faced by conventional chip technology as more and more transistorsare packed together heat becomes harder to dissipate as hundreds and thousands of electron go through aconventional transistor and switching to on and off takes at least one volt In contrast a single electron transistorturned on and off by just one electron runs cool and only consume one tenth as much power Main problems with SET.Although SET promises a great future and have several unique features but still SET suffers from number of majordrawbacks It is not yet clear whether electronics based on SET will replace conventional circuits based on scaleddown versions on field effect transistors However if the pace of miniaturization continues unabated it will becrucial to implement SETs in electronic devices by next decade Some problems with SETs are listed below SETs suffer from offset charges which means that the gate voltage needed to achieve maximum current varies.randomly from device to device such fluctuations makes it impossible to built complex circuits To use SET at room temperature large quantities of monodispersed nanoparticles less than 10nm in diameter must besynthesized It is very difficult to fabricate large quantities of SETs by conventional lithography and semi conductingSET that will operates in normal environment will require features as small as one or two nanometers across which isas small as a size of a molecule today s semiconductor industry is quite far away from doing that controllably Also.SETs that operate at room temperature suffer from problems like low gain high impedance and background charges MOSFET - Metal-Oxide-Semiconductor Field-Effect Transistor The most common field effect transistor in both digital and analog circuits. Uses channel of n or p-type semiconductor, named NMOSFET and PMOSFET, respectively. Silicon is the main choice of semiconductor used, however SiGe is used by some chip manufacturers.