What is Mosfet: Definition and 213 Discussions

The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET), also known as the metal–oxide–silicon transistor (MOS transistor, or MOS), is a type of insulated-gate field-effect transistor that is fabricated by the controlled oxidation of a semiconductor, typically silicon. The voltage of the covered gate determines the electrical conductivity of the device; this ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals.
The MOSFET was invented by Mohamed M. Atalla and Dawon Kahng at Bell Labs in 1959, and first presented in 1960. It is the basic building block of modern electronics, and the most frequently manufactured device in history, with an estimated total of 13 sextillion (1.3×1022) MOSFETs manufactured between 1960 and 2018. It is the dominant semiconductor device in digital and analog integrated circuits (ICs), and the most common power device. It is a compact transistor that has been miniaturised and mass-produced for a wide range of applications, revolutionizing the electronics industry and the world economy, and being central to the digital revolution, silicon age and information age. MOSFET scaling and miniaturization has been driving the rapid exponential growth of electronic semiconductor technology since the 1960s, and enables high-density ICs such as memory chips and microprocessors. The MOSFET is considered the "workhorse" of the electronics industry.
A key advantage of a MOSFET is that it requires almost no input current to control the load current, when compared with bipolar junction transistors (BJTs). In an enhancement mode MOSFET, voltage applied to the gate terminal can increase the conductivity from the "normally off" state. In a depletion mode MOSFET, voltage applied at the gate can reduce the conductivity from the "normally on" state. MOSFETs are also capable of high scalability, with increasing miniaturization, and can be easily scaled down to smaller dimensions. They also have faster switching speed (ideal for digital signals), much smaller size, consume significantly less power, and allow much higher density (ideal for large-scale integration), compared to BJTs. MOSFETs are also cheaper and have relatively simple processing steps, resulting in high manufacturing yield.
MOSFETs can either be manufactured as part of MOS integrated circuit chips or as discrete MOSFET devices (such as a power MOSFET), and can take the form of single-gate or multi-gate transistors. Since MOSFETs can be made with either p-type or n-type semiconductors (PMOS or NMOS logic, respectively), complementary pairs of MOSFETs can be used to make switching circuits with very low power consumption: CMOS (Complementary MOS) logic.
The name "metal–oxide–semiconductor" (MOS) typically refers to a metal gate, oxide insulation, and semiconductor (typically silicon). However, the "metal" in the name MOSFET is sometimes a misnomer, because the gate material can also be a layer of polysilicon (polycrystalline silicon). Along with oxide, different dielectric materials can also be used with the aim of obtaining strong channels with smaller applied voltages. The MOS capacitor is also part of the MOSFET structure.

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  1. Tesladude

    MOSFET not working with digital input gate signal, Help please

    Ok, so i have a picaxe microcontroller putting out a pwm signal to the gate of an irlb3034 "logic level" n-channel mosfet. The mosfet is for grounding on and off about 8v of 20 to 40 amps. When i take my circuit and jump 8v directly to the gate of my mosfet everything works perfectly...
  2. D

    Discharging a P-Channel MOSFET quickly

    I am using trying to familiarize myself with P-Channel mosfets since I don't have too much experience with them. I am trying to use the FET as a switch, being driven in the typical highside FET manner using an NPN transistor. Is there some standard way of quickly discharging the FET during turn...
  3. Y

    MOSFET or Rheostat or Potentiometer pros and cons?

    Preface: I'm a chemical engineering undergraduate student but as small-time and noob electrical engineering hobbyist. I really only have minimal experience in circuitry and the like. I want to build a series of electromagnets with a variable their strength in order to levitate an opposing...
  4. Rx7man

    How to choose transistor types

    I'm working on a few little 12VDC projects, and am wondering on the logic for choosing different types of transistors... Bipolar vs IGBT vs Mosfet... What makes one of them a clear choice in each application? I can see bipolar transistors would be ideally suited for for analog/linear...
  5. C

    MOSFET Drain Voltage Question

    Homework Statement Homework EquationsThe Attempt at a Solution We have been given this question along with some parameters. It asks for find drain votltage, my question is why isn't the drain voltage just equal to 1.8? I mean the resistor should be getting the entire 1.8V so?
  6. Cocoleia

    BJT and MOSFET complete analysis

    Homework Statement I have been given the world's longest transistor problem as an assignment :wink: Here is the circuit: I am asked to find: a) V1, V2 and V3 using DC analysis b) AC equivalent circuit c) AC tension gain: Ava=Vx/Vsig d) AC tension gain: Avb=Vo/Vx e) Total AC tension gain...
  7. A

    Engineering Why Does Vout Become Constant in a MOSFET Circuit at High Vin?

    Homework Statement I would like to plot Vout vs Vin for the following circuit: Homework Equations Square law equations for MOSFET transistors. The Attempt at a Solution I'm calling the threshold voltage Vth. My understanding of the circuit is this: 1. From 0 < Vin < Vth, the transistor...
  8. D

    Question about MOSFET Saturation region

    Ok, so I've read around and have become quite confused with, not only the terminology about whether a device is in linear or saturation or ohmic or active region, but now my whole concept of mosfets is on the brink of breaking down! This is my understanding. In the attached picture, the...
  9. Z

    2n3904/2n3906 driving mosfet gate

    I'm building a MOSFET driver like this. The signal source is 7V peak-to-peak. Vcc is 12V. The push-pull stage is 2n3904/2n3906.(datasheet http://www.kynix.com/uploadfiles/pdf8798/2N3904.pdf) I've tested the push-pull output before adding the transformer, and using a 50 ohm load, the output...
  10. B

    Finding the current in the drain of a MOSFET

    Homework Statement The equations provided require the oxide permittivity (εox)as well as the oxide thickness (tox) to determine the gate oxide capacitance per unit squared (Cox). How to solve this? Homework Equations In triode region: ID = μn * Cox * W/L * ((VGS-Vth)* VDS - VDS2/2 In...
  11. Rx7man

    Sanity check.... Current limiting MOSFET driver

    I'm looking at making a reasonably simple FET driver with current limiting / short circuit protection.. I tried to keep all the pointers in mind from my 'voltage divider with offset' thread from a month or so ago. Goals for this are to have a driver that can run off automotive power sources (I...
  12. G

    Mosfet Operation: Vgs, Vds, and Vth Explained

    Let's say I have a Mosfet with Vth=4V. According to the circumstances for it to be in linear mode Vds<Vgs-Vth, if I apply Vgs of 10volts, my Vds must be lower than 6V in order for the transistor to operate just under saturation. Is that right? And if I want to use it as a switch, I would apply...
  13. F

    Estimating the upper 3dB cutoff in a MOSFET amplifier

    Homework Statement I've found the gain, but now I need to estimate the upper cutoff frequency with the open circuit time constant method, so the upper 3dB cutoff would roughly be $$\sum_{i = 1}^{n} \frac{1}{\tau_i}$$ The attempt at a solution I'm currently trying to make sense of the given...
  14. B

    Engineering Effect of bypass capacitor on MOSFET amplifier circuit

    Homework Statement A bypass capacitor increases gain in the mid-band region. Explain how with the figure and small signal model. Assume gm=0.5mS. Homework Equations Rs = 1 k Ohm The Attempt at a Solution With the bypass capacitor, the source would be treated as grounded and the equations...
  15. Ahmad Kishki

    What is the significance of input and output load lines in microelectronics?

    Homework Statement I am not sure i know what is meant by the input load line and the output load line in parts b and c. I tried looking it up in my book (fundamentals of microelectronics by razavi) but to no avail. Any help is appreciated.
  16. Weightofananvil

    JFET, Mosfet, BJT Design Question

    Hi, In my electronics class we are learning BJT, Mosfet, JFET theory. My gripe at the moment is that when teaching this you are taught how to troubleshoot and solve for circuits already made. This means you are always solving for various voltages, currents, Gm etc etc. With no previous...
  17. K

    Quantum Effects in MOSFET

    Hello to all ! In MOSFET at strong inversion electrons confined to triangular quantum well, electrons occupy only 1 or 2 lowest subbands. and the Van Dort model gives the quantum mechanical intrinsic carrier density in inversion channel via increased energy band-gap(ΔE). NQM = NCL× Exp(-ΔE/2kt)...
  18. P

    DC biasing in MOSFET Rectifier

    Hi there, I m a beginner in Analog IC design field. Currently, I have a project which is to design a high sensitivity rectifier by using Synopsys simulator. However, I m stuck in the beginning part which is the DC biasing of MOSFET transistor. The design specification as below: Technology ...
  19. ernd59

    AC current / volatge with a mosfet in Ltspice

    Hi, my Voltage Multiplier Simulation does not work properly the first transformer is working just fine, the second one does not really seems to work, for the second transformer i tried to creat AC current with a mosfet, but i think I am doing it wrong :/, can you give me some tips how to...
  20. Salvador

    Mosfet gate charge with no voltage across D-S

    Hi , I would like to find out does a mosfet have any gate charge if there is no voltage applied across D-S or no ? my intuition tells me that there shouldn't be any gate chrge as there is no voltage on the " second plate" to attract that charge like would be the case in a capacitor, although...
  21. R

    Solving MOSFET Issues | 180 Ohm Resistor

    I am new to using MOSFET transistors as load switches. Here, I am trying to trigger the P-channel MOSFET to run a current through the 180 ohm resistor. I can not figure out what I am doing wrong. It is supposed to turn on for a small moment (at the zero-crossing moment of the AC phase), then...
  22. D

    MOSFET Current Flow: Explained

    Homework Statement Homework Equations How current flows through n channel mosfet since bassicaly by applying positive voltage to the drain and negative to the substrate we actualy make the depletion layer grow widher. I mean when there is positive voltage at the gate it attracts electrons and...
  23. D

    Electromagnet with transistor

    I'm working on a project where i need to control an electromagnet but I'm not sure how to do it. I tried using a npn but the current passing through the magnet is just to small, should I use a mosfet instead. The specifications for my project say that they will provide us with 9 volts and a...
  24. S

    I want to create an ultrasonic generator amplifier w/ MOSFET

    Firstly, I'm only a beginner at electronics and most of my knowledge comes from googling things. I have (several) ultrasonic transducers (100 watt 40 khz) i'd like to drive with my ultrasonic generator (100 watts 40 khz) but I'd like to up the amplitude of my transducers because I want the...
  25. Tesladude

    Is Increasing the Power Supply Voltage in a Mosfet Amplifier an Easy Upgrade?

    I have an old mosfet amplifier which I plan to upgrade, I have never done this before but I am very experienced in electronics and have built many amplifiers before, just not mosfet amps. I am not 100% sure how the n and p channel mosfets are biased or set up but one upgrade I want to do with...
  26. Q

    MOS Amp Mismatch: Analyzing Effects & Comparing Dominance

    This is not a homework question,so please don't yell at me.. There is a question on my textbook..Analyze in a detailed manner the effects of the mismatch in the differential amplifier MOS.Which one has a dominating effect according to you and why? I know how to analyze the effects of the...
  27. Metallican

    VRG (Vertical Replacement Gate) Mosfet

    Hello, Can someone please describe in a few words the idea behind the VRG Mosfet? Focusing on the Pros and Cons of the device. Thanks!
  28. baby_1

    MOSFET Bias Circuit and Equations

    Hello I'm starting to design my amplifier with Mesfet.I calculated my stable amplifier with scattering parameters,however I don't know how do dc bias because I don't have any dc equations for Mesfet and and I can't extract dc information from datasheet (because datasheets only define IDSS...
  29. D

    How to switch on and off capacitance on a piece of conducting material?

    I don't know if this is the right way of describing it, but I need to activate an area of capacitance on a touchscreen by applying some current to a piece of conducting material like tinfoil. I am needing to remotely turn pages on a touchscreen ereading device with a microcontroller, and this...
  30. CKaiL

    MOSFET Questions: Find VG, R2 & Vs

    Homework Statement Questions ask me to find the value of VG and R2 as well as Vs Homework Equations R = V/I Id = Kn(Vgs - Vth)^2 The Attempt at a Solution Before i find VG and R2 , I would like to find Vs first. Vs = R*I where R= 1k ohm and I = 1mA ? hence , Vs = 1V Is it correct for Vs?
  31. A

    What does negative voltage mean for MOSFET?

    Hi, I'm planning on using a mosfet with my raspberry pi to controll a circuit, using the GPIO pins which can be set to +3.3V or GND but I'm having problems with choosing the type of MOSFET I will need. I've found the data sheet for a possibility here http://www.diodes.com/datasheets/ZVP3306A.pdf...
  32. L

    What does it mean physically to apply a voltage to a MOSFET

    https://en.wikipedia.org/wiki/MOSFETLikewise, the "oxide" in the name can be a misnomer, as different dielectric materials are used with the aim of obtaining strong channels with smaller applied voltages. http://www.electronics-tutorials.ws/transistor/tran_7.html In the saturation or linear...
  33. K

    MOSFET Properties - Turning On/Off with 2n7000

    Hiya, I've been mucking around with a 2n7000 MOSFET and I can successfully turn it on and off, but to turn it off I either have to put the gate at 0v and wait a few seconds and it turns off itself or apply negative voltage to the gate and it'll stay off when I return it to 0v. Is this normal for...
  34. R

    Body effect for NMOS transistor

    I would like to know why the threshold voltage increases for an NMOS transistor when the voltage difference between the source and the body terminals is greater than 0. If, for example, the body terminal is connected to -1V and the source to 0V, holes from the p-substrate are attracted to this...
  35. 1rel

    Electromagnet control circuit

    Recently, I was trying to control the strength of an electromagnet with PWM over a MOSFET or IGBT with an Arduino/microcontroller. It worked but I burnt multiple MOSFETs/IGBTs while testing it, after certain time... so something must have gone wrong... I'd like to build a simple circuit, to...
  36. J

    Bipolar totem-pole mosfet driver

    In a lot of the literature out there, they make reference to the totem pole topology for driving Mosfets (as in an H-bridge) as shown in the figure attached. I for the life of me cannot understand how this is a good circuit. When the output from the PWM controller is high, the upper transistor...
  37. Piyush Gupta

    MOSFET input Voltage for saturation region

    I'm trying to solve for the minimum vIN such that MOSFET is in the saturation region. Here are the given parameters VS+ = 1.0 V VS- = - 1.0 V VT = 0.5 V In order to enter saturation I know that VDS > VGS - VT VGS = VIN - VS- VDS = Vs+ - Vs-, which is 2 V Which means 2V > VIN - VS- - VT 2V...
  38. D

    MOSFET Channel length modulation

    In Sedra&Smith's microelectronic circuits they have the following expression for the drain current in a MOSFET in saturation iD = 1/2µpCox(W/L)Vov2(1+VDS/VA)But I don't see how this can be correct. Wikipedia also has another expression, see...
  39. F

    General-Purpose and RF JFET and MOSFET

    Hey guys, I'm looking for some general-purpose N-channel JFET and/or MOSFET transistors (depletion-zone) to be used as audio frequency and radio frequency amplifiers (although probably not higher than 50 MHz). They likely won't be subject to voltages over 12 volts or current higher than 200...
  40. E

    MOSFET differential amplifier gain

    Hi! Here is my task: For differential amplifier on scheme calculate voltage gains Av1=vout1/(vin1-vin2) and Av2=vout2/(vin1-vin2). MOSFET's M1 and M2 have same characteristics. MOFSTE's M3 and M4 have same characteristics. All MOSFET's are in saturation. Assume that gm*rds>>1. How to use fact...
  41. E

    MOSFET amplifier input resistance

    Hi! My task is to calculate input resistance for circuit below: VDD=10V, Vtn=1V, β=1mA/V^2, VA=100V, load resistance RL=20k. Here is model for AC analysis (DC source and infinite capacitances are short circuits, current directions chosen arbitrarily): After calculationg input current iin...
  42. E

    Solving MOSFET Circuit Problem with Q1 & Q2

    Here is my circuit: Q1 is NMOS and Q2 is PMOS. Q1: VT1=0.7V, beta1=2mA/V^2 Q2: VT2=-0.9V, beta2=1.8mA/V^2. I assumed that both transistors work in saturation. In this mode it must be: Q1: VG1S1 > VT1, VG1D1 < VT1, ID1=beta1*(VG1S1-VT1)^2/2, Q2: VS2G2 > -VT2, VD2G2 < -VT2...
  43. Tesladude

    Why Is My MOSFET-Based Charger Only Outputting 3V Instead of 15V?

    Long story short, I have a circuit board with I programmed smart charger on it. The microcontroller is supposed to put out 5v to trigger an enhancement type n-channel mosfet which simply connects 15v to my battery. But only 3v is coming out of the mosfet. It is an irl510, what is going on?
  44. N

    MOSFET switching loss from datasheet parameters

    Greetings. I am not sure how to approximate a MOSFET's switching energy from datasheet parameters. I have stumbled upon a few ways, but in all cases I've found it is pretty rare to find a datasheet with all the correct parameters. Here are some ways I've found: 1) Eon and Eoff are listed...
  45. L

    How Can I Estimate the Cutoff Voltage of a MOSFET From a Graph?

    Hi, I recently conducted a lab experiment involving several mosfets of varying channel length and width and have plotted Ids against Vds for different values of Vgs (below is one of the graphs). I am now trying to find the threshold voltage of each mosfet using their graphs although I am...
  46. S

    MOSFET Design Doubt: Explaining Positive Voltage

    Can someone explain this sentence in MOSFET design.. The Since the drain will be at a positive voltage relative to the source the two pn junctions can be effectively cut off simply connecting the substrate terminal to source terminal.
  47. V

    Common Source MOSFET Amp problem

    Homework Statement A CS amplifier utilizes a MOSFET with μnCox = 400 μA/V2, W/L = 10, and VA=10v. It is biased at ID=0.2mA and uses RD=6k. Find Rin,AVO,RO Homework Equations VAO= -gm(RD||ro) Ro=RD||r0 The Attempt at a Solution I drew out the equivalent circuit with...
  48. V

    Solve MOSFET Confusion: Establish 0.8mA & 1.5V with Parameters VT, μpCox, L, λ

    Homework Statement The diagram: http://images.fr1ckfr4ck.fastmail.fm/probC.jpg This MOSFET has the following parameters: |VT| = 0.6V μpCox = 100 (μa/V2) L = 0.25μm λ = 0 Establish a drain current of 0.8 mA and a voltage VD of 1.5V. Determine the transistor width W, and the...
  49. Jalo

    Engineering Find the input resistance of the following MOSFET circuit

    Homework Statement Given the following circuit find the input resistance as seen through vo. Homework Equations The Attempt at a Solution To solve this problem I started by drawing the signal equivalent circuit: As we can see the voltage vgs = vi - vo. To find the input resistance I used...
  50. Jalo

    What is the MOSFET bias point?

    Homework Statement Given the following circuit find the bias point (VDS,IDS). Homework Equations The Attempt at a Solution The first thing I did was find the value of VG, the voltage from the gate of the mosfet to the -VDD source. VG = VDD * R2/(R1+R2) To find the...
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