What is Mosfet: Definition and 214 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. PEEng

    Shoot-Through on Synchronous Buck Converter

    Hi, im fairly new to this so this is probably a straight forward question. I'm usimg a half-bridge basically as a synchronous buck converter. I'm not trying to get any specific conversion ratio at the moment, I'm just trying to understand all of the operating principles. One of the things...
  2. M

    Reverse-Flow Protection Mosfet Control?

    Hi, Attached is a circuit diagram for a solar powered, synchronous Buck converter. It appears to have and extra Mosfet, Q1, that is intended to prevent the flow of current, out from the battery, and back toward the unlit solar panel, via the body diode of Q2. Q2, being the regulator's high-side...
  3. core7916

    Mosfet failures in this differential piezo drive circuit

    Hello, i am using a switching circuit with the power mosfets to actuate the piezo loads, but while working on this circuit, my mosfet is getting bad, means i am observing short between mosfet source and drain. ( happend in 4 mosfets) i will attach the circuit daigram of my circuit. switching...
  4. A

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    So here is my dilemma. I have a test setup with multiple coils all lined up in parallel in such a way that one end of each coil is connected together while the other is connected to a switch (mosfet) the switches then connect each coil to ground but that ground can become + based on which coil...
  5. mhr0003

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    I am trying to simulate a Gate-All-Around FET in Silvaco TCAD for my thesis but I can't figure out how to add HZO (Hf0.5Zr0.5O2). I would really appreciate it if anyone could help me with the code for HZO or help me in any other way. Thank you.
  6. core7916

    Is the IXTP86N20X4 MOSFET a Suitable Choice for Driving at 5V?

    Hello. Can any one help me to drive the mosfet - IXTP86N20X4 Mosfet. I tried with 555 timers, amplifiers(opa 404). Unable to drive the mosfet. Is there any other way to drive. Any suggestions. I have attached the datasheet.
  7. A

    Parallel MOSFET safety diagnostics circuit

    I am now faced with a problem. Part of the circuit I'm making consists of a row of many parallel mosfets. Parallel as in the drains are all tied to a rail and the sources also. I wonder, if one of the mosfets goes bad for whatever reason , how could I be able to tell without physically taking...
  8. A

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  9. E

    What is the Effect of Floating MOSFET Base Plate?

    My specific system will benefit from having the MOSFET base plate floating. Are there any downsides to leaving a MOSFET base plate floating? Are there any reasons not to?
  10. N

    AC Hipot Test on MOSFET: Can It Be Done?

    Hi, I have a test board that I would like to do an AC hipot test on a MOSFET with connections across the drain/source. Since because of the built in diode, current flows during the negative half cycle. Is AC hipot possible for a MOSFET, or is DC required?
  11. N

    Using delicate 5V IC to toggle 12V device with MOSFET, Diode, resistor

    Hey all, I have a 5v IC that is triggered by a sensor to unlock the 12v lock, I am using a NPN transistor as a switch with the 5v VCC as the gate, I need it to sink back to the GND of the IC without blowing it, is this safe? If not what changes would you suggest, it has been years since I've had...
  12. KyleGranger

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    I would like to be able to determine the current through a device for a given junction temperature. I am looking at a datasheet and notice that it gives the device power dissipation with different case temperatures. Since the maximum junction temperature is 175 C, I believe that means that lower...
  13. C

    Engineering Depletion region capacitance in MOSFET

    I would like to ask about the behavior of a MOSFET as a capacitor, particularly at the onset of inversion/weak inversion - see Fig 2.6(c) At this stage in Fig 2.6(c), there is positive charge at the gate metal/poly contact, then an insulator oxide and then negative ions (positive holes have...
  14. icesalmon

    Engineering Calculation of the Transconductance for a MOSFET

    This problem was included as an exercise for a section on the small signal equivalent circuit for a MOSFET under the body effect. The problem states ##λ =0## so I believe the Early effect is negligible and ro = 0. I don't see how the body effect would be negated so for part (b). I believe the...
  15. Helena Wells

    Question on MOSFET modes of operation

    I have studied the modes of the MOSFETs from this site https://www.electronics-tutorials.ws/transistor/tran_6.html however in many videos such as this : they don't agree with each other.Which is correct and which isnt?
  16. A

    Mosfet, Mesfet vs Bipolar transistors in RF circuits

    I was wondering in general what types of semiconductors are used in most solid state RF power amplifiers like the ones at cell base stations and elsewhere. Do they use mosfets etc which can only switch a square waveform or are bipolar ones also used that can output sinusoidal outputs that can be...
  17. Boltzman Oscillation

    Engineering Variable Gain Amplifier Analysis help

    I need to find A_v, I want to relate Vin to Vout. To do this I did KVL on the major loop: $$V_{DD} = I_D*R_D + V_{SD1} - V_{SD2} - I_D*R_D$$ Since M1 = M2 then everything would cancel out and I would just get V_dd = 0 which is probably wrong. This is assuming V_sd1 = V_sd2, is that correct?
  18. L

    Solving the 1D Poisson equation for a MOS device

    Hey everyone, I'm currently working on a 1D Poisson Solver for a MOS device (Al-Si-SiO2). Therefore, I programmed a Poisson Solver which is appling a boxintegration (Finite Volume Method) through the structure from φ(0) at the metal-oxide interface and φ(x_bulk = 20 nm) in in the silicon bulk...
  19. F

    MOSFET Transistors as Switches

    I’ve attached two images from my textbook. One describing how MOSFEET’s act like small resistances when in the triode region and open circuits when in the cutoff region, the other a list of equations describing the behavior of an NMOS transistor. I’m having trouble making sense of these two...
  20. M

    Engineering Find the output resistance in a amplifier (MOSFET) small-signal model

    I have to solve a problem related with an 'invented' (non-real) MOSFET working in its saturation region (amplifier). I have solved all the questions, but I'm unable to get the last one. Basically, I need to determine the output resistance of the amplifier as a function of other given 4...
  21. Z

    Si IGBT and SiC MOSFET comparison

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  22. N

    Equivalent MOSFET for AUIRLR2908

    I am currently in need of a MOSFET to replace the AUIRLR2908 I am currently using. This power MOSFET is used in enhancement mode for switching. The data sheet is attached for reference. What are some of the key parametrics I should be concerned with when trying to find a drop in equivalent...
  23. wirefree

    Engineering MOSFET Design: Solving Q4 with R1, R2, k, V_T and I_D

    I greatly appreciate the opportunity afforded by this forum to submit questions. I am presently tackling a 10-part question, fourth of which this post is concerning. Values provided at the start are: R1, R2, k, V_T and I_D. In the previous 3 parts, Source Resistor, Transconductance (g_m) and...
  24. Z

    MOSFET I-Vg Curve: Which Curve is Impossible?

    Homework Statement: Below graph shows the I - Vg curve for different MOSFET, which curve is impossible for MOSFET? Homework Equations: I - Vg I am inclined to select 1), as it is not likely to have a sharp transition from subthreshold to Quadritica region. However, graph 5 also looks strange...
  25. T

    Is anyone familiar with the IR2304 MOSFET driver?

    Hi All, I'm not sure if this is the correct foray to discuss my questions about the specific IR2304 IC chip. However, I've run into some difficulties making my first inverter and I've asked a range of questions on another website...
  26. marino

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    In this circuit i want generate the floatin voltage from the external supply connected by a load to drain of transistors (suppose this is constant). So for me is possible to command the gates without an auxiliary low voltage battery. Taking advantage of the high sensitivity of the mosfet I...
  27. A

    Best multiple/many individual MOSFET driver IC?

    I have a need for a driver ic, here is what I want to do. I have several (10) mosfets of the IRPF type if I remember correctly with the TO-220 type package, I would need a driver with which I can switch those mosfets on and off one at a time in such an order that at least two fets are on at the...
  28. J

    Channel length modulation in a MOSFET

    Hi, I'm struggling to understand how channel length modulation takes place in mosfet. The books n internet said that as drain side is positive, there is less potential difference between positive gate and positive drain, while there is more potential difference between positive gate and zero...
  29. C

    Engineering Input Impedance of a MOSFET circuit

    Homework Statement (From Razavi's Design of Analog CMOS Integrated Circuits - Chapter 6) Homework EquationsThe Attempt at a Solution Not too sure about calculating the input impedance of this. Initially I thought that it would be the series combination of C1 and C2, since we are...
  30. J

    A How is the inversion Channel formed in SOI Mosfet?

    Hi, I'm studying MOSFET in detail and I'm struggling to understand how the channel is formed in case of SOI Mosfet. For normal mosfet A positive Gate to source voltage attracts electrons from P substrate towards Gate and thus a channel is formed. But in case of SOI There is a buried Oxide...
  31. C

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    Homework Statement Razavi's book (Analgoue CMOS Integrated Circuits) says that that "as Vin approaches Vth, M1 begins to turn on, drawing current from Rd and lowering Vout. Transistor M1 turns on in saturation regardless of the values of Vdd and Rd." Why is that? I mean that the condition...
  32. C

    MOSFET KVL Confusion: Finding Vg | Homework Solutions

    Homework Statement Homework EquationsThe Attempt at a Solution My first attempt was to figure out what region the PMOS is operating in so that I could decide what equation to use - so I tried to find Vgs. Vgs = Vg - Vs. Vs is of course just Vdd but for Vg I did a KVL loop as below: My...
  33. C

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    I need to replace a mosfet for a 3D printer. The seller and manufacturer were contacted on this but were not able to fulfill a replacement. See this on mosfet: IRF3205 P705D KCAB Here is photo: https://plus.google.com/photos/photo/103754471497291178620/6538401194800693618 Unable to find...
  34. N

    High-Power Switching using MOSFETs

    For a project, I need a means of switching a high-current circuit between two inductors. The purpose is, each inductor serves as an electromagnet, and they are switched every 15s or so in order for one of the two to cool before starting again. The system I've designed uses arduino as a...
  35. hugo_faurand

    Need help with MOSFETs and photoresistors

    Hello everyone ! At High School I have to make a little robot which is steerable with light. It has 2 photoresistors, if a photoresistor received light it switches on a motor. That allows us to go leftward or rightward. But, I have a problem. I don't manage to link every components between us...
  36. A

    Input resistance into a MOSFET amplifier

    Hello everyone I was hoping you could help me with something, in my analog electronics course.. In the diagram below, is displayed a circuit and its equivalent... I don't understand why the input resistance is only the parallel combination of R1 and R2?? Why doesn't Rsi contribute to the...
  37. T

    Why Choose IGBT Over MOSFET for Low-Frequency Applications?

    Apologies upfront, I have a backlog of PF threads I have created not replied to...I will endeavour to do so when I can. So I've read that IGBTs are more efficient than MOSFETs for lower than 20kHz frequencies (and are capable of use for high voltage rating and better performance than ordinary...
  38. C

    Biasing a MOSFET with constant-current source

    Homework Statement Hi, I'm just going through amplifier circuits and I'm having some trouble with amplifiers in which the MOSFET is biased by a constant current arrangement. Here's my issue: In the MOSFET saturation equation, if we set ID, we will be able to obtain Vgs. Which means that if...
  39. F

    Engineering Stable Load Current and Voltage in a Simple MOSFET Driver Circuit

    Homework Statement Homework EquationsThe Attempt at a Solution I know what the transients should generally look like, the only part that's throwing me off is how to model the intended load voltage of 18V. I'm guessing that when the switch is on (after transients) the load voltage will be close...
  40. C

    MOSFET Common-Source Amplifier Small-Signal

    Homework Statement Hi, so I was trying to derive the small-signal model of a common-source mosfet amplifier that I learned from the notes. Here is what I did, Now the issue is the i_d branch in the final small-signal circuit. In my lecture notes, that i_d branch is not there at all but...
  41. C

    MOSFET Region/Biasing Confusion

    Homework Statement I just encountered some MOSFET problems that made me rethink what biasing and the regions really mean. Okay, so here is what I know: Consider the following circuit The regions of the MOSFET are Cut-Off, Linear and Saturation. Considering Saturation, the conditions for...
  42. G

    Engineering Biasing circuit with a MOSFET: am I missing something

    Homework Statement I have the following circuit with MOSFET (cascode amplifier). [![enter image description here][1]][1] [1]: https://i.stack.imgur.com/BAqQh.png Information given: ##V_t=1V## ##I_1=20\mu A## ##k=10 \mu AV^{-2}## Knowing that ##V_b## is 5V determine the minimum value of the...
  43. J

    Enlighten me about the differences of IGBT and MOSFET please

    Hello guys, Can anybody explain the differences of IGBTs and MOSFETs? Yesterday I found an article entitled What is the Difference Between MOSFET and IGBT (http://www.apogeeweb.net/article/66.html), which theoretically explained this question to a certain degree, but still i want to ask you...
  44. G

    Mosfet equation: how to get it?

    Homework Statement I'm studying the following circuit with a MOSFET [![enter image description here][1]][1] [1]: https://i.stack.imgur.com/gEEdQ.png Homework Equations 3. The Attempt at a Solution [/B] Now for analyzing this circuit my book came out with various equations (which I totally...
  45. L

    Mosfet conduction vs Drain voltage

    When does an N-ch Mosfet conduct when drain voltage varies from 0V to Vdd(like 5V). In case of Source voltage changing between 0V to 5V, all you do is check if VGS > Vth, with Vdrain fixed at 5V. But in case of Drain Voltage changing between 0V to 5V, how does it work?
  46. A

    Bizarre Behavior in Discrete PMOS

    Some of my colleagues and I captured the i_D vs V_ds/V_sd curves for the CD4007 MOSFET IC (http://www.ti.com/lit/ds/symlink/cd4007ub.pdf). We did this for the NMOS and PMOS transistors. I have attached the curves to this post. The NMOS curve is as expected. However, the PMOS curve seems to be...
  47. M

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    hello 3N187, where to find this type of mosfet in ltspice, , because i am reading one good book and i need this 3N187, any help is welcome
  48. C

    Looking for the right MOSFET transistor

    I need a MOSFET transistor that will turn off anywhere between 2.5-2.7V and stay on when above that voltage, looking through the datasheets of these transistors, what spec should I be looking for? Here are some I've found that I think may work...
  49. D

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  50. D

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    Homework Statement Homework Equations Id=K*(Vsg-Vth)2 KVL The Attempt at a Solution On part A, Haven't had much experience with PMOS. Used large signal model, to find Rs. Equivalent circuit: We know that Vs=0. That means Vd=-7.5 V. If we say the voltage across Rs is Vdd-Vd, then that...
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