0
The SiO2 layer acts as an insulator and also it provides high input impedance to the MOSFET. This insulation is needed so that a circuit with high EMI or loads which generate back emf (motors) can be driven by applying gate current from a common circuit.
Add your answer:
Earn +20 pts
What is depletion mosfet?
A depletion mode MOSFET is a FET that is on with no gate bias, and requires a negative bias (with respect to the source) to stop conducting. The channel is normally conductive and with a negative gate bias the channel becomes "depleted" of charge carriers, hence the name depletion mode MOSFET. This is contrary to enhancement type MOSFET's that are non conductive with zero volts gate bias and become conductive when there is a positive bias on their gate.
Difference between de-mosfets e-mosfets and jfets?
The basic theory of operation is the same, but the device structure is different. With both a MOSFET and a JFET, a conductive channel is established between two terminals (the drain and the source). The structure of the gate terminal makes the difference between the two. In a MOSFET, the metal gate is separated from the channel by an insulator (the O in MOSFET means Oxide, the insulator). In a JFET the gate is a doped region essentially within the conductive channel.
What are the differences betweeen e-mosfet and d-mosfet?
An e-mosfet is and "enhancement" mosfet. A d-mosfet is a "depletion" mosfet. These essentially show what mode the mosfet operates in when a voltage is applied to the gate. . An enhancement mode mosfet is normally non-conducting but conducts when the channel is enhanced by applying a voltage to the gate and pulling carriers into the channel. A depletion mode mosfet normally conducts but becomes more and more non-conducting as carriers are depleted or pulled out of the channel by applying a voltage. The polarity of the voltage depends on whether it is an N channel or P channel. P channel uses positively doped silicon while N channel uses negatively doped silicon. N channel fets are used wherever possible because N material conducts better than P material. There are basically two types of fet, the jfet and the mosfet. The jfet uses a single junction to control the channel hence draws some current. Bipolar transistors use two junctions. In the mosfet (Metal Oxide Semiconducting Field Effect Transistor) there is no such junction hence draw so little current for control purposes it can be regarded as zero. The gate is isolated from the channel by a very thin layer of metal oxide (usually chromium dioxide). An enhacement mode mosfet can be turned on by applying a voltage then removing the wire to the gate. The channel will then remain conducting for some time.
Why silicon dioxide used in MOSFET instead of any other material which have high k-dielectric?
Because the gate terminal should highly resistive..silicon dioxide has high resistance and hence gate current is very very low...
What are electrodes called in a MOSFET transistor?
The terminals on a MOSFET are called the "Source", "Drain", and "Gate". Just as with a bipolar junction transistor (BJT) the direction of current flow will be based on the doping configuration of the semiconductor. In a MOSFET, the doping configuration can be either n-channel or p-channel, but with MOSFETS, they also come in a "normally on" or "normally off" configuration, which is specified by being either "depletion mode" or "enhancement mode", respectively.
Why is MOSFET called IGFET?
MOSFET is Metal Oxide Semiconductor Field Effect Transistor. IGFET Insulated Gate Field Effect Transistor. But these expressions are practically synonyms.
What is depletion mosfet?
A depletion mode MOSFET is a FET that is on with no gate bias, and requires a negative bias (with respect to the source) to stop conducting. The channel is normally conductive and with a negative gate bias the channel becomes "depleted" of charge carriers, hence the name depletion mode MOSFET. This is contrary to enhancement type MOSFET's that are non conductive with zero volts gate bias and become conductive when there is a positive bias on their gate.
What is the function of enhancement mosfet?
An enhancement MOSFET doesn't conduct current across the drain to source unless a voltage is applied to the gate. When sufficient voltage is applied to the gate of the transistor, currents flows from drain to source. A MOSFET acts as a switch or amplifier in a circuit.
Difference between de mosfet and e mosfet?
The basic difference is between JFET and enhanced MOSFET,although the construction of JFET and depletion MOSFET is different but their most of the characteridtics are same,i.e shockly equation can be applied on both of them,but in JFET we cant give to gate voltage, the +ve value,because it does not works, but in depletion we can give,but some limited +ve value. Now enhanced MOSFET is different,shockly equation cant be applied.The transfer characteristics are purely in +ve Vg region. i.e for E-MOSFET Vg should be > 0,for its proper function.
Advantages and disadvantages of depletion MOSFET?
Since the logic operations of depletion MOSFET is the opposite to the enhancement MOSFET, the depletion MOSFET produces positive logic circuits, such as, buffer, AND, and OR. The most significant advantage of the positive logic circuits is that it can produce positive feedback easily so that a single depletion MOSFET can become a memory cell. In contrast, you will need at least two enhancement MOSFET transistor to produce the positive feedback to build a memory cell. The other advantages of depletion MOSFET are that it is free from sub-threshold leakage current and gate-oxide leakage current. Since there is always a potential difference of Vdd between the gate terminal and channel for an enhancement MOSFET to cause the gate-oxide leakage current, the gate oxide leakage current is unavoidable when the transistor shrinks in size and oxide layer becomes thinner. The depletion MOSFET does not have this problem because there is no potential difference between the gate and channel. As a enhancement MOSFET shrinking in size, there is no way to stop the subthreshold leakage current diffused across from source to drain because the drain and source terminals are closer physically. This is not a problem for depletion MOSFET because a pinched channel will stop the diffusion current completely. The depletion MOSFET is the ideal, perfect transistor. The only disadvantage of depletion MOSFET is its inability to produce negative logic operations.
Main factor which differ De mosfet from an e only mosfet?
An e only(enhancement) ÊMOSFET is off at zero gate-source voltage. Meanwhile, a de (depletion enhancement)ÊMOSFET is on at zero gate-source voltage.
The value of gate voltage for the operation of enhancement of only N channel MOSFET has to be?
high...
What happens if a negative voltage is applied to the gate of the n and p channel MOSFET?
It depends on: 1. technology, whether it's a JFET, enhancement-mode IGFET/MOSFET or depletion-mode IGFET/MOSFET, and 2. polarity, whether it's an N type or P type. More info needed for this one.
Why should a JFET be operated with only reverse bias on the gate?
If the gate-channel junction of a JFET was not reverse biased the JFET would just act as a forward biased diode across that junction and the gate would cease to have any control over the channel conductance. For the same reason in a MOSFET the substrate-source/channel/drain junction must remain reverse biased. The MOSFET could not act as a MOSFET.
Can we replace a thyristor by a mosfet?
No because a mosfet does not work the same as a thyristor. In a thyristor the current flows even when the gate pulse is removed, until the current stops. That is not the case for a FET.
What are depletion and enhancement mosfet?
A depletion MOSFET is a MOSFET that is normally on. It outputs maximum current when the gate-source voltage is 0V. As the gate-source voltage increases, the drain-source channel becomes more resistive and the current decreases. An enhancement MOSFET has the opposite behavior. It is normally off. It outputs no current when the gate-source voltage is 0V. As the gate-source voltage increases, the drain-source channel becomes less resistive and the current increases.
The value of gate voltage for the operation of enhancement of only N channel MOSFET has to be high positive?
yes.
