SEMICONDUCTORES ANALOGA, Study notes of Transmission Systems

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MOSFET

Metal Oxide Semiconductor Field Effect Transistors EBB424E

Dr. Sabar D. Hutagalung

School of Materials & Mineral Resources Engineering, Universiti Sains Malaysia

Different types of FETs  Junction FET (JFET)  Metal-Oxide-Semiconductor FET (MOSFET)  Metal-Semiconductor FET (MESFET)

Different types of FETs  Metal-Oxide-Semiconductor FET (MOSFET)

Different types of FETs  Metal-Semiconductor FET (MESFET)

Basic MOSFET (n- channel)  Increasing the +ve gate voltage pushes the p- type holes further away and enlarges the thickness of the created channel.  As a result increases the amount of current which can go from source to drain — this is why this kind of transistor is called an enhancement mode device.

 Cross-section and circuit symbol of an n-type MOSFET.

Basic MOSFET (p- channel)  These behave in a similar way, but they pass current when a -ve gate voltage creates an effective p-type channel layer under the insulator.  By swapping around p-type for n-type we can make pairs of transistors whose behaviour is similar except that all the signs of the voltages and currents are reversed.  Pairs of devices like this care called complimentary pairs.

 (^) Note that with a n-channel device we apply a +ve gate voltage to allow source-drain current, with a p-channel device we apply a -ve gate voltage. Illustrates the behaviour of a typical complimentary pair of power MOSFETs made by Hitachi for use in hi-fi amplifiers.

Structure and principle of operation  A top view of MOSFET, where the gate length, L , and gate width, W.  (^) Note that L does not equal the physical dimension of the gate, but rather the distance between the source and drain regions underneath the gate.  (^) The overlap between the gate and the source/drain region is required to ensure that the inversion layer forms a continuous conducting path between the source and drain region.  (^) Typically this overlap is made as small as possible in order to minimize its parasitic capacitance.  (^) Top view of an n-type MOSFET

I-V Characteristics of MOSFET

I-V Characteristics of MOSFET

Ideal Output Characteristics of MOSFET

Ideal Transfer Characteristics of MOSFET