MOSFET definition, classification and construction

1. Presentation on
“MOSFET”
Prepared by
Sabbir Ahmed Sayeem (Roll-08)
And
MD. Shahariar Islam Raj (Roll-05)
10th Batch
3rd semsester
Department of EEE
Pundra University Of Science andTechnology

2. Contents
• What is MOSFET?
• Classification of MOSFET.
• Construction of Enhancement MOSFET (n-Channel).
• Construction of Enhancement MOSFET (p-Channel).
• Construction of Depletion MOSFET (n-Channel).
• Construction of Depletion MOSFET (p-Channel).

3. MOSFET is an acronym for Metal Oxide Semi-Conductor Field
EffectTransistor. It is a device in which the variation in the
voltage determines the conductivity of the device.
The MOSFET is a semiconductor device that is widely used for
switching purposes and for the amplification of electronic
signals in electronic devices.
MOSFET is also known as IGFET i.e., insulated gate field effect
transistor. But usually, the word MOSFET is used because most
devices are made using Si for semiconductors and gate
electrode of metal oxide. It is a three terminal device which has a
source, a drain and a gate terminal.These are voltage controlled
devices, in which the current flowing between source and drain
is proportional to the provided input voltage.
What is MOSFET ?

4. Classification Of MOSFET

5. Initially there is no channel in enhancement type MOSFET.
• Two N regions separated by a distance of 25 micrometers with
heavy doping concentration are diffused on a lightly doped
substrate of p-type.Those N-regions are enacted as the
terminals drain and source.
• Over the surface, a thin layer of insulation called silicon dioxide
is developed.The holes made on this layer establishes
aluminum contacts for the terminal’s source and the drain.
• This layer of conduction acts as the terminal gate. It is laid over
the silicon dioxide and on the entire area of the channel.
• But it doesn’t have any physical channel for conduction.
• The p-type substrate extended over the entire silicon dioxide
layer in this type of enhancement MOSFET.
Construction of Enhancement
MOSFET (n-Channel)

6. This MOSFET is designed with the n-substrate
which is lightly doped. The two heavily doped p type
materials are separated by the length (L). This L is
known as the channel length.
The thin layer of type silicon dioxide is
deposited above the substrate. This layer is
generally known as the dielectric layer. The two P
type forms the source and the drain respectively.
The aluminum which is used as the plating above
the dielectric forms the gate terminal. The source
and the MOSFET’s body is connected to the ground.
Construction of
Enhancement
MOSFET (P-Channel)

7. Figure shows the construction of an N-channel depletion
MOSFET. It consists of a highly doped P-type substrate into
which two blocks of heavily doped N-type material are diffused
forming the source and drain. The Drain (D) and Source (S)
connect to the two n-doped regions.These n-doped regions
are connected via n-channel.This n-channel is connected to
the gate (G) via a thin insulating layer of SiO2.
The n-doped material lies on a p-doped substrate that may
have an additional terminal connection called Substrate (SS).
Construction of
Depletion MOSFET

8. Depletion mode p channel MOSFET is shown in the figure.
As per figure we can see that the channel is created by p-
type of drain and source semiconductor device. Channel is
created between drain and source terminal of MOSFET.
Here substrate(body) is n-type material used. In any
depletion type MOSFET, whether it is n channel or p
channel, the channel is already pre-built. Depletion mode
MOSFET is always in ON condition without applications of
gate voltage.After applying the voltage difference between
the source and drain current start flowing through MOSFET.
Construction of
Depletion MOSFET
P-channel