MOSFET

1. R.POORNIMA
AP/ECE
JCT College of engineering and technology
Metal Oxide Semiconductor Field Effect Transistor
(MOSFET)
JCT COLLEGE OF ENGINEERING AND TECHNOLOGY
PICHANUR, COIMBATORE – 641105

2. MOSFET
• Metal Oxide Semiconductor Field Effect Transistor
• A MOSFET is a FET with an insulated gate.
• Today, most transistors are MOSFETs in digital integrated
circuits.
• While the MOSFET has source, gate, and drain terminals like
the FET, its gate lead is not in contact with the body of the
device.
• The MOSFET has an higher input impedance than the JFET
(10 to 100 million mega-ohms).

3. Types of MOSFET
There are two basic types of MOSFET
• Depletion MOSFET
• Enhancement MOSFET
Depletion Type – The transistor requires the Gate-Source voltage,
( VGS ) to switch the device “OFF”. The depletion mode MOSFET is
equivalent to a “Normally Closed” switch.
Enhancement Type – The transistor requires a Gate-Source
voltage, ( VGS ) to switch the device “ON”. The enhancement mode
MOSFET is equivalent to a “Normally Open” switch.

4. MOSFET Symbol

5. Depletion Mode - MOSFET

6. (Cont.,)
 The Depletion-mode MOSFET, which is less common than the
enhancement mode types is normally switched “ON”
(conducting) without the application of a gate bias voltage. That
is the channel conducts when VGS = 0 making it a “normally-
closed” device.
• +VGS means more electrons and more current. While a -
VGS means less electrons and less current. The opposite is also
true for the p-channel types. Then the depletion mode MOSFET
is equivalent to a “normally-closed” switch.

7.  Metals(Conductors)
 Insulators
 Semiconductors
 N-Type Semiconductors
 P-Type Semiconductors
 Intrinsic Semiconductors
 Extrinsic semiconductors
N Channel-Depletion Mode MOSFET

8.  Metals(Conductors)
 Insulators
 Semiconductors
 N-Type Semiconductors
 P-Type Semiconductors
 Intrinsic Semiconductors
 Extrinsic semiconductors
P Channel-Depletion Mode MOSFET

9. Enhancement Mode - MOSFET

10. (Cont.,)
 Enhancement-mode MOSFET is the reverse of the depletion-
mode type. Here the conducting channel is lightly doped or even
undoped making it non-conductive. This results in the device
being normally “OFF” (non-conducting) when the gate bias
voltage, VGS is equal to zero
• +VGS turns the transistor “ON”, while a zero or -VGS turns the
transistor “OFF”. Thus the enhancement-mode MOSFET is
equivalent to a “normally-open” switch..

11. N Channel Enhancement Mode MOSFET

12. P Channel Enhancement Mode MOSFET

13. THANK YOU