The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET). It has an insulated gate, whose voltage determines the conductivity of the device. This ability to change conductivity with the amount of applied voltage can be used for amplifying or switching electronic signals. Although FET is sometimes used when referring to MOSFET devices, other types of field-effect transistors also exist.

1. MOSFET’S
[ METAL-OXIDE SEMICONDUCTOR FIELD
EFFECT TRANSISTOR ]

2. MOSFET’S
 There are 2 types of MOSFET’s:
• Depletion mode MOSFET (D-MOSFET)
• N-channel D-Type MOSFET
• P-channel D-Type MOSFET
• Enhancement Mode MOSFET (E-MOSFET)

3. DEPLETION MODE MOSFET CONSTRUCTION
• The Drain (D) and Source (S) leads connect to the to n-doped regions
• These N-doped regions are connected by an 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 SS

4. BASIC OPERATION
D-MOSFET may be biased to operate in two modes:
• The Depletion mode or The Enhancement mode

5. D-MOSFET DEPLETION MODE OPERATION
The transfer characteristics are similar to the JFET
In Depletion Mode operation:
When VGS = 0V, ID = IDSS
When VGS < 0V, ID < IDSS
When VGS > 0V, ID > IDSS
The formula used to plot the Transfer Curve, is:
 
 
 
2
GS
D DSS
P
V
I = I 1-
V

6. D-MOSFET ENHANCEMENT MODE OPERATION
Enhancement Mode operation
In this mode, the transistor operates with VGS > 0V, and ID increases above IDSS
Shockley’s equation, the formula used to plot the Transfer Curve, still applies but
VGS is positive:
 
 
 
2
GS
D DSS
P
V
I = I 1-
V

7. p-Channel Depletion Mode MOSFET
The p-channel Depletion mode MOSFET is similar to the n-channel except that
the voltage polarities and current directions are reversed

8. D-MOSFET Symbols

9. January2004
ELE
C
121
9
Specification Sheet

10. ENHANCEMENT MODE
MOSFET’S

11. n-Channel E-MOSFET showing channel length L and channel
width W

12. Enhancement Mode MOSFET Construction
The Drain (D) and Source (S) connect to the to n-doped regions
These n-doped regions are not connected via an n-channel without an external
voltage
The Gate (G) connects to the p-doped substrate 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 SS

13. Basic Operation
The Enhancement mode MOSFET only operates in the enhancement mode.
VGS is always positive
IDSS = 0 when VGS < VT
As VGS increases above VT, ID increases
If VGS is kept constant and VDS is increased, then ID saturates (IDSS)
The saturation level, VDSsat is reached.

14. p-Channel Enhancement Mode MOSFETs
The p-channel Enhancement mode MOSFET is similar to the n-channel except
that the voltage polarities and current directions are reversed.

15. E-MOSFET Symbols

16. Specification Sheet

17. SOME PACKAGES OF MOSFET