22-03-2012, 04:00 PM
MOSFET - Metal Oxide Semiconductor Field Effect Transistors
Transistor Physics.pdf (Size: 1.16 MB / Downloads: 209)
How does the transistor switch ?
most simple working mode of a n-channel MOSFET:
Source and substrate are on the same potential
drain potential VD more positive than source
to attract electrons
Transistor is switched on when gate voltage VG is
sufficiently positive to invert the channel
MOS – structure under equilibrium and non-equilibrium condition
As the positive drain voltage takes over electrons,
the electron concentration is lowered under
applied VD in the vicinity of the drain electrode
Drain – current characteristics of a MOSFET device
VG > VT; VD small: linear region
inversion layer charge is induced uniformly in the channel;
current flows from source to drain through conducting channel;
channel acts as resistor and drain current
increases proportional to drain potential
VG > VT; VD = VD Sat: onset of saturation
inversion charge near drain decreases until it becomes zero
close to drain region
VD at which this happens is called pinchoff
drain current starts to saturate
Be the electric engineer: Raise the drain current of the MOSFET device !
The SiO2 thickness in the state-of-the art MOSFET technology is just 1 to 1.5 nm.
Further thickness reduction of the insulator results in unacceptable high leakage currents
on the order of 1 A / cm2 due to the quantum mechanical tunneling effect.
Interesting example how quantum mechanics triggers technology developments
Transistor Physics.pdf (Size: 1.16 MB / Downloads: 209)
How does the transistor switch ?
most simple working mode of a n-channel MOSFET:
Source and substrate are on the same potential
drain potential VD more positive than source
to attract electrons
Transistor is switched on when gate voltage VG is
sufficiently positive to invert the channel
MOS – structure under equilibrium and non-equilibrium condition
As the positive drain voltage takes over electrons,
the electron concentration is lowered under
applied VD in the vicinity of the drain electrode
Drain – current characteristics of a MOSFET device
VG > VT; VD small: linear region
inversion layer charge is induced uniformly in the channel;
current flows from source to drain through conducting channel;
channel acts as resistor and drain current
increases proportional to drain potential
VG > VT; VD = VD Sat: onset of saturation
inversion charge near drain decreases until it becomes zero
close to drain region
VD at which this happens is called pinchoff
drain current starts to saturate
Be the electric engineer: Raise the drain current of the MOSFET device !
The SiO2 thickness in the state-of-the art MOSFET technology is just 1 to 1.5 nm.
Further thickness reduction of the insulator results in unacceptable high leakage currents
on the order of 1 A / cm2 due to the quantum mechanical tunneling effect.
Interesting example how quantum mechanics triggers technology developments