06-04-2012, 11:38 AM
Design and Implementation of VLSI Systems
lecture02.ppt (Size: 702 KB / Downloads: 19)
Impact of doping on silicon resistivity
1 atom in billion 88.6 Ωcm
1 atom in million 0.114 Ωcm
1 atom in thousand 0.00174 Ωcm
1 atom in billion 266.14 Ωcm
1 atom in million 0.344 Ωcm
1 atom in thousand 0.00233 Ωcm
PN-junction regions of operation
In reverse bias, the width of the depletion region increases. The diode acts as voltage-controlled capacitor.
A forward bias decreases the potential drop across the junction. As a result, the magnitude of the electric field decreases and the width of the depletion region narrows.
nMOS transistor
When the gate is at a low voltage (VGS < VTN):
p-type body is at low voltage
source and drain-junctions diodes are OFF
transistor is OFF, no current flows
When the gate is at a high voltage (VGS ≥ VTN):
negative charge attracted to body
inverts a channel under gate to n-type
transistor ON, current flows, transistor
can be viewed as a resistor