Introduction to MOS Transistors
and VLSI Fabrication
Based on:
1. Basic VLSI Design – Douglas A.
Pucknell & Kamran Eshraghian, PHI,
3rd Ed.
2. CMOS VLSI Design – Weste, Harris
A Brief History
• - MOS transistor invented in late 1950s.
• - Commercially viable in 1960s.
• - 1970s: MOS surpassed BJTs due to low
power & high density.
• - CMOS combines NMOS & PMOS for lower
power & better noise immunity.
• - Basis for modern ICs.
• [Pucknell, Weste]
MOS Transistor Theory
• - Voltage-controlled switch/amplifier.
• - Gate, source, drain, body terminals.
• - Gate voltage controls channel conductivity.
• - NMOS & PMOS operation principles.
• [Pucknell, Weste]
Ideal I-V Characteristics
• - Cut-off: transistor OFF.
• - Linear (Triode): acts like variable resistor.
• - Saturation: acts like current source.
• - Describes switching behavior.
• [Weste]
Non-Ideal I-V Effects
• - Channel length modulation.
• - Subthreshold conduction.
• - Velocity saturation.
• - Body effect.
• - Important for real circuit modeling.
• [Pucknell, Weste]
DC Transfer Characteristics
• - Shows input-output relationship.
• - Example: inverter transfer curve.
• - Switching threshold & noise margins.
• - Key for robust logic design.
• [Weste]
NMOS Fabrication
• - Uses NMOS transistors & pull-up resistors.
• - Steps: oxide growth, photolithography,
doping, metallization.
• - Simpler than CMOS but higher static power.
• [Pucknell]
CMOS Fabrication
• - Combines NMOS & PMOS on same
substrate.
• - Methods:
• 1. p-well process
• 2. n-well process (common)
• 3. Twin tub process (both wells)
• - Enables low power & high noise immunity.
• [Weste, Pucknell]
References
• 1. Basic VLSI Design – Douglas A. Pucknell &
Kamran Eshraghian, PHI, 3rd Ed. (1994)
• 2. CMOS VLSI Design – Neil H.E. Weste, David
Harris, Ayan Banerjee, 3rd Ed., Pearson
Education