VLSI Final Exam Questions with Correct Answers Latest Version 2025
What does the mobility in MOS mean and what is the general relation between NMOS and PMOS
mobility? - Answers Mobility means how fast the electrons/holes move in a semiconductor
What is the relation between MOS gate's
i) length & resistance?
ii) width and resistance? - Answers i) when length increases, resistance of the channel increases.
ii) when width increases, resistance of the channel decreases.
Which materials do you to mix with intrinsic Silicon (Si) to create NMOS and PMOS? - Answers NMOS =
Arsenic or Phosphorus
PMOS = Boron
In general, what gate is better to use to build a circuit if you have a choice of NAND or NOR gates. Write
down at least 3 reasons. - Answers 1) smaller overall
2) less leakage
3) add less cap to previous driver
What is HOT electrons? - Answers Due to high electric field at drain, electrons are imparted with high
energy, called hot electrons.
What are 3 effects of HOT electrons in CMOS circuits? - Answers 1) can dislodge holes, push towards
body and create body current.
2) can penetrate gate oxide and create gate current.
3) leads to slow or failure of circuits.
How are P-type semiconductors created? - Answers by doping an intrinsic semiconductor with an
electron acceptor element during manufacture. Silicon (Si) + Boron (Br) = P-type
How are N-type semiconductors created? - Answers by doping an intrinsic semiconductor with an
electron donor element during manufacture. Silicon (Si) + arsenic (A) or phosphorous (P) = N-type
What is the relationship between the mobility of N-type vs P-type materials? - Answers Mobility of N-
type material (μn) = 2 x Mobility of P-type (μp). N = 2P
What does the junction between p-type and n-type semiconductors form? - Answers a diode
What are the nFET Pass Characteristics? What is the voltage range in which nFET passes? - Answers
nFETs pass strong logic 0 voltages, but weak logic 1 values
, nFET can only pass a weak logic 1
nFET is said to pass a strong logic 0
can pass a voltage in the range [0, V1]
What is threshold voltage loss? - Answers When the output voltage Vy is reduced to a value less than
the input voltage VDD
why is nFET weak? - Answers loose p-type
What are the nFET Pass Characteristics? What is the voltage range in which nFET passes? - Answers
pFETs pass strong logic 1 voltages, but weak logic 0 values
When should you use nFET? - Answers Use nFETs to pass logic 0 voltages of VSS = 0 V
When should you use pFET? - Answers Use pFETs to pass logic 1 voltages of VDD
What does the Linear region, Ids depend on? - Answers • How much charge (Qchannel) is in the
channel?
• How fast is the charge moving? How much time (t) each carrier takes to cross.
Where, Ids = Qchannel / t
What is the relationship between mobility and temperature in CMOS circuits? - Answers When
Temperature increases, mobility decreases.
If the supply voltage of a chip increases, the maximum transistor current will? - Answers increase
If the length of a transistor increases, the current will? - Answers decrease
If the width of a transistor increases, its gate capacitance will? - Answers increases
If the length of a transistor increases, the gate capacitance will? - Answers increase
If the supply voltage of a chip increases, the gate capacitance of each transistor will? - Answers not
change
Gate Capacitance (C permicron) is typically about ? fF/um - Answers 2 fF/um
What is the definition of the secondary effect: Short-Channel effect (Channel length modulation) ? -
Answers As the channel is decreased, threshold voltage no longer constant. Vt also decreased.
What is the definition of the secondary effect: Body Effect - Answers When a voltage Vsb is applied
between the source and body, it increases the amount of charge required to invert the channel.
What is the definition of the secondary effect: Temperature Dependency - Answers Carrier mobility
decreases with temperature.
What does the mobility in MOS mean and what is the general relation between NMOS and PMOS
mobility? - Answers Mobility means how fast the electrons/holes move in a semiconductor
What is the relation between MOS gate's
i) length & resistance?
ii) width and resistance? - Answers i) when length increases, resistance of the channel increases.
ii) when width increases, resistance of the channel decreases.
Which materials do you to mix with intrinsic Silicon (Si) to create NMOS and PMOS? - Answers NMOS =
Arsenic or Phosphorus
PMOS = Boron
In general, what gate is better to use to build a circuit if you have a choice of NAND or NOR gates. Write
down at least 3 reasons. - Answers 1) smaller overall
2) less leakage
3) add less cap to previous driver
What is HOT electrons? - Answers Due to high electric field at drain, electrons are imparted with high
energy, called hot electrons.
What are 3 effects of HOT electrons in CMOS circuits? - Answers 1) can dislodge holes, push towards
body and create body current.
2) can penetrate gate oxide and create gate current.
3) leads to slow or failure of circuits.
How are P-type semiconductors created? - Answers by doping an intrinsic semiconductor with an
electron acceptor element during manufacture. Silicon (Si) + Boron (Br) = P-type
How are N-type semiconductors created? - Answers by doping an intrinsic semiconductor with an
electron donor element during manufacture. Silicon (Si) + arsenic (A) or phosphorous (P) = N-type
What is the relationship between the mobility of N-type vs P-type materials? - Answers Mobility of N-
type material (μn) = 2 x Mobility of P-type (μp). N = 2P
What does the junction between p-type and n-type semiconductors form? - Answers a diode
What are the nFET Pass Characteristics? What is the voltage range in which nFET passes? - Answers
nFETs pass strong logic 0 voltages, but weak logic 1 values
, nFET can only pass a weak logic 1
nFET is said to pass a strong logic 0
can pass a voltage in the range [0, V1]
What is threshold voltage loss? - Answers When the output voltage Vy is reduced to a value less than
the input voltage VDD
why is nFET weak? - Answers loose p-type
What are the nFET Pass Characteristics? What is the voltage range in which nFET passes? - Answers
pFETs pass strong logic 1 voltages, but weak logic 0 values
When should you use nFET? - Answers Use nFETs to pass logic 0 voltages of VSS = 0 V
When should you use pFET? - Answers Use pFETs to pass logic 1 voltages of VDD
What does the Linear region, Ids depend on? - Answers • How much charge (Qchannel) is in the
channel?
• How fast is the charge moving? How much time (t) each carrier takes to cross.
Where, Ids = Qchannel / t
What is the relationship between mobility and temperature in CMOS circuits? - Answers When
Temperature increases, mobility decreases.
If the supply voltage of a chip increases, the maximum transistor current will? - Answers increase
If the length of a transistor increases, the current will? - Answers decrease
If the width of a transistor increases, its gate capacitance will? - Answers increases
If the length of a transistor increases, the gate capacitance will? - Answers increase
If the supply voltage of a chip increases, the gate capacitance of each transistor will? - Answers not
change
Gate Capacitance (C permicron) is typically about ? fF/um - Answers 2 fF/um
What is the definition of the secondary effect: Short-Channel effect (Channel length modulation) ? -
Answers As the channel is decreased, threshold voltage no longer constant. Vt also decreased.
What is the definition of the secondary effect: Body Effect - Answers When a voltage Vsb is applied
between the source and body, it increases the amount of charge required to invert the channel.
What is the definition of the secondary effect: Temperature Dependency - Answers Carrier mobility
decreases with temperature.
