VLSI FINAL REVIEW EXAM QUESTIONS AND
ANSWERS
What does the mobility in MOS mean and what is the general relation between
NMOS and PMOS mobility? - ANSWER Mobility means how fast the
electrons/holes move in a semiconductor
What is the relation between the MOS gate's i) length & resistance? ii)
width and resistance? - ANSWER i) when length increases, the resistance of
the channel increases.
ii) when the width increases, the resistance of the channel decreases.
Name materials to be doped with intrinsic Silicon (Si) to produce NMOS and
PMOS - SOLUTION NMOS = Arsenic or Phosphorous
PMOS = Boron
generally speaking. Which gate is better to use to build a circuit if you have a
choice of NAND or NOR gate. Write down at least 3 reasons. - SOLUTION 1)
smaller overall
2) less leakage
3) add less cap to previous driver
HOT electrons - ANSWER On account of high electric filed at drain,
electrons acquire large amounts of energy, called hot electrons.
The hot electrons in CMOS cause these three effects: 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? - ANSWER by doping an intrinsic
semiconductor with an electron acceptor element during manufacture. Silicon
(Si) + Boron (Br) = P-type
How are N-type semiconductors created? - ANSWER by doping an intrinsic
semiconductor with an electron donor element during manufacture. Silicon (Si)
+ arsenic (A) or phosphorous (P) = N-type
What is the relation between mobility of N-type vs P-type materials? -
ANSWER Mobility of N-type material (μn) = 2 x Mobility of P-type (μp). N =
2P
What is formed by the junction between p-type and n-type semiconductors? -
ANSWER a diode
What are the nFET Pass Characteristics? What is the range of voltage in which
nFET passes? - SOLUTION 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? - ANSWER When the output voltage Vy is
reduced to a value less than the input voltage VDD
why nFET weak? - ANSWER loose p-type
ANSWERS
What does the mobility in MOS mean and what is the general relation between
NMOS and PMOS mobility? - ANSWER Mobility means how fast the
electrons/holes move in a semiconductor
What is the relation between the MOS gate's i) length & resistance? ii)
width and resistance? - ANSWER i) when length increases, the resistance of
the channel increases.
ii) when the width increases, the resistance of the channel decreases.
Name materials to be doped with intrinsic Silicon (Si) to produce NMOS and
PMOS - SOLUTION NMOS = Arsenic or Phosphorous
PMOS = Boron
generally speaking. Which gate is better to use to build a circuit if you have a
choice of NAND or NOR gate. Write down at least 3 reasons. - SOLUTION 1)
smaller overall
2) less leakage
3) add less cap to previous driver
HOT electrons - ANSWER On account of high electric filed at drain,
electrons acquire large amounts of energy, called hot electrons.
The hot electrons in CMOS cause these three effects: 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? - ANSWER by doping an intrinsic
semiconductor with an electron acceptor element during manufacture. Silicon
(Si) + Boron (Br) = P-type
How are N-type semiconductors created? - ANSWER by doping an intrinsic
semiconductor with an electron donor element during manufacture. Silicon (Si)
+ arsenic (A) or phosphorous (P) = N-type
What is the relation between mobility of N-type vs P-type materials? -
ANSWER Mobility of N-type material (μn) = 2 x Mobility of P-type (μp). N =
2P
What is formed by the junction between p-type and n-type semiconductors? -
ANSWER a diode
What are the nFET Pass Characteristics? What is the range of voltage in which
nFET passes? - SOLUTION 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? - ANSWER When the output voltage Vy is
reduced to a value less than the input voltage VDD
why nFET weak? - ANSWER loose p-type
