Question

Q1

Which of the following is true for a MOS capacitor with a P-type body?

Select one:

a. The charge in the inversion layer stays approximately constant as the gate voltage is increased above the threshold voltage

b. The charge in the depletion region is proportional to the square root of the depletion region width, assuming that the body is uniformly doped

c. In inversion, the total charge is equal to the sum of the charge in the depletion region plus the charge in the accumulation layer

d. In both inversion and accumulation, the charge varies nonlinearly with the gate voltage, like a reverse-biased PN junction capacitor

e. None of these

Q2

The capacitance of a MOS capacitor in strong inversion is larger when measured at high frequencies than at low frequencies, because at low frequencies there is enough time for generation to supply carriers to the inversion layer.

Select one:

True

False

Q3 What is the threshold voltage in millivolts for a MOS capacitor with an N+ polysilicon gate and an N-type body doped with phosphorus at a concentration of 4.6 x 10^16/cm^3? Assume that the oxide thickness is 68.4 angstroms. Use: kT/q = 26mV and ni = 1.5 x 10^10/cm^3 at 300°K, εs = 11.7, εox = 3.9, ε0 = 8.854 x 10^-14 F/cm, and q = 1.6 x 10^-19 C. Assume that the intrinsic Fermi level, Ei, is in the middle of the band-gap. For this question, be sure to give your answer to the nearest millivolt!

Q4

Which of the following is true about the effective gate oxide thickness, Toxe ?

Select one:

a. It is approximately the same as the physical oxide thickness in newer processes with thinner gate oxides

b. It is significantly different than the physical oxide thickness in older processes with thicker gate oxides

c. It includes the effect of the inversion layer thickness not being equal to zero

d. None of these

e. It includes the effect of the depletion layer thickness in the silicon body

Q5

Sodium contamination is everywhere, and so must be completely eliminated by process engineers in order to avoid shifts in the MOS threshold voltage.

Select one:

True

False

Q6

For an NMOS FET biased with Vgs > Vt and Vds > Vdsat, which of the following is true?

Select one:

a. None of these

b. The voltage from the source to the end of the channel near the drain increases as Vds increases

c. The channel is pinched off near the drain end

d. The channel-to-body voltage is smaller at the drain end of the channel than at the source end

e. The gate-to-channel voltage is smaller at the source end of the channel than at the drain end

Q7

Since Nonvolatile (Flash) Memory cells only use standard CMOS transistors, flash memory can be used on any chip without the need to modify the CMOS process.

Select one:

True

False

Q8 What is the surface mobility of electrons in cm^2/Vs for an NMOS FET with an effective oxide thickness, Toxe, of 71 angstroms and a threshold voltage, Vt, of 0.2V when this transistor is operating with Vgs = 1.5V ?

Q9

For an NMOS FET biased with Vgs > Vt and Vds > Vdsat, which of the following is true?

Select one:

a. The channel-to-body voltage is smaller at the source end of the channel than at the drain end

b. The gate-to-channel voltage is smaller at the source end of the channel than at the drain end

c. The channel extends all the way from the source to the drain

d. All of these

e. The voltage from the source to the end of the channel near the drain increases as Vds increases

Q10

For MOSFETs with very short channels, the maximum current that can flow is limited by the thermal velocity of carriers in the drain.

Select one:

True

False

Answer 1

The answers for the following questions are

1. In inversion, the total charge is equal to the sum of the charge in the depletion region plus the charge in the accumulation layer

2. false

3.

4. It is significantly different than the physical oxide thickness in older processes with thicker gate oxides \

5. false

6. The gate-to-channel voltage is smaller at the source end of the channel than at the drain end

7. true

8. 3

9. The gate-to-channel voltage is smaller at the source end of the channel than at the drain end

10. true