VLSI Interview Questions and Answers focuses on “Basic MOS Transistors-2”.
1. MOS transistors consist of which of the following?
A. semiconductor layer
B. metal layer
C. layer of silicon-di-oxide
D. all of the mentioned
Answer: D
Clarification: MOS transistors is formed as a sandwich consisting of a semiconductor layer, a silicon-di-oxide layer and a metal layer.
2. In MOS transistors _______________ is used for their gate.
A. metal
B. silicon-di-oxide
C. polysilicon
D. gallium
Answer: C
Clarification: In MOS transistors, polycrystalline silicon is used for their gate region instead of metal. Polysilicon gates have replaced all other older devices.
3. The gate region consists of ____________
A. insulating layer
B. conducting layer
C. lower metal layer
D. p type layer
Answer: B
Clarification: The gate region is a sandwich consisting of semiconductor layer, an insulating layer and an upper metal layer.
4. Electrical charge flows from ____________
A. source to drain
B. drain to source
C. source to ground
D. source to gate
Answer: A
Clarification: Electrical charge or current flows from source to drain depending on the charge applied to the gate region.
5. Source in MOS transistors is doped with ______ material.
A. n-type
B. p-type
C. n & p type
D. none of the mentioned
Answer: A
Clarification: Source and drain in the MOS transistors are doped with N-type material and substrate is doped with p-type material.
6. In N channel MOSFET which is the more negative of the elements?
A. source
B. gate
C. drain
D. source and drain
Answer: A
Clarification: In N channel MOSFET, source is the more negative of the elements and in the case of P channel MOSFET, it is the more positive of the elements.
7. If the gate is given sufficiently large charge, electrons will be attracted to ____________
A. drain region
B. channel region
C. switch region
D. bulk region
Answer: B
Clarification: If the gate is given sufficiently large charge, the negative charge carreirs, electrons will be attracted from the bulk of the substrate material into the channel region below the oxide.
8. Enhancement mode device acts as ____ switch, depletion mode acts as _____ switch.
A. open, closed
B. closed, open
C. open, open
D. close, close
Answer: A
Clarification: Enhancement mode transistor acts as open switch whereas depletion mode transistor acts as normally closed switch.
9. Depletion mode MOSFETs are more commonly used as ____________
A. switches
B. resistors
C. buffers
D. capacitors
Answer: B
Clarification: Depletion mode MOSFETs are more commonly used as resistors than as switches. As permanently on switch it has high resistance.
10. Enhancement mode MOSFETs are more commonly used as ____________
A. switches
B. resistors
C. buffers
D. capacitors
Answer: A
Clarification: Enhancement mode MOSFETs are more commonly used as switches and depletion mode devices are more used as resistors.
11. Depletion mode transistor should be large.
A. true
B. false
Answer: A
Clarification: Depletion mode transistors should be made large that is long and thin to create the large ‘on’ resistance.
12. Which expression is true?
A. charging time < discharging time
B. charging time > discharging time
C. charging time = discharging time
D. charging time and discharging time are not related
Answer: B
Clarification: When driving a capacitive output load, charging time will be long compared to the discharging time.
13. Overheating in device occurs due to less number of resistors per unit area.
A. true
B. false
Answer: B
Clarification: When the number of resistors per unit area increases, the device may not dissipate heat very well. This results in device overheating which leads to its failure.
14. In n channel MOSFET ______________ is constant.
A. channel length
B. channel width
C. channel depth
D. channel concentration
Answer: A
Clarification: In all n channel MOSFET transistors, channel length is constant where as channel width can be varied.
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