A. lattice mismatch
B. intrinsic stress
C. thermal mismatch
D. pressure mismatch
Answer: D
Mechanical stability of the thin-film encapsulation layer depends upon stress at the interface and this can originate from lattice mismatch, intrinsic stress, and thermal mismatch.
12. Which has the greatest mismatch?
A. Si
B. Ga
C. GaAs
D. SiO2
Answer: D
SiO2 has the greatest mismatch and its coefficient of thermal expansion is 0.5×10-6/degree celsius.
13. Which was employed as the first level capping material?
A. SiO2
B. SiO
C. Si3N4
D. Si2N4
Answer: A
Si3N4 has a dielectric constant of 7 compared to 3.9 for silicon dioxide and silicon dioxide was initially employed as the first-level capping material.
14. The ohmic contacts are deposited by
A. decomposition
B. evaporation
C. deposition
D. mixing
Answer: B
The ohmic contacts between the metal interconnect and the source and the drain are deposited by evaporation using E-beam technology.
15. Which has high parasitic gate resistance?
A. platinum
B. gold
C. titanium
D. aluminum
Answer: C
Titanium provides a good, high barrier, Schottky contact, and has a high parasitic gate resistance.
16. Which is used as the top layer?
A. gold
B. platinum
C. titanium
D. tungsten
Answer: A
To reduce the parasitic resistance, gold is used as the top layer with platinum or tungsten as the intermediate layer.
17. First layer metallization is accomplished by plasma etching.
A. true
B. false
Answer: A
First layer metallization is accomplished by delineating photoresist patterns, plasma etching, deposition of metal on GaAs wafer, and photoresist lift-off.
18. Deposition rate is given as
A. width per unit time
B. thickness per unit time
C. sputtering rate per unit time
D. depositing rate per unit time
Answer: B
The deposition rate is given as thickness per unit time. It depends upon the sticking coefficient of the depositing material and the nature of sputtering equipment.
19. Passivation is used to protect against contamination.
A. true
B. false
Answer: A
The last step for fabrication in GaAs is passivation. This process is used to protect the device against contamination and moisture.
20. Plasma-enhanced chemical vapour deposition process is used for fabrication of
A. conducting films
B. insulating films
C. conducting & insulating films
D. none of the mentioned
Answer: C
The plasma-enhanced chemical vapor deposition process is a chemical deposition technique used for the fabrication of both insulating and conducting films.
