21. In GaAs technology, deposited dielectric films bring about
A. passivation
B. combination
C. decomposition
D. diffusion
Answer: A
In GaAs technology, due to the absence of a stable native oxide deposited dielectric films bring about passivation or encapsulation.
22. Formation of the n-active layer is achieved by
A. indirect ion implantation
B. direct ion implantation
C. liquifying
D. wafering
Answer: B
The formation of the n-active layer is achieved by direct ion implantation into the GaAs semi-insulating substrate through the insulating layer.
23. Implantation of ________ is done for the formation of source and drain.
A. n- layer
B. n+ layer
C. p- layer
D. p+ layer
Answer: B
Implantation of a deep low resistivity n+ layer is done for the formation of source and drain and n-layer for the formation of the channel layer.
24. The channel resistance is high for
A. source contact
B. drain contact
C. gate contact
D. source and drain contacts
Answer: D
The channel resistance is in the order of 1000 to 2500 ohm/square which is too high for source and drains contacts.
25. Stress at the interface cannot arise from
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.
26. 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.
27. 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.
28. 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.
29. 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.
30. 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.
