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 drain contacts.
102. 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.
103. 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.
104. 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.
105. 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.
106. 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.
107. 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.
108. 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.
109. The 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.
110. 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.
111. The plasma-enhanced chemical vapor deposition process is used for the 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.
112. Which method uses plasma excitation?
A. PECVD
B. low-pressure CVD
C. high-pressure CVD
D. sputtering
Answer: A
PECVD (plasma-enhanced chemical vapor deposition) method uses plasma excitation in addition to usual thermal energy.
113. Which causes degradation of transconductance?
A. low source resistance
B. high source resistance
C. low drain resistance
D. high drain resistance
Answer: B
The very thin undepleted n- layer causes high source resistance and this causes the degradation of the transconductance gm.
114. Cuts are not needed for
A. ohmic contacts
B. Schottky barriers
C. interconnect metallizations
D. joining two layers
Answer: D
Cuts are made in dielectric only where ohmic contacts, Schottky barriers, and interconnect metallizations are required and not for joining any two layers.
115. Which is the less costly material that can be used for first-level metal?
A. gold
B. platinum
C. aluminum
D. titanium
Answer: C
Gold is the more costly material used for first-level and second-level metal layers whereas aluminum is the less costly material that can be used.
116. ________ is controlled by varying ion flux and velocity.
A. doping density
B. doping thickness
C. doping rate
D. doping material
Answer: A
Doping density and dopants distribution in the semi-insulating material is controlled by varying the ion flux and velocity.
117. The extent of damage to crystal depends on
A. target mass
B. mass of the implanted ion
C. dose
D. all of the mentioned
Answer: D
The extent of damage to the crystal depends on several factors such as the mass of the implanted ion, target mass, energy associated with the ion, dose, temperature, and displacement energies.
119. Which has a lightly doped channel?
A. E-MOSFET
B. D-MOSFET
C. E-JFET
D. CE-JFET
Answer: A
The E-MOSFET structure is similar to that of D-MOSFET except for a shallower and more lightly doped channel.
120. To begin conduction, E-MOSFET requires
A. negative gate voltage
B. positive gate voltage
C. negative drain voltage
D. positive drain voltage
Answer: B
In E-MOSFET channel is in pinch-off at zero gate voltage. A positive gate voltage is required for the channel to begin conduction.
