This set of VLSI Questions and Answers for Aptitude test focuses on “GaAs Fabrication -3”.
1. Which has lightly doped channel?
Explanation: The E-MOSFET structure is similare to that of D-MOSFET except for a shallower and more lightly doped channel.
2. To begin conduction, E-MOSFET requires
a) negative gate voltage
b) positive gate voltage
c) negative drain voltage
d) positive drain voltage
Explanation: In E-MOSFET channel is in pinch-off at zero gate voltage. A positive gate voltage is required for the channel to begin conduction.
3. Wafer preparation takes place in
a) first-level metal phase
b) second-level metal phase
c) encapsulation phase
d) ion implantation phase
Explanation: Encapsulation phase is the first phase and it includes wafer preparation. Encapsulation is a process of deposition of first-level insulator Si3N4.
4. Steps involved in ion implantation phase is
c) alignment mark mask
Explanation: Anneal is a process involved in ion implantation phase along with other processes like si+ implant mask, channel implant, source drain mask etc.
5. For the formation of E-MESFET _______ is used
a) n- implantation
b) n+ implantation
c) p- implantation
d) p+ implantation
Explanation: A n- implantation is used for formation of E-MESFET and n+ implantation for the formation of D-MESFET.
6. To activate a dopant, _______ is necessary
a) low temperature stable gate
b) low temperature stable drain
c) high temperature stable gate
d) high temperature stable drain
Explanation: The anneal cycle requires a stable temperature of 850 degree celcius to activate the dopants it is necessary to choose high temperature stable gate.
7. The voltage swing for schottky barrier gate should be
c) very high
d) very low
Explanation: Schottky barrier gates on GaAs cannot be forward biased above 0.7 to 0.8 volt, the permissible voltage swing should be relatively low.
8. The E-MESFET is defined by intersection of
a) red and yellow masks
b) green and red masks
c) brown and red masks
d) green and yellow masks
Explanation: E-MESFET is defined by intersection of green and red masks and D-MESFET is defined by intersection of green, red and yellow masks.
9. E-JFET technology has
a) low voltage swing
b) high current swing
c) high power requirements
d) high voltage swing
Explanation: E-JFET technology for ultra high speed VLSI has reduced power requirements with larger logic voltage swings.
10. In a CE-JFET, the ratio of electron mobility to hole mobility is equal to
Explanation: In a CE-JFET, the ratio of effective channel electron mobility of the n-channel device to hole mobility of the p-channel device is equal to 10.
11. Equal number of p and n devices in a device will consume
a) small area
b) large area
c) all of the mentioned
d) none of the mentioned
Explanation: The circuits requiring equal numbers of p and n devices will consume large areas. Thus one must use other design methods such as precharge techniques.
12. In high electron mobility transistor, the electrons are
a) far apart
b) high mobility
c) near by and low mobility
d) far apart and high mobility
Explanation: The electrons in high electron mobility transistor are spacially separated from ionized donors and they exhibit high mobility.
Sanfoundry Global Education & Learning Series – VLSI.
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