Integrated Circuit (IC) Fabrication MCQ [Free PDF] – Objective Question Answer for IC Fabrication Quiz

81. How the ohmic contact is formed in a metal-semiconductor diode? (AL-Aluminium)

A. n+ diffusion in p-region near AL lead
B. p+ diffusion in p-region near AL lead
C. n+ diffusion in n-region near AL lead
D. p+ diffusion in n-region near AL lead

Answer: C

Aluminum is a p-type impurity in silicon. So, when it is used to make a contact with n-type silicon, its essential contact is ohmic and no PN-junction is formed. Therefore, the contact is done by making n+ diffusion in the region near the surface where aluminum is deposited.

 

82. The flow of current in the Schottky barrier diode is due to

A. Majority and Minority carriers
B. Majority carriers
C. Minority carriers
D. None of the mentioned

Answer: B

When the diode is forward biased, electrons flow from semiconductor to metal (where electrons are abundant). Hence, the majority of carrier ‘electrons’ carry current in the Schottky diode.

 

83. Find the application areas, where the Schottky diode can be used?

A. Radio-frequency
B. Power rectifier
C. Clamping diode
D. All of the mentioned

Answer: D

The Schottky diode can be used for ideal clamping or as a detector in high-frequency microwave ICs. Therefore, it is used for all these applications.

 

84. Which of the following resistor is not used as an integrated resistor?

A. Poly gate resistor
B. Pinched resistor
C. Epitaxial resistor
D. Thin film resistor

Answer: A

Except for poly gate resistors, other resistors are integrated resistors.

 

85. Which of the following is not true about diffused resistors?

A. Limitation due to small range of resistance
B. Resistance depends upon surface geometry
C. Resistance depends on diffusion characteristics of the material
D. Diffused resistors are non-economical

Answer: D

In diffused resistor method, the resistors are very economical as no extra fabrication steps are required.

 

86. Determine the formula for sheet resistance (Rs).

A. R×L×W
B. R×(L×ρ)/W
C. R×(W/L)
D. R×(W×ρ)/L

Answer: C

The formula for sheet resistance of a material of surface dimensions L and W is

Rs = R×(W/L).

 

87. Consider a 52cm×52cm material of uniform resistivity 100Ωm and thickness of 3cm. Find the area and resistance of this sheet of material.

A. 16 m2, 1.923 Ω/square
B. 8112 cm2, 1.733 Ω/square
C. 156 cm2, 33.33 Ω/square
D. 901 cm2, 3.333 Ω/square

Answer: C

Area = L × t= 52cm×3cm=156 cm2

=> Sheet resistance RS = (ρ×L)/(L×t)

= ρ/t = 100 Ω m/3m =33.33 Ω/square.

 

88. If a 25Ω diffused resistor is to be designed for an emitter resistor, determine the pattern in which it is fabricated?

A. 20mil long by 5mil wide
B. 25mil long by 1mil wide
C. 5mil long by 1mil wide
D. 16mil long by 4mil wide

Answer: B

The sheet resistance of n-type diffused resistor is 5Ω/square.

=> L/W=R/RS= 25Ω/5Ω = 5/1

=> 5mil long by 1mil wide.

 

89. The number of squares contained in the integrated resistor by diffused resistor method depends on the ratio of

A. ρ/t
B. ρ×L/W
C. W/L×t
D. L/W

Answer: D

The number of squares contained in the resistor depends on the surface geometry. This is given by, the ratio L/W is called the aspect ratio of surface geometry.

 

90. Match the sheet resistance value for the following region in diffused resistor

1. Epitaxial Collector region i. 200Ω/square
2. p-type base region ii. 1 to 10kΩ/square
3. n-type emitter region iii. 5Ω/square

A. 1-I, 2-ii, 3-iii
B. 1-ii, 2-I, 3-iii
C. 1-iii, 2-I, 3-ii
D. 1-iii, 2-ii, 3-i

Answer: B

The mentioned values are sheet resistance values for the respective diffused resistors.

 

91. Which integrated resistor can achieve a high value of sheet resistance?

A. Pinched resistor
B. Epitaxial resistor
C. Thin film resistor
D. All of the mentioned

Answer: A

In a pinched resistor, the sheet resistivity can be increased by reducing its effective area. This technique is used to achieve a high value of sheet resistance from the ordinary diffused resistor.

 

92. How pinched resistor can give resistance in the order of mega-ohm in a reasonably small area?

A. By increasing fabrication steps
B. By offering bulk resistance in n-region
C. By reducing the conduction path
D. By limiting the thickness of are

Answer: C

In a pinched resistor structure, one of the diodes conducts in the reverse direction and only a small reverse saturation current can flow through n-type material. By doing so, the effective cross-sectional area of the conduction path will be reduced and resistance between two contacts lead increases.

 

93. Which of the following is not used as a metallic film in the thin film resistor?

A. Nichrome (NiCr)
B. Tantalum (TA.
C. Stannic oxide (SnO2)
D. Silicon dioxide (SiO2)

Answer: D

Silicon dioxide is the non-metallic layer on which the metallic thin films are deposited.

 

94. Pick out the incorrect statement

A. Sheet resistance has smaller and lesser parasitic components
B. Value of the resistor can be easily adjusted after fabrication
C. Resistance in the range 100kΩ possible using nichrome resistors
D. Thin film resistors are more stable

Answer: C

Typically, the sheet resistance value of nichrome is 40 – 400Ω/square (depending upon film thickness). So, the resistance in the range of 20 to 50kΩ can only be obtained.

 

95. The capacitance of the junction capacitor does not depend upon

A. Impurity concentration of p-type epitaxial layer
B. Impurity concentration of n-type epitaxial layer
C. Area of the junction
D. Voltage across the junction

Answer: A

There is no p-type epitaxial layer present in junction capacitor. But a p-type substrate is present and it forms one of the junctions in the junction type IC capacitor.

 

96. Which is used as the dielectric layer in MOS Capacitor?

A. Silicon Nitride (Si3N4)
B. Aluminium oxide (Al2O3)
C. Tantalum oxide (Ta2O5)
D. All of the mentioned

Answer: D

Si3N4 offers a higher value of capacitance. Whereas, Al2O3 and Ta2O5 are preferred for large values of capacitance. Hence all of them are used as a dielectric layer.

 

97. Which is considered to be a serious disadvantage of the thin-film capacitors, when Al2O3is used as the dielectric?

A. Additional fabrication step required
B. It requires over-voltage protection
C. Higher dielectric constant value is required
D. All of the mentioned

Answer: B

One of the serious disadvantages of the thin-film capacitor is that it fails when the voltage rating exceeds due to the breakdown of the dielectric, which is a destructive and irreversible failure mechanism and it requires over-voltage protection.

 

98. In MOS capacitor, the preference in the dielectric layer is given to Silicon Nitride (Si3N4) because

A. It makes capacitor non-polar
B. It contains a small resistance
C. It offers less processing step
D. It reduces the failure mechanism

Answer: A

Si3N4 gives more circuit flexibility by being non-polar, that is, it does not matter which plate is positive or negative and the voltage applied.

 

99. Why inductor is avoided in the Integrated Circuit component?

A. They provide many losses compared to other IC components
B. IC devices are essentially two dimensions
C. Device density of IC increases
D. Fabrication process of these components is complicated

Answer: B

Usually, IC devices are very small (~1 to 10µm). Even if an IC inductor is made in form of a flat metallic thin film spirals. The very small value of the order nano henry with a low-quality factor can only be obtained.

 

100. Which circuit is used to replace inductors in IC components?

A. RC active network
B. PN-junction diode
C. LC active network
D. None of the mentioned

Answer: A

Circuit designers go to great lengths to avoid the use of inductors or otherwise simulate them by using RC active networks.

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