Integrated Circuits Interview Questions and Answers:

1. What is an IC?

Ans. An integrated circuit (IC) is one in which all active and passive components such as transistors, diodes, resistors, capacitors etc. are automatically part of a small semiconductor chip.

2. Why are ICs so cheap?

Ans. ICs are so cheap because of simultaneous production of hundreds of similar circuits on a small semiconductor wafer.

3. Why do ICs need small power for their operation?

Ans. ICs need small power because of their small size.

4. Why are ICs more reliable than discrete circuits?

Ans. ICs are more reliable because of elimination of soldered joints and need for fewer interconnections.

5. What are the advantages of ICs over discrete component circuits?

Ans. The advantages of ICs over discrete component circuits are extremely small size, very small weight, very low cost, lower power consumption, more reliability, easy replacement, increased operating speed, close matching, improved functional performance, suitability for small signal operation etc.

6. What are various classification of ICs?

Ans. On the basis of fabrication techniques used ICs can be divided into three classes viz. monolithic ICs, thin- and thick-film ICs and hybrid or multichip ICs.

Based upon the active devices employed the ICs can be clas­sified as bipolar ICs using bipolar active devices (BJTs) and unipolar ICs using unipolar active devices like FETs.

Bipolar and unipolar ICs may further be classified depending upon the isolation technique or type of FET used

On the basis of density, the ICs are classifled as SSI, MSI, LSI, VLSI, ULSI and GSI ICs.

On the basis of mode of operation, ICs are classified as linear or analog ICs, digital ICs and mixed signal ICs.

7. What are linear ICs ?

Ans. ICs are known as linear ICs whose inputs and outputs can take on a continuous range of values and outputs are generally pro­portional to the inputs.

8. Explain the difference between digital and linear ICs.

Ans. Linear ICs are equivalent of discrete transistor networks whereas digital ICs are completely functioning logic networks that are equivalents of basic transistor logic circuits.

Linear ICs are concerned with numerous level of voltages whereas digital ICs are primarily concerned with only two lev­els of voltage (or current) —low or high.

Linear ICs are used as amplifiers, filters, frequency multi­pliers, modulators etc. whereas digital ICs are used to form such circuits as gates, counters, multiplexers, demultiplexers etc.

Linear ICs need accurate control of operating region char­acteristics whereas digital ICs do not need accurate control of operating region characteristics.

9. What is meant by monolithic IC?

Ans. A monolithic IC is one in which all circuit components and their interconnections are formed on a single thin wafer, called the substrate.

10. Why is SiO₂ layer formed over the entire surface in a monolithic IC?

Ans. SiO₂ layer is formed over the entire surface so as to prevent the contamination of the epitaxial layer.

11. How is SiO₂ layer formed in a monolithic IC?

Ans. The SiO₂ layer is grown by exposing the epitaxial layer to an oxygen atmosphere to about 1,000°C.

12. In ICs the substrate is not employed as collector. Why?

Ans. If in ICs the substrate is employed as collector, all transistors fabricated on one substrate would have their collectors con­nected together.

13. Why is the diffusion technique of formation of resistors most widely used?

Ans. The diffused resistors can be processed while diffusing transis­tors, so the diffusion technique is the cheapest and, therefore, is most widely used.

14. Give reasons of choosing silicon for fabricating general pur­pose IC chips.
Ans. Silicon is chosen for fabrication of general purpose IC chips because of the following reasons:

1. Silicon is available in abundance in the form of sand.
2. Silicon is thermally stable, and therefore, can withstand high temperature.
3. Silicon can be grown into single structure using CZ and float zone method.
4. Silicon has less leakage currents because of its moderate band-gap.
5. Silicon forms native oxide SiO₂ which is extremely useful as an insulator.
6. High voltage rectifying devices and certain infrared sensing devices are practical with silicon owing to much higher intrinsic resistivity of silicon (230 Ω-m) as compared to that of germanium (0.47 Ω-m).

15. Why an inductor cannot be fabricated on IC?

Ans. Inductor cannot be fabricated on an IC chip because the inductor has large number of turns and bulky in size and connections interior to the semiconductor chip are not possible in IC, which are essential.

16. Why is the plastic DIP IC package most widely used?

Ans. The plastic dual-in-line package is much cheaper than other types of packages and is, therefore, most widely used.