Linear Integrated Circuits (LIC) - Unit 1 Question Bank with answers


LINEAI INTEGRATED CIRCUITS AND APPLICATION

UNIT-I ICs FABRICATION

Part-A

1. Mention the advantages of integrated circuits.

*Miniaturisation and hence increased equipment density.
*Cost reduction due to batch processing.
*Increased system reliability dueto the elimination of soldered joints
* Improved functional performance.
*Matched devices.
*Increased operating speeds.
*Reduction in power consumption.

2. Write down the various processes used to fabricate IC’s using silicon planar technology.

*Silicon wafer preparation.
* Epitaxial growth
* Oxidation.
*photolithography
*Diffusion
*Ion implantation.
* Isolation.
*Metallisation
*Assemb]y processing and packaging.

3. What is the purpose of oxidation?

*Si02 is an extremely hard protective coating and is unaffected by almost all
reagents.
*By selective etching of Si02, diffusion of impurities through carefully defined
windows can be accomplished to fabricate various components.

4. Why aluminum is preferred for metallization?

*It is a good conductor.
*It is easy to deposit aluminium fi]ms using vacuum deposition,
*lt makes good mechanical bonds with silicon.
*Jt forms a low resistance contact,

5. What are the popular IC packages available?

a. Metal can package.
b. Dua]-in-line package.
c. Ceramic flat package

6. Name the parameters which governthe thickness of the film in the oxidation process.

The main parameters which governs the thickness of the film in the oxidation process is temperature.because to grow the oxide layer high temperature is to be maintained,The other important parameters governing oxide film thicknessare time up to which process is to be carried out and the moisture contents

7. What do you mean by monolithic process?

Monolithic process means a circuit fabricated from a single stone or a single crystal.The origin of the word ‘monolithic’ is from the Greek word monos meaning ‘single’ and lithos meaning ‘stone’,so monolithic integrated circuits are ,in fact,macle in a single piece of single crystal silicon

8. List the advantages of integrated circuits over discrete component circuit

1. Practically size of an IC is thousands of times smaller than the discrete circuits.
2. ICs operate at low voltages
3. The cost of IC is very less
4. The power consumption is less

9. What are various steps involved in basic planar process of IC fabrication.

(a)Crystal growth and wafer preparation :
(b)Epitaxial growth
(c)Oxidation
(d)Lithography
(e)Reactive plasma etching
(f)Diffusion
(g)lon implantation

10. What are the limitations of integrated circuits?

i) Does not withstand higher voltages
ii)lt generate heat while running, but does not withstand in higher temperature. So heat sink (or / and) fan must be placed.

11. What is the advantage of using dry etching process?
I .Gaseous mixture is used as the chemical reagent.
2,Smaller line openings are possible with dry etching
3.lt produces straight walled etching process.

12. What is meant by epitaxial growth?

The epitaxy means arranged upon’. In epitaxy a monocrystallifle film is formed on the top of a monocrystalline surface. The epitaxy is crystalline growth process in which the foundation layer, i.e. substrate works as seed crystal. The epitaxial layer formed on the substrate may be either n-doped or p-doped or intrinsic.

13. What are the advantages of ion implantation technique?

(i)The impurity concentration is highly uniform typically with in 1%,over the wafer
(ii)The degree of uniformity is maintained same form wafer to wafer
(iii)The layer can be formed anywhere with in substrate
(iv)The lateral spread is very small

14. What is ion implantation?,

Ion implantation is the introduction of ionized particles atoms into targets with enough energy to penetrate beyond surface regions.

15. Name the different types of lC packages.

Dual-in-line, Single-in-line, Zigzag-in-line, Quad-in-line, Small outline,Chip carrier, Flat pack, Pin Grid Array (PGA).

16. Classify IC’s based on the fabrication.

Monolithic ICs, thick-thin film ICs, hybrid ICs.
17. Give reason for selecting Si02 for wtidation process n IC fabrication.
(i)lt act as mask
(ii)lt provides surface passivation
(iii) It acts as a component ¡n MOS structure
(iv) It provides electrical isolation between multi-level ititerconnected layers.

Part-B

1. Explain in detail the fabrication of ICs using silicon planar technology. (16)
2. Explain the process of epitaxial growth IC fabrication with neat diagram? (8)
3.Explain the fundamental of monolithic IC technology using suitable circuit? (16)
4.Explain the process of photolithography. (8)
5.Compare Ion implantation with diffusion. (8)
6. What are the different ways by which the diode structure can be realized in IC? (8)
4 Explain the importance of isolation and discuss the method of isolation. (8)
8. Explain the various steps ¡nvolved in the process of fabricating monolithic IC (16)