List the advantages of integrated circuits over discrete components circuits

1 . Miniaturization and hence increased equipment density.
2. Cost reduction due to batch processing
3. Increased system reliability due to the elimination of soldered joints
4. Improve functional performance
5. Matched devices
6. Increased operating speed

Explain why buried layer is needed

In general bipolar integrated circuits use epitaxial layer process in which resistivity epitaxial is formed over low  resistivity substrate to provide isolation between the epitaxial growth and the substrate the doping used in both layers is of opposite type due to this heavily doped buried layer is formed. The buried layer is also called diffusion layer.