The separately manufactured components like resistor, capacitor, diode, and transistor are joined by wires or by printed circuit board (PCB) to form circuits. These circuits are called discrete circuits and they have following disadvantages:
To overcome these problems of space conservation and reliability, the integrated circuits were developed.
Integrated Circuit (IC).
An IC comprises a number of circuit components like resistors, transistor etc. They are interconnected in a single small package to perform the desired electronic function. These components are formed and connected within a small chip of semiconductor material. In IC the following features are observed.
The number of components fitted into a standard size IC represents its integration scale, in other words it’s a density of components. It is classified as follows:
It have less than 100 components (about 10 gates).
It contains less than 500 components or have more than 10 but less than 100 gates.
Here number of components is between 500 and 300000 or have more than 100 gates.
It contains more than 300000 components per chip
It contains more than 1500000 components per chip.
Integrated circuits and discrete circuits can be compare as follows:
Usually electronics components such as diodes, resistors and capacitors are made on monolithic integrated circuit (IC). In order to fabricate these IC components impurities are added or diffused in specific place in the semiconductor wafer (i.e substrate) so PN junction can be made Figure (a) shows the cross section area of the basic monolithic components.
All the four components are made inside the P-type substrate or wafer. N-type and P-type portion are made from N-type and P-type materials inside the P-type substrate. However this is done by diffusion process. In this process P-type and N-type materials (in the form of gas) are added in semiconductor wafer at high temperature. Wafer is placed in a high temperature, furnace (of about 100o C)
At first a thin layer of silicon diode SiO2 layer is made at particular areas of N-type layer which are subject to diffusion. The N-type material is diffused in to substrate. Now the first and large N-type potion is diffused inside the substrate.
Again a thin layer of SiO2 is grown over the other new place is selected to diffuse P-type material inside the N-type material. This same process is repeated to diffuse last potion of N-type material.