BIPOLAR IC CONSTRUCTION:

As mentioned earlier, the components that are commonly used in IC's are diodes, Transistors, resistors and capacitors. 

Diffusing impurities into selected regions of a semiconductor wafer (substrate) can form these components.  This process roduces PN junctions at specific locations and the basic manner in which these four components are formed and the manner in which they are interconnected are shown at Figure.

The circuit shown in figure  is a simple circuit consisting of a capacitor, a PN junction diode, an NPN transistor and a resistor.  Operating voltages and currents can be applied to the circuit through terminals 1,2 and 3 as shown.  This circuit could be easily constructed using four discrete components, however, it can also be produced as a monolithic IC.