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Monolithic IC

2018-01-26 13:58  
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Basic Monolithic IC Circuit

Monolithic IC circuit

Monolithic IC circuit

A simple circuit consisting of a diode, a resistor and a transistor is shown in figure. The cross-sectional view of the IC corresponding to the circuit shown in figure is depicted in other fig. The basic structure of an IC consists of the four layers of different materials. The bottom most layer, typically 200 u m thick, is a P-type silicon and serves as the body or substrate upon which the complete IC is built.

The second layer, typically 25 am thick, is of N-type silicon material which is grown?as a single crystal extension of the substrate. All active and passive elements like diodes, transistors, resistors and capacitors are fabricated or built in this layer employing series of P-type and N-type impurity diffusions.

The third layer is of silicon dioxide (Si02) material and acts as a barrier in the selective diffusion in the second layer. This Si02 layer is etched away from the region where diffusion is desired to be permitted, the rest of the wafer remaining protected against diffusion. The etching is done by subjecting the Si02 layer to a photolithographic process. This Si02 layer serves the additional function of protecting the silicon wafer against contamination.
The fourth layer is a metallic layer of aluminium. This is added at the top in selected regions to permit interconnections between the different fabricated components.

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