Classification Of Integrated Circuits

An integrated circuit (IC) is a self contained chip that has such components as resistors, transistors, capacitors etc in a small package. Other components needed in the circuit can be connected to the IC through its external terminals. The classification below is in accordance to fabrication or manufacturing techniques applied. Thus the ICs are classified as monolithic ICs, thin and thick-film ICs, hybrid ICs.

 

Monolithic ICs
Monolithic ICs are the most commonly used type of ICs. In monolithic ICs, all types of components are fabricated with their interconnections on a single wafer called a substrate. Monolithic ICs have both active components

such as diodes, transistors etc. and passive components such as capacitors and resistors all fabricated on the same wafer. This property allows for mass production of ICs since the same wafer can be used to produce large number of identical ICs. This reduces the cost of production and consequentially the general cost of the circuit and hence making monolithic ICs the most popular ICs in practice.

 

Thin and Thick-film ICs
In thin and thick-film ICs only the passive components like resistors and capacitors are fabricated. The active elements like transistors are attached externally in discrete circuits. The difference between thin and thick-film ICs is the film deposition during fabrication and not their thickness. They actually resemble in size and characteristic.

 

In thin-film ICs, a film of conductor material is deposited on a ceramic or a glass surface while controlling its width. Different resistive materials are

selected and added accordingly to required resistance to form resistors. To make capacitors, an insulating oxide is sandwiched between two conducting films. This fabrication is done by two methods, vacuum evaporation method and cathode sputtering method.

 

In thick-film ICs fabrication, the method of silk-screen printing is applied to create the anticipated circuit patterns on ceramic substrates. Stainless steel meshes are used to make the screens and hence interconnections while the ink pastes used have conductive, dielectric or resistive properties to make resistors and capacitors. To fuse these films to the substrate, the contents are heated in a furnace.

 

Though the thick and thin-film ICs are larger in size than monolithic ICs, they have better tolerances than monolithic ICs. They are also better in flexibility and in circuit design and provide a better high frequency performance than monolithic ICs.

 

Hybrid ICs
Also known as multi-chip ICs, they are circuits fabricated by interconnecting a number of other chips as their names suggest. Interconnections between the chips are provided by wiring a metal plated circuit pattern. The passive and active components are fabricated by diffusing their related elements together. Hybrid ICs are most suitable and most popular in high power applications.