Integrated Circuit is type of circuit has various components like resitor,capactior,diode,transistors are fabricated on a small semi counductor chip.These electronics components are connected within a small chip of semiconductor material.In an IC you can not removed or replace any individual components because various components are automatically part of a small semi conductor chip.
size of IC is extemerly small you need microscope to see the compoents.no components are seen above the surface of the chip.
Advantages and Disadvantages of IC
- Increase reliability
- lesser in weight
- smaller in size
- lower power requirement
- low cost
- require less number of external connection
- handle extreme values of temperature
- if one components from IC goes out whole IC has to be replace with the new one.
- High values of capacitance are not fabricated on the IC
- Transfomer and inductors are not possible to fabricate on the IC
- greater than 10w Power is not possible in IC.It can not produce high power
- Lack of flexibility
Classification of Integrated Circuit
There are four basic types of Integrated ICs
Monolithic Ics are most common type used in practice.The Monolithic word is greek word means “one stone” as name suggest it have only one single chip. In monolithic ic all circuit components are formed on single thin wafer this wafer is know as substrate.
Production process of Monolithic Ic:-
First step to make an IC is p-substrate.a A cylindrical p-type silicon grown size of 25cm long and 2.5 diameter.Then the crystal is cut by a diamond show in wafers as shown in figure.thickness of wafer is 200um.The ICs are produce on this wafer.
Epitaxial N layer:
The second step is put the wafer in diffusion furnace.Mixture of silicon atoms and pentavalent atoms is passed over the wafers, which forms a thin layer of n-type of semiconductor.this thin layer is called as the Epitaxial n layer.Thickness of this layer is 10um.In this layer whole integrated ic are formed.
To prevent the contamination of the epitaxial n layer a thin sio2 layer is deposited over the entire surface of chip.thickness of this layer is 1um. pure oxygen is passed over the epitaxial layer.The oxygen atoms are combine with the silicon atoms to form a layer of silicon dioxide.
Using diffusion process appropriate materials are added to the substrate at specific location to produce different components.resistor,capacitors,diodes and transistors are produce using the diffusion process.
oxide layer is etched before any impurity is added to the substrate.The etching process exposes the epitaxial layer and permits the production of desired components.Desire location are etched using eatching.
Wafer are divided into large number of areas.Each of this areas form a seperate chips.The manufacture produce hundreds of Ics on wafer over each area.after that using glass cutting the wafer is divided into small chips.this the main reason for the low cost of Integrated Ics.after the chip is cut mounting and connections are made between IC and external leads.
Thin Film IC
This IC is fabricated on surface of glass or ceramic using depositing films of conducting material. Different components are fabricated by the thick films. The resistors are fabricated by controlling the width and thickness of the films. Different materials are selected for their resistivity.
For capacitors two conducting films sandwiched between the films of the insulating dioxide. For inductor spiral form of film is used. There are two methods are used for producing the thin films. One method is vacuum evaporation and other method is cathode sputtering method. In Vacuum evaporation vaporized material is deposited on a substrate. In cathode sputtering desired film material are deposited between a cathode and an anode.
Thick Film IC
It is also known as the printed thin film circuits. The desired circuit pattern is obtained on ceramic substance using the silk screen printing technique. The inks used for printing are materials that have resistive, conductive or dielectric properties. All these materials are selected by the manufacturer.
The fabrication process of thick film IC is same as the thin film IC.Thick films have advantages over the monolithic ICs. They have a better isolation, better tolerance between the components which provide higher flexibility In circuit design. and also helps in providing high frequency performance. But disadvantages of thick film ICs are they required higher dimensions and space.
Hybrid IC consists of different individual chips on the one chip. This types of ICs are mostly used in high power audio amplifier from 5 watts to 50 watts applications. The active and passive components are diffused on a single chip.The passive components may be thin film components and interconnection are made using metalized pattern.The process is too expensive for the mass production.Based upon the active devices ICs can be classified as the bipolar active devices and unipolar active devices.
Different types of Ic Packages
- Dual in Line Package
- flat pack
- hermatic package
- TO-5 package