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INTEGRATED CIRCUITS ppt
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     An integrated circuit (IC) is a miniature ,low cost electronic circuit consisting of active and passive components fabricated together on a  single crystal of silicon. The active components are transistors and diodes and passive components are resistors and capacitors.
 
 
INTEGRATED CIRCUITS
 
Advantages of integrated circuits
Miniaturization and hence increased equipment density.
Cost reduction due to batch processing.
Increased system reliability due to the elimination of soldered joints.
Improved functional performance.
Matched devices.
Increased operating speeds.
Reduction in power consumption
 
Basic processes involved in fabricating Monolithic ICs
 
1.         Silicon wafer (substrate) preparation
2.         Epitaxial growth
3.         Oxidation
4.         Photolithography
5.         Diffusion
6.         Ion  implantation
7.         Isolation technique
8.         Metallization
9.         Assembly processing & packaging
 
Silicon wafer (substrate) preparation
 
1.Crystal growth &doping
2.Ingot trimming & grinding
3.Ingot slicing
4.Wafer policing & etching
5.Wafer cleaning
 
Epitaxy means growing  a single crystal    silicon structure upon a original silicon substrate, so that the resulting layer is an extension of the substrate crystal structure.
The   basic    chemical    reaction   in the epitaxial growth  process of  pure  silicon is  the  hydrogen reduction  of  silicon tetrachloride.                                                                                          
                                                     1200oC 
                                    SiCl+ 2H <----------->  Si + 4 HCl 
 
1. SiO2 is an extremely hard protective coating & is unaffected by almost all reagents except by hydrochloric acid. Thus it stands against any contamination.
2.  By selective etching of SiO2, diffusion of impurities through carefully defined through windows  in the SiO2 can be accomplished to fabricate various components.
 
Oxidation
 
                              
     The silicon wafers are stacked up in a quartz boat & then inserted into quartz furnace tube. The Si wafers are raised to a high temperature in the range of 950 to 1150 oC &  at the same time, exposed to a gas containing O2 or H2O or both. The chemical action is
 
                 Si + 2HO-----------> Si O2+ 2H2
 
Oxidation
 
oxide
thickness
 
    Photolithography
 
             The  process   of  photolithography    makes   it  possible   to  produce  microscopically  small circuit  and  device  pattern on  si wafer
 
 
        Two processes involved in photolithography

      a)  Making a photographic mask

       b)  Photo etching
 
           The development of photographic mask involves the preparation of initial artwork and its diffusion.  reduction, decomposition of initial artwork or layout into several mask layers.
 
            Photo etching
 
            Photo etching is used for the removal of SiO2 from desired regions so that the desired2impurities can be diffused
 
Diffusion
 
                        The process of introducing impurities into selected regions of a  silicon wafer is called diffusion. The rate at which various impurities diffuse into the silicon  will  be of the order of 1µm/hr at the temperature range of 9000 C  to  11000C .The impurity atoms have the tendency to move from regions  of  higher concentrations to lower concentrations
 
Ion implantation technique
 
1.  It is performed at low temperature. Therefore, previously diffused regions have a lesser tendency for lateral spreading.
2.  In diffusion process, temperature has to be controlled over a large area inside the oven, where as in ion implantation process, accelerating potential & beam content are dielectrically controlled from outside.
 
Dielectric isolation
 
In dielectric isolation, a layer of solid dielectric such as SiO2 or ruby completely surrounds each components thereby producing isolation, both electrical & physical. This isolating dielectric layer is thick enough so that its associated capacitance is negligible. Also, it is possible to fabricate both pnp & npn transistors within the same silicon substrate. 
 
Metallization
 
                         The process of producing a thin metal film layer that will serve to make interconnection of the various  components  on the chip is called metallization.
 
Aluminium is preferred for metallization
 
It is a good conductor
it is easy to deposit aluminium films using vacuum deposition.
It makes good mechanical bonds with silicon
It forms a low resistance contact



IC packages available
 
Metal can package.
Dual-in-line package.
Ceramic flat package.
 
UNIT-II
Characteristics of Op-Amp
 
OPERATION AMPLIFIER
 
                        An operational amplifier is a direct coupled high gain amplifier consisting of one or more differential amplifiers, followed by a level translator and an output stage.
 
                        It is a versatile device that can be used to amplify ac as well as dc input signals & designed for computing mathematical functions such as addition, subtraction ,multiplication, integration & differentiation
Op-amp symbol
 
Ideal characteristics of   OPAMP
 
Open loop gain infinite
Input impedance infinite
Output impedance low
Bandwidth  infinite
Zero offset, ie, Vo=0 when V1=V2=0
 
Inverting Op-Amp
 
Non-Inverting Amplifier
 
Voltage follower
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