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Integrated Circuits

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Introduction

Integration allows complex circuits consisting of thousands of transistors, diodes,

resistors and capacitors to be included in a chip of semiconductor.

Advantages of integration includes:

Low cost (many identical circuits can be built simultaneously on a single silicon

wafer. this process is called batch fabrication. Although processing steps for

wafer are complex and expensive, the large number of resulting IC makes theultimate cost fairly low).

Reliability (all devices and interconnection are made on the same substrate

minimizing failures due to soldered interconnections of discrete components).

Reduces the overall size of the unit.

Feasible to replace. Better response time and the speed of signal transfer between the circuits.

Reduction of parasitic between circuits.

High yield.

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Types of integrated circuits

ICs can be classified in two ways: may be on the basis of their

fabrication(monolithic and hybrid) or the basis of theirapplications (linear and digital).

Linear IC performs amplification or other linear operations on

the signals. e.g op-amps and simple amplifiers. Digital IC require only on-off operation of transistors. They

involve logic and memory. They find application in calculators,computers etc.

IC that are included entirely on a single chip is calledmonolithic IC.

A hybrid IC may contain one or more monolithic IC bonded toan insulating substrate with appropriate interconnections.

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nMOS process Integration

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TESTING, BONDING AND PACKAGING

The handling and packaging of individual circuits can be most critical steps from theviewpoints of cost and reliability. The individual IC chip must be connected properly tooutside leads and packaged in a way convenient for use in larger circuits.

Testing

After the wafer of monolithic circuits has been processed and finalmetallization pattern defined, it is placed in a holder under microscope andaligned for testing by multiple point probe. A series of tests are made to checkelectrical properties of device. The information is fed into the computer whichcompares the result with information stored in its memory, and a decision ismade regarding the acceptability of the IC. Then each die that passed the testis picked up and placed in a package.

Bonding

The method used for making contacts from monolithic chip to the package wasbonding of fine Au or Al wires. If a chip is to be wire bonded, it is first mountedsolidly on metalized region of the package . Once the chip is mounted, theinterconnecting wires are attached from various contact pads to posts on thepackage.

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Packaging The final step in IC fabrication is packaging the device in a suitable

medium that can protect it from the environment. The choice of

package types must be made within the requirements of the

application and cost considerations. The chip is mounted on astamped metal lead frame and wire bonding is done between chip and

the leads. The package is formed by applying a ceramic or plastic case.

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IC packages