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UNIT 2: Modeling and Simulation
Module 1 : Logical faults due to physical faults
TOPIC : Introduction to Faults
Fault
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Fault is any deficiency in the system either during design
or manufacturing which ultimately results in the
deviation in the expected value.
Faults need to be identified and corrected.
A faulty sub-part in a chip might ask for the entire
reconstruction of the chip.
Why to model faults?
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To verify the interconnections of the circuit
Real defects are difficult to analyze
A fault model identifies targets for testing
A fault model makes fault analysis easy
Causes of faults
Faults due to materials
 Faults due to masks
 Faults due to improper order of process steps
 Faults due to error in the design rules
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It is difficult to simulate these faults. So there is a need to
visualize these faults as logical faults so that the analysis
become easier.
Contd …
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Material defects
◦ Surface impurities
◦ Body defects
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Processing defects
◦ Missing contact windows
◦ Parasitic transistors
◦ Oxide breakdown
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Packaging defects
◦ Contact degradation
◦ Seal leaks
Physical faults  Logical faults
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Any physical fault can be represented by logical fault.
Advantages
◦ Fault analysis becomes logical analysis rather than a physical
problem
◦ Many physical faults can be modeled by one logical fault
◦ Logical fault models are technology independent
◦ Some physical faults are too complex to be analyzed