​ EMIR meaning:

• Electromigration / IR drop
• Mainly occurs when the cross-sectional area of metal interconnects is less.

1] Electromigration
Occurs when: High current density passes through a smaller cross-section area metal interconnect
How: The momentum of current-carrying electrons get transferred to the metal ions during the collision between them
Causes: Due to the momentum transfer, the metal ions may get drifted in the direction of the motion of electrons.


    

electromigration effect: Drift of metal ions from their original position
current density: The amount of electric current traveling per unit cross-section area
Momentum: mass in motion, here electron

J = I/A
I: current 
A: cross-section of the area of interconnect
J: Current Density


Moore's Law: the number of transistors on a microchip doubles every two years

 technology node ∝ Cross-sectional area of the metal interconnects
       <90 nm                 smaller
 

As Area 'A' decreases, Current Density 'J' increases.
current density ‘J’ = charge density * velocity
momentum , so when v increases, momentum increases.
So, more chance of electromigration effect.

Mean Time To Failure (MTTF) is an indication of the life span of an integrated circuit. MTTF is calculated using Black's equation as below.

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Where A = Cross-Section area
            J = Current density
            N = Scaling factor (normally set to 2)
            Ea = Activation energy
            K = Boltzmann's constant = 1.38064852 × 10-23 m2 kg s-2 K-1
            T = Temperature in Kelvin 

Scaling factor: an integer by which the dimensions of interconnects shrink down.
Activation energy: the minimum amount of energy that is required to activate atoms or molecules to a condition in which they can undergo physical transport.



Effects of EM

Void: If the incoming ion flux is lesser than the outgoing ion flux, It will create a void in interconnect. A void can lead to a discontinuity in the interconnect and result in an open circuit. 
Hillocks: If incoming ion flux is greater than the outgoing ion flux, It will cause the accumulation of ions and create a hillock in the interconnect. A hillock can increase the width of a metal interconnect and touch the neighboring metal interconnect which may result in a short circuit.

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Prevention techniques for  EM:

• Copper instead of Aluminium: withstand approximately 5 times more current as compared to Aluminium
• Increase the metal width to reduce the current density
• Reduce the frequency
• Lower the supply voltage
• Keep the wire length sort
• Reduce the buffer size in clock lines

2] IR drop issue
                          
                  ​
V2 = V1 - I.R

two types of IR drop:
Static IR drop: the circuit is in the static stage
Dynamic IR drop: the circuit is in a functional state
 
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Reasons:

• Poor design of power delivery network (lesser metal width and more separation in the power stripes)
• Inadequate number of decap cells availability

• degradation of individual deep-submicron transistors à hot-carrier-Induced (HCI) degradation

Deep submicron technology means, using transistors of smaller size with faster switching rates.
‘Submicron’ Name is due to 0.35um>0.25um>0.18um>0.13um as reduced in sizes of micron level.
   
Electric fields  ∝ increase in speed of carriers
Acceleration of carriers increases, they travel from source to drain, and on the drain side they shatter the surrounding silicon atoms, results in the splitting of each atom into two new carriers:

• one-electron
• one-hole