Electromigration (EM) is generally considered to be the result of momentum transfer from the electrons due to high current density. Atoms get displaced from their original position causing voids(opens) & hillocks(shorts) in the metal layer
Joule heating also accelerates EM because higher temperatures cause a higher number of metal ions to diffuse. Under extreme joule heating, melting can occur.
EM causing opens EM causing shorts
Cell EM
Cell EM rules address the EM caused by current within a cell. Cell EM rules operate on the principle that, although the currents within a cell cannot be calculated due to a lack of physical layout information, they can be controlled based on external physical entities.The tool estimates the detrimental effects of currents within a cell as a function of its:
• Output load
• Input slew
• Switching frequency
Wire EM
There are two types of wire EM:
Signal EM -- It is performed net by net ,simulating the charging and discharging for all possible paths to determine the worst case average and rms current for each wire segment.Once currents are determined ,current density is computed.
Power EM -- EM effects produced on power nets is noted as power EM
Techniques to solve EM:
1) Increase the width of the wire
2) Buffer insertion
3) Upsize the driver
4) Switch the net to higher metal layer
Joule heating also accelerates EM because higher temperatures cause a higher number of metal ions to diffuse. Under extreme joule heating, melting can occur.
EM causing opens EM causing shorts
Cell EM rules address the EM caused by current within a cell. Cell EM rules operate on the principle that, although the currents within a cell cannot be calculated due to a lack of physical layout information, they can be controlled based on external physical entities.The tool estimates the detrimental effects of currents within a cell as a function of its:
• Output load
• Input slew
• Switching frequency
Wire EM
There are two types of wire EM:
Signal EM -- It is performed net by net ,simulating the charging and discharging for all possible paths to determine the worst case average and rms current for each wire segment.Once currents are determined ,current density is computed.
Power EM -- EM effects produced on power nets is noted as power EM
Techniques to solve EM:
1) Increase the width of the wire
2) Buffer insertion
3) Upsize the driver
4) Switch the net to higher metal layer
I understand how increasing the width or switching the metal layer of the net help in fixing em ,can you also explain how adding a buffer and upsizing the net helps ?
ReplyDeleteif you buffer the design you effectively reduce the load on the cell.....as you break the net so the effective cap seen by the cell reduces.......
ReplyDeleteif you buffer the design you effectively reduce the load on the cell.....as you break the net so the effective cap seen by the cell reduces.......
ReplyDeleteDriver size should be downsized to solve EM
ReplyDeleteYou should downsize the driver.
ReplyDeleteYes , we should downsize the inverter driver
ReplyDelete