Library Exchange Format (LEF)

LEF stands for Library Exchange Format. It is also termed as physical library, because this file contains physical abstract information of Layers and standard cells / macros. It is implemented in ASCII format, so it can be readable by human.These physical libraries generated by the library vendors or foundries.

Physical libraries are two types:

• Technology LEF
• Standard cell/macro LEF

Technology LEF

Technology LEF will have information of library version, units, manufacturing grid and layers information.

• Library version: This field show the library version.
  • Example: VERSION 5.1
• Unit definition:This field contains information ofunits likedatabase, time, capacitance and resistance information. Values specified in the file will be multiplied with units.
  • Example:CAPACITANCE PICOFARADS 1 ;
• Manufacturing grid: The minimum metal length that can be manufacturedis called manufacturing grid.
  • Example:MANUFACTURINGGRID 0.005 ;
•  Site: Site is the minimum standard cell area that can be manufacturable.
  Example: SITE CoreSite
  CLASS CORE ;
  SIZE 0.2 BY 1.71 ;
  END CoreSite
• Layer information:This field contains information like Layer name, Type, Direction, Pitch, Width, Area, Spacing and thickness, etc…,
  • Template: Layer name (like poly, contact, via1, metal1 etc)

                         Layer type ( like routing, masterslice, cut etc)

                         Prefered direction (like horizontal or vertical)

                         Pitch

                         Minimum width

                         Spacing 

                         Sheet resistance

Following images shows the example of basic technology LEF file:

Standard Cell/Macro LEF

This LEF contains abstract view of each and every standard cell. The cell LEF contains basic information like Cell name, Class, Origin, Size, Symmetry, Pin information(pin name, direction, shape, etc…)