Technology LEF

Technology LEF contains the rules pertaining to the process you are using for fabrication.
The LEF file is an ASCII representation and includes layer, via, placement site type etc.

A technology LEF file contains all of the LEF technology information for a design, such as
placement and routing design rules, and process information for layers. A technology LEF file
can include any of the following LEF statements:

> [VERSION statement]  
> [BUSBITCHARS statement]  
> [DIVIDERCHAR statement]  
> [UNITS statement]  
> [MANUFACTURINGGRID statement]  
> [USEMINSPACING statement]  
> [CLEARANCEMEASURE statement ;]  
> [PROPERTYDEFINITIONS statement]  
> [LAYER (Nonrouting) statement  
> | LAYER (Routing) statement] …  
> [MAXVIASTACK statement]  
> [VIA statement] …  
> [VIARULE statement] …  
> [VIARULE GENERATE statement] …  
> [NONDEFAULTRULE statement] …  
> [SITE statement] …  
> [BEGINEXT statement] …  
> [END LIBRARY]

Let us see some of the important statements

Bus Bit Characters

[BUSBITCHARS "delimiterPair" ;]

Specifies the pair of characters used to specify bus bits when LEF names are mapped to or
from other databases. For exampmle,

BUSBITCHARS "[]" ;

Default is "[]"
Another common busbit character is "<>"

Divider Character

Specifies the character used to express hierarchy.

DIVIDERCHAR "/" ;

An instance in the design will be represented as follows, where "/" denotes the hierarchy separator. inst_top/inst_submodule/inst_and1

Units

Defines the units of measure in LEF.

UNITSDATABASE MICRONS 1000 ;END UNITS

MANUFACTURINGGRID

Defines the manufacturing grid for the design. The manufacturing grid is used for geometry
alignment. Shapes and cells are placed in locations that snap to the
manufacturing grid

MANUFACTURINGGRID 0.005 ;

LAYER
LAYER specifies the layer for the various width and spacing values. Every routing layer must have a WIDTH keyword and value specified. All other keywords are optional.

> LAYER POLY  
> TYPE MASTERSLICE ;  
> END POLY
> 
> LAYER PCONT  
> TYPE CUT ;  
> END PCONT

> LAYER MET1  
> TYPE ROUTING ;  
> DIRECTION HORIZONTAL ;  
> PITCH 0.24 ;  
> OFFSET 0.0 ;  
> WIDTH 0.120 ;  
> THICKNESS 0.240 ;  
> AREA 0.058 ;  
> MINENCLOSEDAREA 0.200 ;
> 
> SPACINGTABLE  
> PARALLELRUNLENGTH 0.0 0.52 1.50 4.50  
> WIDTH 0.0 0.12 0.12 0.12 0.12  
> WIDTH 0.30 0.12 0.17 0.17 0.17  
> 
> MINIMUMCUT 2 WIDTH 0.42 ;  
> MINIMUMCUT 4 WIDTH 1.14 ;  
> END MET1

> LAYER VIA1  
> TYPE CUT ;  
> SPACING 0.15 ;  
> SPACING 0.17 ADJACENTCUTS 3 WITHIN 0.19 ;
> 
> ANTENNAAREARATIO 20.000 ;  
> END VIA1

Site

Defines the placement site in a design. This gives the placement grid for macros and standard cells in the design. Standard cell rows are also created according to the SITE's size parameters.

SITE CORE_7H
      CLASS core ;
      SYMMETRY Y ;
      SIZE 2 BY 7 ;
END CORE_7H