Assuming you are using xRC (and probably xACT, but not sure), your SVRF rule file needs a Unit Capacitance statement that matches the extraction rules. One of the interesting quirks is that parasitic rules created by xCalibrate default to femtofarads, but xRC defaults to picofarads. The Unit Capacitance information warns
"The capacitance calculations generated by the xCalibrate rule file generator have a default unit of femtofarads. The Unit Capacitance statement must match the units used in the capacitance calculations or the results will be incorrect."
yes, I use xRC and SVRF file has default UNIT CAPACITANCE of picofarads. I think that is the problem. We suppose a design of SRAM bitline, which has length 105.20um (25 cells), then the capacity of bitline is 18.98pf. My opinion, that capacitance of the metal wire is extremely huge due to size of access transistors. After that, there is no possibility to design bigger memory array like 256x128 (words x columns) cells. Question is, may I change picofarad to femtofarad in SVRF? After that, I changed the unit capacitance, simulations works very well, but it is corect?
Thanks a lot!
Yep, it is correct.