Depending on what type of MOSFET
you are needing and what your voltage levels are
will determine what kind of model parameters you
will be needing. For instance, if it is for large
voltages (>5 V) you will be needing a different
type of MOS with different parameters than one which
is less than 5 V.
I don't know much about
higher voltage FETs, but for <5 V applications
an okay place to start is through the MOSIS web
They keep a detailed list of SPICE parameters for
different size technologies (from 1.2um CMOS down
to 90nm) with different runs so that you can see
the process variations. As far as needing an ft
of greater than 20 GHz, you will need to use at
least 0.35um CMOS. Even then, it may be pushing
If you can't find the information
you need on the MOSIS site, you can always check
foundry web sites. Sometimes they post their SPICE
parameters there for older processes and you can
see if they are in the ballpark that you are in.
Hope this helps.