It seems that the keyword "temp" can not be recognized by Hspice unless I use it after "sweep", which is not i want.
---------- Post added at 10:00 ---------- Previous post was at 09:32 ----------
By the way, I tried to use "time" in other parameter, like .param VDD= 'time'.
A warning will occur:
**warning** parameter vdd is defined as an expression containing output signals,
which may cause incorrect result. Suggest to use user defined functions to replace.
And then VDD will be set to 0, not changed with time.