I believe that "" has the meaning of trust or believing in something, for example:
>
> Do you believe in fairies?
Whereas "" is the word I would use for a more "serious" kind of trust, for example:
>
> I have complete trust in my doctor.
If you want the term "faith" in a religious sense for your tattoo I would look into "" instead. Another example:
>
> My mother believes in Christianity.
I took all of these examples from Jisho.org, a place I would recommend you consult before getting your tattoo!