How to disable PIN and use biometric security only?

[j123456789]

What's the point to have a fingerprint scan if all you need is the PIN code to unlock the phone?

I have look ever where to see if I can disable the PIN (or swipe, password etc..) and use biometric security only, but it seems impossible. 

Am I missing something here?

[Toed]

Reading these post and having set up fingerprint scan for extra security was amazed to find that pin will always over ride fingerprint scan. So what is the point of it then Asia serves no security purposes apart from unlocking the phone quicker.