Apple just released the iOS 9.3 with the option to protect and lock notes with a password or fingerprint. to put and set password for Note in iPhone & iPad devices, running iOS 9.3 or later, do as follows:
1. Open the Notes on your iPhone devices
2. Create a new note or open an already existed note
3. Tap the Share button on the top right of the screen to open the two rows of actions
4. On the second row, touch the Lock Note button and if this is your first time using this option, you are asked to enter a new password, verify it, and provide a hint.
5. Now your Note is Locked and Protected and you have to enter the password to read the content. (The title is only shown if a note is locked)
6. From now on, you just need to enter your password to lock or unlock any of your Notes.