As simply as possible, could someone try to explain how one would go about calculating the probability of a electron/(electric voltage) quantum tunneling through an insulator (preferably using an example please)? And how small would the insulator, and how large would the current/voltage have to be for it to be a practical to observe that tunneling took place, and how much would you expect to observe? Also, as a bit of a side not, how small is the insulator generally in a MIM diode? and what about in a MIIM diode? and how much electricity goes through each of them, and how quickly?