Tunneling is the way electrons cross the gate in some forms of transistor and a failure mode in othershttp://ece.gmu.edu/~qli/ECE685/single-electron-tra...http://nanosioe.ee.ntu.edu.tw/Download/Paper/!!!ot...http://books.google.com/books?hl=en&lr=&id=j6YhHqj...http://www.nature.com/nature/journal/v479/n7373/fu...