1. A circuit structure comprising: a fuse comprising: a first conductor layer; a second conductor layer on said first conductor layer; and a third conductor layer on said second conductor layer, said first conductor layer and said third conductor layer each having a relatively high atomic diffusion resistance as compared to said second conductor layer; a voltage source; and electrical connections between said voltage source and said first conductor layer, between said voltage source and opposite ends of said second conductor layer, and between said voltage source and said third conductor layer, said voltage source being selectively controllable so as to allow voltage polarity at selected ones of said electrical connections to be varied in order to selectively control bi-directional flow of electrons within said second conductor layer and, thereby to selectively control formation of any of non-destructive opens and shorts within said second conductor layer at interfaces with said first conductor layer and said third conductor layer.