1. An integrated circuit structure comprising: a crystalline substrate having a plurality of circuits formed on the surface thereof; power supply conductors provided for connection to each of said circuits; and a circuit disconnect conductor provided to supply a power disconnect signal to each of said circuits; each of said circuits including a power disconnect circuit having a gate coupled between one of said power supply conductors and said each circuit, said gate being coupled to said circuit disconnect conductor by a switch characterized by a phase transition with an associated large resistance change upon receipt of a circuit disconnect signal on said circuit disconnect conductor.