to the sides of the insulating layer 202 and the second electrode 201 the interface between the spacer and the second electrode defines a phase change region as a high resistance material is more easily used for a second electrode than for the buried diffusion this figure illustrates a buried diffusion without need for contact via in alternate embodiments a contact via could connect the buried diffusion through the additional insulating layer to layers below fig3 depicts an additional structure that may be combined with a spacer memory structure in particular an isolation transistor is illustrated one pole 321 of the transistor is electrically connected to the contact 105 a gate 322 controls the flow of current from the other pole 323 to the contact use of an isolation transistor may be useful as the electrical resistance of a programmable resistive material is unlikely ever to be so great as to block current leakage from the first electrode to the second electrode alternatively an isolation junction or an isolation diode may be incorporated in the structure a conventional sequence for forming a spacer is generally illustrated in fig1 a 1c fig1 a illustrates a multilayer structure formed using conventional method in fig1 b a programmable resistive material 111 is the deposited over the multilayer structure techniques for depositing such a film include sputtering and chemical vapor deposition a.