A memory device comprising a first electrode having a top side, a second electrode having a top side and an insulating member between the first electrode and the second electrode. The insulating member has a thickness between the first and second electrodes near the top side of the first electrode and the top side of the second electrode extends outwardly from the top sides of the first and second electrodes defining a wall of insulating material having top side. A bridge of memory material crosses the insulating member over the top of the wall, and defines an inter-electrode path between the first and second electrodes across the insulating member. An array of such memory cells is provided. The bridge comprises an active layer of memory material on the top side of the wall, having at least two solid phases and a layer of thermal insulating material overlying the memory material having thermal conductivity less than a thermal conductivity of the first and second electrodes.