A phase change memory structure, including a substrate having a cavity extending from a surface of the substrate into an interior region thereof, wherein the cavity is bounded by side wall surface, wherein the cavity is coated on the side wall surface with a film of phase change memory material defining a core that is at least partially filled with dielectric material such as alumina. Such phase change memory structure can be fabricated in a substrate containing a cavity closed at one end thereof with a bottom electrode, by a method including: conformally coating sidewall surface of the cavity and surface of the bottom electrode closing the cavity, with a phase change memory material film, to form an open core volume bounded by the phase change memory material film; at least partially filling the open core volume with alumina or other dielectric material; and forming a top electrode at an upper portion of the cavity.