1. A method comprising: forming a stack comprising forming a metal heater layer, forming a chalcogenide over the metal heater layer such that a lowermost portion of the chalcogenide is only partially in contact with the metal heater, and forming a first dielectric on top of the chalcogenide; defining the first dielectric using a photo resist as a mask, defining the first dielectric being followed by removing the photo resist prior to defining the chalcogenide; defining the chalcogenide using the defined first dielectric as a mask; and sealing sidewalls of the chalcogenide with a second dielectric.