A three-dimensional memory array (657; 671; 980; 981), comprising: a stack comprising a plurality of first conductive lines (622; 922), at a number of levels separated from one another by at least an insulation material, wherein the plurality of first conductive lines (622; 922) comprise word lines; at least one conductive extension (654; 954) arranged to extend substantially perpendicular to the plurality of first conductive lines (622; 922), such that the at least one conductive extension (654; 954) passes through a portion of each of the plurality of first conductive lines (622; 922); a plurality of second conductive lines wherein each second conductive line of the plurality of second conductive lines is formed over the plurality of first conductive lines (622; 922) and the at least one conductive extension (654; 954), and wherein the at least one conductive extension (654; 954) is coupled to a respective one of the plurality of second conductive lines; and storage element material (652; 952) and cell select material (650; 950) arranged one around the other and around the at least one conductive extension (654; 954; a heater material (645; 945), adjacent to, and communicatively coupled with, each of the plurality of first conductive lines (622; 922), the heater material (645; 945) having a cross-sectional area smaller than that of at least one of the plurality of first conductive lines (622,922), the heater material (645; 945) being arranged in series between a respective one of the plurality of first conductive lines (622; 922) and the storage element material (652; 952), and characterized in that the heater material (645; 945) is a different material than the plurality of first conductive lines (622;922) and in that the heater is configured to concentrate current flow so as to confine volume of storage material (652,952) involved in a phase change. a stack comprising a plurality of first conductive lines (622; 922), at a number of levels separated from one another by at least an insulation material, wherein the plurality of first conductive lines (622; 922) comprise word lines; at least one conductive extension (654; 954) arranged to extend substantially perpendicular to the plurality of first conductive lines (622; 922), such that the at least one conductive extension (654; 954) passes through a portion of each of the plurality of first conductive lines (622; 922); a plurality of second conductive lines wherein each second conductive line of the plurality of second conductive lines is formed over the plurality of first conductive lines (622; 922) and the at least one conductive extension (654; 954), and wherein the at least one conductive extension (654; 954) is coupled to a respective one of the plurality of second conductive lines; and storage element material (652; 952) and cell select material (650; 950) arranged one around the other and around the at least one conductive extension (654; 954; a heater material (645; 945), adjacent to, and communicatively coupled with, each of the plurality of first conductive lines (622; 922), the heater material (645; 945) having a cross-sectional area smaller than that of at least one of the plurality of first conductive lines (622,922), the heater material (645; 945) being arranged in series between a respective one of the plurality of first conductive lines (622; 922) and the storage element material (652; 952), and characterized in that the heater material (645; 945) is a different material than the plurality of first conductive lines (622;922) and in that the heater is configured to concentrate current flow so as to confine volume of storage material (652,952) involved in a phase change.