Patent ID: 7233017

Claim:
A multibit phase change memory device comprising: a first insulating layer formed on a semiconductor substrate; a plurality of lower electrodes formed on the first insulating layer; a plurality of heating electrodes being in contact with the plurality of lower electrodes; a phase change material layer having a plurality of contact portions being in contact with the heating electrodes, and having a plurality of active regions, each active region forming a unit phase change memory device; a second insulating layer defining the active region between the heating electrodes and the phase change material layer; and an upper electrode being in contact with each of the plurality of active regions of the phase change material layer; wherein the active regions of the phase change material layer include a (i) first active region group being in contact with a first lower electrode selected from the plurality of lower electrodes, (ii) a second active region group being in contact with a second lower electrode selected from the plurality of lower electrodes, and (iii) a third active region group being in contact with a third lower electrode selected from the plurality of lower electrodes, wherein the number of active regions in the first, second and third active region groups are different from one another; wherein the phase change material layer includes a plurality of arrays each of which includes one or more of the unit phase change memory devices, each array including a different quantity of the unit phase change memory devices from one another, wherein the number of arrays and the number of lower electrodes are the same.