Patent ID: 8896045

Claim:
An integrated circuit comprising: a wafer substrate; a first electrode; a second electrode; resistivity changing material extending from a first contact with the first electrode to a second contact with the second electrode; and a sidewall spacer contacting the second electrode and a sidewall of the resistivity changing material adjacent to the second contact, the sidewall spacer comprising a material with a higher resistance against etching than the resistivity changing material, and the sidewall spacer aligned with a portion of the first electrode in a direction perpendicular to the wafer substrate, wherein the first electrode is between the wafer substrate and the second electrode, and wherein the sidewall spacer comprises a first surface contacting the second electrode and a second surface coplanar with a surface of the first electrode, the second surface of the sidewall spacer being opposite to the first surface of the sidewall spacer, the first surface of the sidewall spacer and the second surface of the sidewall spacer being perpendicular to the wafer substrate, and the first surface of the sidewall spacer being spaced apart from the second surface of the sidewall spacer in a direction parallel to the wafer substrate; wherein the resistivity changing material comprises a first stack of phase change material in contact with a second stack of phase change material, wherein the first stack of phase change material is different in composition relative to the second stack of phase change material.