Patent ID: 7169454

Claim:
A multi-stack optical data storage medium for rewritable recording using a focused radiation beam entering through an entrance face of the medium during recording, comprising: a substrate having deposited on a side thereof: a first recording stack comprising a phase-change type recording layer, said first recording stack being present at a position most remote from the entrance face, at least one further recording stack, which comprises a phase-change type recording layer, being present closer to the entrance face than the first recording stack, and a metal reflective layer, transparent for the radiation beam, and a transparent spacer layer between the recording stacks, said transparent spacer layer having a thickness larger than the depth of focus of the focused laser-light beam, characterized in that the metal reflective layer mainly comprises the element Cu and has a thickness value selected from the range of 2 to 10 nm, and wherein the multi-stack optical data storage medium further comprises a further metal reflective layer in the first recording stack at a side of the recording layer of the first recording stack most remote from the further recording stack.