Patent ID: 6861117

Claim:
A multi-stack optical data storage medium ( 20 ) for rewritable recording by means of a focused laser-light beam ( 30 ), said medium ( 20 ) having a substrate ( 1 ) with deposited on a side thereof: a first recording stack ( 2 ) comprising a phase-change type recording layer ( 6 ), said first recording stack ( 2 ) being present most remote for the focused laser-light beam ( 30 ), at least one further recording stack ( 3 ) comprising a phase-change type recording layer ( 12 ), a transparent spacer layer ( 9 ) between the recording stacks ( 2 , 3 ), said transparent spacer ( 9 ) layer having a thickness larger than the depth of focus of the focused laser-light beam ( 30 ), characterized in that at least one heat sink layer ( 8 , 10 , 14 ), comprising a compound represented by the formula HfN x and in which formula x is the number of atoms N per Hf atom and 1.1≦×≦1.6, is present in at least one of the recording stacks ( 3 ).