MULTI-STACK OPTICAL DATA STORAGE MEDIUM AND USE OF SUCH MEDIUM

摘要

The present invention relates to a multi-stack optical data storage medium (10). The medium comprises a first substrate (1a) with present on a side thereof a first recording stack (13) named L0, a second substrate (1b) with present on a side thereof a second recording stack (12) named L1 comprising a recordable type L1 recording layer (4) having a thickness tRL1 and a complex refractive index nlambda - i*klambda at a wavelength lambda. A second reflective layer (6) is present adjacent the L1 recording layer (4) at a side most remote from a radiation beam (20) entrance face (11) of the medium. The second recording stack L1 (12) is present at a position closer to the entrance face (11) than the L0 recording stack (13). A radiation beam transparent spacer layer (9) is sandwiched between the recording stacks (12, 13). In order to achieve compatibility with the DVD-9 ROM standard as far as reflection levels are concerned, the second reflective layer (6) mainly comprises the metal Cu and has a thickness tMLn selected from the range of 8 - 20 nm and the thickness tRL1 and klambda of the recordable L1 recording layer (4) fulfils the formula tRL1*klambda <= 8 nm.