Stability of Te–Cu amorphous alloy thin films for optical recording

We have studied the structure and optical stability of Te–Cu thin film alloy candidates for write-once optical recording. Films prepared by rf diode sputtering with 20–50 at. % Cu are amorphous, as-sputtered. One of these, Te65 Cu35 , has a relatively high crystallization temperature (150 °C), as determined by x-ray diffraction. Near the eutectic composition (∼29 at .% Cu), alloy films have stable optical properties after accelerated aging at 60 °C and 85% relative humidity. The mechanism for film stability near the eutectic was studied by x-ray photoelectron spectroscopy and depth profiling using ion scattering spectroscopy. We found that a Cu-enriched surface oxide, formed at ambient conditions, passivates the film and is responsible for its subsequent stability after accelerated aging. We also demonstrated that a 14 in. diam, multilayer optical disk with a Te65 Cu35 recording medium exhibits excellent linearity for 3 and 8 MHz pulses, good written pulse length stability, and high signal-to-noise ratio. Thus, a Te–Cu recording medium can effectively use run-length-limited codes, which allow very high data storage capacity and data transfer rates.