Stability issues of photopolymer layers in optical disks

Photopolymerization (2P) processes are used to produce polymer layers that can be used for servo information in optical storage. The authors have studied the stability of such polymer layers in structures involving a substrate / polymer layer / magneto-optic disk package. The polymer layer carried servo information in the form of grooves with a pitch of 2.5 um. Experiments at elevated temperatures (80 to 150°C) have been performed on these structures as part of a stability test. It is found that (depending upon structures, coatings, materials) a wave structure can develop in the underlying 2P layers which continuously grows in amplitude (e.g. 100A to 1000A) when the structure is aged at e.g. 100C. Further experiments have been carried out, which show that the instability can be controlled and prevented.