Optical recording characteristics of molybdenum oxide films prepared by pulsed laser deposition method

Molybdenum-oxide (MoO₃)films were deposited on glass substrates (Corning #7059 with an area of 26 × 38 mm²) by pulsed laser deposition using an ArF excimer laser. It was found that after annealing at 340 °C for 10 min, the film thickness became 2.3 times that (approximately 30 nm) of the as-deposited film thickness. The difference in the transmittance, ΔT, between the annealed state and the as-deposited state was about 40% at a wavelength of 400 nm. X-ray diffraction spectra indicated that oxygen was absorbed into the MoO₃ films through the annealing process. From revolution testing of 30 nm-thick MoO₃ films without a protective layer deposited on a polycarbonate DVD-R disk substrate (120 mm?, 0.6 mm thickness), a write peak-power dependence of carrier-to-noise ratio (CNR) (recording on-land, at λ = 406 nm, NA = 0.65) of the 3T signal (58.5 MHz) was measured at a linear velocity of 5 m/s and a read power of 0.6 mW. Consequently, CNR near 50dB was obtained in the wide write-power margin ΔP of 7 mW (at peak powers between 3.5 and 10.5 mW). From SEM observations, it was recognized that bits of 0.25-0.30 μm size, corresponding to a storage capacity of 7-10GB/in² in the case of NA = 0.65, were formed. For the sample structure with an Al₂O₃ protective layer of ~ 20 nm thickness, a CNR near 50dB was obtained in the peak-power margin ΔP of 12 mW (at peak powers between 6.0 and 18.0 mW). Larger values of the CNR can be obtained if the film thickness of each layer including both the active and protective layers is optimized.