High-Transmittance Phase-Change Media with TiO₂ Film for Rewritable Dual-Layer Blu-ray Discs

Abstract

We have developed a semitransparent layer structure that is ideally suited to the laser-incident-side (front-side) recording layer of a rewritable dual-layer Blu-ray Disc (BD-RE). A TiO 2 top film and a memory film of GeTe-Sb 2 Te 3 characterize this layer structure. The TiO 2 film has a large refractive index, which works to increase the transmittance of the entire recording layer to more than 50%. It simultaneously increases the reflectivity contrast, defined by ðR cry À R amo Þ=ðR cry þ R amo Þ, where R cry and R amo (R cry > R amo ) are the reflectivities of the optical disc in the crystalline and amorphous parts, respectively. The GeTe-Sb 2 Te 3 memory film has optical constants that are appropriate for balancing the transmittance between the crystalline part (T cry ) and the amorphous part (T amo ) in the laser wavelength region of approximately 405 nm. Our experimental dual-layer disc shows high transmittances of T cry ¼ 51:6% and T amo ¼ 52:0% and a high reflectivity contrast of 0.71 in the laserincident-side layer. Dynamic examination showed that both recording layers have a good jitter value, satisfying the BD-RE specifications; more specifically, the laser-incident-side layer jitter value is 7.4% (spec.: 8.5%) and the back-side layer jitter value is 6.4% (spec.: 6.5%) through the front-side layer.

Origin, secret, and application of the ideal phase‐change material GeSbTe

“…In this triple layer optical disk, various novel technologies are used. The technologies are new dielectric material ZrSiO for the protection film [20], GeTe-rich GeSbTe phase-change films, and TiO 2 -based film with high refractive index (2.75) working to increase the total transmittance [21]. Consequently, the difficulties were solved, as listed in Table 1.…”

Nanoscale phase changes in crystalline Ge2Sb2Te5 films using scanning probe microscopes

“…And, in the optical phase-change system, the capacity is in principle governed by the mark size, the smallest in the present commercial systems being ϳ150 nm in diameter. 4 However, this diameter is governed by the diffraction-limited spot size of blue laser light with a wavelength of 405 nm, and the ultimate material-limited size has not been known.…”

Current-driven phase-change optical gate switch using indium–tin-oxide heater

“…[1][2][3] PCMs have been utilized for optical data storage (CDs, DVDs, Blu-ray, etc.) 4,5) and solid-state memory called phase-change random-access memory. 6,7) Additionally, photonic memory using PCM and SiN waveguides was reported.…”