Itaru Shibata

A new protective film for magneto‐optical TbFeCo media

A new protective film, Tb‐SiO2, was developed to increase the lifetime of TbFeCo magneto‐optical disks. Since Tb, a rare‐earth metal, is quite easily oxidizable, an efficient protective layer is essential to assure the stability of magneto‐optical disks. Given that vacuum‐deposited SiO2 film acts as an oxidation‐inducing layer, unlike SiO2 on a thermally oxidized silicon wafer, we invented a new protective film, Tb‐SiO2, in which Tb is intended to trap active oxygen in the vacuum‐deposited SiO2. The results were excellent and we estimate the lifetime of TbFeCo disks with Tb‐SiO2 as an underlayer and overlayer, at more than 20 years at 40 °C, 90% relative humidity. The properties and protection effects of Tb‐SiO2 are described.

A New Servo Method Which Increases Track Following Range Of A One-Beam Optical Head

A simple and reliable optical head is needed for practical application of optical mass data storage. The so-called push-pull tracking method is widely used in pregrooved disc systems. A disadvantage of this tracking method is that track following range is limited to a few tens of microns, which is too little for practical use. The limited range is due to disc eccentricity, which displaces the axis of the reflected beam. The authors have overcome this problem by a new servo method which compensates electrically the undesirable influence by detecting the displacement from the driving signal of the tracking actuator, and have improved the track following range to 350 μm.