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66 2 Extremely Short-External-Cavity Laser Diode

0.1MHz 1MHz

Fig. 2.43. Reproduced signals of the written bit at 0.1 and 1 MHz for a duty cycle
of 50%

is 6.9ms −1 . Figure 2.43 shows the reproduced signals for 0.1 and 1.0 MHz,
both with high SNR.

Reliability Test

In an actual disk drive, contact between the slider and the disk is inevitable.
We therefore identify a combination of slider and protective layer materials
that reduces wear (scratching) during contact start/stop (CSS).
We have investigated experimentally the protective films such as silicon-
dioxyside (SiO 2 ), zinc-sulfide (ZnS), and silicon-nitride (SiN). We also evalu-
ated their thermal conductivity for writingsensitivity and thermal expansion
difference between the multi layers described earlier. The SiN protective layer
had smallest amount of scratch caused by repeated CSS with the AlN slider.
Fabrication of the film was also studied with regard to internal stress and ad-
hesion strength. The films, containing hydrogen atoms a-SiN:H (hydrogenated
amorphous silicon nitride), showed good write sensitivity. Its mechanical prop-
erty is also good because it has a high tensile force and resists scratching.
Figure 2.44 is an SEM photograph of the LD facet after 10,000 CSS
cycles (900 rpm) in an office environment (class 350,000). The disk has a
SiN/GeSbTe/SiN/Plastic substrate structure. Protuberance dust (particles)
adheres to the LD facet. The chemical composition of twelve randomly selected
¨
samples of protuberance dusts, analyzed by Auger electron spectroscopy, is
primarily C, O, Al, Si, and S, that is, the dust element included in the air.
The elements from slider and protective layer are included only two of the 12
dusts (samples). These results indicate very small amount of slider/disk wear
were produced even if scratch on the medium can not be seen with an optical
microscope.
The LD–PD reliability and the dust in the air is evaluated by free-running
test at 3,600 rpm, 4 mW light power, and with h 0 =1 µm in an experimental
room environment (class 30,000). This test shows that the head has a lifetime
(before bias current increases by 20%) of 2,040 h. This corresponds to 4.4 ×
8
10 passes. Contact start/stop (CSS) test, bias current for constant signal
amplitude versus the number of CSS cycles, shows that the head signal is