Tribological Properties of Pulse-Biased Hydrogenated Amorphous Carbon Films

Hydrogenated amorphous carbon films have been prepared on Si substrates in plasma CVD system by using pulse bias techniques. ERDA analysis showed that pulse-biased film prepared at a duty ratio of 10% included large amount of hydrogen compared to the dc-biased films prepared at the same bias voltage of -1kV. Mechanical properties showed that the density, hardness and internal stress of pulse-biased films decreased compared to the dc-biased films. The film hardness decreased from 33 Gpa of dc-biased one to 15.5 Gpa in pulse-biased one. Film stress decreased from 2.9 Gpa for dc-biased one to 0.5 Gpa for pulse-biased one. Tribological properties by a ball-on-disk friction tester in the dry air condition showed that friction coefficient of dc-biased film with a counterpart of SiC ball was 0.06 and that of pulse-biased films was 0.045, which did not show clear difference. However the specific wear rate had a much difference between these two films. The wear rate of dc-biased films was 6 x 10-8 mm3/Nm and that of pulse one is 5 x 10-9 mm3/Nm showing the extremely low wear in dry air condition. The reason was thought to be due to the decrease of internal stress of the films because of the increase of hydrogen content and the existence of mixed structures of hydrocarbon bonding.