Fabrication of Ridge-and-Groove Servo Pattern Consisting of Self-Assembled Dots for 2.5 $\hbox {Tb/\in}^{2}$ Bit Patterned Media

Bit patterned media (BPM) is fabricated by a directed self-assembled polymer mask. CoPt magnetic dots with 17 nm pitch (2.5 Tb/in²) consists of ridge-and-groove servo patterns as well as circular data tracks. Distribution of dot size and dot pitch is 16% and 15%, respectively. The position error signal (PES) is estimated numerically employing a simulation model using estimated deviation of dot size and pitch. PES linearity was found to be fairly good in spite of large dot pitch deviation. Distribution of dot size and dot pitch causes distortion in the reproduced waveform, but it does not degrade the phase information of the servo signal. This result indicates that the ridge-and-groove servo has a high tolerance to the amplitude noise and is suitable for BPM. When the width of the read head is close to the dot pitch, the linearity error increases owing to the dot size and dot pitch deviation. Reduction of these distributions is necessary in order to apply BPM to hard disk drives.