Improvement of RRO using hybrid-type STW for hard disk drives

Accurate servo track writers (STWs) are indispensable for hard disk drives (HDDs) with high track density. We have developed a prototype hybrid-type STW which has two writing stages. In the first stage, master patterns are written on one surface of the master disk prior to drive assembly. In the second stage, the master disk is assembled with several raw disks in a HDD, and the servo patterns are written on the all disks, including the master, based on the master patterns. In this paper, a new servo compensator and a new algorithm to compensate for position signal nonlinearity are proposed. These are necessary items for the hybrid-type STW. Finally, experimental results are described showing that the hybrid-type STW reduces the maximum value of repeatable runout (RRO) and write-to-write track mis-registration.