Transmission Loss Analysis and Design of Transmission Lines for High-Data-Rate HDDs

Abstract

The suspension used in a hard disk drive (HDD) mainly supports the magnetic head, which flies at a height of several nanometers over a recording medium. Micro-strip transmission lines for the read and write data signals are installed on the stainless steel of the suspension. The conventional transmission line system uses stainless steel as the base metal, which determines the suspension’s mechanical characteristics. This stainless steel base metal is the dominant contributor to high-frequency signal losses. The base metal signal loss contributions are revealed by electromagnetic field simulation. At high frequencies, a significant amount of power is consumed in the base metal by induced currents and the base metal’s resistance. To reduce the base metal power, we calculated the power consumption, using a copper base metal. Electromagnetic simulation results support our findings on the contributions of the base metal to the signal losses. The results indicate that the thickness of the copper base metal should be more than 2 micrometers. We suggest a new layer structure for the suspension with reduced transmission loss. To confirm that the new layer structure of the transmission line system reduces the transmission loss, measurements were made on sample coupons using copper base metal and coupons using stainless steel base metal. The results clearly show the benefits of using a copper base metal suspension to reduce the transmission loss for suspension interconnects.