Hitachi and Hitachi Global Storage Technologies (Hitachi GST) announced today they have developed the world’s smallest read-head technology for hard disk drives, which is expected to quadruple current storage capacity limits to four terabytes on a desktop hard drive and one TB on a notebook hard drive.

From GMR to TMR to CPP-GMR

The discovery of the giant magnetoresistance (GMR) effect occurred in 1988, and that body of work was recognized just last week with a Nobel Prize for physics. In 1997, nine years after the initial discovery of GMR technology, IBM implemented the industry’s first GMR heads in the Deskstar 16GXP. GMR heads allowed the HDD industry to continue its capacity growth and enabled the fastest growth period in history, when capacity doubled every year in the early 2000s.

Tunnel magnetoresistance (TMR) effect at room temperatures was discovered back in 1995 and was used to create heads for hard drives featuring perpendicular magnetic recording starting from 2005.

Researchers at Hitachi have successfully reduced existing recording heads by more than a factor of two to achieve new heads in the 30nm – 50nm range. Called current perpendicular-to-the-plane giant magnetoresistive (CPP-GMR) heads, Hitachi’s new technology is expected to be implemented in shipping products in 2009 and reach its full potential in 2011.

Hitachi believes CPP-GMR heads will enable hard disk drive (HDD) recording densities of 500 gigabits per square inch (Gb/inch²) to 1Tb/inch², a quadrupling of today’s highest areal densities. Earlier this year, Hitachi GST delivered the industry’s first one-terabyte hard drive at 148Gb/inch², whereas the industry’s highest areal density shipping in products today is about 260Gb/inch². These products use existing TMR head technology.

The recording head and media are the two key technologies controlling the miniaturization evolution and the exponential capacity growth of the HDD.

Cutting Through the Noise

The continued advancements of HDDs requires the ability to squeeze more, and thus, smaller data bits onto the recording media, necessitating the continued miniaturization of the recording heads to read those bits. However, as the head becomes smaller, electrical resistance increases, which, in turn, also increases the noise output and compromises the head’s ability to correctly read the data signal.

High signal output and low noise is what is desired in hard drive read operations; thus, researchers try to achieve a high signal-to-noise (S/N) ratio in developing effective read-head technology. Using TMR head technology, researchers predict that accurate read operations would not be conducted with confidence as recording densities begin to surpass 500Gb/inch².

The CPP-GMR device, compared to the TMR device, exhibits less of an electrical resistance, resulting in lower electrical noise but also a smaller output signal. Therefore, issues such as producing a high output signal while maintaining a reduced noise to increase the S/N ratio needed to be resolved before the CPP-GMR technology became practical.

In response to this challenge, Hitachi and Hitachi GST have co-developed high-output technology and noise-reduction technology for the CPP-GMR head. A high electron-spin-scattering magnetic film material was used in the CPP-GMR layer to increase the signal output from the head, and new technology for damage-free fine patterning and noise suppression was developed. As a result, the signal-to-noise ratio, an important factor in determining the performance of a head, was drastically improved. For heads with track widths of 30nm to 50nm, industry-leading S/N ratios of 30 decibels (dB) and 40dB, respectively, were recently achieved with the heads co-developed at Hitachi GST’s San Jose research center and Hitachi’s central research laboratory in Japan.

Recording heads with 50nm track widths are expected to debut in commercial products in 2009, and those with 30nm track widths will be implemented in products in 2011. Current TMR heads, shipping in products today, have track widths of 70nm.

Hitachi will present these achievements at the 8^th perpendicular magnetic recording conference (PMRC 2007) to be held October 15-17, 2007 at the Tokyo International Forum in Japan.