Hard Drive Research: Coating Thickness Drops Below 1 Nanometer

The building blocks for ever-higher hard drive capacities have long been known to manufacturers: helium filling, SMR recording, and energy-assisted recording are standard. In development are lithographically ordered magnetic material, and later possibly Heated-Dot Magnetic Recording (HDMR), where individual magnets in a row represent a track.

The distance between the write head and the magnetic layer also plays a crucial role in increasing capacity. The smaller this distance, the weaker the magnetic field the write head can work with, and the better the signals received by the read heads. However, there is little room for improvement in the flying height above the platters: today, they already hover just 1 to 2 nanometers above the platters, which rotate at up to 7200 revolutions per minute.

However, current coatings are around 2.5 nanometers thick, meaning the distance between the heads and the magnetic material is 3.5 to 4.5 nanometers. Researchers at the National University of Singapore now aim to reduce this distance with a new process.

Paper in the journal Advanced Materials

An international research team led by Hongji Zhang and Artem K. Grebenko presents a new protective coating for hard drives in the journal Advanced Materials. They call the material MAC – monolayer amorphous carbon. The layer is only 0.8 nanometers thick, making it about a third as thick as the currently common 2.5-nanometer-thick coatings made of diamond-like carbon.

The researchers grew MAC directly on commercial 2.5-inch hard drive media. The process uses a combination of laser and plasma at relatively low temperatures of around 300 degrees Celsius. The process damages neither the magnetic recording layer nor the surface structure of the platters. The roughness before and after coating remains practically identical, and the magnetic domains also remain intact.

Despite its low thickness, the MAC layer reportedly protects against corrosion just as well as conventional coatings. In electrochemical tests, it achieved 82.7 percent corrosion protection. This value corresponds to that of a 2.5-nanometer-thick commercial protective layer.

Thermal stability is particularly relevant for future storage technologies. In heat-assisted magnetic recording (HAMR), lasers heat the magnetic bits to around 450 degrees Celsius to make them easier to write. The MAC layer withstood laser irradiation under HAMR-like conditions without measurable structural changes. According to the researchers, the manufacturing process meets important requirements for industrial implementation. It can be scaled up to platters up to 4 inches in size and is compatible with double-sided coating. The growth time is currently in the range of minutes. The researchers see potential for optimization to further shorten this time.

Assessment

A thinner protective layer is necessary but not sufficient for higher capacities, a hard drive manufacturer's developer said when asked. For higher storage densities, all factors must scale: write head dimensions, the TMR sensor for reading, grain sizes and other factors in the media, and also the distance between the head elements and the magnetic coating on the disk. Only the thickness of the carbon coating contributes to the latter.

However, extensive tests will be needed to determine whether MAC proves its worth in mass production. Long-term stability under real operating conditions and the economic viability of the process remain open questions. The fundamental research is promising, but the path to series production is still long. (ll)