There is a rapid increase in the generation of daily data in our modern technological age where data is considered everything. In 2016, the annual data generation was about 16 ZB/year and in 2025, it is expected to be as much as 163 ZB/year. There are lots of devices that are being used for storing digital information like hard disk drives, flash drives, and magnetic tapes. Among them, a hard disk drive will remain the choice of everyone for the primary as well as a secondary storage option because of its large storage capacity and low costing. It is assumed that hard disk drive will rule the storage technology universe for more than the next 10 years according to its production, shipment, price, and capacity. However solid-state drives are considered as the biggest competition for the future of hard disk drive. Therefore we are required to develop high areal density in the hard disk drive. This can be achieved by reducing the head-hard disk medium spacing as this will effectively reduce the signal-to-noise ratio and also helpful in limiting areal density growth. There are several contributions made in context to the head-hard disk medium spacing in which hard disk medium overcoat is the key component.
We widely use carbon-based overcoats for protecting hard disk medium from corrosion and other mechanical damages for ensuring its effective durability and functionality. However, current technologies are unable to design advanced carbon-based overcoats having properties like corrosion protection, Young’s Modulus, wear resistance, and anti-friction, when we come to the thickness below 2 nm. The best overcoat should ideally provide the below-enlisted features –
1. Protection against corrosion without any pinholes.
2. Coefficient of friction to be in the range of 0.3-0.5 nm and wear resistance of approx. 400 GPa Young’s Modulus providing features like elasticity, hardness, and lubricating property.
3. Surface smoothness.
4. Lubricant compatibility.
For enabling ultra-high areal density hard disk drive, we are required to develop novel overcoats or this can be done by mastering engineering works on the existing overcoats. Another critical challenge that hinders the growth in areal density is considered as the superparamagnetic limit that links three very critical problems like increase in areal density, writability, and thermal stability. However, the complications of writability in materials having large magnetic anisotropy can be solved by using heat-assisted magnetic recording technology. Heat-assisted magnetic recording technology uses laser technology for heating the given magnetic medium for about 1 ns. This will result in decrement of its coercivity and effectively bring the temperature to the material’s Curie temperature, Tc. Writability can be done above the Curie temperature when the magnetic field is provided of about 0.8 T that can be done using conventional technologies. Hence data can be easily retained as soon as coercivity gains its original value when the temperature cools down reaching room temperature.
Graphene as Carbon-based Overcoats
We can efficiently use graphene for ultra-high areal density hard disk drives. This will result in tenfold jumping when compared to current commercial technologies. This result has been successfully shown by the researchers at the Cambridge Graphene Center. The hard disk drive was developed in the 1950s and we started using it as a storage device in the 1980s. Along with time, it becomes smaller in size and denser in its storage capability. Solid-state drives are popularly used in smartphones while hard disk drives are used in computers and various other devices because of their low production cost. Researchers got a successful achievement in replacing the commercial carbon-based overcoats with 1-4 layers of graphene which resulted in the efficient capability of lubricant, thermal stability, wear, corrosion, and friction. Graphene provides unbeatable thickness along with fulfilling the ideal qualities for an ultra-high areal density hard disk drive overcoat like surface smoothness, lubricant compatibility, hardness, wear resistance, low friction, and corrosion protection. Graphene is capable of reducing friction by two times than that commercial HDDs along with providing better wear and corrosion resistance. A single layer of graphene is effectively capable of reducing corrosion by about 2.5 times.
In an experiment, graphene was transferred on an iron-platinum hard disk to form a magnetic recording layer and was tested for heat-assisted magnetic recording. This resulted in developing new advanced technology that is capable of increasing the storage density through heating the recording layer. Hence, graphene along with heat-assisted magnetic recording technology could easily outperform the commercial carbon-based overcoats, as they are unable to perform recoding at such high temperatures. The data density that can be achieved using graphene is as high as 10 terabytes per square inch.
Hard disk drives are a very essential secondary storage system used in various electronic gadgets because of their large storage capacity and cheap costs. As there is a huge exponential increase in the amount of data, there is a requirement for increasing the areal storage density above 1 Tb/in2. This will require minimizing the carbon overcoat thickness to be lesser than 2 nm. However several critical challenges occur while we reduce the thickness to less than 2 nm like thermal stability, corrosion, wear, and friction. This can be done in spite of limited current technology by restricting carbon overcoat integration using heat-assisted magnetic recording technology, also known as HAMR. However, we can easily overcome these limitations by using the graphene-based overcoat method. Using this technique we can obtain two-fold reduced friction and achieve better wear and corrosion resistance than the old traditional carbon overcoat method.
This can be done withstanding heat-assisted magnetic recording technology conditions. Hence the expectation from graphene overcoat technology would help us bring the areal density of hard disk drive to be 4-10 Tb/in2 when we employ several recoding technologies like HAMR or HAMR+bit. Technological developments in graphene as carbon-based overcoats are considered a milestone in history and will open several doors towards a sustainable age where storage will never be considered a problem for anyone. In 2020, about 1 billion terabytes carbon-based overcoat hard disk drive was manufactured. Through this, we can imagine the demand for graphene-based hard disk drives in our modern digital world.