Once again graphene has turned the heads of researchers, this time in the world of computing. According to scientists, recent developments have led to a new method which means the material could be an essential component for the evolution of the next generation of enhanced, high-speed and compact super-computers.
Over at the University of California Santa Barbara (UCSB) engineering researchers in computing and electrics have devised a method to utilize nanometer-scale doped multilayer graphene (DMG) interconnects well suited to the mass-production of integrated circuits.
Yet, one of the hurdles that faces this innovation becoming reality is that it could be met with some resistance from the multi-billion-dollar semi-conductor industry. So, it may be some time before we see super-computers equipped with this pioneering material.
However, graphene is considered to be a highly logical choice when considering suitable materials for interconnects, the basic components that connect scores of transistors on microchips in computers and a wide range of other electronic devices in today’s technological landscape.
This is due to the fact that graphene is 100 to 300 times stronger than steel and carries a maximum electrical current density order of magnitude that exceeds that of copper as well as being highly flexible at just one-atom-thick – this surely makes it the thinnest, strongest and most reliable electrically conductive material in the world.
For more than 20 years interconnects have been manufactured using copper as the base material, yet, the limitations of this metal when shrinking it to the nanoscale resistivity increases which poses a, “fundamental threat to the $500 billion semiconductor industry,” say researchers at UCSB. Graphene holds the potential to resolve this issue as a global desire for smarter, faster, lighter and affordable technology and devices continues to expand.
“As you reduce the dimensions of copper wires, their resistivity shoots up,” states Kaustav Banerjee, a professor in the Department of Electrical and Computer Engineering.
Resistivity is a material property that is not supposed to change, but at the nanoscale, all properties change.
Since graphene was discovered back in 2004, scientists and researchers around the world have been working to establish commercially scalable applications and processes for this supercharged material. The UCSB team now believe they have found a promising method to use graphene for interconnects.
However, it is not a case of simply replacing copper with graphene in the manufacturing process as research is still being carried out. Therefore, transposing the material from the university or other facility testing environments to high-volume production and wide-spread usage is yet another obstacle that must be overcome.
Professor Banerjee states that the only way the semiconductor industry will move forwards is when, “you find a way to synthesize graphene directly onto silicon wafers.” Issues arise back-end synthesizing after the transistors are fabricated – you face a thermal budget that can’t exceed a temperature of about 500 degrees Celsius.
If the silicon wafer gets too hot during the back-end processes employed to fabricate the interconnects, other elements that are already on the chip may get damaged, or some impurities may start diffusing, changing the characteristics of the transistors
Now, after a pursuit of over a decade, Professor Banerjee’s lab has developed an innovative pressure-assisted solid-phase diffusion method that enables the direct synthesis of high-quality multi-layer graphene compatible with typical standard industry processes for the mass production of integrated circuits. A method that requires the application of pressure and temperature to two materials in close contact so to cause them to diffuse into one another. Thus, overcoming the bottleneck of risking damage or diffusing any impurities to other elements present on the chips and keeping the characteristics of the transistors intact.
The process began with the UCSB team depositing solid-phase carbon in the form of graphite onto a deposited layer of nickel metal of optimized thickness. Then, exposing the graphite powder to heat (about 300 degrees Celsius) and pressure caused disintegration in the graphite. The high diffusivity of carbon in nickel enables it to move quickly through the metal film forming multiple graphene layers as the carbon atoms then recombine on the other surface of the nickel closer to the dielectric substrate.
Junkai Jiang, Lead author of UCSB’s research paper explaining the process, said the lab was able to, “optimize the nickel thickness and other process parameters to obtain precisely the number of graphene layers we want at the dielectric surface”.
“Because our process involves relatively low temperatures that pose no threat to the other fabricated elements on the chip, including the transistors, we can make the interconnects right on top of them,” Mr. Jiang continues. UCSB has since filed a provisional patent on their innovative process, hoping to overcome certain barriers that have so far prevented graphene from replacing copper.
The challenge remains in getting tech-giants such as Intel – who produce a vast amount of chips each year with great profits – to accept replacing copper with graphene into its manufacturing process. UCSB’s Banerjee has been in negotiations with industry partners that have demonstrated an interest in licensing the compatible graphene synthesis technology, which could pave the way for what would be the first 2D material to enter the mainstream semiconductor industry.
So, whilst graphene interconnects help to create more compact, faster, and flexible, integrated circuits that are both more reliable and more cost-effective. The next challenge is wooing industry into accepting this material into the fold and seeing it as a compatible partner for the future of supercomputing and other advances in science and technology.