Boffins baking big-data single chip architecture
Graphene, electrons and the end of 'conventional silicon electronics'
Graphene saves the day
The work builds on earlier breakthroughs: the idea of spin-based computing using a magnetologic gate that was devised at UC San Diego in 2007 and on tunneling spin injection and spin transport in graphene from a group led by Kawakami in 2010.
In 2010, Kawakami’s team realised that graphene was good for helping create electron spin with the help of a magnet working at room temperature. This was a vital breakthrough because it put the economics of constructing an affordable device and physics of making it work into the realms of the possible.
Kawakami said: "After our breakthrough on performance in 2010, we ran numbers we got on graphene and found it could run very fast, at the gigahertz level, and the amount of power used would be very low. This is a potentially viable technology... by integrating the memory with the logic especially for any applications that use lots and lots of data, like search, image recognition and compression."
But the hard work of bringing all that work and theory together is now underway, and that’s what will be funded by that $1.58m.
The really big challenge comes in mastering spin: a materials issue, Kawakami said. “We need to get control over that process," he said. "We’ve done the best anyone can do, but it’s still not enough for this project."
The gate’s electrodes are ferromagnets. A small current is applied to the magnet that replicates the data as electron spins in the graphene. The idea, ultimately, is for the electrons in the graphene to mix and match the data to produce a logic operation, thereby achieving the goal of combined memory and logic operation on one chip.
Only, there are a couple of problems.
The first is how long a spin lasts: the best results are obtained the longer the spin lasts but right now the number of spins is well below the theoretical ceiling – by a factor of 1,000. Kawakami says the reason for this is unclear. “What’s limiting the spin is a big scientific mystery,” he says, noting that experiments are underway to improve the manufacture of graphene itself.
The other challenge is making the spin of the electrons – that's the process of copying the data from the electrode and putting it in the graphene – uniform. Right now, the process isn’t uniform or predictable enough for product, as some electrodes produce too much spin and others too little.
Kawakami’s team are piggybacking on evolving research in the field of magnetic RAM for answers and are developing new methods compatible with graphene. They are looking at spin torque, which controls the orientation of the magnetic electrode and thereby whether something is recorded as a zero or a one.
“We have to develop a special type of electrode geometry to get the spin torque to work with the graphene: that’s the main challenge,” he says.
This isn’t just about data transfer, however. The research is also considering the ramifications of power consumption – thereby determining the efficiency and green credentials of the finished magnetologic gate. “We think this is a really important part of the device because this will be the step that uses the most energy,“ Kawakami says. “So, we want to optimise this process as much as possible because this will be the energy cost of running the device.”
To further help control spin, a tunnel barrier is needed between the electrodes and graphene. The problem with spin is that it likes to leak out of the graphene, says Kawakami.