Boffins baking big-data single chip architecture
Graphene, electrons and the end of 'conventional silicon electronics'
The spin doctor
The answer, it has been discovered, is to add a layer of insulation that keeps the spin inside the graphene, a discovery that saw the injection of half an atomic layer of titanium into the material. To achieve this, Kawakami’s team worked out how to grow graphene in sheets, something this material doesn’t like to do naturally.
“We put in a small amount of atoms – half an atomic layer of titanium – before we grow this film, and that prevents the molecules from forming balls,” Kawakami said. “I think there was a sense this was the important first step to make this material and it would work better.”
The benefit has been increased data retention, as the lifetime of spins has increased from 100 picoseconds to two nanoseconds.
Milestones planned for the next two years include the development of a completely new type of tunneling barrier and the demonstration of a new form of spin torque, writing magnetic bits that are compatible with graphene.
Long term, the team must work on the logic problem: how to assemble logic from different electrodes and spins. “We are doing experimental and laboratory work to understand basic processes," says Kawakami. "We have a fuzzy idea this could be good for logic and computation in general but that’s not our expertise.
“In our team, we have a concrete plan of a circuit we want to make. But that’s fairly rare... The general challenge is you have these gates that do these particular digital logic operations, or used to, and the challenge is how do you connect one device to another and transmit the other.
"Normally that’s done using volatile states. One of the general questions for doing spin logic is how do you connect different devices so an operation in one gate can be combined with logic operations on another gate to produce a higher level function?”
The first function the circuit will be built for is high-speed search.
Other challenges remain: can the graphene conduct the electrons fast enough while on power? Kawakami has just asked a colleague for deeper analysis.
Kawakami believes a working magnetologic gate can be delivered for use as a building block in other systems in three years’ time.
The reason is the project's remaining challenges are not show-stoppers. The real roadblock was blown away by the University of Manchester’s earlier work on graphene, which delivered the properties required for the construction of the gate and also on how to achieve spin at room temperature.
Now, it’s a matter of fine-tuning the graphene. When it comes to RAM, the team has options that include magnetic RAM, flash RAM and ferroelectric RAM. “There are many different candidates of other memory, It’s not a case of does it work but does it work better than other methods,” Kawakami said.
The University of Manchester has also been pushing the frontier on graphene in the area of tunnel barriers. “At a level where we can make this device – be able to make this device work - that part I’m very confident we can do,” Kawakami says.
He pauses, and re-phrases: “I've learned talking to engineers: there are more issues that come up that I hadn’t thought about. But at the level of can we make a gate, make it operate and operate well – definitely, we can do that.” ®
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