Cambridge researchers promise breakthrough in 3D chip design

Physicists at the University of Cambridge have developed a new way of transferring data and logic signals from one layer of a 3D chip to another.

Although it is possible to transfer date using conventional circuitry, such a traditional approach is cumbersome and generates a lot of heat inside the 3D circuit. However, the physicists managed to develop a spintronic shift register that allows information to be passed between different layers of the chip, Gizmag reports.

At the moment, 3D chips appear to be the only way of overcoming limitations in chip design, posed by lithography, materials and thermal limitations. Chip designers could use the 3D approach for the next decade or two, as it will allow them to stack multiple layers of circuitry in a single package. However, until now there was no good way to transfer information between the layers. Using currently available technology, the advantages of 3D chips could be nullified, as they would eventually have to use most of their circuitry to pass information back and forth between different layers.

Professor Russell Cowburn and his team took up the challenge and came up with a vertically layered spintronics shift register to move data vertically between the layers, without the need for specialised circuitry. High density hard drives and magnetic random access memory currently use Spintronics. It relies on electronic current with parallel electron spins to pass information. Spin polarised current is sent through an ultrathin magnetic layer and the size of the current that passes depends on the orientation of the magnetic field and the spin direction. Since the current is controlled by a magnetic field, it can be used to read data.

Professor Cowburn’s team replicated the approach by using ultrathin layers of various materials to demonstrate how spintronics could be used to transfer data between 3D circuitry layers. They used a 2nm magnetic cobalt-iron-boron layer and a ruthenium layer, less than a single nanometer in thickness. The use of ultrathin films would allow developers to create very thin spin-up and spin-down domains, about 6nm in width.

However, a lab demonstration revealed the rapidly flipping magnetic fields are not good for super-large-scale integrated circuitry. The researchers hope to improve the technique by moving magnetically encoded data by flowing spin-polarised currents from layer to layer, causing the entire domain structure to climb within the stack. The lab demonstrator is hard wired and it can only send information upward.