How Edge of Chaos could transform chip design

To keep the signal strong, engineers use a system of amplifiers and repeaters, but these add complexity, increase cost, and limit the design of smaller, more efficient chips.

Researchers from Sandia National Laboratories, Stanford University, and Texas T&M University, published a study in Nature introducing a new method for transmitting electrical signals that doesn’t rely on bulky amplifiers, but instead draws inspiration from how biological neurons – specifically, the axons in nerve cells – transmit signals efficiently over long distances.

The limitations of current technology

Today’s electronic chips are becoming more densely packed, with narrower interconnects, and as these interconnects become smaller and longer, the signal losses due to resistance increase. To solve this problem, engineers break the transmission line into sections and place amplifiers, buffers, or repeaters in between which boost the signal as it travels, but this also creates complexity and inefficiencies in the design.

For example, in modern chips, delays in signal transmission are more commonly caused by the resistance and capacitance of the interconnects than by the transistors themselves. This means that improving the transmission lines has become just as important as making better transistors.

Axons and self-amplification

In contrast to how electronics handle signals, biology has developed an elegant solution over millions of years. Axons, the long, slender projections of nerve cells, can transmit electrical signals over distances without losing strength. They do this through a process called self-amplification where the signal is continually regenerated as it travels along the axon, meaning it doesn’t require external amplification.

Axons achieve this by using ion channels that open and close in response to electrical signals, allowing ions to flow in and out of the cell, which regenerates the signal. This biological mechanism inspired the researchers to develop a new method for transmitting electrical signals in electronic systems.

Welcome to the Edge of Chaos

The breakthrough in this study is based on the concept of the Edge of Chaos (EOC), a state where a system is active enough to amplify small signals but stable enough to avoid becoming chaotic. This state, though theorised for many years in both biological and electronic systems, has been challenging to reproduce in experiments.

The researchers managed to isolate the semi-stable EOC state by using a special material called LaCoO3, which has unique properties that allow it to amplify electrical signals. In their experiment, a metallic line was placed on top of a layer of LaCoO3, which was electrically biased (meaning it was supplied with a controlled electric current). The signal entering one end of the metallic line emerged from the other end stronger than it was at the start, and without the need for any additional amplifiers.

What makes LaCoO3 special?

LaCoO3, or lanthanum cobalt oxide, is a material that changes its properties depending on temperature and electric current. In this study, it was used to access the Edge of Chaos state. When electrically biased, LaCoO3 enables a phenomenon called negative differential resistance (NDR), where the material’s resistance decreases as the current increases which is vital for amplifying small electrical signals.

By accessing this NDR region, the researchers could achieve continuous signal amplification. Unlike typical electronics, where signals decay as they travel through resistive materials, the signal in this system grows stronger as it moves along the metallic line.

A new way forward for electronics

Currently, transmission lines are broken into smaller sections with amplifiers placed between them; However, this method makes the chips harder to design and limits how small they can be. By eliminating the need for external amplifiers and repeaters, this system allows for simpler, more compact chip designs.

This new approach allows for continuous signal amplification along an unbroken path, meaning that devices can be smaller, faster, and more efficient, as they won’t need to rely on thousands of repeaters or amplifiers. And, unlike superconductors, which require extremely low temperatures to work, this method operates at normal temperatures and pressures, making it more practical for everyday use.

What’s next?

The next steps for the researchers are to better understand how the energy used for signal amplification can be managed more efficiently and how to increase the frequency range at which this amplification occurs. They will also explore other materials and configurations that might enhance the performance of this system. If successful, this method could alleviate the current bottleneck in chip design caused by signal losses in densely packed interconnects.