Inside the memristor

The old guard of circuit theory were the resistor, capacitor and inductor. Now we have the memristor and a revolution.

The basic building blocks of circuit theory, which have been all but etched in stone, teach us the essential elements of the resistor, capacitor, and inductor – it is with these that the abundant joy of electronic wonderment (aka, your beloved PC) is made manifest. Deep in the heart of your baby, these building blocks define the very nature of your gear.

But for almost 40 years now it’s been postulated that one more element should exist. First described by then electrical engineering student Leon Chua in 1971, the concept of the memristor (aka ‘memory resistor’) was a proverbial missing link for circuit theory. Importantly, the memristor – at least as a theory – would stand on its own because its properties can’t be duplicated by any combination of the other three elements. And should it exist, it could revolutionise not only circuit design, but the technology that we take for granted every day.

Until recently, that is. While Chua formulated the existence of the memristor, it took Hewlett Packard Senior Fellow Stanley Williams and his team to discover it, or rather build it. And suddenly the pair became big news.




The missing link
So significant is the memristor that both Williams and Chua are saying electronics engineering textbooks will need to be re-written – this isn’t just a hot new tech, it’s a revolution of technology we’ve come to take for granted, and the very basis by which circuits are designed.

Based on Chua’s work, Williams and his team at HP were able to create a physics-based model of a memristor, and then create one in their lab at the nanoscale level. In fact, it’s a property of the memristor that its efficiency scales with size – and nanoscale is where it’s at. According to Williams, the key operation of a memristor involves atoms that change place when voltage is applied (more on this below), and this happens easier at the nanoscale.

Which leads us into how memristors are going to re-write the books – Chua suggests that traditional circuit theory that deals in the relationship between voltage and charge is all wrong. And in the past when inaccuracies popped up in circuit theory and design, they have always been dismissed as anomalies.

But if laws of cause and effect are anything to go by, there’s no such thing as an anomaly and Chua believes the memristor is the missing piece of the puzzle, stating “Electronic theorists have been using the wrong pair of variables all these years – voltage and charge. The missing part of electronic theory was that the fundamental pair of variables is flux and charge”. Or in other words, the changes between voltage and charge.

And this is the theory that enabled Williams to embark on creating the world’s first memristor.