Could piezoelectrics solve the smartphone battery conundrum?

In 1991 Sony commercialised new lithium-ion battery technology, which took the electronics of the transistor and made it portable; revolutionising mobile telephones and laptops in the process and paving the way for the tablet and smartphone.

25 years later this technology has not significantly developed. In its early years it had no need to, solving early problems for Sony, such as the size and weight of batteries needed for handheld video, and providing an adequate battery solution for the first consumer mobile phones.

This remained the case until the early 2000’s, when batteries in mobile phones would regularly last for days without the need to be recharged. However, the last decade has been the era of the smartphone, and as functionality and performance has improved, one thing has remained constant: the inadequacy of the battery life.

The latest smartphones are more than 10 times faster than their predecessors, but the battery is still lucky to last the day with average usage. Given the huge gap between the iPhone 1 and iPhone 6, keeping this comparable is impressive but more to do with better processors than improved batteries.

But researchers have now developed new transistor materials that could see processors working at one tenth of the current voltage, consuming up to 100 times less power as a result and greatly improving battery life.

The new materials - called 'piezoelectric' materials - change their shape, or ‘strain’, in response to applied voltages. This relationship is reversible, so these new materials act as transistors, switching from an insulator to a conductor and back. This acts as a series of 1s and 0s and therefore offers the possibility of reading and writing digital information.

Researchers at IBM have filed the first patents for PET (Piezoelectric-Effect-Transistor) technologies and developed a prototype device. It consists of a piezoresistive material sandwiched between a piezoelectric material and a rigid structure. Applying a voltage to the prototype can switch it between a conducting and an insulating state almost instantly and far more efficiently than the laws of physics allow for traditional transistors. IBM is currently developing the devices at its research facilities in Zurich.

The increased efficiency is the key to the PET technology advantage. Inefficiencies are nearly always realised in the form of heat. As anyone who has tried to overclock their PC processor knows, faster computing equals more heat. This has become such a problem in server farms that Microsoft have suggested building them underwater to beat the heat.

So far PET technology and prototypes have been restricted to the laboratory. To develop them further and accelerate their route to market we need new, more accurate measurements and best practice to better understand how these materials work and how they can be best exploited. This is the objective of the Nanostrain project; to enable the exploitation of commercial opportunities arising from controlled strain in nanoscale piezoelectrics. It is funded by the European Metrology Research Programme (EMRP) and brings together national laboratories, world-class research instrument facilities and commercial companies from across Europe to achieve its aim.

The Nanostrain project is developing new tools for the characterisation of nanostrain under real-life, high stress conditions. One example is where a team of scientists from the UK’s National Physical Laboratory collaborated with the XMaS beamline based at the ESRF in Grenoble to develop a new measurement technique to measure strain limits in thin films. The instrumentation developed presents a method to understand the electronic transport properties of materials.

If successful the Nanostrain project could help to provide an array of benefits to those of us who rely on smartphones, tablets and laptops through delivering greater processing power. With these benefits, we could potentially reinstate Moore's Law and see a new era of computing.

Mark Stewart, Senior Research Scientist at the National Physical Laboratory