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Mark Stewart, senior research scientist at the National Physical Laboratory, discusses his work on the EMRP Nanostrain project and how it will drastically improve the life of mobile devices.
In 1991 Sony commercialised lithium-ion battery technology, taking the electronics of the transistor and making it portable. It revolutionised mobile telephones and laptops and paved the way for the smartphone.
25 years later this technology has not significantly changed. In its early years it had no need to; it solved problems for Sony, such as the size and weight of batteries for handheld video.
This remained the case until the early 2000’s. However, the last decade has been the era of the smartphone, and as functionality and performance have improved, one thing has remained constant: the inadequacy of the battery life.
Now researchers have developed new piezoelectric 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 piezoelectric materials change their shape (‘strain’), in response to applied voltages. Withdrawing the voltage causes the material to return to its original form. As this relationship is reversible, a piezoelectric actuator can cause a piezoresistive material to switch between an insulator and conductor, offering 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 can switch it between a conducting and an insulating state. This changes the thickness of the piezoelectric layer so that it exerts a very large strain-induced stress on the piezoresistive material. This sequence of events occurs almost instantly and far more efficiently than is possible in traditional transistors. IBM is currently developing the devices at its research facilities in Zurich.
The increased efficiency in this process is the benefit of the PET technology. Inefficiencies are nearly always realised as heat, so faster computing equals more heat. This has become such a problem in server farms that Microsoft has suggested building them underwater.
So far PET technology and prototypes have been restricted to the laboratory. To accelerate their route to market we need new, more accurate measurements to better understand how these materials work and how they can be used. This is the objective of the Nanostrain project; funded by the European Metrology Research Programme (EMRP), it brings together national laboratories, world-class research instrument facilities and commercial companies to achieve its aim.
Nanostrain is developing tools for the characterisation of strain under real-life, high stress conditions. One example is a collaboration between the UK’s National Physical Laboratory and the XMaS beamline at the ESRF in Grenoble to develop a technique to measure strain limits in thin films. The instrumentation developed helps us explore how materials react to applications of voltage and reveals a detailed picture of their electronic transport properties.
If successful the Nanostrain project could provide wide benefits to those who rely on smartphones, tablets and laptops by allowing greater processing power. These include faster internet access, longer battery life and lower energy consumption. With these capabilities, we could reinstate Moore’s Law and see a new era of computing.
