In 1991, Sony commercialised 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.
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A quarter of a century later, this technology has not significantly developed any further. In its early years, it had no need to. It solved some early problems for Sony, such as the size and weight of batteries needed for handheld video, and provided an adequate battery solution for the first consumer mobile phones.
This remained the case until the early 2000s, when batteries in mobile phones would regularly last for days on end without needing to be recharged. However, the last decade has truly been the era of the smartphone, and as the functionality and performance of phones have improved, one thing has remained constant – the inadequacy of battery life.
The latest smartphones are more than 10 times faster than their predecessors, but the battery is still lucky to last a day with average usage. Given the huge gap between the original iPhone and the iPhone 6s, keeping this comparable is still impressive, although it is more to do with better processors than improved batteries.
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, or ‘strain’, in response to applied voltages. Applying a voltage to the material causes strains in it that result in tiny changes in shape, and withdrawing the voltage causes the material to return to its original form.
The close relationship between the mechanical and electrical properties of piezoelectric materials means that an applied voltage forces a reorientation of a material’s molecular dipole moments and therefore physical shape. As this relationship is reversible, the addition of strain produced by a piezoelectric actuator can cause a piezoresistive material to switch from being an insulator to a conductor and back, offering the possibility of reading and writing digital information.
Researchers at IBM have filed the first patents for piezoelectric-effect transistor (PET) technologies and have developed a prototype device based on these materials. It consists of a piezoresistive material sandwiched between a piezoelectric material and a rigid structure made of a high-yield material, in this case a nano-indenter and a sapphire plate.
Applying a voltage to the prototype 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 the laws of physics allow for traditional transistors. IBM is currently developing the devices at its research facilities in Zurich.
It is this increased efficiency that is the key to the PET technology advantage. The inefficiencies are nearly always realised in the form of heat, and 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 has 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 best be exploited.
This is the objective of the Nanostrain project – to enable the exploitation of commercial opportunities arising from controlled strain in nanoscale piezoelectrics. Nanostrain 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.
Using a range of novel techniques, the Nanostrain project is developing new tools for the characterisation of nanostrain under real-life, relevant conditions of high stress and electric fields. One example is where a team of scientists from the UK’s National Physical Laboratory collaborated with the XMaS beamline based at the European Synchrotron Radiation Facility (ESRF) in Grenoble to develop a new technique to measure strain limits in thin films.
The instrumentation developed presents a method to explore how such material reacts to applications of voltage and reveals a detailed picture of the structural and therefore electronic transport properties of such material.
If successful, the Nanostrain project could help to provide an array of benefits to those of us who rely on smartphones, tablets and laptops by delivering greater processing power. These benefits include faster internet access, reduced device weight, longer battery life and lower energy consumption – the exact issues plaguing smartphone manufacturers today.
With these capabilities, we could potentially reinstate Moore’s Law and see a new era of computing.
Mark Stewart is senior research scientist at the National Physical Laboratory and is working on the EMRP Nanostrain project