US based scientists have developed a samarium nickelate-based transistor that matches the electron switching abilities of silicon. This may enable the unprecedented shrinkage of consumer electronics.
Silicon currently dominates the electronics industry thanks to its unrivalled electronic properties and cheapness of manufacture. However, with consumers demanding ever smaller electronic devices, silicon’s position at the top is looking less certain. Physical limitations such as heat dissipation dictate how small electronic components made of silicon such the switchable valves that control the flow of electrons in a circuit (transistors) can become.
The search is therefore on to find a semiconducting material that performs as well, or better, than silicon that can be shrunk further. The on/off ratio is one of the most important measures of a transistor’s performance. This is a measure of the difference between the electrical resistance of a transistor’s on and off state, and if the difference isn’t great enough the switch will still conduct electrons even when it is ‘off’. Silicon transistors have an on/off ratio of at least 10,000; but previous metal oxide-based transistors explored have only managed a factor of 100 at room temperature.
Now, Shriram Ramanathan and his team at Harvard University in the US have developed a hydrogen ion-doped samarium nickelate-based transistor that has an on/off ratio greater than 100,000. This work is published in Nature Communications [Shi J., Nat. Commun. (2014) doi: 10.1038/ncomms5860].
The key to Ramanathan’s team’s approach is the movement of hydrogen ions between a thin film of samarium nickelate and a neighbouring thin film of yttrium-doped barium zirconate.
When the transistor is switched, the change in external electric field causes the protons and electrons to move between the two thin film layers within the device. This influx or loss of electrons in the samarium nickelate film causes the modulation of the material’s band gap, resulting in an unprecedented change in electrical resistance and therefore on/off ratio. This modulation of the material’s band gap is the novelty of this approach, as doping is normally just used to change the number of available electrons in a material.
The team also showed that this phenomenon is not linked to external temperature, meaning the device can operate at the same temperature as conventional electronics. The transistor also remembers its present state when the power is switched off, an important property for energy efficiency.
“The doped and insulating phase we have observed is essentially a new metastable material whose properties are mostly unknown,” Ramanathan told Materials Today. “We plan to study this systematically to better understand the physical properties. At the same time, we are interested in exploring scaled devices with our transistor to measure the switching dynamics.”