Traditionally, graphene has been considered as a perfect candidate channel material for Radio Frequency (RF) flexible electronics. At IEMN-CNRS, Graphenea and Nokia, Scientists have recently demonstrated flexible graphene transistors with a record high cut-off frequency of 39 GHz.
The graphene devices, composed of flexible polymer substrates are stable against fatigue and bending of repeated flexing.
Driven by a potentially huge market for smart devices and wearables, flexible electronics has become a highly active research and application field. It is anticipated that in the near future people will be wearing recreation, medical and entertainment devices on their clothes, a goal which requires sensors to be positioned on numerous types of flexible supports. These devices and sensors will communicate with each other, which will need an additional layer of flexible RF electronics.
Graphene Field Effect Transistor
Transistors form the core building blocks of RF electronic components such as amplifiers and mixers, so a new generation of flexible RF transistors is the answer to enabling the smart devices and wearables markets.
Graphene, a strong, flexible, thin material with exceptionally high carrier mobility, is a perfect option for channel material for such types of transistors. Flexible graphene transistors are an active research direction but this latest work, published in the Nanoscale journal, shows a record high frequency by taking device fabrication to a new level.
Figure: Flexible graphene RF transistor (reproduced from Nanoscale 2016, 8, 14097-14103 with permission from The Royal Society of Chemistry).
The graphene field effect transistor (GFET) is developed from high-quality CVD grown graphene with a carrier mobility of ~2500 cm2 V-1 s-1 on a flexible Kapton substrate with a thin alumina dielectric spacer in the channel region.
The use of such optimized and advanced materials leads to stability against bending and a record high frequency performance. The GFET continues to function even after 1,000 bending cycles and can be flexed to a radius of 12 mm with a cut-off frequency change of up to 10%.
Lastly, the device is examined for thermal stability. Thermal stability is a key issue in flexible electronics, because of the poor thermal conductivity of the polymer substrates normally used in such devices. The Researchers demonstrate that at high voltage bias, the device heats up and performance worsens irreversibly.
This new research on flexible GFETs sets a new record for the bandwidth and at the same time shows that degradation typically seen in these devices at high bias is due to thermal deformation of the substrate.
As research in this direction progresses, it is becoming clear that flexible GFETs are going to be around for a long time and will serve as crucial building blocks of future wearable technology.
This information has been sourced, reviewed and adapted from materials provided by Graphenea.
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