Ecole Polytechnique Federale de Lausanne researchers have created a tiny, tunable, graphene-based device that could significantly increase the efficiency and speed of wireless communications. Newly developed device, which they named Graphene Quantum Capacitor (GQC), works at extremely high frequencies, delivering unprecedented results and could revolutionize on how “Internet of Things” devices connect and interact in the future.
We all use wireless communications every day. We would in fact be lost without it. Computers using Bluetooth to connect to portable sensors, mobile phones using 4G or 5G and GPS devices are a few examples. For all of these devices to be compatible, they have to be able to operate across a wide range of frequencies and preferably use as little hardware as possible to make them lightweight and portable.
Most portable, wireless systems come equipped with circuits that can be reconfigured to adjust the devices to transmit and receive data in various frequency bands. The biggest problem is that current technologies mostly use silicon or metal, and these materials do not work well at high frequencies.
Graphene is a conductor that is both flexible and transparent. It also has some additional properties that make it truly extraordinary. Not only does it conduct electricity and heat efficiently, but it is also about 100 times stronger than steel. It can be levitated by Nd-Fe-B magnets and shows a nonlinear diamagnetism that is large. With sales in the electronics, semiconductor, composites and battery energy industries, it is no wonder that its global market in 2012 exceeded $9 billion. Further applications can be found in solar cells, touch panels, light-emitting diodes (LED) and smartphone screens.
The latest device developed and produced in EPFL’s Nanoelectronic Devices Laboratory is graphene-based, tunable and works at very high frequencies. The results achieved with the device has been described by experts in the field as unprecedented. Data can travel at its fastest at high frequencies, but this is something not achievable by either MEMS or MOS capacitors. The new graphene-based solution aims to replace current tunable capacitors, a component found in all wireless devices. Other limitations of traditional tunable capacitors are their inability to be tuned using low energy, bad performance at high frequency and miniaturization limitations. The new device will overcome all of these shortcomings.
Clara Moldovana, researcher at the EPDL, explains that the surface area of the new device is a thousand times smaller than what would be required by conventional capacitors to achieve the same results. In spite of this, it is compatible with traditional circuits and consumes very little energy. Even with its miniaturized design it easily outperforms its competitors. Although graphene is seen as a miracle material due to its flexibility, light weight, good electrical and thermal conductivity and sturdiness, its atomic thickness results in a high effective resistance which makes it extremely difficult to integrate into electronic systems.
EPDLs solution uses a clever sandwich structure that utilizes graphene’s unique characteristics. A two-dimensional gas of electrons can behave like a quantum capacitance in a quantum well and the structure takes advantage of this. As a specific amount of energy is required to fill a quantum well with electrons, a single-atom layer of graphene can easily measure quantum capacitance. By changing the charge density in graphene with a very low voltage, the graphene becomes tunable. This is a key advantage over conventional capacitors, which need a higher voltage.
Graphene quantum capacitors (GQC) are facilitators of radio-frequency (RF) functions through voltage-tuning of their electrical capacity. GQC enhances MOSFETs and MEMS in terms of performance for their tunability and high frequency analog applications. Researchers introduced a CMOS compatible fabrication process and describe the first experimental assessment of their performance at microwaves frequencies (up to 10 GHz), showing experimental GQCs in the pF range with a tuning ratio of 1.34:1 within 1.25 V, and Q-factors up to 12 at 1 GHz. The value of graphene variable capacitor figures are studied thoroughly from 150 to 350 K.
Potential applications for the EPFL researchers’ graphene quantum capacitor device are numerous. Due to its tiny size (only several hundred micrometers, about 0.05 cm / 0.02 inch, long and wide), its use could lead to devices that are even more compact. Not only does it improve the flow of data between connected devices, it could extend battery life due to its low power requirements and when in its flexible form it could easily be used as sensors fixed in clothing or placed directly on the human body. Moldovan concludes that the results achieved in tests confirm that graphene will most likely revolutionize the future of wireless communications.
EPFL has professors, staff and students from over 120 nations and is described as Europe’s most cosmopolitan technical university. They have three missions: teaching, research and technology transfer. To achieve these missions, EPFL works to bring about real impact for society by working with an extensive network of partners. These include developing and emerging countries, other universities and institutes of technology, secondary schools and colleges, political circles, industry and economy and the general public.
Their research has been published in Nanoletters journal.