The 2018 highlights of the graphene research include its applications in chemical sensors, advanced uses of its mechanical properties, along with high-frequency uses, such as in ultrafast graphene transistors and optical communications.
Since the beginning of applied graphene research, trace detection of harmful chemicals has been the focal point. An array of graphene sensors for sensitive and selective detection of ammonia has been developed last year by MIT and Graphenea. It includes 160 graphene pixels, which allow the generation of large statistics, and that ultimately leads to improved sensing performance.
The sensors are also widely tested for a number of real-life operational conditions, which is one more step towards their practical use. Porphyrin molecules are attached to graphene and those make it more functionalized, meaning that the sensors become selective - sensitive only to ammonia.
Functionalization has established itself as a universal way of implementing selectivity. Devices as advanced as an “electronic nose” possess a bunch of graphene sensors that have the ability to “sniff” the chemicals that are present in the environment.
Applying Machine Learning on Bare Graphene Sensors
Another way to implement selectivity is to apply machine learning on bare graphene sensors. Machine learning is used more and more in many scientific and technological fields. It is based on self-improving algorithms that consider thousands of examples in order to optimize a certain outcome.
When it comes to graphene sensors, the algorithm learns from the electronic response of hundreds of examples of graphene exposition to a variety of chemicals. Therefore, a single sheet of unprocessed graphene can be used to detect and differentiate the presence of compounds, such as acetone, chloroform, toluene, hexane, acetic acid and more.
The mechanical properties of graphene are superior; however, the way they can be applied has not been extensively studied yet. A significant advance in putting to use the exceptional mechanical properties of graphene, such as large strength, light weight and thinness, was achieved last year.
A publication in Nature Communications highlights the use of graphene in GIMOD – graphene interferometric modulator display. An interferometric modulator display makes use of a number of mechanical pixels that change color under applied voltage. A key constituent of mechanical pixels is a detached membrane that changes position when voltage is applied. It scans through optical interference fringes in order to create a specified color.
Benefits of Graphene IMODs
IMODs made from other materials have a major drawback – low frame rates and limited color gamut, which make their use harder. By contrast, graphene IMODs have proven to operate at up to 400 Hz and cover the full visible spectrum, yet exhibiting reduced flicker effect. The demonstrated GIMOD prototype has 2500 pixels per inch, equivalent to more than 12 K resolution, which is higher than UHDTV.
The practical use of NEMS/MEMS devices, based on graphene, was explored by the German-Spanish project NanoGraM, which ended in 2018. The project was a collaboration between four companies and one university, and they managed to produce graphene microphones, pressure sensors, and Hall sensors. Graphene microphones exhibit higher sensitivity than traditional ones across the audible and ultrasonic parts of the spectrum. Pressure and magnetic field sensors made of graphene have enhanced signal-to-noise ratios, sensitivity and robustness. The project achieved seven scientific publications and three patent applications.
Due to the technological development which helps to provide graphene of higher quality and better circuit integration, the performance of graphene for high-frequency applications keeps advancing. For instance, contact engineering has been able to lower the contact resistance between graphene and metal to a record low of just 23 Wmm for gold contacts. Contact resistance below 50 Wmm is desired and it is the typical value in high-frequency transistors used for computation.
Applications of Graphene
The fields of optoelectronics and optical communication are yet another place where the improved integration of graphene in semiconductor devices has enabled a topnotch performance. In 2016, the bandwidth of graphene photodetectors reached 65 GHz, utilizing graphene/silicon pn junctions with potential bit rates of ~90 Gbit s-1.
As soon as 2017, graphene photodetectors with a bandwidth exceeding 75 GHz were fabricated in a 6” wafer process line. In 2018 the Mobile World Congress was held in Barcelona and those record-breaking devices were showcased there. It was made possible for visitors to experience the world’s first all-graphene optical communication link operating at a data rate of 25 Gbit s-1 per channel.
In the demonstration, all active electro-optic operations were performed on graphene devices. The data was processed on the transmitter side of the network by a graphene modulator, which at the same time encoded an electronic data stream to an optical signal.
On the side of the receiver, the opposite was done by a graphene photodetector, which converted the optical modulation into an electronic signal. The devices were made with Graphenea CVD graphene and were showcased at the Graphene Pavilion.
The application of graphene in chemical sensors, high-frequency electronics and mechanical devices are only some of the wide variety of application of graphene that are advancing and enabling new technology.
The Graphene Flagship midterm annual report is a good starting point for getting a comprehensive overview of the myriad of applications that are in development and about to reach the markets in the next several years.
This information has been sourced, reviewed and adapted from materials provided by Graphenea.
For more information on this source, please visit Graphenea.