Tag Archives: letter-pulse-tech

Germanene is a 2D material that derives from germanium and is related to graphene. As it is not stable outside the vacuum chambers in which is it produced, no real measurements of its electronic properties have been made. Scientists led by Prof. Justin Ye of the University of Groningen have now managed to produce devices with stable germanene. The material is an insulator, and it becomes a semiconductor after moderate heating and a very good metallic conductor after stronger heating. The results were published in the journal Nano Letters.

Germanane is converted into germanene by thermal annealing, which removes the hydrogen (red). Credit: Ye Lab / University of Groningen

Materials of just one atomic layer are of interest in the construction of new types of microelectronics. The best known of these, graphene, is an excellent conductor. Materials like silicon and germanium could be interesting as well, as they are fully compatible with well-established protocols for device fabrication, and could be seamlessly integrated into the present semiconductor technology.

Unstable

‘But the 2D version of germanium, germanene, is very unstable’, explains University of Groningen Associate Professor of Device Physics Justin Ye. Germanene is made from germanium by adding calcium. The calcium ions create 2D layers from a 3D crystal and are then replaced by hydrogen. These 2D layers of germanium and hydrogen are called germanane. But once the hydrogen is removed to form germanene, the material becomes unstable.

Ye and his colleagues solved this in a remarkably simple way. They made devices with the stable germanane, and then heated the material to remove the hydrogen. This resulted in stable devices with germanene, which allowed the scientists to study its electronic properties.

Hydrogen

‘The initial material was an insulator’, says Ye. A Ph.D. student from his group heated these devices, which is a tried and tested method to increase conductivity. He noted that the material became very conductive, and its resistance was just one order of magnitude above that of graphene. ‘So it became an excellent metallic conductor.’ Further experiments showed that moderate heating (up to 200°C) produced semiconducting germanane.

Germanene can, therefore, be an insulator, a semiconductor or a metallic conductor, depending on the heat treatment with which it is processed. It remains stable after being cooled to room temperature. The heating causes multilayer flakes of germanene to become thinner – confirmation that the change in conductivity is most likely caused by the disappearance of hydrogen.

Spintronic device

Germanene could be of interest in the construction of spintronic devices. These devices use a current of electron spins. This is a quantum mechanical property of electrons, which can best be imagined as electrons spinning around their own axis, causing them to behave like small compass needles. Graphene is an excellent conductor of electron spins, but it is hard to control spins in this material because of their weak interaction with the carbon atoms (spin-orbit coupling).

‘The germanium atoms are heavier, which means there is a stronger spin-orbit coupling’, says Ye. This would provide better control of spins. Being able to construct metallic germanene with both excellent conductivity and strong spin-orbit coupling should therefore pave the way to spintronic devices.

Leti, an institute of CEA-Tech, has developed a novel retinal-projection concept for augmented reality (AR) uses based on a combination of integrated optics and holography. The lens-free optical system uses disruptive technologies to overcome the limitations of existing AR glasses, such as limited field-of-view and bulky optical systems.

TVs and smartphones that project digital images emit light all around them, as quasi-isotropic sources. Because the images are projected generally over the air without directivity, many viewers see the same image. In typical AR glasses, images are transmitted close to the eyes (high directivity) by a microdisplay that includes an optical system and an optical combiner.

These microdisplays create a small near-to-eye image, which is transformed by the optical system, enabling the user to see it despite the short focusing distance. The combiner superimposes the digital image to the viewers’ vision of the real environment.

CEA-Leti’s innovation is a transparent retinal-projection device that projects various light waves to the eyes from a glass surface. Images are formed in the retina by the interference of light waves, which eliminates the need for optical systems or combiners. The light propagating in the air doesn’t form an image until it interferes precisely in the retina.

CEA-Leti presented its results Feb. 6 at SPIE Photonics West 2019 in a paper titled “Integrated Optical Network Design for a Retinal Projection Concept Based on Single-Mode Si3N4 Waveguides at 532 nm”.

The project focused on the design and numerical simulations of integrated Si3N4 optical components and the optical circuit at λ = 532 nm. It required building blocks for designing an optical integrated circuit capable of creating an array of emissive points. Starting with single-mode waveguides to efficiently transport light around the circuit, many other components were designed to manipulate light in different locations. Components for extracting the light, such as diffraction gratings, were also designed and simulated. The team minimized losses of different parts of the circuit, such as waveguide-bending areas, to increase energy efficiency of the system.

CEA-Leti’s integration of the device and its use of a holographic layer also allow creation of compact AR glasses with a larger field-of-view than existing systems, while the transparent retinal projection device allows ambient light to pass through the device for enhanced AR applications.

“Combining integrated optics and holography is a new research area for the scientific community developing display applications,” said Basile Meynard, a Ph.D. student and lead author of the paper. “It is also a way to imagine a display device that works more as a data transfer system than as an imaging system.”

The novel approach will require further development before it reaches the commercialization stage. In the medium to long term, the retinal projection concept is expected to support more compact and higher virtual-image quality applications similar to existing AR glasses.

This research project builds on CEA-Leti’s many years of development of micro-displays for near-to-eye displays, such as organic LED technologies (OLED) and liquid crystal devices (LCD). More recently, the institute has made significant strides in the field of inorganic LED display manufacturing.

“Our teams are continuously looking for potential disruptive technologies that could pave the way to new families of display devices down the road,” said Christophe Martinez, optical senior scientist and project leader in Leti. “The investigation on retinal displays is part of this exploration of future optical solutions.”

Nanolasers have recently emerged as a new class of light sources that have a size of only a few millionths of a meter and unique properties remarkably different from those of macroscopic lasers. However, it is almost impossible to determine at what current the output radiation of the nanolaser becomes coherent, while for practical applications, it is important to distinguish between the two regimes of the nanolaser: the true lasing action with a coherent output at high currents and the LED-like regime with incoherent output at low currents. Researchers from the Moscow Institute of Physics and Technology developed a method that allows to find under what circumstances nanolasers qualify as true lasers. The research was published in Optics Express.

Nanolaser test. Credit: @tsarcyanide/MIPT Press Office

Lasers are widely used in household appliances, medicine, industry, telecommunications, and more. Several years ago, lasers of a new kind were created, called nanolasers. Their design is similar to that of the conventional semiconductor lasers based on heterostructures, which have been known for several decades. The difference is that the cavities of nanolasers are exceedingly small, on the order of the wavelength of the light emitted by these light sources. Since they mostly generate visible and infrared light, the size is on the order of one millionth of a meter.

In the near future, nanolasers will be incorporated into integrated optical circuits, where they are required for the new generation of high-speed interconnects based on photonic waveguides, which would boost the performance of CPUs and GPUs by several orders of magnitude. In a similar way, the advent of fiber optic internet has enhanced connection speeds, while also boosting energy efficiency.

And this is by far not the only possible application of nanolasers. Researchers are already developing chemical and biological sensors, mere millionths of a meter large, and mechanical stress sensors as tiny as several billionths of a meter. Nanolasers are also expected to be used for controlling neuron activity in living organisms, including humans.

For a radiation source to qualify as a laser, it needs to fulfill a number of requirements, the main one being that it has to emit coherent radiation. One of the distinctive properties of a laser, which is closely associated with coherence, is the presence of a so-called lasing threshold. At pump currents below this threshold value, the output radiation is mostly spontaneous and it is no different in its properties from the output of conventional light emitting diodes (LEDs). But once the threshold current is reached, the radiation becomes coherent. At this point the emission spectrum of a conventional macroscopic laser narrows down and its output power spikes. The latter property provides for an easy way to determine the lasing threshold — namely, by investigating how output power varies with pump current (figure 1A).

Many nanolasers behave the way their conventional macroscopic counterparts do, that is, they exhibit a threshold current. However, for some devices, a lasing threshold cannot be pinpointed by analyzing the output power versus pump current curve, since it has no special features and is just a straight line on the log-log scale (red line in figure 1B). Such nanolasers are known as “thresholdless.” This begs the question: At what current does their radiation become coherent, or laserlike?

The obvious way to answer this is by measuring the coherence. However, unlike the emission spectrum and output power, coherence is very hard to measure in the case of nanolasers, since this requires equipment capable of registering intensity fluctuations at trillionths of a second, which is the timescale on which the internal processes in a nanolaser occur.

Andrey Vyshnevyy and Dmitry Fedyanin from the Moscow Institute of Physics and Technology have found a way to bypass the technically challenging direct coherence measurements. They developed a method that uses the main laser parameters to quantify the coherence of nanolaser radiation. The researchers claim that their technique allows to determine the threshold current for any nanolaser (figure 1B). They found that even a “thresholdless” nanolaser does in fact have a distinct threshold current separating the LED and lasing regimes. The emitted radiation is incoherent below this threshold current and coherent above it.

Surprisingly, the threshold current of a nanolaser turned out to be not related in any way to the features of the output characteristic or the narrowing of the emission spectrum, which are telltale signs of the lasing threshold in macroscopic lasers. Figure 1B clearly shows that even if a well-pronounced kink is seen in the output characteristic, the transition to the lasing regime occurs at higher currents. This is what laser scientists could not expect from nanolasers.

“Our calculations show that in most papers on nanolasers, the lasing regime was not achieved. Despite researches performing measurements above the kink in the output characteristic, the nanolaser emission was incoherent, since the actual lasing threshold was orders of magnitude above the kink value,” Dmitry Fedyanin says. “Very often, it was simply impossible to achieve coherent output due to self-heating of the nanolaser,” Andrey Vyshnevyy adds.

Therefore, it is highly important to distinguish the illusive lasing threshold from the actual one. While both the coherence measurements and the calculations are difficult, Vyshnevyy and Fedyanin came up with a simple formula that can be applied to any nanolaser. Using this formula and the output characteristic, nanolaser engineers can now rapidly gauge the threshold current of the structures they create.

The findings reported by Vyshnevyy and Fedyanin enable predicting in advance the point at which the radiation of a nanolaser — regardless of its design — becomes coherent. This will allow engineers to deterministically develop nanoscale lasers with predetermined properties and guaranteed coherence.

Researchers from the University of Houston have reported significant advances in stretchable electronics, moving the field closer to commercialization.

Researchers from the University of Houston have reported significant advances in the field of stretchable, rubbery electronics. Credit: University of Houston

In a paper published Friday, Feb. 1, in Science Advances, they outlined advances in creating stretchable rubbery semiconductors, including rubbery integrated electronics, logic circuits and arrayed sensory skins fully based on rubber materials.

Cunjiang Yu, Bill D. Cook Assistant Professor of mechanical engineering at the University of Houston and corresponding author on the paper, said the work could lead to important advances in smart devices such as robotic skins, implantable bioelectronics and human-machine interfaces.

Yu previously reported a breakthrough in semiconductors with instilled mechanical stretchability, much like a rubber band, in 2017.

This work, he said, takes the concept further with improved carrier mobility and integrated electronics.

“We report fully rubbery integrated electronics from a rubbery semiconductor with a high effective mobility … obtained by introducing metallic carbon nanotubes into a rubbery semiconductor with organic semiconductor nanofibrils percolated,” the researchers wrote. “This enhancement in carrier mobility is enabled by providing fast paths and, therefore, a shortened carrier transport distance.”

Carrier mobility, or the speed at which electrons can move through a material, is critical for an electronic device to work successfully, because it governs the ability of the semiconductor transistors to amplify the current.

Previous stretchable semiconductors have been hampered by low carrier mobility, along with complex fabrication requirements. For this work, the researchers discovered that adding minute amounts of metallic carbon nanotubes to the rubbery semiconductor of P3HT – polydimethylsiloxane composite – leads to improved carrier mobility by providing what Yu described as “a highway” to speed up the carrier transport across the semiconductor.

CEA-Leti today announced it has prototyped a next-generation optical chemical sensor using mid-infrared silicon photonics that can be integrated in smartphones and other portable devices.

Mid-IR chemical sensors operate in the spectral range of 2.5µm to 12µm, and are considered the paradigm of innovative silicon-photonic devices. In less than a decade, chemical sensing has become a key application for these devices because of the growing potential of spectroscopy, materials processing, and chemical and biomolecular sensing, as well as security and industrial applications. Measurement in this spectral range provides highly selective, sensitive and unequivocal identification of chemicals.

The coin-size, on-chip, IoT-ready sensors prototyped by Leti combine high performance and low power consumption and enable such consumer uses as air-quality monitoring in homes and vehicles, and wearable health and well-being applications. Industrial uses include real-time air-quality monitoring and a range of worker-safety applications.

Mid-IR optical sensors available on the market today are typically bulky, shoebox-size or bigger, and cost more than €10,000. Meanwhile, current miniaturized and inexpensive sensors cannot meet consumer requirements for accuracy, selectivity and sensitivity. While size and price are not the most critical concerns for industrial applications, bulky and costly optical sensors represent a major barrier for consumer applications, which require wearability and integration in a range of portable devices.

CEA-Leti presented its R&D results Feb. 05 at SPIE Photonics West 2019 in a paper titled “Miniaturization of Mid-IR Sensors on Si: Challenges and Perspectives”.

“Mid-IR silicon photonics has enabled creation of a novel class of integrated components, allowing the integration at chip level of the main building blocks required for chemical sensing,” said Sergio Nicoletti, lead author of the paper. “Key steps in this development extend the wavelength range available from a single source, handling and routing of the beams using photonic-integrated circuits, and the investigation of novel detection schemes that allow fully integrated on-chip sensing.”

CEA-Leti’s breakthrough combined three existing technologies necessary to produce on-chip optical chemical sensors:

  • Integrating a mid-IR laser on silicon
  • Developing photonic integrated circuits (PICs) in the mid-IR wavelength range, and
  • Miniaturizing a photoacoustic detector on silicon chips.

“While other R&D efforts have had similar results, our project’s key achievement is the use of tools and processes typical of the IC and MEMS industries,” Nicoletti said. “Our focus on the choice of the architectures and processes, and the specific linkage of the series of steps also were critical to developing this optical chemical sensor, which CEA-Leti is now realizing as demo prototypes.”

By bombarding an ultrathin semiconductor sandwich with powerful laser pulses, physicists at the University of California, Riverside, have created the first “electron liquid” at room temperature.

The achievement opens a pathway for development of the first practical and efficient devices to generate and detect light at terahertz wavelengths — between infrared light and microwaves. Such devices could be used in applications as diverse as communications in outer space, cancer detection, and scanning for concealed weapons.

The research could also enable exploration of the basic physics of matter at infinitesimally small scales and help usher in an era of quantum metamaterials, whose structures are engineered at atomic dimensions.

The UCR physicists published their findings online Feb. 4 in the journal Nature Photonics. They were led by Associate Professor of Physics Nathaniel Gabor, who directs the UCR Quantum Materials Optoelectronics Lab. Other co-authors were lab members Trevor Arp and Dennis Pleskot, and Associate Professor of Physics and Astronomy Vivek Aji.

A video depicting the research is available here.

In their experiments, the scientists constructed an ultrathin sandwich of the semiconductor molybdenum ditelluride between layers of carbon graphene. The layered structure was just slightly thicker than the width of a single DNA molecule. They then bombarded the material with superfast laser pulses, measured in quadrillionths of a second.

“Normally, with such semiconductors as silicon, laser excitation creates electrons and their positively charged holes that diffuse and drift around in the material, which is how you define a gas,” Gabor said. However, in their experiments, the researchers detected evidence of condensation into the equivalent of a liquid. Such a liquid would have properties resembling common liquids such as water, except that it would consist, not of molecules, but of electrons and holes within the semiconductor.

“We were turning up the amount of energy being dumped into the system, and we saw nothing, nothing, nothing — then suddenly we saw the formation of what we called an ‘anomalous photocurrent ring’ in the material,” Gabor said. “We realized it was a liquid because it grew like a droplet, rather than behaving like a gas.”

“What really surprised us, though, was that it happened at room temperature,” he said. “Previously, researchers who had created such electron-hole liquids had only been able to do so at temperatures colder than even in deep space.”

The electronic properties of such droplets would enable development of optoelectronic devices that operate with unprecedented efficiency in the terahertz region of the spectrum, Gabor said. Terahertz wavelengths are longer than infrared waves but shorter than microwaves, and there has existed a “terahertz gap” in the technology for utilizing such waves. Terahertz waves could be used to detect skin cancers and dental cavities because of their limited penetration and ability to resolve density differences. Similarly, the waves could be used to detect defects in products such as drug tablets and to discover weapons concealed beneath clothing.

Terahertz transmitters and receivers could also be used for faster communication systems in outer space. And, the electron-hole liquid could be the basis for quantum computers, which offer the potential to be far smaller than silicon-based circuitry now in use, Gabor said.

More generally, Gabor said, the technology used in his laboratory could be the basis for engineering “quantum metamaterials,” with atom-scale dimensions that enable precise manipulation of electrons to cause them to behave in new ways.

In further studies of the electron-hole “nanopuddles,” the scientists will explore their liquid properties such as surface tension.

“Right now, we don’t have any idea how liquidy this liquid is, and it would be important to find out,” Gabor said.

Gabor also plans to use the technology to explore basic physical phenomena. For example, cooling the electron-hole liquid to ultra-low temperatures could cause it to transform into a “quantum fluid” with exotic physical properties that could reveal new fundamental principles of matter.

In their experiments, the researchers used two key technologies. To construct the ultrathin sandwiches of molybdenum ditelluride and carbon graphene, they used a technique called “elastic stamping.” In this method, a sticky polymer film is used to pick up and stack atom-thick layers of graphene and semiconductor.

And to both pump energy into the semiconductor sandwich and image the effects, they used “multi-parameter dynamic photoresponse microscopy” developed by Gabor and Arp. In this technique, beams of ultrafast laser pulses are manipulated to scan a sample to optically map the current generated.

SEMI-FlexTech, an industry-led, public/private partnership, today issued a Request for Proposals (RFP) for artificial intelligence (AI), Human-Machine Interface (HMI), sensor system and other projects to advance the flexible hybrid electronics (FHE) ecosystem. Approximately $5 million is allocated for these projects. Manufacturers and developers in the electronics supply chain are encouraged to respond to the SEMI-FlexTech 2019 RFP. Primary funding will be provided by the U.S. Army Research Laboratory (ARL) through SEMI-FlexTech.

Topics in this 2019 Solicitation are:

  1. Reference designs for FHE sensor systems
  2. FHE Power
  3. Artificial Intelligence (AI) for additive manufacturing
  4. Mixed mode interconnect and metallization for FHE
  5. Human-Machine Interfaces (HMI)
  6. Open concepts for sensor and FHE technologies and agile, expedient manufacturing

Details about each topic are included in the full RFP.

SEMI-FlexTech’s R&D program focuses on developing the infrastructure required to support world-class manufacturing capabilities for FHE devices and products. Because flexible and printed electronics development often requires expertise across multiple disciplines including printing, materials science and advanced semiconductor packaging, SEMI-FlexTech prefers multi-institutional teams. Participation of organizations new to the SEMI-FlexTech program is especially welcome.

The program is designed to support more risky technical approaches, as well as those proposing step improvements to current technology. The proposal process consists of two stages:

  1. White paper submission
  2. Submission of full proposal from respondents selected after white paper review

White papers will be accepted until March 1, 2019, at 5:00 p.m. PST. Full proposals will be due by April 15, 2019, and award notifications will be issued on or about June 1, 2019.

“SEMI-FlexTech is excited to again partner with ARL in advancing the flexible electronics industry,” said Dr. Melissa Grupen-Shemansky, SEMI CTO for flexible electronics and advanced packaging. “The topics provided are a rich set of technology initiatives that will appeal to many of our members.”

SEMI-FlexTech and ARL personnel will be available for consultation at FLEX 2019 in Monterey, California, February 18-21, 2019.  A webinar for those interested in learning more will be held on Friday, February 8, 2019, at 10:00 a.m. PST.

Today, Mobile Semiconductor announced a new 55nm HD (High Density) memory compiler targeted at the cost sensitive IoT market. The new memory compiler boasts one of the highest density footprints in the industry dramatically reducing the die area and reducing customer product costs for sensors, smart locks, trackers and smart light bulbs.

Cameron Fisher, CEO and Founder of Mobile Semiconductor, said, “We believe that our success in the current 55nm Memory Compilers sets us apart from competitive offerings.  This new high-density product is well positioned to support our customer’s IoT products as they grow in features and capabilities. Our goal is to ensure that our customers can meet and exceed their silicon area goals and therefore reduce their costs.”

Key features include:

  • 15% to 33% smaller than previous 55nm compilers
  • At least 11% smaller than competitive solutions
  • Built on Mobile Semi’s volume designs at 55nm and 65nm
  • Available off the shelf today

Fisher continued, “Mobile Semiconductor remains the leader in providing memory compliers that target the needs of specific industries. We are proud of the fact that repeat customer purchases are close to 100%.  This includes customers moving to the next smaller node or building new products on the same node. Reducing the memory size offered by this new 55nm memory compiler gives our customers a compelling reason to choose Mobile Semiconductor for their cost sensitive IoT products.”

The 55nm HD memory compiler takes advantage of industry standard Bitcells provided by the top foundries.  All Mobile Semiconductor memory compilers are supported by a wide range of industry leading licensing options.

A team of researchers from Lehigh University, Oak Ridge National Laboratory, Lebanon Valley College and Corning Inc. has demonstrated, for the first time, that crystals manufactured by lasers within a glass matrix maintain full ferroelectric functionality.

Ferroelectric single-crystal-architecture-in-glass is a new class of metamaterials that would enable active integrated optics if the ferroelectric behavior is preserved within the confines of glass. We demonstrate using lithium niobate crystals fabricated in lithium niobosilicate glass by femtosecond laser irradiation that not only such behavior is preserved, the ferroelectric domains can be engineered with a DC bias. A piezoresponse force microscope is used to characterize the piezoelectric and ferroelectric behavior. The piezoresponse correlates with the orientation of the crystal lattice as expected for unconfined crystal, and a complex micro- and nano-scale ferroelectric domain structure of the as-grown crystals is revealed. Credit: Keith Veenhuizen, Sean McAnany, Rama Vasudevan, Daniel Nolan, Bruce Aitken, Stephen Jesse, Sergei V. Kalinin, Himanshu Jain and Volkmar Dierolf

“This includes the ability to uniformly orient and reverse orient the ferroelectric domains with an electric field?despite the fact that the crystal is strongly confined by the surrounding glass,” says Volkmar Dierolf, Chair of Lehigh University’s Department of Physics and one of the scientists who worked on the experiments that resulted in these findings.

Dierolf, who holds a joint appointment with Lehigh’s Department of Materials Science and Engineering part of the P.C. Rossin College of Engineering and Applied Science, is co-Principal Investigator on a National Science Foundation (NSF)-funded project, Crystal in Glass, along with Principal Investigator Himanshu Jain, Diamond Distinguished Chair of Lehigh’s Department of Materials Science and Engineering. The group has become a world leader in producing single crystals in glass by localized laser irradiation. Read more about their work: “Crossing a critical threshold” and “Lehigh scientists fabricate a new class of crystalline solid.”

The team conducted the first detailed examination of the piezoelectric and ferroelectric properties of laser induced crystals confined in glass. They found that the as-grown crystals possess a complex ferroelectric domain structure that can be manipulated via the application of a DC bias. The findings have been published online today in MRS Communications in a paper called “Ferroelectric domain engineering of lithium niobate single crystal confined in glass.”

“The findings open up the possibility of a new collection of optical devices that use fully functional laser-fabricated crystals in glass which rely on the precise control of the ferroelectric domain structure of the crystal,” said Keith Veenhuizen, currently Assistant Professor, Department of Physics at Lebanon Valley College and the lead author of the paper, which builds on the work he did as a graduate student at Lehigh.

Applications for such technology include use in modern fiber optic technology used for data transmission.

“Being able to embed such functional single crystal architectures within a glass enables high efficiency coupling to existing glass fiber networks,” says Dierolf. “Such low loss links?that maximize performance?are of particular importance for future quantum information transfer system that are projected to take over the current schemes for optical communication,” adds Dierolf.

Water molecules distort the electrical resistance of graphene, but a team of European researchers has discovered that when this two-dimensional material is integrated with the metal of a circuit, contact resistance is not impaired by humidity. This finding will help to develop new sensors -the interface between circuits and the real world- with a significant cost reduction.

The many applications of graphene, an atomically-thin sheet of carbon atoms with extraordinary conductivity and mechanical properties, include the manufacture of sensors. These transform environmental parameters into electrical signals that can be processed and measured with a computer.

Due to their two-dimensional structure, graphene-based sensors are extremely sensitive and promise good performance at low manufacturing cost in the next years.

To achieve this, graphene needs to make efficient electrical contacts when integrated with a conventional electronic circuit. Such proper contacts are crucial in any sensor and significantly affect its performance.

But a problem arises: graphene is sensitive to humidity, to the water molecules in the surrounding air that are adsorbed onto its surface. H2O molecules change the electrical resistance of this carbon material, which introduces a false signal into the sensor.

However, Swedish scientists have found that when graphene binds to the metal of electronic circuits, the contact resistance (the part of a material’s total resistance due to imperfect contact at the interface) is not affected by moisture.

“This will make life easier for sensor designers, since they won’t have to worry about humidity influencing the contacts, just the influence on the graphene itself,” explains Arne Quellmalz, a PhD student at KTH Royal Institute of Technology (Sweden) and the main researcher of the research.

The study, published in the journal ACS Applied Materials & Interfaces, has been carried out experimentally using graphene together with gold metallization and silica substrates in transmission line model test structures, as well as computer simulations.

“By combining graphene with conventional electronics, you can take advantage of both the unique properties of graphene and the low cost of conventional integrated circuits.” says Quellmalz, “One way of combining these two technologies is to place the graphene on top of finished electronics, rather than depositing the metal on top the graphene sheet.”

As part of the European CO2-DETECT project, the authors are applying this new approach to create the first prototypes of graphene-based sensors. More specifically, the purpose is to measure carbon dioxide (CO2), the main greenhouse gas, by means of optical detection of mid-infrared light and at lower costs than with other technologies.

In addition to the KTH Royal Institute of Technology, the companies SenseAir AB from Sweden and Amo GmbH from Germany are likewise participants in the CO2-DETECT project, as is the Catalan Institute of Nanotechnology (ICN) from Barcelona.