Transistors - Page 7

Researchers at the U.S-based University of Rochester, along with colleagues at Delft University of Technology in the Netherlands, have designed a way to produce graphene materials using a novel technique: mixing oxidized graphite with bacteria. Their method is reportedly a more cost-efficient, time-saving, and environmentally friendly way of producing graphene materials versus those produced chemically, and could lead to the creation of innovative computer technologies and medical equipment.

From left to right:graphite (Gr), graphene oxide (GO), microbially‐reduced graphene oxide (mrGO), and chemically‐reduced graphene oxide (crGO)

"For real applications you need large amounts," says Anne S. Meyer, an associate professor of biology at the University of Rochester. "Producing these bulk amounts is challenging and typically results in graphene that is thicker and less pure. This is where our work came in". In order to produce larger quantities of graphene materials, Meyer and her colleagues started with a vial of graphite. They exfoliated the graphite-shedding the layers of material-to produce graphene oxide (GO), which they then mixed with the bacteria Shewanella. They let the beaker of bacteria and precursor materials sit overnight, during which time the bacteria reduced the GO to a graphene material.

Researchers at Osaka University have invented a graphene-based biosensor to detect bacteria such as those that attack the stomach lining and that have been linked to stomach cancer. When the bacteria interact with the biosensor, chemical reactions are triggered which are detected by the graphene.

To enable detection of the chemical reaction products, the researchers used microfluidics to contain the bacteria in extremely tiny droplets close to the sensor surface.

Graphene Flagship partner, Emberion, will be launching a VIS-SWIR graphene photodetector at Laser World of Photonics, from 24 to 27 June in Munich, Germany. The linear array covers a wide spectral range, detecting wavelengths from the visible at 400nm into the shortwave infrared up to 1,800nm. Traditionally, it would require both silicon and InGaAs sensors to image across this wavelength range.

Emberion estimates that replacing a system using silicon and InGaAs sensors with its graphene photodetector would result in a 30% cost reduction.

Mitsubishi has reportedly developed graphene-based MWIR sensors with extraordinarily high sensitivity. Thanks to an internal graphene FET gain, the responsivity is said to be 10 times higher than that of quantum-type IR sensors with no internal amplification. Mitsubishi uses graphene FET and leverages its high electron mobility.

Other than a graphene-based FET, reports suggest that there is "a light-amplifying part" that produces photoelectrons and photoholes and is placed under the graphene. At a very low temperature of, for example, 80K, the responsivity increases even more, by a factor of 100x.

Researchers in India have made graphene field-effect transistors based on discrete inorganic structures that reportedly work for over 10 months. The approach has led them to produce a graphene logic inverter that is stable in ambient conditions.

Conventional electronics are silicon based, due to the ease of doping silicon with either electrons or holes. These two forms of silicon, n- and p-type, are the building blocks of electronic devices. However, it isn’t possible to make silicon electronics on the nanoscale, so many researchers are turning to materials like graphene.

University of Cambridge spin-out company, Paragraf, recently announced that it started producing graphene at up to eight inches (20cm) in diameter, large enough for commercial electronic devices.

Paragraf is producing graphene ‘wafers’ and graphene-based electronic devices, which could be used in transistors, where graphene-based chips could deliver speeds more than ten times faster than silicon chips; and in chemical and electrical sensors, where graphene could increase sensitivity by a factor of more than 30. The company’s first device will reportedly be available in the next few months.

Scientists from Manchester University, the Ulsan National Institute of Science & Technology and the Korea Institute of Science and Technology have developed a novel technology, which combines the fabrication procedures of planar and vertical heterostructures in order to assemble graphene-based single-electron transistors.

The schematic structure of the devices

In the study, it was demonstrated that high-quality graphene quantum dots (GQDs), regardless of whether they were ordered or randomly distributed, could be successfully synthesized in a matrix of monolayer hexagonal boron nitride (hBN). Here, the growth of GQDs within the layer of hBN was shown to be catalytically supported by the platinum (Pt) nanoparticles distributed in-between the hBN and supporting oxidised silicon (SiO₂) wafer, when the whole structure was treated by the heat in the methane gas (CH₄). It was also shown, that due to the same lattice structure (hexagonal) and small lattice mismatch (~1.5%) of graphene and hBN, graphene islands grow in the hBN with passivated edge states, thereby giving rise to the formation of defect-less quantum dots embedded in the hBN monolayer.

A new study led by the Ulsan National Institute of Science and Technology in South Korea reveals a technology capable of fabricating highly ordered arrays of graphene quantum dots.

Graphene quantum dots of various sizes in a stable, ordered array

The research team demonstrated a novel way of synthesizing GQDs, embedded inside a hexagonal boron nitride (hBN) matrix. Thus, they demonstrated simultaneous use of in-plane and van der Waals heterostructures to build vertical single-electron tunneling transistors.

Researchers from Italy's ISOF-CNR, University of Naples "Federico II" and Università di Modena e Reggio Emilia have developed new organic n-type FET transistors (OFETs) based on CVD graphene sheets. The researchers say that the new process and materials they used can enable flexible, transparent and short-channel OFETs - which could be used in the future for OLED or OLET (organic light emitting transistor) displays.

To create the new transistors, the researchers used thermally evaporated thin-films of PDIF-CN2 (a perylene diimide derivative) as the the organic semiconductor for the active channel of the transistor with the single-layer CVD graphene (grown at Italy's IIT institute) as the electrode material. The final device architectures have been fabricated via Electron-Beam-Lithography (EBL) and Reactive Ion Etching (RIE).

This is a sponsored post by Graphenea

Graphenea recently launched a graphene foundry service GFAB. The company will manufacture custom circuit designs on graphene wafers up to 6. The service is aimed at enabling fast device prototyping and accelerating development of new applications, lowering entry barriers to graphene-based solutions.

Graphenea states that in view of the market demands, the offer now includes small batch sizes (1-3 wafers). Lithography masks can be manufactured by Graphenea or provided by the customer. GFAB includes graphene growth, transfer on 4 and 6 wafers, metal contact deposition and lift-off, and graphene lithography with etching.