Transistors - Page 8

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.

The Industrial Technology and Science group in IBM Research-Brazil, along with other academic collaboration partners, has reportedly proven for the first time that it is possible to electrify graphene so that it deposits material at any desired location at a solid surface with an almost-perfect turnout of 97%. Using graphene in this way enables the integration of nanomaterials at wafer scale and with nanometer precision.

Artistic rendering of electric field-assisted placement of nanoscale materials between pairs of opposing graphene electrodes structured into a large graphene layer located on top of a solid substrate

Not only has this new work shown that it is possible to deposit material at a specific, nanoscale location, it was also reported that this can be done in parallel, at multiple deposition sites, meaning it’s possible to integrate nanomaterials at mass scale. This work has been patented.

Researchers at EMPA (Swiss Federal Laboratories for Materials Science and Technology), along with colleagues from the Max Planck Institute for Polymer Research in Mainz and other partners, have succeeded in precisely controlling the properties of graphene nano-ribbons (GNRs) by specifically varying their shape. This can be used to generate specific local quantum states, and could in the future be used for precise nano-transistors or possibly even quantum computing.

The team has shown that if the width of a narrow graphene nano-ribbon changes, in this case from seven to nine atoms, a special zone is created at the transition: because the electronic properties of the two areas differ in a special, topological way, a "protected" and thus very robust new quantum state is created in the transition zone. This local electronic quantum state can be used as a basic component to produce tailor-made semiconductors, metals or insulators - and perhaps even as a component in quantum computers.

Computers based on fluids instead of silicon is not a new concept, and now researchers at the National Institute of Standards and Technology (NIST) have shown how computational logic operations could be performed in a liquid medium by simulating the trapping of ions (charged atoms) in graphene floating in saline solution. The scheme might also be used in applications such as water filtration, energy storage or sensor technology.

NIST's ion-based transistor and logic operations are simpler in concept than earlier proposals. The new simulations show that a special film immersed in liquid can act like a solid silicon-based semiconductor. For example, the material can act like a transistor, the switch that carries out digital logic operations in a computer. The film can be switched on and off by tuning voltage levels like those induced by salt concentrations in biological systems.

Graphenea has launched sales of GFETs (graphene field effect transistors) aimed at lowering barriers to adoption of graphene, especially the sensors market. Researchers needing GFETs for their applications, whether in gas, biosensing, or other applications, can now purhcase high-quality GFET devices.

Graphenea has started by launching two standard GFET-for-sensing configurations called GFET-S10 and GFET-S20, each including 36 individual GFETs on a one square centimeter die, but differing in device layout. The GFET-S10 has devices distributed evenly over the die and the GFET-S20 has the devices concentrated in the center of the die with electrical pads located at the die edge. The GFET-S20 devices all have a 2-probe geometry for probing electrical properties during sensing, whereas the GFET-S10 houses 30 devices with the Hall bar geometry and 6 with 2-probe geometry. The Hall bars enable magnetic field sensing, apart from applications in graphene device research, bioelectronics, biosensing, chemical sensing, and photodetectors that the 2-probe geometry also allows.

Researchers at MIT and Harvard University have found that graphene can be tuned to behave at two electrical extremes: as an insulator, in which electrons are completely blocked from flowing; and as a superconductor, in which electrical current can stream through without resistance.

Researchers in the past, including this team, have been able to synthesize graphene superconductors by placing the material in contact with other superconducting metals — an arrangement that allows graphene to inherit some superconducting behaviors. In this new work, the team found a way to make graphene superconduct on its own, demonstrating that superconductivity can be an intrinsic quality in the purely carbon-based material.

Researchers from the Pierre Aigrain Laboratory in the ENS Physics department in Paris, France, have discovered a new cooling mechanism for electronic components made of graphene deposited on boron nitride. The efficiency of this mechanism reportedly allowed the team to reach electric intensities at the intrinsic limit of the laws of conduction.

Current-voltage (left) and temperature-voltage (right) characteristics of a graphene on boron nitride transistor. The transistor effect is visible by modulation of the current as a function of the gate voltage in the Zener-Klein tunnel transport regime.

Heat dissipation is vital in order to prevent deterioration or destruction of electronic components. The laws of physics dictate that increasing the density of components on a chipset implies increasing dissipation and thus heat. Nowadays, with the advances in 2D material devices, this question becomes particularly critical since components are required to be one atom thick. By producing a graphene-based transistor deposited on a boron nitride substrate, the team demonstrated a new cooling mechanism 10 times more efficient than basic heat diffusion. This new mechanism, which exploits the two-dimensional nature of the materials opens a "thermal bridge" between the graphene sheet and the substrate.

An international team of researchers from Empa, the Max Planck Institute for Polymer Research in Mainz and the University of California at Berkeley has succeeded in growing graphene ribbons exactly nine atoms wide with a regular armchair edge from precursor molecules. The specially prepared molecules are evaporated in an ultra-high vacuum for this purpose. After several process steps, they are put on a gold base to form the desired nanoribbons of about one nanometer in width and up to 50 nanometers in length.

These structures have a relatively large and, most importantly, precisely defined energy gap. This enabled the researchers to go one step further and integrate the graphene ribbons into nanotransistors. Initially, however, the first attempts were not so successful: Measurements showed that the difference in the current flow between the "ON" state (i.e. with applied voltage) and the "OFF" state (without applied voltage) was far too small. The problem was the dielectric layer of silicon oxide, which connects the semiconducting layers to the electrical switch contact. In order to have the desired properties, it needed to be 50 nanometers thick, which in turn influenced the behavior of the electrons.

Teams from the University of York and Roma Tre University state showed that ultra-low-power transistors could be built using composite materials based on single layers of graphene and transition metal dichalcogenides (TMDC). These materials, they note, could be used to achieve a sought-after electrical control over electron spin.

The teams explained we found this can be achieved with little effort when 2D graphene is paired with certain semiconducting layered materials. Our calculations show that the application of small voltages across the graphene layer induces a net polarization of conduction spins". The team showed that when a small current is passed through the graphene layer, the electrons’ spin polarize in plane due to ‘spin-orbital’ forces brought about by the proximity to the TMDC base. They also showed the efficiency of charge-to-spin conversion can be quite high, even at room temperature.

Researchers from Cambridge University have demonstrated how graphene and other related 2D materials (namely hBN) can be directly printed onto textiles to create fully inkjet-printed dielectrically gated field effect transistors (FETs) with solution processed 2D materials.

According to the team, these devices are washable, flexible, cheap, safe, comfortable to wear and environmentally-friendly, essential requirements for applications in wearable electronics. The team also demonstrated the first reprogrammable memories, inverters and logic gates with solution processed 2D materials by coupling these FETs together to create integrated circuits, the most fundamental components of a modern-day computer.