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（Metal-semiconductor-metal junction (tunnel barrier) incorporated into a single graphene nanoribbon: The atomic and electronic structure of the nanoribbons can be probed with atomic resolution using advanced microscopic techniques.）   Essential electronic components, such as diodes and tunnel barriers, can be incorporated in single graphene wires (nanoribbons) with atomic precision. The goal is to create graphene-based electronic devices with extremely fast operational speeds. The discovery was made in a collaboration between Aalto University and their colleagues at Utrecht University and TU Delft in the Netherlands. The work is published in Nature Communications. The 'wonder material' graphene has many interesting characteristics, and researchers around the world are looking for new ways to utilise them. Graphene itself does not have the characteristics needed to switch electrical currents on and off and smart solutions must be found for this particular problem. "We can make graphene structures with atomic precision. By selecting certain precursor substances (molecules), we can code the structure of the electrical circuit with extreme accuracy," explains Peter Liljeroth from Aalto University, who conceived the research project together with Ingmar Swart from Utrecht University. Seamless integration The electronic properties of graphene can be controlled by synthesizing it into very narrow strips (graphene nanoribbons). Previous research has shown that the ribbon's electronic characteristics are dependent on its atomic width. A ribbon that is five atoms wide behaves similarly to a metallic wire with extremely good conduction characteristics, but adding two atoms makes the ribbon a semiconductor. "We are now able to seamlessly integrate five atom-wide ribbons with seven atom-wide ribbons. That gives you a metal-semiconductor junction, which is a basic building block of electronic components," according to Ingmar Swart. Chemistry on a surface The researchers produced their electronic graphene structures through a chemical reaction. They evaporated the precursor molecules onto a gold crystal, where they react in a very controlled way to yield new chemical compounds. "This is a different method from that currently used to produce electrical nanostructures, such as those on computer chips. For graphene, it is so important that the structure is precise at the atomic level and it is likely that the chemical route is the only effective method," Ingmar Swart concludes. Electronic characteristics The researchers used advanced microscopic techniques to also determine the electronic and transport characteristics of the resulting structures. It was possible to measure electrical current through a graphene nanoribbon device with an exactly known atomic structure. "This is the first time where we can create e.g. a tunnel barrier and really know its exact atomic structure. Simultaneous measurement of electrical current through the device allows us to compare theory and experiment on a very quantitative level," says Peter Liljeroth.  Source:Aalto University Ref.MN3306STTH2002G-TR 

At this week's IEEE IEDM conference, world-leading research and innovation hub for nano-electronics and digital technology, imec, reported for the first time the CMOS integration of vertically stacked gate-all-around (GAA) silicon nanowire MOSFETs. Key in the integration scheme is a dual-work-function metal gate enabling matched threshold voltages for the n- and p-type devices. Also, the impact of the new architecture on intrinsic ESD performance was studied, and an ESD protection diode is proposed. These breakthrough results advance the development of GAA nanowire MOSFETs, which promise to succeed FinFETs in future technology nodes. GAA nanowire transistors are promising candidates to succeed FinFETs in 7nm and beyond technology nodes. They offer optimal electrostatic control, thereby enabling ultimate CMOS device scaling. In a horizontal configuration, they are a natural extension of today's mainstream FinFET technology. In this configuration, the drive current per footprint can be maximized by vertically stacking multiple horizontal nanowires. Earlier this year, imec scientists demonstrated GAA FETs based on vertically stacked 8nm diameter Si nanowires. These devices showed excellent electrostatic control, but were fabricated for n- and p-FETs separately.Imec now reports on the CMOS integration of vertically stacked GAA Si nanowire MOSFETs, with matched threshold voltages for n- and p-type devices. Key in the integration scheme is the implementation of dual-work-function metal gates to set the threshold voltages of the n- and p-FETs independently. In this process step, p-type work function metal (PWFM) is deposited in the gate trenches of all devices, followed by selectively etching the PWFM down to the HfO2 from the n-FETs and subsequent deposition of the n-type work function metal. The observation of matched threshold voltages (VT,SAT = 0.35V) for nMOS and pMOS devices validates the dual-work-function metal integration scheme.The impact of this new device architecture on the intrinsic ESD performance was investigated as well. Two different ESD protection diodes have been proposed, i.e. a gate-structure defined diode (gated diode) and a shallow-trench isolation defined diode (STI diode). The STI diode was the better ESD protection device, showing an excellent ratio of failure current (It2) over parasitic capacitance (C). Measurements and TCAD simulations also prove that the ESD performance in GAA nanowire based diodes is maintained in comparison to bulk FinFET diodes."GAA nanowire transistors enable ultimate CMOS device scaling, with low degree of added complexity compared to alternative scaling scenarios," stated Dan Mocuta, Director Logic Device and Integration at imec. The proposed integration scheme for Si GAA CMOS technology and the results on ESD protection are important achievements towards realizing these 7nm and beyond technology nodes. Future work will focus, among others, on further optimizing individual process steps, for example through the co-optimization of the junction and nanowire formation."Ref:KY56-2SA1987KY56-KSC5024RTUKY56-MJL4302A          

The world's smallest diode, the size of a single molecule, has been developed collaboratively by U.S. and Israeli researchers from the University of Georgia and Ben-Gurion University of the Negev (BGU).     "Creating and characterizing the world's smallest diode is a significant milestone in the development of molecular electronic devices," explains Dr. Yoni Dubi, a researcher in the BGU Department of Chemistry and Ilse Katz Institute for Nanoscale Science and Technology. "It gives us new insights into the electronic transport mechanism." Continuous demand for more computing power is pushing the limitations of present day methods. This need is driving researchers to look for molecules with interesting properties and find ways to establish reliable contacts between molecular components and bulk materials in an electrode, in order to mimic conventional electronic elements at the molecular scale. An example for such an element is the nanoscale diode (or molecular rectifier), which operates like a valve to facilitate electronic current flow in one direction. A collection of these nanoscale diodes, or molecules, has properties that resemble traditional electronic components such as a wire, transistor or rectifier. The emerging field of single molecule electronics may provide a way to overcome Moore's Law— the observation that over the history of computing hardware the number of transistors in a dense integrated circuit has doubled approximately every two years - beyond the limits of conventional silicon integrated circuits. Prof. Bingqian Xu's group at the College of Engineering at the University of Georgia took a single DNA molecule constructed from 11 base pairs and connected it to an electronic circuit only a few nanometers in size. When they measured the current through the molecule, it did not show any special behavior. However, when layers of a molecule called "coralyne," were inserted (or intercalated) between layers of DNA, the behavior of the circuit changed drastically. The current jumped to 15 times larger negative vs. positive voltages—a necessary feature for a nano diode. "In summary, we have constructed a molecular rectifier by intercalating specific, small molecules into designed DNA strands," explains Prof. Xu. Dr. Dubi and his student, Elinor Zerah-Harush, constructed a theoretical model of the DNA molecule inside the electric circuit to better understand the results of the experiment. "The model allowed us to identify the source of the diode-like feature, which originates from breaking spatial symmetry inside the DNA molecule after coralyne is inserted." Reference: CLCS145V0-G PACDN004SR  SLVU2.8.TCT    

Use of copper as a fluorescent material allows for the manufacture of inexpensive and environmentally compatible organic light-emitting diodes (OLEDs). Thermally activated delayed fuorescence (TADF) ensures high light yield. Scientists of Karlsruhe Institute of Technology (KIT), CYNORA, and the University of St Andrews have now measured the underlying quantum mechanics phenomenon of intersystem crossing in a copper complex. The results of this fundamental work are reported in the Science Advances journal and contribute to enhancing the energy efficiency of OLEDs.  Organic light-emitting diodes are deemed tomorrow's source of light. They homogeneously emit light in all observation directions and produce brilliant colors and high contrasts. As it is also possible to manufacture transparent and flexible OLEDs, new application and design options result, such as flat light sources on window panes or displays that can be rolled up. OLEDs consist of ultra-thin layers of organic materials, which serve as emitter and are located between two electrodes. When voltage is applied, electrons from the cathode and holes (positive charges) from the anode are injected into the emitter, where they form electron-hole pairs. These so-called excitons are quasiparticles in the excited state. When they decay into their initial state again, they release energy.Excitons may assume two different states: Singlet excitons decay immediately and emit light, whereas triplet excitons release their energy in the form of heat. Usually, 25 percent singlets and 75 percent triplets are encountered in OLEDs. To enhance energy efficiency of an OLED, also triplet excitons have to be used to generate light. In conventional light-emitting diodes heavy metals, such as iridium and platinum, are added for this purpose. But these materials are expensive, have a limited availability, and require complex OLED production methods.It is cheaper and environmentally more compatible to use copper complexes as emitter materials. Thermally activated delayed fluorescence (TADF) ensures high light yields and, hence, high efficiency: Triplet excitons are transformed into singlet excitons which then emit photons. TADF is based on the quantum mechanics phenomenon of intersystem crossing (ISC), a transition from one electronic excitation state to another one of changed multiplicity, i.e. from singlet to triplet or vice versa. In organic molecules, this process is determined by spin-orbit coupling. This is the interaction of the orbital angular momentum of an electron in an atom with the spin of the electron. In this way, all excitons, triplets and singlets, can be used for the generation of light. With TADF, copper luminescent material reaches an efficiency of 100 percent.Stefan Bräse and Larissa Bergmann of KIT's Institute of Organic Chemistry (IOC), in cooperation with researchers of the OLED technology company CYNORA and the University of St Andrews, United Kingdom, for the first time measured the speed of intersystem crossing in a highly luminescent, thermally activated delayed fluorescence copper(I) complex in the solid state. The results are reported in the Science Advances journal. The scientists determined a time constant of intersystem crossing from singlet to triplet of 27 picoseconds (27 trillionths of a second). The reverse process – reverse intersystem crossing – from triplet to singlet is slower and leads to a TADF lasting for an average of 11.5 microseconds. These measurements improve the understanding of mechanisms leading to TADF and facilitate the specific development of TADF materials for energy-efficient OLEDs.Reference:KY59-0202NYKY59-S101D2LCD-S301C31TR 

Induction cooking appliances commonly make use of resonant topologies which allow bidirectional current flow. Additionally they demand a discrete IGBT that performs best at switching frequencies from 18 to 40kHz and has low losses. Infineon has launched a family of discrete IGBTs to address these needs. The RC-E devices are cost optimised and specifically meet the demands of low- to mid-price range induction cookers and induction rice cookers.Monolithically integrated reverse conduction diodeThe RC-E family features an IGBT with monolithically integrated reverse conduction diode for resonant switching. The technology used in RC-E IGBTs is also optimised for low switching and conduction losses. Lower losses allow designers to achieve efficiency and power targets for induction cooking applications more easily. Thus, less energy is consumed for cooking, leading to lower operating costs for consumers. With low E off, V F, R th and V ce(sat) this device sets a new industry benchmark in price/performance and ease-of-use.The new devices offer Infineon’s proven quality in discrete RC IGBTs and fulfill all the requirements for soft switching applications and efficiency as well as EMI standards. The RC-E delivers the well-established high-performance of its predecessors with a more attractive price for lower BoM cost. The RC-E is offered in a standard TO-247 package allowing a drop-in replacement for existing designs.Samples are available now and the devices are in production. The family will be launched with two devices: 15 A and 25 A, both with the most commonly used blocking voltage of 1200V.Reference:KY56-MN3306KY0-SE40PJ-M3/86A

A new semiconductor device capable of emitting two distinct colours has been created by a group of researchers in the US, potentially opening up the possibility of using light emitting diodes (LEDs) universally for cheap and efficient lighting.The proof-of-concept device takes advantage of the latest nano-scale materials and processes to emit green and red light separated by a wavelength of 97 nanometres—a significantly larger bandwidth than a traditional semiconductor.Furthermore, the device is much more energy efficient than traditional LEDs as the colours are emitted as lasers, meaning they emit a very sharp and specific spectral line—narrower than a fraction of a nanometre—compared to LEDs which emit colours in a broad bandwidth.One of the main properties of semiconductors is that they emit light in a certain wavelength range, which has resulted in their widespread use in LEDs. The wavelength range in which a given semiconductor can emit light—also known as its bandwidth—is typically limited in the range of just tens of nanometres. For many applications such as lighting and illumination, the wavelength range needs to be over the entire visible spectrum and thus have a bandwidth of 300 nm.Single semiconductor devices cannot emit across the entire visible spectrum and therefore need to be 'put' together to form a collection that can cover the entire range. This is very expensive and is, to a large extent, the reason why semiconductor LEDs are not yet used universally for lighting.In this study, the researchers, from Arizona State University, used a process known as chemical vapour deposition to create a 41 micrometer-long nanosheet made from Cadmium Sulphide and Cadmium Selenide powders, using silicon as a substrate.Lead author of the study, Professor Cun-Zheng Ning, said: "Semiconductors are traditionally 'grown' together layer-by- layer, on an atom-scale, using the so-called epitaxial growth of crystals. Since different semiconductor crystals typically have different lattice constants, layer-by-layer growth of different semiconductors will cause defects, stress, and ultimately bad crystals, killing light emission properties."It is because of this that current LEDs cannot have different semiconductors within them to generate red, green and blue colours for lighting.However, recent developments in the field of nanotechnology mean that structures such as nanowires, nanobelts and nanosheets can be grown to tolerate much larger mismatches of lattice structures, and thus allow very different semiconductors to grow together without too many defects."Multi-colour light emission from a single nanowire or nanobelt has been realized in the past but what is important in our paper is that we realized lasers at two distinct colours. To physically 'put' together several lasers of different colors is too costly to be useful and thus our proof-of concept experiment becomes interesting and potentially important technologically."In addition to being used for solid state lighting and full color displays, such technology can also be used as light sources for fluorescence bio and chemical detection," continued Professor Ning.