Tag Archives: letter-dd-tech

Gadgets are set to become flexible, highly efficient and much smaller, following a breakthrough in measuring two-dimensional ‘wonder’ materials by the University of Warwick.

This is a heterostructure of two-dimensional 'wonder' materials. Credit: Gabriel Constantinescu

This is a heterostructure of two-dimensional ‘wonder’ materials. Credit: Gabriel Constantinescu

Dr Neil Wilson in the Department of Physics has developed a new technique to measure the electronic structures of stacks of two-dimensional materials — flat, atomically thin, highly conductive, and extremely strong materials – for the first time.

Multiple stacked layers of 2D materials — known as heterostructures — create highly efficient optoelectronic devices with ultrafast electrical charge, which can be used in nano-circuits, and are stronger than materials used in traditional circuits.

Various heterostructures have been created using different 2D materials — and stacking different combinations of 2D materials creates new materials with new properties.

Dr Wilson’s technique measures the electronic properties of each layer in a stack, allowing researchers to establish the optimal structure for the fastest, most efficient transfer of electrical energy.

The technique uses the photoelectric effect to directly measure the momentum of electrons within each layer and shows how this changes when the layers are combined.

The ability to understand and quantify how 2D material heterostructures work – and to create optimal semiconductor structures — paves the way for the development of highly efficient nano-circuitry, and smaller, flexible, more wearable gadgets.

Solar power could also be revolutionised with heterostructures, as the atomically thin layers allow for strong absorption and efficient power conversion with a minimal amount of photovoltaic material.

Dr. Wilson comments on the work:

“It is extremely exciting to be able to see, for the first time, how interactions between atomically thin layers change their electronic structure. This work also demonstrates the importance of an international approach to research; we would not have been able to achieve this outcome without our colleagues in the USA and Italy.”

Dr Wilson worked formulated the technique in collaboration with colleagues in the theory groups at the University of Warwick and University of Cambridge, at the University of Washington in Seattle, and the Elettra Light Source, near Trieste in Italy.

Understanding how interactions between the atomic layers change their electronic structure required the help of computational models developed by Dr Nick Hine, also from Warwick’s Department of Physics.

A new study, affiliated with Ulsan National Institute of Science and Technology (UNIST), South Korea, has introduced a novel method for fabrication of world’s thinnest oxide semiconductor that is just one atom thick. This may open up new possibilities for thin, transparent, and flexible electronic devices, such as ultra-small sensors.

This new ultra-thin oxide semiconductors was created by a team of scientists, led by Professor Zonghoon Lee of Materials Science and Engineering at UNIST. In the study, Professor Lee has succeeded in demonstrating the formation of two-dimensional zinc oxide (ZnO) semiconductor with one atom thickness.

The above graphic displays the growth of ZnO on graphene layer, consists of interconnected hexagons of carbon atoms. Zinc atom shown as red spheres, oxygen atom as green spheres. Credit: UNIST

The above graphic displays the growth of ZnO on graphene layer, consists of interconnected hexagons of carbon atoms. Zinc atom shown as red spheres, oxygen atom as green spheres. Credit: UNIST

This material is formed by directly growing a single-atom-thick ZnO layer on graphene, using atomic layer deposition. It is also the thinnest heteroepitaxial layer of semiconducting oxide on monolayer graphene.

“Flexible, high-performance devices are indispensable for conventional wearable electronics, which have been attracting attention recently,” says Professor Lee. “With this new material, we can achieve truly high-performance flexible devices.”

Semiconductor technology continually moves toward smaller feature sizes and greater operational efficiency and the existing silicon semiconductors seem to also follow this trend. However, as the fabrication process becomes finer, the performance becomes much critical issue and there has been much research on next-generation semiconductors, which can replace silicon.

Graphene has superior conductivity properties, but it cannot be directly used as an alternative to silicon in semiconductor electronics because it has no band gap. A bandgap gives a material the ability to start and stop the flow of electrons that carry electricity. In graphene, however, electrons move randomly at a constant speed no matter their energy and they cannot be stopped.

To solve this, the research team decided to demonstrate atom-by-atom growth of zinc and oxygen at the preferential zigzag edge of a ZnO monolayer on graphene through in situ observation. Then, they experimentally determine that the thinnest ZnO monolayer has a wide band gap (up to 4.0 eV), due to quantum confinement and graphene-like ‘hyper-honeycomb’ structure, and high optical transparency.

The currently-existing oxide semiconductors have a relatively large bandgap in the range of 2.9-3.5 eV. The greater the band gap energy, the lower the leakage current and excess noise.

“This is the first time to actually observe the in situ formation of hexagonal structure of ZnO,” says Hyo-Ki Hong of Materials Science and Engineering, first author of the paper. “Through this process, we could understand the process and principle of 2D ZnO semiconductor productiom.”

“The heteroepitaxial stack of the thinnest 2D oxide semiconductors on graphene has potential for future optoelectronic device applications associated with high optical transparency and flexibility,” says Professor Lee. “This study can lead to a new class of 2D heterostructures including semiconducting oxides formed by highly controlled epitaxial growth through a deposition route.”

Today, at the 2017 International Solid-State Circuits Conference in San Francisco, imec, the world-leading research and innovation hub in nanoelectronics and digital technologies, Holst Centre (established by imec and TNO) and Cartamundi demonstrate a world first thin-film tag on plastic, compatible with the near field communication (NFC) Barcode protocol, a subset of ISO14443-A, which is available as standard in many commercial smartphones. The innovative NFC tag is manufactured in a thin-film transistor technology using indium gallium zinc oxide thin-film transistors (IGZO TFT) on a plastic substrate.

Plastic electronics offers an appealing vision of low-cost smart electronic devices in applications where silicon chips were never imagined before. Item-level identification, smart food packaging, brand protection and electronic paper are just a few examples. Such new applications will require a continuous supply of countless disposable devices.  Imec’s IGZO TFT technology uses large-area manufacturing processes that allow for inexpensive production in large quantities – an ideal technology for ubiquitous electronic devices in the Internet-of-Everything.

“Making a plastic electronics device compatible to the ISO standard originally designed for silicon CMOS was a very challenging research and development expedition” stated Kris Myny, senior researcher at imec. “Our collaboration with Cartamundi enabled us to develop a truly industry-relevant solution”.

The researchers developed a self-aligned TFT architecture with scaled devices optimized for low parasitic capacitance and high cut-off frequency. This allowed design of a clock division circuit to convert incoming 13.56 MHz carrier frequency into system clock of the plastic chip. Optimizations at logic gate and system level reduced power consumption down to 7.5mW, enabling readout by commercial smartphones. “These research innovations are the first major achievements of my ERC starting grant”, stated Kris Myny, principal investigator and holder of the prestigious ERC starting grant FLICs (716426).

 “This innovative hardware solution of plastic NFC tags opens up several new possibilities for NFC deployments,” stated Alexander Mityashin, program manager at imec. “Thanks to the nature of thin-film plastics, the new tags can be made much thinner and they are mechanically very robust. Moreover, the self-aligned IGZO TFT technology offers manufacturing of chips in large volumes and at low cost”.

The results were presented in paper 15.2 (“A Flexible ISO14443-A Compliant 7.5mW 128b Metal-Oxide NFC Barcode Tag with Direct Clock Division Circuit from 3.56MHz Carrier”, by K. Myny, Y.-C Lai, N. Papadopoulos, F. De Roose, M. Ameys, M. Willegems, S. Smout, S. Steudel, W. Dehaene, J. Genoe, Feb. 7, 2017).

Leti, a research institute of CEA Tech, today announced it has developed a μLED fabrication process to create high-resolution arrays at 10-micron pitch. That pixelization and the 873 x 500 resolution that are enabled by the new process exceed technology.

Designed for micro-display applications such as augmented-reality or virtual-reality tools and wearable devices, the blue or green GaN/InGaN µLED arrays use Leti’s proprietary self-aligned technology. That process is key to achieving such a small pixel pitch. A combination of several damascene metallization steps used to create a common cathode is also expected to provide good thermal dissipation and prevent voltage drops within the micro-LED matrix. Electro-optical measurements showcase record efficiency and brightness exceeding requirements for device integration.

The results were presented Feb. 2 at SPIE Photonics West in San Francisco in a paper: “Processing and Characterization of High-Resolution GaN/InGaN LED Arrays at 10-Micron Pitch for Micro-Display Applications”.

“Leti’s self-aligned process allows the creation of high-resolution µLED matrices with a reduced pixel pitch of 10µm and paves the way towards even smaller pitches for next-generation devices,” said Ludovic Dupré, one of the paper’s authors. “In addition, the use of the damascene metallization process of the cathode, which also is a new process developed at Leti, is a breakthrough compared to previous demonstrations of micro-LED matrices. The common cathode indeed fills the whole volume between the micro-LEDs and provides metallic spreading of electrical current between them, as well as thermal dissipation. These results are promising for integrating a micro-LED matrix in micro-display devices by hybridization on CMOS active matrices, and first prototypes are currently being tested.”

Reproducibility is a necessity for science but has often eluded researchers studying the lifetime of organic light-emitting diodes (OLEDs). Recent research from Japan sheds new light on why: impurities present in the vacuum chamber during fabrication but in amounts so small that they are easily overlooked.

Organic light-emitting diodes use a stack of organic layers to convert electricity into light, and these organic layers are most commonly fabricated by heating source materials in vacuum to evaporate and deposit them onto a lower temperature substrate.

While issues affecting the efficiency of OLEDs are already well understood, a complete picture of exactly how and why OLEDs degrade and lose brightness over time is still missing.

Complicating matters is that devices fabricated with seemingly the same procedures and conditions but by different research groups often degrade at vastly different rates even when the initial performance is the same.

Unable to attribute these reproducibility issues to known sources such as the amount of residual water in the chamber and the purity of the starting materials, a report published online in Scientific Reports on December 13, 2016, adds a new piece to the puzzle by focusing on the analysis of the environment in the vacuum chamber.

“Although we often idealize vacuums as being clean environments, we detected many impurities floating in the vacuum even when the deposition chamber is at room temperature,” says lead author Hiroshi Fujimoto, chief researcher at Fukuoka i3-Center for Organic Photonics and Electronics Research (i3-OPERA) and visiting associate professor of Kyushu University.

Because of these impurities in the deposition chamber, the researchers found that the time until an OLED under operation dims by a given amount because of degradation, known as the lifetime, sharply increased for OLEDs that spent a shorter time in the deposition chamber during fabrication.

This trend remained even after considering changes in residual water and source material purity, indicating the importance of controlling and minimizing the device fabrication time, a rarely discussed parameter.

Research partners at Sumika Chemical Analysis Service Ltd. (SCAS) confirmed an increase of accumulated impurities with time by analyzing the materials that deposited on extremely clean silicon wafers that were stored in the deposition chamber when OLED materials were not being evaporated.

Using a technique called liquid chromatography-mass spectrometry, the researchers found that many of the impurities could be traced to previously deposited materials and plasticizers from the vacuum chamber components.

“Really small amounts of these impurities get incorporated into the fabricated devices and are causing large changes in the lifetime,” says Professor Chihaya Adachi, director of Kyushu University’s Center for Organic Photonics and Electronics Research (OPERA), which also took part in the study.

In fact, the new results suggest that the impurities amount to less than even a single molecular layer.

To improve lifetime reproducibility, a practice often adopted in industry is the use of dedicated deposition chambers for specific materials, but this can be difficult in academic labs, where often only a limited number of deposition systems are available for testing a wide variety of new materials.

In these cases, deposition chamber design and cleaning in addition to control of the deposition time are especially important.

“This is an excellent reminder of just how careful we need to be to do good, reproducible science,” comments Professor Adachi.

Faster production of advanced, flexible electronics is among the potential benefits of a discovery by researchers at Oregon State University’s College of Engineering.

Taking a deeper look at photonic sintering of silver nanoparticle films — the use of intense pulsed light, or IPL, to rapidly fuse functional conductive nanoparticles — scientists uncovered a relationship between film temperature and densification. Densification in IPL increases the density of a nanoparticle thin-film or pattern, with greater density leading to functional improvements such as greater electrical conductivity.

The engineers found a temperature turning point in IPL despite no change in pulsing energy, and discovered that this turning point appears because densification during IPL reduces the nanoparticles’ ability to absorb further energy from the light.

This previously unknown interaction between optical absorption and densification creates a new understanding of why densification levels off after the temperature turning point in IPL, and further enables large-area, high-speed IPL to realize its full potential as a scalable and efficient manufacturing process.

Rajiv Malhotra, assistant professor of mechanical engineering at OSU, and graduate student Shalu Bansal conducted the research. The results were recently published in Nanotechnology.

“For some applications we want to have maximum density possible,” Malhotra said. “For some we don’t. Thus, it becomes important to control the densification of the material. Since densification in IPL depends significantly on the temperature, it is important to understand and control temperature evolution during the process. This research can lead to much better process control and equipment design in IPL.”

Intense pulsed light sintering allows for faster densification — in a matter of seconds – over larger areas compared to conventional sintering processes such as oven-based and laser-based. IPL can potentially be used to sinter nanoparticles for applications in printed electronics, solar cells, gas sensing and photocatalysis.

Earlier research showed that nanoparticle densification begins above a critical optical fluence per pulse but that it does not change significantly beyond a certain number of pulses.

This OSU study explains why, for a constant fluence, there is a critical number of pulses beyond which the densification levels off.

“The leveling off in density occurs even though there’s been no change in the optical energy and even though densification is not complete,” Malhotra said. “It occurs because of the temperature history of the nanoparticle film, i.e. the temperature turning point. The combination of fluence and pulses needs to be carefully considered to make sure you get the film density you want.”

A smaller number of high-fluence pulses quickly produces high density. For greater density control, a larger number of low-fluence pulses is required.

“We were sintering in around 20 seconds with a maximum temperature of around 250 degrees Celsius in this work,” Malhotra. “More recent work we have done can sinter within less than two seconds and at much lower temperatures, down to around 120 degrees Celsius. Lower temperature is critical to flexible electronics manufacturing. To lower costs, we want to print these flexible electronics on substrates like paper and plastic, which would burn or melt at higher temperatures. By using IPL, we should be able to create production processes that are both faster and cheaper, without a loss in product quality.”

Products that could evolve from the research, Malhotra said, are radiofrequency identification tags, a wide range of flexible electronics, wearable biomedical sensors, and sensing devices for environmental applications.

Scientists at The Australian National University (ANU) have designed a nano crystal around 500 times smaller than a human hair that turns darkness into visible light and can be used to create light-weight night-vision glasses.

Professor Dragomir Neshev from ANU said the new night-vision glasses could replace the cumbersome and bulky night-vision binoculars currently in use.

“The nano crystals are so small they could be fitted as an ultra-thin film to normal eye glasses to enable night vision,” said Professor Neshev from the Nonlinear Physics Centre within the ANU Research School of Physics and Engineering.

“This tiny device could have other exciting uses including in anti-counterfeit devices in bank notes, imaging cells for medical applications and holograms.”

Co-researcher Dr Mohsen Rahmani said the ANU team’s achievement was a big milestone in the field of nanophotonics, which involves the study of behaviour of light and interaction of objects with light at the nano-scale.

“These semiconductor nano-crystals can transfer the highest intensity of light and engineer complex light beams that could be used with a laser to project a holographic image in modern displays,” said Dr Rahmani, a recipient of the Australian Research Council (ARC) Discovery Early Career Researcher Award based at the ANU Research School of Physics and Engineering.

PhD student Maria del Rocio Camacho-Morales said the team built the device on glass so that light can pass through, which was critical for optical displays.

“This is the first time anyone has been able to achieve this feat, because growing a nano semi-conductor on a transparent material is very difficult,” said Ms Camacho-Morales from the Nonlinear Physics Centre at ANU.

Last night at the Printed Electronics USA conference in Santa Clara, Calif., Kateeva’s YIELDjet FLEX inkjet printing system was named the winner of the prestigious Technical Development Manufacturing Award. Presented annually by conference organizer IDTechEx, the award honors the most significant development of a manufacturing device process or production plant in the printed electronics industry over the previous 24 months. In particular, manufacturing developments that optimize the process of lab-scale or mass-scale production by improving productivity, quality, reliability, uniformity, or scale.

Since its debut in late 2014, Kateeva’s YIELDjet FLEX system has become the leading high-yield mass-production tool for the key organic layer deposition step in the OLED Thin Film Encapsulation (TFE) market. Customers include the world’s largest flat panel display manufacturers located in Asia. With its novel features and capabilities, it solves critical technical problems that previously made it economically impractical to mass produce flexible OLEDs.

Raghu Das, CEO of IDTechEx, reports: “This is printed electronics in action, where inkjet printing is used to enable commercial consumer electronics devices today. Kateeva has built a system that continuously provides uniform, reliable and precise function required for the demanding display business.”

In accepting the award, Kateeva’s Chief Product Officer Eli Vronsky thanked the Judging Panel and called the accolade a considerable honor. “Engineering the YIELDjet FLEX system was an extraordinary opportunity for our team,” he said. “But as any product designer will confess, watching it catalyze an industry shift is the greater thrill. We’re proud that by solving certain OLED mass-production challenges, our tool has helped customers clear the path for exciting mobile products that are bendable, foldable and even roll-able. We’re grateful to be recognized for this achievement by our friends in the printed electronics industry.”

Today at the Printed Electronics USA Conference, Kateeva technologist, Xiao Chen, Ph.D. will reveal how YIELDjet technology will soon be applied to mass produce the RGB OLED layer to enable affordable OLED TVs. Dr. Chen’s talk begins at 11:40am.

Leti, an institute of CEA Tech, and PYXALIS, a French SME specializing in high-performance image sensors, today announced a new technology that lowers readout noise for image sensors down to 0.5 electron noise and dramatically improves low-light image sensing capabilities.

The new technology, called Owly-eyed, is based on a patented electrical architecture of the pixel readout that can be integrated in image sensors. Designed to meet growing demand for more sensitive CMOS image sensors, it has been adapted for PYXALIS, which will offer it in its next-generation image sensors.

“In this common lab with PYXALIS, we’ve developed a low-noise image technology that provides state-of-the-art advanced imaging for next-generation applications in a wide range of markets and industries,” said Marie Semeria, Leti’s CEO. “This CMOS-based device, which can be adapted for multiple uses, is another strong example of how Leti’s broad technology innovations make our partners more competitive in their industries.”

“Leti’s Owly-eyed technology is a major improvement in low-noise imaging,” said PYXALIS CEO Philippe Rommeveaux. “Combined with our capacity to offer advanced sensors with high digital integration and high dynamic range, it will allow us to establish a new performance standard in image sensors that address the growing demand for low-light applications in the surveillance, biomedical, science, defense and aerospace markets.”

In the Owly-eyed technology demonstrator, a sub-0.5 e−rms temporal read noise has been achieved on a VGA format CMOS image sensor implemented in a standard CMOS process. The low-noise performance is achieved exclusively through circuit optimization without any process refinements.

Leti also is developing many other technologies for innovative sensors and image processing that perform in low-power and low-latency operating modes.

Leti will demonstrate the Owly-eyed technology and a set of advanced smart-image-processing solutions at Vision 2016, Nov. 8-10 in Stuttgart, Germany, inHall 1, booth H01. The PYXALIS team will be available in Hall 1, booth D41.

Edwards, one of the world’s largest manufacturers of integrated vacuum and abatement solutions, launched a new Thermal Management System (TMS) at SEMICON Europa today. The new Smart TMS adds feedback control to accurately maintain gas temperature in vacuum pump fore lines and exhaust lines. Unheated lines can be clogged by condensed process materials and by-products. The Smart TMS reduces downtime and risks to service personnel tasked with cleaning out these often hazardous materials. The Smart TMS also improves energy efficiency and functionality with programmable remote controllers that interface readily to fab control software.

“We have worked extensively with our customers to improve their process productivity, as well as their fab safety,” states Ralph Loske, Business Line Manager, Semi & DSL for Edwards. “One of the major perceived risks associated with condensation is blockage of the exhaust pipe and a consequent process interruption. However, there are also other serious hazards that may result from condensed materials in exhaust pipes. For example, an exhaust fire can occur when partly reacted silicon compounds condense in exhaust pipes during a deposition process, and are subsequently exposed to fluorine during a chamber-cleaning process.”

To counter the condensation threat and improve system safety and productivity, the Smart TMS system controls gas temperatures between the pump exhaust port and the abatement inlet. It includes temperature monitoring within the heating elements, enabling feedback control to accurately maintain exhaust temperature at a specified set-point.

Ralph adds, “Our global applications group is able to holistically look at each customer’s system to customize the right solution for their specific application requirements. The Smart TMS solution is also valuable to manufacturers of flat panel displays (FPD) and solar cells, who use similar processes, including: chemical vapor deposition (CVD), epitaxy, oxide etch and poly etch, which have the potential for condensation and deposition in the exhaust lines.”

tms