Category Archives: Flexible Displays

Researchers have developed an imaging technique that uses a tiny, super sharp needle to nudge a single nanoparticle into different orientations and capture 2-D images to help reconstruct a 3-D picture. The method demonstrates imaging of individual nanoparticles at different orientations while in a laser-induced excited state.

The findings, published in The Journal of Chemical Physics, brought together researchers from the University of Illinois and the University of Washington, Seattle in a collaborative project through the Beckman Institute for Advanced Science and Technology at the U. of I.

Nanostructures like microchip semiconductors, carbon nanotubes and large protein molecules contain defects that form during synthesis that cause them to differ in composition from one another. However, these defects are not always a bad thing, said Martin Gruebele, the lead author and an Illinois chemistry professor and chair.

“The term ‘defect’ is a bit of a misnomer,” Gruebele said. “For example, semiconductors are manufactured with intentional defects that form the ‘holes’ that electrons jump into to produce electrical conductivity. Having the ability to image those defects could let us better characterize them and control their production.”

As advances in technology allow for smaller and smaller nanoparticles, it is critical for engineers to know the precise number and location of these defects to assure quality and functionality.

The study focused on a class of nanoparticles called quantum dots. These dots are tiny, near-spherical semiconductors used in technology like solar panels, live cell imaging and molecular electronics – the basis for quantum computing.

The team observed the quantum dots using a single-molecule absorption scanning tunneling microscope fitted with a needle sharpened to a thickness of only one atom at its tip. The needle nudges the individual particles around on a surface and scans them to get a view of the quantum dot from different orientations to produce a 3-D image.

The researchers said there are two distinct advantages of the new SMA-STM method when compared with the current technology – the Nobel Prize-winning technique called cryogenic electron tomography.

For a video related to this research can be found here.

“Instead of an image produced using an average of thousands of different particles, as is done with CryoET, SMA-STM can produce an image from a single particle in about 20 different orientations,” Gruebele said. “And because we are not required to chill the particles to near-absolute zero temperatures, we can capture the particles at room temperature, not frozen and motionless.”

The researchers looked at semiconductor quantum dots for this study, but SMA-STM can also be used to explore other nanostructures such as carbon nanotubes, metal nanoparticles or synthetic macromolecules. The group believes the technique can be refined for use with soft materials like protein molecules, Gruebele said.

The researchers are working to advance SMA-STM into a single-particle tomography technique, meaning that they will need to prove that method is noninvasive.

“For SMA-STM to become a true single-particle tomography technique, we will need to prove that our nudges do not damage or score the nanoparticle in any way while rolled around,” Gruebele said. “Knocking off just one atom can fundamentally alter the defect structure of the nanoparticle.”

Despite slower demand from end market and panel price erosion, the large thin-film transistor (TFT) display market expanded in 2017 in all three aspects — unit shipments, area shipments and revenue. According to a new report from business information provider IHS Markit (Nasdaq: INFO), unit shipments of larger than 9-inch TFT displays increased by 4 percent in 2017 compared to a year ago, while area shipments rose 6 percent and revenues up 13 percent during the same period.

“Revenue growth was higher than that of area shipments, which was again bigger than that of unit shipments. This indicates that the display market is moving to larger screens in all applications, and the penetration of high specification products with a higher price tag, such as high resolution, wide viewing angle and slim design panels, has increased,” said Robin Wu, principal analyst at IHS Markit. Large TFT display revenues reached $63.7 billion in 2017, according to the latest Large Area Display Market Tracker by IHS Markit.

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By area shipments, TV displays, which grew 6 percent year over year, accounted for 78 percent of total large TFT display market, leading the overall market growth. Despite ongoing decline in TV panel prices, which started in the middle of 2017, revenue continued to grow by a double digit as panel makers have focused on high-end products, such as 4K TVs and 55-inch-and-larger TVs. Shipments of 4K TV panels amounted to 92 million units in 2017, up 46 percent year over year, making up 35 percent of the entire TV display market. OLED TV panels also continued its growth, marking unit shipments of 1.8 million with a 102 percent growth from 2016.

BOE led the large TFT display market with a 21 percent share in 2017 in terms of unit shipments, followed by LG Display with 20 percent and Innolux with 16 percent. It was the first time that a Chinese panel maker took the top position in an annual base result. However, in the TV panel market by unit shipments, LG Display retained its lead with a 19 percent share, followed by BOE with 17 percent. In terms of area shipments, South Korean panel makers remained strong, with LG Display accounting for 23 percent and Samsung Display for 17 percent.

The Large Area Display Market Tracker by IHS Markit provides information about the entire range of large display panels shipped worldwide and regionally, including monthly and quarterly revenues and shipments by display area, application, size and aspect ratio for each supplier.

The 2018 FLEXI Awards today recognized groundbreaking accomplishments in the Flexible Hybrid Electronics (FHE) sector in 2017. Presented at the opening session of the 17th annual 2018FLEX Conference and Exhibition, in Monterey, California, the awards spotlighted the following leaders in the categories of R&D Achievements, Product Innovation and Commercialization, Education Leadership and Industry Leadership.

Product Innovation – E Ink, creator of Dazzle, the world’s largest electronic paper installation, won a FLEXI for product design and ingenuity, and potential market adoption and revenue generation. Made from electrophoretic display technology, the programmable art installation adorns one side of San Diego International Airport’s new rental car center.

R&D Achievement – The Wearable Device for Dynamic Assessment of Hydration team – consisting of GE Global Research, UES, The University of Arizona, University of Connecticut, University of Massachusetts Amherst, Dublin City University and AFRL – won a FLEXI for developing a paper-based biofluid patch that collects sweat for human hydration index monitoring. Award criteria included research approach, originality and commercial potential for expanding the bounds of flexible or printed electronics.

Technology Leadership In Education – James Turner, research scientist at Binghamton University, won a FLEXI for outstanding leadership and attention to mentoring students during the development of an FHE electrocardiography (ECG) patch. Turner led a group of students through the development which included a multi-disciplinary approach as well as coordination with industry and several academic institutions to correlate reliability data, simulations and optimize design features of the revolutionary patch.

Industry Leadership – David Morton, formerly with the Army Research Laboratory, won a FLEXI for his dedication to building awareness of advanced flexible hybrid electronics in the broader field of electronics. Award criteria include outstanding leadership in public forums and contributions to industry associations.

Technology Champion – Robert Reuss, former program manager in the Microsystems Technology Office at DARPA, won a FLEXI for his extraordinary dedication to growing the flexible electronics industry, early recognition of the impact of large area electronics and strong contributions to helping build the FLEX Conference.

FLEXIs have been the industry’s premier award for distinguished organizations and individuals since 2009. See full list of awardees. The FLEXI Awards are sponsored by FlexTech, a SEMI Strategic Association Partner, an organization dedicated to the success of the FHE sector. The 2018 FLEXI award ceremony was sponsored by SCREEN Holdings.

2018FLEX – February 12-15 in Monterey, California – spotlights FHE innovation drivers in smart medtech, smart transportation, smart manufacturing, smart data, Internet of Things (IoT) and consumer electronics.

Total shipments of mobile phone displays, including thin-film transistor liquid crystal display (TFT LCD) and active matrix organic light-emitting diode (AMOLED) panels, reached 2.01 billion units in 2017, up 3 percent from 2016, according to preliminary estimate from business information provider IHS Markit (Nasdaq: INFO).

In the growing mobile phone display market, shipments of low-temperature-poly-silicon (LTPS) TFT LCD panels, which realize high-resolution images, increased by 21 percent to 620 million units in 2017 compared to the previous year. Shipments of amorphous silicon (a-Si) TFT LCD mobile phone panels declined 4 percent to 979 million units during the same period. Even though shipments of AMOLED panels jumped in the second half of 2017 thanks to the launch of the iPhone X, combined with the weak demand in the first half, its shipments were up just 3 percent to 402 million units in 2017.

In the smartphone-use LTPS TFT LCD market, Tianma, a leading small and medium panel supplier in China, has shown significant growth, expanding its shipments to Chinese smartphone set brands, such as Huawei and Xiaomi. In 2017, Tianma shipped 105 million LTPS TFT LCD panels for smartphones, almost double its shipments in 2016, with a market share of 17 percent, up 6 percentage points from 2016. It ranked the second largest LTPS TFT LCD supplier for smartphones in 2017, taking over LG Display with 16 percent, down 4 percentage points, and Sharp with 13 percent, down 1 percentage point. In 2017, Japan Display continued its market leader position but shed its share by 10 percentage points to 26 percent in 2017, according to the latest Smartphone Display Intelligent Service report by IHS Markit.

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“LTPS TFT is a key technology to produce high-resolution displays for smartphones, and experience is required to optimize highly complex LTPS manufacturing process in each production fab. In terms of experience, Japanese and South Korean panel makers have a competitive advantage compared to Chinese makers,” said Hiroshi Hayase, senior director at IHS Markit. “However, Chinese LCD makers, such as Tianma and BOE, are catching up LTPS technology fast enough to support high demand from Chinese smartphone set makers.”

The Smartphone Display Intelligent Service by IHS Markit contains quarterly updates of smartphone display shipments and revenue by application, size, resolution and technology. It also provides supply chain information between display and set makers, as well as monthly smartphone display shipment and pricing information.

This year again, the Las Vegas Consumer Electronics Show, 2018 edition allowed us to discover the latest innovations in numerous fields including the microLED displays sector. “The Wall”, a 146” microLED TV powered by Samsung, has been probably the most impressive announcement. The Korea-based LED maker Lumens also proposed a 139” display, with smaller 0.8 mm pitch. In both cases, technology developed by these leaders is not strictly microLED related but confirms the attractiveness of microLEDs solutions. Yole Développement’s (Yole) analyst, Dr. Eric Virey attended the show and proposed a snapshot on i-micronews.com.

“Initial success in smartwatches could accelerate technology and supply chain maturation, making microLED competitive against OLED in high end TVs, tablets and laptops”, explains Dr. Eric Virey from Yole. “In Yole’s most optimistic scenario, the market for microLED displays could reach up to 330 million units by 2025 (1) .”

The microLED display sector has been deeply analyzed by Yole and KnowMade, both parts of Yole Group of Companies. The partners propose today a detailed patent analysis titled: Microled Displays: Intellectual Property Landscape. Under this new report, they identified key patents, technology nodes and players related to microLED technologies for display applications. This latest analysis confirms the growing interest around the microLED technologies.
Which companies own the patents? What are their major thrust areas and portfolio strength? Yole Group of Companies invites you to discover the latest insights of this dynamic industry.

Yole Group of Companies confirms the buzz: as of today close to 1,500 patents relevant to the microLED display field have been filed by 125 companies and organizations. Among these are multiple startups, display makers, OEMs , semiconductor companies, LED makers, and research institutions.

“The overall corpus is relatively young, with an average age of 3.2 years across all families”, asserts Dr. Nicolas Baron, CEO & Founder, KnowMade. The first patents were filed in 2000 – 2001, but the bulk of the activity started after 2012. Thus, only a minority of patents have been granted so far.

Pioneers include Sony, Sharp, MIT, and others, although the bulk of the initial developments were conducted by a variety of research institutions including Kansas State University, University of Hong Kong, Strathclyde University & Tyndall Institute (which spun-off mLED, InfiniLED, and X-Celeprint), University of Illinois, and startup companies like Luxvue and, later on, Playnitride and Mikro Mesa.

Yole Group of Companies’ study also reveals a number of companies that have not yet been identified as players in the microLED display field. Moreover, this study confirms the commitment of many more companies, which are not typically associated with display technology. Intel and Goertek are part of them. On the flip side, various companies known to be active in the field (i.e. Huawei) have yet to see any of their patent in the field published.

Overall, the activity is still led mostly by startups (including those such as Luxvue or eLux) acquired by larger organization) and research institutions. With the exception of Sharp and Sony, display makers and LED makers are relative latecomers. Many companies started ramping up their microLED research and development activities after Apple showed faith in microLED with its acquisition of Luxvue. As of December 2017, Apple appears to have the most complete IP portfolio, covering almost all key technology nodes. However, many of its patents pertain to the technological ecosystem developed around the company’s MEMS transfer technology. Other companies like Sony, with a smaller portfolio but which had a head start, might own more fundamental design patents with strong blocking power.

What is the status of the microLED display supply chain? Enabling large-scale microLED display manufacturing requires bringing together three major disparate technologies and supply chain bricks: LED manufacturing, backplane manufacturing, and microchip mass transfer & assembly.

“The supply chain is complex and lengthy compared to typical displays,” comments Dr. Eric Virey from Yole. “Every process is critical and it’s a challenge to effectively manage every aspect. No one company appears positioned to master and execute across a supply chain that will likely be more horizontal, compared to other established display technologies.”

The IP landscape reflects these challenges through the variety of players involved, but requirements differ from one application to another. For low-volume, high added-value applications like microdisplays for augmented/mixed reality for the enterprise, military, and medical markets, one can envision a well-funded startup with good technology efficiently managing the supply chain. However, consumer applications such as TVs and smartphones will require significant investments to unlock large scale manufacturing.

Though only a few companies have a broad IP portfolio covering all major technology nodes (transfer chip structure, display architecture, etc.), enough players have patents across many technology bricks to guarantee that complex licensing and legal battles will arise once microLED displays enter volume manufacturing and reach the market. Small companies with strong positions in various technology bricks will attempt to obtain licensing fees from larger players involved in manufacturing. Large corporations will try to block each other and prevent their competitors from entering the market. To prepare for such events, some latecomers appear to be filing large quantities of patents, sometimes with little substance.

Kateeva, a developer of inkjet deposition equipment solutions for OLED display manufacturing, today announced that the company has expanded its executive team by appointing Marc Haugen as chief operating officer (COO).

Mr. Haugen brings extensive semiconductor equipment industry experience to Kateeva. As a former executive at Applied Materials and Lam Research, he implemented operational disciplines designed to maximize supply-chain and manufacturing efficiencies. As COO, his role will be to help drive Kateeva’s operational performance as a technology leader and key enabler of the global display industry. He reports to chairman and chief executive officer (CEO), Dr. Alain Harrus.

Mr. Haugen assumes the COO title from Kateeva co-founder, Dr. Conor Madigan, who remains president, and who will now focus on leading the company’s technology and new product development.

“We believe that Marc’s operational roles for global capital equipment companies make him particularly well-qualified to help Kateeva extend its market leadership by applying operational disciplines that will allow us to scale our operations effectively,” said Dr. Harrus.  “We also expect his expertise will enrich our capability to deliver the technology solutions our customers need to win in their marketplace.”

“We’re very pleased to welcome Marc to Kateeva,” noted Dr. Madigan. “As COO, we expect he will further tighten interaction between the field, manufacturing, engineering, finance, and other key functions to support our product development, sales, and operations performance. In addition, he will be responsible for implementing processes to improve efficiency, predictability and reliability, with the goal of reducing overall operating costs.”

“I believe that Kateeva enjoys a strong foundation to build momentum for growth,” said Mr. Haugen. “The technology is industry-leading, the team is outstanding, and the customer base includes leading display companies. This is a terrific opportunity to support Kateeva’s innovation roadmap by driving operational excellence across the company.”

Mr. Haugen has spent three decades working in the semiconductor industry. As group vice president of worldwide operations and supply chain for Applied Materials from 2013-2016, he led a team of thousands of people in factories across the globe, with an annual multi-billion-dollar spend. From his base in Singapore, he directed supply chain operations, volume manufacturing, new product manufacturing, quality and logistics to support the company’s semiconductor systems, display and energy business segments.

Before that, he was corporate vice president of global product operations at Lam Research. While there, he directed the integration of products, product operations, and product development processes, including Lam’s acquisition of Novellus Systems, as well as its acquisition of Austria-based SEZ. During this time, he also served as vice president/managing director of SEZ.

Immediately prior to Kateeva, Mr. Haugen was EVP of global operations and engineering at Cepheid, a molecular diagnostics company. He began his career in 1987 as a surface warfare officer in the U.S. Navy. After that, he held operations roles with increasing responsibility at Applied Materials and Lam Research.

Mr. Haugen holds a BS degree in industrial and systems engineering from the University of Southern California. He earned his MBA with a special focus on international/Asia business strategy from the University of California Los Angeles and the National University of Singapore (UCLA/NUS Executive MBA Program).

By Jay Chittooran, Manager, Public Policy, SEMI

International trade is one of the best tools to spur growth and create high-skill and high-paying jobs. Over 40 million American jobs rely on trade, and this is particularly true in the semiconductor supply chain. Over the past three decades, the semiconductor industry has averaged nearly double-digit growth rates in revenue and, by 2030, the semiconductor supply chain is forecast to reach $1 trillion. Trade paves the way for this growth.

Unfortunately, despite its importance to the industry, trade has been transformed from an economic issue into a political one, raising many new trade challenges to companies throughout the semiconductor industry.

GHz-ChinaChina’s investments in the industry will continue to anchor the country as a major force in the semiconductor supply chain. China’s outsized spending has spawned concern among other countries about the implications of these investments. According to SEMI’s World Fab Forecast, 20 fabs are being built in China – and construction on 14 more is rumored to begin in the near term – compared to the 10 fabs under construction in the rest of the world. China is clearly outpacing the pack.

The Trump Administration has levied intense criticism of China, citing unfair trade practices, especially related to intellectual property issues. The U.S. Trade Representative has launched a Section 301 investigation into whether China’s practice of forced technology transfer has discriminated against U.S. consumers. Even as the probe unfolds, expectations are growing that the United States will take action against China, raising fears of not only possible retaliation in time but rising animosity between two trading partners that rely deeply on each other.

A number of other open investigations also cloud the future. The Administration launched two separate Section 232 investigations into steel and aluminum industry practices by China, claiming Chinese overproduction of both items are a threat to national security. The findings from these investigations will be submitted to the President, who, in the coming weeks, will decide an appropriate response, which could include imposing tariffs and quotas.

Another high priority area is Korea. While U.S. threats to withdraw from the U.S.-Korea Free Trade Agreement (KORUS) reached a fever pitch in August, rhetoric has since tempered. Informal discussions between the countries on how best to amend the trade deal are ongoing. The number of KORUS implementation issues aside, continued engagement with Korea – instead of scrapping a comprehensive, bilateral trade deal – will be critically important for the industry.

Lastly, negotiations to modernize the North American Free Trade Agreement (NAFTA) will continue this year. The United States wants to conclude talks by the end of March, but with the deadline fast approaching and the promise of resolution waning, tensions are running high. Notably, the outcome of the NAFTA talks will inform and set the tone for other trade action.

What’s more, a number of other actions on trade will take place this year. As we wrote recently, Congress has moved to reform the Committee on Foreign Investment in the United States (CFIUS), a government body designed to review sales and transfer of ownership of U.S. companies to foreign entities. Efforts have also started to revise the export control regime – a key component to improving global market access and making international trade more equitable.

SEMI will continue its work on behalf of its members around the globe to open up new markets and lessen the burden of regulations on cross-border trade and commerce. In addition, SEMI will continue to educate policymakers on the critical importance of unobstructed trade in continuing to push the rapid advance of semiconductors and the emerging technologies they enable into the future. If you are interested in more information on trade, or how to be involved in SEMI’s public policy program, please contact Jay Chittooran, Manager, Public Policy, at [email protected].

2018FLEX, the Flexible Hybrid Electronics (FHE) Conference and Exhibition, will bring together more than 600 experts from around the world for business-critical insights and the latest technology in both flexible electronics and MEMS and sensors. 2018FLEX – February 13-15 in Monterey, California – will spotlight FHE innovation drivers in smart medtech, smart automotive, smart manufacturing, Internet of Things (IoT) and consumer electronics. The event, hosted by SEMI FlexTech, will feature more than 100 market and technical presentations, 60 exhibits, short courses and opportunities to connect with industry visionaries.

This year 2018FLEX will co-locate with the MEMS & Sensors Technical Congress (MSTC). February 13-14, MSTC will highlight leading-edge MEMS and sensors system-level solutions, technology and applications. Click here to register for both events.

The flexible and printed electronics markets are expected to reach $20 billion by 2022, with a compound annual growth rate (CAGR) of 21.5 percent from 2016 to 2022, according to Zion Research. Flexible hybrid electronics and printed electronics enable new form factors and economics for a diverse set of applications. Examples include minimally invasive implantable systems that treat major depression and post-traumatic stress disorder (PTSD), the ability to repair or reproduce failed devices during space exploration, and head-up displays (HUDs) that will use ultra-thin holographic films to project transparent images on car windshields for safer driving.

“Global demand for technical expertise on materials, manufacturing and component technologies in FHE and printed electronics is rapidly growing,” said Melissa Grupen-Shemansky, CTO, Flexible Electronics and Advanced Packaging, SEMI. “2018FLEX offers the latest business and technology insights into applications such as flexible biosensors, flexible displays, drones, smart packaging, 3D printing and human-machine interfaces.”

2018FLEX will also showcase the latest technologies and solutions developed by contractors involved in the public/private research and development funding programs in FlexTech, NanoBio Manufacturing Consortium (NBMC), and NextFlex.

Keynotes headlining 2018FLEX will include:

  • Cortera Neurotechnologies – Minimally invasive implantable biosensors for treating major psychiatric illnesses
  • NASA – In-Space Manufacturing, a multi-material Fab Lab for the International Space Station
  • Luminit – Holographic Optical Element technologies for automotive HUD
  • Panasonic – Flexible hybrid electronics applications for lithium-ion batteries
  • Draper Labs – Flexible drones

2018FLEX will also highlight these exciting technologies:

  • Bonbouton – Graphene-based smart insoles for preventative diabetic healthcare
  • PARC – Latest application projects in environmental monitoring, wearables and supply chain solutions
  • Tekscan – Thin, flexible, tactile sensing technology for intelligent surgical, diagnostic and home healthcare applications

About 2018FLEX

The Flexible Electronics Conference and Exhibition (2018FLEX), now in its 17th year, will be held at the Hyatt Regency Monterey Hotel & Spa in Monterey. Highlights will include significant technical achievements, opportunities and challenges within the FHE and printed electronics industries.

A nanostructured gate dielectric may have addressed the most significant obstacle to expanding the use of organic semiconductors for thin-film transistors. The structure, composed of a fluoropolymer layer followed by a nanolaminate made from two metal oxide materials, serves as gate dielectric and simultaneously protects the organic semiconductor – which had previously been vulnerable to damage from the ambient environment – and enables the transistors to operate with unprecedented stability.

Image shows organic-thin film transistors with a nanostructured gate dielectric under continuous testing on a probe station. (Credit: Rob Felt, Georgia Tech)

Image shows organic-thin film transistors with a nanostructured gate dielectric under continuous testing on a probe station. (Credit: Rob Felt, Georgia Tech)

The new structure gives thin-film transistors stability comparable to those made with inorganic materials, allowing them to operate in ambient conditions – even underwater. Organic thin-film transistors can be made inexpensively at low temperature on a variety of flexible substrates using techniques such as inkjet printing, potentially opening new applications that take advantage of simple, additive fabrication processes.

“We have now proven a geometry that yields lifetime performance that for the first time establish that organic circuits can be as stable as devices produced with conventional inorganic technologies,” said Bernard Kippelen, the Joseph M. Pettit professor in Georgia Tech’s School of Electrical and Computer Engineering (ECE) and director of Georgia Tech’s Center for Organic Photonics and Electronics (COPE). “This could be the tipping point for organic thin-film transistors, addressing long-standing concerns about the stability of organic-based printable devices.”

The research was reported January 12 in the journal Science Advances. The research is the culmination of 15 years of development within COPE and was supported by sponsors including the Office of Naval Research, the Air Force Office of Scientific Research, and the National Nuclear Security Administration.

Transistors comprise three electrodes. The source and drain electrodes pass current to create the “on” state, but only when a voltage is applied to the gate electrode, which is separated from the organic semiconductor material by a thin dielectric layer. A unique aspect of the architecture developed at Georgia Tech is that this dielectric layer uses two components, a fluoropolymer and a metal-oxide layer.

“When we first developed this architecture, this metal oxide layer was aluminum oxide, which is susceptible to damage from humidity,” said Canek Fuentes-Hernandez, a senior research scientist and coauthor of the paper. “Working in collaboration with Georgia Tech Professor Samuel Graham, we developed complex nanolaminate barriers which could be produced at temperatures below 110 degrees Celsius and that when used as gate dielectric, enabled transistors to sustain being immersed in water near its boiling point.”

The new Georgia Tech architecture uses alternating layers of aluminum oxide and hafnium oxide – five layers of one, then five layers of the other, repeated 30 times atop the fluoropolymer – to make the dielectric. The oxide layers are produced with atomic layer deposition (ALD). The nanolaminate, which ends up being about 50 nanometers thick, is virtually immune to the effects of humidity.

“While we knew this architecture yielded good barrier properties, we were blown away by how stably transistors operated with the new architecture,” said Fuentes-Hernandez. “The performance of these transistors remained virtually unchanged even when we operated them for hundreds of hours and at elevated temperatures of 75 degrees Celsius. This was by far the most stable organic-based transistor we had ever fabricated.”

For the laboratory demonstration, the researchers used a glass substrate, but many other flexible materials – including polymers and even paper – could also be used.

In the lab, the researchers used standard ALD growth techniques to produce the nanolaminate. But newer processes referred to as spatial ALD – utilizing multiple heads with nozzles delivering the precursors – could accelerate production and allow the devices to be scaled up in size. “ALD has now reached a level of maturity at which it has become a scalable industrial process, and we think this will allow a new phase in the development of organic thin-film transistors,” Kippelen said.

An obvious application is for the transistors that control pixels in organic light-emitting displays (OLEDs) used in such devices as the iPhone X and Samsung phones. These pixels are now controlled by transistors fabricated with conventional inorganic semiconductors, but with the additional stability provided by the new nanolaminate, they could perhaps be made with printable organic thin-film transistors instead.

Internet of things (IoT) devices could also benefit from fabrication enabled by the new technology, allowing production with inkjet printers and other low-cost printing and coating processes. The nanolaminate technique could also allow development of inexpensive paper-based devices, such as smart tickets, that would use antennas, displays and memory fabricated on paper through low-cost processes.

But the most dramatic applications could be in very large flexible displays that could be rolled up when not in use.

“We will get better image quality, larger size and better resolution,” Kippelen said. “As these screens become larger, the rigid form factor of conventional displays will be a limitation. Low processing temperature carbon-based technology will allow the screen to be rolled up, making it easy to carry around and less susceptible to damage.

For their demonstration, Kippelen’s team – which also includes Xiaojia Jia, Cheng-Yin Wang and Youngrak Park – used a model organic semiconductor. The material has well-known properties, but with carrier mobility values of 1.6 cm2/Vs isn’t the fastest available. As a next step, they researchers would like to test their process on newer organic semiconductors that provide higher charge mobility. They also plan to continue testing the nanolaminate under different bending conditions, across longer time periods, and in other device platforms such as photodetectors.

Though the carbon-based electronics are expanding their device capabilities, traditional materials like silicon have nothing to fear.

“When it comes to high speeds, crystalline materials like silicon or gallium nitride will certainly have a bright and very long future,” said Kippelen. “But for many future printed applications, a combination of the latest organic semiconductor with higher charge mobility and the nanostructured gate dielectric will provide a very powerful device technology.”

A discovery by an international team of researchers from Princeton University, the Georgia Institute of Technology and Humboldt University in Berlin points the way to more widespread use of an advanced technology generally known as organic electronics.

The research, published in the journal Nature Materials, focused on organic semiconductors, a class of materials prized for their applications in emerging technologies such as flexible electronics, solar energy conversion, and high-quality color displays for smartphones and televisions. In the short term, the advancement could particularly help with organic light-emitting diodes that operate at high energy to emit colors such as green and blue.

Researchers used ultraviolet light to excite molecules in a semiconductor, triggering reactions that split up and activated a dopant. Credit: Princeton University / Jing Wang and Xin Lin

Researchers used ultraviolet light to excite molecules in a semiconductor, triggering reactions that split up and activated a dopant. Credit: Princeton University / Jing Wang and Xin Lin

“Organic semiconductors are ideal materials for the fabrication of mechanically flexible devices with energy-saving, low-temperature processes,” said Xin Lin, a doctoral student and a member of the Princeton research team. “One of their major disadvantages has been their relatively poor electrical conductivity. In some applications, this can lead to difficulties and inefficient devices. We are working to improve the electrical properties of organic semiconductors.”

Semiconductors, typically made of silicon, are the foundation of modern electronics because engineers can take advantage of their unique properties to control electrical currents. Among many applications, semiconductor devices are used for computing, signal amplification, and switching. They are used in energy-saving devices such as light-emitting diodes and devices that convert energy such as solar cells.

Essential to these functionalities is a process called doping, in which the semiconductor’s chemical makeup is modified by adding a small amount of chemicals or impurities. By carefully choosing the type and amount of dopant, researchers can alter semiconductors’ electronic structure and electrical behavior in a variety of ways.

In their Nature Materials paper, the researchers have described a new approach for greatly increasing the conductivity of organic semiconductors, formed of carbon-based molecules rather than silicon atoms. The dopant, a ruthenium-containing compound, was a reducing agent, which means it added electrons to the organic semiconductor as part of the doping process. The addition of the electrons was the key to increasing the semiconductor’s conductivity. The compound belongs to a newly-introduced class of dopants called dimeric organometallic dopants. Unlike many other powerful reducing agents, these dopants are stable when exposed to air but still work as strong electron donors both in solution and solid state.

Georgia Tech’s Seth Marder, a Regents Professor in the School of Chemistry and Biochemistry, and Stephen Barlow, a research scientist in the school, led the development of the new dopant. They called the ruthenium compound a “hyper-reducing dopant.”

They said it was unusual, not only in its combination of electron donation strength and air stability but also in its ability to work with a class of organic semiconductors that have previously been very difficult to dope. In studies conducted at Princeton, the researchers found that the new dopant increased the conductivity of these semiconductors by about a million times.

The ruthenium compound was a dimer, meaning it consisted of two identical molecules, or monomers, connected by a chemical bond.  As is, the compound proved relatively stable and, when added to these difficult-to-dope semiconductors, it did not react and remained in its equilibrium state. That posed a problem because to increase the conductivity of the organic semiconductor, the ruthenium dimer needed to split and release its two identical monomers.

Princeton’s Lin, the study’s lead author, said the researchers looked for different ways to break up the ruthenium dimer and activate the doping. Eventually, he and Berthold Wegner, a visiting graduate student from the group of Norbert Koch at Humboldt University, took a hint from how photosynthetic systems work. They irradiated the system with ultraviolet light, which excited molecules in the semiconductor and initiated the reaction. Under exposure to the light, the dimers were able to dope the semiconductor, leading to a roughly 100,000 times increase in the conductivity.

After that, the researchers made an interesting observation.

“Once the light was turned off, one might naively expect the reverse reaction to occur and the increased conductivity to disappear,” said Georgia Tech’s Marder, who is also associate director of the Center for Organic Photonics and Electronics (COPE) at Georgia Tech. “However, this was not the case.”

The researchers found that the ruthenium monomers remained isolated in the semiconductor, increasing conductivity, even though thermodynamics should have returned the molecules to their original configuration as dimers. Antoine Kahn, a Princeton professor who led the research team, said the physical layout of the molecules inside the doped semiconductor provides a likely answer to this puzzle. The hypothesis is that the monomers are scattered in the semiconductor in such a way that it was very difficult for them to return to their original configuration and re-form the ruthenium dimer. To recombine, he said, the monomers would have to have faced in the correct orientation, but in the mixture, they remained askew. So, even though thermodynamics showed that dimers should reform, most never snapped back together.

“The question is why aren’t these things moving back together into equilibrium,” said Kahn, who is Stephen C. Macaleer ’63 Professor in Engineering and Applied Science. “The answer is they are kinetically trapped.”

In fact, the researchers observed the doped semiconductor for over a year and found very little decrease in the electrical conductivity. Also, by observing the material in light-emitting diodes fabricated by the group of Barry Rand, an assistant professor of electrical engineering at Princeton and the Andlinger Center for Energy and the Environment, the researchers discovered that doping was continuously re-activated by the light produced by the device.

“The light activates the system more, which leads to more light production and more activation until the system is fully activated, said Marder, who is Georgia Power Chair in Energy Efficiency. “This alone is a novel and surprising observation.”

The paper was co-authored by Kyung Min Lee, Michael A. Fusella, and Fengyu Zhang, of Princeton, and Karttikay Moudgil of Georgia Tech. Research was funded by the National Science Foundation (grants DMR-1506097, DMR-1305247), the Department of Energy’s Energy Efficiency & Renewable Energy Solid-State Lighting program (award DE-EE0006672) and the DoE’s Office of Basic Energy Sciences, Division of Materials Sciences and Engineering (award DE-SC0012458), the Deutsche Forschungsgemeinschaft (project SFB 951) and the Helmholtz Energy-Alliance Hybrid Photovoltaics project.