Monthly Archives: April 2016

Whether it’s the Internet of Things (IoT), wearables, or industrial automation, new devices and applications are portable, battery-operated and require continuous power.  Wireless connectivity is required for connecting to the Internet.  Today’s devices collect and transmit data from sensors, are always or almost always on and require power.  The semiconductor industry has met the challenge to design devices for low power operation.  But eventually batteries still run out of energy and have to be replaced or recharged.  Energy harvesting can extend battery life or possibly replace batteries altogether for continuous operation.  The new Semico Research report “Energy Harvesting: The Next Billion Dollar Market for Semiconductors” projects semiconductor sales for this market will reach $3 billion by 2020.

An energy harvesting solution requires more than just the energy harvester or transducer.  The key components include a power converter, power management IC (PMIC), MCU, and energy storage.  “An ecosystem of semiconductor vendors is emerging for the nascent energy harvesting market,” says Tony Massimini, Semico Research’s Chief of Technology.  “The ecosystems are gravitating around the vendors of key power components.  They are forming partnerships with producers of energy harvesters, battery suppliers, and other components.”

This study examines the market opportunity for energy harvesting outside of large installations and commercial power generation.  A broad range of markets will employ energy harvesting to either replace batteries or extend battery life. These applications cover wireless sensor nodes (WSN) for bridges, infrastructure, building automation and controls, and home automation (including lighting, security and environmental). Energy harvesting will grow in automotive applications, cell phones, wearables and other consumer electronics.

“The vendors of MCUs, sensors, RF, analog and other components will continue to develop lower power devices”, according to Massimini. “While this puts less drain on a battery and will extend its life, it also lessens the load for an energy harvesting solution.  Energy harvesting solutions are also expected to improve during the forecast period.”

The ASPs for the semiconductor components continue to decline, lowering the costs for an energy harvesting solution.  This is driving higher penetration rates.

Key findings of the report include:

  • The number of energy harvesting solutions will grow to 777 million units by 2020 (CAGR ’15 to ’20 = 80.6%).
  • Smartphone market will become the largest by volume by 2020.
  • WSN in commercial and industrial applications, including bridges, will be the second largest market by 2020
  • Semiconductor revenues in Energy Harvesting will reach $3 billion by 2020(CAGR ’15 to ’20 = 71.4%).

In its recent report “Energy Harvesting: The Next Billion Dollar Marketfor Semiconductors” (MP112-16), presents the market for energy harvesting by key end use markets and the semiconductor content.  Readers will see which market segment is growing fastest and which semiconductor components account for sales potential.  The report discusses the latest trends in energy harvesting, the growing ecosystem, and technical innovations.  Included are profiles of silicon vendors involved with energy harvesting and other key vendors in the ecosystem. The report is 70 pages long and includes 11 tables and 24 figures.

Companies cited in the report: Analog Devices, Atmel, Audience, Cherry Switches, Cymbet, Cypress, enOcean, Linear Technology, Maxim Integrated, Microchip Technology, NXP, Powercast, Renesas, Semtech, Silicon Labs, Silicon Reef, STmicroelectronics, Texas Instruments, Imprint Energy, Sakti3, Solid Power, Apple, Laird, MicroGen, Micropelt, Thermo Life, Thermogen Technologies, Sanyo, EnerBee, Energy Harvesters, K3OPS, Nikola Labs and Imec.

This report is part of Semico Research’s IoT and MEMS portfolios, which also include:

The Smart Economy: The Internet of Everything

IoT Security: At What Cost?

Sensors in Wearables and Mobile: The Many Players

The Smart Home: Big Brother or Swarm Intelligence?

Scientists at the U.S. Naval Research Laboratory (NRL) have devised a clever combination of materials — when used during the thin-film growth process — to reveal that particle atomic layer deposition, or p-ALD, deposits a uniform nanometer-thick shell on core particles regardless of core size, a discovery having significant impacts for many applications since most large scale powder production techniques form powder batches that are made up of a range of particles sizes.

Image shows high magnification bright field transmission electron microscopy (TEM) image showing obvious delineation of alumina film and surface of particle. Credit: (US Naval Research Laboratory)

Image shows high magnification bright field transmission electron microscopy (TEM) image showing obvious delineation of alumina film and surface of particle. Credit: (US Naval Research Laboratory)

“Particle atomic layer deposition is highlighted as a technology that can create new and exciting designer core/shell particles to be used as building blocks for the next generation of complex multifunctional nanocomposites,” said Dr. Boris Feygelson, research engineer, NRL Electronics Science and Technology Division. “Our work is important because shell-thickness is most often a crucial parameter in applications where core-shell materials can be used to enhance performance of future materials.”

Atomic layer deposition is a layer-by-layer chemical vapor deposition-based thin-film growth technique used extensively in the electronics industry to deposit nanometer-thick films of dielectric materials on devices. Combined with other deposition and shadowing masking techniques, ALD is an integral part of electronic chip and device manufacturing. The same gas-phase process can be applied in a rotary or fluidizing powder bed reactor to grow nanometer-thick films that are highly conformal and uniformly thick on individual particles.

Previous research on p-ALD, patented by ALD NanoSolutions, Inc., has shown that growth of each layer during the deposition process varies with particle size, with the underlying assumption that larger particles will always have less growth. To observe this growth phenomenon, the NRL team grew alumina on nano- and micron-sized particles of tungsten and measured the shell thickness in a transmission electron microscope. Because of the huge mass/density difference of the two materials, this pairing provides maximum contrast in the electron microscope and delineation was easily distinguishable between the particle core and shell.

In their research, the scientists created core and shell powders consisting of a tungsten particle core and thin alumina shell that were then synthesized using atomic layer deposition in a rotary reactor. Standard atomic layer deposition of trimethylaluminum and water was performed on varying batches of powder with different average particle sizes.

“Amazingly, we found that the growth per cycle of the alumina film on an individual particle in a batch was shown to be independent of the size of an individual particle, and therefore, a powder batch — which consists of particles sizes spanning orders of magnitude — has constant shell thicknesses on all particles. This result upsets the current understanding of ALD on particles,” said Dr. Kedar Manandhar, ASEE postdoc, NRL Electronics Science and Technology Division and leading author of the research paper.

The work, published recently in the Journal of Vacuum Science and Technology A, suggests that water, a reactant in the ALD process, is reason for the same rate of growth on different particles. This uniformity of thickness on different particle sizes in a particular batch is determined to be due to the difficulty of removing residual water molecules from the powder during the purging cycle of the atomic layer deposition (ALD) process. “Water is very sticky and it is very difficult to remove the last mono-layer from surfaces,” Feygelson says. “And when you have a tumbling bed of powders, the water sticks around between the particles and results in consistent shell growth in the tumbling powder.

Applications for this research demonstrate implications for use in materials like abrasion resistant paints, high surface area catalyst, electron tunneling barriers, ultra-violet adsorption or capture in sunscreens or solar cells and even beyond when core-shell nanoparticles are used as buildings blocks for making new artificial nanostructured solids with unprecedented properties.

One secret to creating the world’s fastest silicon-based flexible transistors: a very, very tiny knife.

Working in collaboration with colleagues around the country, University of Wisconsin-Madison engineers have pioneered a unique method that could allow manufacturers to easily and cheaply fabricate high-performance transistors with wireless capabilities on huge rolls of flexible plastic.

The researchers — led by Zhenqiang (Jack) Ma, the Lynn H. Matthias Professor in Engineering and Vilas Distinguished Achievement Professor in electrical and computer engineering, and research scientist Jung-Hun Seo — fabricated a transistor that operates at a record 38 gigahertz, though their simulations show it could be capable of operating at a mind-boggling 110 gigahertz. In computing, that translates to lightning-fast processor speeds.

It’s also very useful in wireless applications. The transistor can transmit data or transfer power wirelessly, a capability that could unlock advances in a whole host of applications ranging from wearable electronics to sensors.

The team published details of its advance April 20 in the journal Scientific Reports.

The researchers’ nanoscale fabrication method upends conventional lithographic approaches — which use light and chemicals to pattern flexible transistors — overcoming such limitations as light diffraction, imprecision that leads to short circuits of different contacts, and the need to fabricate the circuitry in multiple passes.

Using low-temperature processes, Ma, Seo and their colleagues patterned the circuitry on their flexible transistor — single-crystalline silicon ultimately placed on a polyethylene terephthalate (more commonly known as PET) substrate — drawing on a simple, low-cost process called nanoimprint lithography.

In a method called selective doping, researchers introduce impurities into materials in precise locations to enhance their properties — in this case, electrical conductivity. But sometimes the dopant merges into areas of the material it shouldn’t, causing what is known as the short channel effect. However, the UW-Madison researchers took an unconventional approach: They blanketed their single crystalline silicon with a dopant, rather than selectively doping it.

Then, they added a light-sensitive material, or photoresist layer, and used a technique called electron-beam lithography — which uses a focused beam of electrons to create shapes as narrow as 10 nanometers wide — on the photoresist to create a reusable mold of the nanoscale patterns they desired. They applied the mold to an ultrathin, very flexible silicon membrane to create a photoresist pattern. Then they finished with a dry-etching process — essentially, a nanoscale knife — that cut precise, nanometer-scale trenches in the silicon following the patterns in the mold, and added wide gates, which function as switches, atop the trenches.

With a unique, three-dimensional current-flow pattern, the high performance transistor consumes less energy and operates more efficiently. And because the researchers’ method enables them to slice much narrower trenches than conventional fabrication processes can, it also could enable semiconductor manufacturers to squeeze an even greater number of transistors onto an electronic device.

Ultimately, says Ma, because the mold can be reused, the method could easily scale for use in a technology called roll-to-roll processing (think of a giant, patterned rolling pin moving across sheets of plastic the size of a tabletop), and that would allow semiconductor manufacturers to repeat their pattern and mass-fabricate many devices on a roll of flexible plastic.

“Nanoimprint lithography addresses future applications for flexible electronics,” says Ma, whose work was supported by the Air Force Office of Scientific Research. “We don’t want to make them the way the semiconductor industry does now. Our step, which is most critical for roll-to-roll printing, is ready.”

Polymer semiconductors, which can be processed on large-area and mechanically flexible substrates with low cost, are considered as one of the main components for future plastic electronics. However, they, especially n-type semiconducting polymers, currently lag behind inorganic counterparts in the charge carrier mobility – which characterizes how quickly charge carriers (electron) can move inside a semiconductor – and the chemical stability in ambient air.

Recently, a joint research team, consisting of Prof. Kilwon Cho and Dr. Boseok Kang with Pohang University of Science and Technology, and Prof. Yun-Hi Kim and Dr. Ran Kim with Gyungsang National University, has developed a new n-type semiconducting polymer with superior electron mobility and oxidative stability. The research outcome was published in Journal of the American Chemical Society (JACS) as a cover article and highlighted by the editors in JACS Spotlights.

The team modified a n-type conjugated polymer with semi-fluoroalkyl side chains – which are found to have several unique properties, such as hydrophobicity, rigidity, thermal stability, chemical and oxidative resistance, and the ability to self-organize. As a result, the modified polymer was shown to form a superstructure composed of polymer backbone crystals and side-chain crystals, resulting in a high degree of semicrystalline order. The team explained this phenomenon is attributed to the strong self-organization of the side chains and significantly boosts charge transport in polymer semiconductors.

Prof. Cho emphasized “We investigated the effects of semi-fluoroalkyl side chains of conjugated polymers at the molecular level and suggested a new strategy to design highly-performing polymeric materials for next-generation plastic electronics”.

This research was supported by the Center for Advanced Soft Electronics under the Global Frontier Research Program and the National Research Foundation (NRF) of Korea funded by the Ministry of Science, ICT and Future Planning.

Reflecting the semiconductor industry’s ongoing transition from a focus on geometric scaling to the integration of heterogeneous technologies that will enable the future “smart society,” the annual Symposia on VLSI Technology & Circuits has announced its 2016 program around the theme “Inflections for a Smart Society.” Uniquely positioned at the intersection of IC technology development and the evolving strategies for advanced circuit architecture, the Symposia program will explore the future direction of the microelectronics industry for chipmakers, foundries, and academic researchers.

Focus sessions 

Focus sessions for both Symposia will explore different aspects of this theme. Technology focus sessions include “Systems & Embedded Memory” and “Interconnect & 3D Integration,” addressing the challenges of advanced device design. The Circuits focus sessions are “Industrial & Power Circuit Directions for a Smart Society” and “Innovative Systems for a Smart Society,” examining the development of sensors and power circuits for interconnected systems. Joint focus sessions shared by the Technology and Circuits program include “Smart Power,” “Analog/RF Integration & Design-technology Co-Optimization in CMOS,” “Embedded Memories,” and “Design in Scaled Technologies,” enabling participants from each of the Symposia to share ideas on the intersection of these critical technology areas.

Panel discussions 

Panel discussions provide an opportunity for Symposia participants to interact with leading industry experts in examining critical issues surrounding major industry developments. The Technology panel, “How Moore’s Law, Industry Consolidation and System Trends Are Shaping the Memory Roadmap,” will explore the technical and economic limits of DRAM and NAND Flash memories, along with the system requirements driving future memory technology.

Two Circuits panels approach the Symposia theme with topics focused on innovation and co-optimization at the circuit level, including “Top Circuit Techniques: Life With & Without Them,” which reviews high-impact circuit design techniques; while “It’s All A Common Platform – How Do I Build A Differentiated Product?” which examines how software and hardware co-design, user interface, and other innovations continue to drive competitive products at the circuit level.

A joint Technology & Circuits panel moderated by Professor Subramanian Iyer from UCLA debates the crucial question of how Moore’s Law is being adapted by the IC industry to new business opportunities in the IoT era, in a session titled “More Moore, More than Moore or Mo(o)re Slowly?” with a high profile panel composed of industry executives and experts.

Short Courses 

Full-day short courses by leading industry and academic experts precede each Symposia, enabling participants to more fully explore subjects related to the conference theme, including a Technology Short course, “Inflections in VLSI Technologies – Cloud & Beyond,” with sessions that cover high performance computing, silicon photonics, memory technologies, cloud computing and novel power devices.

Two Circuits short courses are offered, including “Advanced Wirelines Techniques,” which covers 28 – 56Gb/s design standards, low power CMOS, analog NRZ and silicon photonic transceivers, and integrated electronic-photonic communications circuits. A second short course, “Circuit Design in FinFET, FDSOI & Advanced Memory Technologies,” examines the impact of FinFETs in processor design, analog & mixed-signal CMOS and embedded memory designs; as well as UTBB FDSOI technology for SRAM and digital logic. (Short courses require a separate registration fee.)

This year, the annual Symposium on VLSI Technology and Circuits will be held at the Hilton Hawaiian Village, Honolulu, Hawaii from June 13-16, 2016 (Technology) and June 14-17, 2016 (Circuits). This year marks the 36th anniversary for the Symposium on VLSI Technology, and the 30th anniversary for the Symposium on VLSI Circuits. The two conferences have been held together since 1987, providing an opportunity for the world’s top device technologists, circuit and system designers to exchange leading edge research on microelectronics technology, with alternating venues between Hawaii and Japan.

Sponsoring Organizations

The Symposium on VLSI Technology is sponsored by the IEEE Electron Devices Society and the Japan Society of Applied Physics, in cooperation with the IEEE Solid State Circuits Society.

The Symposium on VLSI Circuits is sponsored by the IEEE Solid State Circuits Society and the Japan Society of Applied Physics, in cooperation with the Institute of Electronics, Information and Communication Engineers.

Further Information, Registration and complete program 
Visit: http://www.vlsisymposium.org.

Dow Corning will present an exclusive glimpse of upcoming products and technologies at LIGHTFAIR International 2016 (Booth #3657), and showcase new advances in LED lamp and luminaire lighting that its broad commercial portfolio of cutting-edge optical silicone solutions are enabling worldwide.

“Three years ago, Dow Corning’s optical silicones technology sparked a surge of breakthrough innovations in LED lighting designs, and the demand for these uniquely advanced materials has only grown as the industry seeks to maintain the momentum they have helped build,” said Hugo da Silva, global industry director for LED lighting at Dow Corning. “Dow Corning is as committed as ever to working closely with customers to expand on their early successes, and formulate new optical silicone solutions to help them usher in the next-generation of LED illumination.”

Dow Corning will offer an early glimpse at LIGHTFAIR 2016 of at least one of those upcoming optical silicone solutions – Dow Corning MS-4002 Moldable Silicone. Planned for launch later this year, this high-performing material signals the latest advance in the company’s award-winning Moldable Silicone portfolio. Currently in development and testing, MS-4002 Moldable Silicone aims to offer the optimum balance of material toughness for reaching high IP and IK ratings, high light transmittance rate and smooth surface feel for secondary optics in LED lamp and luminaire applications for both indoor and outdoor.

As the global leader in silicone innovation and technology, Dow Corning is changing the game for LED design, and the company will show exactly how during LIGHTFAIR 2016. The booth will feature the company’s broad and growing range of proven solutions at three corner kiosks, focusing on:

  • Dow Corning Moldable Silicones, where visitors can explore how these materials are delivering proven solutions for enhancing the optical quality, efficiency and reliability of lamp and luminaire designs
  • Protection & Assembly Solutions, where customer products illustrate how Dow Corning’s innovative silicone protection, assembly and optical solutions have helped develop products with longer life cycles and greater efficiency in outdoor/architectural, interior/specialty, display and automotive lighting applications
  • Silicone-Enabled Designs demonstrating new ways to shape, direct and diffuse light more efficiently with Dow Corning Optical Silicones. Visitors can also explore how silicone materials have expanded innovative design possibilities as LumenFlow Corp. takes them step by step through the LED design ideas process

In addition to offering an exclusive sneak peek at upcoming technologies, Dow Corning Lighting experts will be on hand to discuss the unique design flexibilities, proven reliability and simpler processability enabled by Dow Corning’s optical silicones. A market leader in materials, expertise and collaborative innovation for LED lighting concepts, Dow Corning offers solutions that span the entire LED value chain, adding reliability and efficiency for sealing, protecting, adhering, cooling and shaping light across all lighting applications.

LIGHTFAIR International is the world’s largest annual architectural and commercial lighting trade show and conference. Held at San Diego’s Convention Center from April 26-28, this year’s edition is expected to attract over 28,000 design, lighting, architectural, design, engineering, energy, facility and industry professionals from around the world to set future trends for lighting, design and technology innovation.

Invensas Corporation, a wholly owned subsidiary of Tessera Technologies, Inc. (Nasdaq: TSRA), announced today that Sandia National Laboratories signed a new license agreement for ZiBond and Direct Bond Interconnect (DBI) technologies. With this license Sandia will have access to the most advanced 3D integration technologies available, for use in a wide range of semiconductor applications.

For more than 60 years, Sandia National Laboratories has been the premier science and engineering laboratory in the United States for national security and innovation. Working closely with U.S. government agencies, private industry and academic institutions, Sandia has led the charge to research, develop and deliver essential technologies used to solve many of the nation’s most important security, climate change and sustainable energy challenges.

“The demand for cost-effective, versatile, 2.5D and 3D integration technologies has risen significantly, as research and commercial enterprises seek to expand overall performance and functionality of electronics products,” said Craig Mitchell, President Invensas Corporation. “ZiBond and DBI technologies are currently deployed in leading edge semiconductor products, and we are pleased to now make them available to Sandia, a premier government research institution.”

ZiBond is a low-temperature homogeneous bonding technology, that enables room temperature die or wafer-level 3D integration, without the need for the application of external pressure. DBI is a low temperature, hybrid bonding technology with integrated electrical interconnects, that offers the industry’s finest pitch and lowest cost-of-ownership 3D interconnect platform.

Both ZiBond and DBI deliver the fastest bonding throughput currently available in the industry, resulting in up to a 15x increase in wafer bonding throughput. Both technologies offer the thinnest available 2.5D and 3D semiconductor assemblies, while reducing wafer warpage, increasing reliability and improving thermal performance. Additionally, low processing temperatures significantly reduce equipment and process cost for high volume manufacturing.

For more information on ZiBond and DBI technologies as well as other Invensas solutions, please visit www.invensas.com or www.tessera.com.

The Electronic System Design (ESD) Alliance (formerly the EDA Consortium) and Semico Research today announced that they have entered into a joint marketing agreement (JMA) to work together on several business initiatives in support of the semiconductor design ecosystem.

The JMA will enable the ESD Alliance and Semico, a semiconductor marketing and consulting research company noted for its coverage of the intellectual property (IP) market, to promote their common business goals. Semico will assist the ESD Alliance in broadening its reach into the IP community, a large part of the semiconductor design ecosystem, by promoting it at Semico events, on its website and through promotional emails.

Additionally, Semico will provide a discount to ESD Alliance members for purchase of individual research reports, offer enterprise-wide access to its IPI Monthly Report and extend admission discounts to Semico conference events.

In exchange, Semico has become an associate member of the ESD Alliance, an international association of companies providing goods and services throughout the semiconductor design ecosystem. The ESD Alliance will post availability of new Semico research reports and provide a link to its website for Semico blogs and articles.

“Semico is connected to and understands the needs of IP community,” says Bob Smith, the ESD Alliance’s executive director. “Our new mission is focused on representing the design ecosystem and IP is a key component. We will rely on its Semico’s expertise as we expand our presence and showcase our benefits to IP vendors and suppliers.”

“The ESD Alliance recognizes that the IP community is an important element of the semiconductor design ecosystem and one that will benefit from its newly expanded charter and ongoing initiatives,” notes Jim Feldham, president of Semico. “We look forward to working with the the ESD Alliance to raise the visibility of the importance of the IP market.”

For more information on other aspects of the ESD Alliance and Semico partnership, visit: www.esd-alliance.org or www.semico.com.

IC Insights’ March Update to the 2016 McClean Report refreshed the forecasts for 33 major IC product categories through 2020.  The complete list of all 33 major IC product categories ranked by the updated forecast growth rates for 2016 is shown in Figure 1.  Fourteen product categories—topped by Cellphone Application Processors and Signal Conversion (analog) devices—are expected to exceed the 2% growth rate forecast for the total IC market this year. Another five product categories are expected to grow at the same 2% rate as the total IC market.  The total number of IC categories forecast to register sales growth in 2016 increases to 20 products from only nine in 2015.

Growth of Cellphone Application MPUs (10%) is forecast to remain near the top on the growth list for a fifth consecutive year. Though the rate of growth for cellphone application MPUs has cooled in recent years, IC Insights still forecasts a solid 10% growth year for this market as smartphone shipments remain an attractive end-use application for IC markets.  Signal Conversion (DAC analog, etc.) devices are also expected to show a 10% increase in 2016 thanks to their implementation across a wide variety of consumer, communication, and computing devices, and in other systems to monitor and control the interface between analog and digital signals.   The market for 32-bit MCUs is forecast to increase 8% with “intelligent” cars the catalyst for much of this growth.  Driver information systems and many of the increasing number of semi-autonomous driving features such as self-parking, advanced cruise control, and collision-avoidance rely on 32-bit MCUs. Complex 32-bit MCUs are expected to account for over 25% of the processing power in vehicles in the next few years.

Other notable categories include the previously high-flying Tablet MPU market, which is forecast to sputter to just 2% growth in 2016 as enthusiasm fades for these systems. DRAM is expected to show a steep market decline this year and drop to become the second-largest IC product category (trailing only the standard PC, server MPU market) in 2016.  After registering big gains in 2013 and 2014, the DRAM market fell 3% in 2015 and is forecast to tumble another 8% in 2016 as oversupply and waning desktop and notebook computer demand force suppliers to slash average selling prices to move product.  Worldwide DRAM ASP growth was down 4% in 2015 and is on track to fall 11% in 2016.

2016 forecast of ic market

Figure 1

Liquid crystals, discovered more than 125 years ago, are at work behind the screens of TV and computer monitors, clocks, watches and most other electronics displays, and scientists are still discovering new twists–and bends–in their molecular makeup.

Liquid crystals are an exotic state of matter that flows like a fluid but in which the molecules may be oriented in a crystal-like way. At the microscopic scale, liquid crystals come in several different configurations, including a naturally spiraling “twist-bend” molecular arrangement, discovered in 2013, that has excited a flurry of new research.

Now, using a pioneering X-ray technique developed at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), a research team has recorded the first direct measurements confirming a tightly wound spiral molecular arrangement that could help unravel the mysteries of its formation and possibly improve liquid-crystal display (LCD) performance, such as the speed at which they selectively switch light on or off in tiny screen areas.

Researchers examined the spiral 'twist-bend' structure (right) formed by boomerang-shaped liquid crystal molecules (left and center) measuring 3 nanometers in length, using a pioneering X-ray technique at Berkeley Lab's Advanced Light Source. A better understanding of this spiral form, discovered in 2013, could lead to new applications for liquid crystals and improved liquid-crystal display screens. (Credit: Zosia Rostomian/Berkeley Lab; Physical Review Letters, DOI: 10.1103/PhysRevLett.116.147803; Journal of Materials Chemistry C, DOI: 10.1039/C4TC01927J)

Researchers examined the spiral ‘twist-bend’ structure (right) formed by boomerang-shaped liquid crystal molecules (left and center) measuring 3 nanometers in length, using a pioneering X-ray technique at Berkeley Lab’s Advanced Light Source. A better understanding of this spiral form, discovered in 2013, could lead to new applications for liquid crystals and improved liquid-crystal display screens. (Credit: Zosia Rostomian/Berkeley Lab; Physical Review Letters, DOI: 10.1103/PhysRevLett.116.147803; Journal of Materials Chemistry C, DOI: 10.1039/C4TC01927J)

The findings could also help explain how so-called “chiral” structure–molecules can exhibit wildly different properties based on their left- or right-handedness (chirality), which is of interest in biology, materials science and chemistry–can form from organic molecules that do not exhibit such handedness.

“This newly discovered ‘twist-bend’ phase of liquid crystals is one of the hottest topics in liquid crystal research,” said Chenhui Zhu, a research scientist at Berkeley Lab’s Advanced Light Source (ALS), where the X-ray studies were performed.

“Now, we have provided the first definitive evidence for the twist-bend structure. The determination of this structure will without question advance our understanding of its properties, such as its response to temperature and to stress, which may help improve how we operate the current generation of LCDs.”

Zhu was the lead author on a related research paper published in the April 7 edition of Physical Review Letters.

While there are now several competing screen technologies to standard LCDs, the standard LCD market is still huge, representing more than one-third of the revenue in the electronic display market. The overall display market is expected to top $150 billion in revenue this year.

The individual molecules in the structure determined at Berkeley Lab are constructed like flexible, nanoscale boomerangs, just a few nanometers, or billionths of a meter, in length and with rigid ends and flexible middles. In the twist-bend phase, the spiraling structure they form resembles a bunch of snakes lined up and then wound snugly around the length of an invisible pole.

Zhu tuned low-energy or “soft” X-rays at the ALS to examine carbon atoms in the liquid crystal molecules, which provided details about the molecular orientation of their chemical bonds and the structure they formed. The technique he used for the study is known as soft X-ray scattering. The spiraling, helical molecular arrangement of the liquid crystal samples would have been undetectable by conventional X-ray scattering techniques.

The measurements show that the liquid crystals complete a 360-degree twist-bend over a distance of just 8 nanometers at room temperature, which Zhu said is an “amazingly short” distance given that each molecule is 3 nanometers long, and such a strongly coiled structure is very rare.

The driving force for the formation of the tight spiral in the twist-bend arrangement is still unclear, and the structure exhibits unusual optical properties that also warrant further study, Zhu said.

Researchers found that the spiral “pitch,” or width of one complete spiral turn, becomes a little longer with increasing temperature, and the spiral abruptly disappears at sufficiently high temperature as the material adopts a different configuration.

“Currently, this experiment can’t be done anywhere else,” Zhu said. “We are the first team to use this soft X-ray scattering technique to study this liquid-crystal phase.”

Standard LCDs often use nematic liquid crystals, a phase of liquid crystals that naturally align in the same direction–like a group of compass needles that are parallel to one another, pointing in one direction.

In these standard LCD devices, rod-like liquid crystal molecules are sandwiched between specially treated plates of glass that cause the molecules to “lie down” rather than point toward the glass. The glass is typically treated to induce a 90-degree twist in the molecular arrangement, so that the molecules closest to one glass plate are perpendicular to those closest to the other glass plate.

It’s like a series of compass needles made to face north at the top, smoothly reorienting to the northeast in the middle, and pointing east at the bottom. This molecularly twisted state is then electrically distorted to allow polarized light to pass through at varying brightness, for example, or to block light (by straightening the twist completely).

Future experiments will explore how the spirals depend on molecular shape and respond to variations in temperature, electric field, ultraviolet light, and stress, Zhu added.

He also hopes to explore similar spiraling structures, such as a liquid crystal phase known as the helical nanofilament, which shows promise for solar energy applications. Studies of DNA, synthetic proteins, and amyloid fibrils such as those associated with Alzheimer’s disease, might help explain the role of handedness in how organic molecules self-assemble.

With brighter, more laser-like X-ray sources and faster X-ray detectors, it may be possible to see details in how the spiraling twist-bend structure forms and fluctuates in real time in materials, Zhu also said.

“I am hoping our ongoing experiments can provide unique information to benefit other theories and experiments in this field,” he noted.