Tag Archives: letter-leds-tech

Ultratech, Inc., a supplier of lithography, laser­ processing and inspection systems used to manufacture semiconductor devices and high­brightness LEDs (HB­ LEDs), as well as atomic layer deposition (ALD) systems, announced that its proprietary LXA nanosecond melt laser annealing technology enabled the world’s lowest contact resistivity for FinFETs in an R&D environment.  In collaboration with multiple companies, this record achievement, as well as additional results, was presented in a paper at the 2016 Symposia on VLSI Technology and Circuits held June 13-17, at the Hilton Hawaiian Village in Honolulu, Hawaii.

In the development of today’s advanced CMOS logic FinFET devices, the electrical resistance at the contact junction (contact resistance) is widely recognized to play an increasingly significant role in overall device performance. In larger device nodes, the contact pads provide a relatively large area over which to transfer electrical current. But as devices continue to shrink, so does the available area to form the contact, creating an electrical current bottleneck that reduces the performance of the device and impacts battery life. In order to realize the desired benefits of the scaled transistor architecture, including improved device performance and greater battery life, it will be necessary to make significant advancements over the current process. One emerging solution is to improve the characteristics of the contact by modifying the material properties of the contact using a unique nanosecond melt laser annealing technology. Using Ultratech’s patent pending LXA melt laser annealing technology these researchers reported world record results in contact resistance.

Yun Wang, Ph.D., Senior Vice President and Chief Technologist, Laser Processing at Ultratech, said, “The great achievement in lowering the contact resistivity for FinFETs is that it provides faster on/off switching of the transistor using the same input voltage. Since the input voltage doesn’t need to be increased to provide faster transistor switching, a low supply voltage can be maintained, which saves battery life.  The result is a FinFET transistor that operates very quickly at a lower voltage for faster performance and longer battery life. As we continue our R&D, we expect that Ultratech’s unique LXA nanosecond melt laser anneal technology will address a wide range of applications at the 7-nm and below nodes, and enable use of new materials anticipated at 5nm and below. We plan to use this record achievement as a benchmark to continue to improve our LXA technology.”

On Tuesday, June 14 at HAST, the paper by Hiroaki Niimi</span, Zuoguang Liu, Oleg Gluschenkov and others, titled, 'Sub-2×10-9 Ω‐cm2 N‐ and P-Contact Resistivity with Si:P and Ge:Ga Metastable Alloys for FinFET CMOS  Technology' was presented during Session 7 – Contact Resistance Innovations for Sub‐10nm Scaling, at the 2016 Symposia on VLSI Technology and Circuits.

Ultratech’s LXA Nanosecond Melt Laser Annealing Technology

Ultratech’s LXA technology is a proprietary technology for achieving nanosecond anneal utilizing a millisecond process in-situ with a nanosecond spike anneal to provide ultra-low thermal budget with added process flexibility for a wide range of materials and applications. The LXA technology is targeted for advanced junction formation, contact anneal, and multiple middle-of-line applications.  As more exotic materials are used for 7nm and below devices, it is expected that Ultratech’s LXA nanosecond melt laser annealing technology will play a bigger role and include wider applications in the manufacture of leading-edge transistors.

Perovskite materials have shown great promise for use in next-generation solar cells, light-emitting devices (LEDs), sensors, and other applications, but their instability remains a critical limitation.

Researchers at UC Santa Cruz attacked this problem by focusing on perovskite nanocrystals, in which the instability problems are magnified by the large surface area of the particles relative to their volume. Atoms on the surface are vulnerable to reactions that can degrade the material, so molecules that bind to the surface–called surface ligands or capping ligands–are used both to stabilize perovskite nanocrystals and to control their properties.

In a paper published June 13 in Angewandte Chemie, the UCSC researchers reported the results of experiments using unique branched ligands to synthesize perovskite nanocrystals with greatly improved stability and uniform particle size.

“This new strategy to stabilize organometal-halide perovskites is an important step in the right direction,” said corresponding author Jin Zhang, professor of chemistry and biochemistry at UC Santa Cruz. “Our hope is that this could be used not only for perovskite nanocrystals but also for bulk materials and thin films used in applications such as photovoltaics.”

Zhang’s team tested the effects of different types of capping ligands on the stability of perovskite nanocrystals. Conventional perovskite nanocrystals capped with ligands consisting of long straight-chain amines show poor stability in solvents such as water and alcohol. Zhang’s lab identified unique branched molecules that proved much more effective as capping ligands.

According to Zhang, the branching structure of the ligands protects the surface of the nanocrystals by occupying more space than straight-chain molecules, creating a mechanical barrier through an effect known as steric hindrance. “The branching molecules are more cone-shaped, which increases steric hindrance and makes it harder for the solvent to access the surface of the nanocrystals,” he said.

The researchers were able to control the size of the nanocrystals by adjusting the amount of branched capping ligands used during synthesis. They could obtain uniform perovskite nanocrystals in sizes ranging from 2.5 to 100 nanometers, with high photoluminescence quantum yield, a measure of fluorescence that is critical to the performance of perovskites in a variety of applications.

Zhang’s lab is exploring the use of perovskite nanocrystals in sensors to detect specific chemicals. He is also working with UC Santa Cruz physicist Sue Carter on the use of perovskite thin films in photovoltaic cells for solar energy applications.

Imagine a device that is selectively transparent to various wavelengths of light at one moment, and opaque to them the next, following a minute adjustment.

Such a gatekeeper would enable powerful and unique capabilities in a wide range of electronic, optical and other applications, including those that rely on transistors or other components that switch on and off.

In a May 20 paper in the journal Physical Review Letters, researchers in the University at Buffalo School of Engineering and Applied Sciences report a discovery that brings us one step closer to this imagined future.

A photograph (left) shows the experimental set-up used to confirm the existence of the Bloch wave resonance, which was first predicted theoretically. An illustration (right) shows the interior of the experimental device, called a hollow periodic waveguide, which consists of two corrugated metallic plates separated by a variable distance of about one inch, and the upper plate can slide with respect to the lower. When researchers shot microwaves between the plates through the air, they were able to control which wavelengths of microwaves were allowed through by varying the position of the upper plate. Credit: Lab of Victor Pogrebnyak/University at Buffalo

A photograph (left) shows the experimental set-up used to confirm the existence of the Bloch wave resonance, which was first predicted theoretically. An illustration (right) shows the interior of the experimental device, called a hollow periodic waveguide, which consists of two corrugated metallic plates separated by a variable distance of about one inch, and the upper plate can slide with respect to the lower. When researchers shot microwaves between the plates through the air, they were able to control which wavelengths of microwaves were allowed through by varying the position of the upper plate. Credit: Lab of Victor Pogrebnyak/University at Buffalo

The finding has to do with materials that are periodic, which means that they’re made up of parts or units that repeat. Crystals fall into this category, as do certain parts of the wings of butterflies, whose periodic structure helps give them color by reflecting specific colors of light.

Scientists have known since the early 20th century that periodic materials have special qualities when it comes to light. Such materials can reflect light, as butterfly wings do, and if you understand the internal structure of a periodic material, you can use an equation called Bragg’s law to determine which wavelengths will pass through the material, and which will be blocked due to reflection.

The new UB study shows that a completely periodic material structure is not needed for this kind of predictable reflection to take place.

Similar effects occur when you sandwich a non-periodic material between two boundary layers of material that have a periodic shape. This set-up will be transparent to certain wavelengths of light and opaque to others, and engineers can quickly alter which wavelengths are allowed through by simply moving one of the periodic boundaries.

Better yet, the effect not only applies to light waves, but rather to a broad range of wave phenomena that span the quantum to the continuum scale.

“We have shown that Bragg’s law is a special case of a more generalized phenomenon that was discovered in this study and named as a Bloch wave resonance,” said Victor A. Pogrebnyak, an adjunct associate professor of electrical engineering at UB. “This discovery opens up new opportunities in photonics, nanoelectronics, optics and acoustics and many other areas of science and technology that exploit band gap wave phenomena for practical use.”

“Electrons behave as waves that can also exhibit a Bloch resonance, which can be used as a powerful method to control currents in nanoelectronic circuits,” said Edward Furlani, Pogrebnyak’s co-author and a UB professor in the Departments of Chemical and Biological Engineering and Electrical Engineering.

A key advantage that Bloch wave resonance offers: It enables the blocking of a larger range of wavelengths simultaneously than previously known effects described by Bragg’s law.

Applications that could take advantage of this broader “band gap” range include white light lasers and a new type of fast-switching transistor.

GC Asahi Glass (AGC) today announced it has developed a uniform amorphous thin film using a unique sputtering target material, and has started industrialization and commercial production of the material. Called C12A7 Electride, the material is essential to mass production of both the new thin film and large organic electroluminescent (EL) panels – also known as organic LEDs (OLEDs) – utilizing the film.

Asahi Glass Co. Electride Target

Asahi Glass Co. Electride Target

Currently, lithium fluoride (LiF) and alkali-doped organic materials are used as the electron injection material for an OLED display. However, these materials are unstable and are used in an unstable state, which contributes to manufacturing challenges associated with OLED. To address this problem, the AGC Group developed the more stable amorphous C12A7 Electride thin film.

C12A7 is a component of alumina cement. Its structure comprises interconnected “cages,” measuring about 0.4 nanometers (nm) in inner diameter, that contain oxygen ions. C12A7 Electride was developed at the Tokyo Institute of Technology by a research group under Professor Hideo Hosono, a material scientist known for the discovery of iron-based superconductors. All of the oxygen ions in the cages are replaced with electrons, enabling the material to conduct electric current like a metal, maintain chemical and thermal stability, and be easy to handle, while retaining the characteristic of readily emitting electrons.

The amorphous C12A7 Electride thin film, which can be formed through a sputtering process [1] at room temperature using the AGC Group-developed target material, has the following unique characteristics: it is transparent in the visible range; it can emit electrons as easily as metal lithium can; and it is chemically stable even in the atmosphere. By combining this with the TFT element, which uses a transparent amorphous oxide semiconductor (TAOS), the low-driving-voltage electron transport layer can be manufactured stably and with high production yields, even when used in an OLED display with an inverted structure.

Market research firm IDTechEx forecasts the market for OLED displays will reach nearly US$16 billion this year and will grow to US$57 billion in 2026. AGC Group’s Naomichi Miyakawa, Principal Manager, New Product R&D Center, Technology General Division, noted, “TAOS-TFT is suitable for driving a large OLED panel, but there was no available material that functions properly as both an electron injection layer and an electron transport layer – both of which are necessary to realize the inverted structure that makes the best of the panel’s performance. With the commercialization of our C12A7 Electride material, we expect to see substantially improved production of oxide TFT-driven OLED panels.”

AGC anticipates OLED panels integrating the new C12A7 Electride-based thin film to begin manufacture in the year of Tokyo Olympic Games, 2020 or earlier.

TowerJazz, the global specialty foundry, today announced volume production of a new RF technology capable of integrating a wireless front-end module (FEM) on a single chip, tailored to meet the challenges of Internet of Things (IoT) applications. Analysts estimate that the number of IoT connected devices will grow at a 15-20% growth rate annually, reaching up to 30 billion units by 2020. McKinsey Global Institute recently estimated that IoT could generate up to $11 trillion in global value by 2025.

The TowerJazz process enables integration of power amplifiers, switches, and low noise amplifiers as well as CMOS digital and power control on a single die. TowerJazz is delivering this product today for smartphones, tablets and wearables, and this technology also meets the more universal requirements of IoT applications by providing cost, power, performance, and form factor benefits vs. competing solutions.

As an example, TowerJazz has partnered with Skyworks Solutions, Inc., an innovator of high performance analog semiconductors connecting people, places and things, to deliver a first of its kind integrated wireless FEM using this technology.

“We are pleased that our long partnership with TowerJazz on SiGe BiCMOS for PA based products is now in volume production for key customers of Skyworks Solutions,” said Bill Vaillancourt, GM/VP Skyworks Connectivity Solutions.

TowerJazz’s new RF technology includes a 0.18um SiGe PA device with best in class silicon-based performance, a low Ron-Coff switch device, a SiGe low noise amplifier device, 5V CMOS for power control, 0.18um CMOS for integrating MIPI or other digital content as well as thick Cu metal layers for low-loss inductors and matching components. By offering all active components typically required for a wireless FEM, this technology enables a new family of products that can integrate multiple communication standards (WiFi, Bluetooth, 802.15.4 or NFC) that form the backbone of the IoT fabric today onto the same chip.

“This new technology complements our existing suite of SiGe PA and RF SOI switch technology offerings and provides customers new architectural options by enabling the combination of these elements on a single die while offering best in class silicon-based PA performance,” said Marco Racanelli, Sr. VP and GM of RF/High Performance Analog and US Aerospace & Defense Business Groups, and Newport Beach Site Manager, TowerJazz.

TowerJazz will exhibit and demonstrate its advanced process technologies for specialty IC manufacturing in booth #1532 at IMS2016, the premier conference in the RF and microwave industry. Please visit the company website for more information on TowerJazz’s RF and high performance analog technology offerings.

Ultratech, Inc., a supplier of lithography, laser­ processing and inspection systems used to manufacture semiconductor devices and high­brightness LEDs (HB­ LEDs), as well as atomic layer deposition (ALD) systems, announced the formation of a research collaboration with Professor Thomas J. Webster, Ph.D. at Northeastern University, to study the use of nano-materials produced via ALD for medical applications. The initial research has focused on inhibiting bacterial growth and inflammation and promoting cell and tissue growth.

Dr. Thomas Webster, Chair and Professor of Chemical Engineering at Northeastern, said, “We are very excited to embark on this collaboration with Ultratech-CNT. While we are in the early stages of this study, the initial results of our work suggest that the materials and processes we are developing could have long-range impact in this field.”

Ultratech-CNT Senior Research Scientist Ritwik Bhatia, Ph.D., who has been working closely with Professor Webster, explained, “This type of work is a marked departure from the traditional applications and uses for ALD and dramatically opens up a new field where material science and life sciences intersect. I am extremely pleased to be part of this research program and excited by the potential benefits for healthy surgical outcomes that this research represents.”

Arthur W. Zafiropoulo, Ultratech’s Chairman and Chief Executive Officer, said, “At Ultratech, we have long maintained and understood that material science would play a key role in moving many emerging technological fields forward. We also feel that it can serve a much larger role, namely in improving the quality of life. In linking the expertise of Prof. Webster and his research group with Ultratech-CNT’s ALD group, we believe we are taking steps to solidly and efficiently pursue our scientific and commercial goals.”

A team led by researchers from the National University of Singapore (NUS) has developed a method to enhance the photoluminescence efficiency of tungsten diselenide, a two-dimensional semiconductor, paving the way for the application of such semiconductors in advanced optoelectronic and photonic devices.

Tungsten diselenide is a single-molecule-thick semiconductor that is part of an emerging class of materials called transition metal dichalcogenides (TMDCs), which have the ability to convert light to electricity and vice versa, making them strong potential candidates for optoelectronic devices such as thin film solar cells, photodetectors flexible logic circuits and sensors. However, its atomically thin structure reduces its absorption and photoluminescence properties, thereby limiting its practical applications.

By incorporating monolayers of tungsten diselenide onto gold substrates with nanosized trenches, the research team, led by Professor Andrew Wee of the Department of Physics at the NUS Faculty of Science, successfully enhanced the nanomaterial’s photoluminescence by up to 20,000-fold. This technological breakthrough creates new opportunities of applying tungsten diselenide as a novel semiconductor material for advanced applications.

Ms Wang Zhuo, a PhD candidate from the NUS Graduate School for Integrative Sciences and Engineering (NGS) and first author of the paper, explained, “This is the first work to demonstrate the use of gold plasmonic nanostructures to improve the photoluminescence of tungsten diselenide, and we have managed to achieve an unprecedented enhancement of the light absorption and emission efficiency of this nanomaterial.”

Elaborating on the significance of the novel method, Prof Wee said, “The key to this work is the design of the gold plasmonic nanoarray templates. In our system, the resonances can be tuned to be matched with the pump laser wavelength by varying the pitch of the structures. This is critical for plasmon coupling with light to achieve optimal field confinement.”

The novel research was first published online in the journal Nature Communications on 6 May 2016.

This article originally appeared on EECatalog.com.

By Venetia Espinoza, BrightVolt

Are the power solutions the IoT needs arriving quickly enough?

The massive game-changing potential of the Internet of Things (IoT) connected devices has been limited by a lack of effective power solutions. The solid-state thin film battery market is forecasted to reach $1.3 bil­lion worldwide by 2021 as published by Custom Market Insights. Fueling this growth is the rise of IoT—wear­ables, medical devices and sensors. Traditional battery technologies simply cannot provide the new features and designs that these new applications demand.

However, arriving on the market are thin-film, flexible batteries which are ultra-thin, flexible, rollable, stretch­able and can withstand high temperatures.

Many applications are still emerging, and their require­ments are evolving fast. Because target specs are also very diverse, each with unique requirements for power, thinness, cost, safety, shelf life, reliability, and flex­ibility, a customized power source makes sense.

BrightVolt is one company tackling the demand for small powered solutions.

Figure 1: Traditional battery technologies are giving way to new designs, which can reduce design complexity. (Courtesy BrightVolt)

Low power/long battery life—As IoT infrastructure becomes ubiquitous, many use-cases require designing and building low power and small form factor batteries, both primary and rechargeable. BrightVolt’s Flexion™ batteries have 3.0V, multiple capacity options such as 10, 14, 20, 25mAh and varied tab con­figurations such as extended tab, terminal support, terminal support with ACF. They also have attachment options such as ultrasonic welding, soldering, conductive epoxy and conductive film and a shelf life of 3-5+ years.

Customized—Battery designs are available that are as thin as 0.37mm. For example, BrightVolt Flexion batteries were designed to operate continuously over a wide temperature range (-10 ºC to +60 ºC). They utilize a patented solid polymer electrolyte and contain no volatile liquids or gelling agents. Self-connecting battery terminals using anisotropic conductive film. BrightVolt can custom-build the size, shape, power, capacity, tab configurations and attachment options that are needed for these diverse requirements.

Scalable Manufacturing—BrightVolt has already shipped millions of units. Scalability is our key differentiator. We can take a solution from prototype to full production and anything in between. Our enduring quality, durability, and built-in intelligence is what makes us the best choice for custom product designs.

Safe—It is now possible to find batteries that are non-toxic, non-corrosive and environ­mentally friendly. It’s also important to choose an Inherently safe design that reduces the need for additional battery safety circuitry. Polymer matrix electrolyte provides outstanding thermal stability with no volatile liquids or gels.

Medical Miracles and Thin Batteries

Nanotechnology itself dates back to the 1980s, when U.S. engineer Eric Drexler coined it. Today, nanotechnology and tiny batteries are changing the medical device industry.

Applicable medical uses include the ability to use small form batteries to power the circuitry associated wit skin-based monitoring devices that can detect the glucose levels, for example. Trans­dermal drug delivery and patches could change how injectable drugs are delivered in a more effective time-released manner through a battery-powered patch.

Additionally, the combination of a nanosensor used in conjunction with a smartphone could be used to track auto­immune diseases and cancer. It could also be an effective screening tool for rejection in patients with organ transplants.

Sensors, Smart Packaging and the IoT

It is anticipated that the temperature monitoring market will reach over $3.2 billion by 2020. Smart sensor labels answer the needs for numerous indus­tries, particularly perishable goods. These printed electronics devices and labeling enable the IoT to reduce waste and improve consumer safety.

This technology allows pharmaceutical companies to keep temperature-sensitive products safe and effective, while pre­venting the unnecessary ruin of usable products. Retailers who use temperature-monitoring labels during shipment of produce and other food products as well as cosmetics and off-the-shelf healthcare items will have immediate insight with regards to both shelf life and food safety.

Some of the most ubiquitous wearables are fitness trackers like FitBit and Jaw­bone that hit the market like wildfire in 2013. 1 in 5 Americans today wear this technology to track their activity levels, sleep and more. Wearables will continue to evolve in size, usability, form factors and diverse power needs.

Assisted living and eldercare is another compelling and demanding wearable technology market. Wearable sensors for this market pose massive potential in generating big data for IoT, with a great applicability to biomedicine and ‘ambient assisted living’ (AAL). ‘Ambient intelligence’ in eldercare is being sensi­tive and responsive to the presence of people. Recent advancements in several technological areas have helped the vision of AAL to become a reality. These tech­nologies include of course smart homes, assistive robotics, and, in small form: e-textile, mobile and wearable sensors.

Another significant advancement is detecting common medical issues such as sleep apnea, which used to require an uncomfortable in-clinic sleep study. No more. Today, a patient can wear a device overnight in the privacy of their own home and send the results off to their physician. Other exciting uses include trackers in clothing, interactive toys, games and more.

Embedding Security

Target’s $10 million 2013 class action data breach lawsuit and privacy issue hammered home just how devastating security fraud really is. Since that time, many credit cards are now embedded with an EMV chip but there’s an even better solution emerging. Not only will a small form battery the size of a postage stamp power these new cards, a com­puter chip randomizes the code number about every hour, adding to its security. This renders the card useless to anyone who has written down your card number, expiration date and code. This applica­tion will effectively eliminate ‘card not present’ fraud. Other ultra-thin battery uses in a credit card could allow for a tiny screen on your card itself that displays your balance.

When Apple launched its biometric ID fingerprint reader on its iPhone 5S, many people adjusted quickly to the convenience of the fingerprint password. Building on that same technology, travel documents including drivers’ licenses and passports, as well as vital health information, can be included in one ultra-thin battery-powered, pocket-sized card that fits in your wallet.

Conclusion

By assessing the considerations outlined in this article, a product designer can effectively achieve a small-form factor product able to reliably operate with the right battery. Custom batteries can eliminate design complexities and opti­mize battery use for many applications.

About the Author

Venetia Espinoza is in charge of market­ing at BrightVolt, a worldwide leader in the design, development and scale manufacturing of thin film batteries. She holds more than 25 years of marketing and product experience with premier technology companies. She also served as Vice President and General Manager of Softcard, a joint venture established by industry giants Verizon, AT&T and T-Mobile. She holds an MBA and BS de­gree in Industrial Engineering.

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.

Researchers from the University of Illinois at Urbana-Champaign have demonstrated a new approach to modifying the light absorption and stretchability of atomically thin two-dimensional (2D) materials by surface topographic engineering using only mechanical strain. The highly flexible system has future potential for wearable technology and integrated biomedical optical sensing technology when combined with flexible light-emitting diodes.

“Increasing graphene’s low light absorption in visible range is an important prerequisite for its broad potential applications in photonics and sensing,” explained SungWoo Nam, an assistant professor of mechanical science and engineering at Illinois. “This is the very first stretchable photodetector based exclusively on graphene with strain-tunable photoresponsivity and wavelength selectivity.”

Graphene–an atomically thin layer of hexagonally bonded carbon atoms–has been extensively investigated in advanced photodetectors for its broadband absorption, high carrier mobility, and mechanical flexibility. Due to graphene’s low optical absorptivity, graphene photodetector research so far has focused on hybrid systems to increase photoabsorption. However, such hybrid systems require a complicated integration process, and lead to reduced carrier mobility due to the heterogeneous interfaces.

According to Nam, the key element enabling increased absorption and stretchability requires engineering the two-dimensional material into three-dimensional (3D) “crumpled structures,” increasing the graphene’s areal density. The continuously undulating 3D surface induces an areal density increase to yield higher optical absorption per unit area, thereby improving photoresponsivity. Crumple density, height, and pitch are modulated by applied strain and the crumpling is fully reversible during cyclical stretching and release, introducing a new capability of strain-tunable photoabsorption enhancement and allowing for a highly responsive photodetector based on a single graphene layer.

“We achieved more than an order-of-magnitude enhancement of the optical extinction via the buckled 3D structure, which led to an approximately 400% enhancement in photoresponsivity,” stated Pilgyu Kang, and first author of the paper, “Crumpled Graphene Photodetector with Enhanced, Strain-tunable and Wavelength-selective Photoresponsivity,” appearing in the journal, Advanced Materials. “The new strain-tunable photoresponsivity resulted in a 100% modulation in photoresponsivity with a 200% applied strain. By integrating colloidal photonic crystal–a strain-tunable optomechanical filter–with the stretchable graphene photodetector, we also demonstrated a unique strain-tunable wavelength selectivity.”

“This work demonstrates a robust approach for stretchable and flexible graphene photodetector devices,” Nam added. “We are the first to report a stretchable photodetector with stretching capability to 200% of its original length and no limit on detection wavelength. Furthermore, our approach to enhancing photoabsorption by crumpled structures can be applied not only to graphene, but also to other emerging 2D materials.”