Category Archives: FPDs and TFTs

For much the same reason LCD televisions offer eye-popping performance, a thermomagnetic processing method developed at the Department of Energy’s Oak Ridge National Laboratory can advance the performance of polymers.

Polymers are used in cars, planes and hundreds of consumer products, and scientists have long been challenged to create polymers that are immune to shape-altering thermal expansion.  One way to achieve this goal is to develop highly directional crystalline structures that mimic those of transparent liquid crystal diode, or LCD, films of television and computer screens. Unfortunately, polymers typically feature random microstructures rather than the perfectly aligned microstructure – and transparency – of the LCD film.

ORNL’s Orlando Rios and collaborators at Washington State University have pushed this barrier aside with a processing system that changes the microstructure and mechanical properties of a liquid crystalline epoxy resin.  Their finding, outlined in a paper published in the American Chemical Society journal Applied Materials and Interfaces, offers a potential path to new structural designs and functional composites with improved properties.

The method combines conventional heat processing with the application of powerful magnetic fields generated by superconducting magnets. This provides a lever researchers can use to control the orientation of the molecules and, ultimately, the crystal alignment.

“In this way, we can achieve our goal of a zero thermal expansion coefficient and a polymer that is highly crystalline,” said Rios, a member of ORNL’s Deposition Science Group. “And this means we have the potential to dial in the desired properties for the epoxy resin polymers that are so prevalent today.”

Epoxy is commonly used in structural composites, bonded magnets and coatings. Rios noted that thermosets such as epoxy undergo a chemical cross-linking reaction that hardens or sets the material. Conventional epoxy typically consists of randomly oriented molecules with the molecular chains pointing in every direction, almost like a spider web of atoms.

“Using thermomagnetic processing and magnetically responsive molecular chains, we are able to form highly aligned structures analogous to many stacks of plates sitting on a shelf,” Rios said. “We confirmed the directionality of this structure using X-ray measurements, mechanical properties and thermal expansion.”

Co-authors of the paper, “Thermomagnetic processing of liquid crystalline epoxy resins and their mechanical characterization using nanoindentation,” are Yuzhan Li and Michael Kessler of Washington State’s School of Mechanical and Materials Engineering. The ORNL portion of the research was supported by the Critical Materials Institute, an Energy Innovation Hub funded by DOE’s Office of Energy Efficiency and Renewable Energy. Washington State’s research was funded by the Air Force Office of Scientific Research.

UT-Battelle manages ORNL for the Department of Energy’s Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.

At first glance, the static, greyscale display created by a group of researchers from the Hong Kong University of Science and Technology, China might not catch the eye of a thoughtful consumer in a market saturated with flashy, colorful electronics. But a closer look at the specs could change that: the ultra-thin LCD screen described today in a paper in The Optical Society’s (OSA) journal Optics Letters is capable of holding three-dimensional images without a power source, making it a compact, energy-efficient way to display visual information.

Liquid crystal displays (LCDs) are used in numerous technological applications, from television screens to digital clock faces. In a traditional LCD, liquid crystal molecules are sandwiched between polarized glass plates. Electrodes pass current through the apparatus, influencing the orientation of the liquid crystals inside and manipulating the way they interact with the polarized light. The light and dark sections of the readout display are controlled by the amount of current flowing into them.

The new displays ditch the electrodes, simultaneously making the screen thinner and decreasing its energy requirements. Once an image is uploaded to the screen via a flash of light, no power is required to keep it there. Because these so-called bi-stable displays draw power only when the image is changed, they are particularly advantageous in applications where a screen displays a static image for most of the time, such as e-book readers or battery status monitors for electronic devices.

“Because the proposed LCD does not have any driving electronics, the fabrication is extremely simple. The bi-stable feature provides a low power consumption display that can store an image for several years,” said researcher Abhishek Srivastava, one of the authors of the paper.

The researchers went further than creating a simple LCD display, however—they engineered their screen to display images in 3D. Real-world objects appear three-dimensional because the separation between your left eye and your right creates perspective. 3D movies replicate this phenomenon on a flat screen by merging two films shot from slightly different angles, and the glasses that you wear during the film selectively filter the light, allowing one view to reach your left eye and another to fall on your right to create a three-dimensional image.

However, instead of displaying multiple images on separate panels and carefully aligning them—a tedious and time-consuming process—the researchers create the illusion of depth from a single image by altering the polarization of the light passing through the display. They divide the image into three zones: one in which the light is twisted 45 degrees to the left, another in which it is twisted 45 degrees to the right, and a third in which it is unmodified. When passed through a special filter, the light from the three zones is polarized in different directions. Glasses worn by the viewer then make the image appear three-dimensional by providing a different view to each eye.

This technology isn’t ready to hit the television market just yet: it only displays images in greyscale and can’t refresh them fast enough to show a film. However, Srivastava and his colleagues are in the process of optimizing their device for consumer use by adding color capabilities and improving the refresh rate. The thin profile and minimal energy requirements of devices could also make it useful in flexible displays or as a security measure on credit cards.

MarketResearchReports.Biz released a new market research report this week entitled “Metal Oxide TFT Backplanes For Displays 2014-2024: Technologies, Forecasts, Players.”

According to the new report, metal oxide display backplanes have already gone commercial. Sharp has invested in establishing a Gen8 IGZO plant at its Kameyama plant in Japan while LG has also selected IGZO backplanes for its large-sized white OLED technology. At the same time, Chinese companies such as BOE are fast playing catch up with both prototype and production capacity announcements.

IDTechEx estimates that 7 km sqr of metal oxide backplanes will be used in the OLED industry in 2024, enabling a 16 billion USD market at the display module level. The LCD display market will add an extra demand of at least 1 km sqr per year in 2024 for metal oxide backplanes.

The display industry continues to rapidly change and seek new markets. Long term trends are still prevalent and shape global activity. Examples include reducing power consumption, improving image resolution, and decreasing device thickness. At the same, the need to differentiate and capture new markets such as wearable electronics is first bringing in robust and then flexible and bendable displays. These trends will drastically affect the technology requirements at many levels including the backplane level. This will stretch several existing solutions beyond likely performance limits, thereby creating openings and opportunities for new entrants and the technology space for backplanes is complex. It consists of (a) mature technologies such as amorphous and polycrystalline silicon, (b) emerging technologies such as organic and metal oxides and (c) early state technologies such as graphene, carbon nanotubes, nanowires, etc. No single technology offers a one-size-fits-all solution and many technologies will co-exist in the market. Betting on the right technology will remain a decision-making nightmare.

It is within this emerging, complex yet changing space that metal oxide are emerging. They promise low leakage currents, high mobility, amorphousity, stability and wide bandgap. These attributes promise to enable, respectively, power consumption reduction, compatibility with current-driven OLEDs and/or 3D displays, image uniformity over large areas, long lifetime and transparency.

In the short term, this will help enable higher resolution and lower power consumption levels in displays including LCDs (particularly in medium- to large-sized displays); while in the medium- to long-term metal oxides will help enable uniform medium- to large-sized OLED displays.

The report specifically addresses the big picture – including OLED displays and lighting, to thin film photovoltaics to flexible sensors and much more. Importantly, it includes not only electronics which are printed, organic and/or flexible now, but it also covers those that will be. Realistic timescales, case studies, existing products and the emergence of new products are given, as are impediments and opportunities for the years to come.

Over 3,000 organizations are pursuing printed, organic, flexible electronics, including printing, electronics, materials and packaging companies. While some of these technologies are in use now – indeed there are three sectors which have created billion dollar markets – others are commercially embryonic.

When it comes to electronics, silicon may one day have to share the spotlight. In a paper recently published in Nature Communications, researchers from the USC Viterbi School of Engineering describe how they have overcome a major issue in carbon nanotube technology by developing a flexible, energy-efficient hybrid circuit combining carbon nanotube thin film transistors with other thin film transistors. This hybrid could take the place of silicon as the traditional transistor material used in electronic chips, since carbon nanotubes are more transparent, flexible, and can be processed at a lower cost.

Electrical engineering professor Dr. Chongwu Zhou and USC Viterbi graduate students Haitian Chen, Yu Cao, and Jialu Zhang developed this energy-efficient circuit by integrating carbon nanotube (CNT) thin film transistors (TFT) with thin film transistors comprised of indium, gallium and zinc oxide (IGZO).

“I came up with this concept in January 2013,” said Dr. Chongwu Zhou, professor in USC Viterbi’s Ming Hsieh Department of Electrical Engineering. “Before then, we were working hard to try to turn carbon nanotubes into n-type transistors and then one day, the idea came to me. Instead of working so hard to force nanotubes to do something that they are not good for, why don’t we just find another material which would be ideal for n-type transistors—in this case, IGZO—so we can achieve complementary circuits?”

Carbon nanotubes are so small that they can only be viewed through a scanning electron microscope. This hybridization of carbon nanotube thin films and IGZO thin films was achieved by combining their types, p-type and n-type, respectively, to create circuits that can operate complimentarily, reducing power loss and increasing efficiency. The inclusion of IGZO thin film transistors was necessary to provide power efficiency to increase battery life. If only carbon nanotubes had been used, then the circuits would not be power-efficient. By combining the two materials, their strengths have been joined and their weaknesses hidden.

Zhou likened the coupling of carbon nanotube TFTs and IGZO TFTs to the Chinese philosophy of yin and yang.

“It’s like a perfect marriage,” said Zhou. “We are very excited about this idea of hybrid integration and we believe there is a lot of potential for it.”

The potential applications for this kind of integrated circuitry are numerous, including Organic Light Emitting Diodes (OLEDs), digital circuits, radio frequency identification (RFID) tags, sensors, wearable electronics, and flash memory devices. Even heads-up displays on vehicle dashboards could soon be a reality.

The new technology also has major medical implications. Currently, memory used in computers and phones is made with silicon substrates, the surface on which memory chips are built. To obtain medical information from a patient such as heart rate or brainwave data, stiff electrode objects are placed on several fixed locations on the patient’s body. With this new hybridized circuit, however, electrodes could be placed all over the patient’s body with just a single large but flexible object.

With this development, Zhou and his team have circumvented the difficulty of creating n-type carbon nanotube TFTs and p-type IGZO TFTs by creating a hybrid integration of p-type carbon nanotube TFTs and n-type IGZO TFTs and demonstrating a large-scale integration of circuits. As a proof of concept, they achieved a scale ring oscillator consisting of over 1,000 transistors. Up to this point, all carbon nanotube-based transistors had a maximum number of 200 transistors.

“We believe this is a technological breakthrough, as no one has done this before,” said Haitian Chen, research assistant and electrical engineering PhD student at USC Viterbi. “This gives us further proof that we can make larger integrations so we can make more complicated circuits for computers and circuits.”

The next step for Zhou and his team will be to build more complicated circuits using a CNT and IGZO hybrid that achieves more complicated functions and computations, as well as to build circuits on flexible substrates.

“The possibilities are endless, as digital circuits can be used in any electronics,” Chen said. “One day we’ll be able to print these circuits as easily as newspapers.”

Zhou and Chen believe that carbon nanotube technology, including this new CNT-IGZO hybrid, could be commercialized in the next five to 10 years.

“I believe that this is just the beginning of creating hybrid integrated solutions,” said Zhou. “We will see a lot of interesting work coming up.”

Dow Corning today introduced new Dow Corning EA-2000 Silicone Adhesive, a high-performance terminal sealant for faster, more cost-effective manufacturing of thin-film transistor (TFT) LCD displays. This low-viscosity, room-temperature vulcanizing (RTV) silicone sealant combines high flowability and good adhesion with a fast, non-corrosive cure to facilitate higher throughputs and thinner, more reliable display architectures. Like other silicone materials, Dow CorningEA-2000 Silicone Adhesive provides long-lasting durability compared with organic materials.

“As the accelerating global demand for tablets, smart phones and other consumer electronics continues to drive the growth of LCD displays, panel manufacturers need advanced new materials to help speed production, control costs and improve the reliability of their devices,” said Hu Nan, global  marketing segment leader for Displays at Dow Corning.

EA-2000 Adhesive’s low viscosity allows fast and simple automated or manual dispensing with conventional equipment, minimizing conversion costs. This advanced new terminal sealant also cures quickly without the need for ultraviolet lamps to further streamline processing operations.

Unlike many organic sealants, EA-2000 Adhesive is solventless, and ensures a durable seal against moisture, dust and mechanical shock. Its non-corrosive cure reduces risk to sensitive metal components, and the sealant delivers unprimed adhesion to many materials – including reactive metals, ceramics and glass, as well as selected laminates, resins and plastics. In addition, Dow Corning EA-2000 Adhesive delivers excellent dielectric properties for optimal TFT LCD display performance, as well as good thermal stability in most conditions.

The Centre for Process Innovation (CPI) has developed novel backplane fabrication processes to allow the bending of Organic Thin Film Transistors (OTFT) arrays to small radii (1 mm) without a significant reduction in device performance. The work undertaken demonstrates progress towards optimum Organic Semiconductor (OSC)/OTFT processing and performance to enable their integration into ultra-flexible active matrix organic light emitting diode AMOLED backplanes. High performance OSC materials with charge mobility suitable for OLED driving were used in the tests on 50 micron thick PEN film. A demonstration video of the bend testing of the array can be viewed here.

In order to achieve the tight bend radius, the multiple interfaces present in the device stack were optimised to allow good adhesion under the strains experienced in the bending test.  Using patterned OSC layers and additional passivation layer processing, display pixel size OTFTs were fabricated and these were repeatedly bent (up to 10,000 times) to a radius of 1 mm, which equates to a strain of 2.5%.  Minimal change in the turn on voltage and on current were observed for the elongated cycle test.

This demonstration of bend resistance in high performance OTFT devices is part of ongoing work to integrate these materials into active matrix backplanes for AMOLED. It is expected that within 2014 the first plastic based display demonstrators will be completed using OTFT in project ROBOLED, which has received funding through the Technology Strategy Board.

CPI is the UK’s National Centre for Printable Electronics. Focused on the development, scale-up and commercialisation of printable electronics applications, CPI is equipped with an extensive range of assets specifically chosen and developed to allow clients to understand how their products and processes perform under pilot manufacturing conditions.

bending backplane

Slide 8

Delft University of Technology researchers will describe a novel low-temperature method for fabricating solution-processed polysilicon thin-film transistors (TFTs) for use with a wide range of arbitrary large-area substrates, including paper. The TFTs had electron mobilities of 23.5 and 21.0 cm2/Vs (for PMOS and NMOS, respectively).

Although other solution-processed polysilicon and single-grain silicon TFTs have higher electron mobilities, they require high-temperature annealing which rules out low-cost plastic or paper substrates. Meanwhile, other TFTs made at low temperatures but from organic or metal-oxide materials have poor mobilities, only half as much as the Delft devices at best, meaning their performance is limited.

The Delft team made the devices by casting a quantity of liquid polysilane onto a substrate, and forming a thin film from it by “doctor-blading,” or skimming it with a blade. High-performance polysilicon channel regions then were formed by laser annealing, using short pulses of coherent light to selectively crystallize the disordered film. The maximum temperature required was only 150ºC, making the TFTs suitable for paper and plastic substrates such as PET and PEN.

(Paper #26.5, “Solution-Processed Poly-Si TFTs Fabricated at a Maximum Temperature of 150°C,” M. Trifunovic et al, Delft University of Technology) 

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Applied Materials, Inc. today announced new technology systems for manufacturing large size and ultra-high definition (UHD) LCD and OLED displays that meet the demand for greater screen performance, clarity, color and brightness. The Applied AKT-PiVot 55K DT PVD, Applied AKT-PiVot 25K DT PVD and Applied AKT 55KS PECVD systems extend Applied’s leadership in metal oxide (MO) films and technologies for smaller, faster thin film transistors (TFTs) required to create high-resolution displays.  Through precision materials engineering and productivity innovations, these PVD and PECVD systems provide an optimized, cost-effective solution for volume production of future MO-enabled displays.

MO-based TFTs help enable low-power, high-resolution smart phones and tablets as well as some OLED TV technologies. Future 4K TVs are also expected to adopt MO TFTs. The uniformity and particle control of Applied’s PVD and CVD systems help customers deliver these new display technologies with high yield in mass production.

“Our new PVD and PECVD systems will accelerate display industry roadmaps by enabling customers to transition to MO materials using proven technologies,” said Ali Salehpour, senior vice president and general manager, Applied Global Services and Growth Markets. “We worked closely with customers to develop these solutions to address their critical uniformity, particle control and stability challenges, clearing major implementation hurdles, especially with regard to OLED. We can support the various product strategies of our customers by expanding these solutions to different substrate sizes, allowing for multiple technology paths for manufacturing large-area TVs or energy-efficient screens for mobile devices.”

Applied’s AKT-PiVot DT PVD systems (55K for 2200mm x 2500mm and 25K for 1500mm x 1850mm substrates) extend the company’s proprietary rotary cathode array technology to deliver proven highly uniform, homogeneous and low-defect, active-layer deposition for MO (e.g. IGZO), as well as interconnect metals and pixel electrodes. Enabling high TFT stability with uniform PiVot-deposited IGZO films is critical for display quality, and is key to realizing MO backplanes for small- and large-area OLEDs. As TFTs get smaller and substrates get larger, the impact of uniformity and particles on yield is significantly magnified. The systems’ self-cleaning rotary targets with directional plasma control deliver notably fewer defects and outstanding uniformity compared to conventional planar targets. To effectively provide this high-value performance cost, the system’s independent dual processing tracks on a single platform provide high production capacity in a small footprint. The deposition of robust, mura-free IGZO films, combined with uniform, low defect metals, pixel electrodes and new integrated passivation layers (AlOx), allows for unprecedented technical performance and flexibility.

Applied’s new AKT 55KS PECVD system brings precision PECVD technology to 2200mm x 2500mm size substrates. It deposits a dielectric-layer interface for MO transistors with a new advanced-quality silicon oxide (SiO2) process that minimizes hydrogen impurities to improve long-term transistor stability and optimize screen performance. By maintaining the uniformity performance and particle control required to achieve high production yields, the AKT-55KS PECVD system provides a rapid, easy to implement path for manufacturing high-quality MO displays.

OLED, a self-light-emitting diode, has been touted as the next big thing in display technology for its exceptional properties including no need for a backlight, wide viewing angle, quick responding speed and low current consumption. In particular, LG unveiled the world’s first 55-inch flat OLED TV in early 2013 followed by 55-inch curved OLED TV in April. With Samsung joining the fray with its latest 55-inch curved OLED TV, a fierce competition is expected in the OLED TV industry.

In anticipation of the OLED TV market coming into full bloom next year and encroaching the LCD TV market, developing mass production technology for OLED panels will soon emerge as a major issue. Extensive R&D efforts are under way to refine the OLED manufacturing process, namely, TFT backplane, color patterning, encapsulation and driving circuit. Especially, a lot of research has centered on the development of compensation circuit, as threshold voltage and IR-drop reduce the luminance of a driving TFT for an AMOLED display.

Read more: AMOLED panel shipments get boost from premium smartphones

OLED is a current driving circuit whose luminance properties are extremely sensitive to current changes. Driving TFTs for each pixel circuit of an AMOLED display can have different threshold voltages, which undermines the consistency of luminance of the panel.

In addition, when a VDD line passes each pixel circuit, it creates an IR-drop, resulting in a gradual decrease in pixel luminance towards the bottom of the panel that requires compensation.

Displaybank now offers a report examining a number of selected U.S. patents, analyzes patent application trends and patents filed by major companies and pinpoints key patents and new technology patents, offering a wide array of in-depth analyses. These analyses are expected to help keep pace with development trends for an AMOLED pixel driving circuit technology that compensates the threshold voltage and IR-drop as well as key patented technologies.

amoled shipments

Patent Application Trends
The number of U.S. patent applications for AMOLED pixel driving circuit (Vth and IR-drop compensation) technology is generally on the rise, with threshold voltage (Vth) compensation taking the biggest share. Top assignees are Samsung Display, Global OLED Technology, LG Display, Chimei Innolux, and Sharp, in the order of the number of applications.

amoled patent analysis

Key Patent Analysis
Out of 244 U.S. patents, those listed in the top 50 issued patents in terms of the number of forward citations were selected as key patents and subjected to an in-depth analysis: technology development trends, overview of key patents and case analysis.

Weak demand and rising production in China, combined with efforts by South Korean suppliers to cut manufacturing charges in order to stimulate demand, is resulting in pronounced price reductions in the third quarter for popular sizes of liquid-crystal display television (LCD TV) panels.

Read more: LCD TV panel inventory rises to excess levels, spurring price drops

Average pricing for 32- , 40- and 50-inch LCD TV open cell panels is set to decline in a range from 4.6 percent to 5.1 percent in September compared to June. Pricing for these panels for the previous period from March to June declined t a more moderate rate ranging from 2.0 percent to 3.4 percent.

Surprisingly, weakness is coming at a time when pricing and demand normally should be robust as the holiday season approaches.

“A number of factors are conspiring to cause weak pricing for LCD TV panels,” said Ricky Park, senior manager for large-area displays at IHS. “TV panel demand is tepid worldwide and particularly in China, where the end of a popular government incentive has led to a major sales slowdown. Meanwhile, Chinese panel manufacturers are adding new capacity—exacerbating the glut currently plaguing the industry. Finally, in an attempt to spur sales, some panel suppliers are offering attractive deals on certain panel sizes, causing pricing to fall.”

The 32-inch conundrum

The Chinese government’s move to discontinue its eco-subsidy program at the end of May had a broad impact on panel sales, but the biggest repercussion was in the 32-inch size. And because 32-inch is the most popular size in China, sales and pricing for this dimension plunged worldwide.

Meanwhile, production capacity for 32-inch panels still exceeds demand. The combination of weak demand and oversupply is expected to drive down the lowest price of 32-inch open cell panels to $90 in the first quarter of 2014, down from $96 during this year’s first quarter.

South Korea acts on 40-inch panels

Samsung’s aggressive stance on 40-inch panels also has impacted prices for similar-sized LCDs. As a result, prices for 39- and 42-inch panels are expected to decline by 5.2 percent and 4.2 percent, respectively, in the third quarter.

South Korean makers in general reportedly are planning to produce 48- and 49-inch panels in 2014, and both 46- and 47-inch panels will then be phased out. Anticipation of such developments caused a $4 to $5 price deduction in June for the 46- and 47-inch panel categories.

Taiwan cuts 50-inch prices

For their part, Taiwanese manufacturers cut prices for 50-inch panels to maintain a reasonable gap with 46- and 47-inch panels. And like the South Koreans, the Taiwanese are planning to offer panels in new 48- and 49-inch sizes. This is likely to further drive down pricing for 50-inch LCD TV panels.

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