Printed Electronics Start to Show Up in Volume Hybrid Products
By Paula Doe, SEMI Emerging Markets
Despite its huge potential for making low-cost large-area lighting, solar panels, and displays, printed electronics has struggled to find commercial applications. So far, it’s been hard to match the cost or performance of vacuum deposition on wafers or glass. But now real electronics products using unconventional organic materials, solution-processed layers, or flexible substrates are starting to come to market —incorporating these newer technologies loosely called printed electronics into conventional vacuum process flows or with conventional electronic components in hybrid products announced at Printed Electronics USA in December.
Printed electronics is currently only about a $600 million market in 2011, and 70 percent of that is inks, according to IDTechEx. But the market research firm figures some $2.4 billion worth of electronics products now could potentially be organic, printed or flexible in the future. Most of that potential future value is OLED displays for smart phones, already a significant market using organic materials, but almost all deposited by vacuum processes on glass. Costs and lifetimes are still problematic for bigger, longer lasting applications, but big Asian TV makers say commercial OLED TV is now two to three years away, reports IDTechEx CEO Raghu Das, though noting that they’ve been two to three years away for some time.
But 2012 will see introduction of an assortment of potentially significant new applications of wide-area, solution-processed materials in commercial lighting and displays, including potentially lower cost OLED light panels, better ITO alternatives, force-sensitive touch screens, and possibly even some flexible display backplanes.
Lower-cost Approaches for Partially Printed OLED Lighting Hit the Market
Panasonic high-efficiency OLED panels will reduce CO2 emissions; better than fluorescent lamps in the near future (Source: Panasonic Idemitsu website)
Panasonic Idemitsu OLED Lighting has just introduced OLED panels with what it touts as industry leading performance, based partly on results from the recent Japanese government-sponsored NEDO research project to reduce costs by improving process equipment technology.
Panasonic Electric Works research director Takuya Komoda reported development of thin-film coating technology for printing a uniform initial hole injection layer with Tazmo Co. Ltd.’s slot die printer, depositing a 30nm layer of material from Nissan Chemical at throughput of 200mm/second. But more important may be the improvements to the vapor deposition of the emitters and other layers, with a new continuous deposition tool developed with Choshu Industries. Komoda says valve-controlled input and evaporating the material off the hot walls of the chamber increases the deposition rate from 0.2nm/second to more than 10nm/second, and cuts waste of the expensive organic emitters down to about 30 percent, from as much as 90 percent with some other technologies. The next phase of research now underway has switched from Idemitsu’s new deep blue fluorescent emitter to UDC’s phosphorescent blue emitter and added a high-refractive-index light outcoupling layer that has bumped efficiency to 80lm/W, but at some sacrifice of lifetime.
At the conclusion of the first phase of the project late last year, Panasonic and Idemitsu formed a joint venture to market OLED panels to lighting fixture makers worldwide.
Panasonic Electric Works planned to launch modules with control electronics in December. The initial 97x90mm units claim bright 3,000 cd/m2 luminance of warm 3,000K light with good color quality (CRI>90), with 10,000 hour life (70 percent lumen maintenance), though at only 30lm/W efficiency. Idemitsu is starting production of the materials at a new plant in Korea.
Aixtron says its OPVD tools’ delivery of OLED materials in carrier gas also allows high quality vapor-deposited films at improved throughput and less material waste. Juergen Kreis, senior department manager, business development, reports that delivering source materials from separate chambers in carrier gas through a close-coupled showerhead can now get >60 percent materials utilization, increasing to 70 percent or better over larger substrate sizes of G4 and above. Deposition speed of hole transport layers can be 40Å/sec at temperatures of 200°C or less.
Inorganic LED Die Coated on to Wide-area Substrates Aim for Low-cost Lighting
Taking a rather less conventional approach, Nth Degree Technologies says it’s starting production this quarter of printed light fixtures that can be cheaper than fluorescents, with some 2 million units already pre-sold. Key to the technology is skipping the organic emitters, and relying on averaging many small inorganic LED die over a wide area for acceptable performance, targeting good-enough light quality at very low cost. The company makes basically conventional InGaN LEDs on sapphire or silicon wafers, etches around the little 27µm hexagonal units, lifts them off the wafer and puts them into solution for coating onto low-cost mylar or aluminum with a conventional screen printing press.
Clever use of fluid dynamics makes the die de-wet to control placement and orientation. “It’s a statistical process,” says founder and chief scientist Bill Ray. “If some of them don’t work, we don’t care.” Color consistency is the average wavelength output from a whole wafer. Also key is a transparent conductive layer of nano fiber silver, that Ray says is cheaper than ITO, with 97 percent transparency at resistance <50 ohms per square. The material will be marketed separately by Henkel.
Ray says the company is working with a large electrical contractor and a large hospital chain who’ve calculated a two-year payback period, then significant electrical cost savings for the remaining life. The first generation 2’x4’ panels on aluminum reportedly produce 5000lm at 20lm/W and will cost somewhere around $135. Ray says the generation for commercial release aims at 40lm/W. Lifetime remains unproven, but the systems have reportedly been running for 3,000-4,000 hours so far with no appreciable degradation, and Ray expects the failure mechanism to be phosphor degradation and lifespan to be about like other LEDs at perhaps 40,000 hours. The relatively dispersed die over the large area heat sink sheet keep heat down which helps performance and durability.
Nanotechnology in Solution-coated Films Replace ITO, Create Force-sensitive Touch Film
The booming market for touch screens is creating a real market opportunity at last for nanoparticles and nanowires, and plenty of companies claim innovative solutions for transparent conductive and touch-responsive films for displays. Among those with real sales is Cambrios Technologies’ silver nanowire coating on polymer film, now replacing ITO in hundreds of thousands, though not yet millions, of Android cell phones, says Rahul Gupta, senior director of business development. The highly conductive, single-crystal, high aspect ratio, flexible silver strands form a planar network, for potentially better performance at lower cost than ITO. Adding more nanowires to the ink cuts the resistance, but brings down the transparency. Gupta reported transmissivity of 98-99 percent for the nanowire layer only, 92 percent on film for resistances between 30-250 ohms/square, and 88 percent at 10 ohms/square on glass (94 percent for the nanowire layer only). Patterning can be done with wet etch or laser removal, and the company is working on direct patterning with gravure and reverse offset printing for OLED and display applications.
Also reportedly ramping commercial sales is Peratech Ltd., with its transparent force-sensitive film for more sensitive touch screen control, based on quantum tunneling between nanostructured spiky metal conductive particles in an elastomeric polymer insulator. The solution-coated film is an insulator when unstressed, but increases its conductivity as pressure on it increases, as the spiky particles get closer together and charge gets more likely to jump across the smaller gaps between them. The company has licensed its earlier non transparent version to Samsung EMI and says a major touch screen supplier has licensed the transparent version. It reportedly has some $2 million in orders.
Printing TFT Backplanes Makes Flexible Displays, Rugged if Not Cheap
Samsung has said it plans to introduce an OLED on a flexible substrate in a mobile phone this year, touting the flexible display prototype it showed at CES for its ruggedness, not its low cost. The display is expected to use polyimide made by the JV with Ube Materials, coated on a rigid substrate for processing and then removed.
Plastic Logic speakers and partners repeatedly slammed its no-glass device on the floor to show off its ruggedness, but noted it intended to target only the specific markets would pay extra for unbreakable displays, like the government-supported Russian textbook market and other B-to-B verticals like factories. The company is now setting up mass production in Russia for its e-reader with printed polymer backplane. The 10.7 inch displays have 1.2M OTFTs, and 150ppi resolution. VP of process engineering Peter Fisher reminded folks just how challenging it was to ramp production of an entirely new process for thin film transistors, combining wet and dry processes, printing, spraying and laser ablation on plastic with customized G3.5 LCD equipment. Process control and testing of the new materials was particularly difficult, he noted, requiring developing new kinds of in situ measurements and electrical and optical tests to identify new kinds of failure modes when SEM images don’t show anything, and to develop effective inline controls. Embedded particles turned out to be a particular issue.
Polymer Vision is also still pursuing flexible displays with a solution-coated organic backplane, targeting larger displays that roll out from smaller devices. The company bonds its thin plastic to a glass plate for processing on its G2.5 AM LCD line in the Netherlands, then rolls the finished display off the plate at the end. CTO Edzer Huitema reports the pentacene semiconductor in the OTFT gets 0.2-0.3 cm2/Vs mobility, for a 6-inch SVGA electrophoretic display. He says the company also has a ZnO process flow established on its G1 development line for higher mobility, and is working on making an OLED display on the flexible backplane as well.
Nanoparticle makers see potential in solution-processed backplane films as well. NanoGram Corp. says it is getting mobilities of up to 2cm2/Vs for some of its low-temperature sintered films of Si nanoparticles on plastic, now sampling to key customers for development.
Progress in Printing Quantum Dot Emitters and Hole Transport Layers
Quantum dot emitters could potentially eventually be twice as efficient than OLEDs, and more easily printable with a lower cost bill of materials, argued QD Vision founder and CTO Seth Coe-Sullivan, noting early research results show about the same EQE as OLEDs, and higher Cd/A and lm/W. The company prints red, green and blue stripes of quantum dot emitters on a metal-oxide electron transport layer on the ITO cathode, then vapor deposits the organic electron transport and injection layers and the anode for its experimental stack. The red and green emitters are 20-25lm/W efficient with lifetimes approaching 10,000 hours, and blue emitter efficiency is over 6 percent EQE, though its lifetime remains very limited. “We think we know the mechanism, and expect we may be able to achieve about an order-of-magnitude improvement each year,” says Coe-Sullivan. The working demonstration display showed nice deep colors, though with some lineout defects from the backplane.
In more incremental improvements, Plextronics reported progress in improving performance of solution-processed hole transport layers, which still don’t match vapor-deposited alternatives, though solution-processed hole injection layers may now actually be better than vapor deposited one. Mary Boone, director, ink business management, says development work with Solvay Chemical (Belgium) is showing solution- processed HTL performance in the lab that’s getting close to vapor processed levels – and lifetimes are actually better, at 8,300 vs 5,600 hours. The company is also developing a new non-aqueous solution-processed HIL material optimized for the UDC stack of emitters to eliminate the water-related, wash-away defects of the usual aqueous solutions to extend lifetime, though perhaps at a drop in efficiency. First early runs on the company’s slot die line were reportedly getting 25nm films with <10 percent uniformity.
With three of the five suppliers who together account for some 90 percent share of the $125 billion flat panel display market pouring development dollars into disruptive materials and processes, large area OLED displays and TVs will surely happen in the foreseeable future, argued Boone, noting Display Bank’s projection of a $12 billion OLED Market by 2015.
Other Printed Electronics Products Find Real Markets
Unlike past years’ focus on technologies still searching for a market, this year at last more companies were talking about introducing real products to meet real user needs in innovative ways, mostly with hybrid systems combining new printed technologies with conventional electronic components. Potentially poised for high-volume adoption is an anti-theft alarm printed on conventional retail packaging, thanks to the current hot nanotechnology material graphene that enables the low-cost circuitry. The secure packaging will be printed by major $5 billion consumer packaging supplier MWV Packaging, and will be distributed by major retail security systems supplier Alpha High Shrink Solutions, with Home Depot among the first customers. With retail theft reaching $5 billion a year at Walmart alone, MWV Packaging director of open innovation Michael Londo said the market was receptive to a better solution-- retailers expected the system to be more effective against shoplifting than current alternatives, brand owners liked that it didn’t cover their package designs like some current “spider wraps,” and consumers would find it more convenient not to have to deal with locked cases and impossible-to-open casings.
The enabling material for printing the circuitry on the packaging is graphene particles in ink from Vorbeck Materials, which targets good-enough performance (<275 kΩ) at low cost. The rest of the electronics of the system are conventional and put in a separate re-useable clip-on unit, which sets off an alarm if the circuit is broken or the package taken from the store before the unit is removed by the clerk at check-out.
Other products heading into volume production include T-Ink’s plastic automotive console unit that replaces a ~3-inch thick 3D assembly of electronic components and wiring with a 0.25 inch thin 2D plastic sheet, allowing simpler assembly and more headroom. T-Ink expects to ship more than 1 million units this year in 2012 model Fords. Printed battery supplier Blue Spark says it has a design win for a vehicle tracking application for its battery- assisted passive RF ID labels that could total millions of units by year end. The battery assist reportedly allows the tags to be read at a wider range than typical passive tags, but keeps costs lower than active tags. The RF ID system can be easily printed on a single substrate because all three of the battery component layers are arrayed in the same horizontal plane, which just needs some printed circuit traces added, and an IC die flip chipped on to the traces.
January 10, 2012