A Review of the Opportunities and Processes for Printed Electronics (Part 5): The Future of PE
Flexible thin-film solar cells on plastic film have enormous potential. New applications will take advantage of their attributes of being lightweight and flexible. Applications include solar cells on T-shirts and jackets, modules on cars, boats and light aircraft, mobile and camping energy and novel toys like LED night kites. Since these materials can be tailored to shapes, architectural drapes and roof and wall coatings are all practical.
Figure 1: OE-A roadmaps give a best guess on how rapidly the PE market will develop.
An energy technology that is complementary and compatible with flexible solar cells is thin flexible batteries made in similar ways to CIGS thin-film PC devices. There are electrodes in the battery, but instead of generating electricity, electrolytes will store electricity. Zinc manganese dioxide (ZnMnO2) is a typical electrolyte, as is lithium-ion (Li-ion).
The novelty of these inexpensive batteries is that they can be eco-friendly, single-use and disposable without causing pollution, releasing any toxic compounds or combusting. They can be used in innovations such as cosmetic teeth whitening, anti-aging electric wrinkle care and moisturizing, electrophoresis hair removal, RFID, toys and even medicine delivery.
Thin flexible batteries can be made out of simple paper (as thin as 0.6mm) using a spacer that is made largely of cellulose and printed with carbon nanotubes with electrolytes that are soaked into the paper. The batteries are available in 1.5, 3, 4.5 and 6V at 4.5mAh/cm2 and weigh less than a gram. They can have a shelf life of three years and can operate at temperatures ranging from -20°C to 60°C. These green batteries are produced by screen printing, disposable and free of toxic chemicals. They cannot overheat, explode or cause burns and are non-toxic and non-flammable. Power Paper of Israel has perfected this technology. There are other companies producing thin flexible batteries.
The most exciting of these new developments is from Planar Energy, a spin-off of the US National Renewable Energy Center in Colorado. Their solid-state nanofilm electrolysis technology produces conductivity metrics equivalent to liquid electrolytes with three times the energy density of current Li-ion batteries and cost less than half the price per kilowatt hour. Their roll-to-roll deposition process is called SPEED (Streaming Protocol for Electroless Electrochemical Deposition). Thin-film nanomaterials are deposited sequentially on the flexible substrate, resulting in lower costs and increased control compared to vacuum deposition.
Low cost e-paper and other PE displays continue to be a major research focus. In addition to OLED technology on flex, there is also electrophoretic, electrochromic and electroluminescent displays. OLED displays are used in mobile phones. They use Universal Display's phosphorescent red, green and blue OLED materials, which have been proven to significantly reduce power consumption in numerous glass-based AMOLED products.
Figure 2: Displays.
The displays use an active matrix array of thin-film transistors fabricated on DuPont Teijin Films Teonex film using substrate handling and processing technologies developed at the Flexible Display Center (FDC) at Arizona State University. Versions using transistors made with both low-temperature amorphous silicon and higher performance indium gallium zinc oxide have been produced.
It was previously thought that amorphous silicon backplanes were unsuitable for OLED due to stability problems. However, Ignis Innovation has solved the stability problems, paving the way for this first product.
"The performance is equivalent to polysilicon AMOLED. The product also incorporates Ignis’s latest all-in-one driver chip for amorphous silicon AMOLED, which is the first of its kind in today's AMOLED market," says Paul Arsenault, president and CEO. "This opens the door for RiTdisplay and other manufacturers to make state-of-the-art AMOLED displays using existing amorphous silicon equipment that is currently being used for LCD. This is the start of a new era where AMOLED displays can be made in much greater volumes, and with lower cost, than they are today with polysilicon."
Ignis Innovation is the leading provider of technology that makes AMOLED displays last longer, look better and cost less. Ignis works with display manufacturers to improve AMOLED displays using innovative circuit designs, driving algorithms and embedded software.
RiTdisplay, established in 2000, is the first company in Taiwan devoted in OLED research and development and manufacturing. It is currently the only company capable of manufacturing both OLED and polymer light-emitting diode (PLED) products. By adopting a customer-oriented marketing strategy together with the most advanced technology capability, RiTdisplay offers the most advanced display products to meet the demand in a variety of applications.
The different OLED manufacturing process lends itself to several advantages over flat-panel displays made with LCD technology.
Lower cost in the future
OLEDs can be printed onto any suitable substrate by an inkjet printer or even by screen printing, theoretically making them cheaper to produce than LCD or plasma displays. However, fabrication of the OLED substrate is more costly than that of a TFT LCD, until mass production methods lower cost through scalability. Roll-to-roll vapor deposition methods for organic devices allow mass production of thousands of devices per minute for minimal cost. However, this technique can induce problems due to the challenges associated with manufacturing multilayer devices.
Lightweight, flexible plastic substrates
OLED displays can be fabricated on flexible plastic substrates leading to the possibility of flexible organic light-emitting diodes in other new applications such as roll-up displays embedded in fabrics or clothing. Since substrates such as PET can be flexible, the displays may be produced inexpensively.
Wider viewing angles and improved brightness
OLEDs can enable a greater artificial contrast ratio (dynamic range and static, measured in purely dark conditions) and viewing angle compared to LCDs because OLED pixels directly emit light. OLED pixel colors appear correct and unshifted, even as the viewing angle approaches 90° from normal.
Better power efficiency
LCDs filter the light emitted from a backlight, allowing a small fraction of light through so they cannot show true black, while an inactive OLED element does not produce light or consume power.
OLEDs can also have faster response times than standard LCD screens. Whereas LCD displays are capable of response times between 2 milliseconds and 8 milliseconds, offering a frame rate of +/-200 Hz, an OLED can theoretically have a response time of less than 0.01 milliseconds, enabling 100,000 Hz refresh rates.
Many startups are involved in OLED displays. Universal Display Corp (UDC) is the only company purely focused on OLED display, but other OLED companies include Merck, Sumitomo, LG, Samsung, Philips, TDK and Osram.
Similar to display technology, OLED technology on flex and electrophoretic, electrochromic and electroluminescent display panels can create low power lighting. These panels can be flexible, foldable and built to include PE battery storage and PE PV to create electricity, resulting in a multi-tiered device to generate electricity, store electricity and provide low energy solid-state lighting.
The history of lighting technology efficiency can be seen in Figure 3. Incandescent lights have not changed much since Edison’s time, but solid-state lighting using LEDs and OLEDs has improved significantly since 2000 to nearly 200lm/W, nearly nine times more efficient.
Radio frequency identification (RFID) is a technology that uses communication with radio waves to exchange data between a reader and an electronic tag attached to an object for identification and tracking.
Figure 3: History of lighting technology efficiency.
RFID makes it possible to give each product in a grocery store its own unique identifying number and to provide assets, people, work in process, medical devices, etc., all with individual unique identifiers. RFID is like a license plate on a car, but can be used for every item in the world. RFID is a vast improvement over paper and pencil tracking or bar code tracking that has been used since the 1970s. With bar codes, for example, it is only possible to identify the brand and type of package in a grocery store. Passive RFID tags (those without a battery) can be read if passed within close enough proximity to an RFID reader. It is not necessary to show the tag to the reader device like showing a bar code to a bar code scanner. In other words, it does not require line of sight to see an RFID tag. The tag can be read from inside a case, carton, box or other container, and unlike barcodes, RFID tags can be read hundreds at a time. Bar codes can only be read one at a time.
Most RFID tags contain at least two parts:
- integrated circuit for storing and processing information, modulating and demodulating a radio frequency (RF) signal and other specialized functions
- antenna for receiving and transmitting the signal
RFID can be either passive (using no battery), active (with an on-board battery that always broadcasts or beacons its signal) or battery-assisted passive (BAP), which has a small battery on board that is activated in the presence of an RFID reader. In 2011, passive tags start at $0.05 each and can go as high as $5 for special tags meant to be mounted on metal or withstand gamma sterilization. Active tags for tracking containers and medical assets or monitoring environmental conditions in data centers start at $50 and can go up to over $100 each. BAP tags are in the $3 to $10 range and have the capability of sensing temperature and humidity. (See OE-A roadmap in Figure 1).
There are other RFID-like sensors that are inexpensive or disposable, especially for medical/patient monitoring. Biometric data like temperature, blood pressure, blood oxygen and electrical measures (EKG/ECG) can be measured and utilized for laboratory or patient monitoring. When matched with display technology, simple medical appliances can be created at low cost (Figure 4).
The market for low-cost, disposable sensors can be quite large. Environmental, safety, energy, medical, communication, personal safety and identification are just some of the potential applications.
Figure 4: RFID in medical applications.
Toys are a natural for PE. Simple circuits using PE sensors and batteries can be manufactured at low cost and placed into toys or novelties like singing or speaking greeting cards. A simple flash memory IC is attached like an RFID. PE printed memory and OLED displays are possible, with PV for battery charging. Adding sensors makes various forms of human interaction possible.
Wearables and fashion
The next PE application will surely be fashion and clothing. PE will offer the opportunity to customize clothing, colors and fashions, and can even incorporate messages utilizing PE energy collection, storage and display. It is even possible to preprogram fashions and patterns in small cards to allow users to purchase an item and customize it, like customizing ring tones for mobile phones. Implementation can be achieved by embedding PE devices on a garment or by using OLED coatings on yarn to be woven. Glass fiber light pipes that bring the display from a more convenient location are also possible.
Signage and advertising
As the cost of PE displays come down, they will appear in magazines, signs and advertising. The October 2010 copy of Esquire magazine had an e-paper active matrix display printed onto its cover. More and more, because of its color and motion, PE temporary and disposable displays will play a role in attracting customers.
PE memory is never going to approach the scale or size of semiconductor memory. However, there will be requirements for smaller, simpler memory for displays, sensors, medical toys and clothing. ThinFilm (Oslo, Norway) said that 40-bit passive memory arrays are in test production, and engineering samples will be available in late 2011. A 121-bit memory array is planned for production in 2012. It is aimed at ticketing, archiving and other applications that can use encryption for user-programmed stored identification. Thin Film projects prototypes for addressable memory in 2011 and the transfer of 128-bit memory to production in 2012, aimed at ID tags, sensor tags, disposable price labels and other smart labels. Thin film typically works with ferroelectric polythiophene active layers such as poly (3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT-PSS).
The coming generation of printed electronics, printed circuits and advanced integrated printed circuits appears to be headed down a path which is both familiar and new. Although the concept of printing both rigid and flexible circuits has a long history, those who pioneered early solutions would be amazed to see the developments currently underway. Similarly, those engaged in the current effort to expand the horizons of flexible printed electronics will be amazed at the technologies that will build on what is happening at this moment. Printing technology, beginning with Gutenberg's invention, has altered the course of human history by making knowledge more accessible to more people. The coming generation of printed electronics will build on and advance Gutenberg's efforts to create and provide printed products that improve the spread of knowledge and information using new products. Printed electronic readers and displays, made possible by recent and developing technologies, will facilitate the expansion of global education more cost-effectively than paper books.
One way to view the future is the OE-A Roadmap on Printed Electronics Applications, seen in Figure 1. Whether one of the technologies mentioned or technologies yet to be developed will dominate the future of printed electronics is an open question. What is a bit more certain is that flexible base materials printed using printed electronics solutions and processed in roll-to-roll fashion will be an element of successful future technologies. Practical industrial printing solutions that are currently evolving or yet unimagined make the future of printed electronics an exciting mystery.
You can read the Part 1 of this article series here; Part 2 here; Part 3 here; and Part 4 here.
Editor's Note: This paper has been published in the proceedings of SMTA International.