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FlexTech News
Product Designers are Key to Next Phase of Flexible Electronics Say Panel of Experts at FlexTech Alliance Workshop On Metal Oxide Thin Film Transistors
Aug 7, 2012
It was standing room only at the one-day workshop “Metal Oxide TFT Devices and Technology” organized by the FlexTech Alliance on July 11, 2012, in partnership with SEMI. The workshop focused on the progress of producing thin film transistors as an enabling technology for the flexible electronics industry.
Subject matter experts from different sectors, including, manufacturing equipment and materials giants Applied Materials and Eastman Kodak; display companies like Sharp Labs and CBRITE; development groups from PARC and Cambridge NanoTech; and, research university contingents from Oregon State, Arizona State and Penn State, reported developments in TFT materials, fabrication and processing techniques, device applications and manufacturability.
“A paradigm shift in products and manufacturing is approaching,” said Dr. Malcolm J. Thompson, Chief Technical Advisor for FlexTech Alliance. “products will be fabricated on $100,000 worth of printing equipment as opposed to $1 billion or more in traditional semiconductor fabrication equipment. The new flexible display and electronics industry we are creating will provide low cost fabrication and fast deployment of new products.”
View Dr. Malcolm J. Thompson’s video interview.
The workshop included a lively panel discussion about market drivers for the industry. Panelists agreed that while the underlying technology is in an advanced development stage, a killer application in health care or consumer products will require more than good engineering. Product designers are key to the growth of the flexible electronics industry.
David Barnes, principal at BizWitz and a workshop panelist, noted that we are going back to the future by revisiting some of the compound materials considered decades ago for new applications such as large scale sensing devices and superior HD TV.
View David Barnes’ video interview.
Videos courtesy of MCA PR.
While the exact product or application that will ignite the industry is yet to be determined – anything from low power disposable diagnostics that manage pandemics to large-scale, portable roll-up displays that can be carried from home to home – developers have been focused on enabling technologies. Advancements presented at this workshop prove that solutions will be ready when product designers dream of the next killer application.
Moving to manufacturing is critical. For large-scale manufacturing, a consensus at the workshop agreed that a significant challenge was to develop a TFT process flow that does not require rigorous alignment among patterns in different layers.
Also, the group noted that the fabrication of devices with lightweight and flexible substrates requires processing at low temperatures, often resulting in a performance trade off.
Following are highlights of the technical presentations. Full workshop proceedings are available.
• Dr. Tolis Voutsas of Sharp Labs of America began the presentations with a materials discussion and focused on display applications of amorphous oxide semiconductors (AOS) and their importance to thin film devices like TFTs. He highlighted the fundamental materials and device properties behind the success of AOS, reviewed the large-volume manufacturers that have commercialized AOS-based devices and speculated on future applications such as medica and 3D displays and digital outdoor signage.
• CBRITE, Inc. has come up with a proprietary self-aligned process which enables large size display back panels to be made in an R2R process with a flexible substrate. The company says it has developed high performance metal-oxide TFTs with mobility and stability as good as LTPS TFT and with off-current, uniformity and process simplicity as good as a-Si TFT. The self-aligned technique can be deployed in free standing or roll to roll processing to minimize the impact of substrate deformation.
• Dr. Neil Morrison, Manager of Applied Materials R&D R2R, commented that significant advances have been made in device patterning enabling the mass production of a variety of flexible electronic devices. He displayed feature sizes of less than 40nm produced on thin film layer stacks deposited on 50 micron thick polymeric substrates. He also acknowledged the important challenges in terms of deposition technologies used in roll-to-roll (R2R) manufacturing of these devices. Dr. Morrison reviewed the other principal challenges to R2R TFT device manufacturing including: choice of substrate, thermal budget, layer stack stress, patterning, defects and yield.
• Eastman Kodak’s approach to the patterning and alignment of thin-film transistors on flexible substrates is a vertical transistor architecture, reported at the workshop by Dr. Shelby F. Nelson. The design has both high alignment tolerance and sub-micron channel lengths and it is compatible with flexible supports. Showing comparable materials properties to planar zinc oxide transistors, these devices demonstrate remarkable current-carrying properties, along with steep sub-threshold slope, and good yield.
• Cambridge NanoTech Inc. discussed its development of a high-speed Atomic Layer Deposition (ALD) system targeted to operate at the high volumes necessary for commercial roll-to-roll practices. By means of a unique high-speed precursor delivery and extraction mechanism, the system is able to deposit a range of materials from single component oxides for dielectric and conductive layers to more complicated binary and ternary semiconductors.
• Dr. Douglas A. Kezler from the Center for Sustainable Materials Chemistry at Oregon State University presented unique materials and processes for enabling high-performance operation of thin-film oxide transistors. Particular consideration was given to the deposition of insulators and passivation layers at modest temperatures by using water-based precursor chemistries.
Developing technologies are bringing these products from the research lab to the marketplace.
• Dr. Bob Street from Palo Alto Research Center (PARC) reviewed device successes in specific applications. PARC recently came out with a prototype flat panel flexible x-ray image sensor based on oxide TFTs. Dr. Street cited that oxide TFTs have a faster response than a-Si for fluoroscopy and have the high mobility needed for pixel amplifiers, with lower manufacturing cost than LTPS.
• Dr. Thomas Jackson of Pennsylvania State University talked about some of the issues related to the widespread application of active thin film devices to real world applications, like a recent temperature sensor for implantable medical use PSU has developed. He discussed zinc oxide TFT technology to illustrate some of the challenges and potential solutions for active thin film electronics.
• Dr. David Allee of the Flexible Display Center at Arizona State University asserted that near term, viable applications for metal oxide TFTs include large area sensing arrays for radioactive particles, acoustic and ultra-sound waves, x-rays and other photons. Electronic textiles may also be achievable implementing wearable sensing arrays.
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