Printed everything: PE/PV show highlights flexible 3D interconnects, biosensors, memory, PV cell hybrids

by Michael A. Fury, Techcet Group

December 9, 2010 – The second day of the IDTechEx combined Printed Electronics USA 2010 and Photovoltaics USA 2010 expanded from three parallel tracks to four, adding one degree of difficulty to covering the talks of interest. (Still, this was a cakewalk compared to covering an ECS or MRS meeting…I just wonder how long it will stay that way!)

Mike O’Reilly of Optomec described their ink atomizer system for printing inks up to 1000 cP viscosity and several microns thick, much more than can be done by inkjet. One application is a 3D stacked chip interconnect scheme that prints 10μm lines at a 30μm pitch. This sounds like the interconnect scheme developed by Vertical Circuits Inc., a Scotts Valley startup. The Optomec print nozzle delivers atomized ink focused by a shroud gas, so a 150μm nozzle can print 30μm traces that are 6μm tall.

Click to EnlargeJoshua Windmiller of UC San Diego talked about textile printed biosensors in the UCSD nanoengineering program. These flexible sensors are screen printed down to 100μm features on fabrics that contact the skin. Active elements include, for example, glucose oxidase in a graphite electrode on a Nafion film. Flexing the substrate exposes more active enzyme, thus enhancing the sensitivity of the sensor. The combined requirements of skin contact and flexing make the elastic waist band of underwear the obvious location for these sensors. Another example shown was a disposable wipe for high-sensitivity detection of explosives using a Gore-TEX substrate. These were not intended for use with underwear — the market consists of only one individual.

Heliovolt boasts the highest efficiency for CIGS PV at 11.5% peak, with a volume production average of >10%, noted company CEO Billy Stanbery. The material is the result of a CRADA (cooperative R&D agreement) with NREL, and is due to the exceptionally large grain size they are able to produce.

David Icke of MC10 has integrated off-the-shelf components with flexible substrates to product a class of stretchable electronics that are highly conformal. One application is a brain overlay sensor array that is 13-25μm thick. (Do not try this at home!) Other applications paper-based medical diagnostics and sensing devices.

Stan Farnsworth at NovaCentrix talked again this year about their Pulse Forge equipment that enables flash annealing of metals on plastic substrates without delamination or deformation. Tools have been shipped to labs and pilot lines, and products manufactured with the process will start to ship in 2011. In conjunction with their equipment, NovaCentrix developed a copper ink called Metalor, which is printed as copper oxide with a reducing agent. It is a screen printing paste that sells for $75/kg, making it an attractive alternative to silver paste. The reduced copper is mesoporous but still quite conductive.

Tony Killard of the Biomedical Diagnostics Institute at Dublin City University is developing a family of biosensors with screen printed materials with the intention of migrating them to inkjet systems. Demonstrated components include sensors for NH3, urea, glucose, and cholesterol. The goal is to combine several sensors into what he calls a "smart integrated miniaturized sensor system" that includes heterogeneous integration of the sensors with a display, power, electronics and communications.

Erik Garnett of Stanford described their advanced nanostructured PV that combines Si and OPV into a single cell for greater conversion efficiency. The Si substrate is processed to form vertical Si nanowire arrays for light trapping; this surface exhibits absorption 70× greater than Si with conventional surface roughening. The gaps between the Si fingers are then filled with PEDOT for the OPV component. The vertical nanowire arrays are formed by coating the Si surface with a self-assembled monolayer of uniform SiO2 spheres which act as a plasma etch mask. After Si etching, the SiO2 is removed with HF, leaving the free-standing forest of Si pillars.

Davor Sutija of Thin Film Electronics showed a family of printed rewritable permanent memory devices using a ferroelectric polymer ink that was originally co-developed with Intel. The devices are fully R2R printable, with a single roll holding 3.6M memory devices with 20 bits each. It takes 50μsec and 20μC charge to set/reset the bits. The first commercial products are for games, in the form of their Toy Development Kit now available. In October 2010 they formed an alliance with PARC for 128-bit EPC memories with bipolar transistors. In 24-30 months they expect to have system products with 1000-5000 transistors.

Warren Jackson at HP is working on ZnSnO-channel transistors for R2R production on flexible substrates. The entire device film stack is blanket deposited on the roll, including a thick photoresist top layer. The thick resist is then patterned by a 3D roller stamp, which allows regions to selectively remove the layers down to the gate for contact. They are building 7×7cm display devices as a yield learning vehicle, using the eyeball as a rapid inexpensive tester.

Stephan Kirchmeyer at Heraeus Clevios (HC Stark Clevios GmbH) is using PEDOT-PSS as an ITO replacement for OPV, achieving 100Ω/square at 90% transparency. They are also working on materials for OLED that can serve as an ITO replacement for hole injection.

Shiv Chiruvolu of NanoGram talked about their 5-10nm Si particle inks, available in both n+ and p+. The different formulations can be applied by spin coating or screen printing. Inkjet is still in development, though already achieving 70μm lines at 100μm pitch. For TFT applications, they use low temperature laser sintering <180°C on a polycarbonate substrate. The company was acquired by Teijin in July 2010.

For the final stretch of the conference, all of the attendees were brought back to a single track. However, one room provided adequate capacity for the die-hards whereas the conference opening was 3× as large.

John Knight of PARC talked about fostering the PE product development infrastructure through their collaboration with Soligie. There is a gap between PE R&D and product realization/commercialization, which this alliance intends to bridge. There is also a gap between PE R&D and materials & process & equipment suppliers, which PARC intends to bridge. The objective of this PARC-Soligie alliance is to provide one stop shopping for PE product designers, a service that does not exist elsewhere.

Jani-Mikael Kuusisto of VTT Technical Research Center of Finland described their government-funded strategic initiative to foster R&D for product development and pilot production of several technologies, including PE. Successful programs include Orion Diagnostica and PrintoCent.

Peter Harrop of event organizer IDTechEx provided the last hurrah, looking forward to PE in 2010-2020. This market is expected to be $300B in <20 years. This is not unreasonable, considering that a good portion of PE will be directed toward consumer goods, itself a whopping $3T market. "The driver is to modernize print, not electronicsm," he said.

On both days of the conference, the schedule included an extended lunch break that allowed time for the exhibit floor, networking, and supplier seminars. This is a good arrangement that returns value to the supplier effort and expense of exhibiting.

The conference concluded on Dec.3 with five more short courses. The topics were:

  • Displays and lighting
  • Creating new products with PE
  • Flexible substrates, transparent conductors, and barriers for flexible electronics
  • RFID and its progress toward being printed
  • Energy harvesting and storage for small electronic devices

 


Michael A. Fury, Ph.D, is senior technology analyst at Techcet Group, LLC, P.O. Box 29, Del Mar, CA 92014; e-mail mfury@techcet.com.

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