Printable, flexible, low-cost electronics without the organic route

Sara Ver-Bruggen - 07 Aug 2012

Silicon and inorganic thin film semiconductor materials have proven performance but in many applications, like photovoltaics or wearable electronics, their limitations can range from cost to form factor.

Flexible, lightweight and unobtrusive electronics are being created by cost effective means, bypassing some organic materialsTechnology companies are overcoming the problem by miniaturising wafers, dramatically reducing the amount of semiconductor material used, and enabling circuitry that is flexible, lightweight and unobtrusive.

Leading the field is MC10, a Massachusetts-based start-up. The company has maintained high performance characteristics possible with silicon-based CMOS based electronics and created conformable circuits that can be embedded into flexible substrates such as latex, or fabric. In addition to medical implants, the company has big plans, with its partner Reebok, to shake up sportswear by developing semiconductor-based sensor circuits that can be worn on, or close to, the skin to provide athletes with real time data about their bodies in training.

Since 2008, when it was founded, MC10 has made fast progress. The company has now turned its attention to solar cells that can be integrated into the fabric cover of combat helmets and rucksacks. The project, funded by the US Army Natick Soldier RD&E Centre, builds on previous work led by the company's co-founder John Rogers, demonstrating high efficiency gallium arsenide solar cells, stamped onto stretchable semiconducting sheets. The aim of the one-year project is to develop wearable solar plants that can provide up to 50% increase in the battery life of soldiers' power packs, enabling them to carry fewer.

Small wafers

At Sandia National Laboratories researchers are using microdesign and microfabrication techniques to produce microsystems enabled photovoltaics (MEPV), roughly 14 microns thick and 250 microns wide. The MEMS are added to a solution that can then be printed onto a low-cost substrate with embedded contacts and microlenses for focusing sunlight onto the cells.

Nth Degree has developed printed lighting and solar cellsThe Arizona-based start-up Nth Degree Technologies is developing printed lighting and solar cells using gallium nitride wafers as a starting point. The wafers are diced into miniaturised versions, just a few microns in size, and suspended in a solution to make an ink. A single 4in x 4in wafer can produce 10 million LEDs. The ink can be printed onto any substrate using gravure, flexography or screen presses in sequential patterning passes from the substrate up.

The first layer is the bottom conductor ink, the second is the company's Random Diode Ink (RDI), followed by a dielectric layer and a final transparent conductor layer. The flexible circuits can then be converted into different shapes and designs, to provide light over a large area or around curved surfaces. Nth Degree Technologies is also working on printable solar cells and an alternative to indium tin oxide (ITO) and transparent polymer conductors and electrode materials.

On-going advances in packaging technologies, reductions in product costs and design innovation means the LED lighting industry is fast colonising those attributes and advantages that once defined the OLED lighting industry. LED is an unbeatable solid state lighting technology, believes Bob Karlicek director of the Smart Lighting Engineering Research Centre at Rensselaer Polytechnic Institute in New York.

The combination of mature semiconductor industry tools, processes and high volume deposition techniques, such as printing, are proving that low cost, high volume and flexible electronics are no longer the domain of organic semiconductor materials.

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