Vol. II, No. 2  --  Spring 2007

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Caltech Chips Could Transform Medical Electronics

By Ahmed Enany,Editor-in-Chief

The goal of etching high performance electronic circuits using standard silicon-based techniques on a piece of flexible plastic has eluded researchers for quite some time. This is because silicon chips require processing temperatures high enough to melt any plastic base holding the silicon crystals in place. But, thanks to pioneering research on nanowires at Caltech, the goal of producing complex silicon circuits on flexible plastic substrates is now within reach.

A paper recently published in Nature Materials(1)  by the James Heath Research Group at Caltech describes a method for etching nanowires into a wafer of silicon, then peeling them off and transferring them to plastic. This method results in high-performance electronics on low-cost, flexible, and transparent plastic substrates.

James Heath, Ph.D., of Caltech is regarded as the world’s foremost expert on molecular electronics and nanowire fabrication technologies.

The Caltech research holds significant promise because the consumer and medical markets are developing an appetite for flexible electronics. Experts predict that this market could easily top $120 billion by the year 2020(2). And the race to satisfy demand for enabling technologies, including new chip designs, is heating up.

Digital Living: The New Investment Craze?

Established firms, such as Intel, IBM, Kodak, Motorola, and Xerox, are pouring millions of dollars into internal research and scouting academic research labs around the world in pursuit of tools heralding the age of “digital living.” Ideas include flexible displays that promise to disrupt everything from newspaper publishing to mobile phones(3), flexible batteries for efficient energy generation(4), architectural electronics, and a host of other tools to endow everyday products --  from food and medicine containers to fabric and paper -- with a modicum of computer smarts(5).

Entrepreneurial startups with VC-backing also see the opportunity. One recent example featured in Red Herring(6) is the British startup Plastic Logic, which succeeded in lining up $100 million from top VCs, including Oak Investment Partners, Amadeus Capital, and hedge fund Tudor Investment Corporation. All attention is on producing e-paper, i.e., flexible displays that you can roll up and put in your pocket. The idea was attractive enough to lure other investors such as Intel Capital, Bank of America, and BASF Venture Capital.

In the biomedical field, San Francisco Bay Area-based Bioident and Nanoident have lined up venture backers to invest in plastic chips for biometrics and chemical agent detection(7). Taking a different approach is Los Angeles-based ORFID, which is using an organic chip platform to produce flexible displays for RFID applications in hospital settings as well as for tagging medicine containers(8).

Nanowires to the Rescue:

The ability of established and entrepreneurial companies to meet demand for flexible electronics is restrained by the limitations of prevailing plastic chip technology. Devices, such as e-paper and roll-up displays for mobile devices, rely on transistors made of either organic polymer printed like ink on plastic substrate or amorphous, noncrystalline, silicon.

According to Mike McAlpine, Ph.D., lead author of the Caltech paper, most of these chips have limitations. Although organic transistors can be processed at low temperatures, “they perform poorly because of their propensity to degrade over time,” he said. And, when it comes to speed, these chips don’t fare well either. “The mobility [speed] of silicon is 1000 times higher than organics. Furthermore, since they are inorganic materials, they are much more stable in air than organics,” he added.

To overcome the limitations of organic chips, the Caltech team resorted to nanotechnology to combine high quality semiconductors with plastic. Their approach involved etching nanowires —1000 times smaller than

The production of Caltech's plastic chip required unprecedented advances in assembly, integration, and device reliability of nanoscale materials.

Michael McAlpine, Ph.D., a member of the James Heath Research Group at Caltech and lead author of the Nature Materials article, was first to conceive of the nanowire-on-plastic process while at Charles Lieber’s lab at Harvard five years ago.

a human hair — into a wafer of silicon of the same quality as that used in Intel computer chips. These nanowires were then transferred to plastic at room temperature.

In fact, the Caltech team is the first to assemble such well-ordered, densely packed nanowires on a piece of flexible plastic. The resulting product is not only much more stable thermally and chemically, but also expected to perform much faster than chips made of organics or hybrid materials.

According to McAlpine, the Caltech team takes pride in the fact that the production of its plastic chip “required unprecedented advances in assembly, integration, and device reliability of nanoscale materials.” Nonetheless, the team believes that the micro-fabrication procedures involved are compatible with large-scale industrial production. These procedures are expected to result in competitively priced, yet high-performance, electronics.

As for applications, the Caltech researchers think the sky is the limit. Imagine a myriad of new gadgets with important applications in biosensing and medicine. Examples include highly portable chemical and biological threat detectors and DNA sensors that could be packed into a small chip to spot pathogens in blood samples. Furthermore, since plastic is biocompatible, the Caltech team believes that the chip could one day facilitate the commercial production of fully implantable or wearable continuous health monitoring systems.


  1. Michael C. McAlpine, Habib Ahmad, Dunwei Wang & James R. Heath, “Highly Ordered Nanowire Arrays on Plastic Substrates for Ultra-sensitive Flexible Chemical Sensors,” Nature Materials, April, 2007
  2. US Display Consortium, Dec. 19, 2006
  3. Olga Kharif, “Computing’s New Screen Gems: Display Technologies Are Moving Rapidly to Thinner, More Flexible, and Efficient Systems. Even CRTs Are Getting Rethought,” Business Week, June 8, 2004 
  4. Battery Innovations: The Current Scene,” ePower, Sep – Oct, 2003. 
  5. Otis Port, Rachel Tiplady, Faith Arner “Just Two Words: Plastic Chips,” Business Week, May 10, 2004. 
  6. Ken Schachter, “Plastic Logic Lands $100M,” Red Herring, January 4, 2007  
  7. Adena DeMonte, “Nanoident: Plastic Chip Plant,” Red Herring, March 13, 2007.  
  8. Jeyling Chou, “Los Angeles-Based Startup Combines UCLA Research with High-Tech Company’s Savvy & VC Funds,” SoCalBio Synergies, Summer 2004.  

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