Roll-to-Roll Processing of Electronics Under Development

Rolltronics (Menlo Park, Calif.) is laying the foundation for a new approach to electronic manufacturing — producing electronic devices on flexible substrates using roll-to-roll manufacturing techniques instead of on silicon wafers. Collectively, transistors (ICs), memory, power and display elements are all of the necessary components required to make a fully integrated computing device such as an electronic book or electronic paper. Rolltronics has so far obtained patents for fabricating transistors and memory devices on thin films and has partnered with a company that specializes in making thin-film solar modules using roll-to-roll technology. At press time, the company expected to demonstrate the feasibility of the process by building transistors out of amorphous silicon by the end of July. Afterward, the plan is to move on to the more difficult process of converting the amorphous silicon to polysilicon.

"Lawrence Livermore National Labs has succeeded in a breakthrough of being able to create recrystallization of amorphous silicon into poly by using a pulsed excimer laser and by very carefully controlling the pulse characteristics," explained Michael Sauvante, CEO of Rolltronics, in an interview with Semiconductor International. "They wound up being able to melt the top surface layer of the amorphous and convert it into poly, and yet by turning it on and off, the heat migration through the amorphous and down into the substrate would be controlled to keep it below 100-125°C. They could actually do this on PET, the material used for overhead transparencies." The mobility of the transistors produced was more than good enough for use as logic circuitry in active matrix displays. Rolltronics has one of two licenses Lawrence Livermore is issuing on this technology.

Sauvante said he did not see a need to develop a proprietary solution for the other two building blocks of display and power. Instead, the company is focused on adapting present display and power technologies, plus the transistor and memory technologies it owns, to roll-to-roll manufacturing, which he says requires far less capital and is substantially less harmful to the environment than existing semiconductor manufacturing.

To this end, Rolltronics recently announced a strategic alliance with Iowa Thin Film Technologies (ITFT, Ames), manufacturers of flexible, lightweight, thin-film solar modules. "Over the last 12 years, ITFT has been perfecting a process for building amorphous silicon solar cells on plastic using roll-to-roll processing," Sauvante said. "They're the first and only company in the world to successfully build a commercially viable semiconductor device using true roll-to-roll processing. When you combine that capability with the technology in our patent portfolios, the possibilities are tremendous."

These developments position Rolltronics to achieve, by the end of this year, an important milestone by demonstrating the first-ever working thin-film transistor manufactured on a plastic substrate using true roll-to-roll, or web, processing. "Our automated module manufacturing equipment is ideal for making the type of electronic devices that Rolltronics envisions," said Frank Jeffrey, president of ITFT. "Roll-to-roll processing introduces an entirely new level of flexibility, not just to the products, but to the design process as well."

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