Tech Startup Unveils Printed-Silicon Transistor

Nov 14, 2007In the world of electronics, RFID tags are relatively simple devices, consisting of a low-memory integrated circuit (IC) and an antenna. And yet, to date, the RFID industry has had to rely on the same basic, time- and resource-consuming silicon fabrication processes for making the integrated circuits as other industries that produce more advanced electronics.

For that reason, considerable research has gone into developing ICs without silicon, instead using organic, polymeric semiconductors than can be deposited through printing processes. OrganicID, PolyIC and other firms have had some success in building out tag prototypes, but such tags tend to perform poorly compared to silicon-based tags.

While silicon is a better conductor than organic materials, printing with silicon-based inks has been considered impossible. Now, however, a venture-backed firm in Silicon Valley called Kovio claims it has found a way to do just that, and has unveiled a thin-film transistor (TFT) printed with a silicon ink using an ink-jet printing process. The transistor is a building block for a complete IC, which will contain multiple TFTs used for different functions on the chip. Kovio's CEO and chairman, Amir Mashkoori, says that by the end of next year, his company expects to have a fully functional printed-silicon integrated circuit that will be used to make high-frequency (HF) RFID tags.

According to Mashkoori, although Kovio is not the first company to be able to print thin-film transistors with silicon, its offering has the highest charge mobility of any silicon-based printed TFT. The high charge mobility of the Kovio TFT, Mashkoori explains, enables it to support the transmission of ultra-high frequency (UHF) RF signals, which other TFTs and transistors printed with organic materials can not do (see Printed RFID Tags Still Several Years Away).

But the real value proposition of printed transistors compared with traditionally rendered silicon chips, Mashkoori says, is that they could be mass-produced at a fraction of the cost, and much more quickly, by consuming only 4 percent of the chemicals and 25 percent of the energy needed for traditionally rendered silicon chips. This he says, is because the printing of transistors is an additive process rather than a subtractive process. Kovio's integrated circuits are larger than conventional ICs, but that could be an advantage when making RFID inlays, he says, because that will make it easier to attach an antenna (also printed) to the Kovio chip to form an inlay than it is to attach one to tiny fabricated silicon chips, which requires more precision. "We'll use a stainless steel substrate—a foil—and we can make it large enough to make antenna attaching a more forgiving process," he says.

Mashkoori declines to provide a firm estimate of the retail price for a Kovio RFID inlay, but indicates it will be cheaper than any RFID inlay currently available and will come "as close as possible" to the much-anticipated 5-cent per-tag price point. He adds that Kovio will either manufacture entire inlays, which converters will embed into labels or other tag carriers, or provide just the ICs that will be used to make the inlays. Because printed tag antennas are becoming more common and easier to integrate into packaging, he foresees companies in the consumer packaged goods (CPG) industry printing labels directly onto packaging and adding the Kovio IC to the antenna to form a complete tag.

According to Mashkoori, Kovio has its sights set on the market for item-level tags and those used to replace magnetic-stripe technology in industries such as transportation, where mag-stripes are employed on fare cards. Its first products will be HF tags, he says, which the company plans to make compliant with existing ISO standards. Kovio has inked two separate joint development and supply agreements with Toppan Forms, a printable-electronics firm, and Cubic Transportation Systems, a provider of automated fare-collection solutions for public transport systems. Toppan will help Kovio create high-speed, large-scale IC printing systems, while Cubic will collaborate with Kovio on RFID-enabled transit cards.

In addition, Mashkoori says, Kovio also plans to develop printed UHF RFID inlays, after its HF tags are fully developed. In the long term, he states, the company intends to combine RFID with biosensors and printable displays to create such items as "a transit fare card that tells you how many rides you have left," or a medical bottle with an integrated blood-sugar detector.