A fabulous way to go fabless
For a manager wanting complete visibility into his supply chain, item-level radio frequency identification offers great promise. But a significant hurdle in making this potential a reality is the cost of silicon-based tags — typically priced between 10¢ and 30¢ apiece — as industry analysts claim RFID will not mature until the tags reach the 5¢ mark.
Several tag companies continue to make advancements that have resulted in smaller chip sizes and lower prices (see stories on pages 9 and 50), but the fact remains that silicon processing is an inherently expensive endeavor. With this in mind, a Motorola laboratory is developing a technology that bypasses costly “clean” rooms and other silicon processes in favor of letting readily available, standard color printing presses produce circuitry inexpensive enough to make item-level tagging of even low-cost items feasible.
Known as printed electronics, Motorola’s technology enables transistor circuits to be printed on cheap substrates such as paper or plastic instead of more expensive silicon, said Tim Collins, a member of the technical staff at Motorola’s Physical Realization Research Center (PRRC).
“The whole intent is to have printing done in the environment used to make giant posters,” Collins said. “That’s how we keep the costs low. When you start to have clean rooms and bunny suits, then the costs start going up. And it really doesn’t make business sense to start going down that path when you really don’t have to.”
In addition to the savings associated with producing the RFID tag, the fact that the printed electronics can be integrated with the normal printing process potentially would eliminate the need for a separate process to affix RFID tags to products, further reducing costs. Paper transistors also would be more environmentally friendly than silicon processors, according to Motorola.
The design of printed electronics transistors is similar to their silicon predecessors, including fundamental source, gate and drain-conducting components, said Marc Chason, PRRC technical staff director (see diagram). But instead of electrons being conducted by semiconducting material on a silicon substrate, the electrons are conducted by printable inks on a paper or plastic substrate, he said.
Printing is done with machinery used in the traditional four-color printing process, in which cyan, magenta, yellow and black (CMYK) inks are layered on material — typically paper — to produce a printed product, Chason said.
For instance, with printed electronic technology, the cyan drum would be filled with a conductive ink printed as the gate, the magenta drum would be filled with a dialectric ink that insulates the gate, the yellow drum would be filled with conductive ink that performs as the source and drain electrodes, and the black drum would be filled with ink that performs as the active material between the source and drain, he said.
“One of the keys here is that you have to have ink systems that are compatible,” Chason said. “So when I print one layer and let it dry, and then I print another layer on top of that, it can’t dissolve the first layer.”
The viability of the technology depends on finding inks that conduct electrons at the speeds necessary to deliver the kind of performance needed for a given task. Motorola’s initial tests utilized inks that operated at only 1 Hz to 5 Hz — far below the minimum threshold of 125 KHz that Motorola is targeting — but the labs are in the process of evaluating new inks that may conduct better, Chason said.
“The inks we’re sampling now, the vendors suggest that they have higher mobility — in other words, the electrons move faster through them; therefore, you could have a circuit that works at higher frequencies,” he said. “We’re hopeful, with these next generation of inks, we can approach the kilohertz regimes.”
Although Motorola’s initial goal is to print transistors capable of 125 KHz, which is the first frequency range used in RFID, enabling operations at 13.56 MHz speeds would “open another range of RFID applications,” Chason said.
“Once we get an ink that we think is viable, we think we can get our prototypes fairly quickly after that,” he said, indicating that printed electronics prototypes could be available within two years.
Collins is confident that printed electronics can achieve those speeds and much more in the future, based on the development of silicon processors in recent decades.
“It’ll go down the same kind of curve: The geometries will get smaller; the materials will get better. Over the years, you’ll see this stuff going faster and faster. Will it ever achieve the speeds of traditional silicon? I don’t believe that will ever happen. There’s always going to be a need for high-frequency, Gigahertz Pentium-type chips for computers.”
Indeed, one problem that would have to be overcome if printed electronics could be operated at high-performance speeds would be the heat generated, Collins said.
“When the speeds start getting faster, the amount of current that circuits require increases, and so does the heat — and we’re talking about doing this on paper,” he said. “It would be a bad thing if we burned everybody up.”
With such limitations, Chason noted that the need for silicon-based RFID tags likely will continue to exist, even if printed electronics becomes the preferred method for item tagging. Printed electronic tags will have limited signal range, so the reader has to be close in proximity. Chason said future RFID systems could contain a hierarchy of tags and readers.
“We’re not suggesting that the RFID that we’re looking at is the single solution for the whole supply chain,” he said. “It plays very nicely at the item-level space, we believe, but it might not be the best thing to use in the warehouse.”
Nevertheless, there certainly will be a market for printed-electronic RFID should the technical hurdles be overcome, said Sara Shah, ABI Research analyst.
“I think the printed electronics will be important to reduce costs,” Shah said. “Because, no matter how cheap the tags are in the form factor of the label, they’ll never be cheaper than a printed tag would be.”
Motorola’s Collins said he is confident that even the first generation of printed-electronic RFID tags will be less expensive than the 5¢ chips the industry now seeks. If the technology becomes as ubiquitous as bar codes, the costs could drop even more dramatically.
“There’s no reason to believe that this technology can’t go down that same learning curve as traditional silicon,” Collins said. “So when people ask, ‘How cheap can it get?’ my imagination can’t go that far. There’s too much potential in this technology.”
By using conventional printing technology, printed electronics provide greater savings, not only in material costs but production availability. Instead of waiting months for transistors to come from a billion-dollar fabrication plant, printing presses could generate product daily.
“You can push out transistors much, much faster than you could with traditional silicon processing,” Collins said. “By doing that, you can manufacture a lot more chips.”
Chason noted that Motorola’s technology means the production of electronic circuitry could become simply another facet of the printing business, along with printing newspapers, books and magazines. That would be a development that likely would be welcomed by printing companies, Collins said.
“That’s one of the nice thing about this technology — it can be printed on low-cost printing substrates with a traditional printer,” he said. “It’s giving life to that industry that kind of got quiet with the Internet emerging. This is a whole new marketplace they are going to be able to start entering to give them a whole new life.”
