SOUTH SAN FRANCISCO, Calif. — After several false starts, developers of thin-film transistor circuits last week claimed breakthroughs that they believe will finally push the technology to market. If successful, the efforts could enable a long-promised low-cost class of electronic paper, displays, labels, RFID tags, sensors, smart cards and perhaps even programmable wallpaper.

But will the claims hold up this time, or are they just more hype?

For years, promoters have been billing thin-film transistor circuits--and the broader category of printed or plastic electronics--as the next step beyond wafer-based ICs. The technology uses inkjet printers and polymer inks to print cheap, low-density ICs on a system, display or just about anything else. As such, it promises to make the IC ubiquitous, open- ing a host of new applications.

But despite the millions of dollars that have been invested in R&D over the years, a number of companies--including mighty Intel Corp.--have failed to move thin-film transistor circuits into production. The transistors are working in the lab, but not one company has "sold anything" in the commercial market thus far, said Peter Harrop, chairman of consulting firm IDTechEx Ltd. (Cambridge, U.K.).

At last week's Printed Electronics USA event here, 3T Technologies, Kovio, Orfid, PolyIC, STMicroelectronics, Thin Film Electronics and other concerns tipped details on printed electronics for a range of applications. Vendors claimed to have solved many of the problems associated with the technology,

including lackluster transistor performance, poor mobility and integration issues for the polymer materials.

More than 150 organizations are scrambling to develop the technology in one form or another. Many seek shares of a thin-film transistor and memory market that IDTechEx predicts will grow from nearly zero today to $40 million by 2009 and $8 billion by 2017.

The promising thin-film circuit field is one of several technologies in the broader printed-electronics market. Printed (or plastic) electronics is a catchall phrase that describes the method of depositing simple electronic circuits on a system via inkjet printer or related means.

The broader printed-electronics market, according to IDTechEx, includes conductive inks, electrophoretic displays, organic LEDs, thin-film photovoltaics, and transistor circuits and memories. In total, the market for printed electronics, including organics, inorganics and composites, is projected to grow from $1.8 billion in 2007 to $48.18 billion by 2017, according to IDTechEx.

The fastest-growing market segments are for thin-film transistors and memory, according to the firm. Unlike traditional silicon chips, thin-film transistor circuits do not use crystalline or amorphous silicon; instead, thin-film products are based on organic or inorganic compounds that enable flexible circuits.

"The transistors are the key to huge new markets that the silicon chip will never reach," Harrop wrote in a recent report. "The new transistors can be deposited on low-cost flexible substrates, aluminum or stainless-steel foil. [At present] they are much larger than today's silicon transistors, but they can be one-hundredth of the cost, thinner and lighter in weight."

There are still some downsides. Transistor speeds, for one, are limited to frequencies around tens of megahertz.

"Reliability and stability of organic [thin-film transistors] is the major problem at present," according to a paper from the Fraunhofer Institute for Physical Measurement Techniques (Freiburg, Germany). "Typical problems, which mostly are not yet completely understood, are that the mobility is typically reduced, and the threshold voltage and the subthreshold region of the [transistor] are sensitive to environmental conditions."

For those and other reasons, developers have failed to bring the technology into the commercial markets. In 2001, for example, startup FlexICs attempted to develop semiconductors on plastic substrates for flat-panel display and related applications. But by 2005, FlexICs, which was funded in part by Intel, had folded and put its assets up for auction.