Emerging commercial applications of nano electronics

07/01/2009

Nanoscale properties enable improved thermoelectrics, NEMS gas sensors

By Dr. Paula Doe, contributing editor

The much-hyped properties of materials at the nanoscale are finally starting to be applied to some real electronics applications, ranging from near-ideal thermoelectric material based on spray-on semiconductor nanocrystals, to transparent conductive films made from on carbon nanotubes and self assembled silver nanoparticles, to ultrasensitive nanoscale MEMS gas sensors.

Nanoscale materials properties are enabling efficient, low-cost thermoelectric materials. Though long studied, thermoelectric conversion of heat to electricity have never been efficient enough to be practical for most applications. “They were stuck with natural materials,” says Evident Technologies CEO Clinton Ballinger. “But with nano-structured materials you have a lot more materials to work with. You can change the thermal properties.” That means it is possible to design something that approximates the ideal thermoelectric material, conducting electricity well but not heat. Modeling suggests that the most efficient structure would be point sources of excited electrons distributed evenly in a matrix–and that ideal efficient material can be approximated quite well by a low-cost solution, using colloidal ink containing semiconductor nanocrystals to create a bulk material while retaining the nano properties.

Ballinger suggests that some of the first markets for this technology will be in the semiconductor industry, where it could enable efficient, flexible, solid-state cooling for integrated circuits and LEDs. This could greatly reduce the size or need for a heat sink, he argues, and potentially improve performance. “Right now we’re just spraying it on with an airbrush,” he notes. “So it could likely be coated right on the chip for thermoelectric cooling.”

First application is likely to be for less sophisticated solid-state cooling, though, such as spot cooling for things like wine coolers. But eventual markets for low-cost roll-to-roll coated thermoelectric films could also include waste heat recovery in automobiles and central power stations, general heating and cooling, and even power generation.

Likely closer to market are transparent conductive films using innovative nanomaterials to potentially challenge ITO. Unidym is sampling a transparent conductive film based on carbon nanotubes for touch panel displays and readying production capacity. CimaNanotech is similarly sampling its flexible film product based on self assemble of silver nano particles, for which Toray Advanced Films is the production coating partner.

Pushing MEMS to the nanoscale opens up new potential as well. “The advantages go beyond scaling,” says Caltech professor Michael Roukes, whose lab has been driving developments for the last 15 years. “The physics scales in a profound way.” This means MEMS-based detectors in an electronic nose can be made significantly more sensitive, as well as scaled down in size by about a million fold, compared to the existing state-of-the-art–and made with efficient wafer-scale processes.

Roukes’ lab and CEA-Leti are now routinely mass producing arrays of these nano MEMS sensors on 8-in. wafers, and recruiting corporate partners to their Alliance for Nanosystems VLSI for the final stage of developing the MEMS and CMOS processes to integrate them into practical low-cost gas-phase chemical sensors, to monitor toxic industrial gases and gas phase processes, or to analyze human breath to detect diseases.

The detectors are essentially arrays of nanoscale MEMS resonators–fancy versions of guitar strings–set within MEMS flow channels. The resonators are coated with a kind of chemical sponge that absorbs the target material, which changes the mass of the resonator. The gas is first sent through a chipscale version of a gas chromotograph process, to simplify the identification problem.

Though first markets will likely be military and industrial, the most interesting potential may be in medical diagnostics. “There are a few validated tests for detecting lung cancer and other diseases from the gases in the breath, enough to suggest this is a fertile area,” says Roukes, even though studies so far require large-scale lab instrumentation, so are hard to do. “The more easily and routinely this could be deployed, the more deeply it could be studied,” he notes.

All these structures can be made at 90nm, though 45nm would be preferable, says Roukes. He notes that with the device arrays successfully being produced at wafer-scale, current efforts are directed towards precursor systems including surface chemical functionalization and integration en masse with both MEMS flow channels and CMOS circuits for data post processing.

These companies will be among those discussing their latest developments in the program on Emerging Commercial Applications of Nanoelectronics at SEMICON West, July 14-16 in San Francisco. SRC Nano Electronics Initiative director Jeff Welser will also give a mini keynote on the interesting properties of graphene and spin wave transistors with potential to impact the semiconductor industry further out. The program is part of the Extreme Electronics series on emerging technology opportunities for the semiconductor manufacturing supply chain. For details, see www.semiconwest.org.