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Winter 2004

Team Building Wireless 'Electronic Noses' Using Nanoscale Sensors

ECE researchers are developing multifunctional gas nanosensors integrated with wireless communications, signal processing and readout capabilities. (Diagram) Conceptual diagram of a wireless gas sensor node with nanosensor devices that are assembled on an IC chip. (Photo) A scanning electron micrograph of a proof-of-concept prototype. In this case, a Rhodium nanowire — about 3 micrometers long x 300 nanometers in diameter (see inset) — was assembled on a prototype Silicon CMOS IC.

ECE researchers in the Wireless Microsystems Laboratory are working to integrate functional nano-scale gas sensors with wireless communications microsystems — using a new assembly process that would allow low-cost batch fabrication and the ability to incorporate distinct sensor devices to monitor different chemicals and gases.

Their ultra-miniature "electronic nose" would be sensitive to a variety of gas and chemical compositions and incorporate readout, signal processing, and communications circuitry.

Ultra-Sensitive, Low-Power Sensors
"Sensory devices with nanometer-scale dimensions can give us ultra-high sensitivity," said Sanjay Raman, director of the laboratory. Sensitive nano-sensors can detect their target at the molecular level, he explained. "For example, in gas detection, this can give a very early warning, allowing people to react before any damage is done," he said.

Networks of Nano-Sensors
"We are working to integrate nanosensors with smart silicon circuitry, so the sensor microsystem can sense, think, and communicate," he said. Independent sensing nodes can then be deployed in networks for situations ranging from exterior or interior environments and structures, to miniature, remotely piloted vehicles. The sensing networks can be used for real-time monitoring of vehicles and structures, such as roads or bridges, environmental monitoring for health and safety, and security and battlefield surveillance.

Assembled Devices
Raman's team is collaborating with Stephane Evoy of the University of Pennsylvania to develop the gas nanosensor systems. Instead of using the conventional method of direct machining the nano-devices from the substrate, they are using a "bottom-up" assembly process.

Their goal is to design and fabricate silicon IC chips with integrated wireless communications, readout, and sensor assembly functions, and subsequently assemble the nanosensor devices onto the prefabricated chip. The nanosensors are assembled by placing a drop of fluid containing suspended nanowires and nanorods on the chip. Using probes, electrical stimuli are applied that polarize the suspended nanowires and coax them to assemble on and between selected electrodes.

Batch Fabrication
The batch fabrication assembly technique is expected to reduce manufacturing costs compared to other nanomachining processes. "This technique is compatible with standard foundry technologies," Raman said, which is important for low-cost manufacturing of the devices.

The gas sensor project is funded by a contract from the National Science Foundation (NSF). For more information, please visit the Wireless Microsystems Laboratory website at www.ece.vt.edu/wml/.

 

 

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Last updated: Tue, Apr 20, 2004